SUSE Linux Enterprise Server 15 SP7 64-bit

chmod +x ~/bin/hello.sh If you have fulfilled all the above prerequisites, you can execute the script in the following ways: 1. As absolute path.  The script can be executed with an absolute path. In our case, it is ~/ bin/hello.sh . 2. Everywhere.  If the PATH environment variable contains the directory where the script is located, you can execute the script with hello.sh . 1.3 Redirecting command events Each command can use three channels, either for input or output: Standard output.  This is the default output channel. Whenever a command prints some- thing, it uses the standard output channel. Standard input.  If a command needs input from users or other commands, it uses this channel. Standard error.  Commands use this channel for error reporting. To redirect these channels, there are the following possibilities: Command > File Saves the output of the command into a le, the existing le is deleted. For example, the ls command writes its output into the le listing.txt : > ls > listing.txt 10 Redirecting command events SLES 15 SP6Command >> File Appends the output of the command to a le. For example, the ls command appends its output to the le listing.txt : > ls >> listing.txt Command < File Reads the le as input for the given command. For example, the read command reads in the content of the le into the variable: > read a < foo Command1 | Command2 Redirects the output of the left command as input for the right command. For example, the cat command outputs the content of the /proc/cpuinfo le. This output is used by grep to filter only those lines which contain cpu : > cat /proc/cpuinfo | grep cpu Every channel has a le descriptor: 0 (zero) for standard input, 1 for standard output and 2 for standard error. It is allowed to insert this le descriptor before a < or > character. For example, the following line searches for a le starting with foo , but suppresses its errors by redirecting it to /dev/null : > find / -name "foo*" 2>/dev/null 1.4 Using aliases An alias is a shortcut definition of one or more commands. The syntax for an alias is: alias NAME=DEFINITION For example, the following line defines an alias lt that outputs a long listing (option -l ), sorts it by modification time ( -t ), and prints it in reverse sorted order ( -r ): > alias lt=''ls -ltr'' To view all alias definitions, use alias . Remove your alias with unalias and the corresponding alias name. 11 Using aliases SLES 15 SP61.5 Using variables in Bash A shell variable can be global or local. Global variables, or environment variables, can be ac- cessed in all shells. In contrast, local variables are visible in the current shell only. To view all environment variables, use the printenv command. If you need to know the value of a variable, insert the name of your variable as an argument: > printenv PATH A variable, be it global or local, can also be viewed with echo : > echo $PATH To set a local variable, use a variable name followed by the equal sign, followed by the value: > PROJECT="SLED" Do not insert spaces around the equal sign, otherwise you get an error. To set an environment variable, use export : > export NAME="tux" To remove a variable, use unset : > unset NAME The following table contains common environment variables that you can use in you shell scripts: TABLE 1.5: USEFUL ENVIRONMENT VARIABLES HOME the home directory of the current user HOST the current host name LANG when a tool is localized, it uses the language from this environment variable. English can also be set to C PATH the search path of the shell, a list of directo- ries separated by colon 12 Using variables in Bash SLES 15 SP6PS1 specifies the normal prompt printed before each command PS2 specifies the secondary prompt printed when you execute a multi-line command PWD current working directory USER the current user 1.5.1 Using argument variables For example, if you have the script foo.sh you can execute it like this: > foo.sh "Tux Penguin" 2000 To access all the arguments which are passed to your script, you need positional parameters. These are $1 for the rst argument, $2 for the second, and so on. You can have up to nine parameters. To get the script name, use $0 . The following script foo.sh prints all arguments from 1 to 4: #!/bin/sh echo \"$1\" \"$2\" \"$3\" \"$4\" If you execute this script with the above arguments, you get: "Tux Penguin" "2000" "" "" 1.5.2 Using variable substitution Variable substitutions apply a pattern to the content of a variable either from the left or right side. The following list contains the possible syntax forms: ${VAR#pattern} removes the shortest possible match from the left: > file=/home/tux/book/book.tar.bz2 > echo ${file#*/} home/tux/book/book.tar.bz2 13 Using argument variables SLES 15 SP6${VAR##pattern} removes the longest possible match from the left: > file=/home/tux/book/book.tar.bz2 > echo ${file##*/} book.tar.bz2 ${VAR%pattern} removes the shortest possible match from the right: > file=/home/tux/book/book.tar.bz2 > echo ${file%.*} /home/tux/book/book.tar ${VAR%%pattern} removes the longest possible match from the right: > file=/home/tux/book/book.tar.bz2 > echo ${file%%.*} /home/tux/book/book ${VAR/pattern_1/pattern_2} substitutes the content of VAR from the PATTERN_1 with PATTERN_2 : > file=/home/tux/book/book.tar.bz2 > echo ${file/tux/wilber} /home/wilber/book/book.tar.bz2 1.6 Grouping and combining commands Shells allow you to concatenate and group commands for conditional execution. Each command returns an exit code which determines the success or failure of its operation. If it is 0 (zero) the command was successful, everything else marks an error which is specific to the command. The following list shows, how commands can be grouped: Command1 ; Command2 executes the commands in sequential order. The exit code is not checked. The following line displays the content of the le with cat and then prints its le properties with ls regardless of their exit codes: > cat filelist.txt ; ls -l filelist.txt 14 Grouping and combining commands SLES 15 SP6Command1 && Command2 runs the right command, if the left command was successful (logical AND). The following line displays the content of the le and prints its le properties only, when the previous command was successful (compare it with the previous entry in this list): > cat filelist.txt && ls -l filelist.txt Command1 || Command2 runs the right command, when the left command has failed (logical OR). The following line creates only a directory in /home/wilber/bar when the creation of the directory in /home/tux/foo has failed: > mkdir /home/tux/foo || mkdir /home/wilber/bar funcname(){ ... } creates a shell function. You can use the positional parameters to access its arguments. The following line defines the function hello to print a short message: > hello() { echo "Hello $1"; } You can call this function like this: > hello Tux which prints: Hello Tux 1.7 Working with common flow constructs To control the ow of your script, a shell has while , if , for and case constructs. 1.7.1 The if control command The if command is used to check expressions. For example, the following code tests whether the current user is Tux: if test $USER = "tux"; then echo "Hello Tux." 15 Working with common flow constructs SLES 15 SP6else echo "You are not Tux." fi The test expression can be as complex or simple as possible. The following expression checks if the le foo.txt exists: if test -e /tmp/foo.txt ; then echo "Found foo.txt" fi The test expression can also be abbreviated in square brackets: if [ -e /tmp/foo.txt ] ; then echo "Found foo.txt" fi Find more useful expressions at https://bash.cyberciti.biz/guide/If..else..fi . 1.7.2 Creating loops with the for command The for loop allows you to execute commands to a list of entries. For example, the following code prints certain information about PNG les in the current directory: for i in *.png; do ls -l $i done 1.8 More information Important information about Bash is provided in the man pages man bash . More about this topic can be found in the following list: https://tldp.org/LDP/Bash-Beginners-Guide/html/index.html —Bash Guide for Beginners https://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO.html —BASH Programming - Introduc- tion HOW-TO https://tldp.org/LDP/abs/html/index.html —Advanced Bash-Scripting Guide https://www.grymoire.com/Unix/Sh.html —Sh - the Bourne Shell 16 Creating loops with the for command SLES 15 SP62 sudo basics Running certain commands requires root privileges. However, for security reasons and to avoid mistakes, it is not recommended to log in as root . A safer approach is to log in as a regular user, and then use sudo to run commands with elevated privileges. On SUSE Linux Enterprise Server, sudo is configured to work similarly to su . However, su- do provides a flexible mechanism that allows users to run commands with privileges of any other user. This can be used to assign roles with specific privileges to certain users and groups. For example, it is possible to allow members of the group users to run a command with the privileges of user wilber . Access to the command can be further restricted by disallowing any command options. While su always requires the root password for authentication with PAM, sudo can be configured to authenticate with your own credentials. This means that the users do not need to share the root password, which improves security. 2.1 Basic sudo usage The following chapter provides an introduction to basic usage of sudo . 2.1.1 Running a single command As a regular user, you can run any command as root by adding sudo before it. This prompts you to provide the root password. If authenticated successfully, this runs the command as root : > id -un 1 tux > sudo id -un root''s password: 2 root > id -un tux 3 > sudo id -un 4 root 1 The id -un command prints the login name of the current user. 2 The password is not shown during input, neither as clear text nor as masking characters. 3 Only commands that start with sudo run with elevated privileges. 17 Basic sudo usage SLES 15 SP64 The elevated privileges persist for a certain period of time, so you do not need to provide the root password again. Tip: I/O redirection When using sudo , I/O redirection does not work: > sudo echo s > /proc/sysrq-trigger bash: /proc/sysrq-trigger: Permission denied > sudo cat < /proc/1/maps bash: /proc/1/maps: Permission denied In the example above, only the echo and cat commands run with elevated privileges. The redirection is done by the user''s shell with user privileges. To perform redirection with elevated privileges, either start a shell as in Section 2.1.2, “Starting a shell” or use the dd utility: echo s | sudo dd of=/proc/sysrq-trigger sudo dd if=/proc/1/maps | cat 2.1.2 Starting a shell Using sudo every time to run a command with elevated privileges is not always practical. While you can use the sudo bash command, it is recommended to use one of the built-in mechanisms to start a shell: sudo -s ( ) Starts a shell specified by the SHELL environment variable or the target user''s default shell. If a command is specified, it is passed to the shell (with the -c option). Otherwise the shell runs in interactive mode. tux:~ > sudo -s root''s password: root:/home/tux # exit tux:~ > sudo -i ( ) Similar to -s , but starts the shell as a login shell. This means that the shell''s start-up les ( .profile etc.) are processed, and the current working directory is set to the target user''s home directory. 18 Starting a shell SLES 15 SP6tux:~ > sudo -i root''s password: root:~ # exit tux:~ > Tip: Environment variables By default, sudo does not propagate environment variables. This behavior can be changed using the env_reset option (see Useful flags and options). 2.2 Configuring sudo sudo provides a wide range on configurable options. Note: Locked yourself out of sudo If you accidentally locked yourself out of sudo , use su - and the root password to start a root shell. To x the error, run visudo . Warning: Example configurations are for demonstration purposes only The example rules outlined below are purely for demonstration purposes. Use them to understand the general syntax of sudo configuration les. Do not use them in real-world setups, because they do not reflect the complexity of these environments. 2.2.1 sudo configuration best practices Before you start, here are a few ground rules for maintaining sudo configurations: Always use visudo to edit sudo configuration files Any changes to the sudo configuration should be done using the visudo command. vi- sudo is a tailor-made tool that allows you to edit the sudo configuration les and runs basic syntax checks, making sure that the configuration remains intact and functional. A faulty sudo configuration can result in a user being locked out of their own system. 19 Configuring sudo SLES 15 SP6Always create custom configurations under /etc/sudoers.d/ Custom configurations must reside under /etc/sudoers.d/ to be pulled in by sudo . Settings in the custom configuration les take precedence over the ones in the default configuration in /etc/sudoers . Always mind the order in which configurations are read To make sure the custom configurations are read in the correct order, prefix them with numbers. Use leading zeroes to establish the order in which the les are read. For example, 01_myfirstconfig is parsed before 10_myotherconfig . If a directive has been set in a le that is read before another le that contains conflicting information, the last-read directive is applied. Always use descriptive file names Use le names that hint at what the configuration le does. This helps you keep track of what your sudo setup is supposed to do. 2.2.2 Create a user-specific configuration file Create a sudo configuration le that allows a normal user ( tux ) to use the useradd command with their own password instead of the root password. EXAMPLE 2.1: CREATE A USER-SPECIFIC CONFIGURATION FILE 1. As system administrator ( root ), create a custom configuration le that holds the new user-specific directives by starting visudo . Use both numbering and a descriptive name: # visudo -f /etc/sudoers.d/02_usermanagement 2. Create a rule that allows tux to execute the /usr/sbin/useradd binary in the entire environment that this sudo configuration is applied to: tux 1 ALL 2 = /usr/sbin/useradd 3 1 Specify the user or group. List users by name or #UID , and groups by %GROUPNAME . Separate multiple items with commas. To negate entries, use ! . 2 Specify one or several (separated by commas) hosts. Use (fully qualified) host names or IP addresses. Add ALL to enforce this setting globally across all hosts. Use ! for negations. 20 Create a user-specific configuration file SLES 15 SP63 Specify one or several executables (separated by commas). When specifying them, make sure to mind the following rules: /usr/sbin/useradd Without any additional options added, this allows the execution of every pos- sible useradd command. /usr/sbin/useradd -c If you explicitly specify an option, then that option is the only one that is al- lowed. Nothing else would be available to the user you specified above. /usr/sbin/useradd "" This would just let the user invoke a mere useradd without any option at all. In the example above, you would want to either allow all options and subcommands or limit them to a few for security reasons, but forbidding a user from specifying any option at all would be pointless in this context. 3. To let the user use their own password instead of the root password, add the following line: Defaults:tux !targetpw When active, this ag requires the user to enter the password of the target user, that is, root . This ag is enabled by default on any SUSE Linux Enterprise Server system. Negate it using ! to require the user to just enter their own password instead of the root password. 4. Save the configuration, leave the editor and open a second shell to test whether sudo honors your new configuration. 2.2.3 Create custom configurations by grouping items Modify the configuration from Example 2.1, “Create a user-specific configuration file” so that a group of named users can run the useradd command without the need for the root password. Also, add the usermod and userdel to the list of commands available to this group. 21 Create custom configurations by grouping items SLES 15 SP6EXAMPLE 2.2: CREATE CUSTOM CONFIGURATIONS BY GROUPING ITEMS 1. To modify the example configuration, open it as system administrator with visudo : # visudo /etc/sudoers.d/02_usermanagement 2. Add more users to the rule in a comma-separated list: tux, wilber ALL = /usr/sbin/useradd 3. To allow the listed users to execute a list of commands, specify the commands as a com- ma-separated list: tux, wilber ALL = /usr/sbin/useradd, /usr/sbin/usermod, /usr/sbin/userdel 4. To let the listed users use their own password instead of the root password, add the following line: Defaults:tux, wilber !targetpw When active, this ag requires the listed users to enter the password of the target user, that is, root . This ag is enabled by default on any SUSE Linux Enterprise Server system. Negate it using ! to require the listed users to just enter their own password instead of the root password. 5. Save the configuration, leave the editor and open a second shell to test whether sudo honors your new configuration. 2.2.4 Simplify configurations by applying aliases Use aliases to simplify your custom configuration from Example 2.2, “Create custom configurations by grouping items” even further. Grouping items helps to a certain extent, but using global aliases for users, commands and hosts is the most efficient way to keep a clean and lean sudo config- uration. Using aliases and groups instead of lists is a much better way to address changes in your setup. Should a user leave, just remove them from the global User_Alias declaration in your alias declaration le instead of scouring all the separate custom configuration les. The same proce- dure applies for any other type of alias ( Host_Alias , Cmnd_Alias and Runas_Alias ). 22 Simplify configurations by applying aliases SLES 15 SP6EXAMPLE 2.3: SIMPLIFY CONFIGURATIONS BY APPLYING ALIASES 1. Create a new le to hold your global alias definitions: # visudo /etc/sudoers.d/01_aliases 2. Add the following line to create the TEAMLEADERS alias: User_Alias TEAMLEADERS = tux, wilber 3. Add the following line to create the USERMANAGEMENT alias: Cmnd_Alias USERMANAGEMENT = /usr/sbin/useradd, /usr/sbin/usermod, /usr/sbin/ userdel 4. Save your changes and exit visudo . 5. As system administrator, start visudo to edit the example configuration le: # visudo -f /etc/sudoers.d/02_usermanagement 6. Delete the previous rule and replace it with the following rule that uses the aliases you have just defined above: TEAMLEADERS ALL = USERMANAGEMENT 7. To let all the users defined by User_Alias use their own password instead of the root password, add the following line: Defaults:TEAMLEADERS !targetpw 8. Save the configuration, leave the editor and open a second shell to test whether sudo honors your new configuration. 2.2.5 Basic sudoers configuration syntax The sudoers configuration les contain two types of options: strings and ags. While strings can contain any value, ags can be turned either ON or OFF. The most important syntax constructs for sudoers configuration les are as follows: # Everything on a line after # is ignored 1 Defaults !insults # Disable the insults flag 2 Defaults env_keep += "DISPLAY HOME" # Add DISPLAY and HOME to env_keep 23 Basic sudoers configuration syntax SLES 15 SP6tux ALL = NOPASSWD: /usr/bin/frobnicate, PASSWD: /usr/bin/journalctl 3 1 There are two exceptions: #include and #includedir are regular commands. 2 Remove the ! character to set the desired ag to ON. 3 See Section 2.2.6, “Basic sudoers rules”. USEFUL FLAGS AND OPTIONS targetpw This ag controls whether the invoking user is required to enter the password of the target user (ON) (for example root ) or the invoking user (OFF). Defaults targetpw # Turn targetpw flag ON rootpw If set, sudo prompts for the root password. The default is OFF. Defaults !rootpw # Turn rootpw flag OFF env_reset If set, sudo constructs a minimal environment with TERM , PATH , HOME , MAIL , SHELL , LOGNAME , USER , USERNAME , and SUDO_* . Additionally, variables listed in env_keep are imported from the calling environment. The default is ON. Defaults env_reset # Turn env_reset flag ON env_keep List of environment variables to keep when the env_reset ag is ON. # Set env_keep to contain EDITOR and PROMPT Defaults env_keep = "EDITOR PROMPT" Defaults env_keep += "JRE_HOME" # Add JRE_HOME Defaults env_keep -= "JRE_HOME" # Remove JRE_HOME env_delete List of environment variables to remove when the env_reset ag is OFF. # Set env_delete to contain EDITOR and PROMPT Defaults env_delete = "EDITOR PROMPT" Defaults env_delete += "JRE_HOME" # Add JRE_HOME Defaults env_delete -= "JRE_HOME" # Remove JRE_HOME The Defaults token can also be used to create aliases for a collection of users, hosts, and commands. Furthermore, it is possible to apply an option only to a specific set of users. 24 Basic sudoers configuration syntax SLES 15 SP6For detailed information about the sudoers configuration les, consult man 5 sudoers . 2.2.6 Basic sudoers rules Each rule follows the following scheme ( [] marks optional parts): #Who Where As whom Tag What User_List Host_List = [(User_List)] [NOPASSWD:|PASSWD:] Cmnd_List SUDOERS RULE SYNTAX User_List One or several (separated by comma) identifiers: either a user name, a group in the format %GROUPNAME , or a user ID in the format #UID . Negation can be specified with the ! prefix. Host_List One or several (separated by comma) identifiers: either a (fully qualified) host name or an IP address. Negation can be specified with the ! prefix. ALL is a common choice for Host_List . NOPASSWD:|PASSWD: The user is not prompted for a password when running commands matching Cmd_List after NOPASSWD: . PASSWD is the default. It only needs to be specified when both PASSWD and NOPASSWD are on the same line: tux ALL = PASSWD: /usr/bin/foo, NOPASSWD: /usr/bin/bar Cmnd_List One or several (separated by comma) specifiers: a path to an executable, followed by an optional allowed argument. /usr/bin/foo # Anything allowed /usr/bin/foo bar # Only "/usr/bin/foo bar" allowed /usr/bin/foo "" # No arguments allowed ALL can be used as User_List , Host_List , and Cmnd_List . A rule that allows tux to run all commands as root without entering a password: tux ALL = NOPASSWD: ALL 25 Basic sudoers rules SLES 15 SP6A rule that allows tux to run systemctl restart apache2 : tux ALL = /usr/bin/systemctl restart apache2 A rule that allows tux to run wall as admin with no arguments: tux ALL = (admin) /usr/bin/wall "" Warning: Unsafe rules Do not use rules like ALL ALL = ALL without Defaults targetpw . Otherwise anyone can run commands as root . Important: Winbind and sudo When specifying the group name in the sudoers le, make sure that you use the NetBIOS domain name instead of the realm, for example: %DOMAIN\\GROUP_NAME ALL = (ALL) ALL Keep in mind that when using winbindd, the format also depends on the winbind sep- arator option in the smb.conf le. By default, it is \ . If it is changed, for example, to + , then the account format in the sudoers le must be DOMAIN+GROUP_NAME . 2.3 Using sudo with X.Org applications Starting graphical applications with sudo normally results in the following error: > sudo xterm xterm: Xt error: Can''t open display: %s xterm: DISPLAY is not set A simple workaround is to use xhost to temporarily allow the root user to access the local user''s X session. This is done using the following command: xhost si:localuser:root The command below removes the granted access: xhost -si:localuser:root 26 Using sudo with X.Org applications SLES 15 SP6Warning: Potential security issue Running graphical applications with root privileges has security implications. It is rec- ommended to enable root access for a graphical application only as an exception. It is also recommended to revoke the granted root access as soon as the graphical application is closed. 2.4 More information The sudo --help command offers a brief overview of the available command line options, while the man sudoers command provides detailed information about sudoers and its con- figuration. 27 More information SLES 15 SP63 Using YaST YaST is a SUSE Linux Enterprise Server tool that provides a graphical interface for all essential installation and system configuration tasks. Whether you need to update packages, configure a printer, modify firewall settings, set up an FTP server, or partition a hard disk—you can do it using YaST. Written in Ruby, YaST features an extensible architecture that makes it possible to add new functionality via modules. Additional information about YaST is available on the project''s official Web site at https:// yast.opensuse.org/ . 3.1 YaST interface overview YaST has two graphical interfaces: one for use with graphical desktop environments like KDE and GNOME, and an ncurses-based pseudo-graphical interface for use on systems without an X server (see Chapter 4, YaST in text mode). In the graphical version of YaST, all modules in YaST are grouped by category, and the naviga- tion sidebar allows you to quickly access modules in the desired category. The search eld at the top makes it possible to nd modules by their names. To nd a specific module, enter its name into the search eld, and you should see the modules that match the entered string as you type. Important: List of installed YaST modules The list of installed modules for the ncurses-based and GUI version of YaST may differ. Before starting any YaST module, verify that it is installed for the version of YaST that you are using. 3.2 Useful key combinations The graphical version of YaST supports keyboard shortcuts Print Screen Take and save a screenshot. It may not work on certain desktop environments. Shift – F4 Enable and disable the color palette optimized for visually impaired users. 28 YaST interface overview SLES 15 SP6Shift – F7 Enable/disable logging of debug messages. Shift – F8 Open a le dialog to save log les to a user-defined location. Ctrl – Shift – Alt – D Send a DebugEvent. YaST modules can react to this by executing special debugging actions. The result depends on the specific YaST module. Ctrl – Shift – Alt – M Start and stop macro recorder. Ctrl – Shift – Alt – P Replay macro. Ctrl – Shift – Alt – S Show stylesheet editor. Ctrl – Shift – Alt – T Dump widget tree to the log le. Ctrl – Shift – Alt – X Open a terminal window (xterm). Useful for installation process via VNC. Ctrl – Shift – Alt – Y Show widget tree browser. 29 Useful key combinations SLES 15 SP64 YaST in text mode The ncurses-based pseudo-graphical YaST interface is designed primarily to help system admin- istrators to manage systems without an X server. The interface offers several advantages com- pared to the conventional GUI. You can navigate the ncurses interface using the keyboard, and there are keyboard shortcuts for practically all interface elements. The ncurses interface is light on resources, and runs fast even on modest hardware. You can run the ncurses-based version of YaST via an SSH connection, so you can administer remote systems. Keep in mind that the minimum supported size of the terminal emulator in which to run YaST is 80x25 characters. FIGURE 4.1: MAIN WINDOW OF YAST IN TEXT MODE To launch the ncurses-based version of YaST, open the terminal and run the sudo yast2 com- mand. Use the →| or arrow keys to navigate between interface elements like menu items, elds and buttons. All menu items and buttons in YaST can be accessed using the appropriate function keys or keyboard shortcuts. For example, you can cancel the current operation by pressing F9 , while the F10 key can be used to accept the changes. Each menu item and button in YaST''s ncurses-based interface has a highlighted letter in its label. This letter is part of the keyboard shortcut assigned to the interface element. For example, the letter Q is highlighted in the Quit button. This means that you can activate the button by pressing Alt – Alt+Q . 30 SLES 15 SP6Tip: Refreshing YaST dialogs If a YaST dialog gets corrupted or distorted, for example, while resizing the window, press Ctrl – L to refresh and restore its contents. 4.1 Navigation in modules The following description of the control elements in the YaST modules assumes that all function keys and Alt key combinations work and are not assigned to different global functions. Read Section 4.3, “Restriction of key combinations” for information about possible exceptions. Moving between buttons and selection lists Use →| to move between the buttons and frames containing selection lists. To navigate in the opposite direction, use Alt – →| or Shift – →| combinations. Navigating in selection lists Use the arrow keys ( ↑ and ↓ ) to move through the individual elements in an active frame containing a selection list. If individual entries are longer than the frame''s width, use Shift – → or Shift – ← to scroll horizontally. If the arrow key causes the selection to move to another frame, use Ctrl – E or Ctrl – A instead. Working with buttons, radio buttons, and check boxes To select items with empty square brackets (check boxes) or empty parentheses (radio buttons), press Space or Enter . Alternatively, radio buttons and check boxes can be selected directly with Alt – highlighted_letter . In this case, you do not need to confirm with Enter . If you navigate to an item with →| , press Enter to execute the selected action or activate the respective menu item. Function keys The function keys (from F1 to F12 ) enable quick access to the specific buttons. Available function key combinations ( FX ) are shown in the bottom line of the YaST screen. Which function keys are really mapped to which buttons depend on the active YaST module, because the different modules offer different buttons (Details, Info, Add, Delete, etc.). Use F10 for Accept, OK, Next, and Finish. Press F1 to access the YaST help. 31 Navigation in modules SLES 15 SP6Using the navigation tree Certain YaST modules use a navigation tree in the left part of the window to select con- figuration dialogs. Use the arrow keys ( ↑ and ↓ ) to navigate in the tree. Use Space to open or close tree items. In the ncurses mode, Enter must be pressed after a selection in the navigation tree to show the selected dialog. This is an intentional behavior to save time-consuming redraws when browsing through the navigation tree. Selecting software in the software installation module Use the filters on the left side to list packages matching the specified string. Installed packages are marked with the letter i . To change the status of a package, press Space or Enter . Alternatively, use the Actions menu to select the needed status change (install, delete, update, taboo or lock). FIGURE 4.2: THE SOFTWARE INSTALLATION MODULE 4.2 Advanced key combinations The ncurses-based version of YaST offers several advanced key combinations. Shift – F1 List advanced hotkeys. Shift – F4 Change color schema. 32 Advanced key combinations SLES 15 SP6Ctrl – Q Quit the application. Ctrl – L Refresh screen. Ctrl – D F1 List advanced hotkeys. Ctrl – D Shift – D Dump dialog to the log le as a screenshot. Ctrl – D Shift – Y Open YDialogSpy to see the widget hierarchy. 4.3 Restriction of key combinations If your window manager uses global Alt combinations, the Alt combinations in YaST may not work. Keys like Alt or Shift can also be occupied by the settings of the terminal. Using Alt instead of Esc Alt shortcuts can be executed with Esc instead of Alt . For example, Esc – H replaces Alt – H . (Press Esc , then press H .) Backward and forward navigation with Ctrl – F and Ctrl – B If the Alt and Shift combinations are taken over by the window manager or the ter- minal, use the combinations Ctrl – F (forward) and Ctrl – B (backward) instead. Restriction of function keys The function keys ( F1 ... F12 ) are also used for functions. Certain function keys may be taken over by the terminal and may not be available for YaST. However, the Alt key combinations and function keys should always be fully available on a text-only console. 4.4 YaST command line options Besides the text mode interface, YaST provides a command line interface. To get a list of YaST command line options, use the following command: > sudo yast -h 33 Restriction of key combinations SLES 15 SP64.4.1 Installing packages from the command line If you know the package name, and the package is provided by an active installation repository, you can use the command line option -i to install the package: > sudo yast -i package_name or > sudo yast --install -i package_name package_name can be a single short package name, for example, gvim , installed with depen- dency checking, or the full path to an RPM package, which is installed without dependency checking. While YaST offers basic functionality for managing software from the command line, consider using Zypper for more advanced package management tasks. Find more information on using Zypper in Section 9.1, “Using Zypper”. 4.4.2 Working with individual modules To save time, you can start individual YaST modules using the following command: > sudo yast module_name View a list of all modules available on your system with yast -l or yast --list . 4.4.3 Command line parameters of YaST modules To use YaST functionality in scripts, YaST provides command line support for individual mod- ules. However, not all modules have command line support. To display the available options of a module, use the following command: > sudo yast module_name help If a module does not provide command line support, it is started in a text mode with the following message: This YaST module does not support the command line interface. The following sections describe all YaST modules with command line support, along with a brief explanation of all their commands and available options. 34 Installing packages from the command line SLES 15 SP64.4.3.1 Common YaST module commands All YaST modules support the following commands: help Lists all the module''s supported commands with their description: > sudo yast lan help longhelp Same as help , but adds a detailed list of all command''s options and their descriptions: > sudo yast lan longhelp xmlhelp Same as longhelp , but the output is structured as an XML document and redirected to a le: > sudo yast lan xmlhelp xmlfile=/tmp/yast_lan.xml interactive Enters the interactive mode. This lets you run the module''s commands without prefixing them with sudo yast . Use exit to leave the interactive mode. 4.4.3.2 yast add-on Adds a new add-on product from the specified path: > sudo yast add-on http://server.name/directory/Lang-AddOn-CD1/ You can use the following protocols to specify the source path: http:// ftp:// nfs:// disk:// cd:// or dvd://. 4.4.3.3 yast audit-laf Displays and configures the Linux Audit Framework. Refer to the Book “Security and Hardening Guide” for more details. yast audit-laf accepts the following commands: set Sets an option: > sudo yast audit-laf set log_file=/tmp/audit.log 35 Command line parameters of YaST modules SLES 15 SP6For a complete list of options, run yast audit-laf set help . show Displays settings of an option: > sudo yast audit-laf show diskspace space_left: 75 space_left_action: SYSLOG admin_space_left: 50 admin_space_left_action: SUSPEND action_mail_acct: root disk_full_action: SUSPEND disk_error_action: SUSPEND For a complete list of options, run yast audit-laf show help . 4.4.3.4 yast dhcp-server Manages the DHCP server and configures its settings. yast dhcp-server accepts the following commands: disable Disables the DHCP server service. enable Enables the DHCP server service. host Configures settings for individual hosts. interface Specifies to which network interface to listen to: > sudo yast dhcp-server interface current Selected Interfaces: eth0 Other Interfaces: bond0, pbu, eth1 For a complete list of options, run yast dhcp-server interface help . options Manages global DHCP options. For a complete list of options, run yast dhcp-server options help . 36 Command line parameters of YaST modules SLES 15 SP6status Prints the status of the DHCP service. subnet Manages the DHCP subnet options. For a complete list of options, run yast dhcp-server subnet help . 4.4.3.5 yast dns-server Manages the DNS server configuration. yast dns-server accepts the following commands: acls Displays access control list settings: > sudo yast dns-server acls show ACLs: ----- Name Type Value ---------------------------- any Predefined localips Predefined localnets Predefined none Predefined dnsrecord Configures zone resource records: > sudo yast dnsrecord add zone=example.org query=office.example.org type=NS value=ns3 For a complete list of options, run yast dns-server dnsrecord help . forwarders Configures DNS forwarders: > sudo yast dns-server forwarders add ip=10.0.0.100 > sudo yast dns-server forwarders show [...] Forwarder IP ------------ 10.0.0.100 For a complete list of options, run yast dns-server forwarders help . 37 Command line parameters of YaST modules SLES 15 SP6host Handles “A” and its related “PTR” record at once: > sudo yast dns-server host show zone=example.org For a complete list of options, run yast dns-server host help . logging Configures logging settings: > sudo yast dns-server logging set updates=no transfers=yes For a complete list of options, run yast dns-server logging help . mailserver Configures zone mail servers: > sudo yast dns-server mailserver add zone=example.org mx=mx1 priority=100 For a complete list of options, run yast dns-server mailserver help . nameserver Configures zone name servers: > sudo yast dns-server nameserver add zone=example.com ns=ns1 For a complete list of options, run yast dns-server nameserver help . soa Configures the start of authority (SOA) record: > sudo yast dns-server soa set zone=example.org serial=2006081623 ttl=2D3H20S For a complete list of options, run yast dns-server soa help . startup Manages the DNS server service: > sudo yast dns-server startup atboot For a complete list of options, run yast dns-server startup help . transport Configures zone transport rules. For a complete list of options, run yast dns-server transport help . 38 Command line parameters of YaST modules SLES 15 SP6zones Manages DNS zones: > sudo yast dns-server zones add name=example.org zonetype=master For a complete list of options, run yast dns-server zones help . 4.4.3.6 yast disk Prints information about all disks or partitions. The only supported command is list followed by either of the following options: disks Lists all configured disks in the system: > sudo yast disk list disks Device | Size | FS Type | Mount Point | Label | Model ---------+------------+---------+-------------+-------+------------- /dev/sda | 119.24 GiB | | | | SSD 840 /dev/sdb | 60.84 GiB | | | | WD1003FBYX-0 partitions Lists all partitions in the system: > sudo yast disk list partitions Device | Size | FS Type | Mount Point | Label | Model ---------------+------------+---------+-------------+-------+------ /dev/sda1 | 1.00 GiB | Ext2 | /boot | | /dev/sdb1 | 1.00 GiB | Swap | swap | | /dev/sdc1 | 698.64 GiB | XFS | /mnt/extra | | /dev/vg00/home | 580.50 GiB | Ext3 | /home | | /dev/vg00/root | 100.00 GiB | Ext3 | / | | [...] 4.4.3.7 yast ftp-server Configures FTP server settings. yast ftp-server accepts the following options: SSL, TLS Controls secure connections via SSL and TLS. SSL options are valid for the vsftpd only. > sudo yast ftp-server SSL enable > sudo yast ftp-server TLS disable 39 Command line parameters of YaST modules SLES 15 SP6access Configures access permissions: > sudo yast ftp-server access authen_only For a complete list of options, run yast ftp-server access help . anon_access Configures access permissions for anonymous users: > sudo yast ftp-server anon_access can_upload For a complete list of options, run yast ftp-server anon_access help . anon_dir Specifies the directory for anonymous users. The directory must already exist on the server: > sudo yast ftp-server anon_dir set_anon_dir=/srv/ftp For a complete list of options, run yast ftp-server anon_dir help . chroot Controls change root environment (chroot): > sudo yast ftp-server chroot enable > sudo yast ftp-server chroot disable idle-time Sets the maximum idle time in minutes before FTP server terminates the current connec- tion: > sudo yast ftp-server idle-time set_idle_time=15 logging Determines whether to save the log messages into a log le: > sudo yast ftp-server logging enable > sudo yast ftp-server logging disable max_clients Specifies the maximum number of concurrently connected clients: > sudo yast ftp-server max_clients set_max_clients=1500 max_clients_ip Specifies the maximum number of concurrently connected clients via IP: > sudo yast ftp-server max_clients_ip set_max_clients=20 40 Command line parameters of YaST modules SLES 15 SP6max_rate_anon Specifies the maximum data transfer rate permitted for anonymous clients (KB/s): > sudo yast ftp-server max_rate_anon set_max_rate=10000 max_rate_authen Specifies the maximum data transfer rate permitted for locally authenticated users (KB/s): > sudo yast ftp-server max_rate_authen set_max_rate=10000 port_range Specifies the port range for passive connection replies: > sudo yast ftp-server port_range set_min_port=20000 set_max_port=30000 For a complete list of options, run yast ftp-server port_range help . show Displays FTP server settings. startup Controls the FTP start-up method: > sudo yast ftp-server startup atboot For a complete list of options, run yast ftp-server startup help . umask Specifies the le umask for authenticated:anonymous users: > sudo yast ftp-server umask set_umask=177:077 welcome_message Specifies the text to display when someone connects to the FTP server: > sudo yast ftp-server welcome_message set_message="hello everybody" 4.4.3.8 yast http-server Configures the HTTP server (Apache2). yast http-server accepts the following commands: configure Configures the HTTP server host settings: > sudo yast http-server configure host=main servername=www.example.com \ 41 Command line parameters of YaST modules SLES 15 SP6serveradmin=admin@example.com For a complete list of options, run yast http-server configure help . hosts Configures virtual hosts: > sudo yast http-server hosts create servername=www.example.com \ serveradmin=admin@example.com documentroot=/var/www For a complete list of options, run yast http-server hosts help . listen Specifies the ports and network addresses where the HTTP server should listen: > sudo yast http-server listen add=81 > sudo yast http-server listen list Listen Statements: ================== :80 :81 > sudo yast http-server delete=80 For a complete list of options, run yast http-server listen help . mode Enables or disables the wizard mode: > sudo yast http-server mode wizard=on modules Controls the Apache2 server modules: > sudo yast http-server modules enable=php5,rewrite > sudo yast http-server modules disable=ssl > sudo http-server modules list [...] Enabled rewrite Disabled ssl Enabled php5 [...] 42 Command line parameters of YaST modules SLES 15 SP64.4.3.9 yast kdump Configures kdump settings. For more information on kdump , refer to the Book “System Analysis and Tuning Guide”, Chapter 20 “Kexec and Kdump”, Section 20.7 “Basic Kdump configuration”. yast kdump accepts the following commands: copykernel Copies the kernel into the dump directory. customkernel Specifies the kernel_string part of the name of the custom kernel. The naming scheme is /boot/vmlinu[zx]-kernel_string[.gz] . > sudo yast kdump customkernel kernel=kdump For a complete list of options, run yast kdump customkernel help . dumpformat Specifies the (compression) format of the dump kernel image. Available formats are “none”, “ELF”, “compressed” or “lzo”: > sudo yast kdump dumpformat dump_format=ELF dumplevel Specifies the dump level number in the range from 0 to 31: > sudo yast kdump dumplevel dump_level=24 dumptarget Specifies the destination for saving dump images: > sudo kdump dumptarget target=ssh server=name_server port=22 \ dir=/var/log/dump user=user_name For a complete list of options, run yast kdump dumptarget help . immediatereboot Controls whether the system should reboot immediately after saving the core in the Kdump kernel: > sudo yast kdump immediatereboot enable > sudo yast kdump immediatereboot disable 43 Command line parameters of YaST modules SLES 15 SP6keepolddumps Specifies how many old dump images are kept. Specify zero to keep them all: > sudo yast kdump keepolddumps no=5 kernelcommandline Specifies the command line that needs to be passed o to the Kdump kernel: > sudo yast kdump kernelcommandline command="ro root=LABEL=/" kernelcommandlineappend Specifies the command line that you need to append to the default command line string: > sudo yast kdump kernelcommandlineappend command="ro root=LABEL=/" notificationcc Specifies an e-mail address for sending copies of notification messages: > sudo yast kdump notificationcc email="user1@example.com user2@example.com" notificationto Specifies an e-mail address for sending notification messages: > sudo yast kdump notificationto email="user1@example.com user2@example.com" show Displays kdump settings: > sudo yast kdump show Kdump is disabled Dump Level: 31 Dump Format: compressed Dump Target Settings target: file file directory: /var/crash Kdump immediate reboots: Enabled Numbers of old dumps: 5 smtppass Specifies the le with the plain text SMTP password used for sending notification messages: > sudo yast kdump smtppass pass=/path/to/file smtpserver Specifies the SMTP server host name used for sending notification messages: > sudo yast kdump smtpserver server=smtp.server.com 44 Command line parameters of YaST modules SLES 15 SP6smtpuser Specifies the SMTP user name used for sending notification messages: > sudo yast kdump smtpuser user=smtp_user startup Enables or disables start-up options: > sudo yast kdump startup enable alloc_mem=128,256 > sudo yast kdump startup disable 4.4.3.10 yast keyboard Configures the system keyboard for virtual consoles. It does not affect the keyboard settings in graphical desktop environments, such as GNOME or KDE. yast keyboard accepts the following commands: list Lists all available keyboard layouts. set Activates new keyboard layout setting: > sudo yast keyboard set layout=czech summary Displays the current keyboard configuration. 4.4.3.11 yast lan Configures network cards. yast lan accepts the following commands: add Configures a new network card: > sudo yast lan add name=vlan50 ethdevice=eth0 bootproto=dhcp For a complete list of options, run yast lan add help . delete Deletes an existing network card: > sudo yast lan delete id=0 45 Command line parameters of YaST modules SLES 15 SP6edit Changes the configuration of an existing network card: > sudo yast lan edit id=0 bootproto=dhcp list Displays a summary of network card configuration: > sudo yast lan list id name, bootproto 0 Ethernet Card 0, NONE 1 Network Bridge, DHCP 4.4.3.12 yast language Configures system languages. yast language accepts the following commands: list Lists all available languages. set Specifies the main system languages and secondary languages: > sudo yast language set lang=cs_CZ languages=en_US,es_ES no_packages 4.4.3.13 yast mail Displays the configuration of the mail system: > sudo yast mail summary 4.4.3.14 yast nfs Controls the NFS client. yast nfs accepts the following commands: add Adds a new NFS mount: > sudo yast nfs add spec=remote_host:/path/to/nfs/share file=/local/mount/point 46 Command line parameters of YaST modules SLES 15 SP6For a complete list of options, run yast nfs add help . delete Deletes an existing NFS mount: > sudo yast nfs delete spec=remote_host:/path/to/nfs/share file=/local/mount/point For a complete list of options, run yast nfs delete help . edit Changes an existing NFS mount: > sudo yast nfs edit spec=remote_host:/path/to/nfs/share \ file=/local/mount/point type=nfs4 For a complete list of options, run yast nfs edit help . list Lists existing NFS mounts: > sudo yast nfs list Server Remote File System Mount Point Options ---------------------------------------------------------------- nfs.example.com /mnt /nfs/mnt nfs nfs.example.com /home/tux/nfs_share /nfs/tux nfs 4.4.3.15 yast nfs-server Configures the NFS server. yast nfs-server accepts the following commands: add Adds a directory to export: > sudo yast nfs-server add mountpoint=/nfs/export hosts=*.allowed_hosts.com For a complete list of options, run yast nfs-server add help . delete Deletes a directory from the NFS export: > sudo yast nfs-server delete mountpoint=/nfs/export 47 Command line parameters of YaST modules SLES 15 SP6set Specifies additional parameters for the NFS server: > sudo yast nfs-server set enablev4=yes security=yes For a complete list of options, run yast nfs-server set help . start Starts the NFS server service: > sudo yast nfs-server start stop Stops the NFS server service: > sudo yast nfs-server stop summary Displays a summary of the NFS server configuration: > sudo yast nfs-server summary NFS server is enabled NFS Exports * /mnt * /home NFSv4 support is enabled. The NFSv4 domain for idmapping is localdomain. NFS Security using GSS is enabled. 4.4.3.16 yast nis Configures the NIS client. yast nis accepts the following commands: configure Changes global settings of a NIS client: > sudo yast nis configure server=nis.example.com broadcast=yes For a complete list of options, run yast nis configure help . disable Disables the NIS client: > sudo yast nis disable 48 Command line parameters of YaST modules SLES 15 SP6enable Enables your machine as NIS client: > sudo yast nis enable server=nis.example.com broadcast=yes automounter=yes For a complete list of options, run yast nis enable help . find Shows available NIS servers for a given domain: > sudo yast nis find domain=nisdomain.com summary Displays a configuration summary of a NIS client. 4.4.3.17 yast nis-server Configures a NIS server. yast nis-server accepts the following commands: master Configures a NIS master server: > sudo yast nis-server master domain=nisdomain.com yppasswd=yes For a complete list of options, run yast nis-server master help . slave Configures a NIS worker server: > sudo yast nis-server slave domain=nisdomain.com master_ip=10.100.51.65 For a complete list of options, run yast nis-server slave help . stop Stops a NIS server: > sudo yast nis-server stop summary Displays a configuration summary of a NIS server: > sudo yast nis-server summary 49 Command line parameters of YaST modules SLES 15 SP64.4.3.18 yast proxy Configures proxy settings. yast proxy accepts the following commands: authentication Specifies the authentication options for proxy: > sudo yast proxy authentication username=tux password=secret For a complete list of options, run yast proxy authentication help . enable, disable Enables or disables proxy settings. set Changes the current proxy settings: > sudo yast proxy set https=proxy.example.com For a complete list of options, run yast proxy set help . summary Displays proxy settings. 4.4.3.19 yast rdp Controls remote desktop settings. yast rdp accepts the following commands: allow Allows remote access to the server''s desktop: > sudo yast rdp allow set=yes list Displays the remote desktop configuration summary. 4.4.3.20 yast samba-client Configures the Samba client settings. yast samba-client accepts the following commands: configure Changes global settings of Samba: > sudo yast samba-client configure workgroup=FAMILY 50 Command line parameters of YaST modules SLES 15 SP6isdomainmember Checks whether the machine is a member of a domain: > sudo yast samba-client isdomainmember domain=SMB_DOMAIN joindomain Makes the machine a member of a domain: > sudo yast samba-client joindomain domain=SMB_DOMAIN user=username password=pwd winbind Enables or disables Winbind services (the winbindd daemon): > sudo yast samba-client winbind enable > sudo yast samba-client winbind disable 4.4.3.21 yast samba-server Configures Samba server settings. yast samba-server accepts the following commands: backend Specifies the back-end for storing user information: > sudo yast samba-server backend smbpasswd For a complete list of options, run yast samba-server backend help . configure Configures global settings of the Samba server: > sudo yast samba-server configure workgroup=FAMILY description=''Home server'' For a complete list of options, run yast samba-server configure help . list Displays a list of available shares: > sudo yast samba-server list Status Type Name ============================== Disabled Disk profiles Enabled Disk print$ 51 Command line parameters of YaST modules SLES 15 SP6Enabled Disk homes Disabled Disk groups Enabled Disk movies Enabled Printer printers role Specifies the role of the Samba server: > sudo yast samba-server role standalone For a complete list of options, run yast samba-server role help . service Enables or disables the Samba services ( smb and nmb ): > sudo yast samba-server service enable > sudo yast samba-server service disable share Manipulates a single Samba share: > sudo yast samba-server share name=movies browseable=yes guest_ok=yes For a complete list of options, run yast samba-server share help . 4.4.3.22 yast security Controls the security level of the host. yast security accepts the following commands: level Specifies the security level of the host: > sudo yast security level server For a complete list of options, run yast security level help . set Sets the value of a specific option: > sudo yast security set passwd=sha512 crack=yes For a complete list of options, run yast security set help . 52 Command line parameters of YaST modules SLES 15 SP6summary Displays a summary of the current security configuration: sudoyast security summary 4.4.3.23 yast sound Configures sound card settings. yast sound accepts the following commands: add Configures a new sound card. Without any parameters, the command adds the rst detected card. > sudo yast sound add card=0 volume=75 For a complete list of options, run yast sound add help . channels Lists available volume channels of a sound card: > sudo yast sound channels card=0 Master 75 PCM 100 modules Lists all available sound kernel modules: > sudo yast sound modules snd-atiixp ATI IXP AC97 controller (snd-atiixp) snd-atiixp-modem ATI IXP MC97 controller (snd-atiixp-modem) snd-virtuoso Asus Virtuoso driver (snd-virtuoso) [...] playtest Plays a test sound on a sound card: > sudo yast sound playtest card=0 remove Removes a configured sound card: > sudo yast sound remove card=0 53 Command line parameters of YaST modules SLES 15 SP6> sudo yast sound remove all set Specifies new values for a sound card: > sudo yast sound set card=0 volume=80 show Displays detailed information about a sound card: > sudo yast sound show card=0 Parameters of card ''ThinkPad X240'' (using module snd-hda-intel): align_buffer_size Force buffer and period sizes to be multiple of 128 bytes. bdl_pos_adj BDL position adjustment offset. beep_mode Select HDA Beep registration mode (0=off, 1=on) (default=1). Default Value: 0 enable_msi Enable Message Signaled Interrupt (MSI) [...] summary Prints a configuration summary for all sound cards on the system: > sudo yast sound summary volume Specifies the volume level of a sound card: sudoyast sound volume card=0 play 4.4.3.24 yast sysconfig Controls the variables in les under /etc/sysconfig . yast sysconfig accepts the following commands: clear Sets empty value to a variable: > sudo yast sysconfig clear=POSTFIX_LISTEN 54 Command line parameters of YaST modules SLES 15 SP6Tip: Variable in multiple files If the variable is available in several les, use the VARIABLE_NAME $ FILE_NAME syntax: > sudo yast sysconfig clear=CONFIG_TYPE$/etc/sysconfig/mail details Displays detailed information about a variable: > sudo yast sysconfig details variable=POSTFIX_LISTEN Description: Value: File: /etc/sysconfig/postfix Possible Values: Any value Default Value: Configuration Script: postfix Description: Comma separated list of IP''s NOTE: If not set, LISTEN on all interfaces list Displays summary of modified variables. Use all to list all variables and their values: > sudo yast sysconfig list all AOU_AUTO_AGREE_WITH_LICENSES="false" AOU_ENABLE_CRONJOB="true" AOU_INCLUDE_RECOMMENDS="false" [...] set Sets a value for a variable: > sudo yast sysconfig set DISPLAYMANAGER=gdm Tip: Variable in multiple files If the variable is available in several les, use the VARIABLE_NAME $ FILE_NAME syntax: > sudo yast sysconfig set CONFIG_TYPE$/etc/sysconfig/mail=advanced 55 Command line parameters of YaST modules SLES 15 SP64.4.3.25 yast tftp-server Configures a TFTP server. yast tftp-server accepts the following commands: directory Specifies the directory of the TFTP server: > sudo yast tftp-server directory path=/srv/tftp > sudo yast tftp-server directory list Directory Path: /srv/tftp status Controls the status of the TFTP server service: > sudo yast tftp-server status disable > sudo yast tftp-server status show Service Status: false > sudo yast tftp-server status enable 4.4.3.26 yast timezone Configures the time zone. yast timezone accepts the following commands: list Lists all available time zones grouped by region: > sudo yast timezone list Region: Africa Africa/Abidjan (Abidjan) Africa/Accra (Accra) Africa/Addis_Ababa (Addis Ababa) [...] set Specifies new values for the time zone configuration: > sudo yast timezone set timezone=Europe/Prague hwclock=local summary Displays the time zone configuration summary: > sudo yast timezone summary Current Time Zone: Europe/Prague 56 Command line parameters of YaST modules SLES 15 SP6Hardware Clock Set To: Local time Current Time and Date: Mon 12. March 2018, 11:36:21 CET 4.4.3.27 yast users Manages user accounts. yast users accepts the following commands: add Adds a new user: > sudo yast users add username=user1 password=secret home=/home/user1 For a complete list of options, run yast users add help . delete Deletes an existing user account: > sudo yast users delete username=user1 delete_home For a complete list of options, run yast users delete help . edit Changes an existing user account: > sudo yast users edit username=user1 password=new_secret For a complete list of options, run yast users edit help . list Lists existing users filtered by user type: > sudo yast users list system For a complete list of options, run yast users list help . show Displays details about a user: > sudo yast users show username=wwwrun Full Name: WWW daemon apache List of Groups: www Default Group: wwwrun Home Directory: /var/lib/wwwrun Login Shell: /sbin/nologin 57 Command line parameters of YaST modules SLES 15 SP6Login Name: wwwrun UID: 456 For a complete list of options, run yast users show help . 58 Command line parameters of YaST modules SLES 15 SP65 Changing language and country settings with YaST This chapter explains how to configure language and country settings. You can change the language globally for the whole system, individually for certain users or desktops, or temporarily for single applications. Additionally, you can configure sec- ondary languages and adjust the date and country settings. If you work in different countries or in a multilingual environment, you should configure your system accordingly. SUSE® Linux Enterprise Server can handle different locales in parallel. A locale is a set of parameters that defines the language and country settings reflected in the user interface. The main system language is selected during installation, and keyboard and time zone settings are adjusted accordingly. However, you can install additional languages and determine which of the installed languages should be the default. For those tasks, use the YaST language module as described in Section 5.1, “Changing the system language”. Install secondary languages to get optional localization if you need to start applica- tions or desktops in languages other than the primary one. The YaST time zone module allows you to adjust your country and time zone settings accord- ingly. It also lets you synchronize your system clock against a time server. For details, refer to Section 5.2, “Changing the country and time settings”. 5.1 Changing the system language Depending on how you use your desktop and whether you want to switch the entire system to another language or only the desktop environment, you have several options: Changing the system language globally Proceed as described in Section 5.1.1, “Modifying system languages with YaST” and Section 5.1.2, “Switching the default system language” to install additional localized packages with YaST and to set the default language. Changes are effective after the next login. To ensure that the entire system reflects the change, reboot the system or close and restart all running services, applications and programs. 59 Changing the system language SLES 15 SP6Changing the language for the desktop only Provided you have previously installed the desired language packages for your desktop environment with YaST as described below, you can switch the language of your desk- top using the desktop''s control center. After the X server has been restarted, your entire desktop reflects your new choice of language. Applications not belonging to your desktop framework are not affected by this change and may still appear in the language that was set in YaST. Temporarily switching languages for one application only You can also run a single application in another language (that has already been installed with YaST). To do so, start it from the command line by specifying the language code as described in Section 5.1.3, “Switching languages for standard X and GNOME applications”. 5.1.1 Modifying system languages with YaST YaST supports two different language categories: Primary Language The primary language set in YaST applies to the entire system, including YaST and the desktop environment. This language is used whenever available unless you manually spec- ify another language. Secondary Languages Install secondary languages to make your system multilingual. Languages installed as sec- ondary can be selected manually, when needed. For example, use a secondary language to start an application in a certain language to do word processing in this language. Before installing additional languages, determine which of them should be the default system language (primary language). To access the YaST language module, start YaST and click System Language. Alternatively, start the Languages dialog directly by running sudo yast2 language & from a command line. 60 Modifying system languages with YaST SLES 15 SP6PROCEDURE 5.1: INSTALLING ADDITIONAL LANGUAGES When installing additional languages, YaST allows you to set different locale settings for the user root , see Step 4. The option Locale Settings for User root determines how the locale variables ( LC_* ) in the le /etc/sysconfig/language are set for root . You can set them to the same locale as for regular users. Alternatively, you can keep them unaffected by any language changes, or only set the variable RC_LC_CTYPE to the same values as for the regular users. The RC_LC_CTYPE variable sets the localization for language-specific function calls. 1. To add languages in the YaST language module, select the Secondary Languages you want to install. 2. To make a language the default language, set it as Primary Language. 3. Additionally, adapt the keyboard to the new primary language and adjust the time zone, if appropriate. 61 Modifying system languages with YaST SLES 15 SP6Tip: Advanced settings For advanced keyboard or time zone settings, select Hardware System Keyboard Layout or System Date and Time in YaST. For more information, refer to Chapter 32, Setting up your system keyboard layout and Section 5.2, “Changing the country and time settings”. 4. To change language settings specific to the user root , click Details. a. Set Locale Settings for User root to the desired value. For more information, click Help. b. Decide whether to use Use UTF-8 Encoding for root or not. 5. If your locale was not included in the list of primary languages available, try specifying it with Detailed Locale Setting. However, this may result in certain locales being incomplete. 6. Confirm the changes in the dialogs with OK. If you have selected secondary languages, YaST installs the localized software packages for the additional languages. The system is now multilingual. However, to start an application in a language other than the primary one, you need to set the desired language explicitly as explained in Section 5.1.3, “Switch- ing languages for standard X and GNOME applications”. 5.1.2 Switching the default system language To globally change the default language of a system, use the following procedure: 1. Start the YaST language module. 2. Select the desired new system language as Primary Language. Important: Deleting former system languages If you switch to a different primary language, the localized software packages for the former primary language gets removed from the system. To switch the default system language but keep the former primary language as an additional language, add it as Secondary Language by selecting the respective check box. 3. Adjust the keyboard and time zone options as desired. 62 Switching the default system language SLES 15 SP64. Confirm your changes with OK. 5. After YaST has applied the changes, restart current X sessions (for example, by logging out and logging in again) to make YaST and the desktop applications reflect your new language settings. 5.1.3 Switching languages for standard X and GNOME applications After you have installed the respective language with YaST, you can run a single application in another language. Start the application from the command line by using the following command: LANG=LANGUAGE application For example, to start f-spot in German, run LANG=de_DE f-spot . For other languages, use the appropriate language code. Get a list of all language codes available with the locale  -av command. 5.2 Changing the country and time settings Using the YaST date and time module, adjust your system date, clock and time zone information to the area you are working in. To access the YaST module, start YaST and click System Date and Time. Alternatively, start the Clock and Time Zone dialog directly by running sudo yast2 timezone & from a command line. 63 Switching languages for standard X and GNOME applications SLES 15 SP6First, select a general region, such as Europe. Choose an appropriate country that matches the one you are working in, for example, Germany. Depending on which operating systems run on your workstation, adjust the hardware clock settings accordingly: If you run another operating system on your machine, such as Microsoft Windows*, your system may not use UTC, but local time. In this case, deactivate Hardware Clock Set To UTC. If you only run Linux on your machine, set the hardware clock to UTC and have the switch from standard time to daylight saving time performed automatically. Important: Set the hardware clock to UTC The switch from standard time to daylight saving time (and vice versa) can only be per- formed automatically when the hardware clock (CMOS clock) is set to UTC. This also applies if you use automatic time synchronization with NTP, because automatic synchro- nization is only performed if the time difference between the hardware and system clock is less than 15 minutes. Since a wrong system time can cause serious problems (missed backups, dropped mail messages, mount failures on remote le systems, etc.) it is strongly recommended to always set the hardware clock to UTC. 64 Changing the country and time settings SLES 15 SP6You can change the date and time manually or opt for synchronizing your machine against an NTP server, either permanently or only for adjusting your hardware clock. PROCEDURE 5.2: MANUALLY ADJUSTING TIME AND DATE 1. In the YaST timezone module, click Other Settings to set date and time. 2. Select Manually and enter date and time values. 3. Confirm your changes. PROCEDURE 5.3: SETTING DATE AND TIME WITH NTP SERVER 1. Click Other Settings to set date and time. 2. Select Synchronize with NTP Server. 3. Enter the address of an NTP server, if not already populated. 4. With the Configure button, you can open the advanced NTP configuration. For details, see Section 38.1, “Configuring an NTP client with YaST”. 5. Confirm your changes. 65 Changing the country and time settings SLES 15 SP66 Managing users with YaST During installation, you may have created a local user for your system. With the YaST module User and Group Management you can add users or edit existing ones. It also lets you configure your system to authenticate users with a network server. 6.1 User and group administration dialog To administer users or groups, start YaST and click Security and Users User and Group Man- agement. Alternatively, start the User and Group Administration dialog directly by running sudo yast2 users & from a command line. FIGURE 6.1: YAST USER AND GROUP ADMINISTRATION Every user is assigned a system-wide user ID (UID). Apart from the users that can log in to your machine, there are also several system users for internal use only. Each user is assigned to one or more groups. Similar to system users, there are also system groups for internal use. 66 User and group administration dialog SLES 15 SP6The main window shows several tabs, depending on the set of users (local users, network users, system users) you choose to view and modify. The tabs allow you to perform the following tasks: Managing user accounts From the Users tab create, modify, delete or temporarily disable user accounts as described in Section 6.2, “Managing user accounts”. Learn about advanced options like enforcing pass- word policies, using encrypted home directories, or managing disk quotas in Section 6.3, “Additional options for user accounts”. Changing default settings Local user accounts are created according to the settings defined on the Defaults for New Users tab. Learn how to change the default group assignment, or the default path and access permissions for home directories in Section 6.4, “Changing default settings for local users”. Assigning users to groups Learn how to change the group assignment for individual users in Section 6.5, “Assigning users to groups”. Managing groups From the Groups tab, you can add, modify or delete existing groups. Refer to Section 6.6, “Managing groups” for information on how to do this. Changing user authentication method When your machine is connected to a network that provides user authentication methods like NIS or LDAP, you can choose between several authentication methods on the Authen- tication Settings tab. For more information, refer to Section 6.7, “Changing the user authenti- cation method”. For user and group management, the dialog provides similar functionality. You can easily switch between the user and group administration view by choosing the appropriate tab at the top of the dialog. Filter options allow you to define the set of users or groups you want to modify: on the Users or Group tab, click Set Filter to view and edit users or groups. They are listed according to certain categories, such as Local Users or LDAP Users, if applicable. With Set Filter Customize Filter you can also set up and use a custom filter. Depending on the filter you choose, not all the following options and functions may be available from the dialog. 67 User and group administration dialog SLES 15 SP66.2 Managing user accounts YaST allows you to create, modify, delete or temporarily disable user accounts. Do not modify user accounts unless you are an experienced user or administrator. Note: Changing user IDs of existing users File ownership is bound to the user ID, not to the user name. After a user ID change, the les in the user''s home directory are automatically adjusted to reflect this change. However, after an ID change, the user no longer owns the les they created elsewhere in the le system unless the le ownership for those les is manually modified. The following instructions demonstrate how to set up default user accounts. For further options, refer to Section 6.3, “Additional options for user accounts”. PROCEDURE 6.1: ADDING OR MODIFYING USER ACCOUNTS 1. Open the YaST User and Group Administration dialog and click the Users tab. 2. With Set Filter define the set of users you want to manage. The dialog lists users in the system and the groups the users belong to. 3. To modify options for an existing user, select an entry and click Edit. To create a new user account, click Add. 4. Enter the appropriate user data on the rst tab, such as Username (which is used for login) and Password. This data is sufficient to create a new user. If you click OK now, the system automatically assigns a user ID and sets all other values as default. 5. Activate Receive System Mail if you want system notifications to be delivered to this user''s mailbox. This creates a mail alias for root and the user can read the system mail without having to rst log in as root . The mails sent by system services are stored in the local mailbox /var/spool/ mail/ USERNAME , where USERNAME is the login name of the selected user. To read e-mails, you can use the mail command. 6. To adjust further details such as the user ID or the path to the user''s home directory, do so on the Details tab. If you need to relocate the home directory of an existing user, enter the path to the new home directory there and move the contents of the current home directory with Move to New Location. Otherwise, a new home directory is created without any of the existing data. 68 Managing user accounts SLES 15 SP67. To force users to regularly change their password or set other password options, switch to Password Settings and adjust the options. For more details, refer to Section 6.3.2, “Enforcing password policies”. 8. If all options are set according to your wishes, click OK. 9. Click OK to close the administration dialog and to save the changes. A newly added user can now log in to the system using the login name and password you created. Alternatively, to save all changes without exiting the User and Group Administration dialog, click Expert Options Write Changes Now. Warning: Do not rename the root account While it is technically possible to rename the root account, certain applications, scripts or third-party products may rely on the existence of a user called root . While such a configuration always targets individual environments, necessary adjustments could be overwritten by vendor updates, so this becomes an ongoing task rather than a one-time setting. This is especially true in complex setups involving third-party applications, where it needs to be verified with every vendor involved whether a rename of the root account is supported. As the implications for renaming the root account cannot be foreseen, SUSE does not support renaming the root account. Usually, the idea behind renaming the root account is to hide it or make it unpredictable. However, /etc/passwd requires 644 permissions for regular users, so any user of the system can retrieve the login name for the user ID 0. For better ways to secure the root account, refer to Book “Security and Hardening Guide”, Chapter 14 “User management”, Sec- tion 14.5 “Restricting root logins” and Book “Security and Hardening Guide”, Chapter 14 “User management”, Section 14.5.3 “Restricting SSH logins”. Tip: Matching user IDs It is useful to match the (local) user ID to the ID in the network. For example, a new (local) user on a laptop should be integrated into a network environment with the same user ID. This ensures that the le ownership of the les the user creates “offline” is the same as if they had created them directly on the network. 69 Managing user accounts SLES 15 SP6PROCEDURE 6.2: DISABLING OR DELETING USER ACCOUNTS 1. Open the YaST User and Group Administration dialog and click the Users tab. 2. To temporarily disable a user account without deleting it, select the user from the list and click Edit. Activate Disable User Login. The user cannot log in to your machine until you enable the account again. 3. To delete a user account, select the user from the list and click Delete. Choose if you also want to delete the user''s home directory or to retain the data. 6.3 Additional options for user accounts Besides the settings for a default user account, SUSE® Linux Enterprise Server offers further options. For example, options to enforce password policies, use encrypted home directories or define disk quotas for users and groups. 6.3.1 Automatic login and passwordless login If you use the GNOME desktop environment you can configure Auto Login for a certain user and Passwordless Login for all users. Auto login causes a user to become automatically logged in to the desktop environment on boot. This functionality can only be activated for one user at a time. Login without password allows all users to log in to the system after they have entered their user name in the login manager. Warning: Security risk Enabling Auto Login or Passwordless Login on a machine that can be accessed by more than one person is a security risk. Without the need to authenticate, any user can gain access to your system and your data. If your system contains confidential data, do not use this functionality. To activate auto login or login without password, access these functions in the YaST User and Group Administration with Expert Options Login Settings. 70 Additional options for user accounts SLES 15 SP66.3.2 Enforcing password policies On any system with multiple users, it is a good idea to enforce at least basic password security policies. Users should change their passwords regularly and use strong passwords that cannot easily be exploited. For local users, proceed as follows: PROCEDURE 6.3: CONFIGURING PASSWORD SETTINGS 1. Open the YaST User and Group Administration dialog and select the Users tab. 2. Select user and click Edit. 3. Switch to the Password Settings tab. The user''s last password change is displayed on the tab. 4. To make the user change their password at next login, activate Force Password Change. 5. To enforce password rotation, set a Maximum Number of Days for the Same Password and a Minimum Number of Days for the Same Password. 6. To remind the user to change their password before it expires, set the number of Days before Password Expiration to Issue Warning. 7. To restrict the period of time the user can log in after their password has expired, change the value in Days after Password Expires with Usable Login. 8. You can also specify a certain expiration date for the complete account. Enter the Expiration Date in YYYY-MM-DD format. This setting is not password-related but rather applies to the account itself. 9. For more information about options and default values, click Help. 10. Apply your changes with OK. 6.3.3 Managing quotas To prevent system capacities from being exhausted without notification, system administrators can set up quotas for users or groups. Quotas can be defined for one or more le systems and restrict the amount of disk space that can be used and the number of inodes (index nodes) that can be created there. Inodes are data structures on a le system that store basic information about a regular le, directory or other le system object. They store all attributes of a le system object (like user and group ownership, read, write or execute permissions), except le name and contents. 71 Enforcing password policies SLES 15 SP6SUSE Linux Enterprise Server allows usage of soft and hard quotas. Additionally, grace in- tervals can be defined that allow users or groups to temporarily exceed their quotas by certain amounts. Soft quota Defines a warning level at which users are informed that they are nearing their limit. Administrators may urge the users to clean up and reduce their data on the partition. The soft quota limit is normally lower than the hard quota limit. Hard quota Defines the limit at which write requests are denied. When the hard quota is reached, no more data can be stored and applications may crash. Grace period Defines the time between the overflow of the soft quota and a warning being issued. Nor- mally set to a rather low value of one or several hours. PROCEDURE 6.4: ENABLING QUOTA SUPPORT FOR A PARTITION To configure quotas for certain users and groups, you need to enable quota support for the respective partition in the YaST Expert Partitioner rst. Note: Quotas for Btrfs partitions Quotas for Btrfs partitions are handled differently. For more information, see Book “Storage Administration Guide”, Chapter 1 “Overview of file systems in Linux”, Section 1.2.5 “Btrfs quota support for subvolumes”. 1. In YaST, select System Partitioner and click Yes to proceed. 2. In the Expert Partitioner, select the partition for which to enable quotas and click Edit. 3. Click Fstab Options and activate Enable Quota Support. If the quota package is not already installed, it will be installed when you confirm the respective message with Yes. 4. Confirm your changes and leave the Expert Partitioner. 5. Make sure the service quotaon is running by entering the following command: > sudo systemctl status quotaon.service It should be marked as being active . If this is not the case, start it with the command systemctl start quotaon.service . 72 Managing quotas SLES 15 SP6PROCEDURE 6.5: SETTING UP QUOTAS FOR USERS OR GROUPS Now you can define soft or hard quotas for specific users or groups and set time periods as grace intervals. 1. In the YaST User and Group Administration, select the user or the group you want to set the quotas for and click Edit. 2. On the Plug-Ins tab, select the Manage User Quota entry and click Launch to open the Quota Configuration dialog. 3. From File System, select the partition to which the quota should apply. 4. Below Size Limits, restrict the amount of disk space. Enter the number of 1 KB blocks the user or group may have on this partition. Specify a Soft Limit and a Hard Limit value. 5. Additionally, you can restrict the number of inodes the user or group may have on the partition. Below Inodes Limits, enter a Soft Limit and Hard Limit. 6. You can only define grace intervals if the user or group has already exceeded the soft limit specified for size or inodes. Otherwise, the time-related text boxes are not activated. Specify the time period for which the user or group is allowed to exceed the limits set above. 7. Confirm your settings with OK. 73 Managing quotas SLES 15 SP68. Click OK to close the administration dialog and save the changes. Alternatively, to save all changes without exiting the User and Group Administration dialog, click Expert Options Write Changes Now. SUSE Linux Enterprise Server also ships command line tools like repquota or warnquota . System administrators can use these tools to control the disk usage or send e-mail notifications to users exceeding their quota. Using quota_nld , administrators can also forward kernel messages about exceeded quotas to D-BUS. For more information, refer to the repquota , the warnquota and the quota_nld man page. 6.4 Changing default settings for local users When creating new local users, several default settings are used by YaST. These include, for example, the group the user belongs to, or the access permissions of the user''s home directory. You can change these default settings to meet your requirements: 1. Open the YaST User and Group Administration dialog and select the Defaults for New Users tab. 2. To change the group the new users should automatically belong to, select another group from Default Group. 3. If you do not want to use /home/USERNAME as the default path for new users'' home direc- tories, modify the Path Prefix for Home Directory. 4. To change the default permission modes for newly created home directories, adjust the umask value in Umask for Home Directory. For more information about umask, refer to Book “Security and Hardening Guide”, Chapter 19 “Access control lists in Linux” and to the umask man page. 5. For information about the individual options, click Help. 6. Apply your changes with OK. 74 Changing default settings for local users SLES 15 SP66.5 Assigning users to groups Local users are assigned to several groups according to the default settings, which you can access from the User and Group Administration dialog on the Defaults for New Users tab. In the following, learn how to modify an individual user''s group assignment. If you need to change the default group assignments for new users, refer to Section 6.4, “Changing default settings for local users”. PROCEDURE 6.6: CHANGING A USER''S GROUP ASSIGNMENT 1. Open the YaST User and Group Administration dialog and click the Users tab. It lists users and the groups the users belong to. 2. Click Edit and switch to the Details tab. 3. To change the group the user belongs to, click Default Group and select the group from the list. 4. To assign the user additional secondary groups, activate the corresponding check boxes in the Additional Groups list. 5. Click OK to apply your changes. 6. Click OK to close the administration dialog and save the changes. Alternatively, to save all changes without exiting the User and Group Administration dialog, click Expert Options Write Changes Now. 6.6 Managing groups With YaST you can also easily add, modify or delete groups. PROCEDURE 6.7: CREATING AND MODIFYING GROUPS 1. Open the YaST User and Group Management dialog and click the Groups tab. 2. With Set Filter define the set of groups you want to manage. The dialog lists groups in the system. 3. To create a new group, click Add. 4. To modify an existing group, select the group and click Edit. 75 Assigning users to groups SLES 15 SP65. In the following dialog, enter or change the data. The list on the right shows an overview of all available users and system users which can be members of the group. 6. To add existing users to a new group select them from the list of possible Group Members by checking the corresponding box. To remove them from the group deactivate the box. 7. Click OK to apply your changes. 8. Click OK to close the administration dialog and save the changes. Alternatively, to save all changes without exiting the User and Group Administration dialog, click Expert Options Write Changes Now. To delete a group, it must not contain any group members. To delete a group, select it from the list and click Delete. Click OK to close the administration dialog and save the changes. Alterna- tively, to save all changes without exiting the User and Group Administration dialog, click Expert Options Write Changes Now. 76 Managing groups SLES 15 SP66.7 Changing the user authentication method When your machine is connected to a network, you can change the authentication method. The following options are available: NIS Users are administered centrally on a NIS server for all systems in the network. For details, see Book “Security and Hardening Guide”, Chapter 3 “Using NIS”. SSSD The System Security Services Daemon (SSSD) can locally cache user data and then allow users to use the data, even if the real directory service is (temporarily) unreachable. For details, see Book “Security and Hardening Guide”, Chapter 4 “Setting up authentication clients using YaST”, Section 4.2 “SSSD”. Samba SMB authentication is often used in mixed Linux and Windows networks. For details, see Book “Storage Administration Guide”, Chapter 20 “Samba” . To change the authentication method, proceed as follows: 1. Open the User and Group Administration dialog in YaST. 2. Click the Authentication Settings tab to show an overview of the available authentication methods and the current settings. 3. To change the authentication method, click Configure and select the authentication method you want to modify. This takes you directly to the client configuration modules in YaST. For information about the configuration of the appropriate client, refer to the following sections: NIS: Book “Security and Hardening Guide”, Chapter 3 “Using NIS”, Section 3.2 “Configuring NIS clients” LDAP: Book “Security and Hardening Guide”, Chapter 4 “Setting up authentication clients using YaST”, Section 4.1 “Configuring an authentication client with YaST” Samba: Book “Storage Administration Guide”, Chapter 20 “Samba”, Section 20.5.1 “Configuring a Samba client with YaST” 77 Changing the user authentication method SLES 15 SP6SSSD: Book “Security and Hardening Guide”, Chapter 4 “Setting up authentication clients using YaST”, Section 4.2 “SSSD” 4. After accepting the configuration, return to the User and Group Administration overview. 5. Click OK to close the administration dialog. 6.8 Default system users By default, SUSE Linux Enterprise Server creates user names, which cannot be deleted. These users are typically defined in the Linux Standard Base (see https://refspecs.linuxfoundation.org/ls- b.shtml ). The following list provides the common user names and their purpose: COMMON USER NAMES INSTALLED BY DEFAULT bin , daemon Legacy user, included for compatibility with legacy applications. New applications should no longer use this user name. gdm Used by GNOME Display Manager (GDM) to provide graphical logins and manage local and remote displays. lp Used by the Printer daemon for Common Unix Printing System (CUPS). mail User reserved for mailer programs like sendmail or postfix . man Used by man to access man pages. messagebus Used to access D-Bus (desktop bus), a software bus for inter-process communication. Dae- mon is dbus-daemon . nobody User that owns no les and is in no privileged groups. Nowadays, its use is limited as it is recommended by Linux Standard Base to provide a separate user account for each daemon. 78 Default system users SLES 15 SP6nscd Used by the Name Service Caching Daemon. This daemon is a lookup service to improve performance with NIS and LDAP. Daemon is nscd . polkitd Used by the PolicyKit Authorization Framework, which defines and handles authorization requests for unprivileged processes. Daemon is polkitd . postfix Used by the Postfix mailer. pulse Used by the Pulseaudio sound server. root Used by the system administrator, providing all appropriate privileges. rpc Used by the rpcbind command, an RPC port mapper. rtkit Used by the rtkit package providing a D-Bus system service for real time scheduling mode. salt User for parallel remote execution provided by Salt. Daemon is named salt-master . scard User for communication with smart cards and readers. Daemon is named pcscd . srvGeoClue Used by the GeoClue D-Bus service to provide location information. sshd Used by the Secure Shell daemon (SSH) to ensure secured and encrypted communication over an insecure network. statd Used by the Network Status Monitor protocol (NSM), implemented in the rpc.statd daemon, to listen for reboot notifications. 79 Default system users SLES 15 SP6systemd-coredump Used by the /usr/lib/systemd/systemd-coredump command to acquire, save and process core dumps. systemd-timesync Used by the /usr/lib/systemd/systemd-timesyncd command to synchronize the local system clock with a remote Network Time Protocol (NTP) server. 6.9 Default system groups By default, SLE creates multiple user groups that are used by system services. The following list describes examples of required and common optional groups. root Administrative group with all privileges. bin Included for compatibility with legacy applications. New applications should not use this group. daemon Previously used to limit daemons'' access to the system. Daemons should run under their own UID/GID now to separate daemons from one another. audio Privileges for audio devices. gdm Privileges for the GNOME Display Manager. chrony Privileges for the time synchronization service. kvm Privileges for the QEMU machine emulator toolkit. libvirt Privileges for virtualization stack. lp Privileges for printer operation. 80 Default system groups SLES 15 SP6mail Privileges for mail services. man Privileges specific to manual pages and the man command. sshd Privileges for SSH communication protocol daemon. 81 Default system groups SLES 15 SP67 YaST online update SUSE offers a continuous stream of software security updates for your product. By default, the update applet is used to keep your system up to date. Refer to Section 8.5, “The GNOME package updater” for further information on the update applet. This chapter covers the alternative tool for updating software packages: YaST Online Update. The current patches for SUSE® Linux Enterprise Server are available from an update software repository. If you have registered your product during the installation, an update repository is already configured. If you have not registered SUSE Linux Enterprise Server, you can do so by starting the Product Registration in YaST. Alternatively, you can manually add an update repos- itory from a source you trust. To add or remove repositories, start the Repository Manager with Software Software Repositories in YaST. Learn more about the Repository Manager in Section 8.4, “Managing software repositories and services”. Note: Error on accessing the update catalog If you are not able to access the update catalog, this may happen because of an expired subscription. Normally, SUSE Linux Enterprise Server comes with a one-year or three- year subscription, during which you have access to the update catalog. This access will be denied after the subscription ends. If an access to the update catalog is denied, you can see a warning message prompting you to visit the SUSE Customer Center and check your subscription. The SUSE Customer Center is available at https://scc.suse.com// . Note: Firewall settings for receiving updates By default, the firewall on SUSE Linux Enterprise Server only blocks incoming connec- tions. If your system is behind another firewall that blocks outgoing traffic, make sure to allow connections to https://scc.suse.com/ and https://updates.suse.com on ports 80 and 443 in order to receive updates. SUSE provides updates with different relevance levels: Security updates Fix severe security hazards and should always be installed. 82 SLES 15 SP6Recommended updates Fix issues that could compromise your computer. Optional updates Fix non-security relevant issues or provide enhancements. 7.1 The online update dialog To open the YaST Online Update dialog, start YaST and select Software Online Update. Alterna- tively, start it from the command line with yast2 online_update . The Online Update window consists of four sections. FIGURE 7.1: YAST ONLINE UPDATE The Summary section on the left lists the available patches for SUSE Linux Enterprise Server. The patches are sorted by security relevance: security , recommended , and optional . You can change the view of the Summary section by selecting one of the following options from Show Patch Category: Needed patches (default view) Non-installed patches that apply to packages installed on your system. 83 The online update dialog SLES 15 SP6Unneeded patches Patches that either apply to packages not installed on your system, or patches that have requirements which have already have been fulfilled (because the relevant packages have already been updated from another source). All patches All patches available for SUSE Linux Enterprise Server. Each list entry in the Summary section consists of a symbol and the patch name. For an overview of the possible symbols and their meaning, press Shift – F1 . Actions required by Security and Recommended patches are automatically preset. These actions are Autoinstall, Autoupdate and Autodelete. If you install an up-to-date package from a repository other than the update repository, the requirements of a patch for this package may be fulfilled with this installation. In this case, a check mark is displayed in front of the patch summary. The patch is visible in the list until you mark it for installation. This does not install the patch (because the package already is up to date), but mark the patch as having been installed. Select an entry in the Summary section to view a short Patch Description at the bottom left corner of the dialog. The upper right section lists the packages included in the selected patch (a patch can consist of several packages). Click an entry in the upper right section to view details about the respective package that is included in the patch. 7.2 Installing patches The YaST Online Update dialog allows you to either install all available patches at once or manually select the desired patches. You may also revert patches that have been applied to the system. By default, all new patches (except optional ones) that are currently available for your system are already marked for installation. They will be applied automatically once you click Accept or Apply. If one or multiple patches require a system reboot, you will be notified about this before the patch installation starts. You can then either decide to continue with the installation of the selected patches, skip the installation of all patches that need rebooting and install the rest, or go back to the manual patch selection. PROCEDURE 7.1: APPLYING PATCHES WITH YAST ONLINE UPDATE 1. Start YaST and select Software Online Update. 84 Installing patches SLES 15 SP62. To automatically apply all new patches (except optional ones) that are currently avail- able for your system, click Apply or Accept. 3. First modify the selection of patches that you want to apply: a. Use the respective filters and views that the interface provides. For details, refer to Section 7.1, “The online update dialog”. b. Select or deselect patches according to your needs and wishes by right-clicking the patch and choosing the respective action from the context menu. Important: Always apply security updates Do not deselect any security -related patches without a good reason. These patches x severe security hazards and prevent your system from being ex- ploited. c. Most patches include updates for several packages. To change actions for single pack- ages, right-click a package in the package view and choose an action. d. To confirm your selection and apply the selected patches, proceed with Apply or Accept. 4. After the installation is complete, click Finish to leave the YaST Online Update. Your system is now up to date. 7.3 Viewing retracted patches Maintenance updates are carefully tested to minimize the risk of introducing a bug. If a patch proves to contain a bug, it is automatically retracted. A new update (with a higher version number) is issued to revert the buggy patch, and is blocked from being installed again. You can see retracted patches, and their history, on the Package Classification tab. 85 Viewing retracted patches SLES 15 SP6FIGURE 7.2: VIEWING RETRACTED PATCHES AND HISTORY 7.4 Automatic online update You may configure automatic updates with a daily, weekly or monthly schedule with YaST. Install the yast2-online-update-configuration package. By default, updates are downloaded as delta RPMs. Since rebuilding RPM packages from delta RPMs is a memory- and processor-intensive task, certain setups or hardware configurations may require you to disable the use of delta RPMs for the sake of performance. Certain patches, such as kernel updates or packages requiring license agreements, require user interaction, which would cause the automatic update procedure to stop. You can configure skipping patches that require user interaction. Use the Patches tab in the YaST Software module to review available and installed patches, including references to bug reports and CVE bulletins. PROCEDURE 7.2: CONFIGURING THE AUTOMATIC ONLINE UPDATE 1. After installation, start YaST and select Software Online Update. Choose Configura- tion Online Update. If the yast2-online-update-configuration is not installed, you will be prompted to do that. 86 Automatic online update SLES 15 SP6FIGURE 7.3: YAST ONLINE UPDATE CONFIGURATION Alternatively, start the module with yast2  online_update_configuration from the command line. 2. Choose the update interval: Daily, Weekly, or Monthly. 3. Sometimes patches may require the attention of the administrator, for example when restarting critical services. For example, this might be an update for Docker Open Source Engine that requires all containers to be restarted. Before these patches are installed, the user is informed about the consequences and is asked to confirm the installation of the patch. Such patches are called “Interactive Patches”. When installing patches automatically, it is assumed that you have accepted the installa- tion of interactive patches. If you prefer to review these patches before they get installed, check Skip Interactive Patches. In this case, interactive patches will be skipped during auto- mated patching. Make sure to periodically run a manual online update, to check whether interactive patches are waiting to be installed. 4. To automatically accept any license agreements, activate Agree with Licenses. 5. To automatically install all packages recommended by updated packages, activate Include Recommended Packages. 6. To disable the use of delta RPMs (for performance reasons), un-check Use Delta RPMs. 87 Automatic online update SLES 15 SP67. To filter the patches by category (such as security or recommended), check Filter by Cate- gory and add the appropriate patch categories from the list. Only patches of the selected categories will be installed. It is a good practice to enable only automatic Security updates, and to manually review all others. Patching is normally reliable, but you may wish to test non-security patches, and roll them back if you encounter any problems. Packagemanager and YaST supply patches for package management and YaST fea- tures and modules. Security patches provide crucial updates and bugfixes. Recommended patches are optional bugfixes and enhancements. Optional are new packages. Other is equivalent to miscellaneous. Document is unused. 8. Confirm your configuration by clicking OK. The automatic online update does not automatically restart the system afterward. If there are package updates that require a system reboot, you need to do this manually. 88 Automatic online update SLES 15 SP68 Installing or removing software Using YaST''s software management module, you can search for software packages as well as install and remove them. When installing packages, YaST automatically resolves all dependencies. To install packages that are not on the installation medi- um, you can add software repositories and YaST to manage them. You can also keep your system up to date by managing software updates using the update applet. The YaST Software Manager makes it possible to manage software sources on your system. There are two versions of this YaST module: a graphical version for X Window and a text-based version to use with the command line. The graphical flavor is described below—for details on the text- based YaST, see Chapter 4, YaST in text mode. Note: Confirmation and review of changes When installing, updating or removing packages, any changes in the Software Manager are only applied after clicking Accept or Apply. YaST maintains a list with all actions, allowing you to review and modify your changes before applying them to the system. 8.1 Definition of terms The following terms are important for understanding installing and removing software in SUSE Linux Enterprise Server. Repository A local or remote directory containing packages, plus additional information about these packages (package metadata). (Repository) alias/repository name A short name for a repository (called Alias within Zypper and Repository Name within YaST). It can be chosen by the user when adding a repository and must be unique. Repository description files Each repository provides les describing content of the repository (package names, ver- sions, etc.). These repository description les are downloaded to a local cache that is used by YaST. 89 Definition of terms SLES 15 SP6Product Represents a whole product, for example, SUSE® Linux Enterprise Server. Pattern A pattern is an installable group of packages dedicated to a certain purpose. For example, the Laptop pattern contains all packages that are needed in a mobile computing environ- ment. Patterns define package dependencies (such as required or recommended packages) and come with a preselection of packages marked for installation. This ensures that the most important packages needed for a certain purpose are available on your system af- ter installation of the pattern. If necessary, you can manually select or deselect packages within a pattern. Package A package is a compressed le in rpm format that contains the les for a particular pro- gram. Patch A x or compilation of fixes released by SUSE to correct operation defects (program bugs) in SUSE products. A patch can contain one or multiple les to replace or enhance existing executables, programs, applications or documents. A patch consists of one or more packages and may be applied by delta RPMs. It may also introduce dependencies to packages that are not installed yet. Resolvable A generic term for product, pattern, package or patch. The most commonly used type of resolvable is a package or a patch. Delta RPM A delta RPM consists only of the binary di between two defined versions of a package, and therefore has the smallest download size. Before being installed, the full RPM package is rebuilt on the local machine. Package dependencies Certain packages are dependent on other packages, such as shared libraries. In other terms, a package may require other packages—if the required packages are not available, the package cannot be installed. Besides dependencies (package requirements) that must be fulfilled, certain packages recommend other packages. These recommended packages are only installed if they are available, otherwise they are ignored and the package recom- mending them is installed nevertheless. 90 Definition of terms SLES 15 SP68.2 Registering an installed system If you skip registration during installation, or you want to re-register your system, you can register the system at any time. Use the YaST module Product Registration or the command line tool SUSEConnect . 8.2.1 Registering with YaST To register the system, start YaST and switch to Software, then Product Registration. By default the system is registered with the SUSE Customer Center. If your organization provides local registration servers, you can either choose one from the list of auto-detected servers or provide the URL manually. 8.2.2 Registering with SUSEConnect To register from the command line, use the command > sudo SUSEConnect -r REGISTRATION_CODE -e EMAIL_ADDRESS Replace REGISTRATION_CODE with the registration code you received with your copy of SUSE Linux Enterprise Server. Replace EMAIL_ADDRESS with the e-mail address associated with the SUSE account you or your organization uses to manage subscriptions. To register with a local registration server, also provide the URL to the server: > sudo SUSEConnect -r REGISTRATION_CODE -e EMAIL_ADDRESS --url "URL" 8.3 Using the YaST software manager Start the software manager from the YaST Control Center by choosing Software Software Man- agement. 91 Registering an installed system SLES 15 SP68.3.1 Searching software The YaST software manager can install packages or patterns from all currently enabled reposi- tories. It offers different views and filters to make it easier to nd the software you are searching for. The Search view is the default view of the window. To change view, click View and select one of the following entries from the drop-down box. The selected view opens in a new tab. VIEWS FOR SEARCHING PACKAGES OR PATTERNS Patterns Lists all patterns available for installation on your system. Package Groups Lists all packages sorted by groups such as Graphics, Programming, or Security. Languages A filter to list all packages needed to add a new system language. Repositories A filter to list packages by repository. To select more than one repository, hold the Ctrl key while clicking repository names. The “pseudo repository” @System lists all packages currently installed. 92 Searching software SLES 15 SP6Services Shows which packages belong to a certain module or extension. Select an entry (for ex- ample, Basesystem or High Availability ) to display a list of packages that belong to this module or extension. Search Lets you search for a package according to certain criteria. Enter a search term and press Enter . Refine your search by specifying where to Search In and by changing the Search Mode. For example, if you do not know the package name but only the name of the applica- tion that you are searching for, try including the package Description in the search process. Installation Summary If you have already selected packages for installation, update or removal, this view shows the changes that will be applied to your system when you click Accept. To filter for packages with a certain status in this view, activate or deactivate the respective check boxes. Press Shift – F1 for details on the status ags. Tip: Finding packages not belonging to an active repository To list all packages that do not belong to an active repository, choose View Reposito- ries @System and then choose Secondary Filter Unmaintained Packages. This is useful, for example, if you have deleted a repository and want to make sure no packages from that repository remain installed. Tip: Searching software online The online search feature allows searching for packages across all registered and unreg- istered modules and extensions. PROCEDURE 8.1: SEARCHING SOFTWARE ONLINE To search for software packages online, perform the following steps: 1. Open the online search window with Extras Search Online. 2. Enter a Package Name and press Enter or click Search. YaST contacts the SUSE Customer Center and shows the results in a table, including the module or extension of each package. Select a package to see additional details. 93 Searching software SLES 15 SP63. Select one or more packages for installation by clicking the corresponding table row and Toggle Selection. Alternatively, you can double-click a row. If the package belongs to an unregistered module or extension, YaST asks for confirmation to reg- ister it. 4. Click Next, review the changes, and install the packages. 8.3.2 Installing and removing packages or patterns Certain packages are dependent on other packages, such as shared libraries. Several packages cannot coexist with others on the system. If possible, YaST automatically resolves these depen- dencies or conflicts. If your choice results in a dependency conflict that cannot be automatically solved, you need to solve it manually as described in Section 8.3.4, “Package dependencies”. Note: Removal of packages When removing any packages, by default YaST only removes the selected packages. If you want YaST to also remove any other packages that become unneeded after removal of the specified package, select Options Cleanup when deleting packages from the main menu. 1. Search for packages as described in Section 8.3.1, “Searching software”. 2. The packages found are listed in the right pane. To install a package or remove it, right- click it and choose Install or Delete. If the relevant option is not available, check the package status indicated by the symbol in front of the package name—press Shift – F1 for help. Tip: Applying an action to all packages listed To apply an action to all packages listed in the right pane, go to the main menu and choose an action from Package All in This List. 3. To install a pattern, right-click the pattern name and choose Install. 4. It is not possible to remove a pattern. Instead, select the packages for the pattern you want to remove and mark them for removal. 5. To select more packages, repeat the steps mentioned above. 94 Installing and removing packages or patterns SLES 15 SP66. Before applying your changes, you can review or modify them by clicking View Installa- tion Summary. By default, all packages that will change status are listed. 7. To revert the status for a package, right-click the package and select one of the following entries: Keep if the package was scheduled to be deleted or updated, or Do Not Install if it was scheduled for installation. To abandon all changes and quit the Software Manager, click Cancel and Abandon. 8. When you are finished, click Accept to apply your changes. 9. If YaST nds additional dependencies, it shows a list of related packages to install, update or remove. Click Continue to accept them. After all selected packages are installed, updated or removed, the YaST Software Manager automatically closes. Note: Installing source packages Installing source packages with YaST Software Manager is not possible at the moment. Use the command line tool zypper for this purpose. For more information, see Section 9.1.3.5, “Installing or downloading source packages”. 8.3.3 Updating packages Instead of updating individual packages, you can also update all installed packages or all pack- ages from a certain repository. When mass updating packages, the following aspects are gener- ally considered: priorities of the repositories that provide the package, architecture of the package (for example, AMD64/Intel 64), version number of the package, package vendor. Which of the aspects has the highest importance for choosing the update candidates depends on the respective update option you choose. 1. To update all installed packages to the latest version, choose Package All Packages Up- date if Newer Version Available from the main menu. 95 Updating packages SLES 15 SP6All repositories are checked for possible update candidates, using the following policy: YaST rst tries to restrict the search to packages with the same architecture and vendor as the installed one. If the search is positive, the “best” update candidate from those is selected according to the process below. However, if no comparable package of the same vendor can be found, the search is expanded to all packages with the same architecture. If still no comparable package can be found, all packages are considered and the “best” update candidate is selected according to the following criteria: 1. Repository priority: prefer the package from the repository with the highest priority. 2. If more than one package results from this selection, choose the one with the “best” architecture (best choice: matching the architecture of the installed one). If the resulting package has a higher version number than the installed one, the installed package is updated and replaced with the selected update candidate. This option tries to avoid changes in architecture and vendor for the installed packages, but under certain circumstances, they are tolerated. Note: Update unconditionally If you choose Package All Packages Update Unconditionally instead, the same cri- teria apply but any candidate package found is installed unconditionally. Thus, choosing this option may lead to downgrading certain packages. 2. To make sure that the packages for a mass update derive from a certain repository: a. Choose the repository from which to update as described in Section 8.3.1, “Searching software” . b. On the right hand side of the window, click Switch system packages to the versions in this repository. This explicitly allows YaST to change the package vendor when replacing the packages. When you proceed with Accept, all installed packages are replaced by packages de- riving from this repository, if available. This may lead to changes in vendor and ar- chitecture and even to downgrading certain packages. c. To refrain from this, click Cancel switching system packages to the versions in this repos- itory. You can only cancel this until you click the Accept button. 96 Updating packages SLES 15 SP63. Before applying your changes, you can review or modify them by clicking View Installa- tion Summary. By default, all packages that will change status, are listed. 4. If all options are set according to your wishes, confirm your changes with Accept to start the mass update. 8.3.4 Package dependencies Most packages are dependent on other packages. If a package, for example, uses a shared library, it is dependent on the package providing this library. Certain packages cannot coexist, causing a conflict (for example, you can only install one mail transfer agent: sendmail or postfix). When installing or removing software, the Software Manager makes sure no dependencies or conflicts remain unsolved to ensure system integrity. In case there exists only one solution to resolve a dependency or a conflict, it is resolved auto- matically. Multiple solutions always cause a conflict which needs to be resolved manually. If solving a conflict involves a vendor or architecture change, it also needs to be solved manually. When clicking Accept to apply any changes in the Software Manager, you get an overview of all actions triggered by the automatic resolver which you need to confirm. By default, dependencies are automatically checked. A check is performed every time you change a package status (for example, by marking a package for installation or removal). This is generally useful, but can become exhausting when manually resolving a dependency conflict. To disable this function, go to the main menu and deactivate Dependencies Autocheck. Manual- ly perform a dependency check with Dependencies Check Now. A consistency check is always performed when you confirm your selection with Accept. To review a package''s dependencies, right-click it and choose Show Solver Information. A map showing the dependencies opens. Packages that are already installed are displayed in a green frame. Note: Manually solving package conflicts Unless you are experienced, follow the suggestions YaST makes when handling package conflicts, otherwise you may not be able to resolve them. Keep in mind that every change you make potentially triggers other conflicts, so you can easily end up with a steadily increasing number of conflicts. In case this happens, Cancel the Software Manager, Aban- don all your changes and start again. 97 Package dependencies SLES 15 SP6FIGURE 8.1: CONFLICT MANAGEMENT OF THE SOFTWARE MANAGER 8.3.5 Handling package recommendations In addition to the hard dependencies required to run a program (for example a certain library), a package can also have weak dependencies, which add for example extra functionality or trans- lations. These weak dependencies are called package recommendations. When installing a new package, recommended packages are still installed by default. When updating an existing package, missing recommendations are not be installed automatically. To change this, set PKGMGR_RECOMMENDED="yes" in /etc/sysconfig/yast2 . To install all miss- ing recommendations for already installed packages, start YaST Software Manager and choose Extras Install All Matching Recommended Packages. To disable the installation of recommended packages when installing new packages, deactivate Dependencies Install Recommended Packages in the YaST Software Manager. When using the command-line tool Zypper to install packages, use the option --no-recommends. 98 Handling package recommendations SLES 15 SP68.4 Managing software repositories and services To install third-party software, add software repositories to your system. By default, product repositories such as SUSE Linux Enterprise Server-DVD 15 SP6 and a matching update reposi- tory are automatically configured when you register your system. For more information about registration, see Book “Deployment Guide”, Chapter 9 “Installation steps”, Section 9.7 “Registration” or Book “Upgrade Guide”, Chapter 4 “Upgrading offline”, Section 4.8 “Registering your system”. Depending on the initially selected product, an additional repository containing translations, dictionaries, etc. might also be configured. To manage repositories, start YaST and select Software Software Repositories. The Configured Software Repositories dialog opens. Here, you can also manage subscriptions to Services by chang- ing the View at the right corner of the dialog to All Services. A Service in this context is a Repos- itory Index Service (RIS) that can offer one or more software repositories. Such a Service can be changed dynamically by its administrator or vendor. Each repository provides les describing repository content (package names, versions, etc.). YaST downloads these repository description les to a local cache. To ensure their integrity, software repositories can be signed with the GPG Key of the repository maintainer. Whenever you add a new repository, YaST offers the ability to import its key. Warning: Trusting external software sources Before adding external software repositories to your list of repositories, make sure this repository can be trusted. SUSE is not responsible for any problems arising from software installed from third-party software repositories. 8.4.1 Adding software repositories You can either add repositories from DVD/CD, a USB ash drive, a local directory, an ISO image, or a network source. To add repositories from the Configured Software Repositories dialog in YaST proceed as follows: 1. Click Add. 99 Managing software repositories and services SLES 15 SP62. Select one of the options listed in the dialog: FIGURE 8.2: ADDING A SOFTWARE REPOSITORY To scan your network for installation servers announcing their services via SLP, select Scan Using SLP and click Next. To add a repository from a removable medium, choose the relevant option and insert the medium or connect the USB device to the machine, respectively. Click Next to start the installation. For the majority of repositories, you will be asked to specify the path (or URL) to the media after selecting the respective option and clicking Next. Specifying a Repository Name is optional. If none is specified, YaST will use the product name or the URL as repository name. The option Download Repository Description Files is activated by default. If you deactivate the option, YaST will automatically download the les later, if needed. 3. Depending on the repository you add, you may be prompted to import the repository''s GPG key or asked to agree to a license. After confirming, YaST will download and parse the metadata. It will add the repository to the list of Configured Repositories. 4. If needed, adjust the repository Properties as described in Section 8.4.2, “Managing repository properties”. 100 Adding software repositories SLES 15 SP65. Confirm your changes with OK to close the configuration dialog. 6. After having successfully added the repository, the software manager starts and you can install packages from this repository. For details, refer to Chapter 8, Installing or removing software. 8.4.2 Managing repository properties The Configured Software Repositories overview of the Software Repositories lets you change the following repository properties: Status The repository status can either be Enabled or Disabled. You can only install packages from repositories that are enabled. To turn a repository o temporarily, select it and deactivate Enable. You can also double-click a repository name to toggle its status. To remove a repos- itory completely, click Delete. Refresh When refreshing a repository, its content description (package names, versions, etc.) is downloaded to a local cache that is used by YaST. It is sufficient to do this once for static repositories such as CDs or DVDs, whereas repositories whose content changes often should be refreshed frequently. The easiest way to keep a repository''s cache up to date is to choose Automatically Refresh. To do a manual refresh click Refresh and select one of the options. Keep Downloaded Packages Packages from remote repositories are downloaded before being installed. By default, they are deleted upon successful installation. Activating Keep Downloaded Packages prevents the deletion of downloaded packages. The download location is configured in /etc/zypp/ zypp.conf , by default it is /var/cache/zypp/packages . Priority The Priority of a repository is a value between 1 and 200 , with 1 being the highest priority and 200 the lowest priority. Any new repositories that are added with YaST get a priority of 99 by default. If you do not care about a priority value for a certain repository, you can also set the value to 0 to apply the default priority to that repository ( 99 ). If a package is available in more than one repository, then the repository with the highest priority takes precedence. This is useful to avoid downloading packages unnecessarily from the Internet by giving a local repository (for example, a DVD) a higher priority. 101 Managing repository properties SLES 15 SP6Important: Priority compared to version The repository with the highest priority takes precedence in any case. Therefore, make sure that the update repository always has the highest priority, otherwise you might install an outdated version that will not be updated until the next online update. Name and URL To change a repository name or its URL, select it from the list with a single-click and then click Edit. 8.4.3 Managing repository keys To ensure their integrity, software repositories can be signed with the GPG Key of the repository maintainer. Whenever you add a new repository, YaST offers to import its key. Verify it as you would do with any other GPG key and make sure it does not change. If you detect a key change, something might be wrong with the repository. Disable the repository as an installation source until you know the cause of the key change. To manage all imported keys, click GPG Keys in the Configured Software Repositories dialog. Select an entry with the mouse to show the key properties at the bottom of the window. Add, Edit, or Delete keys with a click on the respective buttons. 8.5 The GNOME package updater SUSE offers a continuous stream of software security patches and updates for your product. They can be installed using tools available with your desktop or by running the YaST online update module. This section describes how to update the system from the GNOME desktop using the Package Updater. Contrary to the YaST Online Update module, the GNOME Package Updater not only offers to install patches from the update repositories, but also new versions of packages that are already installed. (Patches x security issues or malfunctions; the functionality and version number is usually not changed. New versions of a package increase the version number and add function- ality or introduce major changes.) Whenever new patches or package updates are available, GNOME shows a notification in the notification area or on the lock screen. 102 Managing repository keys SLES 15 SP6FIGURE 8.3: UPDATE NOTIFICATION ON GNOME DESKTOP To configure the notification settings for the Package Updater, start GNOME Settings and choose Notifications Package Updater. PROCEDURE 8.2: INSTALLING PATCHES AND UPDATES WITH THE GNOME PACKAGE UPDATER 1. To install the patches and updates, click the notification message. This opens the GNOME Package Updater. Alternatively, open the updater from Activities by typing package U and choosing Package Updater. 103 The GNOME package updater SLES 15 SP62. Updates are sorted into four categories: Security updates (patches) Fix severe security hazards and should always be installed. Recommended updates (patches) Fix issues that could compromise your computer. Installing them is strongly recom- mended. Optional updates (patches) Fix non-security relevant issues or provide enhancements. Other updates New versions of packages that are installed. All available updates are preselected for installation. If you do not want to install all updates, deselect unwanted updates rst. It is strongly recommended to always install all security and recommended updates. To get detailed information on an update, click its title and then Details. The information is displayed in a box beneath the package list. 3. Click Install Updates to start the installation. 104 The GNOME package updater SLES 15 SP64. Some updates may require to restart the machine or to log out. Check the message dis- played after installation for instructions. 8.6 Updating packages with GNOME Software In addition to the GNOME Package Updater, GNOME provides GNOME Software which has the following functionality: Install, update, and remove software delivered as an RPM via PackageKit Install, update, and remove software delivered as a Flatpak Install, update, and remove GNOME shell extensions (https://extensions.gnome.org ) Update rmware for hardware devices using Linux Vendor Firmware Service (LVFS, https:// fwupd.org ) GNOME Software also provides screenshots, ratings, and reviews for software. FIGURE 8.4: GNOME SOFTWARE—UPDATES VIEW 105 Updating packages with GNOME Software SLES 15 SP6GNOME Software has the following differences to other tools provided on SUSE Linux Enterprise Server: Unlike YaST or Zypper, for installing software packaged as an RPM, GNOME Software is restricted to software that provides AppStream metadata. This includes most desktop applications. While the GNOME Package Updater updates packages within the running system (forcing you to restart the respective applications), GNOME Software downloads the updates and applies them after reboot. 106 Updating packages with GNOME Software SLES 15 SP69 Managing software with command line tools This chapter describes Zypper and RPM, two command line tools for managing soft- ware. For a definition of the terminology used in this context (for example, repos- itory , patch , or update ) refer to Section 8.1, “Definition of terms”. 9.1 Using Zypper Zypper is a command line package manager for installing, updating, and removing packages. It also manages repositories. It is especially useful for accomplishing remote software management tasks or managing software from shell scripts. 9.1.1 General usage The general syntax of Zypper is: zypper [--global-options] COMMAND  [--command-options] [arguments] The components enclosed in brackets are not required. See zypper help for a list of general options and all commands. To get help for a specific command, type zypper help COMMAND . Zypper commands The simplest way to execute Zypper is to type its name, followed by a command. For example, to apply all needed patches to the system, use: > sudo zypper patch Global options Additionally, you can choose from one or more global options by typing them immediately before the command: > sudo zypper --non-interactive patch In the above example, the option --non-interactive means that the command is run without asking anything (automatically applying the default answers). 107 Using Zypper SLES 15 SP6Command-specific options To use options that are specific to a particular command, type them immediately after the command: > sudo zypper patch --auto-agree-with-licenses In the above example, --auto-agree-with-licenses is used to apply all needed patches to a system without you being asked to confirm any licenses. Instead, licenses will be accepted automatically. Arguments Some commands require one or more arguments. For example, when using the command install , you need to specify which package or which packages you want to install: > sudo zypper install mplayer Some options also require a single argument. The following command will list all known patterns: > zypper search -t pattern You can combine all of the above. For example, the following command will install the mc and vim packages from the factory repository while being verbose: > sudo zypper -v install --from factory mc vim The --from option keeps all repositories enabled (for solving any dependencies) while request- ing the package from the specified repository. --repo is an alias for --from , and you may use either one. Most Zypper commands have a dry-run option that does a simulation of the given command. It can be used for test purposes. > sudo zypper remove --dry-run MozillaFirefox Zypper supports the global --userdata STRING option. You can specify a string with this option, which gets written to Zypper''s log les and plug-ins (such as the Btrfs plug-in). It can be used to mark and identify transactions in log les. > sudo zypper --userdata STRING patch 108 General usage SLES 15 SP69.1.2 Using Zypper subcommands Zypper subcommands are executables that are stored in the directory specified by the zyp- per_execdir configuration option. It is /usr/lib/zypper/commands by default. If a subcom- mand is not found there, Zypper automatically searches the rest of your $PATH locations for it. This lets you create your own local extensions and store them in user space. Executing subcommands in the Zypper shell, and using global Zypper options are not supported. List your available subcommands: > zypper help subcommand [...] Available zypper subcommands in ''/usr/lib/zypper/commands'' appstream-cache lifecycle migration search-packages Zypper subcommands available from elsewhere on your $PATH log Zypper logfile reader (/usr/sbin/zypper-log) View the help screen for a subcommand: > zypper help appstream-cache 9.1.3 Installing and removing software with Zypper To install or remove packages, use the following commands: > sudo zypper install PACKAGE_NAME > sudo zypper remove PACKAGE_NAME Warning: Do not remove mandatory system packages Do not remove mandatory system packages like glibc , zypper , kernel . If they are removed, the system can become unstable or stop working altogether. 109 Using Zypper subcommands SLES 15 SP69.1.3.1 Selecting which packages to install or remove There are various ways to address packages with the commands zypper install and zypper remove . By exact package name > sudo zypper install MozillaFirefox By exact package name and version number > sudo zypper install MozillaFirefox-52.2 By repository alias and package name > sudo zypper install mozilla:MozillaFirefox Where mozilla is the alias of the repository from which to install. By package name using wild cards You can select all packages that have names starting or ending with a certain string. Use wild cards with care, especially when removing packages. The following command will install all packages starting with “Moz”: > sudo zypper install ''Moz*'' Tip: Removing all -debuginfo packages When debugging a problem, you sometimes need to temporarily install a lot of - debuginfo packages which give you more information about running processes. After your debugging session finishes and you need to clean the environment, run the following: > sudo zypper remove ''*-debuginfo'' By capability For example, to install a package without knowing its name, capabilities come in handy. The following command will install the package MozillaFirefox : > sudo zypper install firefox 110 Installing and removing software with Zypper SLES 15 SP6By capability, hardware architecture, or version Together with a capability, you can specify a hardware architecture and a version: The name of the desired hardware architecture is appended to the capability after a full stop. For example, to specify the AMD64/Intel 64 architectures (which in Zypper is named x86_64 ), use: > sudo zypper install ''firefox.x86_64'' Versions must be appended to the end of the string and must be preceded by an operator: < (lesser than), <= (lesser than or equal), = (equal), >= (greater than or equal), > (greater than). > sudo zypper install ''firefox>=74.2'' You can also combine a hardware architecture and version requirement: > sudo zypper install ''firefox.x86_64>=74.2'' By path to the RPM file You can also specify a local or remote path to a package: > sudo zypper install /tmp/install/MozillaFirefox.rpm > sudo zypper install http://download.example.com/MozillaFirefox.rpm 9.1.3.2 Combining installation and removal of packages To install and remove packages simultaneously, use the +/- modifiers. To install emacs and simultaneously remove vim , use: > sudo zypper install emacs -vim To remove emacs and simultaneously install vim , use: > sudo zypper remove emacs +vim To prevent the package name starting with the - being interpreted as a command option, always use it as the second argument. If this is not possible, precede it with -- : > sudo zypper install -emacs +vim # Wrong > sudo zypper install vim -emacs # Correct > sudo zypper install -- -emacs +vim # Correct > sudo zypper remove emacs +vim # Correct 111 Installing and removing software with Zypper SLES 15 SP69.1.3.3 Cleaning up dependencies of removed packages If (together with a certain package), you automatically want to remove any packages that be- come unneeded after removing the specified package, use the --clean-deps option: > sudo zypper rm --clean-deps PACKAGE_NAME 9.1.3.4 Using Zypper in scripts By default, Zypper asks for a confirmation before installing or removing a selected package, or when a problem occurs. You can override this behavior using the --non-interactive option. This option must be given before the actual command ( install , remove , and patch ), as can be seen in the following: > sudo zypper --non-interactive install PACKAGE_NAME This option allows the use of Zypper in scripts and cron jobs. 9.1.3.5 Installing or downloading source packages To install the corresponding source package of a package, use: > zypper source-install PACKAGE_NAME When executed as root , the default location to install source packages is /usr/src/packages/ and ~/rpmbuild when run as user. These values can be changed in your local rpm configura- tion. This command will also install the build dependencies of the specified package. If you do not want this, add the switch -D : > sudo zypper source-install -D PACKAGE_NAME To install only the build dependencies use -d . > sudo zypper source-install -d PACKAGE_NAME Of course, this will only work if you have the repository with the source packages enabled in your repository list (it is added by default, but not enabled). See Section 9.1.6, “Managing repositories with Zypper” for details on repository management. A list of all source packages available in your repositories can be obtained with: > zypper search -t srcpackage 112 Installing and removing software with Zypper SLES 15 SP6You can also download source packages for all installed packages to a local directory. To down- load source packages, use: > zypper source-download The default download directory is /var/cache/zypper/source-download . You can change it using the --directory option. To only show missing or extraneous packages without down- loading or deleting anything, use the --status option. To delete extraneous source packages, use the --delete option. To disable deleting, use the --no-delete option. 9.1.3.6 Installing packages from disabled repositories Normally you can only install or refresh packages from enabled repositories. The --plus-con- tent TAG option helps you specify repositories to be refreshed, temporarily enabled during the current Zypper session, and disabled after it completes. For example, to enable repositories that may provide additional -debuginfo or -debugsource packages, use --plus-content debug . You can specify this option multiple times. To temporarily enable such ''debug'' repositories to install a specific -debuginfo package, use the option as follows: > sudo zypper --plus-content debug \ install "debuginfo(build-id)=eb844a5c20c70a59fc693cd1061f851fb7d046f4" The build-id string is reported by gdb for missing debuginfo packages. Note: Disabled installation media Repositories from the SUSE Linux Enterprise Server installation media are still configured but disabled after successful installation. You can use the --plus-content option to install packages from the installation media instead of the online repositories. Before calling zypper , ensure the media is available, for example by inserting the DVD into the computer''s drive. 9.1.3.7 Utilities To verify whether all dependencies are still fulfilled and to repair missing dependencies, use: > zypper verify 113 Installing and removing software with Zypper SLES 15 SP6In addition to dependencies that must be fulfilled, some packages “recommend” other packages. These recommended packages are only installed if actually available and installable. In case recommended packages were made available after the recommending package has been installed (by adding additional packages or hardware), use the following command: > sudo zypper install-new-recommends This command is very useful after plugging in a Web cam or Wi-Fi device. It will install drivers for the device and related software, if available. Drivers and related software are only installable if certain hardware dependencies are fulfilled. 9.1.4 Updating software with Zypper There are three different ways to update software using Zypper: by installing patches, by in- stalling a new version of a package or by updating the entire distribution. The latter is achieved with zypper dist-upgrade . Upgrading SUSE Linux Enterprise Server is discussed in Book “Up- grade Guide”, Chapter 2 “Upgrade paths and methods”. 9.1.4.1 Installing all needed patches Patching SUSE Linux Enterprise Server is the most reliable way to install new versions of installed packages. It guarantees that all required packages with correct versions are installed and ensures that package versions considered as conflicting are omitted. To install all officially released patches that apply to your system, run: > sudo zypper patch All patches available from repositories configured on your computer are checked for their rele- vance to your installation. If they are relevant (and not classified as optional or feature ), they are installed immediately. If zypper patch succeeds, it is guaranteed that no vulnera- ble version package is installed unless you confirm the exception. Note that the official update repository is only available after registering your SUSE Linux Enterprise Server installation. If a patch that is about to be installed includes changes that require a system reboot, you will be warned before. The plain zypper patch command does not apply patches from third party repositories. To update also the third party repositories, use the with-update command option as follows: > sudo zypper patch --with-update 114 Updating software with Zypper SLES 15 SP6To install also optional patches, use: > sudo zypper patch --with-optional To install all patches relating to a specific Bugzilla issue, use: > sudo zypper patch --bugzilla=NUMBER To install all patches relating to a specific CVE database entry, use: > sudo zypper patch --cve=NUMBER For example, to install a security patch with the CVE number CVE-2010-2713 , execute: > sudo zypper patch --cve=CVE-2010-2713 To install only patches which affect Zypper and the package management itself, use: > sudo zypper patch --updatestack-only Bear in mind that other command options that would also update other repositories will be dropped if you use the updatestack-only command option. 9.1.4.2 Listing patches To nd out whether patches are available, Zypper allows viewing the following information: Number of needed patches To list the number of needed patches (patches that apply to your system but are not yet installed), use patch-check : > zypper patch-check Loading repository data... Reading installed packages... 5 patches needed (1 security patch) This command can be combined with the --updatestack-only option to list only the patches which affect Zypper and the package management itself. List of needed patches To list all needed patches (patches that apply to your system but are not yet installed), use zypper list-patches . List of all patches To list all patches available for SUSE Linux Enterprise Server, regardless of whether they are already installed or apply to your installation, use zypper patches . 115 Updating software with Zypper SLES 15 SP6It is also possible to list and install patches relevant to specific issues. To list specific patches, use the zypper list-patches command with the following options: By Bugzilla issues To list all needed patches that relate to Bugzilla issues, use the option --bugzilla . To list patches for a specific bug, you can also specify a bug number: --bugzilla=NUMBER . To search for patches relating to multiple Bugzilla issues, add commas between the bug numbers, for example: > zypper list-patches --bugzilla=972197,956917 By CVE number To list all needed patches that relate to an entry in the CVE database (Common Vulnera- bilities and Exposures), use the option --cve . To list patches for a specific CVE database entry, you can also specify a CVE number: -- cve=NUMBER . To search for patches relating to multiple CVE database entries, add commas between the CVE numbers, for example: > zypper list-patches --cve=CVE-2016-2315,CVE-2016-2324 List retracted patches In the SUSE Linux Enterprise 15 codestream, some patches are automatically retracted. Maintenance updates are carefully tested, because there is a risk that an update contains a new bug. If an update proves to contain a bug, a new update (with a higher version number) is issued to revert the buggy update, and the buggy update is blocked from being installed again. You can list retracted patches with zypper : > zypper lp --all |grep retracted SLE-Module-Basesystem15-SP3-Updates | SUSE-SLE-Module-Basesystem-15-SP3-2021-1965 | recommended | important | --- | retracted | Recommended update for multipath- tools SLE-Module-Basesystem15-SP3-Updates | SUSE-SLE-Module-Basesystem-15-SP3-2021-2689 | security | important | --- | retracted | Security update for cpio SLE-Module-Basesystem15-SP3-Updates | SUSE-SLE-Module-Basesystem-15-SP3-2021-3655 | security | important | reboot | retracted | Security update for the Linux Kernel See complete information on a retracted (or any) patch: > zypper patch-info SUSE-SLE-Product-SLES-15-2021-2689 Loading repository data... Reading installed packages... 116 Updating software with Zypper SLES 15 SP6Information for patch SUSE-SLE-Product-SLES-15-2021-2689: --------------------------------------------------------- Repository : SLE-Product-SLES15-LTSS-Updates Name : SUSE-SLE-Product-SLES-15-2021-2689 Version : 1 Arch : noarch Vendor : maint-coord@suse.de Status : retracted Category : security Severity : important Created On : Mon 16 Aug 2021 03:44:00 AM PDT Interactive : --- Summary : Security update for cpio Description : This update for cpio fixes the following issues: It was possible to trigger Remote code execution due to a integer overflow (CVE-2021-38185, bsc#1189206) UPDATE: This update was buggy and could lead to hangs, so it has been retracted. There will be a follow up update. [...] Patch with conflicting packages Information for patch openSUSE-SLE-15.3-2022-333: ------------------------------------------------- Repository : Update repository with updates from SUSE Linux Enterprise 15 Name : openSUSE-SLE-15.3-2022-333 Version : 1 Arch : noarch Vendor : maint-coord@suse.de Status : needed Category : security Severity : important Created On : Fri Feb 4 09:30:32 2022 Interactive : reboot Summary : Security update for xen Description : This update for xen fixes the following issues: - CVE-2022-23033: Fixed guest_physmap_remove_page not removing the p2m mappings. (XSA-393) (bsc#1194576) - CVE-2022-23034: Fixed possible DoS by a PV guest Xen while unmapping a grant. (XSA-394) (bsc#1194581) - CVE-2022-23035: Fixed insufficient cleanup of passed-through device IRQs. (XSA-395) (bsc#1194588) 117 Updating software with Zypper SLES 15 SP6Provides : patch:openSUSE-SLE-15.3-2022-333 = 1 Conflicts : [22] xen.src < 4.14.3_06-150300.3.18.2 xen.noarch < 4.14.3_06-150300.3.18.2 xen.x86_64 < 4.14.3_06-150300.3.18.2 xen-devel.x86_64 < 4.14.3_06-150300.3.18.2 xen-devel.noarch < 4.14.3_06-150300.3.18.2 [...] The above patch conflicts with the affected or vulnerable versions of 22 packages. If any of these affected or vulnerable packages are installed, it triggers a conflict, and the patch is classified as needed. zypper patch tries to install all available patches. If it encounters problems, it reports them, thus informing you that not all updates are installed. The con- flict can be resolved by either updating the affected or vulnerable packages or by removing them. Because SUSE update repositories also ship xed packages, updating is a standard way to resolve conflicts. If the package cannot be updated—for example, because of de- pendency issues or package locks—it is deleted after the user''s approval. To list all patches regardless of whether they are needed, use the option --all additionally. For example, to list all patches with a CVE number assigned, use: > zypper list-patches --all --cve Issue | No. | Patch | Category | Severity | Status ------+---------------+-------------------+-------------+-----------+---------- cve | CVE-2019-0287 | SUSE-SLE-Module.. | recommended | moderate | needed cve | CVE-2019-3566 | SUSE-SLE-SERVER.. | recommended | moderate | not needed [...] 9.1.4.3 Installing new package versions If a repository contains only new packages, but does not provide patches, zypper patch does not show any effect. To update all installed packages with newer available versions, use the following command: > sudo zypper update Important zypper update ignores problematic packages. For example, if a package is locked, zyp- per update omits the package, even if a higher version of it is available. Conversely, zypper patch reports a conflict if the package is considered vulnerable. 118 Updating software with Zypper SLES 15 SP6To update individual packages, specify the package with either the update or install command: > sudo zypper update PACKAGE_NAME > sudo zypper install PACKAGE_NAME A list of all new installable packages can be obtained with the command: > zypper list-updates Note that this command only lists packages that match the following criteria: has the same vendor like the already installed package, is provided by repositories with at least the same priority than the already installed pack- age, is installable (all dependencies are satisfied). A list of all new available packages (regardless whether installable or not) can be obtained with: > sudo zypper list-updates --all To nd out why a new package cannot be installed, use the zypper install or zypper update command as described above. 9.1.4.4 Identifying orphaned packages Whenever you remove a repository from Zypper or upgrade your system, some packages can get in an “orphaned” state. These orphaned packages belong to no active repository anymore. The following command gives you a list of these: > sudo zypper packages --orphaned With this list, you can decide if a package is still needed or can be removed safely. 9.1.5 Identifying processes and services using deleted files When patching, updating, or removing packages, there may be running processes on the system which continue to use les having been deleted by the update or removal. Use zypper ps to list processes using deleted les. In case the process belongs to a known service, the service name is listed, making it easy to restart the service. By default zypper ps shows a table: > zypper ps 119 Identifying processes and services using deleted files SLES 15 SP6PID | PPID | UID | User | Command | Service | Files ------+------+-----+-------+--------------+--------------+------------------- 814 | 1 | 481 | avahi | avahi-daemon | avahi-daemon | /lib64/ld-2.19.s-> | | | | | | /lib64/libdl-2.1-> | | | | | | /lib64/libpthrea-> | | | | | | /lib64/libc-2.19-> [...] PID: ID of the process PPID: ID of the parent process UID: ID of the user running the process Login: Login name of the user running the process Command: Command used to execute the process Service: Service name (only if command is associated with a system service) Files: The list of the deleted les The output format of zypper ps can be controlled as follows: zypper ps -s Create a short table not showing the deleted les. > zypper ps -s PID | PPID | UID | User | Command | Service ------+------+------+---------+--------------+-------------- 814 | 1 | 481 | avahi | avahi-daemon | avahi-daemon 817 | 1 | 0 | root | irqbalance | irqbalance 1567 | 1 | 0 | root | sshd | sshd 1761 | 1 | 0 | root | master | postfix 1764 | 1761 | 51 | postfix | pickup | postfix 1765 | 1761 | 51 | postfix | qmgr | postfix 2031 | 2027 | 1000 | tux | bash | zypper ps -ss Show only processes associated with a system service. PID | PPID | UID | User | Command | Service ------+------+------+---------+--------------+-------------- 814 | 1 | 481 | avahi | avahi-daemon | avahi-daemon 817 | 1 | 0 | root | irqbalance | irqbalance 1567 | 1 | 0 | root | sshd | sshd 1761 | 1 | 0 | root | master | postfix 1764 | 1761 | 51 | postfix | pickup | postfix 1765 | 1761 | 51 | postfix | qmgr | postfix zypper ps -sss Only show system services using deleted les. 120 Identifying processes and services using deleted files SLES 15 SP6avahi-daemon irqbalance postfix sshd zypper ps --print "systemctl status %s" Show the commands to retrieve status information for services which might need a restart. systemctl status avahi-daemon systemctl status irqbalance systemctl status postfix systemctl status sshd For more information about service handling refer to Chapter 19, The systemd daemon. 9.1.6 Managing repositories with Zypper All installation or patch commands of Zypper rely on a list of known repositories. To list all repositories known to the system, use the command: > zypper repos The result will look similar to the following output: EXAMPLE 9.1: ZYPPER—LIST OF KNOWN REPOSITORIES > zypper repos # | Alias | Name | Enabled | Refresh --+--------------+---------------+---------+-------- 1 | SLEHA-15-GEO | SLEHA-15-GEO | Yes | No 2 | SLEHA-15 | SLEHA-15 | Yes | No 3 | SLES15 | SLES15 | Yes | No When specifying repositories in various commands, an alias, URI or repository number from the zypper repos command output can be used. A repository alias is a short version of the repository name for use in repository handling commands. Note that the repository numbers can change after modifying the list of repositories. The alias will never change by itself. By default, details such as the URI or the priority of the repository are not displayed. Use the following command to list all details: > zypper repos -d 121 Managing repositories with Zypper SLES 15 SP69.1.6.1 Adding repositories To add a repository, run > sudo zypper addrepo URI ALIAS URI can either be an Internet repository, a network resource, a directory or a CD or DVD (see https://en.opensuse.org/openSUSE:Libzypp_URIs for details). The ALIAS is a shorthand and unique identifier of the repository. You can freely choose it, with the only exception that it needs to be unique. Zypper will issue a warning if you specify an alias that is already in use. 9.1.6.2 Refreshing repositories zypper enables you to fetch changes in packages from configured repositories. To fetch the changes, run: > sudo zypper refresh Note: Default behavior of zypper By default, some commands perform refresh automatically, so you do not need to run the command explicitly. The refresh command enables you to view changes also in disabled repositories, by using the --plus-content option: > sudo zypper --plus-content refresh This option fetches changes in repositories, but keeps the disabled repositories in the same state —disabled. 9.1.6.3 Removing repositories To remove a repository from the list, use the command zypper removerepo together with the alias or number of the repository you want to delete. For example, to remove the repository SLEHA-12-GEO from Example 9.1, “Zypper—list of known repositories”, use one of the following commands: > sudo zypper removerepo 1 > sudo zypper removerepo "SLEHA-12-GEO" 122 Managing repositories with Zypper SLES 15 SP69.1.6.4 Modifying repositories Enable or disable repositories with zypper modifyrepo . You can also alter the repository''s properties (such as refreshing behavior, name or priority) with this command. The following command will enable the repository named updates , turn on auto-refresh and set its priority to 20: > sudo zypper modifyrepo -er -p 20 ''updates'' Modifying repositories is not limited to a single repository—you can also operate on groups: -a : all repositories -l : local repositories -t : remote repositories -m TYPE : repositories of a certain type (where TYPE can be one of the following: http , https , ftp , cd , dvd , dir , file , cifs , smb , nfs , hd , iso ) To rename a repository alias, use the renamerepo command. The following example changes the alias from Mozilla Firefox to firefox : > sudo zypper renamerepo ''Mozilla Firefox'' firefox 9.1.7 Querying repositories and packages with Zypper Zypper offers various methods to query repositories or packages. To get lists of all products, patterns, packages or patches available, use the following commands: > zypper products > zypper patterns > zypper packages > zypper patches To query all repositories for certain packages, use search . To get information regarding par- ticular packages, use the info command. 9.1.7.1 Searching for software The zypper search command works on package names, or, optionally, on package summaries and descriptions. Strings wrapped in / are interpreted as regular expressions. By default, the search is not case-sensitive. 123 Querying repositories and packages with Zypper SLES 15 SP6Simple search for a package name containing fire > zypper search "fire" Simple search for the exact package MozillaFirefox > zypper search --match-exact "MozillaFirefox" Also search in package descriptions and summaries > zypper search -d fire Only display packages not already installed > zypper search -u fire Display packages containing the string fir not followed be e > zypper se "/fir[^e]/" 9.1.7.2 Searching for packages across all SLE modules To search for packages both within and outside of currently enabled SLE modules, use the search-packages subcommand. This command contacts the SUSE Customer Center and searches all modules for matching packages, for example: > zypper search-packages package1 package2 zypper search-packages provides the following options: Search for an exact match of your search string: -x , --match-exact Group the results by module (default: group by package): -g, --group-by-module Display more detailed information about packages: -d , --details Output search results in XML: --xmlout 9.1.7.3 Searching for specific capability To search for packages which provide a special capability, use the command what-provides . For example, if you want to know which package provides the Perl module SVN::Core , use the following command: > zypper what-provides ''perl(SVN::Core)'' 124 Querying repositories and packages with Zypper SLES 15 SP6The what-provides PACKAGE_NAME is similar to rpm -q --whatprovides PACKAGE_NAME , but RPM is only able to query the RPM database (that is the database of all installed packages). Zypper, on the other hand, will tell you about providers of the capability from any repository, not only those that are installed. 9.1.7.4 Showing package information To query single packages, use info with an exact package name as an argument. This displays detailed information about a package. In case the package name does not match any package name from repositories, the command outputs detailed information for non-package matches. If you request a specific type (by using the -t option) and the type does not exist, the command outputs other available matches but without detailed information. If you specify a source package, the command displays binary packages built from the source package. If you specify a binary package, the command outputs the source packages used to build the binary package. To also show what is required/recommended by the package, use the options --requires and --recommends : > zypper info --requires MozillaFirefox 9.1.8 Showing lifecycle information SUSE products are generally supported for 10 years. Often, you can extend that standard lifecycle by using the extended support offerings of SUSE which add three years of support. Depending on your product, nd the exact support lifecycle at https://www.suse.com/lifecycle . To check the lifecycle of your product and the supported package, use the zypper lifecycle command as shown below: # zypper lifecycle Product end of support Codestream: SUSE Linux Enterprise Server 15 2028-07-31 Product: SUSE Linux Enterprise Server 15 SP3 n/a* Module end of support Basesystem Module n/a* Desktop Applications Module n/a* Server Applications Module n/a* 125 Showing lifecycle information SLES 15 SP6Package end of support if different from product: autofs Now, installed 5.1.3-7.3.1, update available 5.1.3-7.6.1 9.1.9 Configuring Zypper Zypper now comes with a configuration le, allowing you to permanently change Zypper''s be- havior (either system-wide or user-specific). For system-wide changes, edit /etc/zypp/zyp- per.conf . For user-specific changes, edit ~/.zypper.conf . If ~/.zypper.conf does not yet exist, you can use /etc/zypp/zypper.conf as a template: copy it to ~/.zypper.conf and adjust it to your liking. Refer to the comments in the le for help about the available options. 9.1.10 Troubleshooting If you have trouble accessing packages from configured repositories (for example, Zypper cannot nd a certain package even though you know it exists in one of the repositories), refreshing the repositories may help: > sudo zypper refresh If that does not help, try > sudo zypper refresh -fdb This forces a complete refresh and rebuild of the database, including a forced download of raw metadata. 9.1.11 Zypper rollback feature on Btrfs file system If the Btrfs le system is used on the root partition and snapper is installed, Zypper automati- cally calls snapper when committing changes to the le system to create appropriate le system snapshots. These snapshots can be used to revert any changes made by Zypper. See Chapter 10, System recovery and snapshot management with Snapper for more information. 126 Configuring Zypper SLES 15 SP69.1.12 More information For more information on managing software from the command line, enter zypper help , zyp- per help  COMMAND or refer to the zypper(8) man page. For a complete and detailed com- mand reference, cheat sheets with the most important commands, and information on how to use Zypper in scripts and applications, refer to https://en.opensuse.org/SDB:Zypper_usage . A list of software changes for the latest SUSE Linux Enterprise Server version can be found at https://en.opensuse.org/openSUSE:Zypper_versions . 9.2 RPM—the package manager RPM (RPM Package Manager) is used for managing software packages. Its main commands are rpm and rpmbuild . The powerful RPM database can be queried by the users, system adminis- trators and package builders for detailed information about the installed software. rpm has ve modes: installing, uninstalling (or updating) software packages, rebuilding the RPM database, querying RPM bases or individual RPM archives, integrity checking of packages and signing packages. rpmbuild can be used to build installable packages from pristine sources. Installable RPM archives are packed in a special binary format. These archives consist of the program les to install and certain meta information used during the installation by rpm to configure the software package or stored in the RPM database for documentation purposes. RPM archives normally have the extension .rpm . Tip: Software development packages For several packages, the components needed for software development (libraries, head- ers, include les, etc.) have been put into separate packages. These development packages are only needed if you want to compile software yourself (for example, the most recent GNOME packages). They can be identified by the name extension -devel , such as the packages alsa-devel and gimp-devel . 127 More information SLES 15 SP69.2.1 Verifying package authenticity RPM packages have a GPG signature. To verify the signature of an RPM package, use the com- mand rpm --checksig  PACKAGE -1.2.3.rpm to determine whether the package originates from SUSE or from another trustworthy facility. This is especially recommended for update packages from the Internet. While fixing issues in the operating system, you might need to install a Problem Temporary Fix (PTF) into a production system. The packages provided by SUSE are signed against a special PTF key. However, in contrast to SUSE Linux Enterprise 11, this key is not imported by default on SUSE Linux Enterprise 12 systems. To manually import the key, use the following command: > sudo rpm --import \ /usr/share/doc/packages/suse-build-key/suse_ptf_key.asc After importing the key, you can install PTF packages on your system. 9.2.2 Managing packages: install, update, and uninstall Normally, the installation of an RPM archive is quite simple: rpm -i PACKAGE .rpm. With this command the package is installed, but only if its dependencies are fulfilled and if there are no conflicts with other packages. With an error message, rpm requests those packages that need to be installed to meet dependency requirements. In the background, the RPM database ensures that no conflicts arise—a specific le can only belong to one package. By choosing different options, you can force rpm to ignore these defaults, but this is only for experts. Otherwise, you risk compromising the integrity of the system and possibly jeopardize the ability to update the system. The options -U or --upgrade and -F or --freshen can be used to update a package (for ex- ample, rpm -F PACKAGE .rpm). This command removes the les of the old version and immedi- ately installs the new les. The difference between the two versions is that -U installs packages that previously did not exist in the system, while -F merely updates previously installed pack- ages. When updating, rpm updates configuration les carefully using the following strategy: If a configuration le was not changed by the system administrator, rpm installs the new version of the appropriate le. No action by the system administrator is required. If a configuration le was changed by the system administrator before the update, rpm saves the changed le with the extension .rpmorig or .rpmsave (backup le) and installs the version from the new package. This is done only if the originally installed le and 128 Verifying package authenticity SLES 15 SP6the newer version are different. If this is the case, compare the backup le ( .rpmorig or .rpmsave ) with the newly installed le and make your changes again in the new le. Afterward, delete all .rpmorig and .rpmsave les to avoid problems with future updates. .rpmnew les appear if the configuration le already exists and if the noreplace label was specified in the .spec le. Following an update, .rpmsave and .rpmnew les should be removed after comparing them, so they do not obstruct future updates. The .rpmorig extension is assigned if the le has not previously been recognized by the RPM database. Otherwise, .rpmsave is used. In other words, .rpmorig results from updating from a foreign format to RPM. .rpmsave results from updating from an older RPM to a newer RPM. .rpmnew does not disclose any information to whether the system administrator has made any changes to the configuration le. A list of these les is available in /var/adm/rpmconfigcheck . Some configuration les (like /etc/httpd/httpd.conf ) are not overwritten to allow continued op- eration. The -U switch is not only an equivalent to uninstalling with the -e option and installing with the -i option. Use -U whenever possible. To remove a package, enter rpm -e PACKAGE . This command only deletes the package if there are no unresolved dependencies. It is theoretically impossible to delete Tcl/Tk, for example, as long as another application requires it. Even in this case, RPM calls for assistance from the data- base. If such a deletion is, for whatever reason, impossible (even if no additional dependencies exist), it may be helpful to rebuild the RPM database using the option --rebuilddb . 9.2.3 Delta RPM packages Delta RPM packages contain the difference between an old and a new version of an RPM package. Applying a delta RPM onto an old RPM results in a completely new RPM. It is not necessary to have a copy of the old RPM because a delta RPM can also work with an installed RPM. The delta RPM packages are even smaller in size than patch RPMs, which is an advantage when transferring update packages over the Internet. The drawback is that update operations with delta RPMs involved consume considerably more CPU cycles than plain or patch RPMs. 129 Delta RPM packages SLES 15 SP6The makedeltarpm and applydelta binaries are part of the delta RPM suite (package deltarpm ) and help you create and apply delta RPM packages. With the following commands, you can create a delta RPM called new.delta.rpm . The following command assumes that old.rpm and new.rpm are present: > sudo makedeltarpm old.rpm new.rpm new.delta.rpm Using applydeltarpm , you can reconstruct the new RPM from the le system if the old package is already installed: > sudo applydeltarpm new.delta.rpm new.rpm To derive it from the old RPM without accessing the le system, use the -r option: > sudo applydeltarpm -r old.rpm new.delta.rpm new.rpm See /usr/share/doc/packages/deltarpm/README for technical details. 9.2.4 RPM queries With the -q option rpm initiates queries, making it possible to inspect an RPM archive (by adding the option -p ) and to query the RPM database of installed packages. Several switches are available to specify the type of information required. See Table 9.1, “Essential RPM query options”. TABLE 9.1: ESSENTIAL RPM QUERY OPTIONS -i Package information -l File list -f FILE Query the package that contains the le FILE (the full path must be specified with FILE ) -s File list with status information (implies -l ) -d List only documentation les (implies -l ) -c List only configuration les (implies -l ) --dump File list with complete details (to be used with -l , -c , or -d ) 130 RPM queries SLES 15 SP6--provides List features of the package that another package can request with --requires --requires , -R Capabilities the package requires --scripts Installation scripts (preinstall, postinstall, uninstall) For example, the command rpm -q -i wget displays the information shown in Example 9.2, “rpm -q -i wget”. EXAMPLE 9.2: rpm -q -i wget Name : wget Version : 1.14 Release : 17.1 Architecture: x86_64 Install Date: Mon 30 Jan 2017 14:01:29 CET Group : Productivity/Networking/Web/Utilities Size : 2046483 License : GPL-3.0+ Signature : RSA/SHA256, Thu 08 Dec 2016 07:48:44 CET, Key ID 70af9e8139db7c82 Source RPM : wget-1.14-17.1.src.rpm Build Date : Thu 08 Dec 2016 07:48:34 CET Build Host : sheep09 Relocations : (not relocatable) Packager : https://www.suse.com/ Vendor : SUSE LLC URL : http://www.gnu.org/software/wget/ Summary : A Tool for Mirroring FTP and HTTP Servers Description : Wget enables you to retrieve WWW documents or FTP files from a server. This can be done in script files or via the command line. Distribution: SUSE Linux Enterprise 15 The option -f only works if you specify the complete le name with its full path. Provide as many le names as desired. For example: > rpm -q -f /bin/rpm /usr/bin/wget rpm-4.14.1-lp151.13.10.x86_64 wget-1.19.5-lp151.4.1.x86_64 If only part of the le name is known, use a shell script as shown in Example 9.3, “Script to search for packages”. Pass the partial le name to the script shown as a parameter when running it. 131 RPM queries SLES 15 SP6EXAMPLE 9.3: SCRIPT TO SEARCH FOR PACKAGES #! /bin/sh for i in $(rpm -q -a -l | grep $1); do echo "\"$i\" is in package:" rpm -q -f $i echo "" done The command rpm -q --changelog PACKAGE displays a detailed list of change information about a specific package, sorted by date. With the installed RPM database, verification checks can be made. Initiate these with -V , or --verify . With this option, rpm shows all les in a package that have been changed since installation. rpm uses eight character symbols to give some hints about the following changes: TABLE 9.2: RPM VERIFY OPTIONS 5 MD5 check sum S File size L Symbolic link T Modification time D Major and minor device numbers U Owner G Group M Mode (permissions and le type) In the case of configuration les, the letter c is printed. For example, for changes to /etc/ wgetrc ( wget package): > rpm -V wget S.5....T c /etc/wgetrc The les of the RPM database are placed in /var/lib/rpm . If the partition /usr has a size of 1 GB, this database can occupy nearly 30 MB, especially after a complete update. If the database is much larger than expected, it is useful to rebuild the database with the option --rebuilddb . 132 RPM queries SLES 15 SP6Before doing this, make a backup of the old database. The cron script cron.daily makes daily copies of the database (packed with gzip) and stores them in /var/adm/backup/rpmdb . The number of copies is controlled by the variable MAX_RPMDB_BACKUPS (default: 5 ) in /etc/ sysconfig/backup . The size of a single backup is approximately 1 MB for 1 GB in /usr . 9.2.5 Installing and compiling source packages All source packages carry a .src.rpm extension (source RPM). Note: Installed source packages Source packages can be copied from the installation medium to the hard disk and un- packed with YaST. They are not, however, marked as installed ( [i] ) in the package manager. This is because the source packages are not entered in the RPM database. Only installed operating system software is listed in the RPM database. When you “install” a source package, only the source code is added to the system. The following directories must be available for rpm and rpmbuild in /usr/src/packages (unless you specified custom settings in a le like /etc/rpmrc ): SOURCES for the original sources ( .tar.bz2 or .tar.gz les, etc.) and for distribution-specific adjustments (mostly .diff or .patch les) SPECS for the .spec les, similar to a meta Makefile, which control the build process BUILD all the sources are unpacked, patched and compiled in this directory RPMS where the completed binary packages are stored SRPMS here are the source RPMs When you install a source package with YaST, all the necessary components are installed in / usr/src/packages : the sources and the adjustments in SOURCES and the relevant .spec le in SPECS . 133 Installing and compiling source packages SLES 15 SP6Warning: System integrity Do not experiment with system components ( glibc , rpm , etc.), because this endangers the stability of your system. The following example uses the wget.src.rpm package. After installing the source package, you should have les similar to those in the following list: /usr/src/packages/SOURCES/wget-1.19.5.tar.bz2 /usr/src/packages/SOURCES/wgetrc.patch /usr/src/packages/SPECS/wget.spec rpmbuild -bX /usr/src/packages/SPECS/wget.spec starts the compilation. X is a wild card for various stages of the build process (see the output of --help or the RPM documentation for details). The following is merely a brief explanation: -bp Prepare sources in /usr/src/packages/BUILD : unpack and patch. -bc Do the same as -bp , but with additional compilation. -bi Do the same as -bp , but with additional installation of the built software. Caution: if the package does not support the BuildRoot feature, you might overwrite configuration les. -bb Do the same as -bi , but with the additional creation of the binary package. If the compile was successful, the binary should be in /usr/src/packages/RPMS . -ba Do the same as -bb , but with the additional creation of the source RPM. If the compilation was successful, the binary should be in /usr/src/packages/SRPMS . --short-circuit Skip some steps. The binary RPM created can now be installed with rpm -i or, preferably, with rpm -U . In- stallation with rpm makes it appear in the RPM database. Keep in mind that the BuildRoot directive in the spec le is deprecated. If you still need this feature, use the --buildroot option as a workaround. 134 Installing and compiling source packages SLES 15 SP69.2.6 Compiling RPM packages with build The danger with many packages is that unwanted les are added to the running system during the build process. To prevent this use build , which creates a defined environment in which the package is built. To establish this chroot environment, the build script must be provided with a complete package tree. This tree can be made available on the hard disk, via NFS, or from DVD. Set the position with build --rpms DIRECTORY . Unlike rpm , the build command looks for the .spec le in the source directory. To build wget (like in the above example) with the DVD mounted in the system under /media/dvd , use the following commands as root : # cd /usr/src/packages/SOURCES/ # mv ../SPECS/wget.spec . # build --rpms /media/dvd/suse/ wget.spec Subsequently, a minimum environment is established at /var/tmp/build-root . The package is built in this environment. Upon completion, the resulting packages are located in /var/tmp/ build-root/usr/src/packages/RPMS . The build script offers several additional options. For example, cause the script to prefer your own RPMs, omit the initialization of the build environment or limit the rpm command to one of the above-mentioned stages. Access additional information with build --help and by reading the build man page. 9.2.7 Tools for RPM archives and the RPM database Midnight Commander ( mc ) can display the contents of RPM archives and copy parts of them. It represents archives as virtual le systems, offering all usual menu options of Midnight Com- mander. Display the HEADER with F3 . View the archive structure with the cursor keys and Enter . Copy archive components with F5 . A full-featured package manager is available as a YaST module. For details, see Chapter 8, In- stalling or removing software. 135 Compiling RPM packages with build SLES 15 SP610 System recovery and snapshot management with Snapper Snapper allows creating and managing le system snapshots. File system snapshots allow keeping a copy of the state of a le system at a certain point of time. The standard setup of Snapper is designed to allow rolling back system changes. How- ever, you can also use it to create on-disk backups of user data. As the basis for this functionality, Snapper uses the Btrfs le system or thinly provisioned LVM volumes with an XFS or Ext4 le system. Snapper has a command line interface and a YaST interface. Snapper lets you create and manage le system snapshots on the following types of le systems: Btrfs, a copy-on-write le system for Linux that natively supports le system snapshots of subvolumes. (Subvolumes are separately mountable le systems within a physical par- tition.) You can also boot from Btrfs snapshots. For more information, see Section 10.3, “System rollback by booting from snapshots”. Thinly provisioned LVM volumes formatted with XFS or Ext4. Using Snapper, you can perform the following tasks: Undo system changes made by zypper and YaST. See Section 10.2, “Using Snapper to undo changes” for details. Restore les from previous snapshots. See Section 10.2.2, “Using Snapper to restore files” for details. Do a system rollback by booting from a snapshot. See Section 10.3, “System rollback by booting from snapshots” for details. Manually create and manage snapshots, within the running system. See Section 10.6, “Man- ually creating and managing snapshots” for details. 136 SLES 15 SP610.1 Default setup Snapper on SUSE Linux Enterprise Server is set up as an undo and recovery tool for system changes. By default, the root partition ( / ) of SUSE Linux Enterprise Server is formatted with Btrfs . Taking snapshots is automatically enabled if the root partition ( / ) is big enough (more than approximately 16 GB). By default, snapshots are disabled on partitions other than / . Tip: Enabling Snapper in the installed system If you disabled Snapper during the installation, you can enable it at any time later. To do so, create a default Snapper configuration for the root le system by running: > sudo snapper -c root create-config / Afterward enable the different snapshot types as described in Section 10.1.4.1, “Disabling/en- abling snapshots”. On a Btrfs root le system, snapshots require a le system with subvolumes configured as proposed by the installer and a partition size of at least 16 GB. When a snapshot is created, both the snapshot and the original point to the same blocks in the le system. So, initially a snapshot does not occupy additional disk space. If data in the original le system is modified, changed data blocks are copied while the old data blocks are kept for the snapshot. Therefore, a snapshot occupies the same amount of space as the data modified. So, over time, the amount of space a snapshot allocates, constantly grows. As a consequence, deleting les from a Btrfs le system containing snapshots may not free disk space. Note: Snapshot location Snapshots always reside on the same partition or subvolume on which the snapshot has been taken. It is not possible to store snapshots on a different partition or subvolume. As a result, partitions containing snapshots need to be larger than partitions not containing snapshots. The exact amount depends strongly on the number of snapshots you keep and the amount of data modifications. As a rule of thumb, give partitions twice as much space as you normally would. To prevent disks from running out of space, old snapshots are automatically cleaned up. Refer to Section 10.1.4.4, “Controlling snapshot archiving” for details. 137 Default setup SLES 15 SP610.1.1 Default settings Disks larger than 16 GB Configuration le: /etc/snapper/configs/root USE_SNAPPER=yes TIMELINE_CREATE=no Disks smaller than 16 GB Configuration le: not created USE_SNAPPER=no TIMELINE_CREATE=yes 10.1.2 Types of snapshots Although snapshots themselves do not differ in a technical sense, we distinguish between three types of snapshots, based on the events that trigger them: Timeline snapshots A single snapshot is created every hour. Using the YaST OS installation method (default), timeline snapshots are enabled, except for the root le system. You can configure timeline snapshots to be taken at different intervals: hourly, daily, weekly, monthly and yearly. Old snapshots are automatically deleted. By default, the rst snapshot of the last ten days, months and years is kept. Installation snapshots Whenever one or more packages are installed with Zypper or YaST, three installation snap- shots are created. In case an important system component such as the kernel has been in- stalled, the snapshot pair is marked as important. Old snapshots are automatically deleted. Installation snapshots are enabled by default. Administration snapshots Whenever you make changes to the system using Zypper or YaST, a pair of snapshots is created: one prior to the system change (“pre”) and the other one after the system change (“post”). Old snapshots are automatically deleted. Administration snapshots are enabled by default. 138 Default settings SLES 15 SP610.1.3 Directories that are excluded from snapshots Certain directories need to be excluded from snapshots for different reasons. The following list shows all directories that are excluded: /boot/grub2/i386-pc , /boot/grub2/x86_64-efi , /boot/grub2/powerpc-ieee1275 , / boot/grub2/s390x-emu A rollback of the boot loader configuration is not supported. The directories listed above are architecture-specific. The rst two directories are present on AMD64/Intel 64 ma- chines, the latter two on IBM POWER and on IBM Z, respectively. /home If /home does not reside on a separate partition, it is excluded to avoid data loss on roll- backs. /opt Third-party products usually get installed to /opt . It is excluded to avoid uninstalling these applications on rollbacks. /srv Contains data for Web and FTP servers. It is excluded to avoid data loss on rollbacks. /tmp All directories containing temporary les and caches are excluded from snapshots. /usr/local This directory is used when manually installing software. It is excluded to avoid unin- stalling these installations on rollbacks. /var This directory contains many variable les, including logs, temporary caches, third party products in /var/opt , and is the default location for virtual machine images and databas- es. Therefore this subvolume is created to exclude all of this variable data from snapshots and has Copy-On-Write disabled. 10.1.4 Customizing the setup SUSE Linux Enterprise Server comes with a reasonable default setup, which should be sufficient for most use cases. However, all aspects of taking automatic snapshots and snapshot keeping can be configured according to your needs. 139 Directories that are excluded from snapshots SLES 15 SP610.1.4.1 Disabling/enabling snapshots Each of the three snapshot types (timeline, installation, administration) can be enabled or dis- abled independently. Disabling/enabling timeline snapshots Enabling.  snapper -c root set-config "TIMELINE_CREATE=yes" Disabling.  snapper -c root set-config "TIMELINE_CREATE=no" Using the YaST OS installation method (default), timeline snapshots are enabled, except for the root le system. Disabling/enabling installation snapshots Enabling: Install the package snapper-zypp-plugin Disabling: Uninstall the package snapper-zypp-plugin Installation snapshots are enabled by default. Disabling/enabling administration snapshots Enabling: Set USE_SNAPPER to yes in /etc/sysconfig/yast2 . Disabling: Set USE_SNAPPER to no in /etc/sysconfig/yast2 . Administration snapshots are enabled by default. 10.1.4.2 Controlling installation snapshots Taking snapshot pairs upon installing packages with YaST or Zypper is handled by the snap- per-zypp-plugin . An XML configuration le, /etc/snapper/zypp-plugin.conf defines, when to make snapshots. By default the le looks like the following: 1 2 3 4 kernel-* 3 5 dracut 6 glibc 7 systemd* 8 udev 9 * 4 10 11 140 Customizing the setup SLES 15 SP61 The match attribute defines whether the pattern is a Unix shell-style wild card ( w ) or a Python regular expression ( re ). 2 If the given pattern matches and the corresponding package is marked as important (for example, kernel packages), the snapshot is also marked as important. 3 Pattern to match a package name. Based on the setting of the match attribute, special characters are either interpreted as shell wild cards or regular expressions. This pattern matches all package names starting with kernel- . 4 This line unconditionally matches all packages. With this configuration snapshot, pairs are made whenever a package is installed (line 9). When the kernel, dracut, glibc, systemd or udev packages marked as important are installed, the snap- shot pair is also marked as important (lines 4 to 8). All rules are evaluated. To disable a rule, either delete it or deactivate it using XML comments. To prevent the system from making snapshot pairs for every package installation for example, comment line 9: 1 2 3 4 kernel-* 5 dracut 6 glibc 7 systemd* 8 udev 9 10 11 10.1.4.3 Creating and mounting new subvolumes Creating a new subvolume underneath the / hierarchy and permanently mounting it is support- ed. Such a subvolume is excluded from snapshots. You need to make sure not to create it inside an existing snapshot, since you would not be able to delete snapshots anymore after a rollback. SUSE Linux Enterprise Server is configured with the /@/ subvolume which serves as an inde- pendent root for permanent subvolumes such as /opt , /srv , /home and others. Any new sub- volumes you create and permanently mount need to be created in this initial root le system. To do so, run the following commands. In this example, a new subvolume /usr/important is created from /dev/sda2 . > sudo mount /dev/sda2 -o subvol=@ /mnt 141 Customizing the setup SLES 15 SP6> sudo btrfs subvolume create /mnt/usr/important > sudo umount /mnt The corresponding entry in /etc/fstab needs to look like the following: /dev/sda2 /usr/important btrfs subvol=@/usr/important 0 0 Tip: Disable copy-on-write (cow) A subvolume may contain les that constantly change, such as virtualized disk images, database les, or log les. If so, consider disabling the copy-on-write feature for this volume, to avoid duplication of disk blocks. Use the nodatacow mount option in /etc/ fstab to do so: /dev/sda2 /usr/important btrfs nodatacow,subvol=@/usr/important 0 0 To alternatively disable copy-on-write for single les or directories, use the command chattr +C PATH . 10.1.4.4 Controlling snapshot archiving Snapshots occupy disk space. To prevent disks from running out of space and thus causing system outages, old snapshots are automatically deleted. By default, up to ten important installation and administration snapshots and up to ten regular installation and administration snapshots are kept. If these snapshots occupy more than 50% of the root le system size, additional snapshots are deleted. A minimum of four important and two regular snapshots are always kept. Refer to Section 10.5.1, “Managing existing configurations” for instructions on how to change these values. 10.1.4.5 Using Snapper on thinly provisioned LVM volumes Apart from snapshots on Btrfs le systems, Snapper also supports taking snapshots on thinly provisioned LVM volumes (snapshots on regular LVM volumes are not supported) formatted with XFS, Ext4 or Ext3. For more information and setup instructions on LVM volumes, refer to Book “Deployment Guide”, Chapter 11 “Expert Partitioner”, Section 11.3 “LVM configuration”. 142 Customizing the setup SLES 15 SP6To use Snapper on a thinly provisioned LVM volume, you need to create a Snapper configuration for it. On LVM it is required to specify the le system with --fstype=lvm(FILESYSTEM) . ext3 , etx4 or xfs are valid values for FILESYSTEM . Example: > sudo snapper -c lvm create-config --fstype="lvm(xfs)" /thin_lvm You can adjust this configuration according to your needs as described in Section 10.5.1, “Managing existing configurations”. 10.2 Using Snapper to undo changes Snapper on SUSE Linux Enterprise Server is preconfigured to serve as a tool that lets you undo changes made by zypper and YaST. For this purpose, Snapper is configured to create a pair of snapshots before and after each run of zypper and YaST. Snapper also lets you restore system les that have been accidentally deleted or modified. Timeline snapshots for the root partition need to be enabled for this purpose—see Section 10.1.4.1, “Disabling/enabling snapshots” for details. By default, automatic snapshots as described above are configured for the root partition and its subvolumes. To make snapshots available for other partitions such as /home for example, you can create custom configurations. Important: Undoing changes compared to rollback When working with snapshots to restore data, it is important to know that there are two fundamentally different scenarios Snapper can handle: Undoing changes When undoing changes as described in the following, two snapshots are being com- pared and the changes between these two snapshots are made undone. Using this method also allows to explicitly select the les that should be restored. Rollback When doing rollbacks as described in Section 10.3, “System rollback by booting from snapshots”, the system is reset to the state at which the snapshot was taken. 143 Using Snapper to undo changes SLES 15 SP6When undoing changes, it is also possible to compare a snapshot against the current system. When restoring all les from such a comparison, this will have the same result as doing a rollback. However, using the method described in Section 10.3, “System rollback by booting from snapshots” for rollbacks should be preferred, since it is faster and allows you to review the system before doing the rollback. Warning: Data consistency There is no mechanism to ensure data consistency when creating a snapshot. Whenever a le (for example, a database) is written at the same time as the snapshot is being created, it will result in a corrupted or partly written le. Restoring such a le will cause problems. Furthermore, certain system les such as /etc/mtab must never be restored. Therefore it is strongly recommended to always closely review the list of changed les and their dis. Only restore les that really belong to the action you want to revert. 10.2.1 Undoing YaST and Zypper changes If you set up the root partition with Btrfs during the installation, Snapper—preconfigured for doing rollbacks of YaST or Zypper changes—will automatically be installed. Every time you start a YaST module or a Zypper transaction, two snapshots are created: a “pre-snapshot” capturing the state of the le system before the start of the module and a “post-snapshot” after the module has been finished. Using the YaST Snapper module or the snapper command line tool, you can undo the changes made by YaST/Zypper by restoring les from the “pre-snapshot”. Comparing two snapshots the tools also allow you to see which les have been changed. You can also display the differences between two versions of a le (di). PROCEDURE 10.1: UNDOING CHANGES USING THE YAST SNAPPER MODULE 1. Start the Snapper module from the Miscellaneous section in YaST or by entering yast2 snapper . 2. Make sure Current Configuration is set to root. This is always the case unless you have manually added own Snapper configurations. 144 Undoing YaST and Zypper changes SLES 15 SP63. Choose a pair of pre- and post-snapshots from the list. Both, YaST and Zypper snapshot pairs are of the type Pre & Post. YaST snapshots are labeled as zypp(y2base) in the Description column; Zypper snapshots are labeled zypp(zypper) . 4. Click Show Changes to open the list of les that differ between the two snapshots. 145 Undoing YaST and Zypper changes SLES 15 SP65. Review the list of les. To display a “di” between the pre- and post-version of a le, select it from the list. 6. To restore one or more les, select the relevant les or directories by activating the re- spective check box. Click Restore Selected and confirm the action by clicking Yes. To restore a single le, activate its di view by clicking its name. Click Restore From First and confirm your choice with Yes. 146 Undoing YaST and Zypper changes SLES 15 SP6PROCEDURE 10.2: UNDOING CHANGES USING THE snapper COMMAND 1. Get a list of YaST and Zypper snapshots by running snapper list -t pre-post . YaST snapshots are labeled as yast MODULE_NAME in the Description column; Zypper snapshots are labeled zypp(zypper) . > sudo snapper list -t pre-post Pre # | Post # | Pre Date | Post Date | Description ------+--------+-------------------------------+-------------------------------+-------------- 311 | 312 | Tue 06 May 2018 14:05:46 CEST | Tue 06 May 2018 14:05:52 CEST | zypp(y2base) 340 | 341 | Wed 07 May 2018 16:15:10 CEST | Wed 07 May 2018 16:15:16 CEST | zypp(zypper) 342 | 343 | Wed 07 May 2018 16:20:38 CEST | Wed 07 May 2018 16:20:42 CEST | zypp(y2base) 344 | 345 | Wed 07 May 2018 16:21:23 CEST | Wed 07 May 2018 16:21:24 CEST | zypp(zypper) 346 | 347 | Wed 07 May 2018 16:41:06 CEST | Wed 07 May 2018 16:41:10 CEST | zypp(y2base) 348 | 349 | Wed 07 May 2018 16:44:50 CEST | Wed 07 May 2018 16:44:53 CEST | zypp(y2base) 350 | 351 | Wed 07 May 2018 16:46:27 CEST | Wed 07 May 2018 16:46:38 CEST | zypp(y2base) 2. Get a list of changed les for a snapshot pair with snapper status PRE .. POST . Files with content changes are marked with c, les that have been added are marked with + and deleted les are marked with -. > sudo snapper status 350..351 +..... /usr/share/doc/packages/mikachan-fonts +..... /usr/share/doc/packages/mikachan-fonts/COPYING +..... /usr/share/doc/packages/mikachan-fonts/dl.html c..... /usr/share/fonts/truetype/fonts.dir c..... /usr/share/fonts/truetype/fonts.scale +..... /usr/share/fonts/truetype/#####-p.ttf +..... /usr/share/fonts/truetype/#####-pb.ttf +..... /usr/share/fonts/truetype/#####-ps.ttf +..... /usr/share/fonts/truetype/#####.ttf c..... /var/cache/fontconfig/7ef2298fde41cc6eeb7af42e48b7d293-x86_64.cache-4 c..... /var/lib/rpm/Basenames c..... /var/lib/rpm/Dirnames c..... /var/lib/rpm/Group c..... /var/lib/rpm/Installtid c..... /var/lib/rpm/Name c..... /var/lib/rpm/Packages c..... /var/lib/rpm/Providename c..... /var/lib/rpm/Requirename c..... /var/lib/rpm/Sha1header c..... /var/lib/rpm/Sigmd5 3. To display the di for a certain le, run snapper diff PRE .. POST FILENAME . If you do not specify FILENAME , a di for all les will be displayed. > sudo snapper diff 350..351 /usr/share/fonts/truetype/fonts.scale 147 Undoing YaST and Zypper changes SLES 15 SP6--- /.snapshots/350/snapshot/usr/share/fonts/truetype/fonts.scale 2014-04-23 15:58:57.000000000 +0200 +++ /.snapshots/351/snapshot/usr/share/fonts/truetype/fonts.scale 2014-05-07 16:46:31.000000000 +0200 @@ -1,4 +1,4 @@ -1174 +1486 ds=y:ai=0.2:luximr.ttf -b&h-luxi mono-bold-i-normal--0-0-0-0-c-0-iso10646-1 ds=y:ai=0.2:luximr.ttf -b&h-luxi mono-bold-i-normal--0-0-0-0-c-0-iso8859-1 [...] 4. To restore one or more les run snapper -v undochange PRE .. POST FILENAMES . If you do not specify a FILENAMES , all changed les will be restored. > sudo snapper -v undochange 350..351 create:0 modify:13 delete:7 undoing change... deleting /usr/share/doc/packages/mikachan-fonts deleting /usr/share/doc/packages/mikachan-fonts/COPYING deleting /usr/share/doc/packages/mikachan-fonts/dl.html deleting /usr/share/fonts/truetype/#####-p.ttf deleting /usr/share/fonts/truetype/#####-pb.ttf deleting /usr/share/fonts/truetype/#####-ps.ttf deleting /usr/share/fonts/truetype/#####.ttf modifying /usr/share/fonts/truetype/fonts.dir modifying /usr/share/fonts/truetype/fonts.scale modifying /var/cache/fontconfig/7ef2298fde41cc6eeb7af42e48b7d293-x86_64.cache-4 modifying /var/lib/rpm/Basenames modifying /var/lib/rpm/Dirnames modifying /var/lib/rpm/Group modifying /var/lib/rpm/Installtid modifying /var/lib/rpm/Name modifying /var/lib/rpm/Packages modifying /var/lib/rpm/Providename modifying /var/lib/rpm/Requirename modifying /var/lib/rpm/Sha1header modifying /var/lib/rpm/Sigmd5 undoing change done 148 Undoing YaST and Zypper changes SLES 15 SP6Warning: Reverting user additions Reverting user additions via undoing changes with Snapper is not recommended. Since certain directories are excluded from snapshots, les belonging to these users will remain in the le system. If a user with the same user ID as a deleted user is created, this user will inherit the les. Therefore it is strongly recommended to use the YaST User and Group Management tool to remove users. 10.2.2 Using Snapper to restore files Apart from the installation and administration snapshots, Snapper creates timeline snapshots. You can use these backup snapshots to restore les that have accidentally been deleted or to restore a previous version of a le. By using Snapper''s di feature you can also nd out which modifications have been made at a certain point of time. Being able to restore les is especially interesting for data, which may reside on subvolumes or partitions for which snapshots are not taken by default. To be able to restore les from home di- rectories, for example, create a separate Snapper configuration for /home doing automatic time- line snapshots. See Section 10.5, “Creating and modifying Snapper configurations” for instructions. Warning: Restoring files compared to rollback Snapshots taken from the root le system (defined by Snapper''s root configuration), can be used to do a system rollback. The recommended way to do such a rollback is to boot from the snapshot and then perform the rollback. See Section 10.3, “System rollback by boot- ing from snapshots” for details. Performing a rollback would also be possible by restoring all les from a root le system snapshot as described below. However, this is not recommended. You may restore single les, for example, a configuration le from the /etc directory, but not the complete list of les from the snapshot. This restriction only affects snapshots taken from the root le system. PROCEDURE 10.3: RESTORING FILES USING THE YAST SNAPPER MODULE 1. Start the Snapper module from the Miscellaneous section in YaST or by entering yast2 snapper . 2. Choose the Current Configuration from which to choose a snapshot. 149 Using Snapper to restore files SLES 15 SP63. Select a timeline snapshot from which to restore a le and choose Show Changes. Timeline snapshots are of the type Single with a description value of timeline. 4. Select a le from the text box by clicking the le name. The difference between the snap- shot version and the current system is shown. Activate the check box to select the le for restore. Do so for all les you want to restore. 5. Click Restore Selected and confirm the action by clicking Yes. PROCEDURE 10.4: RESTORING FILES USING THE snapper COMMAND 1. Get a list of timeline snapshots for a specific configuration by running the following com- mand: > sudo snapper -c CONFIG list -t single | grep timeline CONFIG needs to be replaced by an existing Snapper configuration. Use snapper list- configs to display a list. 2. Get a list of changed les for a given snapshot by running the following command: > sudo snapper -c CONFIG status SNAPSHOT_ID..0 Replace SNAPSHOT_ID by the ID for the snapshot from which you want to restore the les. 3. Optionally list the differences between the current le version and the one from the snap- shot by running > sudo snapper -c CONFIG diff SNAPSHOT_ID..0 FILE NAME If you do not specify , the difference for all les are shown. 4. To restore one or more les, run > sudo snapper -c CONFIG -v undochange SNAPSHOT_ID..0 FILENAME1 FILENAME2 If you do not specify le names, all changed les will be restored. 10.3 System rollback by booting from snapshots The GRUB 2 version included on SUSE Linux Enterprise Server can boot from Btrfs snapshots. Together with Snapper''s rollback feature, this allows to recover a misconfigured system. Only snapshots created for the default Snapper configuration ( root ) are bootable. 150 System rollback by booting from snapshots SLES 15 SP6Important: Supported configuration As of SUSE Linux Enterprise Server 15 SP6 system rollbacks are only supported if the default subvolume configuration of the root partition has not been changed. When booting a snapshot, the parts of the le system included in the snapshot are mounted read-only; all other le systems and parts that are excluded from snapshots are mounted read- write and can be modified. Important: Undoing changes compared to rollback When working with snapshots to restore data, it is important to know that there are two fundamentally different scenarios Snapper can handle: Undoing changes When undoing changes as described in Section 10.2, “Using Snapper to undo changes”, two snapshots are compared and the changes between these two snapshots are re- verted. Using this method also allows to explicitly exclude selected les from being restored. Rollback When doing rollbacks as described in the following, the system is reset to the state at which the snapshot was taken. To do a rollback from a bootable snapshot, the following requirements must be met. When doing a default installation, the system is set up accordingly. REQUIREMENTS FOR A ROLLBACK FROM A BOOTABLE SNAPSHOT The root le system needs to be Btrfs. Booting from LVM volume snapshots is not support- ed. The root le system needs to be on a single device. To check, run sudo /sbin/btrfs filesystem show . It needs to report Total devices 1 . If more than 1 device is listed, your setup is not supported. 151 System rollback by booting from snapshots SLES 15 SP6Note: Directories excluded from snapshots Directories that are excluded from snapshots such as /srv (see Section 10.1.3, “Direc- tories that are excluded from snapshots” for a full list) may reside on separate devices. The system needs to be bootable via the installed boot loader. Only contents of the subvolume / will be rolled back. It is not possible to include other subvolumes. To perform a rollback from a bootable snapshot, do as follows: 1. Boot the system. In the boot menu choose Bootable snapshots and select the snapshot you want to boot. The list of snapshots is listed by date—the most recent snapshot is listed rst. 2. Log in to the system. Carefully check whether everything works as expected. Note that you cannot write to any directory that is part of the snapshot. Data you write to other directories will not get lost, regardless of what you do next. 3. Depending on whether you want to perform the rollback or not, choose your next step: a. If the system is in a state where you do not want to do a rollback, reboot to boot into the current system state. You can then choose a different snapshot, or start the rescue system. b. To perform the rollback, run > sudo snapper rollback and reboot afterward. On the boot screen, choose the default boot entry to reboot into the reinstated system. A snapshot of the le system status before the rollback is created. The default subvolume for root will be replaced with a fresh read-write snapshot. For details, see Section 10.3.1, “Snapshots after rollback”. It is useful to add a description for the snapshot with the -d option. For example: New file system root since rollback on DATE TIME 152 System rollback by booting from snapshots SLES 15 SP6Tip: Rolling back to a specific installation state If snapshots are not disabled during installation, an initial bootable snapshot is created at the end of the initial system installation. You can go back to that state at any time by booting this snapshot. The snapshot can be identified by the description after in- stallation . A bootable snapshot is also created when starting a system upgrade to a service pack or a new major release (provided snapshots are not disabled). 10.3.1 Snapshots after rollback Before a rollback is performed, a snapshot of the running le system is created. The description references the ID of the snapshot that was restored in the rollback. Snapshots created by rollbacks receive the value number for the Cleanup attribute. The rollback snapshots are therefore automatically deleted when the set number of snapshots is reached. Refer to Section 10.7, “Automatic snapshot clean-up” for details. If the snapshot contains important data, extract the data from the snapshot before it is removed. 10.3.1.1 Example of rollback snapshot For example, after a fresh installation the following snapshots are available on the system: # snapper --iso list Type | # | | Cleanup | Description | Userdata -------+---+ ... +---------+-----------------------+-------------- single | 0 | | | current | single | 1 | | | first root filesystem | single | 2 | | number | after installation | important=yes After running sudo snapper rollback snapshot 3 is created and contains the state of the system before the rollback was executed. Snapshot 4 is the new default Btrfs subvolume and thus the system after a reboot. # snapper --iso list Type | # | | Cleanup | Description | Userdata -------+---+ ... +---------+-----------------------+-------------- single | 0 | | | current | single | 1 | | number | first root filesystem | single | 2 | | number | after installation | important=yes 153 Snapshots after rollback SLES 15 SP6single | 3 | | number | rollback backup of #1 | important=yes single | 4 | | | | 10.3.2 Accessing and identifying snapshot boot entries To boot from a snapshot, reboot your machine and choose Start Bootloader from a read-only snapshot. A screen listing all bootable snapshots opens. The most recent snapshot is listed rst, the oldest last. Use the keys ↓ and ↑ to navigate and press Enter to activate the selected snapshot. Activating a snapshot from the boot menu does not reboot the machine immediately, but rather opens the boot loader of the selected snapshot. FIGURE 10.1: BOOT LOADER: SNAPSHOTS Warning: Booting Xen from a Btrfs snapshot using UEFI currently fails Refer to https://www.suse.com/support/kb/doc/?id=000020602 for more details. Each snapshot entry in the boot loader follows a naming scheme which makes it possible to identify it easily: [*] 1 OS 2 (KERNEL 3 ,DATE 4 TTIME 5 ,DESCRIPTION 6 ) 154 Accessing and identifying snapshot boot entries SLES 15 SP61 If the snapshot was marked important , the entry is marked with a * . 2 Operating system label. 4 Date in the format YYYY-MM-DD . 5 Time in the format HH:MM . 6 This eld contains a description of the snapshot. In case of a manually created snapshot this is the string created with the option --description or a custom string (see Tip: Setting a custom description for boot loader snapshot entries). In case of an automatically created snapshot, it is the tool that was called, for example zypp(zypper) or yast_sw_single . Long descriptions may be truncated, depending on the size of the boot screen. Tip: Setting a custom description for boot loader snapshot entries It is possible to replace the default string in the description eld of a snapshot with a custom string. This is for example useful if an automatically created description is not sufficient, or a user-provided description is too long. To set a custom string STRING for snapshot NUMBER , use the following command: > sudo snapper modify --userdata "bootloader=STRING" NUMBER The description should be no longer than 25 characters—everything that exceeds this size will not be readable on the boot screen. 10.3.3 Limitations A complete system rollback, restoring the complete system to the identical state as it was in when a snapshot was taken, is not possible. 10.3.3.1 Directories excluded from snapshots Root le system snapshots do not contain all directories. See Section 10.1.3, “Directories that are excluded from snapshots” for details and reasons. As a general consequence, data from these di- rectories is not restored, resulting in the following limitations. 155 Limitations SLES 15 SP6Add-ons and third-party software may be unusable after a rollback Applications and add-ons installing data in subvolumes excluded from the snapshot, such as /opt , may not work after a rollback if other parts of the application data are also installed on subvolumes included in the snapshot. Re-install the application or the add- on to solve this problem. File access problems If an application had changed le permissions and/or ownership in between snapshot and current system, the application may not be able to access these les. Reset permissions and/or ownership for the affected les after the rollback. Incompatible data formats If a service or an application has established a new data format in between snapshot and current system, the application may not be able to read the affected data les after a rollback. Subvolumes with a mixture of code and data Subvolumes like /srv may contain a mixture of code and data. A rollback may result in non-functional code. A downgrade of the PHP version, for example, may result in broken PHP scripts for the Web server. User data If a rollback removes users from the system, data that is owned by these users in directories excluded from the snapshot, is not removed. If a user with the same user ID is created, this user will inherit the les. Use a tool like find to locate and remove orphaned les. 10.3.3.2 No rollback of boot loader data A rollback of the boot loader is not possible, since all “stages” of the boot loader must t together. This cannot be guaranteed when doing rollbacks of /boot . 156 Limitations SLES 15 SP610.4 Enabling Snapper in user home directories You may enable snapshots for users'' /home directories, which supports several use cases: Individual users may manage their own snapshots and rollbacks. System users, for example, database, system, and network admins who want to track copies of configuration les, documentation, and so on. Samba shares with home directories and Btrfs back-end. Each user''s directory is a Btrfs subvolume of /home . It is possible to set this up manually (see Section 10.4.3, “Manually enabling snapshots in home directories”). However, a more convenient way is to use pam_snapper . The pam_snapper package installs the pam_snapper.so module and helper scripts, which automate user creation and Snapper configuration. pam_snapper provides integration with the useradd command, pluggable authentication mod- ules (PAM), and Snapper. By default it creates snapshots at user login and logout, and also cre- ates time-based snapshots as certain users remain logged in for extended periods of time. You may change the defaults using the normal Snapper commands and configuration les. 10.4.1 Installing pam_snapper and creating users The easiest way is to start with a new /home directory formatted with Btrfs, and no existing users. Install pam_snapper : # zypper in pam_snapper Add this line to /etc/pam.d/common-session : session optional pam_snapper.so Use the /usr/lib/pam_snapper/pam_snapper_useradd.sh script to create a new user and home directory. By default the script performs a dry run. Edit the script to change DRYRUN=1 to DRYRUN=0 . Now you can create a new user: # /usr/lib/pam_snapper/pam_snapper_useradd.sh \ username group passwd=password Create subvolume ''/home/username'' useradd: warning: the home directory already exists. Not copying any file from skel directory into it. 157 Enabling Snapper in user home directories SLES 15 SP6The les from /etc/skel will be copied into the user''s home directory at their rst login. Verify that the user''s configuration was created by listing your Snapper configurations: # snapper list --all Config: home_username, subvolume: /home/username Type | # | Pre # | Date | User | Cleanup | Description | Userdata -------+---+-------+------+------+---------+-------------+--------- single | 0 | | | root | | current | Over time, this output will become populated with a list of snapshots, which the user can manage with the standard Snapper commands. 10.4.2 Removing users Remove users with the /usr/lib/pam_snapper/pam_snapper_userdel.sh script. By default it performs a dry run, so edit it to change DRYRUN=1 to DRYRUN=0 . This removes the user, the user''s home subvolume, Snapper configuration, and deletes all snapshots. # /usr/lib/pam_snapper/pam_snapper_userdel.sh username 10.4.3 Manually enabling snapshots in home directories These are the steps for manually setting up users'' home directories with Snapper. /home must be formatted with Btrfs, and the users not yet created. # btrfs subvol create /home/username # snapper -c home_username create-config /home/username # sed -i -e "s/ALLOW_USERS=\"\"/ALLOW_USERS=\"username\"/g" \ /etc/snapper/configs/home_username # yast users add username=username home=/home/username password=password # chown username.group /home/username # chmod 755 /home/username/.snapshots 10.5 Creating and modifying Snapper configurations The way Snapper behaves is defined in a configuration le that is specific for each partition or Btrfs subvolume. These configuration les reside under /etc/snapper/configs/ . 158 Removing users SLES 15 SP6In case the root le system is big enough (approximately 12 GB), snapshots are automatically enabled for the root le system / upon installation. The corresponding default configuration is named root . It creates and manages the YaST and Zypper snapshot. See Section 10.5.1.1, “Configuration data” for a list of the default values. Note: Minimum root file system size for enabling snapshots As explained in Section 10.1, “Default setup”, enabling snapshots requires additional free space in the root le system. The amount depends on the amount of packages installed and the amount of changes made to the volume that is included in snapshots. The snapshot frequency and the number of snapshots that get archived also matter. There is a minimum root le system size that is required to automatically enable snapshots during the installation. Currently this size is approximately 12 GB. This value may change in the future, depending on architecture and the size of the base system. It depends on the values for the following tags in the le /control.xml from the installation media: It is calculated with the following formula: ROOT_BASE_SIZE * (1 + BTRFS_IN- CREASE_PERCENTAGE /100) Keep in mind that this value is a minimum size. Consider using more space for the root le system. As a rule of thumb, double the size you would use when not having enabled snapshots. You may create your own configurations for other partitions formatted with Btrfs or existing subvolumes on a Btrfs partition. In the following example we will set up a Snapper configu- ration for backing up the Web server data residing on a separate, Btrfs -formatted partition mounted at /srv/www . After a configuration has been created, you can either use snapper itself or the YaST Snapper module to restore les from these snapshots. In YaST you need to select your Current Configura- tion, while you need to specify your configuration for snapper with the global switch -c (for example, snapper -c myconfig list ). To create a new Snapper configuration, run snapper create-config : > sudo snapper -c www-data 1 create-config /srv/www 2 159 Creating and modifying Snapper configurations SLES 15 SP61 Name of configuration le. 2 Mount point of the partition or Btrfs subvolume on which to take snapshots. This command will create a new configuration le /etc/snapper/configs/www-data with reasonable default values (taken from /etc/snapper/config-templates/default ). Refer to Section 10.5.1, “Managing existing configurations” for instructions on how to adjust these defaults. Tip: Configuration defaults Default values for a new configuration are taken from /etc/snapper/config-tem- plates/default . To use your own set of defaults, create a copy of this le in the same directory and adjust it to your needs. To use it, specify the -t option with the create-con- fig command: > sudo snapper -c www-data create-config -t MY_DEFAULTS /srv/www 10.5.1 Managing existing configurations The snapper command offers several subcommands for managing existing configurations. You can list, show, delete and modify them: Listing configurations Use the subcommand snapper list-configs to get all existing configurations: > sudo snapper list-configs Config | Subvolume -------+---------- root | / usr | /usr local | /local Showing a configuration Use the subcommand snapper -c CONFIG get-config to display the specified configu- ration. Replace CONFIG with one of the configuration names shown by snapper list- configs . For more information about the configuration options, see Section 10.5.1.1, “Con- figuration data”. To display the default configuration, run: > sudo snapper -c root get-config 160 Managing existing configurations SLES 15 SP6Modifying a configuration Use the subcommand snapper -c CONFIG set-config OPTION=VALUE to modify an option in the specified configuration. Replace CONFIG with one of the configuration names shown by snapper list-configs . Possible values for OPTION and VALUE are listed in Section 10.5.1.1, “Configuration data”. Deleting a configuration Use the subcommand snapper -c CONFIG delete-config to delete a configuration. Replace CONFIG with one of the configuration names shown by snapper list-configs . 10.5.1.1 Configuration data Each configuration contains a list of options that can be modified from the command line. The following list provides details for each option. To change a value, run snapper -c CONFIG set-config "KEY=VALUE" . ALLOW_GROUPS , ALLOW_USERS Granting permissions to use snapshots to regular users. See Section 10.5.1.2, “Using Snapper as regular user” for more information. The default value is "" . BACKGROUND_COMPARISON Defines whether pre and post snapshots should be compared in the background after cre- ation. The default value is "yes" . EMPTY_* Defines the clean-up algorithm for snapshots pairs with identical pre and post snapshots. See Section 10.7.3, “Cleaning up snapshot pairs that do not differ” for details. FSTYPE File system type of the partition. Do not change. The default value is "btrfs" . NUMBER_* Defines the clean-up algorithm for installation and administration snapshots. See Sec- tion 10.7.1, “Cleaning up numbered snapshots” for details. 161 Managing existing configurations SLES 15 SP6QGROUP / SPACE_LIMIT Adds quota support to the clean-up algorithms. See Section 10.7.5, “Adding disk quota support” for details. SUBVOLUME Mount point of the partition or subvolume to snapshot. Do not change. The default value is "/" . SYNC_ACL If Snapper is used by regular users (see Section 10.5.1.2, “Using Snapper as regular user”), the users must be able to access the .snapshot directories and to read les within them. If SYNC_ACL is set to yes , Snapper automatically makes them accessible using ACLs for users and groups from the ALLOW_USERS or ALLOW_GROUPS entries. The default value is "no" . TIMELINE_CREATE If set to yes , hourly snapshots are created. Valid values: yes , no . The default value is "no" . TIMELINE_CLEANUP / TIMELINE_LIMIT_* Defines the clean-up algorithm for timeline snapshots. See Section 10.7.2, “Cleaning up time- line snapshots” for details. 10.5.1.2 Using Snapper as regular user By default Snapper can only be used by root . However, there are cases in which certain groups or users need to be able to create snapshots or undo changes by reverting to a snapshot: Web site administrators who want to take snapshots of /srv/www Users who want to take a snapshot of their home directory For these purposes, you can create Snapper configurations that grant permissions to users or/ and groups. The corresponding .snapshots directory needs to be readable and accessible by the specified users. The easiest way to achieve this is to set the SYNC_ACL option to yes . PROCEDURE 10.5: ENABLING REGULAR USERS TO USE SNAPPER All steps in this procedure need to be run by root . 162 Managing existing configurations SLES 15 SP61. If a Snapper configuration does not exist yet, create one for the partition or subvolume on which the user should be able to use Snapper. Refer to Section 10.5, “Creating and modifying Snapper configurations” for instructions. Example: > sudo snapper --config web_data create /srv/www 2. The configuration le is created under /etc/snapper/configs/CONFIG , where CONFIG is the value you specified with -c/--config in the previous step (for example /etc/ snapper/configs/web_data ). Adjust it according to your needs. For more information, see Section 10.5.1, “Managing existing configurations”. 3. Set values for ALLOW_USERS and/or ALLOW_GROUPS to grant permissions to users and/or groups, respectively. Multiple entries need to be separated by Space . To grant permissions to the user www_admin for example, run: > sudo snapper -c web_data set-config "ALLOW_USERS=www_admin" SYNC_ACL="yes" 4. The given Snapper configuration can now be used by the specified users and/or groups. You can test it with the list command, for example: www_admin:~ > snapper -c web_data list 10.6 Manually creating and managing snapshots Snapper is not restricted to creating and managing snapshots automatically by configuration; you can also create snapshot pairs (“before and after”) or single snapshots manually using either the command-line tool or the YaST module. All Snapper operations are carried out for an existing configuration (see Section 10.5, “Creating and modifying Snapper configurations” for details). You can only take snapshots of partitions or volumes for which a configuration exists. By default the system configuration ( root ) is used. To create or manage snapshots for your own configuration you need to explicitly choose it. Use the Current Configuration drop-down box in YaST or specify the -c on the command line ( snapper -c MYCONFIG COMMAND ). 163 Manually creating and managing snapshots SLES 15 SP610.6.1 Snapshot metadata Each snapshot consists of the snapshot itself and certain metadata. When creating a snapshot you also need to specify the metadata. Modifying a snapshot means changing its metadata—you cannot modify its content. Use snapper list to show existing snapshots and their metadata: snapper --config home list Lists snapshots for the configuration home . To list snapshots for the default configuration (root), use snapper -c root list or snapper list . snapper list -a Lists snapshots for all existing configurations. snapper list -t pre-post Lists all pre and post snapshot pairs for the default ( root ) configuration. snapper list -t single Lists all snapshots of the type single for the default ( root ) configuration. The following metadata is available for each snapshot: Type: snapshot type, see Section 10.6.1.1, “Snapshot types” for details. This data cannot be changed. Number: unique number of the snapshot. This data cannot be changed. Pre Number: specifies the number of the corresponding pre snapshot. For snapshots of type post only. This data cannot be changed. Description: a description of the snapshot. Userdata: an extended description where you can specify custom data in the form of a comma-separated key=value list: reason=testing, project=foo . This eld is also used to mark a snapshot as important ( important=yes ) and to list the user that created the snapshot (user=tux). Cleanup-Algorithm: cleanup-algorithm for the snapshot, see Section 10.7, “Automatic snap- shot clean-up” for details. 10.6.1.1 Snapshot types Snapper knows three different types of snapshots: pre, post and single. Physically they do not differ, but Snapper handles them differently. 164 Snapshot metadata SLES 15 SP6pre Snapshot of a le system before a modification. Each pre snapshot corresponds to a post snapshot. For example, this is used for the automatic YaST/Zypper snapshots. post Snapshot of a le system after a modification. Each post snapshot corresponds to a pre snapshot. For example, this is used for the automatic YaST/Zypper snapshots. single Stand-alone snapshot. For example, this is used for the automatic hourly snapshots. This is the default type when creating snapshots. 10.6.1.2 Cleanup algorithms Snapper provides three algorithms to clean up old snapshots. The algorithms are executed in a daily cron job. It is possible to define the number of different types of snapshots to keep in the Snapper configuration (see Section 10.5.1, “Managing existing configurations” for details). number Deletes old snapshots when a certain snapshot count is reached. timeline Deletes old snapshots having passed a certain age but keeps several hourly, daily, monthly and yearly snapshots. empty-pre-post Deletes pre/post snapshot pairs with empty dis. 10.6.2 Creating snapshots To create a snapshot, run snapper create or click Create in the YaST module Snapper. The following examples explain how to create snapshots from the command line. The YaST interface for Snapper is not explicitly described here but provides equivalent functionality. Tip: Snapshot description Always specify a meaningful description to later be able to identify its purpose. You can also specify additional information via the option --userdata . 165 Creating snapshots SLES 15 SP6snapper create --from 17 --description "with package2" Creates a stand-alone snapshot (type single) from an existing snapshot, which is specified by the snapshot''s number from snapper list . (This applies to Snapper version 0.8.4 and newer.) snapper create --description "Snapshot for week 2 2014" Creates a stand-alone snapshot (type single) for the default ( root ) configuration with a description. Because no cleanup-algorithm is specified, the snapshot will never be deleted automatically. snapper --config home create --description "Cleanup in ~tux" Creates a stand-alone snapshot (type single) for a custom configuration named home with a description. Because no cleanup-algorithm is specified, the snapshot will never be deleted automatically. snapper --config home create --description "Daily data backup" --cleanup-algo- rithm timeline > Creates a stand-alone snapshot (type single) for a custom configuration named home with a description. The snapshot will automatically be deleted when it meets the criteria specified for the timeline cleanup-algorithm in the configuration. snapper create --type pre --print-number --description "Before the Apache config cleanup" --userdata "important=yes" Creates a snapshot of the type pre and prints the snapshot number. First command needed to create a pair of snapshots used to save a “before” and “after” state. The snapshot is marked as important. snapper create --type post --pre-number 30 --description "After the Apache config cleanup" --userdata "important=yes" Creates a snapshot of the type post paired with the pre snapshot number 30 . Second command needed to create a pair of snapshots used to save a “before” and “after” state. The snapshot is marked as important. snapper create --command COMMAND --description "Before and after COMMAND" Automatically creates a snapshot pair before and after running COMMAND . This option is only available when using snapper on the command line. 166 Creating snapshots SLES 15 SP610.6.3 Modifying snapshot metadata Snapper allows you to modify the description, the cleanup algorithm, and the user data of a snapshot. All other metadata cannot be changed. The following examples explain how to mod- ify snapshots from the command line. It should be easy to adopt them when using the YaST interface. To modify a snapshot on the command line, you need to know its number. Use snapper list to display all snapshots and their numbers. The YaST Snapper module already lists all snapshots. Choose one from the list and click Modify. snapper modify --cleanup-algorithm "timeline" 10 Modifies the metadata of snapshot 10 for the default ( root ) configuration. The cleanup algorithm is set to timeline . snapper --config home modify --description "daily backup" -cleanup-algorithm "timeline" 120 Modifies the metadata of snapshot 120 for a custom configuration named home . A new description is set and the cleanup algorithm is unset. 10.6.4 Deleting snapshots To delete a snapshot with the YaST Snapper module, choose a snapshot from the list and click Delete. To delete a snapshot with the command-line tool, you need to know its number. Get it by running snapper list . To delete a snapshot, run snapper delete NUMBER . Deleting the current default subvolume snapshot is not allowed. When deleting snapshots with Snapper, the freed space will be claimed by a Btrfs process running in the background. Thus the visibility and the availability of free space is delayed. In case you need space freed by deleting a snapshot to be available immediately, use the option --sync with the delete command. Tip: Deleting snapshot pairs When deleting a pre snapshot, you should always delete its corresponding post snap- shot (and vice versa). 167 Modifying snapshot metadata SLES 15 SP6snapper delete 65 Deletes snapshot 65 for the default ( root ) configuration. snapper -c home delete 89 90 Deletes snapshots 89 and 90 for a custom configuration named home . snapper delete --sync 23 Deletes snapshot 23 for the default ( root ) configuration and makes the freed space avail- able immediately. Tip: Delete unreferenced snapshots Sometimes the Btrfs snapshot is present but the XML le containing the metadata for Snapper is missing. In this case, the snapshot is not visible for Snapper and needs to be deleted manually: btrfs subvolume delete /.snapshots/SNAPSHOTNUMBER/snapshot rm -rf /.snapshots/SNAPSHOTNUMBER Tip: Old snapshots occupy more disk space If you delete snapshots to free space on your hard disk, make sure to delete old snapshots rst. The older a snapshot is, the more disk space it occupies. Snapshots are also automatically deleted by a daily cron job. Refer to Section 10.6.1.2, “Cleanup algorithms” for details. 10.7 Automatic snapshot clean-up Snapshots occupy disk space and over time the amount of disk space occupied by the snapshots may become large. To prevent disks from running out of space, Snapper offers algorithms to automatically delete old snapshots. These algorithms differentiate between timeline snapshots and numbered snapshots (administration plus installation snapshot pairs). You can specify the number of snapshots to keep for each type. Additionally, you can optionally specify a disk space quota, defining the maximum amount of disk space the snapshots may occupy. It is also possible to automatically delete pre and post snapshots pairs that do not differ. 168 Automatic snapshot clean-up SLES 15 SP6A clean-up algorithm is always bound to a single Snapper configuration, so you need to config- ure algorithms for each configuration. To prevent certain snapshots from being automatically deleted, refer to Q:. The default setup ( root ) is configured to do clean-up for numbered snapshots and empty pre and post snapshot pairs. Quota support is enabled—snapshots may not occupy more than 50% of the available disk space of the root partition. Timeline snapshots are disabled by default, therefore the timeline clean-up algorithm is also disabled. 10.7.1 Cleaning up numbered snapshots Cleaning up numbered snapshots—administration plus installation snapshot pairs—is controlled by the following parameters of a Snapper configuration. NUMBER_CLEANUP Enables or disables clean-up of installation and admin snapshot pairs. If enabled, snap- shot pairs are deleted when the total snapshot count exceeds a number specified with NUMBER_LIMIT and/or NUMBER_LIMIT_IMPORTANT and an age specified with NUM- BER_MIN_AGE . Valid values: yes (enable), no (disable). The default value is "yes" . Example command to change or set: > sudo snapper -c CONFIG set-config "NUMBER_CLEANUP=no" NUMBER_LIMIT / NUMBER_LIMIT_IMPORTANT Defines how many regular and/or important installation and administration snapshot pairs to keep. Ignored if NUMBER_CLEANUP is set to "no" . The default value is "2-10" for NUMBER_LIMIT and "4-10" for NUMBER_LIMIT_IMPOR- TANT . The cleaning algorithms delete snapshots above the specified maximum value, with- out taking the snapshot and le system space into account. The algorithms also delete snapshots above the minimum value until the limits for the snapshot and le system are reached. Example command to change or set: > sudo snapper -c CONFIG set-config "NUMBER_LIMIT=10" 169 Cleaning up numbered snapshots SLES 15 SP6Important: Ranged compared to constant values If quota support is enabled (see Section 10.7.5, “Adding disk quota support”), the limit needs to be specified as a minimum-maximum range, for example, 2-10 . If quota support is disabled, a constant value, for example, 10 , needs to be provided, oth- erwise cleaning up fails with an error. NUMBER_MIN_AGE Defines the minimum age in seconds a snapshot must have before it can automatically be deleted. Snapshots younger than the value specified here will not be deleted, regardless of how many exist. The default value is "1800" . Example command to change or set: > sudo snapper -c CONFIG set-config "NUMBER_MIN_AGE=864000" Note: Limit and age NUMBER_LIMIT , NUMBER_LIMIT_IMPORTANT and NUMBER_MIN_AGE are always evaluated. Snapshots are only deleted when all conditions are met. If you always want to keep the number of snapshots defined with NUMBER_LIMIT* re- gardless of their age, set NUMBER_MIN_AGE to 0 . The following example shows a configuration to keep the last 10 important and regular snapshots regardless of age: NUMBER_CLEANUP=yes NUMBER_LIMIT_IMPORTANT=10 NUMBER_LIMIT=10 NUMBER_MIN_AGE=0 If you do not want to keep snapshots beyond a certain age, set NUMBER_LIMIT* to 0 and provide the age with NUMBER_MIN_AGE . The following example shows a configuration to only keep snapshots younger than ten days: NUMBER_CLEANUP=yes NUMBER_LIMIT_IMPORTANT=0 NUMBER_LIMIT=0 170 Cleaning up numbered snapshots SLES 15 SP6NUMBER_MIN_AGE=864000 10.7.2 Cleaning up timeline snapshots Cleaning up timeline snapshots is controlled by the following parameters of a Snapper config- uration. TIMELINE_CLEANUP Enables or disables clean-up of timeline snapshots. If enabled, snapshots are deleted when the total snapshot count exceeds a number specified with TIMELINE_LIMIT_* and an age specified with TIMELINE_MIN_AGE . Valid values: yes , no . The default value is "yes" . Example command to change or set: > sudo snapper -c CONFIG set-config "TIMELINE_CLEANUP=yes" TIMELINE_LIMIT_DAILY , TIMELINE_LIMIT_HOURLY , TIMELINE_LIMIT_MONTHLY , TIMELINE_LIMIT_WEEKLY , TIMELINE_LIMIT_YEARLY Number of snapshots to keep for hour, day, month, week and year. The default value for each entry is "10" , except for TIMELINE_LIMIT_WEEKLY , which is set to "0" by default. TIMELINE_MIN_AGE Defines the minimum age in seconds a snapshot must have before it can automatically be deleted. The default value is "1800" . EXAMPLE 10.1: EXAMPLE TIMELINE CONFIGURATION TIMELINE_CLEANUP="yes" TIMELINE_CREATE="yes" TIMELINE_LIMIT_DAILY="7" TIMELINE_LIMIT_HOURLY="24" TIMELINE_LIMIT_MONTHLY="12" TIMELINE_LIMIT_WEEKLY="4" TIMELINE_LIMIT_YEARLY="2" TIMELINE_MIN_AGE="1800" This example configuration enables hourly snapshots which are automatically cleaned up. TIMELINE_MIN_AGE and TIMELINE_LIMIT_* are always both evaluated. In this example, the minimum age of a snapshot before it can be deleted is set to 30 minutes (1800 seconds). 171 Cleaning up timeline snapshots SLES 15 SP6Since we create hourly snapshots, this ensures that only the latest snapshots are kept. If TIMELINE_LIMIT_DAILY is set to not zero, this means that the rst snapshot of the day is kept, too. SNAPSHOTS TO BE KEPT Hourly: the last 24 snapshots that have been made. Daily: the rst daily snapshot that has been made is kept from the last seven days. Monthly: the rst snapshot made on the last day of the month is kept for the last twelve months. Weekly: the rst snapshot made on the last day of the week is kept from the last four weeks. Yearly: the rst snapshot made on the last day of the year is kept for the last two years. 10.7.3 Cleaning up snapshot pairs that do not differ As explained in Section 10.1.2, “Types of snapshots”, whenever you run a YaST module or execute Zypper, a pre snapshot is created on start-up and a post snapshot is created when exiting. In case you have not made any changes there will be no difference between the pre and post snapshots. Such “empty” snapshot pairs can be automatically be deleted by setting the following parameters in a Snapper configuration: EMPTY_PRE_POST_CLEANUP If set to yes , pre and post snapshot pairs that do not differ will be deleted. The default value is "yes" . EMPTY_PRE_POST_MIN_AGE Defines the minimum age in seconds a pre and post snapshot pair that does not differ must have before it can automatically be deleted. The default value is "1800" . 172 Cleaning up snapshot pairs that do not differ SLES 15 SP610.7.4 Cleaning up manually created snapshots Snapper does not offer custom clean-up algorithms for manually created snapshots. However, you can assign the number or timeline clean-up algorithm to a manually created snapshot. If you do so, the snapshot will join the “clean-up queue” for the algorithm you specified. You can specify a clean-up algorithm when creating a snapshot, or by modifying an existing snapshot: snapper create --description "Test" --cleanup-algorithm number Creates a stand-alone snapshot (type single) for the default (root) configuration and assigns the number clean-up algorithm. snapper modify --cleanup-algorithm "timeline" 25 Modifies the snapshot with the number 25 and assigns the clean-up algorithm timeline . 10.7.5 Adding disk quota support In addition to the number and/or timeline clean-up algorithms described above, Snapper sup- ports quotas. You can define what percentage of the available space snapshots are allowed to occupy. This percentage value always applies to the Btrfs subvolume defined in the respective Snapper configuration. Btrfs quotas are applied to subvolumes, not to users. You may apply disk space quotas to users and groups (for example, with the quota command) in addition to using Btrfs quotas. If Snapper was enabled during the installation, quota support is automatically enabled. In case you manually enable Snapper at a later point in time, you can enable quota support by running snapper setup-quota . This requires a valid configuration (see Section 10.5, “Creating and mod- ifying Snapper configurations” for more information). Quota support is controlled by the following parameters of a Snapper configuration. QGROUP The Btrfs quota group used by Snapper. If not set, run snapper setup-quota . If already set, only change if you are familiar with man 8 btrfs-qgroup . This value is set with snapper setup-quota and should not be changed. SPACE_LIMIT Limit of space snapshots are allowed to use in fractions of 1 (100%). Valid values range from 0 to 1 (0.1 = 10%, 0.2 = 20%, ...). 173 Cleaning up manually created snapshots SLES 15 SP6The following limitations and guidelines apply: Quotas are only activated in addition to an existing number and/or timeline clean-up al- gorithm. If no clean-up algorithm is active, quota restrictions are not applied. With quota support enabled, Snapper will perform two clean-up runs if required. The rst run will apply the rules specified for number and timeline snapshots. Only if the quota is exceeded after this run, the quota-specific rules will be applied in a second run. Even if quota support is enabled, Snapper will always keep the number of snapshots specified with the NUMBER_LIMIT* and TIMELINE_LIMIT* values, even if the quota will be exceeded. It is therefore recommended to specify ranged values ( MIN-MAX ) for NUM- BER_LIMIT* and TIMELINE_LIMIT* to ensure the quota can be applied. If, for example, NUMBER_LIMIT=5-20 is set, Snapper will perform a rst clean-up run and reduce the number of regular numbered snapshots to 20. In case these 20 snapshots exceed the quota, Snapper will delete the oldest ones in a second run until the quota is met. A minimum of ve snapshots will always be kept, regardless of the amount of space they occupy. 10.8 Showing exclusive disk space used by snapshots Snapshots share data, for efficient use of storage space, so using ordinary commands like du and df will not measure used disk space accurately. When you want to free up disk space on Btrfs with quotas enabled, you need to know how much exclusive disk space is used by each snapshot, rather than shared space. Snapper 0.6 and up reports the used disk space for each snapshot in the Used Space column: # snapper --iso list # | Type | Pre # | Date | User | Used Space | Cleanup | Description | Userdata ----+--------+-------+---------------------+------+------------+--------- +-----------------------+-------------- 0 | single | | | root | | | current | 1* | single | | 2019-07-22 13:08:38 | root | 16.00 KiB | | first root filesystem | 2 | single | | 2019-07-22 14:21:05 | root | 14.23 MiB | number | after installation | important=yes 3 | pre | | 2019-07-22 14:26:03 | root | 144.00 KiB | number | zypp(zypper) | important=no 174 Showing exclusive disk space used by snapshots SLES 15 SP64 | post | 3 | 2019-07-22 14:26:04 | root | 112.00 KiB | number | | important=no 5 | pre | | 2019-07-23 08:19:36 | root | 128.00 KiB | number | zypp(zypper) | important=no 6 | post | 5 | 2019-07-23 08:19:43 | root | 80.00 KiB | number | | important=no 7 | pre | | 2019-07-23 08:20:50 | root | 256.00 KiB | number | yast sw_single | 8 | pre | | 2019-07-23 08:23:22 | root | 112.00 KiB | number | zypp(ruby.ruby2.5) | important=no 9 | post | 8 | 2019-07-23 08:23:35 | root | 64.00 KiB | number | | important=no 10 | post | 7 | 2019-07-23 08:24:05 | root | 16.00 KiB | number | | The btrfs command provides another view of space used by snapshots: # btrfs qgroup show -p / qgroupid rfer excl parent -------- ---- ---- ------ 0/5 16.00KiB 16.00KiB --- [...] 0/272 3.09GiB 14.23MiB 1/0 0/273 3.11GiB 144.00KiB 1/0 0/274 3.11GiB 112.00KiB 1/0 0/275 3.11GiB 128.00KiB 1/0 0/276 3.11GiB 80.00KiB 1/0 0/277 3.11GiB 256.00KiB 1/0 0/278 3.11GiB 112.00KiB 1/0 0/279 3.12GiB 64.00KiB 1/0 0/280 3.12GiB 16.00KiB 1/0 1/0 3.33GiB 222.95MiB --- The qgroupid column displays the identification number for each subvolume, assigning a qgroup level/ID combination. The rfer column displays the total amount of data referred to in the subvolume. The excl column displays the exclusive data in each subvolume. The parent column shows the parent qgroup of the subvolumes. The final item, 1/0 , shows the totals for the parent qgroup. In the above example, 222.95 MiB will be freed if all subvolumes are removed. Run the following command to see which snapshots are associated with each subvolume: # btrfs subvolume list -st / ID gen top level path 175 Showing exclusive disk space used by snapshots SLES 15 SP6-- --- --------- ---- 267 298 266 @/.snapshots/1/snapshot 272 159 266 @/.snapshots/2/snapshot 273 170 266 @/.snapshots/3/snapshot 274 171 266 @/.snapshots/4/snapshot 275 287 266 @/.snapshots/5/snapshot 276 288 266 @/.snapshots/6/snapshot 277 292 266 @/.snapshots/7/snapshot 278 296 266 @/.snapshots/8/snapshot 279 297 266 @/.snapshots/9/snapshot 280 298 266 @/.snapshots/10/snapshot Doing an upgrade from one service pack to another results in snapshots occupying a lot of disk space on the system subvolumes. Manually deleting these snapshots after they are no longer needed is recommended. See Section 10.6.4, “Deleting snapshots” for details. 10.9 Frequently asked questions Q: Why does Snapper never show changes in /var/log , /tmp and other directories? A: For certain directories, we decided to exclude them from snapshots. See Section 10.1.3, “Directories that are excluded from snapshots” for a list and reasons. To exclude a path from snapshots we create a subvolume for that path. Q: Can I boot a snapshot from the boot loader? A: Yes—refer to Section 10.3, “System rollback by booting from snapshots” for details. Q: Can a snapshot be protected from deletion? A: Currently Snapper does not offer means to prevent a snapshot from being deleted man- ually. However, you can prevent snapshots from being automatically deleted by clean- up algorithms. Manually created snapshots (see Section 10.6.2, “Creating snapshots”) have no clean-up algorithm assigned unless you specify one with --cleanup-algorithm . Au- tomatically created snapshots always either have the number or timeline algorithm as- signed. To remove such an assignment from one or more snapshots, proceed as follows: 1. List all available snapshots: > sudo snapper list -a 2. Memorize the number of the snapshots you want to prevent from being deleted. 176 Frequently asked questions SLES 15 SP63. Run the following command and replace the number placeholders with the numbers you memorized: > sudo snapper modify --cleanup-algorithm "" #1 #2 #n 4. Check the result by running snapper list -a again. The entry in the column Cleanup should now be empty for the snapshots you modified. Q: Where can I get more information on Snapper? A: See the Snapper home page at http://snapper.io/ . 177 Frequently asked questions SLES 15 SP611 Live kernel patching with KLP This document describes the basic principles of the Kernel Live Patching (KLP) tech- nology, and provides usage guidelines for the SLE Live Patching service. KLP makes it possible to apply the latest security updates to Linux kernels without rebooting. This maximizes system uptime and availability, which is especially important for mission-critical systems. The information provided in this document relates to the AMD64/Intel 64, POWER, and IBM Z architectures. 11.1 Advantages of Kernel Live Patching KLP offers several benefits. Keeping a large number of servers automatically up to date is essential for organizations obtaining or maintaining certain compliance certifications. KLP can help achieve compli- ance, while reducing the need for costly maintenance windows. Companies that work with service-level agreement contracts must guarantee a specific level of their system accessibility and uptime. Live patching makes it possible to patch systems without incurring downtime. Since KLP is part of the standard system update mechanism, there is no need for specialized training or introduction of complicated maintenance routines. 11.2 Kernel Live Patching overview Kernel live patches are delivered as packages with modified code that are separate from the main kernel package. The live patches are cumulative, so the latest patch contains all fixes from the previous ones for the kernel package. Each kernel live package is tied to the exact kernel revision for which it is issued. The live patch package version number increases with every addition of fixes. 178 Advantages of Kernel Live Patching SLES 15 SP6Note: Live patches and the running kernel To determine the kernel patching status, use the klp -v patches command. The uname command''s output does not change for patched kernels. Important: Live patches compared to kernel updates Live patches contain only critical fixes, and they do not replace regular kernel updates that require a reboot. Consider live patches as temporary measures that protect the kernel until a proper kernel update and a reboot are performed. The diagram below illustrates the overall relationship between live patches and kernel updates. The list of CVEs and defect reports addressed by the currently active live patch can be viewed using the klp -v patches command. 179 Kernel Live Patching overview SLES 15 SP6It is possible to have multiple versions of the kernel package installed along with their live patches. These packages do not conflict. You can install updated kernel packages along with live patches for the running kernel. In this case, you may be prompted to reboot the system. Users with SLE Live Patching subscriptions are eligible for technical support as long as there are live patch updates for the running kernel (see Section 11.5.1, “Checking expiration date of the live patch”). With KLP activated, every kernel update comes with a live patch package. This live patch does not contain any fixes and serves as a seed for future live patches for the corresponding kernel. These empty seed patches are called initial patches . 11.2.1 Kernel Live Patching scope The scope of SLE Live Patching includes fixes for SUSE Common Vulnerability Scoring System (CVSS; SUSE CVSS is based on the CVSS v3.1 system) level 7+ vulnerabilities and bug fixes related to system stability or data corruption. However, it may not be technically feasible to create live patches for all fixes that fall under the specified categories. SUSE therefore reserves the right to skip fixes in situations where creating a kernel live patch is not possible for technical reasons. Currently, over 95% of qualifying fixes are released as live patches. For more informa- tion on CVSS (the base for the SUSE CVSS rating), see Common Vulnerability Scoring System SIG (https://www.first.org/cvss/) . 11.2.2 Kernel Live Patching limitations KLP involves replacing functions and gracefully handling replacement of interdependent func- tion sets. This is done by redirecting calls to old code to updated code in a different memory location. Changes in data structures make the situation more complicated, as the data remain in place and cannot be extended or reinterpreted. While there are techniques that allow indirect alteration of data structures, certain fixes cannot be converted to live patches. In this situation, a system restart is the only way to apply the fixes. 11.3 Activating Kernel Live Patching using YaST To activate KLP on your system, you need to have active SLES and SLE Live Patching subscrip- tions. Visit SUSE Customer Center (https://scc.suse.com/) to check the status of your subscrip- tions and obtain a registration code for the SLE Live Patching subscription. 180 Kernel Live Patching scope SLES 15 SP6To activate Kernel Live Patching on your system, follow these steps: 1. Run the yast2 registration command and click Select Extensions. 2. Select SUSE Linux Enterprise Live Patching 15 in the list of available extensions and click Next. 3. Confirm the license terms and click Next. 4. Enter your SLE Live Patching registration code and click Next. 5. Check the Installation Summary and selected Patterns. The patterns Live Patching and SLE Live Patching Lifecycle Data should be automatically selected for installation along with additional packages to satisfy dependencies. 6. Click Accept to complete the installation. This installs the base Kernel Live Patching com- ponents on your system, the initial live patch, and the required dependencies. 11.4 Activating Kernel Live Patching from the command line To activate Kernel Live Patching, you need to have active SLES and SLES Live Patching sub- scriptions. Visit SUSE Customer Center (https://scc.suse.com/) to check the status of your sub- scriptions and obtain a registration code for the SLES Live Patching subscription. 1. Run sudo SUSEConnect --list-extensions . Note the exact activation command for SLES Live Patching. Example command output (abbreviated): $ SUSEConnect --list-extensions ... SUSE Linux Enterprise Live Patching 15 SP6 x86_64 Activate with: SUSEConnect -p sle-module-live-patching/15.6/x86_64 \ -r ADDITIONAL REGCODE 2. Activate SLES Live Patching using the obtained command followed by -r LIVE_PATCHING_REGISTRATION_CODE , for example: SUSEConnect -p sle-module-live-patching/15.6/x86_64 \ -r LIVE_PATCHING_REGISTRATION_CODE 3. Install the required packages and dependencies using the command zypper install - t pattern lp_sles 181 Activating Kernel Live Patching from the command line SLES 15 SP6At this point, the system has already been live-patched. Here is how the process works behind the scenes: when the package installation system detects that there is an installed kernel that can be live-patched, and that there is a live patch for it in the software channel, the system selects the live patch for installation. The kernel then receives the live patch fixes as part of the package installation. The kernel gets live-patched even before the product installation is complete. 11.5 Performing Kernel Live Patching Kernel live patches are installed as part of regular system updates. However, there are several things you should be aware of. The kernel is live-patched if a kernel-livepatch-* package has been installed for the running kernel. You can use the command zypper se --details kernel-livepatch- * to check what kernel live patch packages are installed on your system. When the kernel-default package is installed, the update manager prompts you to reboot the system. To prevent this message from appearing, you can filter out kernel updates from the patching operation. This can be done by adding package locks with Zypper. SUSE Manager also makes it possible to filter channel contents (see Live Patch- ing with SUSE Manager (https://documentation.suse.com/suma/4.3/en/suse-manager/admin- istration/live-patching.html) ). You can check patching status using the klp status command. To examine installed patches, run the klp -v patches command. Keep in mind that while there may be multiple kernel packages installed on the system, only one of them is running at any given time. Similarly, there may be multiple live patch packages installed, but only one live patch is loaded into the kernel. The active live patch is included in the initrd . This means that in case of an unexpected reboot, the system comes up with the live patch fixes applied, so there is no need to perform patching again. 182 Performing Kernel Live Patching SLES 15 SP611.5.1 Checking expiration date of the live patch Make sure that the lifecycle-data-sle-module-live-patching is installed, then run the zypper lifecycle command. You should see expiration dates for live patches in the Package end of support if different from product section of the output. Every live patch receives updates for one year from the release of the underlying kernel package. The Maintained kernels, patch updates and lifecycle (https://www.suse.com/products/live-patch- ing/current-patches/) page allows you to check expiration dates based on the running kernel version without installing the product extension. 11.6 Troubleshooting Kernel Live Patching issues 11.6.1 Manual patch downgrade If you nd the latest live patch problematic, you can downgrade the currently installed live patch back to its previous version. We recommend performing patch downgrade before the system starts exhibiting issues. Keep in mind that a system with kernel warnings or kernel error traces in the system log may not be suitable for the patch downgrade procedure. If you are unsure whether the system meets the requirements for a patch downgrade, contact SUSE Technical Support for help. PROCEDURE 11.1: MANUAL PATCH DOWNGRADE 1. Identify the running live patch using the klp -v patches command. You can see the currently running patch on the line starting with RPM: . For example: RPM: kernel-livepatch-6_4_0-150600_9-default-1-150600.2.36.x86_64 The 6_4_0-150600_9-default in the example above denotes the exact running kernel version. 2. Use the command zypper search -s kernel-livepatch-RUNNING_KERNEL_VERSION- default to search for previous versions of the patch. The command returns a list of avail- able package versions. Keep in mind that for every new live patch package release, the version number increases by one. Make sure that you choose the version number one re- lease lower than the current one. 183 Checking expiration date of the live patch SLES 15 SP63. Install the desired version with the command zypper in --oldpackage ker- nel-livepatch-RUNNING_KERNEL_VERSION-default=DESIRED_VERSION . 184 Manual patch downgrade SLES 15 SP612 User space live patching This chapter describes the basic principles and usage of user space live patching. 12.1 About user space live patching User space live patching (ULP) refers to the process of applying patches to the libraries used by a running process without interrupting them. Every time a security x is available as a live patch, customer services will be secured after applying the live patch without restarting the processes. Live patching operations are performed using the ulp tool that is part of libpulp . libpulp is a framework that consists of the libpulp.so library and the ulp binary that makes libraries live patchable and applies live patches. Tip You can run the ulp command either as a normal user or a privileged user via the sudo mechanism. The difference is that running ulp via sudo lets you view information of processes or patch processes that are running by root . Tip: Install libpulp-load-default Since SUSE Linux Enterprise Server SP6, the libpulp-load-default is available that automates the requirements and manual steps mentioned in Section 12.1.1, “Prerequisites” and Section 12.1.3, “Using libpulp”. If you install the package, you can skip those sections. 12.1.1 Prerequisites For ULP to work, two requirements must be met. Install the ULP on your system by running: > sudo zypper in libpulp0 libpulp-tools Applications with desired live patch support must be launched preloading the libpulp.so.0 library. See Section 12.1.3, “Using libpulp” for more details. 185 About user space live patching SLES 15 SP612.1.2 Supported libraries Currently, only glibc and openssl ( openssl1_1 ) are supported. Additional packages will be available after they are prepared for live patching. To receive glibc and openssl live patches, install both glibc-livepatches and openssl-livepatches packages: > zypper install glibc-livepatches openssl-livepatches 12.1.3 Using libpulp To enable live patching on an application, you need to preload the libpulp.so.0 library when starting the application: > LD_PRELOAD=/usr/lib64/libpulp.so.0 APPLICATION_CMD 12.1.3.1 Checking if a library is live patchable To check whether a library is live patchable, use the following command: > ulp livepatchable PATH_TO_LIBRARY 12.1.3.2 Checking if a .so file is a live patch container A shared object ( .so ) is a live patch container if it contains the ULP patch description embedded into it. You can verify it with the following command: > readelf -S SHARED_OBJECT | grep .ulp If the output shows that there are both .ulp and .ulp.rev sections in the shared object, then it is a live patch container. 12.1.3.3 Applying live patches Live patches are applied using the ulp trigger command, for example: > ulp trigger -p PID LIVEPATCH.so 186 Supported libraries SLES 15 SP6Replace PID with the process ID of the running process that uses the library to be patched and LIVEPATCH.so with the actual live patch le. The command returns one of the following status messages: SUCCESS The live patching operation was successful. SKIPPED The patch was skipped because it was not designed for any library that is loaded in the process. ERROR An error occurred, and you can retrieve more information by inspecting the libpulp in- ternal message buer. See Section 12.1.3.6, “View internal message queue” for more informa- tion. It is also possible to apply multiple live patches by using wildcards, for example: > ulp trigger ''*.so'' The command tries to apply every patch in the current folder to every process that have the libpulp library loaded. If the patch is not suitable for the process, it is automatically skipped. In the end, the tool shows how many patches it successfully applied to how many processes. 12.1.3.4 Reverting live patches You can use the ulp trigger command to revert live patches. There are two ways to revert live patches. You can revert a live patch by using the --revert switch and passing the live patch container: > ulp trigger -p PID --revert LIVEPATCH.so Alternatively, it is possible to remove all patches associated with a particular library, for exam- ple: > ulp trigger -p PID --revert-all=LIBRARY In the example, LIBRARY refers to the actual library, such as libcrypto.so.1.1 . 187 Using libpulp SLES 15 SP6The latter approach can be useful when the source code of the original live patch is not available. Or you want to remove a specific old patch and apply a new one while the target application is still running a secure code, for example: > ulp trigger -p PID --revert-all=libcrypto.so.1.1 new_livepatch2.so 12.1.3.5 View applied patches It is possible to verify which applications have live patches applied by running: > ulp patches The output shows which libraries are live patchable and patches loaded in programs, as well which bugs the patch addresses: PID: 10636, name: test Livepatchable libraries: in /lib64/libc.so.6: livepatch: libc_livepatch1.so bug labels: jsc#SLE-0000 in /usr/lib64/libpulp.so.0: It is also possible to see which functions are patched by the live patch: > ulp dump LIVEPATCH.so 12.1.3.6 View internal message queue Log messages from libpulp.so are stored in a buer inside the library and are not displayed unless requested by the user. To show these messages, run: > ulp messages -p PID 12.2 More information Further information about libpulp is available in the project''s Git repository (https:// github.com/SUSE/libpulp) . 188 More information SLES 15 SP613 Transactional updates Transactional updates are available in SUSE Linux Enterprise Server as a technolo- gy preview for updating SLES when the root le system is read-only. Transaction- al updates are atomic—all updates are applied only if all succeed—and support roll- backs. It does not affect a running system as no changes are activated until after the system is rebooted. As reboots are disruptive, the administrator must decide if a re- boot is more expensive than disturbing running services. If reboots are too expen- sive then do not use transactional updates. Transactional updates are run daily by the transactional-update script. The script checks for available updates. If there are any updates, it creates a new snap- shot of the root le system in the background, and then fetches updates from the re- lease channels. After the new snapshot is updated, it is marked as active and will be the new default root le system after the next reboot of the system. When trans- actional-update is set to run automatically (which is the default behavior) it also reboots the system. Both the time that the update runs and the reboot maintenance window are configurable. Only packages that are part of the snapshot of the root le system can be updated. If packages contain les that are not part of the snapshot, the update could fail or break the system. RPMs that require a license to be accepted cannot be updated. 13.1 Limitations Currently, there are certain limitations in the functionality of transactional updates. The follow- ing packages do not work with the transactional-update command: The nginx default index.html page may not be available tomcat-webapps and tomcat-admin-webapps phpMyAdmin sca-appliance-* 189 Limitations SLES 15 SP6mpi-selector emacs works except for Emacs games bind and bind-chrootenv docbook* sblim-sfcb* texlive* iso_ent openjade opensp pcp plymouth postgresql-server-10 pulseaudio-gdm-hooks smartmontools The updater component of the system installer does not work with a read-only le system as it has no support for transactional updates. Further considerations: It is a good idea to minimize the time between updating the system and rebooting the machine. Only one update can be applied at a time. Be sure to reboot after an update, and before the next update is applied. update-alternatives should not be run after a transactional update until the machine has been rebooted. Do not create new system users or system groups after a transactional update until after reboot. It is acceptable to create normal users and groups (UID > 1000, GID > 1000). YaST is not yet aware of transactional updates. If a YaST module needs to install additional packages, this does not work. Normal system operations that modify configuration les in /etc work. 190 Limitations SLES 15 SP6For php7-fastcgi , you must manually create a symbolic link, /srv/www/cgi-bin/php , that points to /usr/bin/php-cgi . ntp is part of the Legacy Module for migration from older SLES versions. It is not support- ed on a new SUSE Linux Enterprise Server installation, and has been replaced by chrony . If you continue to use ntp , a fresh installation is required to work correctly with trans- actional updates. sblim-sfcb : the whole sblim ecosystem is incompatible with transactional update. btrfs-defrag from the btrfsmaintenance package does not work with a read-only root le system. For btrfs-balance , the variable BTRFS_BALANCE_MOUNTPOINTS in /etc/syscon- fig/btrfsmaintenance must be changed from / to /.snapshots . For btrfs-scrub , the variable BTRFS_SCRUB_MOUNTPOINTS in /etc/sysconfig/btrf- smaintenance must be changed from / to /.snapshots . 13.2 Enabling transactional-update You must enable the Transactional Server Module during system installation, and then select the Transactional Server System Role. Installing any package from the Transactional Server Module later in a running system is NOT supported and may break the system. Changing the subvolume layout of the root partition, or putting subdirectories or subvolumes of the root partition on their own partitions (except /home , /var , /srv , and /opt ) is not supported, and may break the system. 13.3 Managing automatic updates Automatic updates are controlled by a systemd.timer that runs once per day. This applies all updates, and informs rebootmgrd that the machine should be rebooted. You may adjust the time when the update runs, see systemd.timer(5). To adjust the maintenance window, which is when rebootmgrd reboots the system, see rebootmgrd(8). You can disable automatic transactional updates with this command: # systemctl --now disable transactional-update.timer 191 Enabling transactional-update SLES 15 SP613.4 The transactional-update command The transactional-update command enables atomic installation or removal of updates. Up- dates are applied only if they all can be successfully installed. transactional-update creates a snapshot of your system before the update is applied, and you can restore this snapshot. All changes become active only after reboot. --continue The --continue option is for making multiple changes to an existing snapshot without rebooting. The default transactional-update behavior is to create a new snapshot from the cur- rent root le system. If you forget something, such as installing a new package, you have to reboot to apply your previous changes, run transactional-update again to install the forgotten package, and reboot again. You cannot run the transactional-update command multiple times without rebooting to add more changes to the snapshot, because that creates separate independent snapshots that do not include changes from the previous snapshots. Use the --continue option to make as many changes as you want without rebooting. A separate snapshot is made each time, and each snapshot contains all the changes you made in the previous snapshots, plus your new changes. Repeat this process as many times as you want, and when the final snapshot includes everything you want reboot the system, and your final snapshot becomes the new root le system. Another useful feature of the --continue option is you may select any existing snapshot as the base for your new snapshot. The following example demonstrates running trans- actional-update to install a new package in a snapshot based on snapshot 13, and then running it again to install another package: # transactional-update pkg install package_1 # transactional-update --continue 13 pkg install package_2 The --continue [num] option calls snapper create --from , see Section 10.6.2, “Creating snapshots”. cleanup If the current root le system is identical to the active root le system (after a reboot, before transactional-update creates a new snapshot with updates), all old snapshots without a cleanup algorithm get a cleanup algorithm set. This ensures that old snapshots 192 The transactional-update command SLES 15 SP6are deleted by Snapper. (See the section about cleanup algorithms in snapper(8).) This also removes all unreferenced (and thus unused) /etc overlay directories in /var/lib/ overlay : # transactional-update cleanup pkg in/install Installs individual packages from the available channels using the zypper install com- mand. This command can also be used to install Program Temporary Fix (PTF) RPM les. # transactional-update pkg install package_name or # transactional-update pkg install rpm1 rpm2 pkg rm/remove Removes individual packages from the active snapshot using the zypper remove com- mand. This command can also be used to remove PTF RPM les. # transactional-update pkg remove package_name pkg up/update Updates individual packages from the active snapshot using the zypper update com- mand. Only packages that are part of the snapshot of the base le system can be updated. # transactional-update pkg update package_name up/update If there are new updates available, a new snapshot is created and zypper up/update updates the snapshot. # transactional-update up dup If there are new updates available, a new snapshot is created and zypper dup –no- allow-vendor-change updates the snapshot. The snapshot is activated afterwards and becomes the new root le system after reboot. # transactional-update dup patch If there are new updates available, a new snapshot is created and zypper patch updates the snapshot. 193 The transactional-update command SLES 15 SP6# transactional-update patch rollback This sets the default subvolume. On systems with a read-write le system snapper roll- back is called. On a read-only le system and without any argument, the current system is set to a new default root le system. If you specify a number, that snapshot is used as the default root le system. On a read-only le system, it does not create any additional snapshots. # transactional-update rollback snapshot_number grub.cfg This creates a new GRUB2 configuration. Sometimes it is necessary to adjust the boot con- figuration, for example, adding additional kernel parameters. Edit /etc/default/grub , run transactional-update grub.cfg , and then reboot to activate the change. You must immediately reboot, or the new GRUB2 configuration gets overwritten with the default by the next transactional-update run. # transactional-update grub.cfg reboot This parameter triggers a reboot after the action is completed. # transactional-update dup reboot --help This prints a help screen with options and subcommands. # transactional-update --help 13.5 Troubleshooting If the upgrade fails, run supportconfig to collect log data. Provide the resulting les, including /var/log/transactional-update.log to SUSE Support. 194 Troubleshooting SLES 15 SP614 Remote graphical sessions with VNC Virtual Network Computing (VNC) enables you to access a remote computer via a graphical desktop, and run remote graphical applications. VNC is platform-inde- pendent and accesses the remote machine from any operating system. This chapter describes how to connect to a VNC server with the desktop clients vncviewer and Remmina, and how to operate a VNC server. SUSE Linux Enterprise Server supports two different kinds of VNC sessions: one- time sessions that “live” While the VNC connection from the client is kept up, and persistent sessions that “live” until they are explicitly terminated. A VNC server can offer both kinds of sessions simultaneously on different ports, but an open session cannot be converted from one type to the other. 14.1 The vncviewer client To connect to a VNC service provided by a server, a client is needed. The default in SUSE Linux Enterprise Server is vncviewer , provided by the tigervnc package. 14.1.1 Connecting using the vncviewer CLI To start your VNC viewer and initiate a session with the server, use the command: > vncviewer jupiter.example.com:1 Instead of the VNC display number you can also specify the port number with two colons: > vncviewer jupiter.example.com::5901 Note: Display and port number The actual display or port number you specify in the VNC client must be the same as the display or port number selected when configuring a VNC server on the target machine. See Section 14.4, “Configuring persistent VNC server sessions” for further info. 195 The vncviewer client SLES 15 SP614.1.2 Connecting using the vncviewer GUI When running vncviewer without specifying --listen or a host to connect to, it shows a win- dow asking for connection details. Enter the host into the VNC server eld like in Section 14.1.1, “Connecting using the vncviewer CLI” and click Connect. FIGURE 14.1: VNCVIEWER 14.1.3 Notification of unencrypted connections The VNC protocol supports different kinds of encrypted connections, not to be confused with password authentication. If a connection does not use TLS, the text “(Connection not encrypt- ed!)” can be seen in the window title of the VNC viewer. 14.2 Remmina: the remote desktop client Remmina is a modern and feature-rich remote desktop client. It supports several access methods, for example, VNC, SSH, RDP and Spice. 14.2.1 Installation To use Remmina, verify whether the remmina package is installed on your system, and install it if not. Remember to install the VNC plug-in for Remmina as well: # zypper in remmina remmina-plugin-vnc 196 Connecting using the vncviewer GUI SLES 15 SP614.2.2 Main window Run Remmina by entering the remmina command. FIGURE 14.2: REMMINA''S MAIN WINDOW The main application window shows the list of stored remote sessions. Here you can add and save a new remote session, quick-start a new session without saving it, start a previously saved session, or set Remmina''s global preferences. 14.2.3 Adding remote sessions To add and save a new remote session, click in the top left of the main window. The Remote Desktop Preference window opens. 197 Main window SLES 15 SP6FIGURE 14.3: REMOTE DESKTOP PREFERENCE Complete the elds that specify your newly added remote session profile. The most important are: Name Name of the profile. It will be listed in the main window. Protocol The protocol to use when connecting to the remote session, for example, VNC. Server The IP or DNS address and display number of the remote server. User name, password Credentials to use for remote authentication. Leave empty for no authentication. Color depth, quality Select the best options according to your connection speed and quality. Select the Advanced tab to enter more specific settings. 198 Adding remote sessions SLES 15 SP6Tip: Disable encryption If the communication between the client and the remote server is not encrypted, activate Disable encryption, otherwise the connection fails. Select the SSH tab for advanced SSH tunneling and authentication options. Confirm with Save. Your new profile is now listed in the main window. 14.2.4 Starting remote sessions You can either start a previously saved session, or quick-start a remote session without saving the connection details. 14.2.4.1 Quick-starting remote sessions To start a remote session quickly without adding and saving connection details, use the drop- down box and text box at the top of the main window. FIGURE 14.4: QUICK-STARTING Select the communication protocol from the drop-down list, for example, “VNC”, then enter the VNC server DNS or IP address followed by a colon and a display number, and confirm with Enter . 14.2.4.2 Opening saved remote sessions To open a specific remote session, double-click it from the list of sessions. 14.2.4.3 Remote sessions window Remote sessions are opened in tabs of a separate window. Each tab hosts one session. The toolbar on the left of the window helps you manage the windows/sessions. For example, toggle full- screen mode, resize the window to match the display size of the session, send specific keystrokes to the session, take screenshots of the session, or set the image quality. 199 Starting remote sessions SLES 15 SP6FIGURE 14.5: REMMINA VIEWING REMOTE SESSION 14.2.5 Editing, copying, and deleting saved sessions To edit a saved remote session, right-click its name in Remmina''s main window and select Edit. Refer to Section 14.2.3, “Adding remote sessions” for the description of the relevant elds. To copy a saved remote session, right-click its name in Remmina''s main window and select Copy. In the Remote Desktop Preference window, change the name of the profile, optionally adjust relevant options, and confirm with Save. To Delete a saved remote session, right-click its name in Remmina''s main window and select Delete. Confirm with Yes in the next dialog. 14.2.6 Running remote sessions from the command line If you need to open a remote session from the command line or from a batch le without rst opening the main application window, use the following syntax: > remmina -c profile_name.remmina 200 Editing, copying, and deleting saved sessions SLES 15 SP6Remmina''s profile les are stored in the .local/share/remmina/ directory in your home di- rectory. To determine which profile le belongs to the session you want to open, run Remmina, click the session name in the main window, and read the path to the profile le in the window''s status line at the bottom. FIGURE 14.6: READING PATH TO THE PROFILE FILE While Remmina is not running, you can rename the profile le to a more reasonable le name, such as sle15.remmina . You can even copy the profile le to your custom directory and run it using the remmina -c command from there. 14.3 Configuring one-time sessions on the VNC server A one-time session is initiated by the remote client. It starts a graphical login screen on the server. This way you can choose the user which starts the session and, if supported by the login manager, the desktop environment. When you cancel the client connection to such a VNC session, all applications started within that session are terminated, too. One-time VNC sessions cannot be shared, but it is possible to have multiple sessions on a single host at the same time. PROCEDURE 14.1: ENABLING ONE-TIME VNC SESSIONS 1. Start YaST Network Services Remote Administration (VNC). 2. Check Allow Remote Administration Without Session Management. 3. Activate Enable access using a web browser if you plan to access the VNC session in a Web browser window. 201 Configuring one-time sessions on the VNC server SLES 15 SP64. If necessary, also check Open Port in Firewall (for example, when your network interface is configured to be in the External Zone). If you have more than one network interface, restrict opening the firewall ports to a specific interface via Firewall Details. 5. Confirm your settings with Next. 6. In case not all needed packages are available yet, you need to approve the installation of missing packages. Tip: Restart the display manager YaST makes changes to the display manager settings. You need to log out of your current graphical session and restart the display manager for the changes to take effect. FIGURE 14.7: REMOTE ADMINISTRATION 14.3.1 Available configurations The default configuration on SUSE Linux Enterprise Server serves sessions with a resolution of 1024x768 pixels at a color depth of 16-bit. The sessions are available on ports 5901 for “regular” VNC viewers (equivalent to VNC display 1 ) and on port 5801 for Web browsers. 202 Available configurations SLES 15 SP6Other configurations can be made available on different ports, see Section 14.3.3, “Configuring one- time VNC sessions”. VNC display numbers and X display numbers are independent in one-time sessions. A VNC dis- play number is manually assigned to every configuration that the server supports (:1 in the ex- ample above). Whenever a VNC session is initiated with one of the configurations, it automat- ically gets a free X display number. By default, both the VNC client and server try to communicate securely via a self-signed SSL certificate, which is generated after installation. You can either use the default one, or replace it with your own. When using the self-signed certificate, you need to confirm its signature before the rst connection—both in the VNC viewer and the Web browser. Tip Certain VNC clients refuse to establish a secure connection via the default self-signed certificate. For example, the Vinagre client verifies the certification against the GnuTLS global trust store and fails if the certificate is self-signed. In such a case, either use an encryption method other than x509 , or generate a properly signed certificate for the VNC server and import it to the client''s system trust store. 14.3.2 Initiating a one-time VNC session To connect to a one-time VNC session, a VNC viewer must be installed, see also Section 14.1, “The vncviewer client”. Alternatively use a JavaScript-capable Web browser to view the VNC session by entering the following URL: http://jupiter.example.com:5801 14.3.3 Configuring one-time VNC sessions You can skip this section, if you do not need or want to modify the default configuration. One-time VNC sessions are started via the systemd socket xvnc.socket . By default it offers six configuration blocks: three for VNC viewers ( vnc1 to vnc3 ), and three serving a JavaScript client ( vnchttpd1 to vnchttpd3 ). By default only vnc1 and vnchttpd1 are active. To activate the VNC server socket at boot time, run the following command: > sudo systemctl enable xvnc.socket 203 Initiating a one-time VNC session SLES 15 SP6To start the socket immediately, run: > sudo systemctl start xvnc.socket The Xvnc server can be configured via the server_args option. For a list of options, see Xvnc --help . When adding custom configurations, make sure they are not using ports that are already in use by other configurations, other services, or existing persistent VNC sessions on the same host. Activate configuration changes by entering the following command: > sudo systemctl reload xvnc.socket Important: Firewall and VNC ports When activating Remote Administration as described in Procedure 14.1, “Enabling one-time VNC sessions”, the ports 5801 and 5901 are opened in the firewall. If the network inter- face serving the VNC sessions is protected by a firewall, you need to manually open the respective ports when activating additional ports for VNC sessions. See Book “Security and Hardening Guide”, Chapter 23 “Masquerading and firewalls” for instructions. 14.4 Configuring persistent VNC server sessions A persistent session can be accessed from multiple clients simultaneously. This is ideal for demonstration purposes where one client has full access and all other clients have view-only access. Another use case are training sessions where the trainer may need access to the trainee''s desktop. Tip: Connecting to a persistent VNC session To connect to a persistent VNC session, a VNC viewer must be installed. Refer to Sec- tion 14.1, “The vncviewer client” for more details. Alternatively, use a JavaScript-capa- ble Web browser to view the VNC session by entering the following URL: http:// jupiter.example.com:5801 . 204 Configuring persistent VNC server sessions SLES 15 SP614.4.1 VNC session initiated using vncmanager PROCEDURE 14.2: ENABLING PERSISTENT VNC SESSIONS 1. Start YaST Network Services Remote Administration (VNC). 2. Activate Allow Remote Administration With Session Management. 3. Activate Enable access using a web browser if you plan to access the VNC session in a Web browser window. 4. If necessary, also check Open Port in Firewall (for example, when your network interface is configured to be in the External Zone). If you have more than one network interface, restrict opening the firewall ports to a specific interface via Firewall Details. 5. Confirm your settings with Next. 6. In case not all needed packages are available yet, you need to approve the installation of missing packages. Tip: Restart the display manager YaST makes changes to the display manager settings. You need to log out of your current graphical session and restart the display manager for the changes to take effect. 14.4.1.1 Configuring persistent VNC sessions After you enable the VNC session management as described in Procedure 14.2, “Enabling persistent VNC sessions”, you can normally connect to the remote session with your favorite VNC viewer, such as vncviewer or Remmina. After you log in, the “VNC” icon appears in the system tray of your desktop environment. Click the icon to open the VNC Session window. If your desktop environment does not support icons in the system tray, run vncmanager-controller manually. 205 VNC session initiated using vncmanager SLES 15 SP6FIGURE 14.8: VNC SESSION SETTINGS There are several settings that influence the VNC session''s behavior: Non-persistent, private This is equivalent to a one-time session. It is not visible to others and is terminated after you disconnect from it. Refer to Section 14.3, “Configuring one-time sessions on the VNC server” for more information. Persistent, visible The session is visible to other users and keeps running even after you disconnect from it. Session name Specify the name of the persistent session so that it is easily identified when reconnecting. No password required The session is freely accessible without having to log in under user credentials. Require user login You need to log in with a valid user name and password to access the session. Lists the valid user names in the Allowed users text box. 206 VNC session initiated using vncmanager SLES 15 SP6Allow one client at a time Prevents multiple users from joining the session at the same time. Allow multiple clients at a time Allows multiple users to join the persistent session at the same time. Useful for remote presentations or training sessions. Confirm with OK. 14.4.1.2 Joining persistent VNC sessions After you set up a persistent VNC session as described in Section 14.4.1.1, “Configuring persistent VNC sessions”, you can join it with your VNC viewer. After your VNC client connects to the server, you are prompted to choose whether you want to create a new session or join the existing one: FIGURE 14.9: JOINING A PERSISTENT VNC SESSION After you click the name of the existing session, you may be asked for login credentials, depend- ing on the persistent session settings. 207 VNC session initiated using vncmanager SLES 15 SP614.5 Configuring encryption on the VNC server If the VNC server is set up properly, all communication between the VNC server and the client is encrypted. The authentication happens at the beginning of the session; the actual data transfer only begins afterward. Whether for a one-time or a persistent VNC session, security options are configured via the - securitytypes parameter of the /usr/bin/Xvnc command located on the server_args line. The -securitytypes parameter selects both authentication method and encryption. It has the following options: AUTHENTICATIONS None, TLSNone, x509None No authentication. VncAuth, TLSVnc, x509Vnc Authentication using custom password. Plain, TLSPlain, x509Plain Authentication using PAM to verify user''s password. ENCRYPTIONS None, vncAuth, plain No encryption. TLSNone, TLSVnc, TLSPlain Anonymous TLS encryption. Everything is encrypted, but there is no verification of the remote host. So you are protected against passive attackers, but not against man-in-the- middle attackers. X509None, x509Vnc, x509Plain TLS encryption with certificate. If you use a self-signed certificate, you will be asked to verify it on the rst connection. On subsequent connections you will be warned only if the certificate changed. So you are protected against everything except man-in-the-middle on the rst connection (similar to typical SSH usage). If you use a certificate signed by a certificate authority matching the machine name, then you get full security (similar to typical HTTPS usage). 208 Configuring encryption on the VNC server SLES 15 SP6Tip Certain VNC clients refuse to establish a secure connection via the default self- signed certificate. For example, the Vinagre client verifies the certification against the GnuTLS global trust store and fails if the certificate is self-signed. In such a case, either use an encryption method other than x509 , or generate a properly signed certificate for the VNC server and import it to the client''s system trust store. Tip: Path to certificate and key With X509 based encryption, you need to specify the path to the X509 certificate and the key with -X509Cert and -X509Key options. If you select multiple security types separated by comma, the rst one supported and allowed by both client and server is used. That way, you can configure opportunistic encryption on the server. This is useful if you need to support VNC clients that do not support encryption. On the client, you can also specify the allowed security types to prevent a downgrade attack if you are connecting to a server which you know has encryption enabled (although our vncviewer warns you with the Connection not encrypted! message in that case). 14.6 Compatibility with Wayland The Remote Administration (VNC) feature relies on X11 and may result in an empty screen if Wayland is enabled. The display manager must be configured to use X11 instead of Wayland. For gdm , edit /etc/gdm/custom.conf . In the [daemon] section, add WaylandEnable=false to the configuration le. When logging in, the user must choose an X11-compatible session as well. If you wish to remove the Wayland option for GNOME, you can remove and lock the gnome- session-wayland package. 209 Compatibility with Wayland SLES 15 SP615 File copying with RSync Today, a typical user has several computers: home and workplace machines, a lap- top, a smartphone or a tablet. This makes the task of keeping les and documents in synchronization across multiple devices all the more important. Warning: Risk of data loss Before you start using a synchronization tool, you should familiarize yourself with its features and functionality. Make sure to back up your important les. 15.1 Conceptual overview For synchronizing a large amount of data over a slow network connection, Rsync offers a reliable method of transmitting only changes within les. This applies not only to text les but also binary les. To detect the differences between les, Rsync subdivides the les into blocks and computes check sums over them. Detecting changes requires certain computing power. So make sure that machines on both ends have enough resources, including RAM. Rsync can be particularly useful when large amounts of data containing only minor changes need to be transmitted regularly. This is often the case when working with backups. Rsync can also be useful for mirroring staging servers that store complete directory trees of Web servers to a Web server in a DMZ. Despite its name, Rsync is not a synchronization tool. Rsync is a tool that copies data only in one direction at a time. It does not and cannot do the reverse. If you need a bidirectional tool which can synchronize both source and destination, use Csync. 15.2 Basic syntax Rsync is a command-line tool that has the following basic syntax: rsync [OPTION] SOURCE [SOURCE]... DEST 210 Conceptual overview SLES 15 SP6You can use Rsync on any local or remote machine, provided you have access and write per- missions. It is possible to have multiple SOURCE entries. The SOURCE and DEST placeholders can be paths, URLs or both. Below are the most common Rsync options: -v Outputs more verbose text -a Archive mode; copies les recursively and preserves time stamps, user/group ownership, le permissions, and symbolic links -z Compresses the transmitted data Note: Trailing slashes count When working with Rsync, you should pay particular attention to trailing slashes. A trail- ing slash after the directory denotes the content of the directory. No trailing slash denotes the directory itself. 15.3 Copying files and directories locally The following description assumes that the current user has write permissions to the directory /var/backup . To copy a single le from one directory on your machine to another path, use the following command: > rsync -avz backup.tar.xz /var/backup/ The le backup.tar.xz is copied to /var/backup/ ; the absolute path is /var/backup/back- up.tar.xz . Do not forget to add the trailing slash after the /var/backup/ directory. If you do not insert the slash, the le backup.tar.xz is copied to /var/backup (le) not inside the directory / var/backup/ ! Copying a directory is similar to copying a single le. The following example copies the directory tux/ and its content into the directory /var/backup/ : > rsync -avz tux /var/backup/ 211 Copying files and directories locally SLES 15 SP6Find the copy in the absolute path /var/backup/tux/ . 15.4 Copying files and directories remotely The Rsync tool is required on both machines. To copy les from or to remote directories requires an IP address or a domain name. A user name is optional if your current user names on the local and remote machine are the same. To copy the le file.tar.xz from your local host to the remote host 192.168.1.1 with same users (being local and remote), use the following command: > rsync -avz file.tar.xz tux@192.168.1.1: Depending on what you prefer, these commands are also possible and equivalent: > rsync -avz file.tar.xz 192.168.1.1:~ > rsync -avz file.tar.xz 192.168.1.1:/home/tux In all cases with standard configuration, you are prompted to enter your passphrase of the remote user. This command copies file.tar.xz to the home directory of user tux (normally /home/tux ). Copying a directory remotely is similar to copying a directory locally. The following example copies the directory tux/ and its content into the remote directory /var/backup/ on the 192.168.1.1 host: > rsync -avz tux 192.168.1.1:/var/backup/ Assuming you have write permissions on the host 192.168.1.1 , you can nd the copy in the absolute path /var/backup/tux . 15.5 Configuring and using an rsync server Rsync can run as a daemon ( rsyncd ) listening on default port 873 for incoming connections. This daemon can receive “copying targets”. 212 Copying files and directories remotely SLES 15 SP6The following description explains how to create an Rsync server on a jupiter host with a backup target. This target can be used to store your backups. To create an Rsync server, do the following: PROCEDURE 15.1: SETTING UP AN RSYNC SERVER 1. On jupiter, create a directory to store all your backup les. In this example, we use / var/backup : # mkdir /var/backup 2. Specify ownership. In this case, the directory is owned by user tux in group users : # chown tux.users /var/backup 3. Configure the rsyncd daemon. We separate the configuration le into a main le and certain “modules” which hold your backup target. This makes it easier to add additional targets later. Global values can be stored in /etc/rsyncd.d/*.inc les, whereas your modules are placed in /etc/ rsyncd.d/*.conf les: a. Create a directory /etc/rsyncd.d/ : # mkdir /etc/rsyncd.d/ b. In the main configuration le /etc/rsyncd.conf , add the following lines: # rsyncd.conf main configuration file log file = /var/log/rsync.log pid file = /var/lock/rsync.lock &merge /etc/rsyncd.d 1 &include /etc/rsyncd.d 2 1 Merges global values from /etc/rsyncd.d/*.inc les into the main configu- ration le. 2 Loads any modules (or targets) from /etc/rsyncd.d/*.conf les. These les should not contain any references to global values. c. Create your module (your backup target) in the le /etc/rsyncd.d/backup.conf with the following lines: # backup.conf: backup module 213 Configuring and using an rsync server SLES 15 SP6[backup] 1 uid = tux 2 gid = users 2 path = /var/backup 3 auth users = tux 4 secrets file = /etc/rsyncd.secrets 5 comment = Our backup target 1 The backup target. You can use any name you like. However, it is a good idea to name a target according to its purpose and use the same name in your *.conf le. 2 Specifies the user name or group name that is used when the le transfer takes place. 3 Defines the path to store your backups (from Step 1). 4 Specifies a comma-separated list of allowed users. In its simplest form, it con- tains the user names that are allowed to connect to this module. In our case, only user tux is allowed. 5 Specifies the path of a le that contains lines with user names and plain pass- words. d. Create the /etc/rsyncd.secrets le with the following content and replace PASSPHRASE : # user:passwd tux:PASSPHRASE e. Make sure the le is only readable by root : # chmod 0600 /etc/rsyncd.secrets 4. Start and enable the rsyncd daemon with: # systemctl enable rsyncd # systemctl start rsyncd 5. Test the access to your Rsync server: > rsync jupiter:: You should see a response that looks like this: backup Our backup target 214 Configuring and using an rsync server SLES 15 SP6Otherwise, check your configuration le, firewall and network settings. The above steps create an Rsync server that can now be used to store backups. The example also creates a log le listing all connections. This le is stored in /var/log/rsyncd.log . This is useful to debug your transfers. To list the content of your backup target, use the following command: > rsync -avz jupiter::backup This command lists all les present in the directory /var/backup on the server. This request is also logged in the log le /var/log/rsyncd.log . To start an actual transfer, provide a source directory. Use . for the current directory. For example, the following command copies the current directory to your Rsync backup server: > rsync -avz . jupiter::backup By default, Rsync does not delete les and directories when it runs. To enable deletion, the additional option --delete must be stated. To ensure that no newer les are deleted, the option --update can be used instead. Any conflicts that arise must be resolved manually. 15.6 More information Csync Bidirectional le synchronization tool, see https://csync.org/ . RSnapshot Creates incremental backups, see https://rsnapshot.org . Unison A le synchronization tool similar to CSync but with a graphical interface, see https:// github.com/bcpierce00/unison . Rear A disaster recovery framework, see the Administration Guide of the SUSE Linux Enterprise High Availability, chapter Disaster Recovery with Rear (Relax-and-Recover) (https://documenta- tion.suse.com/sle-ha/15/html/SLE-HA-all/cha-ha-rear.html) . 215 More information SLES 15 SP6II Booting a Linux system 16 Introduction to the boot process 217 17 UEFI (Unified Extensible Firmware Interface) 225 18 The boot loader GRUB 2 234 19 The systemd daemon 25716 Introduction to the boot process Booting a Linux system involves different components and tasks. After a rmware and hardware initialization process, which depends on the machine''s architecture, the kernel is started by the boot loader GRUB 2. After this point, the boot process is controlled by the operating system and handled by systemd . systemd provides a set of “targets” that boot configurations for everyday usage, maintenance or emer- gencies. 16.1 Terminology This chapter uses terms that can be interpreted ambiguously. To understand how they are used here, read the definitions below: init Two different processes are commonly named “init”: The initramfs process mounting the root le system The operating system process that starts all other processes that is executed from the real root le system In both cases, the systemd program is taking care of this task. It is rst executed from the initramfs to mount the root le system. When that has succeeded, it is re-executed from the root le system as the initial process. To avoid confusing these two systemd processes, we refer to the rst process as init on initramfs and to the second one as systemd. initrd / initramfs An initrd (initial RAM disk) is an image le containing a root le system image which is loaded by the kernel and mounted from /dev/ram as the temporary root le system. Mounting this le system requires a le system driver. Beginning with kernel 2.6.13, the initrd has been replaced by the initramfs (initial RAM le system), which does not require a le system driver to be mounted. SUSE Linux En- terprise Server exclusively uses an initramfs . However, since the initramfs is stored as /boot/initrd , it is often called “initrd”. In this chapter we exclusively use the name initramfs . 217 Terminology SLES 15 SP616.2 The Linux boot process The Linux boot process consists of several stages, each represented by a different component: 1. Section 16.2.1, “The initialization and boot loader phase” 2. Section 16.2.2, “The kernel phase” 3. Section 16.2.3, “The init on initramfs phase” 4. Section 16.2.4, “The systemd phase” 16.2.1 The initialization and boot loader phase During the initialization phase, the machine''s hardware is set up, and the devices are prepared. This process differs across hardware architectures. SUSE Linux Enterprise Server uses the boot loader GRUB 2 on all architectures. Depending on the architecture and rmware, starting the GRUB 2 boot loader can be a multi-step process. The purpose of the boot loader is to load the kernel and the initial, RAM-based le system (initramfs). For more information about GRUB 2, refer to Chapter 18, The boot loader GRUB 2. 16.2.1.1 Initialization and boot loader phase on AArch64 and AMD64/ Intel 64 After turning on the computer, the BIOS or the UEFI initializes the screen and keyboard, and tests the main memory. Up to this stage, the machine does not access any mass storage media. Subsequently, the information about the current date, time and the most important peripherals are loaded from the CMOS values. When the boot media and its geometry are recognized, the system control passes from the BIOS/UEFI to the boot loader. On a machine equipped with a traditional BIOS, only code from the rst physical 512-byte data sector (the Master Boot Record, MBR) of the boot disk can be loaded. Only a minimal GRUB 2 ts into the MBR. Its sole purpose is to load a GRUB 2 core image containing le system drivers from the gap between the MBR and the rst partition (MBR partition table) or from the BIOS boot partition (GPT partition table). This image contains le system drivers and therefore is able to access /boot located on the root le system. /boot contains additional modules for GRUB 2 core as well as the kernel and the initramfs image. When it has access to this partition, GRUB 2 loads the kernel and the initramfs image into memory and hands control over to the kernel. 218 The Linux boot process SLES 15 SP6When booting a BIOS system from an encrypted le system that includes an encrypted /boot partition, you need to enter the password for decryption twice. It is rst needed by GRUB 2 to decrypt /boot and then for systemd to mount the encrypted volumes. On machines with UEFI the boot process is much simpler than on machines with a traditional BIOS. The rmware is able to read from a FAT formatted system partition of disks with a GPT partition table. This EFI system-partition (in the running system mounted as /boot/efi ) holds enough space to host a fully edged GRUB 2 which is directly loaded and executed by the rmware. If the BIOS/UEFI supports network booting, it is also possible to configure a boot server that provides the boot loader. The system can then be booted via PXE. The BIOS/UEFI acts as the boot loader. It gets the boot image from the boot server and starts the system, independent of local hard disks. 16.2.1.2 Initialization and boot loader phase on IBM Z On IBM Z the boot process must be initialized by a boot loader called zipl (z initial program load). Although zipl supports reading from multiple le systems, it does not support the SLE default le system (Btrfs) or booting from snapshots. SUSE Linux Enterprise Server therefore uses a two-stage boot process that ensures full Btrfs support at boot-time: 1. zipl boots from the partition /boot/zipl , which can be formatted with the Ext2, Ext3, Ext4, or XFS le system. This partition contains a minimal kernel and an initramfs that are loaded into memory. The initramfs contains a Btrfs driver (among others) and the boot loader GRUB 2. The kernel is started with a parameter initgrub , which tells it to start GRUB 2. 2. The kernel mounts the root le system, so /boot becomes accessible. Now GRUB 2 is started from the initramfs. It reads its configuration from /boot/grub2/grub.cfg and loads the final kernel and initramfs from /boot . The new kernel now gets loaded via Kexec. 16.2.2 The kernel phase When the boot loader has passed on system control, the boot process is the same on all architec- tures. The boot loader loads both the kernel and an initial RAM-based le system ( initramfs ) into memory and the kernel takes over. 219 The kernel phase SLES 15 SP6After the kernel has set up memory management and has detected the CPU type and its features, it initializes the hardware and mounts the temporary root le system from the memory that was loaded with the initramfs . 16.2.2.1 The initramfs file initramfs (initial RAM le system) is a small cpio archive that the kernel can load into a RAM disk. It is located at /boot/initrd . It can be created with a tool called dracut—refer to man 8 dracut for details. The initramfs provides a minimal Linux environment that enables the execution of programs before the actual root le system is mounted. This minimal Linux environment is loaded into memory by BIOS or UEFI routines and does not have specific hardware requirements other than sufficient memory. The initramfs archive must always provide an executable named init that executes the systemd daemon on the root le system for the boot process to proceed. Before the root le system can be mounted and the operating system can be started, the kernel needs the corresponding drivers to access the device on which the root le system is located. These drivers may include special drivers for certain kinds of hard disks or even network drivers to access a network le system. The needed modules for the root le system are loaded by init on initramfs . After the modules are loaded, udev provides the initramfs with the needed devices. Later in the boot process, after changing the root le system, it is necessary to regenerate the devices. This is done by the systemd unit systemd-udev-trigger.service . 16.2.2.1.1 Regenerating the initramfs Because the initramfs contains drivers, it needs to be updated whenever a new version of one of its drivers is available. This is done automatically when installing the package containing the driver update. YaST or zypper informs you about this by showing the output of the command that generates the initramfs . However, there are specific occasions when you need to regenerate an initramfs manually: Adding drivers because of hardware changes If you need to change hardware, for example, hard disks, and this hardware requires dif- ferent drivers to be in the kernel at boot time, you must update the initramfs le. 220 The kernel phase SLES 15 SP6Open or create /etc/dracut.conf.d/10-DRIVER.conf and add the following line (mind the leading blank space): force_drivers+=" DRIVER1 " Replace DRIVER1 with the module name of the driver. If you need to add more than one driver, list them space-separated: force_drivers+=" DRIVER1 DRIVER2 " Proceed with Procedure 16.1, “Generate an initramfs”. Moving system directories to a RAID or LVM Whenever you move swap les, or system directories like /usr in a running system to a RAID or logical volume, you need to create an initramfs that contains support for software RAID or LVM drivers. To do so, create the respective entries in /etc/fstab and mount the new entries (for example with mount -a and/or swapon -a ). Proceed with Procedure 16.1, “Generate an initramfs”. Adding disks to an LVM group or Btrfs RAID containing the root file system Whenever you add (or remove) a disk to a logical volume group or a Btrfs RAID contain- ing the root le system, you need to create an initramfs that contains support for the enlarged volume. Follow the instructions at Procedure 16.1, “Generate an initramfs”. Proceed with Procedure 16.1, “Generate an initramfs”. Changing kernel variables If you change the values of kernel variables via the sysctl interface by editing related les ( /etc/sysctl.conf or /etc/sysctl.d/*.conf ), the change will be lost on the next system reboot. Even if you load the values with sysctl --system at runtime, the changes are not saved into the initramfs le. You need to update it by proceeding as outlined in Procedure 16.1, “Generate an initramfs”. Adding or removing swap devices, re-creating swap area Whenever you add or remove a swap device, or re-create a swap area with a different UUID, update the initramfs as outlined in Procedure 16.1, “Generate an initramfs”. You may also need to update GRUB_CMDLINE_* variables that include the resume= option in /etc/ default/grub , and then regenerate /boot/grub2/grub.cfg as outlined in Section 18.2.1, “The file /boot/grub2/grub.cfg”. 221 The kernel phase SLES 15 SP6PROCEDURE 16.1: GENERATE AN INITRAMFS Important All commands in the following procedure need to be executed as the root user. 1. Enter your /boot directory: # cd /boot 2. Generate a new initramfs le with dracut , replacing MY_INITRAMFS with a le name of your choice: # dracut MY_INITRAMFS Alternatively, run dracut -f FILENAME to replace an existing init le. 3. (Skip this step if you ran dracut -f in the previous step.) Create a symbolic link from the initramfs le you created in the previous step to initrd : # ln -sf MY_INITRAMFS initrd 4. On the IBM Z architecture, additionally run grub2-install . 16.2.3 The init on initramfs phase The temporary root le system mounted by the kernel from the initramfs contains the exe- cutable systemd (which is called init on initramfs in the following, also see Section 16.1, “Terminology”. This program performs all actions needed to mount the proper root le system. It provides kernel functionality for the needed le system and device drivers for mass storage controllers with udev . The main purpose of init on initramfs is to prepare the mounting of and access to the real root le system. Depending on your system configuration, init on initramfs is responsible for the following tasks. Loading kernel modules Depending on your hardware configuration, special drivers may be needed to access the hardware components of your computer (the most important component being your hard disk). To access the final root le system, the kernel needs to load the proper le system drivers. 222 The init on initramfs phase SLES 15 SP6Providing block special files The kernel generates device events depending on loaded modules. udev handles these events and generates the required special block les on a RAM le system in /dev . Without those special les, the le system and other devices would not be accessible. Managing RAID and LVM setups If you configured your system to hold the root le system under RAID or LVM, init on initramfs sets up LVM or RAID to enable access to the root le system later. Managing the network configuration If you configured your system to use a network-mounted root le system (mounted via NFS), init must make sure that the proper network drivers are loaded and that they are set up to allow access to the root le system. If the le system resides on a network block device like iSCSI or SAN, the connection to the storage server is also set up by init on initramfs . SUSE Linux Enterprise Server supports booting from a secondary iSCSI target if the primary target is not available. For more details regarding configuration of the booting iSCSI target refer to Book “Storage Administration Guide”, Chapter 15 “Mass storage over IP networks: iSCSI”, Section 15.3.1 “Using YaST for the iSCSI initiator configuration”. Note: Handling of mount failures If the root le system fails to mount from within the boot environment, it must be checked and repaired before the boot can continue. The le system checker will be automatical- ly started for Ext3 and Ext4 le systems. The repair process is not automated for XFS and Btrfs le systems, and the user is presented with information describing the options available to repair the le system. When the le system has been successfully repaired, exiting the boot environment will cause the system to retry mounting the root le system. If successful, the boot will continue normally. 16.2.3.1 The init on initramfs phase in the installation process When init on initramfs is called during the initial boot as part of the installation process, its tasks differ from those mentioned above. The installation system also does not start systemd from initramfs—these tasks are performed by linuxrc . 223 The init on initramfs phase SLES 15 SP6Finding the installation medium When starting the installation process, your machine loads an installation kernel and a special init containing the YaST installer. The YaST installer is running in a RAM le system and needs to have information about the location of the installation medium to access it for installing the operating system. Initiating hardware recognition and loading appropriate kernel modules As mentioned in Section 16.2.2.1, “The initramfs file”, the boot process starts with a mini- mum set of drivers that can be used with most hardware configurations. On AArch64, POW- ER, and AMD64/Intel 64 machines, linuxrc starts an initial hardware scanning process that determines the set of drivers suitable for your hardware configuration. On IBM Z, a list of drivers and their parameters needs to be provided, for example, via linuxrc or a parmfile. These drivers are used to generate a custom initramfs that is needed to boot the system. If the modules are not needed for boot but for coldplug, the modules can be loaded with systemd ; for more information, see Section 19.6.4, “Loading kernel modules”. Loading the installation system When the hardware is properly recognized, the appropriate drivers are loaded. The udev program creates the special device les and linuxrc starts the installation system with the YaST installer. Starting YaST Finally, linuxrc starts YaST, which starts the package installation and the system con- figuration. 16.2.4 The systemd phase After the “real” root le system has been found, it is checked for errors and mounted. If this is successful, the initramfs is cleaned and the systemd daemon on the root le system is executed. systemd is Linux''s system and service manager. It is the parent process that is started as PID 1 and acts as an init system which brings up and maintains user space services. See Chapter 19, The systemd daemon for details. 224 The systemd phase SLES 15 SP617 UEFI (Unified Extensible Firmware Interface) UEFI (Unified Extensible Firmware Interface) is the interface between the rmware that comes with the system hardware, all the hardware components of the system, and the operating system. UEFI is becoming more and more available on PC systems and thus is replacing the traditional PC-BIOS. UEFI, for example, properly supports 64-bit systems and offers secure booting (“Secure Boot”, rmware version 2.3.1c or better required), which is one of its most important features. Lastly, with UEFI a standard rmware will become available on all x86 platforms. UEFI additionally offers the following advantages: Booting from large disks (over 2 TiB) with a GUID Partition Table (GPT). CPU-independent architecture and drivers. Flexible pre-OS environment with network capabilities. CSM (Compatibility Support Module) to support booting legacy operating systems via a PC-BIOS-like emulation. For more information, see https://en.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface . The following sections are not meant as a general UEFI overview; these are only hints about how certain features are implemented in SUSE Linux Enterprise Server. 17.1 Secure boot In the world of UEFI, securing the bootstrapping process means establishing a chain of trust. The “platform” is the root of this chain of trust; in the context of SUSE Linux Enterprise Server, the mainboard and the on-board rmware could be considered the “platform”. In other words, it is the hardware vendor, and the chain of trust ows from that hardware vendor to the component manufacturers, the OS vendors, etc. The trust is expressed via public key cryptography. The hardware vendor puts a so-called Plat- form Key (PK) into the rmware, representing the root of trust. The trust relationship with op- erating system vendors and others is documented by signing their keys with the Platform Key. Finally, security is established by requiring that no code will be executed by the rmware unless it has been signed by one of these “trusted” keys—be it an OS boot loader, a driver located in the ash memory of certain PCI Express card or on disk, or be it an update of the rmware itself. 225 Secure boot SLES 15 SP6To use Secure Boot, you need to have your OS loader signed with a key trusted by the rmware, and you need the OS loader to verify that the kernel it loads can be trusted. Key Exchange Keys (KEK) can be added to the UEFI key database. This way, you can use other certificates, if they are signed with the private part of the PK. 17.1.1 Implementation on SUSE Linux Enterprise Server Microsoft’s Key Exchange Key (KEK) is installed by default. Note: GUID partitioning table (GPT) required The Secure Boot feature is enabled by default on UEFI/x86_64 installations. You can nd the Enable Secure Boot Support option in the Boot Code Options tab of the Boot Loader Settings dialog. It supports booting when the secure boot is activated in the rmware, while making it possible to boot when it is deactivated. FIGURE 17.1: SECURE BOOT SUPPORT The Secure Boot feature requires that a GUID Partitioning Table (GPT) replaces the old partitioning with a Master Boot Record (MBR). If YaST detects EFI mode during the in- stallation, it will try to create a GPT partition. UEFI expects to nd the EFI programs on a FAT-formatted EFI System Partition (ESP). 226 Implementation on SUSE Linux Enterprise Server SLES 15 SP6Supporting UEFI Secure Boot requires having a boot loader with a digital signature that the rmware recognizes as a trusted key. That key is trusted by the rmware a priori, without requiring any manual intervention. There are two ways of getting there. One is to work with hardware vendors to have them en- dorse a SUSE key, which SUSE then signs the boot loader with. The other way is to go through Microsoft’s Windows Logo Certification program to have the boot loader certified and have Mi- crosoft recognize the SUSE signing key (that is, have it signed with their KEK). By now, SUSE got the loader signed by UEFI Signing Service (that is Microsoft in this case). FIGURE 17.2: UEFI: SECURE BOOT PROCESS At the implementation layer, SUSE uses the shim loader which is installed by default. It is a smart solution that avoids legal issues, and simplifies the certification and signing step consid- erably. The shim loader’s job is to load a boot loader such as GRUB 2 and verify it; this boot loader in turn will load kernels signed by a SUSE key only. There are two types of trusted users: First, those who hold the keys. The Platform Key (PK) allows almost everything. The Key Exchange Key (KEK) allows all a PK can except changing the PK. Second, anyone with physical access to the machine. A user with physical access can reboot the machine, and configure UEFI. 227 Implementation on SUSE Linux Enterprise Server SLES 15 SP6UEFI offers two types of variables to fulfill the needs of those users: The rst is the so-called “Authenticated Variables”, which can be updated from both within the boot process (the so-called Boot Services Environment) and the running OS. This can be done only when the new value of the variable is signed with the same key that the old value of the variable was signed with. And they can only be appended to or changed to a value with a higher serial number. The second is the so-called “Boot Services Only Variables”. These variables are accessible to any code that runs during the boot process. After the boot process ends and before the OS starts, the boot loader must call the ExitBootServices call. After that, these variables are no longer accessible, and the OS cannot touch them. UEFI key lists are of the rst type, as this allows online updating, adding and blacklisting of keys, drivers and rmware fingerprints. It is the second type of variable, the “Boot Services Only Variable”, that helps to implement Secure Boot in a secure and open source-friendly manner, and thus compatible with GPLv3. SUSE starts with shim—a small and simple EFI boot loader signed by SUSE and Microsoft. This allows shim to load and execute. shim then goes on to verify that the boot loader it wants to load is trusted. In a default situation shim will use an independent SUSE certificate embedded in its body. In addition, shim will allow to “enroll” additional keys, overriding the default SUSE key. In the following, we call them “Machine Owner Keys” or MOKs for short. Next the boot loader will verify and then boot the kernel, and the kernel will do the same on the modules. 17.1.2 MOK (Machine Owner Key) To replace specific kernels, drivers or other components that are part of the boot process, you need to use Machine Owner Keys (MOKs). The mokutil tool can help you to manage MOKs. You can create a MOK enrollment request with mokutil . The request is stored in a UEFI runtime (RT) variable called MokNew . During the next boot, the shim boot loader detects MokNew and loads MokManager , which presents you with several options. You can use the Enroll key from disk and Enroll hash from disk options to add the key to the MokList. Use the Enroll MOK option to copy the key from the MokNew variable. 228 MOK (Machine Owner Key) SLES 15 SP6Enrolling a key from disk is normally done when the shim fails to load grub2 and falls back to loading MokManager. As MokNew does not exist yet, you have the option of locating the key on the UEFI partition. 17.1.3 Booting a custom kernel The following is based on https://en.opensuse.org/openSUSE:UEFI#Booting_a_custom_kernel . Secure Boot does not prevent you from using a self-compiled kernel. You must sign it with your own certificate and make that certificate known to the rmware or MOK. 1. Create a custom X.509 key and certificate used for signing: openssl req -new -x509 -newkey rsa:2048 -keyout key.asc \ -out cert.pem -nodes -days 666 -subj "/CN=$USER/" For more information about creating certificates, see https://en.open- suse.org/openSUSE:UEFI_Image_File_Sign_Tools#Create_Your_Own_Certificate . 2. Package the key and the certificate as a PKCS#12 structure: > openssl pkcs12 -export -inkey key.asc -in cert.pem \ -name kernel_cert -out cert.p12 3. Generate an NSS database for use with pesign : > certutil -d . -N 4. Import the key and the certificate contained in PKCS#12 into the NSS database: > pk12util -d . -i cert.p12 5. “Bless” the kernel with the new signature using pesign : > pesign -n . -c kernel_cert -i arch/x86/boot/bzImage \ -o vmlinuz.signed -s 6. List the signatures on the kernel image: > pesign -n . -S -i vmlinuz.signed 229 Booting a custom kernel SLES 15 SP6At that point, you can install the kernel in /boot as usual. Because the kernel now has a custom signature the certificate used for signing needs to be imported into the UEFI rmware or MOK. 7. Convert the certificate to the DER format for import into the rmware or MOK: > openssl x509 -in cert.pem -outform der -out cert.der 8. Copy the certificate to the ESP for easier access: > sudo cp cert.der /boot/efi/ 9. Use mokutil to launch the MOK list automatically. • a. Import the certificate to MOK: > mokutil --root-pw --import cert.der The --root-pw option enables usage of the root user directly. b. Check the list of certificates that are prepared to be enrolled: > mokutil --list-new c. Reboot the system; shim should launch MokManager. You need to enter the root password to confirm the import of the certificate to the MOK list. d. Check if the newly imported key was enrolled: > mokutil --list-enrolled • a. Alternatively, this is the procedure to launch MOK manually: Reboot b. In the GRUB 2 menu press the '' c '' key. c. Type: chainloader $efibootdir/MokManager.efi boot d. Select Enroll key from disk. e. Navigate to the cert.der le and press Enter . 230 Booting a custom kernel SLES 15 SP6f. Follow the instructions to enroll the key. Normally this should be pressing “0” and then “y” to confirm. Alternatively, the rmware menu may provide ways to add a new key to the Signature Database. 17.1.4 Using non-inbox drivers There is no support for adding non-inbox drivers (that is, drivers that do not come with SUSE Linux Enterprise Server) during installation with Secure Boot enabled. The signing key used for SolidDriver/PLDP is not trusted by default. It is possible to install third party drivers during installation with Secure Boot enabled in two different ways. In both cases: Add the needed keys to the rmware database via rmware/system management tools before the installation. This option depends on the specific hardware you are using. Consult your hardware vendor for more information. Use a bootable driver ISO from https://drivers.suse.com/ or your hardware vendor to enroll the needed keys in the MOK list at rst boot. To use the bootable driver ISO to enroll the driver keys to the MOK list, follow these steps: 1. Burn the ISO image above to an empty CD/DVD medium. 2. Start the installation using the new CD/DVD medium, having the standard installation media at hand or a URL to a network installation server. If doing a network installation, enter the URL of the network installation source on the boot command line using the install= option. If doing installation from optical media, the installer will rst boot from the driver kit and then ask to insert the rst installation disk of the product. 3. An initrd containing updated drivers will be used for installation. For more information, see https://drivers.suse.com/doc/Usage/Secure_Boot_Certificate.html . 231 Using non-inbox drivers SLES 15 SP617.1.5 Features and limitations When booting in Secure Boot mode, the following features apply: Installation to UEFI default boot loader location, a mechanism to keep or restore the EFI boot entry. Reboot via UEFI. Xen hypervisor will boot with UEFI when there is no legacy BIOS to fall back to. UEFI IPv6 PXE boot support. UEFI video mode support, the kernel can retrieve video mode from UEFI to configure KMS mode with the same parameters. UEFI booting from USB devices is supported. Since SUSE Linux Enterprise Server 15 SP3, Kexec and Kdump are supported in Secure Boot mode. When booting in Secure Boot mode, the following limitations apply: To ensure that Secure Boot cannot be easily circumvented, certain kernel features are disabled when running under Secure Boot. Boot loader, kernel, and kernel modules must be signed. Hibernation (suspend on disk) is disabled. Access to /dev/kmem and /dev/mem is not possible, not even as root user. Access to the I/O port is not possible, not even as root user. All X11 graphical drivers must use a kernel driver. PCI BAR access through sysfs is not possible. custom_method in ACPI is not available. debugfs for asus-wmi module is not available. the acpi_rsdp parameter does not have any effect on the kernel. 232 Features and limitations SLES 15 SP617.2 More information https://uefi.org — UEFI home page where you can nd the current UEFI specifications. Blog posts by Olaf Kirch and Vojtěch Pavlík (the chapter above is heavily based on these posts): https://www.suse.com/c/uefi-secure-boot-plan/ https://www.suse.com/c/uefi-secure-boot-overview/ https://www.suse.com/c/uefi-secure-boot-details/ https://en.opensuse.org/openSUSE:UEFI —UEFI with openSUSE. 233 More information SLES 15 SP618 The boot loader GRUB 2 This chapter describes how to configure GRUB 2, the boot loader used in SUSE® Linux Enterprise Server. It is the successor to the traditional GRUB boot loader— now called “GRUB Legacy”. GRUB 2 has been the default boot loader in SUSE® Linux Enterprise Server since version 12. A YaST module is available for configur- ing the most important settings. The boot procedure as a whole is outlined in Chap- ter 16, Introduction to the boot process. For details on Secure Boot support for UEFI machines, see Chapter 17, UEFI (Unified Extensible Firmware Interface). 18.1 Main differences between GRUB legacy and GRUB 2 The configuration is stored in different les. More le systems are supported (for example, Btrfs). Can directly read les stored on LVM or RAID devices. The user interface can be translated and altered with themes. Includes a mechanism for loading modules to support additional features, such as le systems, etc. Automatically searches for and generates boot entries for other kernels and operating sys- tems, such as Windows. Includes a minimal Bash-like console. 18.2 Configuration file structure The configuration of GRUB 2 is based on the following les: /boot/grub2/grub.cfg This le contains the configuration of the GRUB 2 menu items. It replaces menu.lst used in GRUB Legacy. grub.cfg should not be edited—it is automatically generated by the command grub2-mkconfig -o /boot/grub2/grub.cfg . 234 Main differences between GRUB legacy and GRUB 2 SLES 15 SP6/boot/grub2/custom.cfg This optional le is directly sourced by grub.cfg at boot time and can be used to add custom items to the boot menu. Starting with SUSE Linux Enterprise Server 12 SP2 these entries are also parsed when using grub-once . /etc/default/grub This le controls the user settings of GRUB 2 and normally includes additional environ- mental settings such as backgrounds and themes. Scripts under /etc/grub.d/ The scripts in this directory are read during execution of the command grub2-mkconfig -o /boot/grub2/grub.cfg . Their instructions are integrated into the main configuration le /boot/grub/grub.cfg . /etc/sysconfig/bootloader This configuration le holds certain basic settings like the boot loader type and whether to enable UEFI Secure Boot support. /boot/grub2/x86_64-efi , /boot/grub2/power-ieee1275 , /boot/grub2/s390x These configuration les contain architecture-specific options. GRUB 2 can be controlled in multiple ways. Boot entries from an existing configuration can be se- lected from the graphical menu (splash screen). The configuration is loaded from the le /boot/ grub2/grub.cfg which is compiled from other configuration les (see below). All GRUB 2 configuration les are considered system les, and you need root privileges to edit them. Note: Activating configuration changes After having manually edited GRUB 2 configuration les, you need to run grub2-mk- config -o /boot/grub2/grub.cfg to activate the changes. However, this is not neces- sary when changing the configuration with YaST, because YaST automatically runs this command. 18.2.1 The file /boot/grub2/grub.cfg The graphical splash screen with the boot menu is based on the GRUB 2 configuration le / boot/grub2/grub.cfg , which contains information about all partitions or operating systems that can be booted by the menu. 235 The file /boot/grub2/grub.cfg SLES 15 SP6Every time the system is booted, GRUB 2 loads the menu le directly from the le system. For this reason, GRUB 2 does not need to be re-installed after changes to the configuration le. grub.cfg is automatically rebuilt with kernel installations or removals. grub.cfg is compiled from the le /etc/default/grub and scripts found in the /etc/ grub.d/ directory when running the command grub2-mkconfig -o /boot/grub2/grub.cfg . Therefore you should never edit the le manually. Instead, edit the related source les or use the YaST Boot Loader module to modify the configuration as described in Section 18.3, “Configuring the boot loader with YaST”. 18.2.2 The file /etc/default/grub More general options of GRUB 2 belong in this le, such as the time the menu is displayed, or the default OS to boot. To list all available options, see the output of the following command: > grep "export GRUB_DEFAULT" -A50 /usr/sbin/grub2-mkconfig | grep GRUB_ You can introduce custom variables and use them later in the scripts found in the /etc/grub.d directory. After having edited /etc/default/grub , update the main configuration le with grub2-mk- config -o /boot/grub2/grub.cfg . Note: Scope All options specified in this le are general options that affect all boot entries. Options specific to a Xen hypervisor include the _XEN_ substring. Important: Escaping inner quotes More complex options with spaces require quoting so that they are processed as one option. Such inner quotes need to be correctly escaped, for example: GRUB_CMDLINE_LINUX_XEN="debug loglevel=9 log_buf_len=5M \"ddebug_query=file drivers/xen/xen-acpi-processor.c +p\"" GRUB_DEFAULT Sets the boot menu entry that is booted by default. Its value can be a numeric value, the complete name of a menu entry, or “saved”. 236 The file /etc/default/grub SLES 15 SP6GRUB_DEFAULT=2 boots the third (counted from zero) boot menu entry. GRUB_DEFAULT="2>0" boots the rst submenu entry of the third top-level menu entry. GRUB_DEFAULT="Example boot menu entry" boots the menu entry with the title “Ex- ample boot menu entry”. GRUB_DEFAULT=saved boots the entry specified by the grub2-once or grub2-set-de- fault commands. While grub2-reboot sets the default boot entry for the next reboot on- ly, grub2-set-default sets the default boot entry until changed. grub2-editenv list lists the next boot entry. GRUB_HIDDEN_TIMEOUT Waits the specified number of seconds for the user to press a key. During the period no menu is shown unless the user presses a key. If no key is pressed during the time specified, the control is passed to GRUB_TIMEOUT . GRUB_HIDDEN_TIMEOUT=0 rst checks whether Shift is pressed and shows the boot menu if yes, otherwise immediately boots the default menu entry. This is the default when only one bootable OS is identified by GRUB 2. GRUB_HIDDEN_TIMEOUT_QUIET If false is specified, a countdown timer is displayed on a blank screen when the GRUB_HIDDEN_TIMEOUT feature is active. GRUB_TIMEOUT Time period in seconds the boot menu is displayed before automatically booting the default boot entry. If you press a key, the timeout is cancelled and GRUB 2 waits for you to make the selection manually. GRUB_TIMEOUT=-1 causes the menu to be displayed until you select the boot entry manually. GRUB_CMDLINE_LINUX Entries on this line are added at the end of the boot entries for normal and recovery modes. Use it to add kernel parameters to the boot entry. GRUB_CMDLINE_LINUX_DEFAULT Same as GRUB_CMDLINE_LINUX but the entries are appended in the normal mode only. GRUB_CMDLINE_LINUX_RECOVERY Same as GRUB_CMDLINE_LINUX but the entries are appended in the recovery mode only. GRUB_CMDLINE_LINUX_XEN_REPLACE This entry replaces the GRUB_CMDLINE_LINUX parameters for all Xen boot entries. 237 The file /etc/default/grub SLES 15 SP6GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT Same as GRUB_CMDLINE_LINUX_XEN_REPLACE but it only replaces parameters of GRUB_CMDLINE_LINUX_DEFAULT . GRUB_CMDLINE_XEN These entries are passed to the Xen hypervisor Xen menu entries for normal and recovery modes. For example: GRUB_CMDLINE_XEN="loglvl=all guest_loglvl=all" Tip: Xen hypervisor options Find a complete list of Xen hypervisor options in https://xenbits.xen.org/docs/unsta- ble/misc/xen-command-line.html GRUB_CMDLINE_XEN_DEFAULT Same as GRUB_CMDLINE_XEN but the entries are appended in the normal mode only. GRUB_TERMINAL Enables and specifies an input/output terminal device. Can be console (PC BIOS and EFI consoles), serial (serial terminal), ofconsole (Open Firmware console), or the default gfxterm (graphics-mode output). It is also possible to enable more than one device by quoting the required options, for example, GRUB_TERMINAL="console serial" . GRUB_GFXMODE The resolution used for the gfxterm graphical terminal. You can only use modes support- ed by your graphics card (VBE). The default is ‘auto’, which tries to select a preferred res- olution. You can display the screen resolutions available to GRUB 2 by typing videoin- fo in the GRUB 2 command line. The command line is accessed by typing C when the GRUB 2 boot menu screen is displayed. You can also specify a color depth by appending it to the resolution setting, for example, GRUB_GFXMODE=1280x1024x24 . GRUB_BACKGROUND Set a background image for the gfxterm graphical terminal. The image must be a le readable by GRUB 2 at boot time, and it must end with the .png , .tga , .jpg , or .jpeg suffix. If necessary, the image is scaled to t the screen. 238 The file /etc/default/grub SLES 15 SP6GRUB_DISABLE_OS_PROBER If this option is set to true , automatic searching for other operating systems is disabled. Only the kernel images in /boot/ and the options from your own scripts in /etc/grub.d/ are detected. SUSE_BTRFS_SNAPSHOT_BOOTING If this option is set to true , GRUB 2 can boot directly into Snapper snapshots. For more information, see Section 10.3, “System rollback by booting from snapshots”. For a complete list of options, see the GNU GRUB manual (https://www.gnu.org/software/grub/ manual/grub/grub.html#Simple-configuration) . 18.2.3 Scripts in /etc/grub.d The scripts in this directory are read during execution of the command grub2-mkconfig -o / boot/grub2/grub.cfg . Their instructions are incorporated into /boot/grub2/grub.cfg . The order of menu items in grub.cfg is determined by the order in which the les in this directory are run. Files with a leading numeral are executed rst, beginning with the lowest number. 00_header is run before 10_linux , which would run before 40_custom . If les with alpha- betic names are present, they are executed after the numerically named les. Only executable les generate output to grub.cfg during execution of grub2-mkconfig . By default all les in the /etc/grub.d directory are executable. Tip: Persistent custom content in grub.cfg Because /boot/grub2/grub.cfg is recompiled each time grub2-mkconfig is run, any custom content is lost. To insert your lines directly into /boot/grub2/grub.cfg without losing them after grub2-mkconfig is run, insert them between ### BEGIN /etc/grub.d/90_persistent ### and ### END /etc/grub.d/90_persistent ### The 90_persistent script ensures that such content is preserved. A list of the most important scripts follows: 239 Scripts in /etc/grub.d SLES 15 SP600_header Sets environmental variables such as system le locations, display settings, themes and previously saved entries. It also imports preferences stored in the /etc/default/grub . Normally you do not need to make changes to this le. 10_linux Identifies Linux kernels on the root device and creates relevant menu entries. This includes the associated recovery mode option if enabled. Only the latest kernel is displayed on the main menu page, with additional kernels included in a submenu. 30_os-prober This script uses os-prober to search for Linux and other operating systems and places the results in the GRUB 2 menu. There are sections to identify specific other operating systems, such as Windows or macOS. 40_custom This le provides a simple way to include custom boot entries into grub.cfg . Make sure that you do not change the exec tail -n +3 $0 part at the beginning. The processing sequence is set by the preceding numbers with the lowest number being executed rst. If scripts are preceded by the same number the alphabetical order of the complete name decides the order. Tip: /boot/grub2/custom.cfg If you create /boot/grub2/custom.cfg and ll it with content, it is automatically in- cluded into /boot/grub2/grub.cfg right after 40_custom at boot time. 18.2.4 Mapping between BIOS drives and Linux devices In GRUB Legacy, the device.map configuration le was used to derive Linux device names from BIOS drive numbers. The mapping between BIOS drives and Linux devices cannot always be guessed correctly. For example, GRUB Legacy would get a wrong order if the boot sequence of IDE and SCSI drives is exchanged in the BIOS configuration. GRUB 2 avoids this problem by using device ID strings (UUIDs) or le system labels when generating grub.cfg . GRUB 2 utilities create a temporary device map on the y, which is normally sufficient, particularly for single-disk systems. 240 Mapping between BIOS drives and Linux devices SLES 15 SP6However, if you need to override the GRUB 2''s automatic device mapping mechanism, create your custom mapping le /boot/grub2/device.map . The following example changes the map- ping to make DISK 3 the boot disk. GRUB 2 partition numbers start with 1 and not with 0 as in GRUB 2 Legacy. (hd1) /dev/disk-by-id/DISK3 ID (hd2) /dev/disk-by-id/DISK1 ID (hd3) /dev/disk-by-id/DISK2 ID 18.2.5 Editing menu entries during the boot procedure Being able to directly edit menu entries is useful when the system does not boot anymore because of a faulty configuration. It can also be used to test new settings without altering the system configuration. 1. In the graphical boot menu, select the entry you want to edit with the arrow keys. 2. Press E to open the text-based editor. 3. Use the arrow keys to move to the line you want to edit. FIGURE 18.1: GRUB 2 BOOT EDITOR 241 Editing menu entries during the boot procedure SLES 15 SP6Now you have two options: a. Add space-separated parameters to the end of the line starting with linux or lin- uxefi to edit the kernel parameters. A complete list of parameters is available at https://en.opensuse.org/Linuxrc . b. Or edit the general options to change, for example, the kernel version. The →| key suggests all possible completions. 4. Press F10 to boot the system with the changes you made or press Esc to discard your edits and return to the GRUB 2 menu. Changes made this way only apply to the current boot process and are not saved permanently. Important: Keyboard layout during the boot procedure The US keyboard layout is the only one available when booting. See Book “Deployment Guide”, Chapter 13 “Troubleshooting”, Section 13.3 “Booting from installation media fails”, US key- board layout. Note: Boot loader on the installation media The Boot Loader of the installation media on systems with a traditional BIOS is still GRUB Legacy. To add boot parameters, select an entry and start typing. Additions you make to the installation boot entry are permanently saved in the installed system. Note: Editing GRUB 2 menu entries on IBM Z Cursor movement and editing commands on IBM Z differ—see Section 18.4, “Differences in terminal usage on IBM Z” for details. 18.2.6 Setting a boot password Even before the operating system is booted, GRUB 2 enables access to le systems. Users without root permissions can access les in your Linux system to which they have no access after the system is booted. To block this kind of access or to prevent users from booting certain menu entries, set a boot password. 242 Setting a boot password SLES 15 SP6Important: Booting requires a password If set, the boot password is required on every boot, which means the system does not boot automatically. Proceed as follows to set a boot password. Alternatively use YaST (Protect Boot Loader with Pass- word ). 1. Encrypt the password using grub2-mkpasswd-pbkdf2: > sudo grub2-mkpasswd-pbkdf2 Password: **** Reenter password: **** PBKDF2 hash of your password is grub.pbkdf2.sha512.10000.9CA4611006FE96BC77A... 2. Paste the resulting string into the le /etc/grub.d/40_custom together with the set superusers command. set superusers="root" password_pbkdf2 root grub.pbkdf2.sha512.10000.9CA4611006FE96BC77A... 3. To import the changes into the main configuration le, run: > sudo grub2-mkconfig -o /boot/grub2/grub.cfg After you reboot, GRUB 2 prompts you for a user name and a password when trying to boot a menu entry. Enter root and the password you typed during the grub2-mkpasswd-pbkdf2 command. If the credentials are correct, the system boots the selected boot entry. For more information, see https://www.gnu.org/software/grub/manual/grub/grub.html#Securi- ty . 18.2.7 Authorized access to boot menu entries You can configure GRUB 2 to allow access to boot menu entries depending on the level of authorization. You can configure multiple user accounts protected with passwords and assign them access to different menu entries. To configure authorization in GRUB 2, follow these steps: 1. Create and encrypt one password for each user account you want to use in GRUB 2. Use the grub2-mkpasswd-pbkdf2 command as described in Section 18.2.6, “Setting a boot password”. 243 Authorized access to boot menu entries SLES 15 SP62. Delete the le /etc/grub.d/10_linux . This prevents outputting the default GRUB 2 menu entries. 3. Edit the /boot/grub2/custom.cfg le and add custom menu entries manually. The fol- lowing template is an example, adjust it to better match your use case: set superusers=admin password admin ADMIN_PASSWORD password maintainer MAINTAINER_PASSWORD menuentry ''Operational mode'' { insmod ext2 set root=hd0,1 echo ''Loading Linux ...'' linux /boot/vmlinuz root=/dev/vda1 $GRUB_CMDLINE_LINUX_DEFAULT $GRUB_CMDLINE_LINUX mode=operation echo ''Loading Initrd ...'' initrd /boot/initrd } menuentry ''Maintenance mode'' --users maintainer { insmod ext2 set root=hd0,1 echo ''Loading Linux ...'' linux /boot/vmlinuz root=/dev/vda1 $GRUB_CMDLINE_LINUX_DEFAULT $GRUB_CMDLINE_LINUX mode=maintenance echo ''Loading Initrd ...'' initrd /boot/initrd } 4. Import the changes into the main configuration le: > sudo grub2-mkconfig -o /boot/grub2/grub.cfg In the above example: The GRUB 2 menu has two entries, Operational mode and Maintenance mode. If no user is specified, both boot menu entries are accessible, but no one can access GRUB 2 command line or edit existing menu entries. admin user can access GRUB 2 command line and edit existing menu entries. maintenance user can select the recovery menu item. 244 Authorized access to boot menu entries SLES 15 SP618.3 Configuring the boot loader with YaST The easiest way to configure general options of the boot loader in your SUSE Linux Enterprise Server system is to use the YaST module. In the YaST Control Center, select System Boot Loader. The module shows the current boot loader configuration of your system and allows you to make changes. Use the Boot Code Options tab to view and change settings related to type, location and advanced loader settings. You can choose whether to use GRUB 2 in standard or EFI mode. Important: EFI systems require GRUB2-EFI If you have an EFI system you can only install GRUB2-EFI, otherwise your system is no longer bootable. Important: Reinstalling the boot loader To reinstall the boot loader, make sure to change a setting in YaST and then change it back. For example, to reinstall GRUB2-EFI, select GRUB2 rst and then immediately switch back to GRUB2-EFI. Otherwise, the boot loader may only be partially reinstalled. Note: Custom boot loader To use a boot loader other than the ones listed, select Do Not Install Any Boot Loader. Read the documentation of your boot loader carefully before choosing this option. 245 Configuring the boot loader with YaST SLES 15 SP618.3.1 Boot loader location and boot code options The default location of the boot loader depends on the partition setup and is either the Master Boot Record (MBR) or the boot sector of the / partition. To modify the location of the boot loader, follow these steps: PROCEDURE 18.1: CHANGING THE BOOT LOADER LOCATION 1. Select the Boot Code Options tab and then choose one of the following options for Boot Loader Location: Boot from Master Boot Record This installs the boot loader in the MBR of the disk containing the directory /boot . Usually this will be the disk mounted to / , but if /boot is mounted to a separate partition on a different disk, the MBR of that disk will be used. Boot from Root Partition This installs the boot loader in the boot sector of the / partition. Custom Root Partition Use this option to specify the location of the boot loader manually. 2. Click OK to apply the changes. FIGURE 18.2: BOOT CODE OPTIONS 246 Boot loader location and boot code options SLES 15 SP6The Boot Code Options tab includes the following additional options: Set Active Flag in Partition Table for Boot Partition Activates the partition that contains the /boot directory. For POWER systems it activates the PReP partition. Use this option on systems with old BIOS and/or legacy operating systems because they may fail to boot from a non-active partition. It is safe to leave this option active. Write Generic Boot Code to MBR If MBR contains a custom ''non-GRUB'' code, this option replaces it with a generic, operat- ing system independent code. If you deactivate this option, the system may become un- bootable. Enable Trusted Boot Support Starts TrustedGRUB2, which supports trusted computing functionality (Trusted Plat- form Module (TPM)). For more information refer to https://github.com/Sirrix-AG/Trusted- GRUB2 . The Protective MBR ag section includes the following options: set This is appropriate for traditional legacy BIOS booting. remove This is appropriate for UEFI booting. do not change This is usually the best choice if you have an already working system. In most cases YaST defaults to the appropriate choice. 18.3.2 Adjusting the disk order If your computer has more than one hard disk, you can specify the boot sequence of the disks. The rst disk in the list is where GRUB 2 will be installed in the case of booting from MBR. It is the disk where SUSE Linux Enterprise Server is installed by default. The rest of the list is a hint for GRUB 2''s device mapper (see Section 18.2.4, “Mapping between BIOS drives and Linux devices”). 247 Adjusting the disk order SLES 15 SP6Warning: Unbootable system The default value is usually valid for almost all deployments. If you change the boot order of disks wrongly, the system may become unbootable on the next reboot. For example, if the rst disk in the list is not part of the BIOS boot order, and the other disks in the list have empty MBRs. PROCEDURE 18.2: SETTING THE DISK ORDER 1. Open the Boot Code Options tab. 2. Click Edit Disk Boot Order. 3. If more than one disk is listed, select a disk and click Up or Down to reorder the displayed disks. 4. Click OK two times to save the changes. 18.3.3 Configuring advanced options Advanced boot parameters can be configured via the Boot Loader Options tab. 248 Configuring advanced options SLES 15 SP618.3.3.1 Boot Loader Options tab FIGURE 18.3: BOOT LOADER OPTIONS Boot Loader Time-Out Change the value of Time-Out in Seconds by typing in a new value and clicking the appro- priate arrow key with your mouse. Probe Foreign OS When selected, the boot loader searches for other systems like Windows or other Linux installations. Hide Menu on Boot Hides the boot menu and boots the default entry. Adjusting the Default Boot Entry Select the desired entry from the “Default Boot Section” list. Note that the “>” sign in the boot entry name delimits the boot section and its subsection. Protect Boot Loader with Password Protects the boot loader and the system with an additional password. For details on man- ual configuration, see Section 18.2.6, “Setting a boot password”. If this option is activated, the boot password is required on every boot, which means the system does not boot automat- 249 Configuring advanced options SLES 15 SP6ically. However, if you prefer the behavior of GRUB 1, additionally enable Protect Entry Modification Only. With this setting, anybody is allowed to select a boot entry and boot the system, whereas the password for the GRUB 2 root user is only required for modifying boot entries. 18.3.3.2 Kernel Parameters tab FIGURE 18.4: KERNEL PARAMETERS Optional Kernel Command Line Parameter Specify optional kernel parameters here to enable/disable system features, add drivers, etc. CPU Mitigations SUSE has released one or more kernel boot command line parameters for all software mit- igations that have been deployed to prevent CPU side-channel attacks. Some of those may result in performance loss. Choose one the following options to strike a balance between security and performance, depending on your setting: Auto.  Enables all mitigations required for your CPU model, but does not protect against cross-CPU thread attacks. This setting may impact performance to some degree, depending on the workload. 250 Configuring advanced options SLES 15 SP6Auto + No SMT.  Provides the full set of available security mitigations. Enables all mitiga- tions required for your CPU model. In addition, it disables Simultaneous Multithreading (SMT) to avoid side-channel attacks across multiple CPU threads. This setting may further impact performance, depending on the workload. Off.  Disables all mitigations. Side-channel attacks against your CPU are possible, depend- ing on the CPU model. This setting has no impact on performance. Manual.  Does not set any mitigation level. Specify your CPU mitigations manually by using the kernel command line options. Use Graphical Console When checked, the boot menu appears on a graphical splash screen rather than in a text mode. The resolution of the boot screen is set automatically by default, but you can manu- ally set it via Console resolution. The graphical theme definition le can be specified with the Console theme le chooser. Only change this if you want to apply your own, custom-made theme. Use Serial Console If your machine is controlled via a serial console, activate this option and specify which COM port to use at which speed. See info grub or https://www.gnu.org/software/grub/ manual/grub.html#Serial-terminal 18.4 Differences in terminal usage on IBM Z On 3215 and 3270 terminals there are certain differences and limitations on how to move the cursor and how to issue editing commands within GRUB 2. 18.4.1 Limitations Interactivity Interactivity is strongly limited. Typing often does not result in visual feedback. To see where the cursor is, type an underscore ( _ ). 251 Differences in terminal usage on IBM Z SLES 15 SP6Note: 3270 compared to 3215 The 3270 terminal is much better at displaying and refreshing screens than the 3215 terminal. Cursor movement “Traditional” cursor movement is not possible. Alt , Meta , Ctrl and the cursor keys do not work. To move the cursor, use the key combinations listed in Section 18.4.2, “Key combinations”. Caret The caret ( ^ ) is used as a control character. To type a literal ^ followed by a letter, type ^ , ^ , LETTER . Enter The Enter key does not work, use ^ – J instead. 18.4.2 Key combinations Common Substitutes: ^ – J engage (“Enter”) ^ – L cancel, return to previous “state” ^ – I tab completion (in edit and shell mode) Keys Available in Menu ^ – A rst entry Mode: ^ – E last entry ^ – P previous entry ^ – N next entry ^ – G previous page ^ – C next page 252 Key combinations SLES 15 SP6^ – F boot selected entry or enter submenu (same as ^ – J ) E edit selected entry C enter GRUB-Shell Keys Available in Edit Mode: ^ – P previous line ^ – N next line ^ – B backward char ^ – F forward char ^ – A beginning of line ^ – E end of line ^ – H backspace ^ – D delete ^ – K delete line ^ – Y yank ^ – O open line ^ – L refresh screen ^ – X boot entry ^ – C enter GRUB-Shell Keys Available in Command ^ – P previous command Line Mode: ^ – N next command from history ^ – A beginning of line 253 Key combinations SLES 15 SP6^ – E end of line ^ – B backward char ^ – F forward char ^ – H backspace ^ – D delete ^ – K delete line ^ – U discard line ^ – Y yank 18.5 Helpful GRUB 2 commands grub2-mkconfig Generates a new /boot/grub2/grub.cfg based on /etc/default/grub and the scripts from /etc/grub.d/ . EXAMPLE 18.1: USAGE OF GRUB2-MKCONFIG grub2-mkconfig -o /boot/grub2/grub.cfg Tip: Syntax check Running grub2-mkconfig without any parameters prints the configuration to STD- OUT where it can be reviewed. Use grub2-script-check after /boot/grub2/ grub.cfg has been written to check its syntax. 254 Helpful GRUB 2 commands SLES 15 SP6Important: grub2-mkconfig cannot repair UEFI Secure Boot tables If you are using UEFI Secure Boot and your system is not reaching GRUB 2 correctly anymore, you may need to additionally reinstall the Shim and regenerate the UEFI boot table. To do so, use: # shim-install --config-file=/boot/grub2/grub.cfg grub2-mkrescue Creates a bootable rescue image of your installed GRUB 2 configuration. EXAMPLE 18.2: USAGE OF GRUB2-MKRESCUE grub2-mkrescue -o save_path/name.iso iso grub2-script-check Checks the given le for syntax errors. EXAMPLE 18.3: USAGE OF GRUB2-SCRIPT-CHECK grub2-script-check /boot/grub2/grub.cfg grub2-once Set the default boot entry for the next boot only. To get the list of available boot entries use the --list option. EXAMPLE 18.4: USAGE OF GRUB2-ONCE grub2-once number_of_the_boot_entry Tip: grub2-once help Call the program without any option to get a full list of all possible options. 18.6 Rescue mode Rescue mode is a specific root user session for troubleshooting and repairing systems where the booting process fails. It offers a single-user environment with local le systems and core system services active. Network interfaces are not activated. To enter the rescue mode, follow these steps. 255 Rescue mode SLES 15 SP6PROCEDURE 18.3: ENTERING RESCUE MODE 1. Reboot the system. The boot screen appears, offering the GRUB 2 boot menu. 2. Select the menu entry to boot and press e to edit the boot line. 3. Append the following parameter to the line containing the kernel parameters: systemd.unit=rescue.target 4. Press Ctrl + X to boot with these settings. 5. Enter the password for root . 6. Make all the necessary changes. 7. Enter normal operating target again by entering systemctl isolate multi-user.tar- get or systemctl isolate graphical.target at the command line. 18.7 More information Extensive information about GRUB 2 is available at https://www.gnu.org/software/grub/ . Also refer to the grub info page. You can also search for the keyword “GRUB 2” in the Technical Information Search at https://www.suse.com/support to get information about special issues. 256 More information SLES 15 SP619 The systemd daemon systemd initializes the system. It has the process ID 1. systemd is started directly by the kernel and resists signal 9, which normally terminates processes. All other programs are started directly by systemd or by one of its child processes. systemd is a replacement for the System V init daemon and is fully compatible with System V init (by supporting init scripts). The main advantage of systemd is that it considerably speeds up boot time by parallelizing service starts. Furthermore, systemd only starts a service when it is really needed. Daemons are not started unconditionally at boot time, but when being required for the rst time. systemd also supports Kernel Control Groups (cgroups), creating snapshots, and restoring the system state. For more details see https://www.freedesktop.org/wiki/Software/systemd/ . Tip: systemd inside WSL Windows Subsystem for Linux (WSL) enables running Linux applications and distribu- tions under the Microsoft Windows operating system. WSL uses its init process instead of systemd . To enable systemd in SLES running in WSL, install the wsl_systemd pattern that automates the process: > sudo zypper in -t pattern wsl_systemd Alternatively, you can edit /etc/wsl.conf and add the following lines manually: [boot] systemd=true Keep in mind that the support for systemd in WSL is partial— systemd unit les must have reasonable process management behavior. 19.1 The systemd concept The following section explains the concept behind systemd . systemd is a system and session manager for Linux, compatible with System V and LSB init scripts. The main features of systemd include: parallelization capabilities socket and D-Bus activation for starting services 257 The systemd concept SLES 15 SP6on-demand starting of daemons tracking of processes using Linux cgroups creating snapshots and restoring of the system state maintains mount and automount points implements an elaborate transactional dependency-based service control logic 19.1.1 Unit file A unit configuration le contains information about a service, a socket, a device, a mount point, an automount point, a swap le or partition, a start-up target, a watched le system path, a timer controlled and supervised by systemd , a temporary system state snapshot, a resource management slice or a group of externally created processes. “Unit le” is a generic term used by systemd for the following: Service.  Information about a process (for example, running a daemon); le ends with .ser- vice Targets.  Used for grouping units and as synchronization points during start-up; le ends with .target Sockets.  Information about an IPC or network socket or a le system FIFO, for sock- et-based activation (like inetd ); le ends with .socket Path.  Used to trigger other units (for example, running a service when les change); le ends with .path Timer.  Information about a timer controlled, for timer-based activation; le ends with .timer Mount point.  Normally auto-generated by the fstab generator; le ends with .mount Automount point.  Information about a le system automount point; le ends with .auto- mount Swap.  Information about a swap device or le for memory paging; le ends with .swap 258 Unit file SLES 15 SP6Device.  Information about a device unit as exposed in the sysfs/udev(7) device tree; le ends with .device Scope / slice.  A concept for hierarchically managing resources of a group of processes; le ends with .scope/.slice For more information about systemd unit les, see https://www.freedesktop.org/software/sys- temd/man/latest/systemd.unit.html 19.2 Basic usage The System V init system uses several commands to handle services—the init scripts, insserv , telinit and others. systemd makes it easier to manage services, because there is only one command to handle most service related tasks: systemctl . It uses the “command plus subcom- mand” notation like git or zypper : systemctl GENERAL OPTIONS SUBCOMMAND SUBCOMMAND OPTIONS See man 1 systemctl for a complete manual. Tip: Terminal output and Bash completion If the output goes to a terminal (and not to a pipe or a le, for example), systemd commands send long output to a pager by default. Use the --no-pager option to turn o paging mode. systemd also supports bash-completion, allowing you to enter the rst letters of a sub- command and then press →| . This feature is only available in the bash shell and re- quires the installation of the package bash-completion . 19.2.1 Managing services in a running system Subcommands for managing services are the same as for managing a service with System V init ( start , stop , ...). The general syntax for service management commands is as follows: systemd systemctl reload|restart|start|status|stop|... MY_SERVICE(S) 259 Basic usage SLES 15 SP6System V init rcMY_SERVICE(S) reload|restart|start|status|stop|... systemd allows you to manage several services in one go. Instead of executing init scripts one after the other as with System V init, execute a command like the following: > sudo systemctl start MY_1ST_SERVICE MY_2ND_SERVICE To list all services available on the system: > sudo systemctl list-unit-files --type=service The following table lists the most important service management commands for systemd and System V init: TABLE 19.1: SERVICE MANAGEMENT COMMANDS Task systemd Command System V init Command Starting.  start start Stopping.  stop stop Restarting.  Shuts down services and starts restart restart them afterward. If a service is not yet run- ning, it is started. Restarting conditionally.  Restarts services if try-restart try-restart they are currently running. Does nothing for services that are not running. Reloading.  Tells services to reload their con- reload reload figuration les without interrupting opera- tion. Use case: tell Apache to reload a modi- fied httpd.conf configuration le. Not all services support reloading. Reloading or restarting.  Reloads services reload-or-restart n/a if reloading is supported, otherwise restarts 260 Managing services in a running system SLES 15 SP6Task systemd Command System V init Command them. If a service is not yet running, it is started. Reloading or restarting conditionally.  Re- reload-or-try-restart n/a loads services if reloading is supported, oth- erwise restarts them if currently running. Does nothing for services that are not run- ning. Getting detailed status information.  Lists in- status status formation about the status of services. The systemd command shows details such as description, executable, status, cgroup, and messages last issued by a service (see Sec- tion 19.6.9, “Debugging services”). The level of details displayed with the System V init dif- fers from service to service. Getting short status information.  Shows is-active status whether services are active or not. 19.2.2 Permanently enabling/disabling services The service management commands mentioned in the previous section let you manipulate ser- vices for the current session. systemd also lets you permanently enable or disable services, so they are automatically started when requested or are always unavailable. You can either do this by using YaST, or on the command line. 261 Permanently enabling/disabling services SLES 15 SP619.2.2.1 Enabling/disabling services on the command line The following table lists enabling and disabling commands for systemd and System V init: Important: Service start When enabling a service on the command line, it is not started automatically. It is sched- uled to be started with the next system start-up or runlevel/target change. To immediate- ly start a service after having enabled it, explicitly run systemctl start MY_SERVICE or rc MY_SERVICE start . TABLE 19.2: COMMANDS FOR ENABLING AND DISABLING SERVICES Task systemd Command System V init Com- mand Enabling.  systemctl enable insserv MY_SERVICE(S) MY_SERVICE(S) , chkconfig -a MY_SERVICE(S) Disabling.  systemctl disable insserv -r MY_SERVICE(S).service MY_SERVICE(S) , chkconfig -d MY_SERVICE(S) Checking.  Shows whether a systemctl is-enabled chkconfig service is enabled or not. MY_SERVICE MY_SERVICE Re-enabling.  Similar to systemctl reenable n/a restarting a service, this MY_SERVICE command rst disables and then enables a service. Use- ful to re-enable a service with its defaults. Masking.  After “disabling” systemctl mask MY_SERVICE n/a a service, it can still be started manually. To disable 262 Permanently enabling/disabling services SLES 15 SP6Task systemd Command System V init Com- mand a service, you need to mask it. Use with care. Unmasking.  A service that systemctl unmask MY_SERVICE n/a has been masked can only be used again after it has been unmasked. 19.3 System start and target management The entire process of starting the system and shutting it down is maintained by systemd . From this point of view, the kernel can be considered a background process to maintain all other processes and adjust CPU time and hardware access according to requests from other programs. 19.3.1 Targets compared to runlevels With System V init the system was booted into a so-called “Runlevel”. A runlevel defines how the system is started and what services are available in the running system. Runlevels are numbered; the most commonly known ones are 0 (shutting down the system), 3 (multiuser with network) and 5 (multiuser with network and display manager). systemd introduces a new concept by using so-called “target units”. However, it remains fully compatible with the runlevel concept. Target units are named rather than numbered and serve specific purposes. For example, the targets local-fs.target and swap.target mount local le systems and swap spaces. The target graphical.target provides a multiuser system with network and display manager capabilities and is equivalent to runlevel 5. Complex targets, such as graphical.target act as “meta” targets by combining a subset of other targets. Since systemd makes it easy to create custom targets by combining existing targets, it offers great flexibility. The following list shows the most important systemd target units. For a full list refer to man 7 systemd.special . 263 System start and target management SLES 15 SP6SELECTED systemd TARGET UNITS default.target The target that is booted by default. Not a “real” target, but rather a symbolic link to an- other target like graphic.target . Can be permanently changed via YaST (see Section 19.4, “Managing services with YaST”). To change it for a session, use the kernel parameter sys- temd.unit=MY_TARGET.target at the boot prompt. emergency.target Starts a minimal emergency root shell on the console. Only use it at the boot prompt as systemd.unit=emergency.target . graphical.target Starts a system with network, multiuser support and a display manager. halt.target Shuts down the system. mail-transfer-agent.target Starts all services necessary for sending and receiving mails. multi-user.target Starts a multiuser system with network. reboot.target Reboots the system. rescue.target Starts a single-user root session without network. Basic tools for system administration are available. The rescue target is suitable for solving multiple system problems, for example, failing logins or fixing issues with a display driver. To remain compatible with the System V init runlevel system, systemd provides special targets named runlevelX.target mapping the corresponding runlevels numbered X . To inspect the current target, use the command: systemctl get-default TABLE 19.3: SYSTEM V RUNLEVELS AND systemd TARGET UNITS System V run- systemd target Purpose level 0 runlevel0.target , halt.tar- System shutdown get , poweroff.target 264 Targets compared to runlevels SLES 15 SP6System V run- systemd target Purpose level 1, S runlevel1.target , rescue.tar- Single-user mode get , 2 runlevel2.target , mul- Local multiuser without remote ti-user.target , network 3 runlevel3.target , mul- Full multiuser with network ti-user.target , 4 runlevel4.target Unused/User-defined 5 runlevel5.target , graphi- Full multiuser with network and cal.target , display manager 6 runlevel6.target , reboot.tar- System reboot get , Important: systemd ignores /etc/inittab The runlevels in a System V init system are configured in /etc/inittab . systemd does not use this configuration. Refer to Section 19.5.5, “Creating custom targets” for instructions on how to create your own bootable target. 19.3.1.1 Commands to change targets Use the following commands to operate with target units: Task systemd Command System V init Command Change the cur- systemctl isolate MY_TARGET .target telinit X rent target/run- level 265 Targets compared to runlevels SLES 15 SP6Task systemd Command System V init Command Change to the systemctl default n/a default tar- get/runlevel Get the current systemctl list-units --type=target who -r target/runlevel With systemd , there is usually more than or one active target. The command lists all cur- runlevel rently active targets. persistently Use the Services Manager or run the follow- Use the Services Manager change the de- ing command: or change the line fault runlevel ln -sf /usr/lib/systemd/system/ id: X :initdefault: MY_TARGET .target /etc/systemd/system/de- in /etc/inittab fault.target Change the de- Enter the following option at the boot Enter the desired run- fault runlevel for prompt level number at the boot the current boot systemd.unit= MY_TARGET .target prompt. process Show a tar- systemctl show -p "Requires" MY_TAR- n/a get''s/runlevel''s GET .target dependencies systemctl show -p "Wants" MY_TAR- GET .target “Requires” lists the hard dependencies (the ones that must be resolved), whereas “Wants” lists the soft dependencies (the ones that get resolved if possible). 19.3.2 Debugging system start-up systemd offers the means to analyze the system start-up process. You can review the list of all services and their status (rather than having to parse /var/log/ ). systemd also allows you to scan the start-up procedure to nd out how much time each service start-up consumes. 266 Debugging system start-up SLES 15 SP619.3.2.1 Review start-up of services To review the complete list of services that have been started since booting the system, enter the command systemctl . It lists all active services like shown below (shortened). To get more information on a specific service, use systemctl status MY_SERVICE . EXAMPLE 19.1: LIST ACTIVE SERVICES # systemctl UNIT LOAD ACTIVE SUB JOB DESCRIPTION [...] iscsi.service loaded active exited Login and scanning of iSC+ kmod-static-nodes.service loaded active exited Create list of required s+ libvirtd.service loaded active running Virtualization daemon nscd.service loaded active running Name Service Cache Daemon chronyd.service loaded active running NTP Server Daemon polkit.service loaded active running Authorization Manager postfix.service loaded active running Postfix Mail Transport Ag+ rc-local.service loaded active exited /etc/init.d/boot.local Co+ rsyslog.service loaded active running System Logging Service [...] LOAD = Reflects whether the unit definition was properly loaded. ACTIVE = The high-level unit activation state, i.e. generalization of SUB. SUB = The low-level unit activation state, values depend on unit type. 161 loaded units listed. Pass --all to see loaded but inactive units, too. To show all installed unit files use ''systemctl list-unit-files''. To restrict the output to services that failed to start, use the --failed option: EXAMPLE 19.2: LIST FAILED SERVICES # systemctl --failed UNIT LOAD ACTIVE SUB JOB DESCRIPTION apache2.service loaded failed failed apache NetworkManager.service loaded failed failed Network Manager plymouth-start.service loaded failed failed Show Plymouth Boot Screen [...] 19.3.2.2 Debug start-up time To debug system start-up time, systemd offers the systemd-analyze command. It shows the total start-up time, a list of services ordered by start-up time and can also generate an SVG graphic showing the time services took to start in relation to the other services. 267 Debugging system start-up SLES 15 SP6Listing the system start-up time # systemd-analyze Startup finished in 2666ms (kernel) + 21961ms (userspace) = 24628ms Listing the services start-up time # systemd-analyze blame 15.000s backup-rpmdb.service 14.879s mandb.service 7.646s backup-sysconfig.service 4.940s postfix.service 4.921s logrotate.service 4.640s libvirtd.service 4.519s display-manager.service 3.921s btrfsmaintenance-refresh.service 3.466s lvm2-monitor.service 2.774s plymouth-quit-wait.service 2.591s firewalld.service 2.137s initrd-switch-root.service 1.954s ModemManager.service 1.528s rsyslog.service 1.378s apparmor.service [...] Services start-up time graphics # systemd-analyze plot > jupiter.example.com-startup.svg 268 Debugging system start-up SLES 15 SP619.3.2.3 Review the complete start-up process The commands above list the services that are started and their start-up times. For a more detailed overview, specify the following parameters at the boot prompt to instruct systemd to create a verbose log of the complete start-up procedure. systemd.log_level=debug systemd.log_target=kmsg Now systemd writes its log messages into the kernel ring buer. View that buer with dmesg : > dmesg -T | less 269 Debugging system start-up SLES 15 SP619.3.3 System V compatibility systemd is compatible with System V, allowing you to still use existing System V init scripts. However, there is at least one known issue where a System V init script does not work with systemd out of the box: starting a service as a different user via su or sudo in init scripts results in a failure of the script, producing an “Access denied” error. When changing the user with su or sudo , a PAM session is started. This session will be termi- nated after the init script is finished. As a consequence, the service that has been started by the init script is also terminated. To work around this error, proceed as follows: 1. Create a service le wrapper with the same name as the init script plus the le name extension .service : [Unit] Description=DESCRIPTION After=network.target [Service] User=USER Type=forking 1 PIDFile=PATH TO PID FILE 1 ExecStart=PATH TO INIT SCRIPT start ExecStop=PATH TO INIT SCRIPT stop ExecStopPost=/usr/bin/rm -f PATH TO PID FILE 1 [Install] WantedBy=multi-user.target 2 Replace all values written in UPPERCASE LETTERS with appropriate values. 1 Optional—only use if the init script starts a daemon. 2 multi-user.target also starts the init script when booting into graphical.tar- get . If it should only be started when booting into the display manager, use graph- ical.target . 2. Start the daemon with systemctl start APPLICATION . 270 System V compatibility SLES 15 SP619.4 Managing services with YaST Basic service management can also be done with the YaST Services Manager module. It supports starting, stopping, enabling and disabling services. It also lets you show a service''s status and change the default target. Start the YaST module with YaST System Services Manager. FIGURE 19.1: SERVICES MANAGER Changing the Default system target To change the target the system boots into, choose a target from the Default System Target drop-down box. The most often used targets are Graphical Interface (starting a graphical login screen) and Multi-User (starting the system in command line mode). Starting or stopping a service Select a service from the table. The State column shows whether it is currently running (Active) or not (Inactive). Toggle its status by choosing Start or Stop. Starting or stopping a service changes its status for the currently running session. To change its status throughout a reboot, you need to enable or disable it. Defining service start-up behavior Services can either be started automatically at boot time or manually. Select a service from the table. The Start column shows whether it is currently started Manually or On Boot. Toggle its status by choosing Start Mode. 271 Managing services with YaST SLES 15 SP6To change a service status in the current session, you need to start or stop it as described above. View a status messages To view the status message of a service, select it from the list and choose Show Details. The output is identical to the one generated by the command systemctl -l status MY_SERVICE . 19.5 Customizing systemd The following sections describe how to customize systemd unit les. 19.5.1 Where are unit files stored? systemd unit les shipped by SUSE are stored in /usr/lib/systemd/ . Customized unit les and unit le drop-ins are stored in /etc/systemd/ . Warning: Preventing your customization from being overwritten When customizing systemd , always use the directory /etc/systemd/ instead of /usr/ lib/systemd/ . Otherwise your changes will be overwritten by the next update of sys- temd . 19.5.2 Override with drop-in files Drop-in les (or drop-ins) are partial unit les that override only specific settings of the unit le. Drop-ins have higher precedence over main configuration les. The command systemctl edit SERVICE starts the default text editor and creates a directory with an empty override.conf le in /etc/systemd/system/NAME.service.d/ . The command also ensures that the running systemd process is notified about the changes. For example, to change the amount of time that the system waits for MariaDB to start, run sudo systemctl edit mariadb.service and edit the opened le to include the modified lines only: # Configures the time to wait for start-up/stop TimeoutSec=300 272 Customizing systemd SLES 15 SP6Adjust the TimeoutSec value and save the changes. To enable the changes, run sudo system- ctl daemon-reload . For further information, refer to the man pages that can be evoked with the man 1 systemctl command. Warning: Creating a copy of a full unit file If you use the --full option in the systemctl edit --full SERVICE command, a copy of the original unit le is created where you can modify specific options. We do not recommend such customization because when the unit le is updated by SUSE, its changes are overridden by the customized copy in the /etc/systemd/system/ directo- ry. Moreover, if SUSE provides updates to distribution drop-ins, they override the copy of the unit le created with --full . To prevent this confusion and always have your customization valid, use drop-ins. 19.5.3 Creating drop-in files manually Apart from using the systemctl edit command, you can create drop-ins manually to have more control over their priority. Such drop-ins let you extend both unit and daemon configura- tion les without having to edit or override the les themselves. They are stored in the following directories: /etc/systemd/*.conf.d/ , /etc/systemd/system/*.service.d/ Drop-ins added and customized by system administrators. /usr/lib/systemd/*.conf.d/ , /usr/lib/systemd/system/*.service.d/ Drop-ins installed by customization packages to override upstream settings. For example, SUSE ships systemd-default-settings . Tip See the man page man 5 systemd.unit for the full list of unit search paths. For example, to disable the rate limiting that is enforced by the default setting of systemd-jour- nald , follow these steps: 1. Create a directory called /etc/systemd/journald.conf.d . 273 Creating drop-in files manually SLES 15 SP6> sudo mkdir /etc/systemd/journald.conf.d Note The directory name must follow the service name that you want to patch with the drop-in le. 2. In that directory, create a le /etc/systemd/journald.conf.d/60-rate-limit.conf with the option that you want to override, for example: > cat /etc/systemd/journald.conf.d/60-rate-limit.conf # Disable rate limiting RateLimitIntervalSec=0 3. Save your changes and restart the service of the corresponding systemd daemon. > sudo systemctl restart systemd-journald Note: Avoiding name conflicts To avoid name conflicts between your drop-ins and les shipped by SUSE, it is recom- mended to prefix all drop-ins with a two-digit number and a dash, for example, 80- override.conf . The following ranges are reserved: 0-19 is reserved for systemd upstream. 20-29 is reserved for systemd shipped by SUSE. 30-39 is reserved for SUSE packages other than systemd . 40-49 is reserved for third-party packages. 50 is reserved for unit drop-in les created with systemctl set-property . Use a two-digit number above this range to ensure that none of the drop-ins shipped by SUSE can override your own drop-ins. 274 Creating drop-in files manually SLES 15 SP6Tip You can use systemctl cat $UNIT to list and verify which les are taken into account in the units configuration. Tip Because the configuration of systemd components can be scattered across different places on the le system, it might be hard to get a global overview. To inspect the con- figuration of a systemd component, use the following commands: systemctl cat UNIT_PATTERN prints configuration les related to one or more systemd units, for example: > systemctl cat atd.service systemd-analyze cat-config DAEMON_NAME_OR_PATH copies the contents of a configuration le and drop-ins for a systemd daemon, for example: > systemd-analyze cat-config systemd/journald.conf 19.5.4 Converting xinetd services to systemd Since the release of SUSE Linux Enterprise Server 15, the xinetd infrastructure has been re- moved. This section outlines how to convert existing custom xinetd service les to systemd sockets. For each xinetd service le, you need at least two systemd unit les: the socket le ( *.sock- et ) and an associated service le ( *.service ). The socket le tells systemd which socket to create, and the service le tells systemd which executable to start. Consider the following example xinetd service le: # cat /etc/xinetd.d/example service example { socket_type = stream protocol = tcp port = 10085 wait = no 275 Converting xinetd services to systemd SLES 15 SP6user = user group = users groups = yes server = /usr/libexec/example/exampled server_args = -auth=bsdtcp exampledump disable = no } To convert it to systemd , you need the following two matching les: # cat /usr/lib/systemd/system/example.socket [Socket] ListenStream=0.0.0.0:10085 Accept=false [Install] WantedBy=sockets.target # cat /usr/lib/systemd/system/example.service [Unit] Description=example [Service] ExecStart=/usr/libexec/example/exampled -auth=bsdtcp exampledump User=user Group=users StandardInput=socket For a complete list of the systemd “socket” and “service” le options, refer to the systemd.socket and systemd.service manual pages ( man 5 systemd.socket , man 5 systemd.service ). 19.5.5 Creating custom targets On System V init SUSE systems, runlevel 4 is unused to allow administrators to create their own runlevel configuration. systemd allows you to create any number of custom targets. It is suggested to start by adapting an existing target such as graphical.target . 1. Copy the configuration le /usr/lib/systemd/system/graphical.target to /etc/ systemd/system/MY_TARGET.target and adjust it according to your needs. 2. The configuration le copied in the previous step already covers the required (“hard”) dependencies for the target. To also cover the wanted (“soft”) dependencies, create a directory /etc/systemd/system/MY_TARGET.target.wants . 276 Creating custom targets SLES 15 SP63. For each wanted service, create a symbolic link from /usr/lib/systemd/system into / etc/systemd/system/MY_TARGET.target.wants . 4. When you have finished setting up the target, reload the systemd configuration to make the new target available: > sudo systemctl daemon-reload 19.6 Advanced usage The following sections cover advanced topics for system administrators. For even more advanced systemd documentation, refer to Lennart Pöttering''s series about systemd for administrators at https://0pointer.de/blog/projects/ . 19.6.1 Cleaning temporary directories systemd supports cleaning temporary directories regularly. The configuration from the previ- ous system version is automatically migrated and active. tmpfiles.d—which is responsible for managing temporary les—reads its configuration from /etc/tmpfiles.d/*.conf , /run/ tmpfiles.d/*.conf , and /usr/lib/tmpfiles.d/*.conf les. Configuration placed in /etc/ tmpfiles.d/*.conf overrides related configurations from the other two directories ( /usr/ lib/tmpfiles.d/*.conf is where packages store their configuration les). The configuration format is one line per path containing action and path, and optionally mode, ownership, age and argument elds, depending on the action. The following example unlinks the X11 lock les: Type Path Mode UID GID Age Argument r /tmp/.X[0-9]*-lock To get the status the tmpfile timer: > sudo systemctl status systemd-tmpfiles-clean.timer systemd-tmpfiles-clean.timer - Daily Cleanup of Temporary Directories Loaded: loaded (/usr/lib/systemd/system/systemd-tmpfiles-clean.timer; static) Active: active (waiting) since Tue 2018-04-09 15:30:36 CEST; 1 weeks 6 days ago Docs: man:tmpfiles.d(5) man:systemd-tmpfiles(8) Apr 09 15:30:36 jupiter systemd[1]: Starting Daily Cleanup of Temporary Directories. Apr 09 15:30:36 jupiter systemd[1]: Started Daily Cleanup of Temporary Directories. 277 Advanced usage SLES 15 SP6For more information on temporary les handling, see man 5 tmpfiles.d . 19.6.2 System log Section 19.6.9, “Debugging services” explains how to view log messages for a given service. How- ever, displaying log messages is not restricted to service logs. You can also access and query the complete log messages written by systemd—the so-called “Journal”. Use the command jour- nalctl to display the complete log messages starting with the oldest entries. Refer to man 1 journalctl for options such as applying filters or changing the output format. 19.6.3 Snapshots You can save the current state of systemd to a named snapshot and later revert to it with the isolate subcommand. This is useful when testing services or custom targets, because it allows you to return to a defined state at any time. A snapshot is only available in the current session and will automatically be deleted on reboot. A snapshot name must end in .snapshot . Create a snapshot > sudo systemctl snapshot MY_SNAPSHOT.snapshot Delete a snapshot > sudo systemctl delete MY_SNAPSHOT.snapshot View a snapshot > sudo systemctl show MY_SNAPSHOT.snapshot Activate a snapshot > sudo systemctl isolate MY_SNAPSHOT.snapshot 19.6.4 Loading kernel modules With systemd , kernel modules can automatically be loaded at boot time via a configuration le in /etc/modules-load.d . The le should be named MODULE .conf and have the following content: # load module MODULE at boot time 278 System log SLES 15 SP6MODULE In case a package installs a configuration le for loading a kernel module, the le gets installed to /usr/lib/modules-load.d . If two configuration les with the same name exist, the one in /etc/modules-load.d tales precedence. For more information, see the modules-load.d(5) man page. 19.6.5 Performing actions before loading a service With System V init actions that need to be performed before loading a service, needed to be specified in /etc/init.d/before.local . This procedure is no longer supported with sys- temd . If you need to do actions before starting services, do the following: Loading kernel modules Create a drop-in le in /etc/modules-load.d directory (see man modules-load.d for the syntax) Creating Files or Directories, Cleaning-up Directories, Changing Ownership Create a drop-in le in /etc/tmpfiles.d (see man tmpfiles.d for the syntax) Other tasks Create a system service le, for example, /etc/systemd/system/before.service , from the following template: [Unit] Before=NAME OF THE SERVICE YOU WANT THIS SERVICE TO BE STARTED BEFORE [Service] Type=oneshot RemainAfterExit=true ExecStart=YOUR_COMMAND # beware, executable is run directly, not through a shell, check the man pages # systemd.service and systemd.unit for full syntax [Install] # target in which to start the service WantedBy=multi-user.target #WantedBy=graphical.target When the service le is created, you should run the following commands (as root ): > sudo systemctl daemon-reload > sudo systemctl enable before 279 Performing actions before loading a service SLES 15 SP6Every time you modify the service le, you need to run: > sudo systemctl daemon-reload 19.6.6 Kernel control groups (cgroups) On a traditional System V init system, it is not always possible to match a process to the service that spawned it. Certain services, such as Apache, spawn a lot of third-party processes (for example, CGI or Java processes), which themselves spawn more processes. This makes a clear assignment difficult or even impossible. Additionally, a service may not finish correctly, leaving certain children alive. systemd solves this problem by placing each service into its own cgroup. cgroups are a ker- nel feature that allows aggregating processes and all their children into hierarchical organized groups. systemd names each cgroup after its service. Since a non-privileged process is not al- lowed to “leave” its cgroup, this provides an effective way to label all processes spawned by a service with the name of the service. To list all processes belonging to a service, use the command systemd-cgls , for example: EXAMPLE 19.3: LIST ALL PROCESSES BELONGING TO A SERVICE # systemd-cgls --no-pager ├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 20 ├─user.slice │ └─user-1000.slice │ ├─session-102.scope │ │ ├─12426 gdm-session-worker [pam/gdm-password] │ │ ├─15831 gdm-session-worker [pam/gdm-password] │ │ ├─15839 gdm-session-worker [pam/gdm-password] │ │ ├─15858 /usr/lib/gnome-terminal-server [...] └─system.slice ├─systemd-hostnamed.service │ └─17616 /usr/lib/systemd/systemd-hostnamed ├─cron.service │ └─1689 /usr/sbin/cron -n ├─postfix.service │ ├─ 1676 /usr/lib/postfix/master -w │ ├─ 1679 qmgr -l -t fifo -u │ └─15590 pickup -l -t fifo -u ├─sshd.service 280 Kernel control groups (cgroups) SLES 15 SP6│ └─1436 /usr/sbin/sshd -D [...] See Book “System Analysis and Tuning Guide”, Chapter 10 “Kernel control groups” for more information about cgroups. 19.6.7 Terminating services (sending signals) As explained in Section 19.6.6, “Kernel control groups (cgroups)”, it is not always possible to assign a process to its parent service process in a System V init system. This makes it difficult to stop a service and its children. Child processes that have not been terminated remain as zombie processes. systemd ''s concept of confining each service into a cgroup makes it possible to identify all child processes of a service and therefore allows you to send a signal to each of these processes. Use systemctl kill to send signals to services. For a list of available signals refer to man 7 signals . Sending SIGTERM to a service SIGTERM is the default signal that is sent. > sudo systemctl kill MY_SERVICE Sending SIGNAL to a service Use the -s option to specify the signal that should be sent. > sudo systemctl kill -s SIGNAL MY_SERVICE Selecting processes By default the kill command sends the signal to all processes of the specified cgroup. You can restrict it to the control or the main process. The latter is, for example, useful to force a service to reload its configuration by sending SIGHUP : > sudo systemctl kill -s SIGHUP --kill-who=main MY_SERVICE 19.6.8 Important notes on the D-Bus service The D-Bus service is the message bus for communication between systemd clients and the systemd manager that is running as pid 1. Even though dbus is a stand-alone daemon, it is an integral part of the init infrastructure. 281 Terminating services (sending signals) SLES 15 SP6Stopping dbus or restarting it in the running system is similar to an attempt to stop or restart PID 1. It breaks the systemd client/server communication and makes most systemd functions unusable. Therefore, terminating or restarting dbus is neither recommended nor supported. Updating the dbus or dbus -related packages requires a reboot. When in doubt whether a reboot is necessary, run the sudo zypper ps -s . If dbus appears among the listed services, you need to reboot the system. Keep in mind that dbus is updated even when automatic updates are configured to skip the packages that require reboot. 19.6.9 Debugging services By default, systemd is not overly verbose. If a service was started successfully, no output is produced. In case of a failure, a short error message is displayed. However, systemctl status provides a means to debug the start-up and operation of a service. systemd comes with its own logging mechanism (“The Journal”) that logs system messages. This allows you to display the service messages together with status messages. The status command works similar to tail and can also display the log messages in different formats, making it a powerful debugging tool. Show service start-up failure Whenever a service fails to start, use systemctl status MY_SERVICE to get a detailed error message: # systemctl start apache2 Job failed. See system journal and ''systemctl status'' for details. # systemctl status apache2 Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled) Active: failed (Result: exit-code) since Mon, 04 Apr 2018 16:52:26 +0200; 29s ago Process: 3088 ExecStart=/usr/sbin/start_apache2 -D SYSTEMD -k start (code=exited, status=1/FAILURE) CGroup: name=systemd:/system/apache2.service Apr 04 16:52:26 g144 start_apache2[3088]: httpd2-prefork: Syntax error on line 205 of /etc/apache2/httpd.conf: Syntax error on li...alHost> 282 Debugging services SLES 15 SP6Show last N service messages The default behavior of the status subcommand is to display the last ten messages a service issued. To change the number of messages to show, use the --lines=N parameter: > sudo systemctl status chronyd > sudo systemctl --lines=20 status chronyd Show service messages in append mode To display a “live stream” of service messages, use the --follow option, which works like tail -f : > sudo systemctl --follow status chronyd Messages output format The --output=MODE parameter allows you to change the output format of service mes- sages. The most important modes available are: short The default format. Shows the log messages with a human readable time stamp. verbose Full output with all elds. cat Terse output without time stamps. 19.7 systemd timer units Similar to cron, systemd timer units provide a mechanism for scheduling jobs on Linux. Al- though systemd timer units serve the same purpose as cron, they offer several advantages. Jobs scheduled using a timer unit can depend on other systemd services. Timer units are treated as regular systemd services, so can be managed with systemctl . Timers can be realtime and monotonic. Time units are logged to the systemd journal, which makes it easier to monitor and trou- bleshoot them. systemd timer units are identified by the .timer le name extension. 283 systemd timer units SLES 15 SP619.7.1 systemd timer types Timer units can use monotonic and realtime timers. Similar to cronjobs, realtime timers are triggered on calendar events. Realtime timers are defined using the option OnCalendar . Monotonic timers are triggered at a specified time elapsed from a certain starting point. The latter could be a system boot or system unit activation event. There are several options for defining monotonic timers including OnBootSec , OnUnitActiveSec , and OnTypeSec . Monotonic timers are not persistent, and they are reset after each reboot. 19.7.2 systemd timers and service units Every timer unit must have a corresponding systemd unit le it controls. In other words, a .timer le activates and manages the corresponding .service le. When used with a timer, the .service le does not require an [Install] section, as the service is managed by the timer. 19.7.3 Practical example To understand the basics of systemd timer units, we set up a timer that triggers the foo.sh shell script. First step is to create a systemd service unit that controls the shell script. To do this, open a new text le for editing and add the following service unit definition: [Unit] Description="Foo shell script" [Service] ExecStart=/usr/local/bin/foo.sh Save the le under the name foo.service in the directory /etc/systemd/system/ . Next, open a new text le for editing and add the following timer definition: [Unit] Description="Run foo shell script" [Timer] 284 systemd timer types SLES 15 SP6OnBootSec=5min OnUnitActiveSec=24h Unit=foo.service [Install] WantedBy=multi-user.target The [Timer] section in the example above specifies what service to trigger ( foo.service ) and when to trigger it. In this case, the option OnBootSec specifies a monotonic timer that triggers the service ve minutes after the system boot, while the option OnUnitActiveSec triggers the service 24 hours after the service has been activated (that is, the timer triggers the service once a day). Finally, the option WantedBy specifies that the timer should start when the system has reached the multiuser target. Instead of a monotonic timer, you can specify a real-time one using the option OnCalendar . The following realtime timer definition triggers the related service unit once a week, starting on Monday at 12:00. [Timer] OnCalendar=weekly Persistent=true The option Persistent=true indicates that the service is triggered immediately after the timer activation if the timer missed the last start time (for example, because of the system being powered o). The option OnCalendar can also be used to define specific dates times for triggering a service using the following format: DayOfWeek Year-Month-Day Hour:Minute:Second . The example below triggers a service at 5am every day: OnCalendar=*-*-* 5:00:00 You can use an asterisk to specify any value, and commas to list possible values. Use two values separated by .. to indicate a contiguous range. The following example triggers a service at 6pm on Friday of every month: OnCalendar=Fri *-*-1..7 18:00:00 To trigger a service at different times, you can specify several OnCalendar entries: OnCalendar=Mon..Fri 10:00 OnCalendar=Sat,Sun 22:00 In the example above, a service is triggered at 10am on week days and at 10pm on weekends. 285 Practical example SLES 15 SP6When you are done editing the timer unit le, save it under the name foo.timer in the /etc/ systemd/system/ directory. To check the correctness of the created unit les, run the following command: > sudo systemd-analyze verify /etc/systemd/system/foo.* If the command returns no output, the les have passed the verification successfully. To start the timer, use the command sudo systemctl start foo.timer . To enable the timer on boot, run the command sudo systemctl enable foo.timer . 19.7.4 Managing systemd timers Since timers are treated as regular systemd units, you can manage them using systemctl . You can start a timer with systemctl start , enable a timer with systemctl enable , and so on. Additionally, you can list all active timers using the command systemctl list-timers . To list all timers, including inactive ones, run the command systemctl list-timers --all . 19.8 More information For more information on systemd refer to the following online resources: Homepage https://systemd.io/ systemd for administrators Lennart Pöttering, one of the systemd authors, has written a series of blog entries (13 at the time of writing this chapter). Find them at https://0pointer.de/blog/projects/ . 286 Managing systemd timers SLES 15 SP6III System 20 32-bit and 64-bit applications in a 64-bit system environment 288 21 journalctl: query the systemd journal 290 22 update-alternatives: managing multiple versions of commands and files 298 23 Basic networking 306 24 Printer operation 379 25 Graphical user interface 394 26 Accessing file systems with FUSE 411 27 Installing multiple kernel versions 413 28 Managing kernel modules 420 29 Dynamic kernel device management with udev 423 30 Special system features 435 31 Using NetworkManager 44720 32-bit and 64-bit applications in a 64-bit system environment SUSE® Linux Enterprise Server is available for several 64-bit platforms. The developers have not ported all 32-bit applications to 64-bit systems. This chapter offers a brief overview of 32- bit support implementation on 64-bit SUSE Linux Enterprise Server platforms. SUSE Linux Enterprise Server for the 64-bit platforms POWER, IBM Z and AMD64/Intel 64 is designed so that existing 32-bit applications run in the 64-bit environment “out-of-the-box.” The corresponding 32-bit platforms are POWER for POWER, and x86 for AMD64/Intel 64. This support means that you can continue to use your preferred 32-bit applications without waiting for a corresponding 64-bit port to become available. The current POWER system runs most applications in 32-bit mode, but you can run 64-bit applications. Note: No support for building 32-bit applications SUSE Linux Enterprise Server does not support compilation of 32-bit applications. It only offers runtime support for 32-bit binaries. 20.1 Runtime support Important: Conflicts between application versions If an application is available for both 32-bit and 64-bit environments, installing both versions may cause problems. In such cases, decide on one version to install to avoid potential runtime errors. An exception to this rule is PAM (pluggable authentication modules). SUSE Linux Enter- prise Server uses PAM in the authentication process as a layer that mediates between user and application. Always install both PAM versions on 64-bit operating systems that also run 32-bit applications. For correct execution, every application requires a range of libraries. Because the names are identical for the 32-bit and 64-bit versions of these libraries, they must be differentiated from each other in another way. 288 Runtime support SLES 15 SP6To retain compatibility with 32-bit versions, 64-bit and 32-bit libraries are stored in the same location. The 32-bit version of libc.so.6 is located under /lib/libc.so.6 in both 32-bit and 64-bit environments. All 64-bit libraries and object les are located in directories called lib64 . The 64-bit object les normally found under /lib and /usr/lib are now found under /lib64 and /usr/lib64 . This means that space is available for 32-bit libraries under /lib and /usr/lib , so the le name for both versions can remain unchanged. If the data content of 32-bit subdirectories under /lib does not depend on word size, they are not moved. This scheme conforms to LSB (Linux Standards Base) and FHS (Filesystem Hierarchy Standard). 20.2 Kernel specifications The 64-bit kernels for AMD64/Intel 64, POWER and IBM Z offer both a 64-bit and a 32-bit kernel ABI (application binary interface). The latter is identical to the ABI for the corresponding 32-bit kernel. This means that communication between both 32-bit and 64-bit applications with 64-bit kernels are identical. The 32-bit system call emulation for 64-bit kernels does not support all the APIs used by system programs. This depends on the platform. For this reason, few applications, like lspci , must be compiled on non-POWER platforms as 64-bit programs to function properly. On IBM Z, not all ioctls are available in the 32-bit kernel ABI. A 64-bit kernel can only load 64-bit kernel modules. You must compile 64-bit modules specifi- cally for 64-bit kernels. It is not possible to use 32-bit kernel modules with 64-bit kernels. Tip: Kernel-loadable modules Certain applications require separate kernel-loadable modules. If you intend to use a 32- bit application in a 64-bit system environment, contact the provider of the application and SUSE. Make sure that the 64-bit version of the kernel-loadable module and the 32- bit compiled version of the kernel API are available for this module. 289 Kernel specifications SLES 15 SP621 journalctl: query the systemd journal systemd features its own logging system called journal. There is no need to run a syslog -based service, as all system events are written to the journal. The journal itself is a system service managed by systemd . Its full name is systemd-jour- nald.service . It collects and stores logging data by maintaining structured indexed journals based on logging information received from the kernel, user processes, standard input, and sys- tem service errors. The systemd-journald service is on by default: > sudo systemctl status systemd-journald systemd-journald.service - Journal Service Loaded: loaded (/usr/lib/systemd/system/systemd-journald.service; static) Active: active (running) since Mon 2014-05-26 08:36:59 EDT; 3 days ago Docs: man:systemd-journald.service(8) man:journald.conf(5) Main PID: 413 (systemd-journal) Status: "Processing requests..." CGroup: /system.slice/systemd-journald.service └─413 /usr/lib/systemd/systemd-journald [...] 21.1 Making the journal persistent The journal stores log data in /run/log/journal/ by default. Because the /run/ directory is volatile by nature, log data is lost at reboot. To make the log data persistent, create the directory /var/log/journal/ and make sure it has the correct access modes and ownership, so the systemd-journald service can store its data. To switch to persistent logging, execute the following commands: > sudo mkdir /var/log/journal > sudo systemd-tmpfiles --create --prefix=/var/log/journal > sudo journalctl --flush Any log data stored in /run/log/journal/ will be ushed into /var/log/journal/ . 21.2 journalctl: useful switches This section introduces several common useful options to enhance the default journalctl behavior. All switches are described in the journalctl man page, man 1 journalctl . 290 Making the journal persistent SLES 15 SP6Tip: Messages related to a specific executable To show all journal messages related to a specific executable, specify the full path to the executable: > sudo journalctl /usr/lib/systemd/systemd -f Shows only the most recent journal messages, and prints new log entries as they are added to the journal. Prints the messages and jumps to the end of the journal, so that the latest entries are visible within the pager. -r Prints the messages of the journal in reverse order, so that the latest entries are listed rst. -k Shows only kernel messages. This is equivalent to the eld match _TRANSPORT=kernel (see Section 21.3.3, “Filtering based on fields”). -u Shows only messages for the specified systemd unit. This is equivalent to the eld match _SYSTEMD_UNIT=UNIT (see Section 21.3.3, “Filtering based on fields”). > sudo journalctl -u apache2 [...] Jun 03 10:07:11 pinkiepie systemd[1]: Starting The Apache Webserver... Jun 03 10:07:12 pinkiepie systemd[1]: Started The Apache Webserver. 21.3 Filtering the journal output When called without switches, journalctl shows the full content of the journal, the oldest entries listed rst. The output can be filtered by specific switches and elds. 21.3.1 Filtering based on a boot number journalctl can filter messages based on a specific system boot. To list all available boots, run 291 Filtering the journal output SLES 15 SP6> sudo journalctl --list-boots -1 097ed2cd99124a2391d2cffab1b566f0 Mon 2014-05-26 08:36:56 EDT—Fri 2014-05-30 05:33:44 EDT 0 156019a44a774a0bb0148a92df4af81b Fri 2014-05-30 05:34:09 EDT—Fri 2014-05-30 06:15:01 EDT The rst column lists the boot offset: 0 for the current boot, -1 for the previous one, -2 for the one before that, etc. The second column contains the boot ID followed by the limiting time stamps of the specific boot. Show all messages from the current boot: > sudo journalctl -b If you need to see journal messages from the previous boot, add an offset parameter. The fol- lowing example outputs the previous boot messages: > sudo journalctl -b -1 Another way is to list boot messages based on the boot ID. For this purpose, use the _BOOT_ID eld: > sudo journalctl _BOOT_ID=156019a44a774a0bb0148a92df4af81b 21.3.2 Filtering based on time interval You can filter the output of journalctl by specifying the starting and/or ending date. The date specification should be of the format 2014-06-30 9:17:16 . If the time part is omitted, midnight is assumed. If seconds are omitted, :00 is assumed. If the date part is omitted, the current day is assumed. Instead of numeric expression, you can specify the keywords yesterday , today or tomorrow . They refer to midnight of the day before the current day, of the current day, or of the day after the current day. If you specify now , it refers to the current time. You can also specify relative times prefixed with - or + , referring to times before or after the current time. Show only new messages since now, and update the output continuously: > sudo journalctl --since "now" -f Show all messages since last midnight till 3:20am: > sudo journalctl --since "today" --until "3:20" 292 Filtering based on time interval SLES 15 SP621.3.3 Filtering based on fields You can filter the output of the journal by specific elds. The syntax of a eld to be matched is FIELD_NAME=MATCHED_VALUE , such as _SYSTEMD_UNIT=httpd.service . You can specify mul- tiple matches in a single query to filter the output messages even more. See man 7 sys- temd.journal-fields for a list of default elds. Show messages produced by a specific process ID: > sudo journalctl _PID=1039 Show messages belonging to a specific user ID: # journalctl _UID=1000 Show messages from the kernel ring buer (the same as dmesg produces): > sudo journalctl _TRANSPORT=kernel Show messages from the service''s standard or error output: > sudo journalctl _TRANSPORT=stdout Show messages produced by a specified service only: > sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service If two different elds are specified, only entries that match both expressions at the same time are shown: > sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1488 If two matches refer to the same eld, all entries matching either expression are shown: > sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service _SYSTEMD_UNIT=dbus.service You can use the + separator to combine two expressions in a logical OR . The following example shows all messages from the Avahi service process with the process ID 1480 together with all messages from the D-Bus service: > sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1480 + _SYSTEMD_UNIT=dbus.service 21.4 Investigating systemd errors This section introduces a simple example to illustrate how to nd and x the error reported by systemd during apache2 start-up. 293 Filtering based on fields SLES 15 SP61. Try to start the apache2 service: # systemctl start apache2 Job for apache2.service failed. See ''systemctl status apache2'' and ''journalctl -xn'' for details. 2. Let us see what the service''s status says: > sudo systemctl status apache2 apache2.service - The Apache Webserver Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled) Active: failed (Result: exit-code) since Tue 2014-06-03 11:08:13 CEST; 7min ago Process: 11026 ExecStop=/usr/sbin/start_apache2 -D SYSTEMD -DFOREGROUND \ -k graceful-stop (code=exited, status=1/FAILURE) The ID of the process causing the failure is 11026. 3. Show the verbose version of messages related to process ID 11026: > sudo journalctl -o verbose _PID=11026 [...] MESSAGE=AH00526: Syntax error on line 6 of /etc/apache2/default-server.conf: [...] MESSAGE=Invalid command ''DocumenttRoot'', perhaps misspelled or defined by a module [...] 4. Fix the typo inside /etc/apache2/default-server.conf , start the apache2 service, and print its status: > sudo systemctl start apache2 && systemctl status apache2 apache2.service - The Apache Webserver Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled) Active: active (running) since Tue 2014-06-03 11:26:24 CEST; 4ms ago Process: 11026 ExecStop=/usr/sbin/start_apache2 -D SYSTEMD -DFOREGROUND -k graceful-stop (code=exited, status=1/FAILURE) Main PID: 11263 (httpd2-prefork) Status: "Processing requests..." CGroup: /system.slice/apache2.service ├─11263 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] ├─11280 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] ├─11281 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] ├─11282 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] ├─11283 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] └─11285 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...] 294 Investigating systemd errors SLES 15 SP621.5 Journald configuration The behavior of the systemd-journald service can be adjusted by modifying /etc/sys- temd/journald.conf . This section introduces only basic option settings. For a complete le description, see man 5 journald.conf . You need to restart the journal for the changes to take effect with > sudo systemctl restart systemd-journald 21.5.1 Changing the journal size limit If the journal log data is saved to a persistent location (see Section 21.1, “Making the journal persis- tent”), it uses up to 10% of the le system the /var/log/journal resides on. For example, if / var/log/journal is located on a 30 GB /var partition, the journal may use up to 3 GB of the disk space. To change this limit, change (and uncomment) the SystemMaxUse option: SystemMaxUse=50M 21.5.2 Forwarding the journal to /dev/ttyX You can forward the journal to a terminal device to inform you about system messages on a preferred terminal screen, for example, /dev/tty12 . Change the following journald options to ForwardToConsole=yes TTYPath=/dev/tty12 21.5.3 Forwarding the journal to syslog facility Journald is backward compatible with traditional syslog implementations such as rsyslog . Make sure the following is valid: rsyslog is installed. > sudo rpm -q rsyslog rsyslog-7.4.8-2.16.x86_64 rsyslog service is enabled. 295 Journald configuration SLES 15 SP6> sudo systemctl is-enabled rsyslog enabled Forwarding to syslog is enabled in /etc/systemd/journald.conf . ForwardToSyslog=yes 21.6 Using YaST to filter the systemd journal For an easy way of filtering the systemd journal (without dealing with the journalctl syntax), you can use the YaST journal module. After installing it with sudo zypper in yast2-journal , start it from YaST by selecting System Systemd Journal. Alternatively, start it from command line by entering sudo yast2 journal . FIGURE 21.1: YAST SYSTEMD JOURNAL The module displays the log entries in a table. The search box on top allows you to search for entries that contain certain characters, similar to using grep . To filter the entries by date and time, unit, le or priority, click Change filters and set the respective options. 296 Using YaST to filter the systemd journal SLES 15 SP621.7 Viewing logs in GNOME You can view the journal with GNOME Logs. Start it from the application menu. To view system log messages, it needs to be run as root, for example, with xdg-su gnome-logs . This command can be executed when pressing Alt – F2 . 297 Viewing logs in GNOME SLES 15 SP622 update-alternatives: managing multiple ver- sions of commands and files Often, there are several versions of the same tool installed on a system. To give ad- ministrators a choice and to make it possible to install and use different versions side by side, the alternatives system allows managing such versions consistently. 22.1 Overview On SUSE Linux Enterprise Server, several programs perform the same or similar tasks. For ex- ample, if Java 1.7 and Java 1.8 are both installed on the system, the alternatives system script ( update-alternatives ) is called from inside the RPM package. By default, the alternatives system will refer to version 1.8: higher versions also have a higher priority. However, the ad- ministrator can change the default and can point the generic name to version 1.7. The following terminology is used in this chapter: TERMINOLOGY Administrative directory The default /var/lib/rpm/alternatives directory contains information about the cur- rent state of alternatives. Alternative The name of a specific le in the le system, which can be made accessible via a generic name using the alternatives system. Alternatives directory The default /etc/alternatives directory containing symbolic links. Generic name A name (for example, /usr/bin/edit ) that refers to one le out of several available using the alternatives system. Link group A set of related symbolic links that can be updated as a group. Master link The link in a link group that determines how the other links in the group are configured. 298 Overview SLES 15 SP6Slave link A link in a link group controlled by the master link. Symbolic link (symlink) A le that is a reference to another le in the same le system. The alternatives system uses symbolic links in the alternatives directory to switch between versions of a le. Symbolic links in the alternatives directory can be modified by the administrator through the update-alternatives command. The alternatives system provides the update-alternatives command to create, remove, main- tain and show information about symbolic links. While these symbolic links normally point to commands, they can also point to JAR archives, man pages, and other les. Examples in this chapter use commands and man pages, but they are also applicable to other le types. The alternatives system uses the alternatives directory to collect links to possible alternatives. When a new package with an alternative is installed, the new alternative is added to the system. Whether the new package''s alternative is selected as the default depends on its priority and on the mode that is set. Packages with a higher version also have a higher priority. The alternatives system can operate in two modes: Automatic mode.  In this mode, the alternatives system ensures that the links in the group point to the highest priority alternatives appropriate for the group. Manual mode.  In this mode, the alternatives system does not make any changes to the system administrator''s settings. For example, the java command has the following link hierarchy in the alternatives system: EXAMPLE 22.1: ALTERNATIVES SYSTEM OF THE java COMMAND /usr/bin/java 1 -> /etc/alternatives/java 2 -> /usr/lib64/jvm/jre-10-openjdk/bin/java 3 1 The generic name. 2 The symbolic link in the alternatives directory. 3 One of the alternatives. 299 Overview SLES 15 SP622.2 Use cases By default, the update-alternatives script is called from inside an RPM package. When a package is installed or removed, the script takes care of all its symbolic links. But you can run it manually from the command line for: displaying the current alternatives for a generic name. changing the defaults of an alternative. creating a set of related les for an alternative. 22.3 Getting an overview of alternatives To retrieve the names of all configured alternatives, use: > ls /var/lib/alternatives To get an overview of all configured alternatives and their values, use > sudo update-alternatives --get-selections asadmin auto /usr/bin/asadmin-2.7 awk auto /usr/bin/gawk chardetect auto /usr/bin/chardetect-3.6 dbus-launch auto /usr/bin/dbus-launch.x11 default-displaymanager auto /usr/lib/X11/displaymanagers/gdm [...] 22.4 Viewing details on specific alternatives The easiest way to check the alternatives is to follow the symbolic links of your command. For example, to nd out what the java command is referring to, use the following command: > readlink --canonicalize /usr/bin/java /usr/lib64/jvm/jre-10-openjdk/bin/java If you see the same path (in our example, it is /usr/bin/java ), there are no alternatives avail- able for this command. To see the full alternatives (including slaves), use the --display option: > sudo update-alternatives --display java 300 Use cases SLES 15 SP6java - auto mode link best version is /usr/lib64/jvm/jre-1.8.0-openjdk/bin/java link currently points to /usr/lib64/jvm/jre-1.8.0-openjdk/bin/java link java is /usr/bin/java slave java.1.gz is /usr/share/man/man1/java.1.gz slave jre is /usr/lib64/jvm/jre slave jre_exports is /usr/lib64/jvm-exports/jre slave keytool is /usr/bin/keytool slave keytool.1.gz is /usr/share/man/man1/keytool.1.gz slave orbd is /usr/bin/orbd slave orbd.1.gz is /usr/share/man/man1/orbd.1.gz [...] 22.5 Setting the default version of alternatives By default, commands in /usr/bin refer to the alternatives directory with the highest priority. For example, by default, the command java shows the following version number: > java -version openjdk version "10.0.1" 2018-04-17 OpenJDK Runtime Environment (build 10.0.1+10-suse-lp150.1.11-x8664) OpenJDK 64-Bit Server VM (build 10.0.1+10-suse-lp150.1.11-x8664, mixed mode) To change the default java command to refer to a previous version, run: > sudo update-alternatives --config java root''s password: There are 2 choices for the alternative java (providing /usr/bin/java). Selection Path Priority Status ------------------------------------------------------------ * 0 /usr/lib64/jvm/jre-10-openjdk/bin/java 2005 auto mode 1 /usr/lib64/jvm/jre-1.8.0-openjdk/bin/java 1805 manual mode 2 /usr/lib64/jvm/jre-10-openjdk/bin/java 2005 manual mode 3 /usr/lib64/jvm/jre-11-openjdk/bin/java 0 manual mode Press to keep the current choice[*], or type selection number: Depending on your system and installed versions, the exact Java version number will be differ- ent. After you have selected 1 , java shows the following version number: > java -version java version "1.8.0_171" OpenJDK Runtime Environment (IcedTea 3.8.0) (build 1.8.0_171-b11 suse-lp150.2.3.1-x86_64) 301 Setting the default version of alternatives SLES 15 SP6OpenJDK 64-Bit Server VM (build 25.171-b11, mixed mode) Also, keep in mind the following points: When working in manual mode and installing another Java version, the alternatives system neither touches the links nor changes the generic name. When working in automatic mode and installing another Java version, the alternatives system changes the Java master link and all slave links (as you can see in Section 22.4, “Viewing details on specific alternatives”). To check the master-slave relationships, use: > sudo update-alternatives --display java 22.6 Installing custom alternatives This section describes how to set up custom alternatives on a system. Warning: No custom alternatives for python3 Do not install custom alternatives for python3. /usr/bin/python3 does not have update alternatives and always points to specific tested versions. Creating a custom python3 al- ternative pointing to a different version—such as python 3.11—breaks dependent system tools. The example makes the following assumptions: There are two scripts, foo-2 and foo-3 , with similar functionality. The scripts are stored in the /usr/local/bin directory to avoid any conflicts with the system tools in /usr/bin . There is a master link foo that points to either foo-2 or foo-3 . To provide alternatives on your system, follow these steps: 1. Copy your scripts into the /usr/local/bin directory. 2. Make the scripts executable: > sudo chmod +x /usr/local/bin/foo-{2,3} 302 Installing custom alternatives SLES 15 SP63. Run update-alternatives for both scripts: > sudo update-alternatives --install \ /usr/local/bin/foo 1 \ foo 2 \ /usr/local/bin/foo-2 3 \ 200 4 > sudo update-alternatives --install \ /usr/local/bin/foo 1 \ foo 2 \ /usr/local/bin/foo-3 3 \ 300 4 The options after --install have the following meanings: 1 The generic name. To avoid confusion, this is normally the script name without any version numbers. 2 The name of the master link. Must be the same. 3 The path to the original scripts located in /usr/local/bin . 4 The priority. We give foo-2 a lower priority than foo-3 . It is good practice to use a significant number increase to separate priorities. For example, a priority of 200 for foo-2 and 300 for foo-3 . 4. Check the master link: > sudo update-alternatives --display foo foo - auto mode link best version is /usr/local/bin/foo-3 link currently points to /usr/local/bin/foo-3 link foo is /usr/local/bin/foo /usr/local/bin/foo-2 - priority 200 /usr/local/bin/foo-3 - priority 300 After you completed the described steps, you can use the master link /usr/local/bin/foo . If needed, you can install additional alternatives. To remove an alternative, use the following command: > sudo update-alternatives --remove foo /usr/local/bin/foo-2 After this script has been removed, the alternatives system for the foo group looks like this: > sudo update-alternatives --display foo foo - auto mode 303 Installing custom alternatives SLES 15 SP6link best version is /usr/local/bin/foo-3 link currently points to /usr/local/bin/foo-3 link foo is /usr/local/bin/foo /usr/local/bin/foo-3 - priority 300 22.7 Defining dependent alternatives If you have alternatives, the script itself is not enough. Most commands are not stand-alone —they ship with additional les, such as extensions, configurations or man pages. To create alternatives which are dependent on a master link, use slave alternatives. Let us assume we want to extend our example in Section 22.6, “Installing custom alternatives” and provide man pages and configuration les: Two man pages, foo-2.1.gz and foo-3.1.gz stored in the /usr/local/man/man1 di- rectory. Two configuration les, foo-2.conf and foo-3.conf , stored in /etc . Follow these steps to add the additional les to your alternatives: 1. Copy the configuration les into /etc : > sudo cp foo-{2,3}.conf /etc 2. Copy the man pages into the /usr/local/man/man1 directory: > sudo cp foo-{2,3}.1.gz /usr/local/man/man1/ 3. Add the slave links to the main scripts with the --slave option: > sudo update-alternatives --install \ /usr/local/bin/foo foo /usr/local/bin/foo-2 200 \ --slave /usr/local/man/man1/foo.1.gz \ foo.1.gz \ /usr/local/man/man1/foo-2.1.gz \ --slave /etc/foo.conf \ foo.conf \ /etc/foo-2.conf > sudo update-alternatives --install \ /usr/local/bin/foo foo /usr/local/bin/foo-3 300 \ --slave /usr/local/man/man1/foo.1.gz \ foo.1.gz \ /usr/local/man/man1/foo-3.1.gz \ 304 Defining dependent alternatives SLES 15 SP6--slave /etc/foo.conf \ foo.conf \ /etc/foo-3.conf 4. Check the master link: foo - auto mode link best version is /usr/local/bin/foo-3 link currently points to /usr/local/bin/foo-3 link foo is /usr/local/bin/foo slave foo.1.gz is /usr/local/man/man1/foo.1.gz slave foo.conf is /etc/foo.conf /usr/local/bin/foo-2 - priority 200 slave foo.1.gz: /usr/local/man/man1/foo-2.1.gz slave foo.conf: /etc/foo-2.conf /usr/local/bin/foo-3 - priority 300 slave foo.1.gz: /usr/local/man/man1/foo-3.1.gz slave foo.conf: /etc/foo-3.conf If you change the links with update-alternatives --config foo to foo-2 , then all slave links will change as well. 305 Defining dependent alternatives SLES 15 SP623 Basic networking Linux offers the necessary networking tools and features for integration into all types of network structures. Network access using a network card can be configured with YaST. Manual configuration is also possible. In this chapter, only the funda- mental mechanisms and the relevant network configuration les are covered. Linux and other Unix operating systems use the TCP/IP protocol. It is not a single network protocol, but a family of network protocols that offer multiple services. The protocols listed in Several protocols in the TCP/IP protocol family are provided for exchanging data between two machines via TCP/IP. Networks combined by TCP/IP, comprising a worldwide network, are also called “the Internet.” RFC stands for Request for Comments. RFCs are documents that describe Internet protocols and implementation procedures for the operating system and its applications. The RFC documents describe the setup of Internet protocols. For more information about RFCs, see https://datatrack- er.ietf.org/ . SEVERAL PROTOCOLS IN THE TCP/IP PROTOCOL FAMILY TCP Transmission Control Protocol: a connection-oriented secure protocol. The data to transmit is rst sent by the application as a stream of data and converted into the appropriate format by the operating system. The data arrives at the respective application on the destination host in the original data stream format it was initially sent. TCP determines whether any data has been lost or jumbled during the transmission. TCP is implemented wherever the data sequence matters. UDP User Datagram Protocol: a connectionless, insecure protocol. The data to transmit is sent in the form of packets generated by the application. The order in which the data arrives at the recipient is not guaranteed and data loss is possible. UDP is suitable for record-oriented applications. It features a smaller latency period than TCP. ICMP Internet Control Message Protocol: this is not a protocol for the end user, but a special control protocol that issues error reports and can control the behavior of machines partic- ipating in TCP/IP data transfer. In addition, it provides a special echo mode that can be viewed using the program ping. 306 SLES 15 SP6IGMP Internet Group Management Protocol: this protocol controls machine behavior when im- plementing IP multicast. As shown in Figure 23.1, “Simplified layer model for TCP/IP”, data exchange takes place in different layers. The actual network layer is the insecure data transfer via IP (Internet protocol). On top of IP, TCP (transmission control protocol) guarantees, to a certain extent, security of the data transfer. The IP layer is supported by the underlying hardware-dependent protocol, such as Ethernet. TCP/IP Model OSI Model Application Layer Application Layer Presentation Layer Session Layer Transport Layer Transport Layer Internet Layer Network Layer Data Link Layer Network Access Layer Physical Layer FIGURE 23.1: SIMPLIFIED LAYER MODEL FOR TCP/IP 307 SLES 15 SP6The diagram provides one or two examples for each layer. The layers are ordered according to abstraction levels. The lowest layer is close to the hardware. The uppermost layer, however, is almost a complete abstraction from the hardware. Every layer has its own special function. The special functions of each layer are implicit in their description. The data link and physical layers represent the physical network used, such as Ethernet. Almost all hardware protocols work on a packet-oriented basis. The data to transmit is collected into packets (it cannot be sent all at once). The maximum size of a TCP/IP packet is approxi- mately 64 KB. Packets are normally small, as the network hardware can be a limiting factor. The maximum size of a data packet on Ethernet is about fifteen hundred bytes. The size of a TCP/IP packet is limited to this amount when the data is sent over Ethernet. If more data is transferred, more data packets need to be sent by the operating system. For the layers to serve their designated functions, additional information regarding each layer must be saved in the data packet. This takes place in the header of the packet. Every layer attaches a small block of data, called the protocol header, to the front of each emerging packet. A sample TCP/IP data packet traveling over an Ethernet cable is illustrated in Figure 23.2, “TCP/ IP Ethernet packet”. The proof sum is located at the end of the packet, not at the beginning. This simplifies things for the network hardware. Ethernet Header IP Header TCP Header Usage Data Checksum (14 bytes) (20 bytes) (20 bytes) (max. 1460 bytes) (2 bytes) FIGURE 23.2: TCP/IP ETHERNET PACKET When an application sends data over the network, the data passes through each layer, all im- plemented in the Linux kernel except the physical layer. Each layer handles preparing the data so it can be passed to the next layer. The lowest layer is ultimately responsible for sending the data. The entire procedure is reversed when data is received. Like the layers of an onion, in each layer the protocol headers are removed from the transported data. Finally, the transport layer handles making the data available for use by the applications at the destination. In this manner, one layer only communicates with the layer directly above or below it. For applications, it is irrelevant whether data is transmitted via a wireless or wired connection. Likewise, it is irrele- vant for the data line which kind of data is transmitted, if packets are in the correct format. 308 SLES 15 SP623.1 IP addresses and routing The discussion in this section is limited to IPv4 networks. For information about IPv6 protocol, the successor to IPv4, refer to Section 23.2, “IPv6—the next generation Internet”. 23.1.1 IP addresses Every computer on the Internet has a unique 32-bit address. These 32 bits (or 4 bytes) are normally written as illustrated in the second row in Example 23.1, “Writing IP addresses”. EXAMPLE 23.1: WRITING IP ADDRESSES IP Address (binary): 11000000 10101000 00000000 00010100 IP Address (decimal): 192. 168. 0. 20 In decimal form, the four bytes are written in the decimal number system, separated by periods. The IP address is assigned to a host or a network interface. It can be used only once throughout the world. There are exceptions to this rule, but these are not relevant to the following passages. The points in IP addresses indicate the hierarchical system. Until the 1990s, IP addresses were strictly categorized in classes. However, this system proved too inflexible and was discontinued. Now, classless routing (CIDR, classless interdomain routing) is used. 23.1.2 Netmasks and routing Netmasks are used to define the address range of a subnet. If two hosts are in the same subnet, they can reach each other directly. If they are not in the same subnet, they need the address of a gateway that handles all the traffic for the subnet. To check if two IP addresses are in the same subnet, simply “AND” both addresses with the netmask. If the result is identical, both IP addresses are in the same local network. If there are differences, the remote IP address, and thus the remote interface, can only be reached over a gateway. To understand how the netmask works, look at Example 23.2, “Linking IP addresses to the netmask”. The netmask consists of 32 bits that identify how much of an IP address belongs to the network. All those bits that are 1 mark the corresponding bit in the IP address as belonging to the network. All bits that are 0 mark bits inside the subnet. This means that the more bits are 1 , the smaller the subnet is. Because the netmask always consists of several successive 1 bits, it is also possible to count the number of bits in the netmask. In Example 23.2, “Linking IP addresses to the netmask” the rst net with 24 bits could also be written as 192.168.0.0/24 . 309 IP addresses and routing SLES 15 SP6EXAMPLE 23.2: LINKING IP ADDRESSES TO THE NETMASK IP address (192.168.0.20): 11000000 10101000 00000000 00010100 Netmask (255.255.255.0): 11111111 11111111 11111111 00000000 --------------------------------------------------------------- Result of the link: 11000000 10101000 00000000 00000000 In the decimal system: 192. 168. 0. 0 IP address (213.95.15.200): 11010101 10111111 00001111 11001000 Netmask (255.255.255.0): 11111111 11111111 11111111 00000000 --------------------------------------------------------------- Result of the link: 11010101 10111111 00001111 00000000 In the decimal system: 213. 95. 15. 0 To give another example: all machines connected with the same Ethernet cable are normally located in the same subnet and are directly accessible. Even when the subnet is physically di- vided by switches or bridges, these hosts can still be reached directly. IP addresses outside the local subnet can only be reached if a gateway is configured for the target network. In the most common case, there is only one gateway that handles all traffic that is external. However, it is also possible to configure several gateways for different subnets. If a gateway has been configured, all external IP packets are sent to the appropriate gateway. This gateway then attempts to forward the packets in the same manner—from host to host— until it reaches the destination host or the packet''s TTL (time to live) expires. SPECIFIC ADDRESSES Base Network Address This is the netmask AND any address in the network, as shown in Example 23.2, “Linking IP addresses to the netmask” under Result . This address cannot be assigned to any hosts. Broadcast Address This could be paraphrased as: “Access all hosts in this subnet.” To generate this, the net- mask is inverted in binary form and linked to the base network address with a logical OR. The above example therefore results in 192.168.0.255. This address cannot be assigned to any hosts. Local Host The address 127.0.0.1 is assigned to the “loopback device” on each host. A connection can be set up to your own machine with this address and with all addresses from the complete 127.0.0.0/8 loopback network as defined with IPv4. With IPv6 there is only one loopback address ( ::1 ). 310 Netmasks and routing SLES 15 SP6Because IP addresses must be unique all over the world, you cannot select random addresses. There are three address domains to use to set up a private IP-based network. These cannot get any connection from the rest of the Internet, because they cannot be transmitted over the Internet. These address domains are specified in RFC 1597 and listed in Table 23.1, “Private IP address domains”. TABLE 23.1: PRIVATE IP ADDRESS DOMAINS Network/Netmask Domain 10.0.0.0 / 255.0.0.0 10.x.x.x 172.16.0.0 / 255.240.0.0 172.16.x.x – 172.31.x.x 192.168.0.0 / 255.255.0.0 192.168.x.x 23.2 IPv6—the next generation Internet Important: IBM Z: IPv6 support IPv6 is not supported by the CTC and IUCV network connections of the IBM Z hardware. Because of the emergence of the World Wide Web (WWW), the Internet has experienced explo- sive growth, with an increasing number of computers communicating via TCP/IP in the past fif- teen years. Since Tim Berners-Lee at CERN (https://public.web.cern.ch ) invented the WWW in 1990, the number of Internet hosts has grown from a few thousand to about a hundred million. As mentioned, an IPv4 address consists of only 32 bits. Also, a few IP addresses are lost—they cannot be used because of the way networks are organized. The number of addresses available in your subnet is two to the power of the number of bits, minus two. A subnet has, for example, 2, 6 or 14 addresses available. To connect 128 hosts to the Internet, for example, you need a subnet with 256 IP addresses, from which only 254 are usable, because two IP addresses are needed for the structure of the subnet itself: the broadcast and the base network address. Under the current IPv4 protocol, DHCP or NAT (network address translation) are the typical mechanisms used to circumvent the potential address shortage. Combined with the convention to keep private and public address spaces separate, these methods can certainly mitigate the 311 IPv6—the next generation Internet SLES 15 SP6shortage. To set up a host in an IPv4 network, you need several address items, such as the host''s own IP address, the subnetmask, the gateway address, and maybe a name server address. All these items need to be known and cannot be derived from somewhere else. With IPv6, both the address shortage and the complicated configuration should be a thing of the past. The following sections tell more about the improvements and benefits brought by IPv6 and about the transition from the old protocol to the new one. 23.2.1 Advantages The most important and most visible improvement brought by the IPv6 protocol is the enormous expansion of the available address space. An IPv6 address is made up of 128 bit values instead of the traditional 32 bits. This provides for as many as several quadrillion IP addresses. However, IPv6 addresses are not only different from their predecessors with regard to their length. They also have a different internal structure that may contain more specific information about the systems and the networks to which they belong. More details about this are found in Section 23.2.2, “Address types and structure”. The following is a list of other advantages of the IPv6 protocol: Autoconfiguration IPv6 makes the network “plug and play” capable, which means that a newly configured system integrates into the (local) network without any manual configuration. The new host uses its automatic configuration mechanism to derive its own address from the information made available by the neighboring routers, relying on a protocol called the neighbor dis- covery (ND) protocol. This method does not require any intervention on the administrator''s part and there is no need to maintain a central server for address allocation—an additional advantage over IPv4, where automatic address allocation requires a DHCP server. Nevertheless if a router is connected to a switch, the router should send periodic advertise- ments with ags telling the hosts of a network how they should interact with each other. For more information, see RFC 2462 and the radvd.conf(5) man page, and RFC 3315. Mobility IPv6 makes it possible to assign several addresses to one network interface at the same time. This allows users to access several networks easily, something that could be compared with the international roaming services offered by mobile phone companies. When you take 312 Advantages SLES 15 SP6your mobile phone abroad, the phone automatically logs in to a foreign service when it enters the corresponding area, so you can be reached under the same number everywhere and can place an outgoing call, as you would in your home area. Secure communication With IPv4, network security is an add-on function. IPv6 includes IPsec as one of its core features, allowing systems to communicate over a secure tunnel to avoid eavesdropping by outsiders on the Internet. Backward compatibility Realistically, it would be impossible to switch the entire Internet from IPv4 to IPv6 at one time. Therefore, it is crucial that both protocols can coexist not only on the Internet, but also on one system. This is ensured by compatible addresses (IPv4 addresses can easily be translated into IPv6 addresses) and by using several tunnels. See Section 23.2.3, “Coexistence of IPv4 and IPv6”. Also, systems can rely on a dual stack IP technique to support both protocols at the same time, meaning that they have two network stacks that are separate, such that there is no interference between the two protocol versions. Custom tailored services through multicasting With IPv4, certain services, such as SMB, need to broadcast their packets to all hosts in the local network. IPv6 allows a much more ne-grained approach by enabling servers to address hosts through multicasting, that is by addressing several hosts as parts of a group. This is different from addressing all hosts through broadcasting or each host individually through unicasting. Which hosts are addressed as a group may depend on the concrete application. There are specific predefined groups to address all name servers (the all name servers multicast group), for example, or all routers (the all routers multicast group). 23.2.2 Address types and structure As mentioned, the current IP protocol has two major limitations: there is an increasing shortage of IP addresses and configuring the network and maintaining the routing tables is becoming a more complex and burdensome task. IPv6 solves the rst problem by expanding the address space to 128 bits. The second one is mitigated by introducing a hierarchical address structure combined with sophisticated techniques to allocate network addresses, and multihoming (the ability to assign several addresses to one device, giving access to several networks). 313 Address types and structure SLES 15 SP6When dealing with IPv6, it is useful to know about three different types of addresses: Unicast Addresses of this type are associated with exactly one network interface. Packets with such an address are delivered to only one destination. Accordingly, unicast addresses are used to transfer packets to individual hosts on the local network or the Internet. Multicast Addresses of this type relate to a group of network interfaces. Packets with such an address are delivered to all destinations that belong to the group. Multicast addresses are mainly used by certain network services to communicate with certain groups of hosts in a well- directed manner. Anycast Addresses of this type are related to a group of interfaces. Packets with such an address are delivered to the member of the group that is closest to the sender, according to the principles of the underlying routing protocol. Anycast addresses are used to make it easier for hosts to nd out about servers offering certain services in the given network area. All servers of the same type have the same anycast address. Whenever a host requests a service, it receives a reply from the server with the closest location, as determined by the routing protocol. If this server should fail, the protocol automatically selects the second closest server, then the third one, and so forth. An IPv6 address is made up of eight four-digit elds, each representing 16 bits, written in hexa- decimal notation. They are separated by colons ( : ). Any leading zero bytes within a given eld may be dropped, but zeros within the eld or at its end may not. Another convention is that more than four consecutive zero bytes may be collapsed into a double colon. However, only one such :: is allowed per address. This kind of shorthand notation is shown in Example 23.3, “Sample IPv6 address”, where all three lines represent the same address. EXAMPLE 23.3: SAMPLE IPV6 ADDRESS fe80 : 0000 : 0000 : 0000 : 0000 : 10 : 1000 : 1a4 fe80 : 0 : 0 : 0 : 0 : 10 : 1000 : 1a4 fe80 : : 10 : 1000 : 1a4 Each part of an IPv6 address has a defined function. The rst bytes form the prefix and specify the type of address. The center part is the network portion of the address, but it may be unused. The end of the address forms the host part. With IPv6, the netmask is defined by indicating the length of the prefix after a slash at the end of the address. An address, as shown in Example 23.4, 314 Address types and structure SLES 15 SP6“IPv6 address specifying the prefix length”, contains the information that the rst 64 bits form the network part of the address and the last 64 form its host part. In other words, the 64 means that the netmask is lled with 64 1-bit values from the left. As with IPv4, the IP address is combined with AND with the values from the netmask to determine whether the host is located in the same subnet or in another one. EXAMPLE 23.4: IPV6 ADDRESS SPECIFYING THE PREFIX LENGTH fe80::10:1000:1a4/64 IPv6 knows about several predefined types of prefixes. Certain are shown in IPv6 prefixes. IPV6 PREFIXES 00 IPv4 addresses and IPv4 over IPv6 compatibility addresses. These are used to maintain compatibility with IPv4. Their use still requires a router able to translate IPv6 packets into IPv4 packets. Several special addresses, such as the one for the loopback device, have this prefix as well. 2 or 3 as the first digit Aggregatable global unicast addresses. As is the case with IPv4, an interface can be as- signed to form part of a certain subnet. Currently, there are the following address spaces: 2001::/16 (production quality address space) and 2002::/16 (6to4 address space). fe80::/10 Link-local addresses. Addresses with this prefix should not be routed and should therefore only be reachable from within the same subnet. fec0::/10 Site-local addresses. These may be routed, but only within the network of the organization to which they belong. In effect, they are the IPv6 equivalent of the current private network address space, such as 10.x.x.x . ff These are multicast addresses. A unicast address consists of three basic components: Public topology The rst part (which also contains one of the prefixes mentioned above) is used to route packets through the public Internet. It includes information about the company or institu- tion that provides the Internet access. 315 Address types and structure SLES 15 SP6Site topology The second part contains routing information about the subnet to which to deliver the packet. Interface ID The third part identifies the interface to which to deliver the packet. This also allows for the MAC to form part of the address. Given that the MAC is a globally unique, xed identifier coded into the device by the hardware maker, the configuration procedure is simplified. In fact, the rst 64 address bits are consolidated to form the EUI-64 token, with the last 48 bits taken from the MAC, and the remaining 24 bits containing special information about the token type. This also makes it possible to assign an EUI-64 token to interfaces that do not have a MAC, such as those based on point-to-point protocol (PPP). On top of this basic structure, IPv6 distinguishes between ve different types of unicast address- es: :: (unspecified) This address is used by the host as its source address when the interface is initialized for the rst time (at which point, the address cannot yet be determined by other means). ::1 (loopback) The address of the loopback device. IPv4 compatible addresses The IPv6 address is formed by the IPv4 address and a prefix consisting of 96 zero bits. This type of compatibility address is used for tunneling (see Section 23.2.3, “Coexistence of IPv4 and IPv6”) to allow IPv4 and IPv6 hosts to communicate with others operating in a pure IPv4 environment. IPv4 addresses mapped to IPv6 This type of address specifies a pure IPv4 address in IPv6 notation. Local addresses There are two address types for local use: link-local This type of address can only be used in the local subnet. Packets with a source or target address of this type should not be routed to the Internet or other subnets. These addresses contain a special prefix ( fe80::/10 ) and the interface ID of the network 316 Address types and structure SLES 15 SP6card, with the middle part consisting of zero bytes. Addresses of this type are used during automatic configuration to communicate with other hosts belonging to the same subnet. site-local Packets with this type of address may be routed to other subnets, but not to the wider Internet—they must remain inside the organization''s own network. Such addresses are used for intranets and are an equivalent of the private address space defined by IPv4. They contain a special prefix ( fec0::/10 ), the interface ID, and a 16-bit eld specifying the subnet ID. Again, the rest is lled with zero bytes. As a new feature introduced with IPv6, each network interface normally gets several IP address- es, with the advantage that several networks can be accessed through the same interface. One of these networks can be configured automatically using the MAC and a known prefix with the result that all hosts on the local network can be reached when IPv6 is enabled (using the link- local address). With the MAC forming part of it, any IP address used in the world is unique. The only variable parts of the address are those specifying the site topology and the public topology, depending on the actual network in which the host is currently operating. For a host to go back and forth between different networks, it needs at least two addresses. One of them, the home address, not only contains the interface ID but also an identifier of the home network to which it normally belongs (and the corresponding prefix). The home address is a static address and, as such, it does not normally change. Still, all packets destined to the mobile host can be delivered to it, regardless of whether it operates in the home network or somewhere outside. This is made possible by new features introduced with IPv6, such as stateless autoconfiguration and neighbor discovery. In addition to its home address, a mobile host gets one or more additional addresses that belong to the foreign networks where it is roaming. These are called care-of addresses. The home network has a facility that forwards any packets destined to the host when it is roaming outside. In an IPv6 environment, this task is performed by the home agent, which takes all packets destined to the home address and relays them through a tunnel. Those packets destined to the care-of address are directly transferred to the mobile host without any special detours. 23.2.3 Coexistence of IPv4 and IPv6 The migration of all hosts connected to the Internet from IPv4 to IPv6 is a gradual process. Both protocols can coexist for a certain time to come. The coexistence on one system is guaranteed where there is a dual stack implementation of both protocols. That still leaves the question of 317 Coexistence of IPv4 and IPv6 SLES 15 SP6how an IPv6 enabled host should communicate with an IPv4 host and how IPv6 packets should be transported by the current networks, which are predominantly IPv4-based. The best solutions offer tunneling and compatibility addresses (see Section 23.2.2, “Address types and structure”). IPv6 hosts that are isolated in the (worldwide) IPv4 network can communicate through tunnels: IPv6 packets are encapsulated as IPv4 packets to move them across an IPv4 network. Such a connection between two IPv4 hosts is called a tunnel. To achieve this, packets must include the IPv6 destination address (or the corresponding prefix) and the IPv4 address of the remote host at the receiving end of the tunnel. A basic tunnel can be configured manually according to an agreement between the hosts'' administrators. This is also called static tunneling. However, the configuration and maintenance of static tunnels is often too labor-intensive to use them for daily communication needs. Therefore, IPv6 provides for three different methods of dynamic tunneling: 6over4 IPv6 packets are automatically encapsulated as IPv4 packets and sent over an IPv4 network capable of multicasting. IPv6 is tricked into seeing the whole network (Internet) as a local area network (LAN). This makes it possible to determine the receiving end of the IPv4 tunnel automatically. However, this method does not scale well and is also hampered because IP multicasting is far from widespread on the Internet. Therefore, it only provides a solution for smaller corporate or institutional networks where multicasting can be enabled. The specifications for this method are laid down in RFC 2529. 6to4 With this method, IPv4 addresses are automatically generated from IPv6 addresses, en- abling isolated IPv6 hosts to communicate over an IPv4 network. However, several prob- lems have been reported regarding the communication between those isolated IPv6 hosts and the Internet. The method is described in RFC 3056. IPv6 tunnel broker This method relies on special servers that provide dedicated tunnels for IPv6 hosts. It is described in RFC 3053. 318 Coexistence of IPv4 and IPv6 SLES 15 SP623.2.4 Configuring IPv6 To configure IPv6, you normally do not need to make any changes on the individual worksta- tions. IPv6 is enabled by default. To disable or enable IPv6 on an installed system, use the YaST Network Settings module. On the Global Options tab, select or deselect the Enable IPv6 option as necessary. To enable it temporarily until the next reboot, enter modprobe -i ipv6 as root . It is impossible to unload the IPv6 module after it has been loaded. Because of the autoconfiguration concept of IPv6, the network card is assigned an address in the link-local network. Normally, no routing table management takes place on a workstation. The network routers can be queried by the workstation, using the router advertisement protocol, for what prefix and gateways should be implemented. The radvd program can be used to set up an IPv6 router. This program informs the workstations which prefix to use for the IPv6 addresses and which routers. Alternatively, use FRR (see https://frrouting.org/ ) for automatic configuration of both addresses and routing. For information about how to set up multiple types of tunnels using the /etc/sysconfig/net- work les, see the man page of ifcfg-tunnel ( man ifcfg-tunnel ). 23.2.5 More information The above overview does not cover the topic of IPv6 comprehensively. For a more in-depth look at the newer protocol, refer to the following online documentation and books: https://pulse.internetsociety.org The starting point for everything about IPv6. http://www.ipv6day.org All information needed to start your own IPv6 network. http://www.ipv6-to-standard.org/ The list of IPv6-enabled products. https://www.bieringer.de/linux/IPv6/ The Linux IPv6-HOWTO and many links related to the topic. RFC 2460 The fundamental RFC about IPv6, see https://www.rfc-editor.org/rfc/rfc2460 . 319 Configuring IPv6 SLES 15 SP6IPv6 essentials A book describing all the important aspects of the topic is IPv6 Essentials by Silvia Hagen (ISBN 0-596-00125-8). 23.3 Name resolution DNS assists in assigning an IP address to one or more names and assigning a name to an IP address. In Linux, this conversion is normally carried out by a special type of software known as bind. The machine that takes care of this conversion is called a name server. The names make up a hierarchical system in which each name component is separated by a period. The name hierarchy is, however, independent of the IP address hierarchy described above. Consider a complete name, such as jupiter.example.com , written in the format host- name.domain . A full name, called a fully qualified domain name (FQDN), consists of a host name and a domain name ( example.com ). The latter also includes the top level domain or TLD ( com ). TLD assignment has become confusing for historical reasons. Traditionally, three-letter domain names are used in the USA. In the rest of the world, the two-letter ISO national codes are the standard. Additionally, longer TLDs were introduced in 2000 that represent certain spheres of activity (for example, .info , .name , .museum ). In the early days of the Internet (before 1990), the le /etc/hosts was used to store the names of all the machines represented over the Internet. This quickly proved to be impractical in the face of the rapidly growing number of computers connected to the Internet. For this reason, a decentralized database was developed to store the host names in a widely distributed manner. This database, similar to the name server, does not have the data pertaining to all hosts in the Internet available, but can dispatch requests to other name servers. The top of the hierarchy is occupied by root name servers. These root name servers manage the top level domains and are run by the Network Information Center (NIC). Each root name server knows about the name servers responsible for a given top level domain. Information about top level domain NICs is available at https://www.internic.net . DNS can do more than resolve host names. The name server also knows which host is receiving e-mails for an entire domain—the mail exchanger (MX). For your machine to resolve an IP address, it must know about at least one name server and its IP address. Easily specify such a name server using YaST. The configuration of name server access with SUSE® Linux Enterprise Server is described in Section 23.4.1.4, “Configuring host name and DNS”. Setting up your own name server is described in Chapter 39, The domain name system. 320 Name resolution SLES 15 SP6The protocol whois is closely related to DNS. With this program, quickly nd out who accounts for a given domain. Note: MDNS and .local domain names The .local top level domain is treated as link-local domain by the resolver. DNS requests are sent as multicast DNS requests instead of normal DNS requests. If you already use the .local domain in your name server configuration, you must switch this option o in / etc/host.conf . For more information, see the host.conf man page. To switch o MDNS during installation, use nomdns=1 as a boot parameter. For more information on multicast DNS, see http://www.multicastdns.org . 23.4 Configuring a network connection with YaST There are many supported networking types on Linux. Most of them use different device names and the configuration les are spread over several locations in the le system. For a detailed overview of the aspects of manual network configuration, see Section 23.5, “Configuring a network connection manually”. All network interfaces with link up (with a network cable connected) are automatically config- ured. Additional hardware can be configured any time on the installed system. The following sections describe the network configuration for all types of network connections supported by SUSE Linux Enterprise Server. Tip: IBM Z: hotpluggable network cards On IBM Z platforms, hotpluggable network cards are supported, but not their automatic network integration via DHCP (as is the case on the PC). After they have been detected, you need to manually configure the interface. 23.4.1 Configuring the network card with YaST To configure your Ethernet or Wi-Fi/Bluetooth card in YaST, select System Network Settings. After starting the module, YaST displays the Network Settings dialog with four tabs: Global Op- tions, Overview, Hostname/DNS and Routing. 321 Configuring a network connection with YaST SLES 15 SP6The Global Options tab allows you to set general networking options such as the network setup method, IPv6, and general DHCP options. For more information, see Section 23.4.1.1, “Configuring global networking options”. The Overview tab contains information about installed network interfaces and configurations. Any properly detected network card is listed with its name. You can manually configure new cards, remove or change their configuration in this dialog. To manually configure a card that was not automatically detected, see Section 23.4.1.3, “Configuring an undetected network card”. To change the configuration of an already configured card, see Section 23.4.1.2, “Changing the configuration of a network card”. The Hostname/DNS tab allows to set the host name of the machine and name the servers to be used. For more information, see Section 23.4.1.4, “Configuring host name and DNS”. The Routing tab is used for the configuration of routing. See Section 23.4.1.5, “Configuring routing” for more information. FIGURE 23.3: CONFIGURING NETWORK SETTINGS 322 Configuring the network card with YaST SLES 15 SP623.4.1.1 Configuring global networking options The Global Options tab of the YaST Network Settings module allows you to set important global networking options, such as the use of NetworkManager, IPv6 and DHCP client options. These settings are applicable for all network interfaces. Note: NetworkManager provided by workstation extension NetworkManager is now provided by the SUSE Linux Enterprise Workstation Extension. To install NetworkManager, activate the Workstation Extension repository, and select the NetworkManager packages. In the Network Setup Method choose the way network connections are managed. If you want a NetworkManager desktop applet to manage connections for all interfaces, choose NetworkMan- ager Service. NetworkManager is well suited for switching between multiple wired and wireless networks. If you do not run a desktop environment, or if your computer is a Xen server, virtual system, or provides network services such as DHCP or DNS in your network, use the Wicked Service method. If NetworkManager is used, nm-applet should be used to configure network options and the Overview, Hostname/DNS and Routing tabs of the Network Settings module are disabled. For more information on NetworkManager, see the SUSE Linux Enterprise Desktop documentation. In the IPv6 Protocol Settings choose whether to use the IPv6 protocol. It is possible to use IPv6 together with IPv4. By default, IPv6 is enabled. However, in networks not using IPv6 protocol, response times can be faster with IPv6 protocol disabled. To disable IPv6, deactivate Enable IPv6. If IPv6 is disabled, the kernel no longer loads the IPv6 module automatically. This setting will be applied after reboot. In the DHCP Client Options configure options for the DHCP client. The DHCP Client Identifier must be different for each DHCP client on a single network. If left empty, it defaults to the hardware address of the network interface. However, if you are running several virtual machines using the same network interface and, therefore, the same hardware address, specify a unique free- form identifier here. The Hostname to Send specifies a string used for the host name option eld when the DHCP client sends messages to DHCP server. Some DHCP servers update name server zones (forward and reverse records) according to this host name (Dynamic DNS). Also, some DHCP servers require 323 Configuring the network card with YaST SLES 15 SP6the Hostname to Send option eld to contain a specific string in the DHCP messages from clients. Leave AUTO to send the current host name (that is the one defined in /etc/HOSTNAME ). Make the option eld empty for not sending any host name. If you do not want to change the default route according to the information from DHCP, deac- tivate Change Default Route via DHCP. 23.4.1.2 Changing the configuration of a network card To change the configuration of a network card, select a card from the list of the detected cards in Network Settings Overview in YaST and click Edit. The Network Card Setup dialog appears in which to adjust the card configuration using the General, Address and Hardware tabs. 23.4.1.2.1 Configuring IP addresses You can set the IP address of the network card or the way its IP address is determined in the Address tab of the Network Card Setup dialog. Both IPv4 and IPv6 addresses are supported. The network card can have No IP Address (which is useful for bonding devices), a Statically Assigned IP Address (IPv4 or IPv6) or a Dynamic Address assigned via DHCP or Zeroconf or both. If using Dynamic Address, select whether to use DHCP Version 4 Only (for IPv4), DHCP Version 6 Only (for IPv6) or DHCP Both Version 4 and 6. If possible, the rst network card with link that is available during the installation is automati- cally configured to use automatic address setup via DHCP. Note: IBM Z and DHCP On IBM Z platforms, DHCP-based address configuration is only supported with network cards that have a MAC address. This is only the case with OSA and OSA Express cards. DHCP should also be used if you are using a DSL line but with no static IP assigned by the ISP (Internet Service Provider). If you decide to use DHCP, configure the details in DHCP Client Options in the Global Options tab of the Network Settings dialog of the YaST network card config- uration module. If you have a virtual host setup where different hosts communicate through the same interface, an DHCP Client Identifier is necessary to distinguish them. 324 Configuring the network card with YaST SLES 15 SP6DHCP is a good choice for client configuration but it is not ideal for server configuration. To set a static IP address, proceed as follows: 1. Select a card from the list of detected cards in the Overview tab of the YaST network card configuration module and click Edit. 2. In the Address tab, choose Statically Assigned IP Address. 3. Enter the IP Address. Both IPv4 and IPv6 addresses can be used. Enter the network mask in Subnet Mask. If the IPv6 address is used, use Subnet Mask for prefix length in format /64 . Optionally, you can enter a fully qualified Hostname for this address, which will be written to the /etc/hosts configuration le. 4. Click Next. 5. To activate the configuration, click OK. Note: Interface activation and link detection During activation of a network interface, wicked checks for a carrier and only applies the IP configuration when a link has been detected. If you need to apply the configuration regardless of the link status (for example, when you want to test a service listening to a certain address), you can skip link detection by adding the variable LINK_REQUIRED=no to the configuration le of the interface in /etc/sysconfig/network/ifcfg . Additionally, you can use the variable LINK_READY_WAIT=5 to specify the timeout for waiting for a link in seconds. For more information about the ifcfg-* configuration les, refer to Section 23.5.2.5, “/ etc/sysconfig/network/ifcfg-*” and man 5 ifcfg . If you use the static address, the name servers and default gateway are not configured automat- ically. To configure name servers, proceed as described in Section 23.4.1.4, “Configuring host name and DNS”. To configure a gateway, proceed as described in Section 23.4.1.5, “Configuring routing”. 23.4.1.2.2 Configuring multiple addresses A single network device can have multiple IP addresses called aliases or labels. 325 Configuring the network card with YaST SLES 15 SP6Note: Aliases are a compatibility feature Aliases or labels work with IPv4 only. Using iproute2 network interfaces makes it pos- sible to have one or more addresses. To set additional addresses for your network card using YaST, proceed as follows: 1. Select a card from the list of detected cards in the Overview tab of the YaST Network Settings dialog and click Edit. 2. In the Address Additional Addresses tab, click Add. 3. Enter IPv4 Address Label, IP Address, and Netmask. Note that IP aliases must be added with the /32 netmask. Do not include the interface name in the alias name. 4. To activate the configuration, confirm the settings. 23.4.1.2.3 Changing the device name and udev rules It is possible to change the device name of the network card when it is used. It is also possible to determine whether the network card should be identified by udev via its hardware (MAC) address or via the bus ID. The latter option is preferable in large servers to simplify hotplugging of cards. To set these options with YaST, proceed as follows: 1. Select a card from the list of detected cards in the Overview tab of the YaST Network Settings dialog and click Edit. 2. Go to the General tab. The current device name is shown in Udev Rules. Click Change. 3. Select whether udev should identify the card by its MAC Address or Bus ID. The current MAC address and bus ID of the card are shown in the dialog. 4. To change the device name, check the Change Device Name option and edit the name. 5. To activate the configuration, confirm the settings. 326 Configuring the network card with YaST SLES 15 SP623.4.1.2.4 Changing network card kernel driver For some network cards, several kernel drivers may be available. If the card is already config- ured, YaST allows you to select a kernel driver to be used from a list of available suitable dri- vers. It is also possible to specify options for the kernel driver. To set these options with YaST, proceed as follows: 1. Select a card from the list of detected cards in the Overview tab of the YaST Network Settings module and click Edit. 2. Go to the Hardware tab. 3. Select the kernel driver to be used in Module Name. Enter any options for the selected driver in Options in the form = = VALUE . If more options are used, they should be space- separated. 4. To activate the configuration, confirm the settings. 23.4.1.2.5 Activating the network device If you use the method with wicked , you can configure your device to either start during boot, on cable connection, on card detection, manually, or never. To change device start-up, proceed as follows: 1. In YaST select a card from the list of detected cards in System Network Settings and click Edit. 2. In the General tab, select the desired entry from Device Activation. Choose At Boot Time to start the device during the system boot. With On Cable Connection, the interface is watched for any existing physical connection. With On Hotplug, the inter- face is set when available. It is similar to the At Boot Time option, and only differs in that no error occurs if the interface is not present at boot time. Choose Manually to control the interface manually with ifup . Choose Never to not start the device. The On NFSroot is similar to At Boot Time, but the interface does not shut down with the systemctl stop network command; the network service also cares about the wicked service if wicked is active. Use this if you use an NFS or iSCSI root le system. 3. To activate the configuration, confirm the settings. 327 Configuring the network card with YaST SLES 15 SP6Tip: NFS as a root file system On (diskless) systems where the root partition is mounted via network as an NFS share, you need to be careful when configuring the network device with which the NFS share is accessible. When shutting down or rebooting the system, the default processing order is to turn o network connections, then unmount the root partition. With NFS root, this order causes problems as the root partition cannot be cleanly unmounted as the network connection to the NFS share is already not activated. To prevent the system from deactivating the relevant network device, open the network device configuration tab as described in Sec- tion 23.4.1.2.5, “Activating the network device” and choose On NFSroot in the Device Activation pane. 23.4.1.2.6 Setting up maximum transfer unit size You can set a maximum transmission unit (MTU) for the interface. MTU refers to the largest allowed packet size in bytes. A higher MTU brings higher bandwidth efficiency. However, large packets can block up a slow interface for some time, increasing the lag for further packets. 1. In YaST select a card from the list of detected cards in System Network Settings and click Edit. 2. In the General tab, select the desired entry from the Set MTU list. 3. To activate the configuration, confirm the settings. 23.4.1.2.7 PCIe multifunction devices Multifunction devices that support LAN, iSCSI, and FCoE are supported. The YaST FCoE client ( yast2 fcoe-client ) shows the private ags in additional columns to allow the user to select the device meant for FCoE. The YaST network module ( yast2 lan ) excludes “storage only devices” for network configuration. For more information about FCoE, see Book “Storage Administration Guide”, Chapter 16 “Fibre Channel storage over Ethernet networks: FCoE”, Section 16.3 “Managing FCoE services with YaST”. 328 Configuring the network card with YaST SLES 15 SP623.4.1.2.8 Infiniband configuration for IP-over-InfiniBand (IPoIB) 1. In YaST select the InfiniBand device in System Network Settings and click Edit. 2. In the General tab, select one of the IP-over-InfiniBand (IPoIB) modes: connected (default) or datagram. 3. To activate the configuration, confirm the settings. For more information about InfiniBand, see /usr/src/linux/Documentation/infini- band/ipoib.txt . 23.4.1.2.9 Configuring the firewall Without having to perform the detailed firewall setup as described in Book “Security and Hardening Guide”, Chapter 23 “Masquerading and firewalls”, Section 23.4 “firewalld”, you can determine the basic firewall configuration for your device as part of the device setup. Proceed as follows: 1. Open the YaST System Network Settings module. In the Overview tab, select a card from the list of detected cards and click Edit. 2. Enter the General tab of the Network Settings dialog. 3. Determine the Firewall Zone to which your interface should be assigned. The following options are available: Firewall disabled This option is available only if the firewall is disabled and the firewall does not run. Only use this option if your machine is part of a greater network that is protected by an outer firewall. Automatically assign zone This option is available only if the firewall is enabled. The firewall is running and the interface is automatically assigned to a firewall zone. The zone which contains the keyword any or the external zone will be used for such an interface. Internal zone (unprotected) The firewall is running, but does not enforce any rules to protect this interface. Use this option if your machine is part of a greater network that is protected by an outer firewall. It is also useful for the interfaces connected to the internal network, when the machine has more network interfaces. 329 Configuring the network card with YaST SLES 15 SP6Demilitarized zone A demilitarized zone is an additional line of defense in front of an internal network and the (hostile) Internet. Hosts assigned to this zone can be reached from the inter- nal network and from the Internet, but cannot access the internal network. External zone The firewall is running on this interface and fully protects it against other—presum- ably hostile—network traffic. This is the default option. 4. To activate the configuration, confirm the settings. 23.4.1.3 Configuring an undetected network card If a network card is not detected correctly, the card is not included in the list of detected cards. If you are sure that your system includes a driver for your card, you can configure it manually. You can also configure special network device types, such as bridge, bond, TUN or TAP. To configure an undetected network card (or a special device) proceed as follows: 1. In the System Network Settings Overview dialog in YaST click Add. 2. In the Hardware dialog, set the Device Type of the interface from the available options and Configuration Name. If the network card is a USB device, activate the respective check box and exit this dialog with Next. Otherwise, you can define the kernel Module Name to be used for the card and its Options, if necessary. In Ethtool Options, you can set ethtool options used by ifup for the interface. For infor- mation about available options, see the ethtool manual page. If the option string starts with a - (for example, -K INTERFACE_NAME rx on ), the second word in the string is replaced with the current interface name. Otherwise (for example, autoneg off speed 10 ) ifup adds -s INTERFACE_NAME to the beginning. 3. Click Next. 4. Configure any needed options, such as the IP address, device activation or firewall zone for the interface in the General, Address, and Hardware tabs. For more information about the configuration options, see Section 23.4.1.2, “Changing the configuration of a network card”. 5. If you selected Wireless as the device type of the interface, configure the wireless connec- tion in the next dialog. 330 Configuring the network card with YaST SLES 15 SP66. To activate the new network configuration, confirm the settings. 23.4.1.4 Configuring host name and DNS If you did not change the network configuration during installation and the Ethernet card was already available, a host name was automatically generated for your computer and DHCP was activated. The same applies to the name service information your host needs to integrate into a network environment. If DHCP is used for network address setup, the list of domain name servers is automatically lled with the appropriate data. If a static setup is preferred, set these values manually. To change the name of your computer and adjust the name server search list, proceed as follows: 1. Go to the Network Settings Hostname/DNS tab in the System module in YaST. 2. Enter the Hostname. Note that the host name is global and applies to all network interfaces. If you are using DHCP to get an IP address, the host name of your computer will be automatically set by the DHCP server. You should disable this behavior if you connect to different networks, because they may assign different host names and changing the host name at runtime may confuse the graphical desktop. To disable using DHCP to get an IP address deactivate Change Hostname via DHCP. 3. In Modify DNS Configuration, select the way the DNS configuration (name servers, search list, the content of the /run/netconfig/resolv.conf le) is modified. If the Use Default Policy option is selected, the configuration is handled by the netconfig script which merges the data defined statically (with YaST or in the configuration les) with data obtained dynamically (from the DHCP client or NetworkManager). This default policy is usually sufficient. If the Only Manually option is selected, netconfig is not allowed to modify the /run/ netconfig/resolv.conf le. However, this le can be edited manually. If the Custom Policy option is selected, a Custom Policy Rule string defining the merge policy should be specified. The string consists of a comma-separated list of interface names to be considered a valid source of settings. Except for complete interface names, basic wild cards to match multiple interfaces are allowed, as well. For example, eth* ppp? will rst target all eth and then all ppp0-ppp9 interfaces. There are two special policy values that indicate how to apply the static settings defined in the /etc/sysconfig/network/config le: STATIC The static settings need to be merged together with the dynamic settings. 331 Configuring the network card with YaST SLES 15 SP6STATIC_FALLBACK The static settings are used only when no dynamic configuration is available. For more information, see the man page of netconfig (8) ( man 8 netconfig ). 4. Enter the Name Servers and ll in the Domain Search list. Name servers must be specified by IP addresses, such as 192.168.1.116, not by host names. Names specified in the Domain Search tab are domain names used for resolving host names without a specified domain. If more than one Domain Search is used, separate domains with commas or white space. 5. To activate the configuration, confirm the settings. It is also possible to edit the host name using YaST from the command line. The changes made by YaST take effect immediately (which is not the case when editing the /etc/HOSTNAME le manually). To change the host name, use the following command: # yast dns edit hostname=HOSTNAME To change the name servers, use the following commands: # yast dns edit nameserver1=192.168.1.116 # yast dns edit nameserver2=192.168.1.117 # yast dns edit nameserver3=192.168.1.118 23.4.1.5 Configuring routing To make your machine communicate with other machines and other networks, routing infor- mation must be given to make network traffic take the correct path. If DHCP is used, this infor- mation is automatically provided. If a static setup is used, this data must be added manually. 1. In YaST go to Network Settings Routing. 2. Enter the IP address of the Default Gateway (IPv4 and IPv6 if necessary). The default gateway matches every possible destination, but if a routing table entry exists that matches the required address, this will be used instead of the default route via the Default Gateway. 3. More entries can be entered in the Routing Table. Enter the Destination network IP address, Gateway IP address and the Netmask. Select the Device through which the traffic to the defined network will be routed (the minus sign stands for any device). To omit any of these values, use the minus sign - . To enter a default gateway into the table, use default in the Destination eld. 332 Configuring the network card with YaST SLES 15 SP6Note: Route prioritization If more default routes are used, it is possible to specify the metric option to deter- mine which route has a higher priority. To specify the metric option, enter - met- ric NUMBER in Options. The lowest possible metric is 0. The route with the lowest metric has the highest priority and is used as default. If the network device is dis- connected, its route will be removed and the next one will be used. 4. If the system is a router, enable IPv4 Forwarding and IPv6 Forwarding in the Network Settings as needed. 5. To activate the configuration, confirm the settings. 23.4.2 IBM Z: configuring network devices SUSE Linux Enterprise Server for IBM Z supports several types of network interfaces. YaST can be used to configure all of them. 23.4.2.1 The qeth-hsi device To add a qeth-hsi (HiperSockets) interface to the installed system, start the System Network Settings module in YaST. Select one of the devices marked Hipersocket to use as the READ device address and click Edit. Enter the device numbers for the read, write and control channels (ex- ample device number format: 0.0.0800 ). Then click next. In the Network Address Setup dialog, specify the IP address and netmask for the new interface and leave the network configuration by clicking Next and OK. 23.4.2.2 The qeth-ethernet device To add a qeth-ethernet (IBM OSA Express Ethernet Card) interface to the installed system, start the System Network Settings module in YaST. Select one of the devices marked IBM OSA Express Ethernet Card to use as the READ device address and click Edit. Enter a device number for the read, write and control channels (example device number format: 0.0.0700 ). Enter the needed port name, port number (if applicable) and some additional options, your IP address, and an appropriate netmask. Leave the network configuration with Next and OK. 333 IBM Z: configuring network devices SLES 15 SP623.4.2.3 The ctc device To add a ctc (IBM parallel CTC Adapter) interface to the installed system, start the System Net- work Settings module in YaST. Select one of the devices marked IBM Parallel CTC Adapter to use as your read channel and click Configure. Choose the Device Settings that t your devices (usually this would be Compatibility Mode). Specify both your IP address and the IP address of the remote partner. If needed, adjust the MTU size with Advanced Detailed Settings. Leave the network configuration with Next and OK. Warning: CTC is no longer supported The use of this interface is deprecated. This interface will not be supported in future versions of SUSE Linux Enterprise Server. 23.4.2.4 The lcs device To add an lcs (IBM OSA-2 Adapter) interface to the installed system, start the System Network Settings module in YaST. Select one of the devices marked IBM OSA-2 Adapter and click Configure. Enter the needed port number, some additional options, your IP address and an appropriate netmask. Leave the network configuration with Next and OK. 23.4.2.5 The IUCV device To add an iucv (IUCV) interface to the installed system, start the System Network Settings module in YaST. Select a device marked IUCV and click Edit. YaST prompts you for the name of your IUCV partner (Peer). Enter the name (this entry is case-sensitive) and select Next. Specify both the IP Address and the Remote IP Address of your partner. If needed, Set MTU size on General tab. Leave the network configuration with Next and OK. Warning: IUCV is no longer supported The use of this interface is deprecated. This interface will not be supported in future versions of SUSE Linux Enterprise Server. 334 IBM Z: configuring network devices SLES 15 SP623.5 Configuring a network connection manually Manual configuration of the network software should be the last alternative. Using YaST is recommended. However, this background information about the network configuration can also assist your work with YaST. 23.5.1 The wicked network configuration The tool and library called wicked provides a new framework for network configuration. One of the challenges with traditional network interface management is that different layers of network management get jumbled together into one single script, or at most two different scripts. These scripts interact with each other in a way that is not well defined. This leads to un- predictable issues, obscure constraints and conventions, etc. Several layers of special hacks for a variety of different scenarios increase the maintenance burden. Address configuration protocols are being used that are implemented via daemons like dhcpcd, which interact rather poorly with the rest of the infrastructure. Funky interface naming schemes that require heavy udev support are introduced to achieve persistent identification of interfaces. The idea of wicked is to decompose the problem in several ways. None of them is entirely novel, but trying to put ideas from different projects together is hopefully going to create a better solution overall. One approach is to use a client/server model. This allows wicked to define standardized facilities for things like address configuration that are well integrated with the overall framework. For example, using a specific address configuration, the administrator may request that an interface should be configured via DHCP or IPv4 zeroconf. In this case, the address configuration service simply obtains the lease from its server and passes it on to the wicked server process that installs the requested addresses and routes. The other approach to decomposing the problem is to enforce the layering aspect. For any type of network interface, it is possible to define a dbus service that configures the network interface''s device layer—a VLAN, a bridge, a bonding, or a paravirtualized device. Common functionality, such as address configuration, is implemented by joint services that are layered on top of these device specific services without having to implement them specifically. The wicked framework implements these two aspects by using a variety of dbus services, which get attached to a network interface depending on its type. Here is a rough overview of the current object hierarchy in wicked. 335 Configuring a network connection manually SLES 15 SP6Each network interface is represented via a child object of /org/opensuse/Network/Inter- faces . The name of the child object is given by its ifindex. For example, the loopback interface, which usually gets ifindex 1, is /org/opensuse/Network/Interfaces/1 , the rst Ethernet in- terface registered is /org/opensuse/Network/Interfaces/2 . Each network interface has a “class” associated with it, which is used to select the dbus interfaces it supports. By default, each network interface is of class netif , and wickedd will automatically attach all interfaces compatible with this class. In the current implementation, this includes the following interfaces: org.opensuse.Network.Interface Generic network interface functions, such as taking the link up or down, assigning an MTU, etc. org.opensuse.Network.Addrconf.ipv4.dhcp, org.opensuse.Network.Addrconf.ipv6.dhcp, org.opensuse.Network.Addrconf.ipv4.auto Address configuration services for DHCP, IPv4 zeroconf, etc. Beyond this, network interfaces may require or offer special configuration mechanisms. For an Ethernet device, for example, you should be able to control the link speed, offloading of check- summing, etc. To achieve this, Ethernet devices have a class of their own, called netif-ether- net , which is a subclass of netif . As a consequence, the dbus interfaces assigned to an Ether- net interface include all the services listed above, plus the org.opensuse.Network.Ethernet service available only to objects belonging to the netif-ethernet class. Similarly, there exist classes for interface types like bridges, VLANs, bonds, or infinibands. How do you interact with an interface like VLAN (which is really a virtual network interface that sits on top of an Ethernet device) that needs to be created rst? For this, wicked defines factory interfaces, such as org.opensuse.Network.VLAN.Factory . Such a factory interface offers a single function that lets you create an interface of the requested type. These factory interfaces are attached to the /org/opensuse/Network/Interfaces list node. 23.5.1.1 wicked architecture and features The wicked service comprises several parts as depicted in Figure 23.4, “wicked architecture”. 336 The wicked network configuration SLES 15 SP6FIGURE 23.4: wicked ARCHITECTURE wicked currently supports the following: Configuration le back-ends to parse SUSE style /etc/sysconfig/network les. An internal configuration back-end to represent network interface configuration in XML. Bring up and shutdown of “normal” network interfaces such as Ethernet or InfiniBand, VLAN, bridge, bonds, tun, tap, dummy, macvlan, macvtap, hsi, qeth, iucv, and wireless (currently limited to one wpa-psk/eap network) devices. A built-in DHCPv4 client and a built-in DHCPv6 client. The nanny daemon (enabled by default) helps to automatically bring up configured inter- faces when the device is available (interface hotplugging) and set up the IP configuration when a link (carrier) is detected. See Section 23.5.1.3, “Nanny” for more information. wicked was implemented as a group of DBus services that are integrated with systemd. So the usual systemctl commands will apply to wicked . 23.5.1.2 Using wicked On SUSE Linux Enterprise, wicked runs by default. If you want to check what is currently enabled and whether it is running, call: systemctl status network 337 The wicked network configuration SLES 15 SP6If wicked is enabled, you will see something along these lines: wicked.service - wicked managed network interfaces Loaded: loaded (/usr/lib/systemd/system/wicked.service; enabled) ... In case something different is running (for example, NetworkManager) and you want to switch to wicked , rst stop what is running and then enable wicked : systemctl is-active network && \ systemctl stop network systemctl enable --force wicked This enables the wicked services, creates the network.service to wicked.service alias link, and starts the network at the next boot. Starting the server process: systemctl start wickedd This starts wickedd (the main server) and associated supplicants: /usr/lib/wicked/bin/wickedd-auto4 --systemd --foreground /usr/lib/wicked/bin/wickedd-dhcp4 --systemd --foreground /usr/lib/wicked/bin/wickedd-dhcp6 --systemd --foreground /usr/sbin/wickedd --systemd --foreground /usr/sbin/wickedd-nanny --systemd --foreground Then bringing up the network: systemctl start wicked Alternatively use the network.service alias: systemctl start network These commands are using the default or system configuration sources as defined in /etc/ wicked/client.xml . To enable debugging, set WICKED_DEBUG in /etc/sysconfig/network/config , for example: WICKED_DEBUG="all" Or, to omit some: WICKED_DEBUG="all,-dbus,-objectmodel,-xpath,-xml" 338 The wicked network configuration SLES 15 SP6Use the client utility to display interface information for all interfaces or the interface specified with IFNAME : wicked show all wicked show IFNAME In XML output: wicked show-xml all wicked show-xml IFNAME Bringing up one interface: wicked ifup eth0 wicked ifup wlan0 ... Because there is no configuration source specified, the wicked client checks its default sources of configuration defined in /etc/wicked/client.xml : 1. firmware: iSCSI Boot Firmware Table (iBFT) 2. compat: ifcfg les—implemented for compatibility Whatever wicked gets from those sources for a given interface is applied. The intended order of importance is firmware , then compat—this may be changed in the future. For more information, see the wicked man page. 23.5.1.3 Nanny Nanny is an event and policy driven daemon that is responsible for asynchronous or unsolicited scenarios such as hotplugging devices. Thus the nanny daemon helps with starting or restarting delayed or temporarily gone devices. Nanny monitors device and link changes, and integrates new devices defined by the current policy set. Nanny continues to set up even if ifup already exited because of specified timeout constraints. By default, the nanny daemon is active on the system. It is enabled in the /etc/wicked/com- mon.xml configuration le: ... 339 The wicked network configuration SLES 15 SP6 true This setting causes ifup and ifreload to apply a policy with the effective configuration to the nanny daemon; then, nanny configures wickedd and thus ensures hotplug support. It waits in the background for events or changes (such as new devices or carrier on). 23.5.1.4 Bringing up multiple interfaces For bonds and bridges, it may make sense to define the entire device topology in one le (ifcfg- bondX), and bring it up in one go. wicked then can bring up the whole configuration if you specify the top level interface names (of the bridge or bond): wicked ifup br0 This command automatically sets up the bridge and its dependencies in the appropriate order without the need to list the dependencies (ports, etc.) separately. To bring up multiple interfaces in one command: wicked ifup bond0 br0 br1 br2 Or also all interfaces: wicked ifup all 23.5.1.5 Using tunnels with Wicked When you need to use tunnels with Wicked, the TUNNEL_DEVICE is used for this. It permits to specify an optional device name to bind the tunnel to the device. The tunneled packets will only be routed via this device. For more information, refer to man 5 ifcfg-tunnel . 23.5.1.6 Handling incremental changes With wicked , there is no need to actually take down an interface to reconfigure it (unless it is required by the kernel). For example, to add another IP address or route to a statically configured network interface, add the IP address to the interface definition, and do another 340 The wicked network configuration SLES 15 SP6“ifup” operation. The server will try hard to update only those settings that have changed. This applies to link-level options such as the device MTU or the MAC address, and network-level settings, such as addresses, routes, or even the address configuration mode (for example, when moving from a static configuration to DHCP). Things get tricky of course with virtual interfaces combining several real devices such as bridges or bonds. For bonded devices, it is not possible to change certain parameters while the device is up. Doing that will result in an error. However, what should still work, is the act of adding or removing the child devices of a bond or bridge, or choosing a bond''s primary interface. 23.5.1.7 Wicked extensions: address configuration wicked is designed to be extensible with shell scripts. These extensions can be defined in the config.xml le. Currently, several classes of extensions are supported: link configuration: these are scripts responsible for setting up a device''s link layer according to the configuration provided by the client, and for tearing it down again. address configuration: these are scripts responsible for managing a device''s address con- figuration. Usually address configuration and DHCP are managed by wicked itself, but can be implemented by means of extensions. firewall extension: these scripts can apply firewall rules. Typically, extensions have a start and a stop command, an optional “pid le”, and a set of environment variables that get passed to the script. To illustrate how this is supposed to work, look at a firewall extension defined in etc/serv- er.xml : 341 The wicked network configuration SLES 15 SP6The extension is attached to the tag and defines commands to execute for the actions of this interface. Further, the declaration can define and initialize environment variables passed to the actions. 23.5.1.8 Wicked extensions: configuration files You can extend the handling of configuration les with scripts as well. For example, DNS up- dates from leases are ultimately handled by the extensions/resolver script, with behavior configured in server.xml : When an update arrives in wickedd , the system updater routines parse the lease and call the ap- propriate commands ( backup , install , etc.) in the resolver script. This in turn configures the DNS settings using /sbin/netconfig , or by manually writing /run/netconfig/resolv.conf as a fallback. 23.5.2 Configuration files This section provides an overview of the network configuration les and explains their purpose and the format used. 23.5.2.1 /etc/wicked/common.xml The /etc/wicked/common.xml le contains common definitions that should be used by all applications. It is sourced/included by the other configuration les in this directory. Although you can use this le to enable debugging across all wicked components, we recommend to use the le /etc/wicked/local.xml for this purpose. After applying maintenance updates you might lose your changes as the /etc/wicked/common.xml might be overwritten. The /etc/ wicked/common.xml le includes the /etc/wicked/local.xml in the default installation, thus you typically do not need to modify the /etc/wicked/common.xml . 342 Configuration files SLES 15 SP6In case you want to disable nanny by setting the to false , restart the wicked- d.service and then run the following command to apply all configurations and policies: > sudo wicked ifup all Note: Configuration files The wickedd , wicked , or nanny programs try to read /etc/wicked/common.xml if their own configuration les do not exist. 23.5.2.2 /etc/wicked/server.xml The le /etc/wicked/server.xml is read by the wickedd server process at start-up. The le stores extensions to the /etc/wicked/common.xml . On top of that this le configures handling of a resolver and receiving information from addrconf supplicants, for example DHCP. We recommend to add changes required to this le into a separate le /etc/wicked/serv- er-local.xml , that gets included by /etc/wicked/server.xml . By using a separate le you avoid overwriting of your changes during maintenance updates. 23.5.2.3 /etc/wicked/client.xml The /etc/wicked/client.xml is used by the wicked command. The le specifies the location of a script used when discovering devices managed by ibft and configures locations of network interface configurations. We recommend to add changes required to this le into a separate le /etc/wicked/client- local.xml , that gets included by /etc/wicked/server.xml . By using a separate le you avoid overwriting of your changes during maintenance updates. 23.5.2.4 /etc/wicked/nanny.xml The /etc/wicked/nanny.xml configures types of link layers. We recommend to add specific configuration into a separate le: /etc/wicked/nanny-local.xml to avoid losing the changes during maintenance updates. 343 Configuration files SLES 15 SP623.5.2.5 /etc/sysconfig/network/ifcfg-* These les contain the traditional configurations for network interfaces. Note: wicked and the ifcfg-* files wicked reads these les if you specify the compat: prefix. According to the SUSE Lin- ux Enterprise Server default configuration in /etc/wicked/client.xml , wicked tries these les before the XML configuration les in /etc/wicked/ifconfig . The --ifconfig switch is provided mostly for testing only. If specified, default config- uration sources defined in /etc/wicked/ifconfig are not applied. The ifcfg-* les include information such as the start mode and the IP address. Possible parameters are described in the manual page of ifup . Additionally, most variables from the dhcp and wireless les can be used in the ifcfg-* les if a general setting should be used for only one interface. However, most of the /etc/sysconfig/network/config variables are global and cannot be overridden in ifcfg les. For example, NETCONFIG_* variables are global. For configuring macvlan and macvtab interfaces, see the ifcfg-macvlan and ifcfg-macv- tap man pages. For example, for a macvlan interface provide a ifcfg-macvlan0 with settings as follows: STARTMODE=''auto'' MACVLAN_DEVICE=''eth0'' #MACVLAN_MODE=''vepa'' #LLADDR=02:03:04:05:06:aa For ifcfg.template , see Section 23.5.2.6, “/etc/sysconfig/network/config, /etc/syscon- fig/network/dhcp, and /etc/sysconfig/network/wireless”. IBM Z IBM Z does not support USB. The names of the interface les and network aliases contain IBM Z-specific elements like qeth . 23.5.2.6 /etc/sysconfig/network/config, /etc/sysconfig/network/ dhcp, and /etc/sysconfig/network/wireless The le config contains general settings for the behavior of ifup , ifdown and ifstatus . dhcp contains settings for DHCP and wireless for wireless LAN cards. The variables in all three configuration les are commented. Some variables from /etc/sysconfig/network/config can also be used in ifcfg-* les, where they are given a higher priority. The /etc/syscon- 344 Configuration files SLES 15 SP6fig/network/ifcfg.template le lists variables that can be specified in a per interface scope. However, most of the /etc/sysconfig/network/config variables are global and cannot be overridden in ifcfg-les. For example, NETWORKMANAGER or NETCONFIG_* variables are global. Note: Using DHCPv6 In SUSE Linux Enterprise 11, DHCPv6 used to work even on networks where IPv6 Router Advertisements (RAs) were not configured properly. Starting with SUSE Linux Enter- prise 12, DHCPv6 requires that at least one of the routers on the network sends out RAs that indicate that this network is managed by DHCPv6. For networks where the router cannot be configured correctly, the ifcfg option allows the user to override this behavior by specifying DHCLIENT6_MODE=''managed'' in the ifcfg le. You can also activate this workaround with a boot parameter in the instal- lation system: ifcfg=eth0=dhcp6,DHCLIENT6_MODE=managed 23.5.2.7 /etc/sysconfig/network/routes and /etc/sysconfig/ network/ifroute-* The static routing of TCP/IP packets is determined by the /etc/sysconfig/network/routes and /etc/sysconfig/network/ifroute-* les. All the static routes required by the various system tasks can be specified in /etc/sysconfig/network/routes : routes to a host, routes to a host via a gateway and routes to a network. For each interface that needs individual rout- ing, define an additional configuration le: /etc/sysconfig/network/ifroute-* . Replace the wild card ( * ) with the name of the interface. The entries in the routing configuration les look like this: # Destination Gateway Netmask Interface Options The route''s destination is in the rst column. This column may contain the IP address of a network or host or, in the case of reachable name servers, the fully qualified network or host name. The network should be written in CIDR notation (address with the associated routing prefix-length) such as 10.10.0.0/16 for IPv4 or fc00::/7 for IPv6 routes. The keyword default indicates that the route is the default gateway in the same address family as the gateway. For devices without a gateway use explicit 0.0.0.0/0 or ::/0 destinations. 345 Configuration files SLES 15 SP6The second column contains the default gateway or a gateway through which a host or network can be accessed. The third column is deprecated; it used to contain the IPv4 netmask of the destination. For IPv6 routes, the default route, or when using a prefix-length (CIDR notation) in the rst column, enter a dash ( - ) here. The fourth column contains the name of the interface. If you leave it empty using a dash ( - ), it can cause unintended behavior in /etc/sysconfig/network/routes . For more information, see the routes man page. An (optional) fth column can be used to specify special options. For details, see the routes man page. EXAMPLE 23.5: COMMON NETWORK INTERFACES AND SOME STATIC ROUTES # --- IPv4 routes in CIDR prefix notation: # Destination [Gateway] - Interface 127.0.0.0/8 - - lo 204.127.235.0/24 - - eth0 default 204.127.235.41 - eth0 207.68.156.51/32 207.68.145.45 - eth1 192.168.0.0/16 207.68.156.51 - eth1 # --- IPv4 routes in deprecated netmask notation" # Destination [Dummy/Gateway] Netmask Interface # 127.0.0.0 0.0.0.0 255.255.255.0 lo 204.127.235.0 0.0.0.0 255.255.255.0 eth0 default 204.127.235.41 0.0.0.0 eth0 207.68.156.51 207.68.145.45 255.255.255.255 eth1 192.168.0.0 207.68.156.51 255.255.0.0 eth1 # --- IPv6 routes are always using CIDR notation: # Destination [Gateway] - Interface 2001:DB8:100::/64 - - eth0 2001:DB8:100::/32 fe80::216:3eff:fe6d:c042 - eth0 23.5.2.8 /var/run/netconfig/resolv.conf The domain to which the host belongs is specified in /var/run/netconfig/resolv.conf (key- word search ). Up to six domains with a total of 256 characters can be specified with the search option. When resolving a name that is not fully qualified, an attempt is made to gen- erate one by attaching the individual search entries. Up to three name servers can be speci- 346 Configuration files SLES 15 SP6fied with the nameserver option, each on a line of its own. Comments are preceded by hash mark or semicolon signs ( # or ; ). As an example, see Example 23.6, “/var/run/netconfig/re- solv.conf”. However, /etc/resolv.conf should not be edited by hand. It is generated by the netconfig script and is a symbolic link to /run/netconfig/resolv.conf . To define static DNS configura- tion without using YaST, edit the appropriate variables manually in the /etc/sysconfig/net- work/config le: NETCONFIG_DNS_STATIC_SEARCHLIST list of DNS domain names used for host name lookup NETCONFIG_DNS_STATIC_SERVERS list of name server IP addresses to use for host name lookup NETCONFIG_DNS_FORWARDER the name of the DNS forwarder that needs to be configured, for example bind or re- solver NETCONFIG_DNS_RESOLVER_OPTIONS arbitrary options that will be written to /var/run/netconfig/resolv.conf , for example: debug attempts:1 timeout:10 For more information, see the resolv.conf man page. NETCONFIG_DNS_RESOLVER_SORTLIST list of up to 10 items, for example: 130.155.160.0/255.255.240.0 130.155.0.0 For more information, see the resolv.conf man page. To disable DNS configuration using netconfig, set NETCONFIG_DNS_POLICY='''' . For more infor- mation about netconfig , see the netconfig(8) man page ( man 8 netconfig ). EXAMPLE 23.6: /var/run/netconfig/resolv.conf # Our domain search example.com # # We use dns.example.com (192.168.1.116) as nameserver 347 Configuration files SLES 15 SP6nameserver 192.168.1.116 23.5.2.9 /sbin/netconfig netconfig is a modular tool to manage additional network configuration settings. It merges statically defined settings with settings provided by autoconfiguration mechanisms as DHCP or PPP according to a predefined policy. The required changes are applied to the system by calling the netconfig modules that are responsible for modifying a configuration le and restarting a service or a similar action. netconfig recognizes three main actions. The netconfig modify and netconfig remove commands are used by daemons such as DHCP or PPP to provide or remove settings to netconfig. Only the netconfig update command is available for the user: modify The netconfig modify command modifies the current interface and service specific dy- namic settings and updates the network configuration. Netconfig reads settings from stan- dard input or from a le specified with the --lease-file FILENAME option and inter- nally stores them until a system reboot (or the next modify or remove action). Already existing settings for the same interface and service combination are overwritten. The in- terface is specified by the -i INTERFACE_NAME parameter. The service is specified by the -s SERVICE_NAME parameter. remove The netconfig remove command removes the dynamic settings provided by an editing action for the specified interface and service combination and updates the network con- figuration. The interface is specified by the -i INTERFACE_NAME parameter. The service is specified by the -s SERVICE_NAME parameter. update The netconfig update command updates the network configuration using current set- tings. This is useful when the policy or the static configuration has changed. Use the -m MODULE_TYPE parameter to update a specified service only ( dns , nis , or ntp ). The netconfig policy and the static configuration settings are defined either manually or using YaST in the /etc/sysconfig/network/config le. The dynamic configuration settings pro- vided by autoconfiguration tools such as DHCP or PPP are delivered directly by these tools with the netconfig modify and netconfig remove actions. When NetworkManager is enabled, netconfig (in policy mode auto ) uses only NetworkManager settings, ignoring settings from 348 Configuration files SLES 15 SP6any other interfaces configured using the traditional ifup method. If NetworkManager does not provide any setting, static settings are used as a fallback. A mixed usage of NetworkManager and the wicked method is not supported. For more information about netconfig , see man 8 netconfig . 23.5.2.10 /etc/hosts In this le, shown in Example 23.7, “/etc/hosts”, IP addresses are assigned to host names. If no name server is implemented, all hosts to which an IP connection will be set up must be listed here. For each host, enter a line consisting of the IP address, the fully qualified host name, and the host name into the le. The IP address must be at the beginning of the line and the entries separated by blanks and tabs. Comments are always preceded by the # sign. EXAMPLE 23.7: /etc/hosts 127.0.0.1 localhost 192.168.2.100 jupiter.example.com jupiter 192.168.2.101 venus.example.com venus 23.5.2.11 /etc/networks Here, network names are converted to network addresses. The format is similar to that of the hosts le, except the network names precede the addresses. See Example 23.8, “/etc/networks”. EXAMPLE 23.8: /etc/networks loopback 127.0.0.0 localnet 192.168.0.0 23.5.2.12 /etc/host.conf Name resolution—the translation of host and network names via the resolver library—is con- trolled by this le. This le is only used for programs linked to libc4 or libc5. For current glibc programs, refer to the settings in /etc/nsswitch.conf . Each parameter must always be en- tered on a separate line. Comments are preceded by a # sign. Table 23.2, “Parameters for /etc/ host.conf” shows the parameters available. A sample /etc/host.conf is shown in Example 23.9, “/etc/host.conf”. 349 Configuration files SLES 15 SP6TABLE 23.2: PARAMETERS FOR /ETC/HOST.CONF order hosts, bind Specifies in which order the services are ac- cessed for the name resolution. Available ar- guments are (separated by blank spaces or commas): hosts: searches the /etc/hosts le bind: accesses a name server nis: uses NIS multi on/o Defines if a host entered in /etc/hosts can have multiple IP addresses. nospoof on spoofalert on/o These parameters influence the name serv- er spoofing but do not exert any influence on the network configuration. trim domainname The specified domain name is separated from the host name after host name resolution (as long as the host name includes the do- main name). This option is useful only if names from the local domain are in the / etc/hosts le, but should still be recog- nized with the attached domain names. EXAMPLE 23.9: /etc/host.conf # We have named running order hosts bind # Allow multiple address multi on 23.5.2.13 /etc/nsswitch.conf The introduction of the GNU C Library 2.0 was accompanied by the introduction of the Name Service Switch (NSS). Refer to the nsswitch.conf(5) man page and The GNU C Library Reference Manual for details. 350 Configuration files SLES 15 SP6The order for queries is defined in the le /etc/nsswitch.conf . A sample nsswitch.conf is shown in Example 23.10, “/etc/nsswitch.conf”. Comments are preceded by # signs. In this example, the entry under the hosts database means that a request is sent to /etc/hosts ( files ) via DNS (see Chapter 39, The domain name system). EXAMPLE 23.10: /etc/nsswitch.conf passwd: compat group: compat hosts: files dns networks: files dns services: db files protocols: db files rpc: files ethers: files netmasks: files netgroup: files nis publickey: files bootparams: files automount: files nis aliases: files nis shadow: compat The “databases” available over NSS are listed in Table  23.3, “Databases available via /etc/nss- witch.conf”. The configuration options for NSS databases are listed in Table 23.4, “Configuration options for NSS “databases””. TABLE 23.3: DATABASES AVAILABLE VIA /ETC/NSSWITCH.CONF aliases Mail aliases implemented by sendmail ; see man   5 aliases . ethers Ethernet addresses. netmasks List of networks and their subnet masks. On- ly needed, if you use subnetting. group User groups used by getgrent . See also the man page for group . 351 Configuration files SLES 15 SP6hosts Host names and IP addresses, used by geth- ostbyname and similar functions. netgroup Valid host and user lists in the network for controlling access permissions; see the net- group(5) man page. networks Network names and addresses, used by get- netent . publickey Public and secret keys for Secure_RPC used by NFS and NIS+. passwd User passwords, used by getpwent ; see the passwd(5) man page. protocols Network protocols, used by getprotoent ; see the protocols(5) man page. rpc Remote procedure call names and address- es, used by getrpcbyname and similar func- tions. services Network services, used by getservent . shadow Shadow passwords of users, used by getsp- nam ; see the shadow(5) man page. TABLE 23.4: CONFIGURATION OPTIONS FOR NSS “DATABASES” files directly access les, for example, /etc/ aliases db access via a database nis , nisplus NIS, see also Book “Security and Hardening Guide”, Chapter 3 “Using NIS” dns can only be used as an extension for hosts and networks 352 Configuration files SLES 15 SP6compat can only be used as an extension for pass- wd , shadow and group 23.5.2.14 /etc/nscd.conf This le is used to configure nscd (name service cache daemon). See the nscd(8) and nscd.conf(5) man pages. By default, the system entries of passwd , groups and hosts are cached by nscd. This is important for the performance of directory services, like NIS and LDAP, because otherwise the network connection needs to be used for every access to names, groups or hosts. If the caching for passwd is activated, it usually takes about fifteen seconds until a newly added local user is recognized. Reduce this waiting time by restarting nscd with: > sudo systemctl restart nscd 23.5.2.15 /etc/HOSTNAME /etc/HOSTNAME contains the fully qualified host name (FQHN). The fully qualified host name is the host name with the domain name attached. This le must contain only one line (in which the host name is set). It is read while the machine is booting. 23.5.3 Testing the configuration Before you write your configuration to the configuration les, you can test it. To set up a test configuration, use the ip command. To test the connection, use the ping command. The command ip changes the network configuration directly without saving it in the configu- ration le. Unless you enter your configuration in the correct configuration les, the changed network configuration is lost on reboot. Note: ifconfig and route are obsolete The ifconfig and route tools are obsolete. Use ip instead. ifconfig , for example, limits interface names to 9 characters. 353 Testing the configuration SLES 15 SP623.5.3.1 Configuring a network interface with ip ip is a tool to show and configure network devices, routing, policy routing, and tunnels. ip is a very complex tool. Its common syntax is ip  OPTIONS OBJECT COMMAND . You can work with the following objects: link This object represents a network device. address This object represents the IP address of device. neighbor This object represents an ARP or NDISC cache entry. route This object represents the routing table entry. rule This object represents a rule in the routing policy database. maddress This object represents a multicast address. mroute This object represents a multicast routing cache entry. tunnel This object represents a tunnel over IP. If no command is given, the default command is used (usually list ). Change the state of a device with the command: > sudo ip link set DEV_NAME For example, to deactivate device eth0, enter > sudo ip link set eth0 down To activate it again, use > sudo ip link set eth0 up 354 Testing the configuration SLES 15 SP6Tip: Disconnecting NIC device If you deactivate a device with > sudo ip link set DEV_NAME down it disables the network interface on a software level. If you want to simulate losing the link as if the Ethernet cable is unplugged or the con- nected switch is turned o, run > sudo ip link set DEV_NAME carrier off For example, while ip link set DEV_NAME down drops all routes using DEV_NAME , ip link set DEV carrier off does not. Be aware that carrier off requires support from the network device driver. To connect the device back to the physical network, run > sudo ip link set DEV_NAME carrier on After activating a device, you can configure it. To set the IP address, use > sudo ip addr add IP_ADDRESS + dev DEV_NAME For example, to set the address of the interface eth0 to 192.168.12.154/30 with standard broad- cast (option brd ), enter > sudo ip addr add 192.168.12.154/30 brd + dev eth0 To have a working connection, you must also configure the default gateway. To set a gateway for your system, enter > sudo ip route add default via gateway_ip_address To display all devices, use > sudo ip link ls To display the running interfaces only, use > sudo ip link ls up To print interface statistics for a device, enter > sudo ip -s link ls DEV_NAME 355 Testing the configuration SLES 15 SP6To view additional useful information, specifically about virtual network devices, enter > sudo ip -d link ls DEV_NAME Moreover, to view network layer (IPv4, IPv6) addresses of your devices, enter > sudo ip addr In the output, you can nd information about MAC addresses of your devices. To show all routes, use > sudo ip route show For more information about using ip , enter ip   help or see the man 8 ip manual page. The help option is also available for all ip subcommands, such as: > sudo ip addr help Find the ip manual in /usr/share/doc/packages/iproute2/ip-cref.pdf . 23.5.3.2 Testing a connection with ping The ping command is the standard tool for testing whether a TCP/IP connection works. It uses the ICMP protocol to send a small data packet, ECHO_REQUEST datagram, to the destination host, requesting an immediate reply. If this works, ping displays a message to that effect. This indicates that the network link is functioning. ping does more than only test the function of the connection between two computers: it also provides some basic information about the quality of the connection. In Example 23.11, “Output of the command ping”, you can see an example of the ping output. The second-to-last line con- tains information about the number of transmitted packets, packet loss, and total time of ping running. As the destination, you can use a host name or IP address, for example, ping   example.com or ping   192.168.3.100 . The program sends packets until you press Ctrl – C . If you only need to check the functionality of the connection, you can limit the number of the packets with the -c option. For example to limit ping to three packets, enter ping   -c 3 example.com . EXAMPLE 23.11: OUTPUT OF THE COMMAND PING ping -c 3 example.com PING example.com (192.168.3.100) 56(84) bytes of data. 356 Testing the configuration SLES 15 SP664 bytes from example.com (192.168.3.100): icmp_seq=1 ttl=49 time=188 ms 64 bytes from example.com (192.168.3.100): icmp_seq=2 ttl=49 time=184 ms 64 bytes from example.com (192.168.3.100): icmp_seq=3 ttl=49 time=183 ms --- example.com ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2007ms rtt min/avg/max/mdev = 183.417/185.447/188.259/2.052 ms The default interval between two packets is one second. To change the interval, ping provides the option -i . For example, to increase the ping interval to ten seconds, enter ping   -i 10 example.com . In a system with multiple network devices, it is sometimes useful to send the ping through a specific interface address. To do so, use the -I option with the name of the selected device, for example, ping   -I wlan1 example.com . For more options and information about using ping, enter ping   -h or see the ping (8) man page. Tip: Pinging IPv6 addresses For IPv6 addresses use the ping6 command. Note, to ping link-local addresses, you must specify the interface with -I . The following command works, if the address is reachable via eth1 : ping6 -I eth1 fe80::117:21ff:feda:a425 23.5.4 Unit files and start-up scripts Apart from the configuration les described above, there are also systemd unit les and various scripts that load the network services while the machine is booting. These are started when the system is switched to the multi-user.target target. Some of these unit les and scripts are described in Some unit files and start-up scripts for network programs. For more information about systemd , see Chapter 19, The systemd daemon and for more information about the systemd targets, see the man page of systemd.special ( man systemd.special ). SOME UNIT FILES AND START-UP SCRIPTS FOR NETWORK PROGRAMS network.target network.target is the systemd target for networking, but its mean depends on the set- tings provided by the system administrator. 357 Unit files and start-up scripts SLES 15 SP6For more information, see https://www.freedesktop.org/wiki/Software/systemd/NetworkTar- get/ . multi-user.target multi-user.target is the systemd target for a multiuser system with all required net- work services. rpcbind Starts the rpcbind utility that converts RPC program numbers to universal addresses. It is needed for RPC services, such as an NFS server. ypserv Starts the NIS server. ypbind Starts the NIS client. /etc/init.d/nfsserver Starts the NFS server. /etc/init.d/postfix Controls the postfix process. 23.6 Basic router setup A router is a networking device that delivers and receives data (network packets) to or from more than one network back and forth. You often use a router to connect your local network to the remote network (Internet) or to connect local network segments. With SUSE Linux Enterprise Server you can build a router with features such as NAT (Network Address Translation) or advanced firewalling. The following are basic steps to turn SUSE Linux Enterprise Server into a router. 1. Enable forwarding, for example in /etc/sysctl.d/50-router.conf net.ipv4.conf.all.forwarding = 1 net.ipv6.conf.all.forwarding = 1 Then provide a static IPv4 and IPv6 IP setup for the interfaces. Enabling forwarding dis- ables several mechanisms, for example IPv6 does not accept an IPv6 RA (router advertise- ment) anymore, which also prevents the creation of a default route. 358 Basic router setup SLES 15 SP62. In many situations (for example, when you can reach the same network via more than one interface, or when VPN usually is used and already on “normal multi-home hosts”), you must disable the IPv4 reverse path filter (this feature does not currently exist for IPv6): net.ipv4.conf.all.rp_filter = 0 You can also filter with firewall settings instead. 3. To accept an IPv6 RA (from the router on an external, uplink, or ISP interface) and create a default (or also a more specific) IPv6 route again, set: net.ipv6.conf.${ifname}.accept_ra = 2 net.ipv6.conf.${ifname}.autoconf = 0 (Note: “ eth0.42 ” needs to be written as eth0/42 in a dot-separated sysfs path.) More router behavior and forwarding dependencies are described in https://www.kernel.org/doc/ Documentation/networking/ip-sysctl.txt . To provide IPv6 on your internal (DMZ) interfaces, and announce yourself as an IPv6 router and “autoconf networks” to the clients, install and configure radvd in /etc/radvd.conf , for example: interface eth0 { IgnoreIfMissing on; # do not fail if interface missed AdvSendAdvert on; # enable sending RAs AdvManagedFlag on; # IPv6 addresses managed via DHCPv6 AdvOtherConfigFlag on; # DNS, NTP... only via DHCPv6 AdvDefaultLifetime 3600; # client default route lifetime of 1 hour prefix 2001:db8:0:1::/64 # (/64 is default and required for autoconf) { AdvAutonomous off; # Disable address autoconf (DHCPv6 only) AdvValidLifetime 3600; # prefix (autoconf addr) is valid 1 h AdvPreferredLifetime 1800; # prefix (autoconf addr) is preferred 1/2 h } } Configure the firewall to masquerade traffic with NAT from the LAN into the WAN and to block inbound traffic on the WAN interface: > sudo firewall-cmd --permanent --zone=external --change-interface=WAN_INTERFACE 359 Basic router setup SLES 15 SP6> sudo firewall-cmd --permanent --zone=external --add-masquerade > sudo firewall-cmd --permanent --zone=internal --change-interface=LAN_INTERFACE > sudo firewall-cmd --reload 23.7 Setting up bonding devices For some systems, there is a desire to implement network connections that comply to more than the standard data security or availability requirements of a typical Ethernet device. In these cases, several Ethernet devices can be aggregated to a single bonding device. The configuration of the bonding device is done by means of bonding module options. The be- havior is mainly affected by the mode of the bonding device. By default, this is active-backup which means that a different bond port will become active if the active port fails. The following bonding modes are available: 0 (balance-rr) Packets are transmitted in round-robin fashion from the rst to the last available interface. Provides fault tolerance and load balancing. 1 (active-backup) Only one network interface is active. If it fails, a different interface becomes active. This setting is the default for SUSE Linux Enterprise Server. Provides fault tolerance. 2 (balance-xor) Traffic is split between all available interfaces based on the number of devices included in the bonding. It requires support from the switch. Provides fault tolerance and load balancing. 3 (broadcast) All traffic is broadcast on all interfaces. Requires support from the switch. Provides fault tolerance. 4 (802.3ad) Aggregates interfaces into groups that share the same speed and duplex settings. Requires ethtool support in the interface drivers, and a switch that supports and is configured for IEEE 802.3ad Dynamic link aggregation. Provides fault tolerance and load balancing. 5 (balance-tlb) Adaptive transmit load balancing. Requires ethtool support in the interface drivers but not switch support. Provides fault tolerance and load balancing. 360 Setting up bonding devices SLES 15 SP66 (balance-alb) Adaptive load balancing. Requires ethtool support in the interface drivers but not switch support. Provides fault tolerance and load balancing. For a more detailed description of the modes, see https://www.kernel.org/doc/Documenta- tion/networking/bonding.txt . Tip: Bonding and Xen Using bonding devices is only of interest for machines where you have multiple real net- work cards available. In most configurations, this means that you should use the bonding configuration only in Dom0. Only if you have multiple network cards assigned to a VM Guest system it may also be useful to set up the bond in a VM Guest. Note: IBM POWER: Bonding modes 5 and 6 (balance-tlb / balance-alb) unsupported by ibmveth There is a conflict with the tlb/alb bonding configuration and Power rmware. In short, the bonding driver in tlb/alb mode sends Ethernet Loopback packets with both the source and destination MAC addresses listed as the Virtual Ethernet MAC address. These packets are not supported by Power rmware. Therefore bonding modes 5 and 6 are unsupported by ibmveth. To configure a bonding device, use the following procedure: 1. Run YaST System Network Settings. 2. Use Add and change the Device Type to Bond. Proceed with Next. 361 Setting up bonding devices SLES 15 SP63. Select how to assign the IP address to the bonding device. Three methods are at your disposal: No IP Address Dynamic Address (with DHCP or Zeroconf) Statically assigned IP Address Use the method that is appropriate for your environment. 4. In the Bond Ports tab, select the Ethernet devices that should be included into the bond by activating the related check box. 5. Edit the Bond Driver Options and choose a bonding mode. 6. Make sure that the parameter miimon=100 is added to the Bond Driver Options. Without this parameter, the data integrity is not checked regularly. 7. Click Next and leave YaST with OK to create the device. 362 Setting up bonding devices SLES 15 SP623.7.1 Hotplugging of bond ports In specific network environments (such as High Availability), there are cases when you need to replace a bond port interface with another one. The reason may be a constantly failing network device. The solution is to set up hotplugging of bond ports. The bond is configured as usual (according to man 5 ifcfg-bonding ), for example: ifcfg-bond0 STARTMODE=''auto'' # or ''onboot'' BOOTPROTO=''static'' IPADDR=''192.168.0.1/24'' BONDING_MASTER=''yes'' BONDING_SLAVE_0=''eth0'' BONDING_SLAVE_1=''eth1'' BONDING_MODULE_OPTS=''mode=active-backup miimon=100'' The bond ports are specified with STARTMODE=hotplug and BOOTPROTO=none : ifcfg-eth0 STARTMODE=''hotplug'' BOOTPROTO=''none'' ifcfg-eth1 STARTMODE=''hotplug'' BOOTPROTO=''none'' BOOTPROTO=none uses the ethtool options (when provided), but does not set the link up on ifup eth0 . The reason is that the bond port interface is controlled by the bond device. STARTMODE=hotplug causes the bond port interface to join the bond automatically when it is available. The udev rules in /etc/udev/rules.d/70-persistent-net.rules need to be changed to match the device by bus ID (udev KERNELS keyword equal to "SysFS BusID" as visible in hwin- fo --netcard ) instead of by MAC address. This allows replacement of defective hardware (a network card in the same slot but with a different MAC) and prevents confusion when the bond changes the MAC address of all its bond ports. For example: SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", KERNELS=="0000:00:19.0", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0" 363 Hotplugging of bond ports SLES 15 SP6At boot time, the systemd network.service does not wait for the hotplug bond ports, but for the bond to become ready, which requires at least one available bond port. When one of the bond port interfaces gets removed (unbind from NIC driver, rmmod of the NIC driver or true PCI hotplug remove) from the system, the kernel removes it from the bond automatically. When a new card is added to the system (replacement of the hardware in the slot), udev renames it using the bus-based persistent name rule to the name of the bond port, and calls ifup for it. The ifup call automatically joins it into the bond. 23.8 Setting up team devices for Network Teaming The term “link aggregation” is the general term which describes combining (or aggregating) a network connection to provide a logical layer. Sometimes you nd the terms “channel teaming”, “Ethernet bonding”, “port trunking”, etc. which are synonyms and refer to the same concept. This concept is widely known as “bonding” and was originally integrated into the Linux kernel (see Section 23.7, “Setting up bonding devices” for the original implementation). The term Network Teaming is used to refer to the new implementation of this concept. The main difference between bonding and Network Teaming is that teaming supplies a set of small kernel modules responsible for providing an interface for teamd instances. Everything else is handled in user space. This is different from the original bonding implementation which contains all of its functionality exclusively in the kernel. For a comparison refer to Table 23.5, “Feature comparison between bonding and team”. TABLE 23.5: FEATURE COMPARISON BETWEEN BONDING AND TEAM Feature Bonding Team broadcast, round-robin TX yes yes policy active-backup TX policy yes yes LACP (802.3ad) support yes yes hash-based TX policy yes yes user can set hash function no yes TX load-balancing support yes yes (TLB) 364 Setting up team devices for Network Teaming SLES 15 SP6Feature Bonding Team TX load-balancing support no yes for LACP Ethtool link monitoring yes yes ARP link monitoring yes yes NS/NA (IPV6) link monitor- no yes ing RCU locking on TX/RX paths no yes port prio and stickiness no yes separate per-port link moni- no yes toring setup multiple link monitoring set- limited yes up VLAN support yes yes multiple device stacking yes yes Source: https://libteam.org/files/teamdev.pp.pdf Both implementations, bonding and Network Teaming, can be used in parallel. Network Team- ing is an alternative to the existing bonding implementation. It does not replace bonding. Network Teaming can be used for different use cases. The two most important use cases are explained later and involve: Load balancing between different network devices. Failover from one network device to another in case one of the devices should fail. 365 Setting up team devices for Network Teaming SLES 15 SP6Currently, there is no YaST module to support creating a teaming device. You need to configure Network Teaming manually. The general procedure is shown below which can be applied for all your Network Teaming configurations: PROCEDURE 23.1: GENERAL PROCEDURE 1. Install the package libteam-tools : > sudo zypper in libteam-tools 2. Create a configuration le under /etc/sysconfig/network/ . Usually it will be ifcfg- team0 . If you need more than one Network Teaming device, give them ascending numbers. This configuration le contains several variables which are explained in the man pages (see man ifcfg and man ifcfg-team ). An example configuration can be found in your system in the le /etc/sysconfig/network/ifcfg.template . 3. Remove the configuration les of the interfaces which will be used for the teaming device (usually ifcfg-eth0 and ifcfg-eth1 ). It is recommended to make a backup and remove both les. Wicked will re-create the configuration les with the necessary parameters for teaming. 4. Optionally, check if everything is included in Wicked''s configuration le: > sudo wicked show-config 5. Start the Network Teaming device team0 : > sudo wicked ifup team0 In case you need additional debug information, use the option --debug all after the all subcommand. 366 Setting up team devices for Network Teaming SLES 15 SP66. Check the status of the Network Teaming device. This can be done by the following com- mands: Get the state of the teamd instance from Wicked: > sudo wicked ifstatus --verbose team0 Get the state of the entire instance: > sudo teamdctl team0 state Get the systemd state of the teamd instance: > sudo systemctl status teamd@team0 Each of them shows a slightly different view depending on your needs. 7. In case you need to change something in the ifcfg-team0 le afterward, reload its con- figuration with: > sudo wicked ifreload team0 Do not use systemctl for starting or stopping the teaming device! Instead, use the wicked command as shown above. To completely remove the team device, use this procedure: PROCEDURE 23.2: REMOVING A TEAM DEVICE 1. Stop the Network Teaming device team0 : > sudo wicked ifdown team0 2. Rename the le /etc/sysconfig/network/ifcfg-team0 to /etc/sysconfig/net- work/.ifcfg-team0 . Inserting a dot in front of the le name makes it “invisible” for wicked. If you really do not need the configuration anymore, you can also remove the le. 3. Reload the configuration: > sudo wicked ifreload all 367 Setting up team devices for Network Teaming SLES 15 SP623.8.1 Use case: load balancing with Network Teaming Load balancing is used to improve bandwidth. Use the following configuration le to create a Network Teaming device with load balancing capabilities. Proceed with Procedure 23.1, “General procedure” to set up the device. Check the output with teamdctl . EXAMPLE 23.12: CONFIGURATION FOR LOAD BALANCING WITH NETWORK TEAMING STARTMODE=auto 1 BOOTPROTO=static 2 IPADDRESS="192.168.1.1/24" 2 IPADDR6="fd00:deca:fbad:50::1/64" 2 TEAM_RUNNER="loadbalance" 3 TEAM_LB_TX_HASH="ipv4,ipv6,eth,vlan" TEAM_LB_TX_BALANCER_NAME="basic" TEAM_LB_TX_BALANCER_INTERVAL="100" TEAM_PORT_DEVICE_0="eth0" 4 TEAM_PORT_DEVICE_1="eth1" 4 TEAM_LW_NAME="ethtool" 5 TEAM_LW_ETHTOOL_DELAY_UP="10" 6 TEAM_LW_ETHTOOL_DELAY_DOWN="10" 6 1 Controls the start of the teaming device. The value of auto means, the interface will be set up when the network service is available and will be started automatically on every reboot. In case you need to control the device yourself (and prevent it from starting automatically), set STARTMODE to manual . 2 Sets a static IP address (here 192.168.1.1 for IPv4 and fd00:deca:fbad:50::1 for IPv6). If the Network Teaming device should use a dynamic IP address, set BOOTPROTO="dhcp" and remove (or comment) the line with IPADDRESS and IPADDR6 . 3 Sets TEAM_RUNNER to loadbalance to activate the load balancing mode. 4 Specifies one or more devices which should be aggregated to create the Network Teaming device. 5 Defines a link watcher to monitor the state of subordinate devices. The default value eth- tool checks only if the device is up and accessible. This makes this check fast enough. However, it does not check if the device can really send or receive packets. If you need a higher confidence in the connection, use the arp_ping option. This sends pings to an arbitrary host (configured in the TEAM_LW_ARP_PING_TARGET_HOST variable). The Network Teaming device is considered to be up only if the replies are received. 368 Use case: load balancing with Network Teaming SLES 15 SP66 Defines the delay in milliseconds between the link coming up (or down) and the runner being notified. 23.8.2 Use case: failover with Network Teaming Failover is used to ensure high availability of a critical Network Teaming device by involving a parallel backup network device. The backup network device is running all the time and takes over if and when the main device fails. Use the following configuration le to create a Network Teaming device with failover capabili- ties. Proceed with Procedure 23.1, “General procedure” to set up the device. Check the output with teamdctl . EXAMPLE 23.13: CONFIGURATION FOR DHCP NETWORK TEAMING DEVICE STARTMODE=auto 1 BOOTPROTO=static 2 IPADDR="192.168.1.2/24" 2 IPADDR6="fd00:deca:fbad:50::2/64" 2 TEAM_RUNNER=activebackup 3 TEAM_PORT_DEVICE_0="eth0" 4 TEAM_PORT_DEVICE_1="eth1" 4 TEAM_LW_NAME=ethtool 5 TEAM_LW_ETHTOOL_DELAY_UP="10" 6 TEAM_LW_ETHTOOL_DELAY_DOWN="10" 6 1 Controls the start of the teaming device. The value of auto means the interface will be set up when the network service is available and will be started automatically on every reboot. In case you need to control the device yourself (and prevent it from starting automatically), set STARTMODE to manual . 2 Sets a static IP address (here 192.168.1.2 for IPv4 and fd00:deca:fbad:50::2 for IPv6). If the Network Teaming device should use a dynamic IP address, set BOOTPROTO="dhcp" and remove (or comment) the line with IPADDRESS and IPADDR6 . 3 Sets TEAM_RUNNER to activebackup to activate the failover mode. 4 Specifies one or more devices which should be aggregated to create the Network Teaming device. 369 Use case: failover with Network Teaming SLES 15 SP65 Defines a link watcher to monitor the state of subordinate devices. The default value eth- tool checks only if the device is up and accessible. This makes this check fast enough. However, it does not check if the device can really send or receive packets. If you need a higher confidence in the connection, use the arp_ping option. This sends pings to an arbitrary host (configured in the TEAM_LW_ARP_PING_TARGET_HOST variable). Only if the replies are received, the Network Teaming device is considered to be up. 6 Defines the delay in milliseconds between the link coming up (or down) and the runner being notified. 23.8.3 Use case: VLAN over team device VLAN is an abbreviation of Virtual Local Area Network. It allows the running of multiple logical (virtual) Ethernets over one single physical Ethernet. It logically splits the network into different broadcast domains so that packets are only switched between ports that are designated for the same VLAN. The following use case creates two static VLANs on top of a team device: vlan0 , bound to the IP address 192.168.10.1 vlan1 , bound to the IP address 192.168.20.1 Proceed as follows: 1. Enable the VLAN tags on your switch. To use load balancing for your team device, your switch needs to be capable of Link Aggregation Control Protocol (LACP) (802.3ad). Consult your hardware manual about the details. 2. Decide if you want to use load balancing or failover for your team device. Set up your team device as described in Section 23.8.1, “Use case: load balancing with Network Teaming” or Section 23.8.2, “Use case: failover with Network Teaming”. 3. In /etc/sysconfig/network create a le ifcfg-vlan0 with the following content: STARTMODE="auto" BOOTPROTO="static" 1 IPADDR=''192.168.10.1/24'' 2 ETHERDEVICE="team0" 3 VLAN_ID="0" 4 VLAN=''yes'' 370 Use case: VLAN over team device SLES 15 SP61 Defines a xed IP address, specified in IPADDR . 2 Defines the IP address, here with its netmask. 3 Contains the real interface to use for the VLAN interface, here our team device ( team0 ). 4 Specifies a unique ID for the VLAN. Preferably, the le name and the VLAN_ID cor- responds to the name ifcfg-vlanVLAN_ID . In our case VLAN_ID is 0 which leads to the le name ifcfg-vlan0 . 4. Copy the le /etc/sysconfig/network/ifcfg-vlan0 to /etc/sysconfig/net- work/ifcfg-vlan1 and change the following values: IPADDR from 192.168.10.1/24 to 192.168.20.1/24 . VLAN_ID from 0 to 1 . 5. Start the two VLANs: # wicked ifup vlan0 vlan1 6. Check the output of ifconfig : # ifconfig -a [...] vlan0 Link encap:Ethernet HWaddr 08:00:27:DC:43:98 inet addr:192.168.10.1 Bcast:192.168.10.255 Mask:255.255.255.0 inet6 addr: fe80::a00:27ff:fedc:4398/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:12 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 b) TX bytes:816 (816.0 b) vlan1 Link encap:Ethernet HWaddr 08:00:27:DC:43:98 inet addr:192.168.20.1 Bcast:192.168.20.255 Mask:255.255.255.0 inet6 addr: fe80::a00:27ff:fedc:4398/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:12 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 b) TX bytes:816 (816.0 b) 371 Use case: VLAN over team device SLES 15 SP623.9 Software-defined networking with Open vSwitch Software-defined networking (SDN) means separating the system that controls where traffic is sent (the control plane) from the underlying system that forwards traffic to the selected destina- tion (the data plane, also called the forwarding plane). This means that the functions previous- ly fulfilled by a single, usually inflexible switch can now be separated between a switch (data plane) and its controller (control plane). In this model, the controller is programmable and can be very flexible and adapt quickly to changing network conditions. Open vSwitch is software that implements a distributed virtual multilayer switch that is compat- ible with the OpenFlow protocol. OpenFlow allows a controller application to modify the con- figuration of a switch. OpenFlow is layered onto the TCP protocol and is implemented in a range of hardware and software. A single controller can thus drive multiple, very different switches. 23.9.1 Advantages of Open vSwitch Software-defined networking with Open vSwitch brings several advantages with it, especially when you used together with virtual machines: Networking states can be identified easily. Networks and their live state can be moved from one host to another. Network dynamics are traceable and external software can be enabled to respond to them. You can apply and manipulate tags in network packets to identify which machine they are coming from or going to and maintain other networking context. Tagging rules can be configured and migrated. Open vSwitch implements the GRE protocol (Generic Routing Encapsulation). This allows you, for example, to connect private VM networks to each other. Open vSwitch can be used on its own, but is designed to integrate with networking hard- ware and can control hardware switches. 23.9.2 Installing Open vSwitch 1. Install Open vSwitch and supplementary packages: # zypper install openvswitch openvswitch-switch 372 Software-defined networking with Open vSwitch SLES 15 SP6If you plan to use Open vSwitch together with the KVM hypervisor, additionally install tunctl . If you plan to use Open vSwitch together with the Xen hypervisor, additionally install openvswitch-kmp-xen . 2. Enable the Open vSwitch service: # systemctl enable openvswitch 3. Either restart the computer or use systemctl to start the Open vSwitch service imme- diately: # systemctl start openvswitch 4. To check whether Open vSwitch was activated correctly, use: # systemctl status openvswitch 23.9.3 Overview of Open vSwitch daemons and utilities Open vSwitch consists of several components. Among them are a kernel module and various user space components. The kernel module is used for accelerating the data path, but is not necessary for a minimal Open vSwitch installation. 23.9.3.1 Daemons The central executables of Open vSwitch are its two daemons. When you start the openvswitch service, you are indirectly starting them. The main Open vSwitch daemon ( ovs-vswitchd ) provides the implementation of a switch. The Open vSwitch database daemon ( ovsdb-server ) serves the database that stores the configura- tion and state of Open vSwitch. 23.9.3.2 Utilities Open vSwitch also comes with several utilities that help you work with it. The following list is not exhaustive, but instead describes important commands only. 373 Overview of Open vSwitch daemons and utilities SLES 15 SP6ovsdb-tool Create, upgrade, compact, and query Open vSwitch databases. Do transactions on Open vSwitch databases. ovs-appctl Configure a running ovs-vswitchd or ovsdb-server daemon. ovs-dpctl , ovs-dpctl-top Create, modify, visualize, and delete data paths. Using this tool can interfere with ovs- vswitchd also performing data path management. Therefore, it is often used for diagnos- tics only. ovs-dpctl-top creates a top -like visualization for data paths. ovs-ofctl Manage any switches adhering to the OpenFlow protocol. ovs-ofctl is not limited to interacting with Open vSwitch. ovs-vsctl Provides a high-level interface to the configuration database. It can be used to query and modify the database. In effect, it shows the status of ovs-vswitchd and can be used to configure it. 23.9.4 Creating a bridge with Open vSwitch The following example configuration uses the Wicked network service that is used by default on SUSE Linux Enterprise Server. To learn more about Wicked, see Section 23.5, “Configuring a network connection manually”. When you have installed and started Open vSwitch, proceed as follows: 1. To configure a bridge for use by your virtual machine, create a le with content like this: STARTMODE=''auto'' 1 BOOTPROTO=''dhcp'' 2 OVS_BRIDGE=''yes'' 3 OVS_BRIDGE_PORT_DEVICE_1=''eth0'' 4 1 Set up the bridge automatically when the network service is started. 2 The protocol to use for configuring the IP address. 3 Mark the configuration as an Open vSwitch bridge. 374 Creating a bridge with Open vSwitch SLES 15 SP64 Choose which device/devices should be added to the bridge. To add more devices, append additional lines for each of them to the le: OVS_BRIDGE_PORT_DEVICE_SUFFIX=''DEVICE'' The SUFFIX can be any alphanumeric string. However, to avoid overwriting a pre- vious definition, make sure the SUFFIX of each device is unique. Save the le in the directory /etc/sysconfig/network under the name ifcfg-br0 . Instead of br0 , you can use any name you want. However, the le name needs to begin with ifcfg- . To learn about further options, refer to the man pages of ifcfg ( man 5 ifcfg ) and ifcfg-ovs-bridge ( man 5 ifcfg-ovs-bridge ). 2. Now start the bridge: # wicked ifup br0 When Wicked is done, it should output the name of the bridge and next to it the state up . 23.9.5 Using Open vSwitch directly with KVM After having created the bridge as described in Section 23.9.4, “Creating a bridge with Open vSwitch”, you can use Open vSwitch to manage the network access of virtual machines created with KVM/ QEMU. 1. To be able to best use the capabilities of Wicked, make some further changes to the bridge configured before. Open the previously created /etc/sysconfig/network/ifcfg-br0 and append a line for another port device: OVS_BRIDGE_PORT_DEVICE_2=''tap0'' Additionally, set BOOTPROTO to none . The le should now look like this: STARTMODE=''auto'' BOOTPROTO=''none'' OVS_BRIDGE=''yes'' OVS_BRIDGE_PORT_DEVICE_1=''eth0'' OVS_BRIDGE_PORT_DEVICE_2=''tap0'' The new port device tap0 will be configured in the next step. 375 Using Open vSwitch directly with KVM SLES 15 SP62. Now add a configuration le for the tap0 device: STARTMODE=''auto'' BOOTPROTO=''none'' TUNNEL=''tap'' Save the le in the directory /etc/sysconfig/network under the name ifcfg-tap0 . Tip: Allowing other users to access the tap device To be able to use this tap device from a virtual machine started as a user who is not root , append: TUNNEL_SET_OWNER=USER_NAME To allow access for an entire group, append: TUNNEL_SET_GROUP=GROUP_NAME 3. Finally, open the configuration for the device defined as the rst OVS_BRIDGE_PORT_DE- VICE . If you did not change the name, that should be eth0 . Therefore, open /etc/ sysconfig/network/ifcfg-eth0 and make sure that the following options are set: STARTMODE=''auto'' BOOTPROTO=''none'' If the le does not exist yet, create it. 4. Restart the bridge interface using Wicked: # wicked ifreload br0 This will also trigger a reload of the newly defined bridge port devices. 5. To start a virtual machine, use, for example: # qemu-kvm \ -drive file=/PATH/TO/DISK-IMAGE 1 \ -m 512 -net nic,vlan=0,macaddr=00:11:22:EE:EE:EE \ -net tap,ifname=tap0,script=no,downscript=no 2 1 The path to the QEMU disk image you want to start. 2 Use the tap device ( tap0 ) created before. 376 Using Open vSwitch directly with KVM SLES 15 SP6For further information on the usage of KVM/QEMU, see Book “Virtualization Guide”. 23.9.6 Using Open vSwitch with libvirt After having created the bridge as described before in Section 23.9.4, “Creating a bridge with Open vSwitch”, you can add the bridge to an existing virtual machine managed with libvirt . Since libvirt has some support for Open vSwitch bridges already, you can use the bridge created in Section 23.9.4, “Creating a bridge with Open vSwitch” without further changes to the networking configuration. 1. Open the domain XML le for the intended virtual machine: # virsh edit VM_NAME Replace VM_NAME with the name of the desired virtual machine. This will open your de- fault text editor. 2. Find the networking section of the document by looking for a section starting with and ending in . Replace the existing section with a networking section that looks somewhat like this: Important: Compatibility of virsh iface-* and Virtual Machine Manager with Open vSwitch At the moment, the Open vSwitch compatibility of libvirt is not exposed through the virsh iface-* tools and Virtual Machine Manager. If you use any of these tools, your configuration can break. 3. You can now start or restart the virtual machine as usual. For further information on the usage of libvirt , see Book “Virtualization Guide”. 377 Using Open vSwitch with libvirt SLES 15 SP623.9.7 More information For more information on SDN, refer to the documentation section of the Open vSwitch project Web site at https://docs.openvswitch.org/en/latest/#documentation . 378 More information SLES 15 SP624 Printer operation SUSE® Linux Enterprise Server supports printing with many types of printers, including remote network printers. Printers can be configured manually or with YaST. For configuration instruc- tions, refer to Chapter 34, Setting up a printer. Both graphical and command line utilities are avail- able for starting and managing print jobs. If your printer does not work as expected, refer to Section 24.8, “Troubleshooting”. CUPS (Common Unix Printing System) is the standard print system in SUSE Linux Enterprise Server. Printers can be distinguished by interface, such as USB or network, and printer language. When buying a printer, make sure that the printer has an interface that is supported (USB, Ethernet or Wi-Fi) and a suitable printer language. Printers can be categorized on the basis of the following three classes of printer languages: PostScript printers PostScript is the printer language in which most print jobs in Linux and Unix are generat- ed and processed by the internal print system. If PostScript documents can be processed directly by the printer and do not need to be converted in additional stages in the print system, the number of potential error sources is reduced. Currently PostScript is being replaced by PDF as the standard print job format. PostScript +PDF printers that can directly print PDF (in addition to PostScript) already exist. For traditional PostScript printers PDF needs to be converted to PostScript in the printing workflow. Standard printers (languages like PCL and ESC/p) For known printer languages, the print system can convert PostScript jobs to the respective printer language with Ghostscript. This processing stage is called interpreting. The best- known languages are PCL (which is used by HP printers and their clones) and ESC/P (which is used by Epson printers). These printer languages are normally supported by Linux and produce an adequate print result. Linux may not be able to address certain special printer functions. Except for HP and Epson, there are currently no printer manufacturers who develop Linux drivers and make them available to Linux distributors under an open source license. 379 SLES 15 SP6Proprietary printers (also called GDI printers) These printers do not support any of the common printer languages. They use their own undocumented printer languages, which are subject to change when a new edition of a model is released. Normally, only Windows drivers are available for these printers. See Section 24.8.1, “Printers without standard printer language support” for more information. Before you buy a new printer, refer to the following sources to check how well the printer you intend to buy is supported: https://www.openprinting.org/printers The OpenPrinting home page with the printer database. The database shows the latest Linux support status. However, a Linux distribution can only integrate the drivers available at production time. Accordingly, a printer currently rated as “perfectly supported” may not have had this status when the latest SUSE Linux Enterprise Server version was released. Thus, the databases may not necessarily indicate the correct status, but only provide an approximation. https://www.ghostscript.com The Ghostscript Web page. /usr/share/doc/packages/ghostscript/catalog.devices List of built-in Ghostscript drivers. 24.1 The CUPS workflow The user creates a print job. The print job consists of the data to print plus information for the spooler. This includes the name of the printer or the name of the print queue, and optionally, information for the filter, such as printer-specific options. At least one dedicated print queue exists for every printer. The spooler holds the print job in the queue until the desired printer is ready to receive data. When the printer is ready, the spooler sends the data through the filter and back-end to the printer. The filter converts the data generated by the application that is printing (normally PostScript or PDF, but also ASCII, JPEG, etc.) into printer-specific data (PostScript, PCL, ESC/P, etc.). The features of the printer are described in the PPD les. A PPD le contains printer-specific options with the parameters needed to enable them on the printer. The filter system makes sure that options selected by the user are enabled. 380 The CUPS workflow SLES 15 SP6If you use a PostScript printer, the filter system converts the data into printer-specific PostScript. This does not require a printer driver. If you use a non-PostScript printer, the filter system con- verts the data into printer-specific data. This requires a printer driver suitable for your printer. The back-end receives the printer-specific data from the filter then passes it to the printer. 24.2 Methods and protocols for connecting printers There are multiple possibilities for connecting a printer to the system. The configuration of CUPS does not distinguish between a local printer and a printer connected to the system over the network. For more information about the printer connection, read the article CUPS in a Nutshell at https://en.opensuse.org/SDB:CUPS_in_a_Nutshell . IBM Z Printers and similar devices provided by the z/VM that connect locally with the IBM Z mainframes are not supported by CUPS. On these platforms, printing is only possible over the network. The cabling for network printers must be installed according to the instructions of the printer manufacturer. Warning: Changing cable connections in a running system When connecting the printer to the machine, do not forget that only USB devices can be plugged in or unplugged during operation. To avoid damaging your system or printer, shut down the system before changing any connections that are not USB. 24.3 Installing the software PPD (PostScript printer description) is the computer language that describes the properties, like resolution, and options, such as the availability of a duplex unit. These descriptions are required for using printer options in CUPS. Without a PPD le, the print data would be forwarded to the printer in a “raw” state, which is not desired. To configure a PostScript printer, the best approach is to get a suitable PPD le. Many PPD les are available in the packages manufacturer-PPDs and OpenPrintingPPDs-postscript . See Section 24.7.3, “PPD files in multiple packages” and Section 24.8.2, “No suitable PPD file available for a PostScript printer”. 381 Methods and protocols for connecting printers SLES 15 SP6New PPD les can be stored in the directory /usr/share/cups/model/ or added to the print system with YaST as described in Section 34.1.1, “Adding drivers with YaST”. Subsequently, the PPD le can be selected during the printer setup. Be careful if a printer manufacturer wants you to install entire software packages. This kind of installation may result in the loss of the support provided by SUSE Linux Enterprise Server. Also, print commands may work differently and the system may no longer be able to address devices of other manufacturers. For this reason, the installation of manufacturer software is not recommended. 24.4 Network printers A network printer can support multiple protocols. Although most of the supported protocols are standardized, certain manufacturers modify the standard. Manufacturers then provide drivers for only a few operating systems and Linux drivers are rarely provided. The current situation is such that you cannot act on the assumption that every protocol works smoothly in Linux. There- fore, you may need to experiment with several options to achieve a functional configuration. CUPS supports the socket , LPD , IPP and smb protocols. socket Socket refers to a connection in which the plain print data is sent directly to a TCP socket. Socket port numbers that are commonly used are 9100 or 35 . The device URI (uniform resource identifier) syntax is: socket:// IP.OF.THE.PRINTER : PORT , for example: sock- et://192.168.2.202:9100/ . LPD (line printer daemon) The LPD protocol is described in RFC 1179. Under this protocol, specific job-related data, such as the ID of the print queue, is sent before the actual print data is sent. Therefore, a print queue must be specified when configuring the LPD protocol. The implementations of diverse printer manufacturers are flexible enough to accept any name as the print queue. If necessary, the printer manual should indicate what name to use. LPT, LPT1, LP1 or similar names are often used. The port number for an LPD service is 515 . An example device URI is lpd://192.168.2.202/LPT1 . 382 Network printers SLES 15 SP6IPP (Internet printing protocol) IPP is based on the HTTP protocol. With IPP, more job-related data is transmitted than with the other protocols. CUPS uses IPP for internal data transmission. The name of the print queue is necessary to configure IPP correctly. The port number for IPP is 631 . Example device URIs are ipp://192.168.2.202/ps and ipp://192.168.2.202/printers/ps . SMB (Windows share) CUPS also supports printing on printers connected to Windows shares. The protocol used for this purpose is SMB. SMB uses the port numbers 137 , 138 and 139 . Example de- vice URIs are smb://user:password@workgroup/smb.example.com/printer , smb:// user:password@smb.example.com/printer , and smb://smb.example.com/printer . The protocol supported by the printer must be determined before configuration. If the manufac- turer does not provide the needed information, the command nmap (which comes with the nmap package) can be used to ascertain the protocol. nmap checks a host for open ports. For example: > nmap -p 35,137-139,515,631,9100-10000 IP.OF.THE.PRINTER 24.5 Configuring CUPS with command line tools CUPS can be configured with command line tools like lpinfo , lpadmin and lpoptions . You need a device URI consisting of a back-end, such as USB, and parameters. To determine valid device URIs on your system use the command lpinfo -v | grep ":/" : > sudo lpinfo -v | grep ":/" direct usb://ACME/FunPrinter%20XL network socket://192.168.2.253 With lpadmin the CUPS server administrator can add, remove or manage print queues. To add a print queue, use the following syntax: > sudo lpadmin -p QUEUE -v DEVICE-URI -P PPD-FILE -E Then the device ( -v ) is available as QUEUE ( -p ), using the specified PPD le ( -P ). This means that you must know the PPD le and the device URI to configure the printer manually. 383 Configuring CUPS with command line tools SLES 15 SP6Do not use -E as the rst option. For all CUPS commands, -E as the rst argument sets use of an encrypted connection. To enable the printer, -E must be used as shown in the following example: > sudo lpadmin -p ps -v usb://ACME/FunPrinter%20XL -P \ /usr/share/cups/model/Postscript.ppd.gz -E The following example configures a network printer: > sudo lpadmin -p ps -v socket://192.168.2.202:9100/ -P \ /usr/share/cups/model/Postscript-level1.ppd.gz -E For more options of lpadmin , see the man page of lpadmin(8) . During printer setup, certain options are set as default. These options can be modified for every print job (depending on the print tool used). Changing these default options with YaST is also possible. Using command line tools, set default options as follows: 1. First, list all options: > sudo lpoptions -p QUEUE -l Example: Resolution/Output Resolution: 150dpi *300dpi 600dpi The activated default option is identified by a preceding asterisk ( * ). 2. Change the option with lpadmin : > sudo lpadmin -p QUEUE -o Resolution=600dpi 3. Check the new setting: > sudo lpoptions -p QUEUE -l Resolution/Output Resolution: 150dpi 300dpi *600dpi When a normal user runs lpoptions , the settings are written to ~/.cups/lpoptions . How- ever, root settings are written to /etc/cups/lpoptions . 384 Configuring CUPS with command line tools SLES 15 SP624.6 Printing from the command line To print from the command line, enter lp -d QUEUENAME FILENAME , substituting the corre- sponding names for QUEUENAME and FILENAME . Several applications rely on the lp command for printing. In this case, enter the correct com- mand in the application''s print dialog, normally without specifying FILENAME , for example, lp -d QUEUENAME . 24.7 Special features in SUSE Linux Enterprise Server Several CUPS features have been adapted for SUSE Linux Enterprise Server. The most important changes are covered here. 24.7.1 CUPS and firewall After completing a default installation of SUSE Linux Enterprise Server, firewalld is active and the network interfaces are configured to be in the public zone, which blocks incoming traffic. When firewalld is active, you may need to configure it to allow clients to browse network printers by allowing mdns and ipp through the internal network zone. The public zone should never expose printer queues. (More information about the firewalld configuration is available in Book “Security and Harden- ing Guide”, Chapter 23 “Masquerading and firewalls”, Section 23.4 “firewalld” and at https://en.open- suse.org/SDB:CUPS_and_SANE_Firewall_settings .) 24.7.1.1 CUPS client Normally, a CUPS client runs on a regular workstation located in a trusted network environment behind a firewall. In this case, it is recommended to configure the network interface to be in the Internal Zone , so the workstation is reachable from within the network. 385 Printing from the command line SLES 15 SP624.7.1.2 CUPS server If the CUPS server is part of a trusted network environment protected by a firewall, the network interface should be configured to be in the Internal Zone of the firewall. It is not recommend- ed to set up a CUPS server in an untrusted network environment unless you ensure that it is protected by special firewall rules and secure settings in the CUPS configuration. 24.7.2 Browsing for network printers CUPS servers regularly announce the availability and status information of shared printers over the network. Clients can access this information to display a list of available printers in printing dialogs, for example. This is called “browsing”. CUPS servers announce their print queues over the network either via the traditional CUPS browsing protocol, or via Bonjour/DNS-SD. To enable browsing network print queues, the ser- vice cups-browsed needs to run on all clients that print via CUPS servers. cups-browsed is not started by default. To start it for the active session, use sudo systemctl start cups- browsed . To ensure it is automatically started after booting, enable it with sudo systemctl enable cups-browsed on all clients. In case browsing does not work after having started cups-browsed , the CUPS servers announce the network print queues via Bonjour/DNS-SD. In this case, you need to additionally install the package avahi and start the associated service with sudo systemctl start avahi-daemon on all clients. See Section 24.7.1, “CUPS and firewall” for information on allowing printer browsing through fire- walld . 24.7.3 PPD files in multiple packages The YaST printer configuration sets up the queues for CUPS using the PPD les installed in / usr/share/cups/model . To nd the suitable PPD les for the printer model, YaST compares the vendor and model determined during hardware detection with the vendors and models in all PPD les. For this purpose, the YaST printer configuration generates a database from the vendor and model information extracted from the PPD les. 386 Browsing for network printers SLES 15 SP6The configuration using only PPD les and no other information sources has the advantage that the PPD les in /usr/share/cups/model can be modified freely. For example, if you have PostScript printers the PPD les can be copied directly to /usr/share/cups/model (if they do not already exist in the manufacturer-PPDs or OpenPrintingPPDs-postscript packages) to achieve an optimum configuration for your printers. Additional PPD les are provided by the following packages: gutenprint : the Gutenprint driver and its matching PPDs splix : the SpliX driver and its matching PPDs OpenPrintingPPDs-ghostscript : PPDs for Ghostscript built-in drivers OpenPrintingPPDs-hpijs : PPDs for the HPIJS driver for non-HP printers 24.8 Troubleshooting The following sections cover the most frequently encountered printer hardware and software problems and ways to solve or circumvent these problems. Among the topics covered are GDI printers, PPD les and port configuration. Common network printer problems, defective print- outs, and queue handling are also addressed. 24.8.1 Printers without standard printer language support These printers do not support any common printer language and can only be addressed with special proprietary control sequences. Therefore they can only work with the operating system versions for which the manufacturer delivers a driver. GDI is a programming interface developed by Microsoft* for graphics devices. Usually the manufacturer delivers drivers only for Windows, and since the Windows driver uses the GDI interface these printers are also called GDI printers. The actual problem is not the programming interface, but that these printers can only be ad- dressed with the proprietary printer language of the respective printer model. Certain GDI printers can be switched to operate either in GDI mode or in one of the standard printer languages. Check the manual of the printer to see whether this is possible. Specific models require special Windows software to do the switch. For example, the Windows printer driver may always switch the printer back into GDI mode when printing from Windows. For other GDI printers there are extension modules for a standard printer language available. 387 Troubleshooting SLES 15 SP6Several manufacturers provide proprietary drivers for their printers. The disadvantage of pro- prietary printer drivers is that there is no guarantee that these work with the installed print system or that they are suitable for the multiple hardware platforms. In contrast, printers that support a standard printer language do not depend on a special print system version or a special hardware platform. Instead of spending time trying to make a proprietary Linux driver work, it may be more cost-ef- fective to purchase a printer which supports a standard printer language (preferably PostScript). This would solve the driver problem once and for all, eliminating the need to install and con- figure special driver software and obtain driver updates that may be required because of new developments in the print system. 24.8.2 No suitable PPD file available for a PostScript printer If the manufacturer-PPDs or OpenPrintingPPDs-postscript packages do not contain a suit- able PPD le for a PostScript printer, it should be possible to use the PPD le from the driver CD of the printer manufacturer or download a suitable PPD le from the Web page of the printer manufacturer. If the PPD le is provided as a zip archive (.zip) or a self-extracting zip archive ( .exe ), unpack it with unzip . First, review the license terms of the PPD le. Then use the cupstestppd utility to check if the PPD le complies with “Adobe PostScript Printer Description File Format Spec- ification, version 4.3.” If the utility returns “FAIL,” the errors in the PPD les are serious and cause major problems. The problem spots reported by cupstestppd should be eliminated. If necessary, ask the printer manufacturer for a suitable PPD le. 24.8.3 Network printer connections Identifying network problems Connect the printer directly to the computer. For test purposes, configure the printer as a local printer. If this works, the problems are related to the network. Checking the TCP/IP network The TCP/IP network and name resolution must be functional. 388 No suitable PPD file available for a PostScript printer SLES 15 SP6Checking a remote lpd Use the following command to test if a TCP connection can be established to lpd (port 515 ) on HOST : > netcat -z HOST 515 && echo ok || echo failed If the connection to lpd cannot be established, lpd may not be active or there may be basic network problems. Provided that the respective lpd is active and the host accepts queries, run the following command as root to query a status report for QUEUE on remote HOST : # echo -e "\004queue" \ | netcat -w 2 -p 722 HOST 515 If lpd does not respond, it may not be active or there may be basic network problems. If lpd responds, the response should show why printing is not possible on the queue on host . If you receive a response like that shown in Example 24.1, “Error message from lpd”, the problem is caused by the remote lpd . EXAMPLE 24.1: ERROR MESSAGE FROM lpd lpd: your host does not have line printer access lpd: queue does not exist printer: spooling disabled printer: printing disabled Checking a remote cupsd A CUPS network server can broadcast its queues by default every 30 seconds on UDP port 631 . Accordingly, the following command can be used to test whether there is a broadcasting CUPS network server in the network. Make sure to stop your local CUPS daemon before executing the command. > netcat -u -l -p 631 & PID=$! ; sleep 40 ; kill $PID If a broadcasting CUPS network server exists, the output appears as shown in Example 24.2, “Broadcast from the CUPS network server”. EXAMPLE 24.2: BROADCAST FROM THE CUPS NETWORK SERVER ipp://192.168.2.202:631/printers/queue IBM Z Take into account that IBM Z Ethernet devices do not receive broadcasts by default. 389 Network printer connections SLES 15 SP6The following command can be used to test if a TCP connection can be established to cupsd (port 631 ) on HOST : > netcat -z HOST 631 && echo ok || echo failed If the connection to cupsd cannot be established, cupsd may not be active or there may be basic network problems. lpstat -h HOST -l -t returns a status report for all queues on HOST , provided the respective cupsd is active and the host accepts queries. The next command can be used to test if the QUEUE on HOST accepts a print job consisting of a single carriage-return character. Nothing should be printed. A blank page may be ejected. > echo -en "\r" \ | lp -d queue -h HOST Troubleshooting a Network Printer or Print Server Machine Spoolers running in a print server machine sometimes cause problems when they need to deal with multiple print jobs. Since this is caused by the spooler in the print server machine, there no way to resolve this issue. As a work-around, circumvent the spooler in the print server machine by addressing the printer connected to the print server machine directly with the TCP socket. See Section 24.4, “Network printers”. In this way, the print server machine is reduced to a converter between the multiple forms of data transfer (TCP/IP network and local printer connection). To use this method, you need to know the TCP port on the print server machine. If the printer is connected to the print server machine and turned on, this TCP port can normally be determined with the nmap utility from the nmap package certain time after the print server machine is powered up. For example, nmap  IP-address may deliver the following output for a print server machine: Port State Service 23/tcp open telnet 80/tcp open http 515/tcp open printer 631/tcp open cups 9100/tcp open jetdirect This output indicates that the printer connected to the print server machine can be ad- dressed via TCP socket on port 9100 . By default, nmap only checks several commonly known ports listed in /usr/share/nmap/nmap-services . To check all possible ports, use the command nmap -p  FROM_PORT - TO_PORT   IP_ADDRESS . For further information, re- fer to the man page of nmap . 390 Network printer connections SLES 15 SP6Enter a command like > echo -en "\rHello\r\f" | netcat -w 1 IP-address port cat file | netcat -w 1 IP-address port to send character strings or les directly to the respective port to test if the printer can be addressed on this port. 24.8.4 Defective printouts without error message For the print system, the print job is completed when the CUPS back-end completes the data transfer to the recipient (printer). If further processing on the recipient fails (for example, if the printer is not able to print the printer-specific data) the print system does not notice this. If the printer cannot print the printer-specific data, select a PPD le that is more suitable for the printer. 24.8.5 Disabled queues If the data transfer to the recipient fails entirely after several attempts, the CUPS back-end, such as USB or socket , reports an error to the print system (to cupsd ). The back-end determines how many unsuccessful attempts are appropriate until the data transfer is reported as impossible. As further attempts would be in vain, cupsd disables printing for the respective queue. After eliminating the cause of the problem, the system administrator must re-enable printing with the command cupsenable . 24.8.6 CUPS browsing: deleting print jobs If a CUPS network server broadcasts its queues to the client hosts via browsing and a suitable local cupsd is active on the client hosts, the client cupsd accepts print jobs from applications and forwards them to the cupsd on the server. When cupsd on the server accepts a print job, it is assigned a new job number. Therefore, the job number on the client host is different from the job number on the server. As a print job is usually forwarded immediately, it cannot be deleted with the job number on the client host This is because the client cupsd regards the print job as completed when it has been forwarded to the server cupsd . 391 Defective printouts without error message SLES 15 SP6To delete the print job on the server, use a command such as lpstat -h cups.example.com -o to determine the job number on the server. This assumes that the server has not already completed the print job by sending it to the printer. Use the obtained job number to delete the print job on the server as follows: > cancel -h cups.example.com QUEUE-JOBNUMBER 24.8.7 Defective print jobs and data transfer errors If you switch the printer o or shut down the computer during the printing process, print jobs remain in the queue. Printing resumes when the computer (or the printer) is switched back on. Defective print jobs must be removed from the queue with cancel . If a print job is corrupted or an error occurs in the communication between the host and the printer, the printer cannot process the data correctly and prints numerous sheets of paper with unintelligible characters. To x the problem, follow these steps: 1. To stop printing, remove all paper from ink jet printers or open the paper trays of laser printers. High-quality printers have a button for canceling the current printout. 2. The print job may still be in the queue, because jobs are only removed after they are sent to the printer. Use lpstat -o or lpstat -h cups.example.com -o to check which queue is currently printing. Delete the print job with cancel QUEUE - JOBNUMBER or cancel - h cups.example.com QUEUE - JOBNUMBER . 3. Certain data may still be transferred to the printer even though the print job has been deleted from the queue. Check if a CUPS back-end process is still running for the respective queue and stop it. 4. Reset the printer by switching it o for a while. Then insert the paper and turn on the printer. 24.8.8 Debugging CUPS Use the following generic procedure to locate problems in CUPS: 1. Set LogLevel debug in /etc/cups/cupsd.conf . 2. Stop cupsd . 392 Defective print jobs and data transfer errors SLES 15 SP63. Remove /var/log/cups/error_log* to avoid having to search through large log les. 4. Start cupsd . 5. Repeat the action that led to the problem. 6. Check the messages in /var/log/cups/error_log* to identify the cause of the problem. 24.8.9 More information In-depth information about printing on SUSE Linux Enterprise Server is presented in the openSUSE Support Database at https://en.opensuse.org/Portal:Printing . Solutions to many spe- cific problems are presented in the SUSE Knowledgebase (https://www.suse.com/support/ ). Locate the relevant articles with a text search for CUPS . 393 More information SLES 15 SP625 Graphical user interface SUSE Linux Enterprise Server includes the X.org server and the GNOME desktop. This chapter describes the configuration of the graphical user interface for all users. 25.1 X Window System The X.org server is the de facto standard for implementing the X11 protocol. X is network-based, enabling applications started on one host to be displayed on another host connected over any kind of network (LAN or Internet). The X Window System needs no configuration in most cases. The hardware is dynamically de- tected during X start-up. The use of xorg.conf is therefore deprecated. If you still need to specify custom options to change the way X behaves, you can still do so by modifying configu- ration les under /etc/X11/xorg.conf.d/ . Tip: IBM Z: configuring the graphical user interface IBM Z does not have any input or output devices supported by X.Org. Therefore, none of the configuration procedures described in this section apply. More relevant information for IBM Z can be found in Book “Deployment Guide”, Chapter 5 “Installation on IBM Z and LinuxONE”. Install the package xorg-docs to get more in-depth information about X11. man 5 xorg.conf tells you more about the format of the manual configuration (if needed). More information on the X11 development can be found on the project''s home page at https://www.x.org . Drivers are found in xf86-video-* packages, for example xf86-video-ati . Many of the dri- vers delivered with these packages are described in detail in the related manual page. For ex- ample, if you use the ati driver, nd more information about this driver in man 4 ati . Information about third-party drivers is available in /usr/share/doc/packages/ . For example, the documentation of x11-video-nvidiaG03 is available in /usr/ share/doc/packages/x11-video-nvidiaG04 after the package was installed. Install the package xrdp on a server and use RDP client software to access the server via the remote desktop protocol. 394 X Window System SLES 15 SP625.2 Installing and configuring fonts Fonts in Linux can be categorized into two parts: Outline or vector fonts Contains a mathematical description as drawing instructions about the shape of a glyph. As such, each glyph can be scaled to arbitrary sizes without loss of quality. Before such a font (or glyph) can be used, the mathematical descriptions need to be transformed into a raster (grid). This process is called font rasterization. Font hinting (embedded inside the font) improves and optimizes the rendering result for a particular size. Rasterization and hinting is done with the FreeType library. Common formats under Linux are PostScript Type 1 and Type 2, TrueType, and OpenType. Bitmap or raster fonts Consists of an array of pixels designed for a specific font size. Bitmap fonts are extremely fast and simple to render. However, compared to vector fonts, bitmap fonts cannot be scaled without losing quality. As such, these fonts are usually distributed in different sizes. These days, bitmap fonts are still used in the Linux console and sometimes in terminals. Under Linux, Portable Compiled Format (PCF) or Glyph Bitmap Distribution Format (BDF) are the most common formats. The appearance of these fonts can be influenced by two main aspects: choosing a suitable font family, rendering the font with an algorithm that achieves results comfortable for the receiver''s eyes. The last point is only relevant to vector fonts. Although the above two points are highly subjec- tive, some defaults need to be created. Linux font rendering systems consist of several libraries with different relations. The basic font rendering library is FreeType (https://www.freetype.org/) , which converts font glyphs of sup- ported formats into optimized bitmap glyphs. The rendering process is controlled by an algo- rithm and its parameters (which may be subject to patent issues). Every program or library which uses FreeType should consult the Fontconfig (https://www.font- config.org/) library. This library gathers font configuration from users and from the system. When a user amends their Fontconfig setting, this change will result in Fontconfig-aware appli- cations. 395 Installing and configuring fonts SLES 15 SP6More sophisticated OpenType shaping needed for scripts such as Arabic, Han or Phags-Pa and other higher level text processing is done using Harfbuzz (https://harfbuzz.github.io/) or Pango (https://www.pango.org/) . 25.2.1 Showing installed fonts To get an overview about which fonts are installed on your system, ask the commands rpm or fc-list . Both will give you a good answer, but may return a different list depending on system and user configuration: rpm Invoke rpm to see which software packages containing fonts are installed on your system: > rpm -qa ''*fonts*'' Every font package should satisfy this expression. However, the command may return some false positives like fonts-config (which is neither a font nor does it contain fonts). fc-list Invoke fc-list to get an overview about what font families can be accessed, whether they are installed on the system or in your home: > fc-list '':'' family Note: Command fc-list The command fc-list is a wrapper to the Fontconfig library. It is possible to query a lot of interesting information from Fontconfig—or, to be more precise, from its cache. See man 1 fc-list for more details. 25.2.2 Viewing fonts If you want to know what an installed font family looks like, either use the command ftview (package ft2demos ) or visit https://fontinfo.opensuse.org/ . For example, to display the FreeMono font in 14 point, use ftview like this: > ftview 14 /usr/share/fonts/truetype/FreeMono.ttf 396 Showing installed fonts SLES 15 SP6If you need further information, go to https://fontinfo.opensuse.org/ to nd out which styles (regular, bold, italic, etc.) and languages are supported. 25.2.3 Querying fonts To query which font is used when a pattern is given, use the fc-match command. For example, if your pattern contains an already installed font, fc-match returns the le name, font family, and the style: > fc-match ''Liberation Serif'' LiberationSerif-Regular.ttf: "Liberation Serif" "Regular" If the desired font does not exist on your system, Fontconfig''s matching rules take place and try to nd the most similar fonts available. This means, your request is substituted: > fc-match ''Foo Family'' DejaVuSans.ttf: "DejaVu Sans" "Book" Fontconfig supports aliases: a name is substituted with another family name. A typical example are the generic names such as “sans-serif”, “serif”, and “monospace”. These alias names can be substituted by real family names or even a preference list of family names: > for font in serif sans mono; do fc-match "$font" ; done DejaVuSerif.ttf: "DejaVu Serif" "Book" DejaVuSans.ttf: "DejaVu Sans" "Book" DejaVuSansMono.ttf: "DejaVu Sans Mono" "Book" The result may vary on your system, depending on which fonts are currently installed. Note: Similarity rules according to fontconfig Fontconfig always returns a real family (if at least one is installed) according to the given request, as similar as possible. “Similarity” depends on Fontconfig''s internal metrics and on the user''s or administrator''s Fontconfig settings. 397 Querying fonts SLES 15 SP625.2.4 Installing fonts To install a new font there are these major methods: 1. Manually install the font les such as *.ttf or *.otf to a known font directory. If it needs to be system-wide, use the standard directory /usr/share/fonts . For installation in your home directory, use ~/.config/fonts . If you want to deviate from the standard directories, Fontconfig allows you to choose another one. Let Fontconfig know by using the element, see Section 25.2.5.2, “Diving into fontconfig XML” for details. 2. Install fonts using zypper . Lots of fonts are already available as a package, be it on your SUSE distribution or in the M17N:fonts (https://download.opensuse.org/repositories/M17N:/ fonts/) repository. Add the repository to your list using the following command. For example, to add a repository for SUSE Linux Enterprise Server 15 SP6: > sudo zypper ar https://download.opensuse.org/repositories/M17N:/fonts/SLE_15/ To search for your FONT_FAMILY_NAME use this command: > zypper se ''FONT_FAMILY_NAME*fonts'' 25.2.5 Configuring the appearance of fonts Depending on the rendering medium, and font size, the result may be unsatisfactory. For exam- ple, an average monitor these days has a resolution of 100dpi which makes pixels too big and glyphs look clunky. There are several algorithms available to deal with low resolutions, such as anti-aliasing (grayscale smoothing), hinting (fitting to the grid), or subpixel rendering (tripling resolution in one direction). These algorithms can also differ from one font format to another. Via Fontconfig, it is possible to select a rendering algorithms for every font individually or for a set of fonts. 398 Installing fonts SLES 15 SP625.2.5.1 Configuring fonts via sysconfig SUSE Linux Enterprise Server comes with a sysconfig layer above Fontconfig. This is a good starting point for experimenting with font configuration. To change the default settings, edit the configuration le /etc/sysconfig/fonts-config . (or use the YaST sysconfig module). After you have edited the le, run fonts-config : > sudo /usr/sbin/fonts-config Restart the application to make the effect visible. Keep in mind the following issues: A few applications do need not to be restarted. For example, Firefox re-reads Fontconfig configuration from time to time. Newly created or reloaded tabs get new font configura- tions later. The fonts-config script is called automatically after every package installation or re- moval (if not, it is a bug of the font software package). Every sysconfig variable can be temporarily overridden by the fonts-config command line option. See fonts-config --help for details. There are several sysconfig variables which can be altered. See man 1 fonts-config or the help page of the YaST sysconfig module. The following variables are examples: Usage of rendering algorithms Consider FORCE_HINTSTYLE , FORCE_AUTOHINT , FORCE_BW , FORCE_BW_MONOSPACE , USE_EMBEDDED_BITMAPS and EMBEDDED_BITMAP_LANGAGES Preference lists of generic aliases Use PREFER_SANS_FAMILIES , PREFER_SERIF_FAMILIES , PREFER_MONO_FAMILIES and SEARCH_METRIC_COMPATIBLE The following list provides some configuration examples, sorted from the “most readable” fonts (more contrast) to “most beautiful” (more smoothed). Bitmap fonts Prefer bitmap fonts via the PREFER_*_FAMILIES variables. Follow the example in the help section for these variables. Be aware that these fonts are rendered black and white, not smoothed and that bitmap fonts are available in several sizes only. Consider using SEARCH_METRIC_COMPATIBLE="no" to disable metric compatibility-driven family name substitutions. 399 Configuring the appearance of fonts SLES 15 SP6Scalable fonts rendered black and white Scalable fonts rendered without antialiasing can result in a similar outcome to bitmap fonts, while maintaining font scalability. Use well hinted fonts like the Liberation families. Unfortunately, there is a lack of well hinted fonts though. Set the following variable to force this method: FORCE_BW="yes" Monospaced fonts rendered black and white Render monospaced fonts without antialiasing only, otherwise use default settings: FORCE_BW_MONOSPACE="yes" Default settings All fonts are rendered with antialiasing. Well hinted fonts will be rendered with the byte code interpreter (BCI) and the rest with autohinter ( hintstyle=hintslight ). Leave all relevant sysconfig variables to the default setting. CFF fonts Use fonts in CFF format. They can be considered also more readable than the default TrueType fonts given the current improvements in FreeType2. Try them out by following the example of PREFER_*_FAMILIES . Possibly make them more dark and bold with: SEARCH_METRIC_COMPATIBLE="no" as they are rendered by hintstyle=hintslight by default. Also consider using: SEARCH_METRIC_COMPATIBLE="no" Autohinter exclusively Even for a well hinted font, use FreeType2''s autohinter. That can lead to thicker, sometimes fuzzier letter shapes with lower contrast. Set the following variable to activate this: FORCE_AUTOHINTER="yes" Use FORCE_HINTSTYLE to control the level of hinting. 25.2.5.2 Diving into fontconfig XML Fontconfig''s configuration format is the eXtensible Markup Language (XML). These few examples are not a complete reference, but a brief overview. Details and other inspiration can be found in man 5 fonts-conf or in /etc/fonts/conf.d/ . 400 Configuring the appearance of fonts SLES 15 SP6The central Fontconfig configuration le is /etc/fonts/fonts.conf , which—along other work —includes the whole /etc/fonts/conf.d/ directory. To customize Fontconfig, there are two places where you can insert your changes: FONTCONFIG CONFIGURATION FILES 1. System-wide changes.  Edit the le /etc/fonts/local.conf (by default, it contains an empty fontconfig element). 2. User-specific changes.  Edit the le ~/.config/fontconfig/fonts.conf . Place Fontcon- fig configuration les in the ~/.config/fontconfig/conf.d/ directory. User-specific changes overwrite any system-wide settings. Note: Deprecated user configuration file The le ~/.fonts.conf is marked as deprecated and should not be used anymore. Use ~/.config/fontconfig/fonts.conf instead. Every configuration le needs to have a fontconfig element. As such, the minimal le looks like this: If the default directories are not enough, insert the dir element with the respective directory: /usr/share/fonts2 Fontconfig searches recursively for fonts. Font-rendering algorithms can be chosen with following Fontconfig snippet (see Example 25.1, “Specifying rendering algorithms”): EXAMPLE 25.1: SPECIFYING RENDERING ALGORITHMS FAMILY_NAME 401 Configuring the appearance of fonts SLES 15 SP6 true true false hintfull Various properties of fonts can be tested. For example, the element can test for the font family (as shown in the example), size interval, spacing, font format, and others. When abandoning completely, all elements will be applied to every font (global change). EXAMPLE 25.2: ALIASES AND FAMILY NAME SUBSTITUTIONS Rule 1 Alegreya SC serif Rule 2 serif Droid Serif Rule 3 serif STIXGeneral 402 Configuring the appearance of fonts SLES 15 SP6The rules from Example 25.2, “Aliases and family name substitutions” create a prioritized family list (PFL). Depending on the element, different actions are performed: from Rule 1 This rule adds a serif family name at the end of the PFL. from Rule 2 This rule adds “Droid Serif” just before the rst occurrence of serif in the PFL, whenever Alegreya SC is in PFL. from Rule 3 This rule adds a “STIXGeneral” family name just after the rst occurrence of the serif family name in the PFL. Putting this together, when snippets occur in the order Rule 1 - Rule 2 - Rule 3 and the user requests “Alegreya SC”, then the PFL is created as depicted in Table 25.1, “Generating PFL from fontconfig rules”. TABLE 25.1: GENERATING PFL FROM FONTCONFIG RULES Order Current PFL Request Alegreya SC Rule 1 Alegreya SC , serif Rule 2 Alegreya SC , Droid Serif , serif Rule 3 Alegreya SC , Droid Serif , serif , STIXGeneral In Fontconfig''s metrics, the family name has the highest priority over other patterns, like style, size, etc. Fontconfig checks which family is currently installed on the system. If “Alegreya SC” is installed, then Fontconfig returns it. If not, it asks for “Droid Serif”, etc. Be careful. When the order of Fontconfig snippets is changed, Fontconfig can return different results, as depicted in Table 25.2, “Results from generating PFL from fontconfig rules with changed order”. TABLE 25.2: RESULTS FROM GENERATING PFL FROM FONTCONFIG RULES WITH CHANGED ORDER Order Current PFL Note Request Alegreya SC Same request performed. 403 Configuring the appearance of fonts SLES 15 SP6Order Current PFL Note Rule 2 Alegreya SC serif not in PFL, nothing is substituted Rule 3 Alegreya SC serif not in PFL, nothing is substituted Rule 1 Alegreya SC , serif Alegreya SC present in PFL, substitution is per- formed Note: Implication Think of the alias as a classification or inclusion of this group (if not installed). As the example shows, should always precede the and aliases of that group. classification is not limited to the generic aliases serif, sans-serif and monospace. See /usr/share/fontconfig/conf.avail/30-metric-aliases.conf for a complex example. The following Fontconfig snippet in Example 25.3, “Aliases and family name substitutions” creates a serif group. Every family in this group could substitute others when a former font is not installed. EXAMPLE 25.3: ALIASES AND FAMILY NAME SUBSTITUTIONS Alegreya SC serif Droid Serif serif STIXGeneral 404 Configuring the appearance of fonts SLES 15 SP6 serif serif Droid Serif STIXGeneral Alegreya SC Priority is given by the order in the alias. Similarly, stronger aliases can be used. Example 25.2, “Aliases and family name substitutions” is expanded by Example 25.4, “Aliases and family names substitutions”. EXAMPLE 25.4: ALIASES AND FAMILY NAMES SUBSTITUTIONS Rule 4 serif Liberation Serif Rule 5 serif DejaVu Serif The expanded configuration from Example 25.4, “Aliases and family names substitutions” would lead to the following PFL evolution: TABLE 25.3: RESULTS FROM GENERATING PFL FROM FONTCONFIG RULES Order Current PFL Request Alegreya SC 405 Configuring the appearance of fonts SLES 15 SP6Order Current PFL Rule 1 Alegreya SC , serif Rule 2 Alegreya SC , Droid Serif , serif Rule 3 Alegreya SC , Droid Serif , serif , STIXGeneral Rule 4 Alegreya SC , Droid Serif , serif , Liberation Serif , STIX- General Rule 5 Alegreya SC , Droid Serif , DejaVu Serif , serif , Liberation Serif , STIXGeneral Note: Implications. In case multiple declarations for the same generic name exist, the dec- laration that is parsed last “wins”. If possible, do not use after user ( / etc/fonts/conf.d/*-user.conf ) when creating a system-wide configuration. In case multiple before user in the system-wide configuration. Every declaration overwrites declarations for the same gener- ic name. If the administrator wants to allow the user to use and not only , the administrator should not use in the system-wide config- uration. On the other hand, as users mostly use , this should not have any detrimental effect. We also see the use of in system-wide configurations. 406 Configuring the appearance of fonts SLES 15 SP625.3 GNOME configuration for administrators 25.3.1 The dconf system Configuration of the GNOME desktop is managed with dconf . It is a hierarchically structured database or registry that allows users to modify their personal settings, and system adminis- trators to set default or mandatory values for all users. dconf replaces the gconf system of GNOME 2. Use dconf-editor to view the dconf options with a graphical user interface. Use dconf to access and modify configuration options with the command line. The GNOME Tweaks tool provides an easy-to-use user interface for additional configuration options beyond the normal GNOME configuration. The tool can be started from the GNOME application menu or from the command line with gnome-tweak-tool . 25.3.2 System-wide configuration Global dconf configuration parameters can be set in the /etc/dconf/db/ directory. This in- cludes the configuration for GDM or locking certain configuration options for users. Use the following procedure as an example to create a system-wide configuration: 1. Create a new directory that ends with a .d in /etc/dconf/db/ . This directory can con- tain an arbitrary amount of text les with configuration options. For this example, create the le /etc/dconf/db/network.d/00-proxy with the following content: # This is a comment [system/proxy/http] host=''10.0.0.1'' enabled=true 2. Parse the new configuration directives into the dconf database format: > sudo dconf update 3. Add the new network configuration database to the default user profile, by creating the le /etc/dconf/profile/user . Then add the following content: system-db:network 407 GNOME configuration for administrators SLES 15 SP6The le /etc/dconf/profile/user is a GNOME default. Other profiles can be defined in the environment variable DCONF_PROFILE . 4. Optional: to lock the proxy configuration for users, create the le /etc/dconf/db/net- work/locks/proxy . Then add a line to this le with the keys that may not be changed: /system/proxy/http/host /system/proxy/http/enabled You can use the graphical dconf-editor to create a profile with one user and then use dconf dump / to list all configuration options. The configuration options can then be stored in a global profile. A detailed description of the global configuration is available at https://wiki.gnome.org/Projects/ dconf/SystemAdministrators . 25.3.3 More information For more information, see https://help.gnome.org/admin/ . 25.4 Switching between Intel and NVIDIA Optimus GPUs with SUSE Prime SUSE Prime is a tool for switching between onboard Intel graphical processing units (GPUs) and NVIDIA GPUs equipped with NVIDIA''s switchable graphics Optimus technology. Optimus provides a mechanism for easily switching between an onboard Intel GPU and a discrete NVIDIA GPU. This is designed for running a laptop in a power-saving mode or at maximum performance: use the Intel GPU to save power, and the NVIDIA GPU for 3D applications. SUSE Prime works only on systems running X11, not Wayland. If your system runs Wayland, you must disable it and fall back to X11 to use SUSE Prime (see Section 25.4.1, “Prerequisites”). 25.4.1 Prerequisites There must not be a /etc/X11/xorg.conf le, and no configuration les with active Server- Layout , Device , or Screen sections in the /etc/X11/xorg.conf.d directory. 408 More information SLES 15 SP6SUSE Prime works only with X11. Use the loginctl command to see if your system is using X11 or Wayland: > loginctl SESSION UID USER SEAT TTY 2 1000 tux seat0 > loginctl show-session 2|grep Type Type=x11 If your system uses Wayland, disable it by editing /etc/gdm/custom.conf and un-commenting WaylandEnable=false . Then reboot. 25.4.2 Installing and using SUSE Prime Your NVIDIA graphics card should already be installed and working. If it is not, see Section 25.4.3, “Installing NVIDIA drivers”. Install the suse-prime package: > sudo zypper install suse-prime To switch your GPU run one of the following commands, then log out and log back in: > sudo prime-select intel > sudo prime-select intel2 > sudo prime-select nvidia Use the intel driver when it is the modesetting driver. intel2 is for systems that use the xf86-video-intel driver. You can get this information by installing and running inxi : > inxi -G Graphics: Device-1: Intel Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controller Display Server: x11(X.org 1.20.1 ) drivers: modesetting (unloaded: fbdev, vesa) Resolution: 1920x1080@60.00hz OpenGL: renderer: Mesa DRI Intel Haswell Desktop version: 4.5 Mesa 18.2.8 Which GPU is currently active? > sudo /usr/sbin/prime-select get-current Driver configured: intel 409 Installing and using SUSE Prime SLES 15 SP625.4.3 Installing NVIDIA drivers If you need to identify your NVIDIA card so you know which driver to use, run the following command: > /sbin/lspci | grep VGA Follow these steps to install the drivers with Zypper. List the available driver packages: > sudo zypper se nvidia Then install the drivers for your NVIDIA graphics card: > sudo zypper se packagename 410 Installing NVIDIA drivers SLES 15 SP626 Accessing file systems with FUSE FUSE is the acronym for Filesystem in Userspace. This means you can configure and mount a le system as an unprivileged user. Normally, you need to be root for this task. FUSE alone is a kernel module. Combined with plug-ins, it allows you to ex- tend FUSE to access almost all le systems like remote SSH connections, ISO im- ages, and more. 26.1 Configuring FUSE Before you can use FUSE, you need to install the package fuse . Depending which le system you want to use, you need additional plug-ins available as separate packages. Generally you do not need to configure FUSE. However, it is a good idea to create a directory where all your mount points are combined. For example, you can create a directory ~/mounts and insert your subdirectories for your different le systems there. 26.2 Mounting an NTFS partition NTFS, the New Technology File System, is the default le system of Windows. Since under normal circumstances the unprivileged user cannot mount NTFS block devices using the external FUSE library, the process of mounting a Windows partition described below requires root privileges. Mounting NTFS partitions is supported on SUSE Linux Enterprise Server and SUSE Linux Enter- prise Desktop with SUSE Linux Enterprise Workstation Extension only. 1. Become root and install the package ntfs-3g . It is available in SUSE Linux Enterprise Workstation Extension. 2. Create a directory that is to be used as a mount point, for example, ~/mounts/windows . 3. Find out which Windows partition you need. Use YaST and start the partitioner module to see which partition belongs to Windows, but do not modify anything. Alternatively, become root and execute /sbin/fdisk -l . Look for partitions with a partition type of HPFS/NTFS . 411 Configuring FUSE SLES 15 SP64. Mount the partition in read-write mode. Replace the placeholder DEVICE with your re- spective Windows partition: > ntfs-3g /dev/DEVICE MOUNT POINT To use your Windows partition in read-only mode, append -o ro : > ntfs-3g /dev/DEVICE MOUNT POINT -o ro The command ntfs-3g uses the current user (UID) and group (GID) to mount the given device. To set the write permissions to a different user, use the command id USER to get the output of the UID and GID values. Set it with: # id tux uid=1000(tux) gid=100(users) groups=100(users),16(dialout),33(video) ntfs-3g /dev/DEVICE MOUNT POINT -o uid=1000,gid=100 Find additional options in the man page. To unmount the resource, run fusermount -u MOUNT POINT . 26.3 More information For more information, see the home page of FUSE at https://github.com/libfuse/libfuse . 412 More information SLES 15 SP627 Installing multiple kernel versions SUSE Linux Enterprise Server supports the parallel installation of multiple kernel versions. When installing a second kernel, a boot entry and an initrd are automat- ically created, so no further manual configuration is needed. When rebooting the machine, the newly added kernel is available as an additional boot parameter. Using this functionality, you can safely test kernel updates while being able to al- ways fall back to the proven former kernel. To do this, do not use the update tools (such as the YaST Online Update or the updater applet), but instead follow the process described in this chapter. Warning: Support entitlement Be aware that you lose your entire support entitlement for the machine when installing a self-compiled or a third-party kernel. Only kernels shipped with SUSE Linux Enterprise Server and kernels delivered via the official update channels for SUSE Linux Enterprise Server are supported. Tip: Check your boot loader configuration kernel It is recommended to check your boot loader configuration after having installed another kernel to set the default boot entry of your choice. See Section 18.3, “Configuring the boot loader with YaST” for more information. 27.1 Enabling and configuring multiversion support Installing multiple versions of a software package (multiversion support) is enabled by default with SUSE Linux Enterprise Server 12 and newer versions. To verify this setting, proceed as follows: 1. Open /etc/zypp/zypp.conf with the editor of your choice as root . 413 Enabling and configuring multiversion support SLES 15 SP62. Search for the string multiversion . If multiversion is enabled for all kernel packages capable of this feature, the following line appears uncommented: multiversion = provides:multiversion(kernel) 3. To restrict multi-version support to certain kernel flavors, add the package names as a comma-separated list to the multiversion option in /etc/zypp/zypp.conf , for exam- ple, multiversion = kernel-default,kernel-default-base,kernel-source 4. Save your changes. Warning: Kernel Module Packages (KMP) Make sure that required vendor-provided kernel modules (Kernel Module Packages) are also installed for the new updated kernel. The kernel update process will not warn about eventually missing kernel modules because package requirements are still fulfilled by the old kernel that is kept on the system. 27.1.1 Automatically deleting unused kernels When frequently testing new kernels with multiversion support enabled, the boot menu quick- ly becomes confusing. Since a /boot partition normally has limited space, you may run into trouble with /boot overflowing. While you can delete unused kernel versions manually with YaST or Zypper (as described below), you can also configure libzypp to automatically delete kernels no longer used. By default no kernels are deleted. 1. Open /etc/zypp/zypp.conf with the editor of your choice as root . 2. Search for the string multiversion.kernels and activate this option by uncommenting the line. This option takes a comma-separated list of the following values: 5.3.18-53.3 : keep the kernel with the specified version number latest : keep the kernel with the highest version number latest-N : keep the kernel with the Nth highest version number running : keep the running kernel 414 Automatically deleting unused kernels SLES 15 SP6oldest : keep the kernel with the lowest version number (the one that was originally shipped with SUSE Linux Enterprise Server) oldest+N .  keep the kernel with the Nth lowest version number Here are several examples multiversion.kernels = latest,running Keep the latest kernel and the one currently running. This is similar to not enabling the multiversion feature, except that the old kernel is removed after the next reboot and not immediately after the installation. multiversion.kernels = latest,latest-1,running Keep the last two kernels and the one currently running. multiversion.kernels = latest,running,5.3.18-53.3 Keep the latest kernel, the one currently running, and 5.3.18-53.3 . Tip: Keep the running kernel Unless you are using a special setup, always keep the kernel marked running . If you do not keep the running kernel, it will be deleted when updating the kernel. In turn, this means that all the running kernel''s modules are also deleted and cannot be loaded anymore. If you decide not to keep the running kernel, always reboot immediately after a kernel upgrade to avoid issues with modules. 27.1.2 Use case: deleting an old kernel after reboot only You want to make sure that an old kernel will only be deleted after the system has rebooted successfully with the new kernel. Change the following line in /etc/zypp/zypp.conf : multiversion.kernels = latest,running The previous parameters tell the system to keep the latest kernel and the running one only if they differ. 415 Use case: deleting an old kernel after reboot only SLES 15 SP627.1.3 Use case: keeping older kernels as fallback You want to keep one or more kernel versions to have one or more “spare” kernels. This can be useful if you need kernels for testing. If something goes wrong (for example, your machine does not boot), you still can use one or more kernel versions which are known to be good. Change the following line in /etc/zypp/zypp.conf : multiversion.kernels = latest,latest-1,latest-2,running When you reboot your system after the installation of a new kernel, the system will keep three kernels: the current kernel (configured as latest,running ) and its two immediate predecessors (configured as latest-1 and latest-2 ). 27.1.4 Use case: keeping a specific kernel version You make regular system updates and install new kernel versions. However, you are also com- piling your own kernel version and want to make sure that the system will keep them. Change the following line in /etc/zypp/zypp.conf : multiversion.kernels = latest,5.3.18-53.3,running When you reboot your system after the installation of a new kernel, the system will keep two kernels: the new and running kernel (configured as latest,running ) and your self-compiled kernel (configured as 5.3.18-53.3 ). 27.2 Installing/removing multiple kernel versions with YaST You can install or remove multiple kernels with YaST: 1. Start YaST and open the software manager via Software Software Management. 2. List all packages capable of providing multiple versions by choosing View Package Clas- sification Multiversion Packages. 416 Use case: keeping older kernels as fallback SLES 15 SP6FIGURE 27.1: THE YAST SOFTWARE MANAGER: MULTIVERSION VIEW 3. Select a package and open its Version tab in the bottom pane on the left. 4. To install a package, click the check box next to it. A green check mark indicates it is selected for installation. To remove an already installed package (marked with a white check mark), click the check box next to it until a red X indicates it is selected for removal. 5. Click Accept to start the installation. 27.3 Installing/removing multiple kernel versions with Zypper You can install or remove multiple kernels with zypper : 1. Use the command zypper se -s ''kernel*'' to display a list of all kernel packages available: S | Name | Type | Version | Arch | Repository 417 Installing/removing multiple kernel versions with Zypper SLES 15 SP6---+----------------------+---------+-------------------+-------- +------------------------------------------------------ i+ | kernel-default | package | 6.4.0-150600.9.2 | x86_64 | SLE- Module-Basesystem15-SP6-Pool | kernel-default-base | package | 6.4.0-150600.9.2.150600.10.40 | x86_64 | SLE- Module-Basesystem15-SP6-Pool | kernel-default-devel | package | 6.4.0-150600.9.2 | x86_64 | SLE- Module-Basesystem15-SP6-Pool | kernel-devel | package | 6.4.0-150600.9.2 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-all | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-amdgpu | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-ath10k | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-ath11k | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-ath12k | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-atheros | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-bluetooth | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-bnx2 | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-brcm | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-chelsio | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-dpaa2 | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-i915 | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-intel | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-iwlwifi | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-liquidio | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-marvell | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-media | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-mediatek | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-mellanox | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-mwifiex | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-network | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-nfp | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-nvidia | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool 418 Installing/removing multiple kernel versions with Zypper SLES 15 SP6| kernel-firmware-nvidia-gsp-G06 | package | 525.116.04-150500.1.1 | x86_64 | SLE- Module-Basesystem15-SP6-Pool | kernel-firmware-nvidia-gspx-G06 | package | 550.54.14-150600.1.1 | x86_64 | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-platform | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-prestera | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-qcom | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-qlogic | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-radeon | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-realtek | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-serial | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-sound | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-ti | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-ueagle | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool i | kernel-firmware-usb-network | package | 20240201-150600.1.1 | noarch | SLE- Module-Basesystem15-SP6-Pool | kernel-macros | package | 6.4.0-150600.9.2 | noarch | SLE- Module-Basesystem15-SP6-Pool 2. Specify the exact version when installing: > sudo zypper in kernel-default-6.4.0-150600.9.2 3. When uninstalling a kernel, use the commands zypper se -si ''kernel*'' to list all kernels installed and zypper rm PACKAGENAME-VERSION to remove the package. 419 Installing/removing multiple kernel versions with Zypper SLES 15 SP628 Managing kernel modules Although Linux is a monolithic kernel, it can be extended using kernel modules. These are special objects that can be inserted into the kernel and removed on demand. In practical terms, kernel modules make it possible to add and remove drivers and interfaces that are not included in the kernel itself. Linux provides several commands for managing kernel modules. 28.1 Listing loaded modules with lsmod and modinfo Use the lsmod command to view what kernel modules are currently loaded. The output of the command may look as follows: > lsmod Module Size Used by snd_usb_audio 188416 2 snd_usbmidi_lib 36864 1 snd_usb_audio hid_plantronics 16384 0 snd_rawmidi 36864 1 snd_usbmidi_lib snd_seq_device 16384 1 snd_rawmidi fuse 106496 3 nfsv3 45056 1 nfs_acl 16384 1 nfsv3 The output is divided into three columns. The Module column lists the names of the loaded modules, while the Size column displays the size of each module. The Used by column shows the number of referring modules and their names. This list may be incomplete. To view detailed information about a specific kernel module, use the modinfo MODULE_NAME command, where MODULE_NAME is the name of the desired kernel module. The modinfo binary resides in the /sbin directory that is not in the user''s PATH environment variable. This means that you must specify the full path to the binary when running modinfo command as a regular user: > /sbin/modinfo kvm filename: /lib/modules/6.4.0-150600.9-default/kernel/arch/x86/kvm/kvm.ko.zst license: GPL author: Qumranet suserelease: SLE15-SP6 srcversion: 9DACE73AC65F98D556DAD60 depends: irqbypass supported: yes retpoline: Y 420 Listing loaded modules with lsmod and modinfo SLES 15 SP6intree: Y name: kvm vermagic: 6.4.0-150600.9-default SMP mod_unload modversions 28.2 Adding and removing kernel modules While it is possible to use insmod and rmmod to add and remove kernel modules, it is recom- mended to use the modprobe tool instead. modprobe offers several important advantages, in- cluding automatic dependency resolution and blacklisting. When used without any parameters, the modprobe command installs a specified kernel module. modprobe must be run with root privileges: > sudo modprobe acpi To remove a kernel module, use the -r parameter: > sudo modprobe -r acpi 28.2.1 Loading kernel modules automatically on boot Instead of loading kernel modules manually, you can load them automatically during the boot process using the systemd-modules-load.service service. To enable a kernel module, add a .conf le to the /etc/modules-load.d/ directory. It is good practice to give the configuration le the same name as the module, for example: /etc/modules-load.d/rt2800usb.conf The configuration le must contain the name of the desired kernel module (for example, rt2800usb ). The described technique allows you to load kernel modules without any parameters. If you need to load a kernel module with specific options, add a configuration le to the /etc/modprobe.d/ directory instead. The le must have the .conf extension. The name of the le should adhere to the following naming convention: priority-modulename.conf , for example: 50-think- fan.conf . The configuration le must contain the name of the kernel module and the desired parameters. You can use the example command below to create a configuration le containing the name of the kernel module and its parameters: > echo "options thinkpad_acpi fan_control=1" | sudo tee /etc/modprobe.d/thinkfan.conf 421 Adding and removing kernel modules SLES 15 SP6Note: Loading kernel modules Most kernel modules are loaded by the system automatically when a device is detected or user space requests specific functionality. Thus, adding modules manually to /etc/ modules-load.d/ is rarely required. 28.2.2 Blacklisting kernel modules with modprobe Blacklisting a kernel module prevents it from loading during the boot process. This can be useful when you want to disable a module that you suspect is causing problems on your system. You can still load blacklisted kernel modules manually using the insmod or modprobe tools. To blacklist a module, create a le /etc/modprobe.d/60-blacklist-MODULE_NAME.conf with the following content: blacklist MODULE_NAME Run the dracut command as root to generate a new initrd image, then reboot your machine (replace NAME with the name of the current initrd and KERNELVERSION with the currently running kernel): > su echo "blacklist nouveau" >> /etc/modprobe.d/60-blacklist-nouveau.conf /usr/bin/dracut --logfile /var/log/YaST2/mkinitrd.log --force /boot/$initrd-NAME $KERNELVERSION reboot To disable a kernel module temporarily only, blacklist it on-the-y during the boot. To do this, press the E key when you see the boot screen. This drops you into a minimal editor that allows you to modify boot parameters. Locate the line that looks as follows: linux /boot/vmlinuz...splash= silent quiet showopts Add the modprobe.blacklist=MODULE_NAME command to the end of the line. For example: linux /boot/vmlinuz...splash= silent quiet showopts modprobe.blacklist=nouveau Press F10 or Ctrl – X to boot with the specified configuration. To blacklist a kernel module permanently via GRUB, open the /etc/default/grub le for editing, and add the modprobe.blacklist=MODULE_NAME option to the GRUB_CMDLINE_LINUX command. Then run the sudo grub2-mkconfig -o /boot/grub2/grub.cfg command to enable the changes. 422 Blacklisting kernel modules with modprobe SLES 15 SP629 Dynamic kernel device management with udev The kernel can add or remove almost any device in a running system. Changes in the device state (whether a device is plugged in or removed) need to be propagated to user space. Devices need to be configured when they are plugged in and recognized. Users of a certain device need to be informed about any changes in this device''s recognized state. udev provides the needed infrastructure to dynamically maintain the device node les and symbolic links in the /dev directory. udev rules provide a way to plug external tools into the kernel device event process- ing. This allows you to customize udev device handling by adding certain scripts to execute as part of kernel device handling, or request and import additional data to evaluate during device handling. 29.1 The /dev directory The device nodes in the /dev directory provide access to the corresponding kernel devices. With udev , the /dev directory reflects the current state of the kernel. Every kernel device has one corresponding device le. If a device is disconnected from the system, the device node is removed. The content of the /dev directory is kept on a temporary le system and all les are rendered at every system start-up. Manually created or modified les do not, by design, survive a reboot. Static les and directories that should always be in the /dev directory regardless of the state of the corresponding kernel device can be created with systemd-tmpfiles. The configuration les are found in /usr/lib/tmpfiles.d/ and /etc/tmpfiles.d/ ; for more information, see the systemd-tmpfiles(8) man page. 29.2 Kernel uevents and udev The required device information is exported by the sysfs le system. For every device the kernel has detected and initialized, a directory with the device name is created. It contains attribute les with device-specific properties. Every time a device is added or removed, the kernel sends a uevent to notify udev of the change. The udev daemon reads and parses all rules from the /usr/lib/udev/rules.d/*.rules and /etc/udev/rules.d/*.rules les at start-up and keeps them in memory. If rules les are 423 The /dev directory SLES 15 SP6changed, added or removed, the daemon can reload their in-memory representation with the command udevadm control --reload . For more details on udev rules and their syntax, refer to Section 29.6, “Influencing kernel device event handling with udev rules”. Every received event is matched against the set of provides rules. The rules can add or change event environment keys, request a specific name for the device node to create, add symbolic links pointing to the node or add programs to run after the device node is created. The driver core uevents are received from a kernel netlink socket. 29.3 Drivers, kernel modules and devices The kernel bus drivers probe for devices. For every detected device, the kernel creates an internal device structure while the driver core sends a uevent to the udev daemon. Bus devices identify themselves by a specially formatted ID, which tells what kind of device it is. These IDs consist of vendor and product ID and other subsystem-specific values. Every bus has its own scheme for these IDs, called MODALIAS . The kernel takes the device information, composes a MODALIAS ID string from it and sends that string along with the event. For a USB mouse, it looks like this: MODALIAS=usb:v046DpC03Ed2000dc00dsc00dp00ic03isc01ip02 Every device driver carries a list of known aliases for devices it can handle. The list is contained in the kernel module le itself. The program depmod reads the ID lists and creates the le modules.alias in the kernel''s /lib/modules directory for all currently available modules. With this infrastructure, module loading is as easy as calling modprobe for every event that carries a MODALIAS key. If modprobe $MODALIAS is called, it matches the device alias composed for the device with the aliases provided by the modules. If a matching entry is found, that module is loaded. All this is automatically triggered by udev . 29.4 Booting and initial device setup All device events happening during the boot process before the udev daemon is running are lost, because the infrastructure to handle these events resides on the root le system and is not available at that time. To cover that loss, the kernel provides a uevent le located in the device directory of every device in the sysfs le system. By writing add to that le, the kernel resends the same event as the one lost during boot. A simple loop over all uevent les in /sys triggers all events again to create the device nodes and perform device setup. 424 Drivers, kernel modules and devices SLES 15 SP6As an example, a USB mouse present during boot may not be initialized by the early boot logic, because the driver is not available at that time. The event for the device discovery was lost and failed to nd a kernel module for the device. Instead of manually searching for connected devices, udev requests all device events from the kernel after the root le system is available, so the event for the USB mouse device runs again. Now it nds the kernel module on the mounted root le system and the USB mouse can be initialized. From user space, there is no visible difference between a device coldplug sequence and a device discovery during runtime. In both cases, the same rules are used to match and the same config- ured programs are run. 29.5 Monitoring the running udev daemon The program udevadm monitor can be used to visualize the driver core events and the timing of the udev event processes. UEVENT[1185238505.276660] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1 (usb) UDEV [1185238505.279198] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1 (usb) UEVENT[1185238505.279527] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0 (usb) UDEV [1185238505.285573] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0 (usb) UEVENT[1185238505.298878] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/ input10 (input) UDEV [1185238505.305026] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/ input10 (input) UEVENT[1185238505.305442] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/ input10/mouse2 (input) UEVENT[1185238505.306440] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/ input10/event4 (input) UDEV [1185238505.325384] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/ input10/event4 (input) UDEV [1185238505.342257] add /devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/ input10/mouse2 (input) The UEVENT lines show the events the kernel has sent over netlink. The UDEV lines show the finished udev event handlers. The timing is printed in microseconds. The time between UEVENT and UDEV is the time udev took to process this event or the udev daemon has delayed its execution to synchronize this event with related and already running events. For example, events for hard disk partitions always wait for the main disk device event to finish, because the partition events may rely on the data that the main disk event has queried from the hardware. 425 Monitoring the running udev daemon SLES 15 SP6udevadm monitor --env shows the complete event environment: ACTION=add DEVPATH=/devices/pci0000:00/0000:00:1d.2/usb3/3-1/3-1:1.0/input/input10 SUBSYSTEM=input SEQNUM=1181 NAME="Logitech USB-PS/2 Optical Mouse" PHYS="usb-0000:00:1d.2-1/input0" UNIQ="" EV=7 KEY=70000 0 0 0 0 REL=103 MODALIAS=input:b0003v046DpC03Ee0110-e0,1,2,k110,111,112,r0,1,8,amlsfw udev also sends messages to syslog. The default syslog priority that controls which messages are sent to syslog is specified in the udev configuration le /etc/udev/udev.conf . The log pri- ority of the running daemon can be changed with udevadm control --log_priority= LEV- EL/NUMBER . 29.6 Influencing kernel device event handling with udev rules A udev rule can match any property the kernel adds to the event itself or any information that the kernel exports to sysfs . The rule can also request additional information from external programs. Events are matched against all rules provided in the directories /usr/lib/udev/ rules.d/ (for default rules) and /etc/udev/rules.d (system-specific configuration). Every line in the rules le contains at least one key value pair. There are two kinds of keys, match and assignment keys. If all match keys match their values, the rule is applied and the assignment keys are assigned the specified value. A matching rule may specify the name of the device node, add symbolic links pointing to the node or run a specified program as part of the event handling. If no matching rule is found, the default device node name is used to create the device node. Detailed information about the rule syntax and the provided keys to match or import data are described in the udev man page. The following example rules provide a basic introduction to udev rule syntax. The example rules are all taken from the udev default rule set /usr/lib/udev/rules.d/50-udev-default.rules . EXAMPLE 29.1: EXAMPLE udev RULES # console 426 Influencing kernel device event handling with udev rules SLES 15 SP6KERNEL=="console", MODE="0600", OPTIONS="last_rule" # serial devices KERNEL=="ttyUSB*", ATTRS{product}=="[Pp]alm*Handheld*", SYMLINK+="pilot" # printer SUBSYSTEM=="usb", KERNEL=="lp*", NAME="usb/%k", SYMLINK+="usb%k", GROUP="lp" # kernel firmware loader SUBSYSTEM=="firmware", ACTION=="add", RUN+="firmware.sh" The console rule consists of three keys: one match key ( KERNEL ) and two assign keys ( MODE , OPTIONS ). The KERNEL match rule searches the device list for any items of the type console . Only exact matches are valid and trigger this rule to be executed. The MODE key assigns special permissions to the device node, in this case, read and write permissions to the owner of this device only. The OPTIONS key makes this rule the last rule to be applied to any device of this type. Any later rule matching this particular device type does not have any effect. The serial devices rule is not available in 50-udev-default.rules anymore, but it is still worth considering. It consists of two match keys ( KERNEL and ATTRS ) and one assign key ( SYMLINK ). The KERNEL key searches for all devices of the ttyUSB type. Using the * wild card, this key matches several of these devices. The second match key, ATTRS , checks whether the product attribute le in sysfs for any ttyUSB device contains a certain string. The assign key ( SYMLINK ) triggers the addition of a symbolic link to this device under /dev/pilot . The operator used in this key ( += ) tells udev to additionally perform this action, even if previous or later rules add other symbolic links. As this rule contains two match keys, it is only applied if both conditions are met. The printer rule deals with USB printers and contains two match keys which must both apply to get the entire rule applied ( SUBSYSTEM and KERNEL ). Three assign keys deal with the naming for this device type ( NAME ), the creation of symbolic device links ( SYMLINK ) and the group membership for this device type ( GROUP ). Using the * wild card in the KERNEL key makes it match several lp printer devices. Substitutions are used in both, the NAME and the SYMLINK keys to extend these strings by the internal device name. For example, the symbolic link to the rst lp USB printer would read /dev/usblp0 . The kernel firmware loader rule makes udev load additional rmware by an external helper script during runtime. The SUBSYSTEM match key searches for the firmware subsystem. The ACTION key checks whether any device belonging to the firmware subsystem has been added. The RUN+= key triggers the execution of the firmware.sh script to locate the rmware that is to be loaded. 427 Influencing kernel device event handling with udev rules SLES 15 SP6General characteristics are common to all rules: Each rule consists of one or more key value pairs separated by a comma. A key''s operation is determined by the operator. udev rules support several operators. Each given value must be enclosed by quotation marks. Each line of the rules le represents one rule. If a rule is longer than one line, use \ to join the different lines as you would do in shell syntax. udev rules support a shell-style pattern that matches the * , ? , and [] patterns. udev rules support substitutions. 29.6.1 Using operators in udev rules Creating keys you can choose from several operators, depending on the type of key you want to create. Match keys will normally be used to nd a value that either matches or explicitly mismatches the search value. Match keys contain either of the following operators: == Compare for equality. If the key contains a search pattern, all results matching this pattern are valid. != Compare for non-equality. If the key contains a search pattern, all results matching this pattern are valid. Any of the following operators can be used with assign keys: = Assign a value to a key. If the key previously consisted of a list of values, the key resets and only the single value is assigned. += Add a value to a key that contains a list of entries. := Assign a final value. Disallow any later change by later rules. 428 Using operators in udev rules SLES 15 SP629.6.2 Using substitutions in udev rules udev rules support the use of placeholders and substitutions. Use them in a similar fashion as you would do in any other scripts. The following substitutions can be used with udev rules: %r , $root The device directory, /dev by default. %p , $devpath The value of DEVPATH . %k , $kernel The value of KERNEL or the internal device name. %n , $number The device number. %N , $tempnode The temporary name of the device le. %M , $major The major number of the device. %m , $minor The minor number of the device. %s{ATTRIBUTE} , $attr{ATTRIBUTE} The value of a sysfs attribute (specified by ATTRIBUTE ). %E{VARIABLE} , $env{VARIABLE} The value of an environment variable (specified by VARIABLE ). %c , $result The output of PROGRAM . %% The % character. $$ The $ character. 429 Using substitutions in udev rules SLES 15 SP629.6.3 Using udev match keys Match keys describe conditions that must be met before a udev rule can be applied. The fol- lowing match keys are available: ACTION The name of the event action, for example, add or remove when adding or removing a device. DEVPATH The device path of the event device, for example, DEVPATH=/bus/pci/drivers/ipw3945 to search for all events related to the ipw3945 driver. KERNEL The internal (kernel) name of the event device. SUBSYSTEM The subsystem of the event device, for example, SUBSYSTEM=usb for all events related to USB devices. ATTR{FILENAME} sysfs attributes of the event device. To match a string contained in the vendor attribute le name, you could use ATTR{vendor}=="On[sS]tream" , for example. KERNELS Let udev search the device path upward for a matching device name. SUBSYSTEMS Let udev search the device path upward for a matching device subsystem name. DRIVERS Let udev search the device path upward for a matching device driver name. ATTRS{FILENAME} Let udev search the device path upward for a device with matching sysfs attribute values. ENV{KEY} The value of an environment variable, for example, ENV{ID_BUS}="ieee1394 to search for all events related to the FireWire bus ID. 430 Using udev match keys SLES 15 SP6PROGRAM Let udev execute an external program. To be successful, the program must return with exit code zero. The program''s output, printed to STDOUT, is available to the RESULT key. RESULT Match the output string of the last PROGRAM call. Either include this key in the same rule as the PROGRAM key or in a later one. 29.6.4 Using udev assign keys In contrast to the match keys described above, assign keys do not describe conditions that must be met. They assign values, names and actions to the device nodes maintained by udev . NAME The name of the device node to be created. After a rule has set a node name, all other rules with a NAME key for this node are ignored. SYMLINK The name of a symbolic link related to the node to be created. Multiple matching rules can add symbolic links to be created with the device node. You can also specify multiple symbolic links for one node in one rule using the space character to separate the symbolic link names. OWNER, GROUP, MODE The permissions for the new device node. Values specified here overwrite anything that has been compiled in. ATTR{KEY} Specify a value to be written to a sysfs attribute of the event device. If the == operator is used, this key is also used to match against the value of a sysfs attribute. ENV{KEY} Tell udev to export a variable to the environment. If the == operator is used, this key is also used to match against an environment variable. RUN Tell udev to add a program to the list of programs to be executed for this device. Keep in mind to restrict this to short tasks to avoid blocking further events for this device. 431 Using udev assign keys SLES 15 SP6LABEL Add a label where a GOTO can jump to. GOTO Tell udev to skip several rules and continue with the one that carries the label referenced by the GOTO key. IMPORT{TYPE} Load variables into the event environment such as the output of an external program. udev imports variables of several types. If no type is specified, udev tries to determine the type itself based on the executable bit of the le permissions. program tells udev to execute an external program and import its output. file tells udev to import a text le. parent tells udev to import the stored keys from the parent device. WAIT_FOR_SYSFS Tells udev to wait for the specified sysfs le to be created for a certain device. For example, WAIT_FOR_SYSFS="ioerr_cnt" informs udev to wait until the ioerr_cnt le has been created. OPTIONS The OPTION key may have several values: last_rule tells udev to ignore all later rules. ignore_device tells udev to ignore this event. ignore_remove tells udev to ignore all later remove events for the device. all_partitions tells udev to create device nodes for all available partitions on a block device. 29.7 Persistent device naming The dynamic device directory and the udev rules infrastructure make it possible to provide stable names for all disk devices—regardless of their order of recognition or the connection used for the device. Every appropriate block device the kernel creates is examined by tools 432 Persistent device naming SLES 15 SP6with special knowledge about certain buses, drive types or le systems. Along with the dynamic kernel-provided device node name, udev maintains classes of persistent symbolic links pointing to the device: /dev/disk |-- by-id | |-- scsi-SATA_HTS726060M9AT00_MRH453M4HWHG7B -> ../../sda | |-- scsi-SATA_HTS726060M9AT00_MRH453M4HWHG7B-part1 -> ../../sda1 | |-- scsi-SATA_HTS726060M9AT00_MRH453M4HWHG7B-part6 -> ../../sda6 | |-- scsi-SATA_HTS726060M9AT00_MRH453M4HWHG7B-part7 -> ../../sda7 | |-- usb-Generic_STORAGE_DEVICE_02773 -> ../../sdd | `-- usb-Generic_STORAGE_DEVICE_02773-part1 -> ../../sdd1 |-- by-label | |-- Photos -> ../../sdd1 | |-- SUSE10 -> ../../sda7 | `-- devel -> ../../sda6 |-- by-path | |-- pci-0000:00:1f.2-scsi-0:0:0:0 -> ../../sda | |-- pci-0000:00:1f.2-scsi-0:0:0:0-part1 -> ../../sda1 | |-- pci-0000:00:1f.2-scsi-0:0:0:0-part6 -> ../../sda6 | |-- pci-0000:00:1f.2-scsi-0:0:0:0-part7 -> ../../sda7 | |-- pci-0000:00:1f.2-scsi-1:0:0:0 -> ../../sr0 | |-- usb-02773:0:0:2 -> ../../sdd | |-- usb-02773:0:0:2-part1 -> ../../sdd1 `-- by-uuid |-- 159a47a4-e6e6-40be-a757-a629991479ae -> ../../sda7 |-- 3e999973-00c9-4917-9442-b7633bd95b9e -> ../../sda6 `-- 4210-8F8C -> ../../sdd1 29.8 Files used by udev /sys/* Virtual le system provided by the Linux kernel, exporting all currently known devices. This information is used by udev to create device nodes in /dev /dev/* Dynamically created device nodes and static content created with systemd-tmpfiles; for more information, see the systemd-tmpfiles(8) man page. The following les and directories contain the crucial elements of the udev infrastructure: /etc/udev/udev.conf Main udev configuration le. 433 Files used by udev SLES 15 SP6/etc/udev/rules.d/* System-specific udev event matching rules. You can add custom rules here to modify or override the default rules from /usr/lib/udev/rules.d/* . Files are parsed in alphanumeric order. Rules from les with a higher priority modify or override rules with lower priority. The lower the number, the higher the priority. /usr/lib/udev/rules.d/* Default udev event matching rules. The les in this directory are owned by packages and will be overwritten by updates. Do not add, remove or edit les here, use /etc/udev/ rules.d instead. /usr/lib/udev/* Helper programs called from udev rules. /usr/lib/tmpfiles.d/ and /etc/tmpfiles.d/ Responsible for static /dev content. 29.9 More information For more information about the udev infrastructure, refer to the following man pages: udev General information about udev , keys, rules and other important configuration issues. udevadm udevadm can be used to control the runtime behavior of udev , request kernel events, manage the event queue and provide simple debugging mechanisms. udevd Information about the udev event managing daemon. 434 More information SLES 15 SP630 Special system features This chapter starts with information about specific software packages, the virtual consoles and the keyboard layout. We talk about software components like bash , cron and logrotate , because they were changed or enhanced during the last re- lease cycles. Even if they are small or considered of minor importance, users should change their default behavior, because these components are often closely coupled with the system. The chapter concludes with a section about language and coun- try-specific settings (I18N and L10N). 30.1 Information about special software packages The following chapter provides basic information about the following tools: bash , cron , logrotate , locate , ulimit and free . 30.1.1 The bash package and /etc/profile Bash is the default system shell. When used as a login shell, it reads several initialization les. Bash processes them in the order they appear in this list: 1. /etc/profile 2. ~/.profile 3. /etc/bash.bashrc 4. ~/.bashrc Make custom settings in ~/.profile or ~/.bashrc . To ensure the correct processing of these les, it is necessary to copy the basic settings from /etc/skel/.profile or /etc/ skel/.bashrc into the home directory of the user. It is recommended to copy the settings from /etc/skel after an update. Execute the following shell commands to prevent the loss of per- sonal adjustments: > mv ~/.bashrc ~/.bashrc.old > cp /etc/skel/.bashrc ~/.bashrc > mv ~/.profile ~/.profile.old 435 Information about special software packages SLES 15 SP6> cp /etc/skel/.profile ~/.profile Then copy personal adjustments back from the *.old les. 30.1.2 The cron package Use cron to automatically run commands in the background at predefined times. cron uses specially formatted time tables, and the tool comes with several default ones. Users can also specify custom tables, if needed. The cron tables are located in /var/spool/cron/tabs . /etc/crontab serves as a systemwide cron table. Enter the user name to run the command directly after the time table and before the command. In Example 30.1, “Entry in /etc/crontab”, root is entered. Package-specific tables, located in /etc/cron.d , have the same format. See the cron man page ( man cron ). EXAMPLE 30.1: ENTRY IN /ETC/CRONTAB 1-59/5 * * * * root test -x /usr/sbin/atrun && /usr/sbin/atrun You cannot edit /etc/crontab by calling the command crontab -e . This le must be loaded directly into an editor, then modified and saved. Several packages install shell scripts to the directories /etc/cron.hourly , /etc/cron.daily , /etc/cron.weekly and /etc/cron.monthly , whose execution is controlled by /usr/lib/ cron/run-crons . /usr/lib/cron/run-crons is run every 15 minutes from the main table ( / etc/crontab ). This guarantees that processes that may have been neglected can be run at the proper time. To run the hourly , daily or other periodic maintenance scripts at custom times, remove the time stamp les regularly using /etc/crontab entries (see Example 30.2, “/etc/crontab: remove time stamp files”, which removes the hourly one before every full hour, the daily one once a day at 2:14 a.m., etc.). EXAMPLE 30.2: /ETC/CRONTAB: REMOVE TIME STAMP FILES 59 * * * * root rm -f /var/spool/cron/lastrun/cron.hourly 14 2 * * * root rm -f /var/spool/cron/lastrun/cron.daily 29 2 * * 6 root rm -f /var/spool/cron/lastrun/cron.weekly 44 2 1 * * root rm -f /var/spool/cron/lastrun/cron.monthly Or you can set DAILY_TIME in /etc/sysconfig/cron to the time at which cron.daily should start. The setting of MAX_NOT_RUN ensures that the daily tasks get triggered to run, even if the user did not turn on the computer at the specified DAILY_TIME for a longer time. The maximum value of MAX_NOT_RUN is 14 days. 436 The cron package SLES 15 SP630.1.3 Stopping cron status messages To avoid the mail ood caused by cron status messages, the default value of SEND_MAIL_ON_NO_ERROR in /etc/sysconfig/cron is set to " no " for new installations. Even with this setting to " no ", cron data output will still be sent to the MAILTO address, as docu- mented in the cron man page. In the update case it is recommended to set these values according to your needs. 30.1.4 Log files: package logrotate There are several system services (daemons) that, along with the kernel itself, regularly record the system status and specific events onto log les. This way, the administrator can regularly check the status of the system at a certain point in time, recognize errors or faulty functions and troubleshoot them with pinpoint precision. These log les are normally stored in /var/log as specified by FHS and grow on a daily basis. The logrotate package helps control the growth of these les. For more details refer to Book “System Analysis and Tuning Guide”, Chapter 3 “System log files”, Section 3.3 “Managing log files with logrotate”. 30.1.5 The locate command locate , a command for quickly finding les, is not included in the standard scope of installed software. If desired, install the package mlocate , the successor of the package findutils-lo- cate . The updatedb process is started automatically every night or about 15 minutes after booting the system. 30.1.6 The ulimit command With the ulimit (user limits) command, it is possible to set limits for the use of system resources and to have these displayed. ulimit is especially useful for limiting available memory for applications. With this, an application can be prevented from co-opting too much of the system resources and slowing or even hanging up the operating system. ulimit can be used with various options. To limit memory usage, use the options listed in Table 30.1, “ulimit: Setting resources for the user”. 437 Stopping cron status messages SLES 15 SP6TABLE 30.1: ulimit: SETTING RESOURCES FOR THE USER -m The maximum resident set size -v The maximum amount of virtual memory available to the shell -s The maximum size of the stack -c The maximum size of core les created -a All current limits are reported Systemwide default entries are set in /etc/profile . Editing this le directly is not recommend- ed, because changes will be overwritten during system upgrades. To customize systemwide pro- file settings, use /etc/profile.local . Per-user settings should be made in ~USER/.profile . EXAMPLE 30.3: ulimit: SETTINGS IN ~/.bashrc # Limits maximum resident set size (physical memory): ulimit -m 98304 # Limits of virtual memory: ulimit -v 98304 Memory allocations must be specified in KB. For more detailed information, see man bash . Important: ulimit support Not all shells support ulimit directives. PAM (for example, pam_limits ) offers com- prehensive adjustment possibilities as an alternative to ulimit . 30.1.7 The free command The free command displays the total amount of free and used physical memory and swap space in the system and the buers and cache consumed by the kernel. The concept of available RAM dates back to before the days of unified memory management. The slogan free memory is bad memory applies well to Linux. As a result, Linux has always made the effort to balance out caches without allowing free or unused memory. 438 The free command SLES 15 SP6The kernel does not have direct knowledge of any applications or user data. Instead, it manages applications and user data in a page cache. If memory runs short, parts of it are written to the swap partition or to les, from which they can initially be read using the mmap command (see man mmap ). The kernel also contains other caches, such as the slab cache, where the caches used for network access are stored. This may explain the differences between the counters in /proc/meminfo . Most, but not all, of them can be accessed via /proc/slabinfo . However, if your goal is to nd out how much RAM is currently being used, nd this information in /proc/meminfo . 30.1.8 Man pages and info pages For some GNU applications (such as tar), the man pages are no longer maintained. For these commands, use the --help option to get a quick overview of the info pages, which provide more in-depth instructions. Info is GNU''s hypertext system. Read an introduction to this system by entering info info . Info pages can be viewed with Emacs by entering emacs -f info or directly in a console with info . You can also use tkinfo, xinfo or the help system to view info pages. 30.1.9 Selecting man pages using the man command To read a man page enter man MAN_PAGE . If a man page with the same name exists in different sections, they will all be listed with the corresponding section numbers. Select the one to display. If you do not enter a section number within a few seconds, the rst man page will be displayed. To change this to the default system behavior, set MAN_POSIXLY_CORRECT=1 in a shell initial- ization le such as ~/.bashrc . 30.1.10 Settings for GNU Emacs GNU Emacs is a complex work environment. The following sections cover the configuration les processed when GNU Emacs is started. More information is available at https://www.gnu.org/ software/emacs/ . 439 Man pages and info pages SLES 15 SP6On start-up, Emacs reads several les containing the settings of the user, system administrator and distributor for customization or preconfiguration. The initialization le ~/.emacs is in- stalled to the home directories of the individual users from /etc/skel . .emacs , in turn, reads the le /etc/skel/.gnu-emacs . To customize the program, copy .gnu-emacs to the home di- rectory (with cp /etc/skel/.gnu-emacs ~/.gnu-emacs ) and make the desired settings there. .gnu-emacs defines the le ~/.gnu-emacs-custom as custom-file . If users make settings with the customize options in Emacs, the settings are saved to ~/.gnu-emacs-custom . With SUSE Linux Enterprise Server, the emacs package installs the le site-start.el in the directory /usr/share/emacs/site-lisp . The le site-start.el is loaded before the ini- tialization le ~/.emacs . Among other things, site-start.el ensures that special configura- tion les distributed with Emacs add-on packages, such as psgml , are loaded automatically. Configuration les of this type are located in /usr/share/emacs/site-lisp , too, and always begin with suse-start- . The local system administrator can specify systemwide settings in default.el . More information about these les is available in the Emacs info le under Init File: in- fo:/emacs/InitFile . Information about how to disable the loading of these les (if necessary) is also provided at this location. The components of Emacs are divided into several packages: The base package emacs . emacs-x11 (usually installed): the program with X11 support. emacs-nox : the program without X11 support. emacs-info : online documentation in info format. emacs-el : the uncompiled library les in Emacs Lisp. These are not required at runtime. Numerous add-on packages can be installed if needed: emacs-auctex (LaTeX), psgml (SGML and XML), gnuserv (client and server operation) and others. 30.2 Virtual consoles Linux is a multiuser and multitasking system. The advantages of these features can be appreci- ated even on a stand-alone PC system. In text mode, there are six virtual consoles available. Switch between them using Alt – F1 through Alt – F6 . The seventh console is reserved for X and the tenth console shows kernel messages. 440 Virtual consoles SLES 15 SP6To switch to a console from X without shutting it down, use Ctrl – Alt – F1 to Ctrl – Alt – F6 . To return to X, press Alt – F7 . 30.3 Keyboard mapping To standardize the keyboard mapping of programs, changes were made to the following les: /etc/inputrc /etc/X11/Xmodmap /etc/skel/.emacs /etc/skel/.gnu-emacs /etc/skel/.vimrc /etc/csh.cshrc /etc/termcap /usr/share/terminfo/x/xterm /usr/share/X11/app-defaults/XTerm /usr/share/emacs/VERSION/site-lisp/term/*.el These changes only affect applications that use terminfo entries or whose configuration les are changed directly ( vi , emacs , etc.). Applications not shipped with the system should be adapted to these defaults. Under X, the compose key (multikey) can be enabled as explained in /etc/X11/Xmodmap . Further settings are possible using the X Keyboard Extension (XKB). Tip: More information Information about XKB is available in the documents listed in /usr/share/doc/pack- ages/xkeyboard-config (part of the xkeyboard-config package). 30.4 Language and country-specific settings The system is, to a very large extent, internationalized and can be modified for local needs. In- ternationalization (I18N) allows specific localization (L10N). The abbreviations I18N and L10N are derived from the rst and last letters of the words and, in between, the number of letters omitted. 441 Keyboard mapping SLES 15 SP6Settings are made with LC_ variables defined in the le /etc/sysconfig/language . This refers not only to native language support, but also to the categories Messages (Language), Character Set, Sort Order, Time and Date, Numbers and Money. Each of these categories can be defined directly with its own variable or indirectly with a master variable in the le language (see the locale man page). LIST OF VARIABLES RC_LC_MESSAGES , RC_LC_CTYPE , RC_LC_COLLATE , RC_LC_TIME , RC_LC_NUMERIC , RC_L- C_MONETARY These variables are passed to the shell without the RC_ prefix and represent the listed categories. The shell profiles concerned are listed below. The current setting can be shown with the command locale . RC_LC_ALL This variable, if set, overwrites the values of the variables already mentioned. RC_LANG If none of the previous variables are set, this is the fallback. By default, only RC_LANG is set. This makes it easier for users to enter their own values. ROOT_USES_LANG This variable can be set to yes or ctype (default). If set to yes , root uses language and country-specific settings, otherwise the system administrator always works in a POSIX environment. The variables can be set with the YaST sysconfig editor. The value of such a variable contains the language code, country code, encoding and modifier. The individual components are joined by special characters: LANG= [[_ ]. [@ ]] 30.4.1 System-wide locale settings systemd reads /etc/locale.conf at early boot. The locale settings configured in this le are inherited by every service or user, unless there are individual settings. 442 System-wide locale settings SLES 15 SP6Note: Behavior of older configuration files under SUSE Linux Enterprise Server SUSE Linux Enterprise Server Earlier versions of SUSE Linux Enterprise Server read locale settings from /etc/syscon- fig/language , /etc/sysconfig/keyboard , and /etc/sysconfig/console . Starting with SUSE Linux Enterprise Server 15 GA, these les are considered obsolete. sys- temd does not read settings from these les anymore. Instead, systemd reads /etc/ locale.conf . However, variables defined in /etc/sysconfig/language will still be used: They over- ride the system-wide locale and can be used to define different locale settings for user shells (see Section 30.4.2, “Some examples”). To set the system-wide locale, you can either: Write your settings in /etc/locale.conf . Each line is a environment-like variable as- signment (see man 5 locale.conf for a list of variables): LANG=de_DE.UTF-8 To ne-tune the settings, you can add additional variables, one variable per line. Use the command localectl : # localectl set-locale LANG=de_DE.UTF-8 Same here, you can also specify additional variables after the localectl set-locale command. To keep backward compatibility with old systems during the update of the systemd package, all variables mentioned will be migrated from sysconfig to their final destinations if they are not already defined there. 30.4.2 Some examples You should always set the language and country codes together. Language settings follow the standard ISO 639 available at https://www.evertype.com/standards/iso639/iso639-en.html and https://www.loc.gov/standards/iso639-2/ . Country codes are listed in ISO  3166, see https:// en.wikipedia.org/wiki/ISO_3166 . 443 Some examples SLES 15 SP6It only makes sense to set values for which usable description les can be found in /usr/lib/ locale . Additional description les can be created from the les in /usr/share/i18n using the command localedef . The description les are part of the glibc-i18ndata package. A description le for en_US.UTF-8 (for English and United States) can be created with: localedef -i en_US -f UTF-8 en_US.UTF-8 LANG=en_US.UTF-8 This is the default setting if American English is selected during installation. If you selected another language, that language is enabled but still with UTF-8 as the character encoding. LANG=en_US.ISO-8859-1 This sets the language to English, country to United States and the character set to ISO-8859-1 . This character set does not support the Euro sign, but it can be useful some- times for programs that have not been updated to support UTF-8 . The string defining the charset ( ISO-8859-1 in this case) is then evaluated by programs like Emacs. LANG=en_IE@euro The above example explicitly includes the Euro sign in a language setting. This setting is obsolete now, as UTF-8 also covers the Euro symbol. It is only useful if an application supports ISO-8859-15 and not UTF-8. Changes to /etc/sysconfig/language are activated by the following process chain: For the Bash: /etc/profile reads /etc/profile.d/lang.sh which, in turn, analyzes /etc/sysconfig/language . For tcsh: At login, /etc/csh.login reads /etc/profile.d/lang.csh which, in turn, analyzes /etc/sysconfig/language . This ensures that any changes to /etc/sysconfig/language are available at the next login to the respective shell, without having to manually activate them. Users can override the system defaults by editing their ~/.bashrc accordingly. For ex- ample, if you do not want to use the system-wide en_US for program messages, include LC_MESSAGES=es_ES so that messages are displayed in Spanish instead. 444 Some examples SLES 15 SP630.4.3 Locale settings in ~/.i18n If you are not satisfied with locale system defaults, change the settings in ~/.i18n according to the Bash scripting syntax. Entries in ~/.i18n override system defaults from /etc/syscon- fig/language . Use the same variable names but without the RC_ namespace prefixes. For ex- ample, use LANG instead of RC_LANG : LANG=cs_CZ.UTF-8 LC_COLLATE=C 30.4.4 Settings for language support Files in the category Messages are, as a rule, only stored in the corresponding language direc- tory (like en ) to have a fallback. If you set LANG to en_US and the message le in /usr/ share/locale/en_US/LC_MESSAGES does not exist, it falls back to /usr/share/locale/en/ LC_MESSAGES . A fallback chain can also be defined, for example, for Breton to French or for Galician to Spanish to Portuguese: LANGUAGE="br_FR:fr_FR" LANGUAGE="gl_ES:es_ES:pt_PT" If desired, use the Norwegian variants Nynorsk and Bokmål instead (with additional fallback to no ): LANG="nn_NO" LANGUAGE="nn_NO:nb_NO:no" or LANG="nb_NO" LANGUAGE="nb_NO:nn_NO:no" In Norwegian, LC_TIME is also treated differently. One problem that can arise is a separator used to delimit groups of digits not being recognized properly. This occurs if LANG is set to only a two-letter language code like de , but the definition le glibc uses is located in /usr/share/lib/de_DE/LC_NUMERIC . Thus LC_NUMERIC must be set to de_DE to make the separator definition visible to the system. 445 Locale settings in ~/.i18n SLES 15 SP630.4.5 More information The GNU C Library Reference Manual, Chapter “Locales and Internationalization”. It is in- cluded in the package glibc-info . Markus Kuhn, UTF-8 and Unicode FAQ for Unix/Linux, currently at https:// www.cl.cam.ac.uk/~mgk25/unicode.html . 446 More information SLES 15 SP631 Using NetworkManager NetworkManager is the ideal solution for laptops and other portable computers. It supports state-of-the-art encryption types and standards for network connections, including connections to 802.1X protected networks. 802.1X is the “IEEE Standard for Local and Metropolitan Area Networks—Port-Based Network Access Control”. With NetworkManager, you need not worry about configuring network interfaces and switching between wired or wireless networks when you are on the move. NetworkManager can automatically connect to known wireless networks or manage several network connections in parallel—the fastest connection is then used as default. Furthermore, you can manually switch between available networks and manage your network connection using an applet in the system tray. Instead of only one connection being active, multiple connections may be active at once. This enables you to unplug your laptop from an Ethernet and remain connected via a wireless con- nection. Important: Support coverage NetworkManager is only supported by SUSE for desktop workloads with SLED or the Workstation extension. All server certifications are done with wicked as the network configuration tool, and using NetworkManager may invalidate them. NetworkManager is not supported by SUSE for server workloads. 31.1 Use cases for NetworkManager NetworkManager provides a sophisticated and intuitive user interface, which enables users to easily switch their network environment. However, NetworkManager is not a suitable solution in the following cases: Your computer provides network services for other computers in your network, for exam- ple, it is a DHCP or DNS server. Your computer is a Xen server or your system is a virtual system inside Xen. 447 Use cases for NetworkManager SLES 15 SP631.2 Enabling or disabling NetworkManager On desktop and laptop computers, NetworkManager is enabled by default. You can disable and enable it at any time using the Network Settings module in YaST. 1. Run YaST and go to System Network Settings. 2. The Network Settings dialog opens. Go to the Global Options tab. 3. To configure and manage your network connections with NetworkManager: a. In the Network Setup Method eld, select User Controlled with NetworkManager. b. Click OK and close YaST. c. Configure your network connections with NetworkManager as described in Sec- tion 31.3, “Configuring network connections”. 4. To deactivate NetworkManager and control the network with your own configuration: a. In the Network Setup Method eld, choose Controlled by wicked. b. Click OK. c. Set up your network card with YaST using automatic configuration via DHCP or a static external IP address. Find a detailed description of the network configuration with YaST in Section 23.4, “Configuring a network connection with YaST”. 31.3 Configuring network connections After enabling NetworkManager in YaST, configure your network connections with the Net- workManager front-end available in GNOME. It shows tabs for all types of network connections, such as wired, wireless, mobile broadband, DSL and VPN connections. To open the network configuration dialog in GNOME, open the settings menu via the status menu and click the Network entry. 448 Enabling or disabling NetworkManager SLES 15 SP6Note: Availability of options Depending on your system setup, you may not be allowed to configure certain connec- tions. In a secured environment, certain options may be locked or require root permis- sion. Ask your system administrator for details. FIGURE 31.1: GNOME NETWORK CONNECTIONS DIALOG PROCEDURE 31.1: ADDING AND EDITING CONNECTIONS 1. Open the Status Menu, click the gear icon to open Settings and click Network from the left menu. 2. To add a Connection: a. Click the + icon next to the connection type tab that you want to add. b. Depending on the connection type, ll the required elds in the corresponding di- alog. c. When you are finished click Add. d. After confirming your changes, the newly configured network connection appears in the list of available networks in the Status Menu. 3. To edit a connection: a. Click the gear icon on the right side of the connection type tab that you want to edit. 449 Configuring network connections SLES 15 SP6b. Insert your changes and click Apply to save them. c. To make your connection available as a system connection go to the Details tab and set the check box Make available to other users. For more information about user and system connections, see Section 31.4.1, “User and system connections”. 31.3.1 Managing wired network connections If your computer is connected to a wired network, use the NetworkManager applet to manage the connection. 1. Open the Status Menu and click Wired to switch it o or click the related right arrow to change the connection details. 2. To change the settings click Wired Settings and then click the gear icon. 3. To switch o all network connections, activate the Airplane Mode setting. 31.3.2 Managing wireless network connections Visible wireless networks are listed in the GNOME NetworkManager applet menu under Wireless Networks. The signal strength of each network is also shown in the menu. Encrypted wireless networks are marked with a shield icon. PROCEDURE 31.2: CONNECTING TO A VISIBLE WIRELESS NETWORK 1. To connect to a visible wireless network, open the Status Menu and click Wi-Fi. 2. Click Turn On to enable it. 3. Click Select Network, select your Wi-Fi Network and click Connect. 4. If the network is encrypted, a configuration dialog opens. It shows the type of encryption the network uses and text boxes for entering the login credentials. PROCEDURE 31.3: CONNECTING TO AN INVISIBLE WIRELESS NETWORK 1. To connect to a network that does not broadcast its service set identifier (SSID or ESSID) and therefore cannot be detected automatically, open the Status Menu and click Wi-Fi. 2. Click Wi-Fi Settings to open the detailed settings menu. 3. Make sure your Wi-Fi is enabled and click Connect to Hidden Network. 450 Managing wired network connections SLES 15 SP64. In the dialog that opens, enter the SSID or ESSID in Network Name and set encryption parameters if necessary. A wireless network that has been chosen explicitly remains connected as long as possible. If a network cable is plugged in during that time, any connections that have been set to Stay connected when possible will be connected, while the wireless connection remains up. 31.3.3 Configuring your Wi-Fi/Bluetooth card as an access point If your Wi-Fi/Bluetooth card supports access point mode, you can use NetworkManager for the configuration. 1. Open the Status Menu and click Wi-Fi. 2. Click Wi-Fi Settings to open the detailed settings menu. 3. Click Use as Hotspot and follow the instructions. 4. Use the credentials shown in the resulting dialog to connect to the hotspot from a remote machine. 31.3.4 NetworkManager and VPN NetworkManager supports several Virtual Private Network (VPN) technologies. For each tech- nology, SUSE Linux Enterprise Server comes with a base package providing the generic support for NetworkManager. Besides that, you also need to install the respective desktop-specific pack- age for your applet. OpenVPN To use this VPN technology, install: NetworkManager-openvpn NetworkManager-openvpn-gnome OpenConnect To use this VPN technology, install: NetworkManager-openconnect NetworkManager-openconnect-gnome 451 Configuring your Wi-Fi/Bluetooth card as an access point SLES 15 SP6PPTP (point-to-point tunneling protocol) To use this VPN technology, install: NetworkManager-pptp NetworkManager-pptp-gnome The following procedure describes how to set up your computer as an OpenVPN client using NetworkManager. Setting up other types of VPNs works analogously. Before you begin, make sure that the package NetworkManager-openvpn-gnome is installed and all dependencies have been resolved. PROCEDURE 31.4: SETTING UP OPENVPN WITH NETWORKMANAGER 1. Open the application Settings by clicking the status icons at the right end of the panel and clicking the wrench and screwdriver icon. In the window All Settings, choose Network. 2. Click the + icon. 3. Select VPN and then OpenVPN. 4. Choose the Authentication type. Depending on the setup of your OpenVPN server, choose Certificates (TLS) or Password with Certificates (TLS). 5. Insert the necessary values into the respective text boxes. For our example configuration, these are: Gateway The remote endpoint of the VPN server User name The user (only available when you have selected Password with Certificates (TLS)) Password The password for the user (only available when you have selected Password with Certificates (TLS)) User Certificate /etc/openvpn/client1.crt CA Certificate /etc/openvpn/ca.crt Private Key /etc/openvpn/client1.key 6. Finish the configuration with Add. 452 NetworkManager and VPN SLES 15 SP67. To enable the connection, in the Network panel of the Settings application click the switch button. Alternatively, click the status icons at the right end of the panel, click the name of your VPN and then Connect. 31.4 NetworkManager and security NetworkManager distinguishes two types of wireless connections: trusted and untrusted. A trust- ed connection is any network that you explicitly selected in the past. All others are untrusted. Trusted connections are identified by the name and MAC address of the access point. Using the MAC address ensures that you cannot use a different access point with the name of your trusted connection. NetworkManager periodically scans for available wireless networks. If multiple trusted networks are found, the most recently used is automatically selected. NetworkManager waits for your selection in case if all networks are untrusted. If the encryption setting changes but the name and MAC address remain the same, Network- Manager attempts to connect, but rst you are asked to confirm the new encryption settings and provide any updates, such as a new key. If you switch from using a wireless connection to offline mode, NetworkManager blanks the SSID or ESSID. This ensures that the card is disconnected. 31.4.1 User and system connections NetworkManager knows two types of connections: user and system connections. User connections require every user to authenticate in NetworkManager, which stores the user''s credentials in their local GNOME keyring so that they do not need to re-enter them every time they connect. System connections are available to all users automatically. The rst user to create the connec- tion enters any necessary credentials, and then all other users have access without needing to know the credentials. The difference in configuring a user or system connection is a single check box, Make available to other users. For information on how to configure user or system connec- tions with NetworkManager, refer to Section 31.3, “Configuring network connections”. 453 NetworkManager and security SLES 15 SP631.4.2 Storing passwords and credentials If you do not want to re-enter your credentials each time you want to connect to an encrypted network, you can use the GNOME Keyring Manager to store your credentials encrypted on the disk, secured by a master password. 31.4.3 Firewall zones FIGURE 31.2: firewalld ZONES IN NETWORKMANAGER The firewall zones set general rules about which network connections are allowed. To configure the zone of firewalld for a wired connection, go to the Identity tab of the connection settings. To configure the zone of firewalld for a Wi-Fi connection, go to the Security tab of the connection settings. If you are in your home network, use the zone home . For public wireless networks, switch to public . If you are in a secure environment and want to allow all connections, use the zone trusted . For details about firewalld, see Book “Security and Hardening Guide”, Chapter 23 “Masquerading and firewalls”, Section 23.4 “firewalld”. 454 Storing passwords and credentials SLES 15 SP631.5 Frequently asked questions In the following, nd several frequently asked questions about configuring special network op- tions with NetworkManager. 1. How to tie a connection to a specific device? By default, connections in NetworkManager are device type-specific: they apply to all physical devices with the same type. If more than one physical device per connection type is available (for example, your machine is equipped with two Ethernet cards), you can tie a connection to a certain device. To do this in GNOME, rst look up the MAC address of your device (use the Connection Information available from the applet, or use the output of command line tools like nm- tool or wicked show all ). Then start the dialog for configuring network connections and choose the connection you want to modify. On the Wired or Wireless tab, enter the MAC Address of the device and confirm your changes. 2. How to specify a certain access point in case multiple access points with the same ESSID are de- tected? When multiple access points with different wireless bands (a/b/g/n) are available, the access point with the strongest signal is automatically chosen by default. To override this, use the BSSID eld when configuring wireless connections. The Basic Service Set Identifier (BSSID) uniquely identifies each Basic Service Set. In an infrastructure Basic Service Set, the BSSID is the MAC address of the wireless access point. In an independent (ad-hoc) Basic Service Set, the BSSID is a locally administered MAC address generated from a 46-bit random number. Start the dialog for configuring network connections as described in Section 31.3, “Config- uring network connections”. Choose the wireless connection you want to modify and click Edit. On the Wireless tab, enter the BSSID. 455 Frequently asked questions SLES 15 SP63. How to share network connections with other computers? The primary device (the device which is connected to the Internet) does not need any special configuration. However, you need to configure the device that is connected to the local hub or machine as follows: 1. Start the dialog for configuring network connections as described in Section 31.3, “Configuring network connections”. Choose the connection you want to modify and click Edit. Switch to the IPv4 Settings tab and from the Method drop-down list, ac- tivate Shared to other computers. That will enable IP traffic forwarding and run a DHCP server on the device. Confirm your changes in NetworkManager. 2. As the DHCP server uses port 67 , make sure that it is not blocked by the firewall: On the machine sharing the connections, start YaST and select Security and Users Fire- wall. Switch to the Allowed Services category. If DHCP Server is not already shown as Allowed Service, select DHCP Server from Services to Allow and click Add. Confirm your changes in YaST. 4. How to provide static DNS information with automatic (DHCP, PPP, VPN) addresses? In case a DHCP server provides invalid DNS information (and/or routes), you can over- ride it. Start the dialog for configuring network connections as described in Section 31.3, “Configuring network connections”. Choose the connection you want to modify and click Ed- it. Switch to the IPv4 Settings tab, and from the Method drop-down box, activate Automatic (DHCP) addresses only. Enter the DNS information in the DNS Servers and Search Domains elds. To Ignore automatically obtained routes click Routes and activate the respective check box. Confirm your changes. 5. How to make NetworkManager connect to password protected networks before a user logs in? Define a system connection that can be used for such purposes. For more information, refer to Section 31.4.1, “User and system connections”. 31.6 Troubleshooting Connection problems can occur. Common problems related to NetworkManager include the ap- plet not starting or a missing VPN option. Methods for resolving and preventing these problems depend on the tool used. 456 Troubleshooting SLES 15 SP6NetworkManager desktop applet does not start The applets starts automatically if the network is set up for NetworkManager control. If the applet does not start, check if NetworkManager is enabled in YaST as described in Section 31.2, “Enabling or disabling NetworkManager”. Then make sure that the NetworkMan- ager-gnome package is also installed. If the desktop applet is installed but is not running, start it manually with the command nm-applet . NetworkManager applet does not include the VPN option Support for NetworkManager, applets, and VPN for NetworkManager is distributed in sep- arate packages. If your NetworkManager applet does not include the VPN option, check if the packages with NetworkManager support for your VPN technology are installed. For more information, see Section 31.3.4, “NetworkManager and VPN”. No network connection available If you have configured your network connection correctly and all other components for the network connection (router, etc.) are also up and running, it sometimes helps to restart the network interfaces on your computer. To do so, log in to a command line as root and run systemctl restart wickeds . 31.7 More information More information about NetworkManager can be found on the following Web sites and direc- tories: NetworkManager project page https://gitlab.freedesktop.org/NetworkManager/NetworkManager Package documentation Also check out the information in the following directories for the latest information about NetworkManager and the GNOME applet: /usr/share/doc/packages/NetworkManager/ , /usr/share/doc/packages/NetworkManager-gnome/ . 457 More information SLES 15 SP6IV Hardware configuration 32 Setting up your system keyboard layout 459 33 Setting up sound cards 460 34 Setting up a printer 463 35 Power management 469 36 Persistent memory 47532 Setting up your system keyboard layout The YaST System Keyboard Layout module lets you define the default keyboard layout for the system (also used for the console). Users can modify the keyboard layout in their individual X sessions, using the desktop''s tools. 1. Start the YaST System Keyboard Configuration dialog by clicking Hardware System Key- board Layout in YaST. Alternatively, start the module from the command line with sudo yast2 keyboard . 2. Select the desired Keyboard Layout from the list. 3. Try the selected keyboard layout in the Test text box. 4. If the result is as expected, confirm your changes and close the dialog. 5. The result is stored in the les /etc/vconsole.conf (for text consoles) and /etc/X11/ xorg.conf.d/00-keyboard.conf (for X11). 6. Advanced keyboard settings can be configured in System Sysconfig Editor Hard- ware Keyboard. Here you can specify the keyboard rate and delay settings, and enable or disable NumLock, CapsLock, and ScrollLock. These settings are stored in /etc/syscon- fig/keyboard . 459 SLES 15 SP633 Setting up sound cards YaST detects most sound cards automatically and configures them with the appropriate values. To change the default settings, or to set up a sound card that could not be configured automat- ically, use the YaST sound module. There, you can also set up additional sound cards or switch their order. Warning If you do not know all details about the setup of your sound system, do not change its settings manually. Instead, let your sound subsystem—PipeWire or PulseAudio— config- ure it for you. Use dedicated desktop application to switch audio devices. As a fallback, use the pavucontrol graphical application. To start the sound module, start YaST and click Hardware Sound. Alternatively, start the Sound Configuration dialog directly by running yast2 sound & as user root from a command line. If the sound module is not available, install it using the sudo zypper install yast2-sound command. PROCEDURE 33.1: CONFIGURING SOUND CARDS If you have added a new sound card or YaST could not automatically configure an existing sound card, follow the steps below. For configuring a new sound card, you need to know your sound card vendor and model. If in doubt, refer to your sound card documentation for the required information. For a reference list of sound cards supported by ALSA with their corresponding sound modules, see https://www.alsa-project.org/main/index.php/Ma- trix:Main . During configuration, you can choose between the following setup options: Quick automatic setup You are not required to go through any of the further configuration steps—the sound card is configured automatically. You can set the volume or any options you want to change later. Normal setup Allows you to adjust the output volume and play a test sound during the configu- ration. 460 SLES 15 SP6Advanced setup with possibility to change options For experts only. Allows you to customize all parameters of the sound card. Important: Advanced configuration Only use this option if you know exactly what you are doing. Otherwise leave the parameters untouched and use the normal or the automatic setup options. 1. Start the YaST sound module. 2. To configure a detected, but Not Configured sound card, select the respective entry from the list and click Edit. To configure a new sound card, click Add. Select your sound card vendor and model and click Next. 3. Choose one of the setup options and click Next. 4. If you have chosen Normal Setup, you can now Test your sound configuration and make adjustments to the volume. You should start at about ten percent volume to avoid damage to your hearing or the speakers. 5. If all options are set according to your wishes, click Next. The Sound Configuration dialog shows the newly configured or modified sound card. 6. To remove a sound card configuration that you no longer need, select the respective entry and click Delete. 7. Click OK to save the changes and leave the YaST sound module. PROCEDURE 33.2: MODIFYING SOUND CARD CONFIGURATIONS 1. To change the configuration of an individual sound card (for experts only!), select the sound card entry in the Sound Configuration dialog and click Edit. This takes you to the Sound Card Advanced Options where you can ne-tune several para- meters. For more information, click Help. 2. To adjust the volume of an already configured sound card or to test the sound card, select the sound card entry in the Sound Configuration dialog and click Other. Select the respective menu item. 461 SLES 15 SP6Note: YaST mixer The YaST mixer settings provide only basic options. They are intended for trou- bleshooting (for example, if the test sound is not audible). Access the YaST mixer settings from Other Volume. For everyday use and ne-tuning of sound options, use the mixer applet provided by your desktop or the alsasound command line tool. 3. For playback of MIDI les, select Other Start Sequencer. 4. When a supported sound card is detected, you can install SoundFonts for playback of MIDI les: a. Insert the original driver CD-ROM into your CD or DVD drive. b. Select Other Install SoundFonts to copy SF2 SoundFonts™ to your hard disk. The SoundFonts are saved in the directory /usr/share/sfbank/creative/ . 5. If you have configured more than one sound card in your system you can adjust the order of your sound cards. To set a sound card as primary device, select the sound card in the Sound Configuration and click Other Set as the Primary Card. The sound device with index 0 is the default device and thus used by the system and the applications. 6. By default, SUSE Linux Enterprise Server uses the PulseAudio sound system. This is an abstraction layer that helps to mix multiple audio streams, bypassing any restrictions the hardware may have. To enable or disable the PulseAudio sound system, click Oth- er PulseAudio Configuration. If enabled, PulseAudio daemon is used to play sounds. Dis- able PulseAudio Support to use something else system-wide. The volume and configuration of all sound cards are saved when you click OK and leave the YaST sound module. The mixer settings are saved to the le /etc/asound.state . The ALSA configuration data is appended to the end of the le /etc/modprobe.d/sound and written to /etc/sysconfig/sound . 462 SLES 15 SP634 Setting up a printer YaST can be used to configure local and network printers. Further information about printing (general information, technical details, and troubleshooting) is available in Chapter 24, Printer operation. In YaST, click Hardware Printer to start the printer module. By default it opens in the Printer Configurations view, displaying a list of all printers that are available and configured. This is especially useful when having access to a lot of printers via the network. From here you can also Print a Test Page and configure printers. Note: Starting CUPS To use the printer connected to your machine, you must have CUPS installed and running on your system. If CUPS is not running, you are prompted to start it. In case CUPS is not started at boot time, you are also prompted to enable it (recommended). 34.1 Configuring printers Normally USB printers are detected automatically. If that does not happen, check whether the printer is switched on and connected to the machine. Configuring a printer is a three-step process: specify the connection type, choose a driver, and name the print queue for this setup. Many printer models may have several available drivers. When configuring the printer, YaST defaults to those marked recommended . Normally, it is not necessary to change the driver. However, if you want a color printer to print only in black and white, you can use a driver that does not support color printing. If you experience performance problems with a PostScript printer when printing graphics, try switching from a PostScript to a PCL driver (provided your printer understands PCL). If no driver for your printer is listed, try selecting a generic driver with an appropriate standard language from the list. Refer to your printer''s documentation to nd out what language (the set of commands controlling the printer) your printer supports. If this does not work, refer to Section 34.1.1, “Adding drivers with YaST” for an alternative solution. 463 Configuring printers SLES 15 SP6A printer is always used through a print queue. This ensures that simultaneous jobs can be queued and processed one by one. Each print queue is assigned to a specific driver, and a printer can have multiple queues. As an example, this makes it possible to set up a second queue on a color printer that prints black and white only. Refer to Section 24.1, “The CUPS workflow” for more information about print queues. PROCEDURE 34.1: ADDING A NEW PRINTER 1. Start the YaST printer module with Hardware Printer. 2. In the Printer Configurations screen click Add. 3. If the printer is already listed under Specify the Connection , proceed with the next step. Otherwise, try Detect More or start the Connection Wizard. 4. In the text box under Find and Assign a Driver enter the vendor name and the model name and click Search for. 5. Choose a driver that matches your printer. It is recommended to choose the driver listed rst. If no suitable driver is displayed, try the following. a. Check the search term. b. Expand the search by clicking Find More. c. Add a driver as described in Section 34.1.1, “Adding drivers with YaST”. 6. Specify the Default paper size . 7. In the Set Arbitrary Name eld, enter a unique name for the print queue. 8. The printer is now configured with the default settings and ready to use. Click OK to return to the Printer Configurations view. The newly configured printer is now visible in the list of printers. 34.1.1 Adding drivers with YaST Not all printer drivers available for SUSE Linux Enterprise Server are installed by default. When adding a printer, if no suitable driver is available in the Find and Assign a Driver dialog, install a driver package containing drivers for the printer: PROCEDURE 34.2: INSTALLING ADDITIONAL DRIVER PACKAGES 1. Start the YaST printer module with Hardware Printer. 464 Adding drivers with YaST SLES 15 SP62. In the Printer Configurations screen, click Add. 3. In the Find and Assign a Driver section, click Driver Packages. 4. Choose one or more suitable driver packages from the list. Do not specify the path to a printer description le. 5. Choose OK and confirm the package installation. 6. To directly use these drivers, proceed as described in Procedure 34.1, “Adding a new printer”. PostScript printers do not need printer driver software. PostScript printers need only a PostScript Printer Description (PPD) le which matches the particular model. PPD les are provided by the printer manufacturer. If no suitable PPD le is available in the Find and Assign a Driver dialog when adding a PostScript printer, install a PPD le for your printer: There are several sources of PPD les. It is recommended to rst try additional driver packages that are shipped with SUSE Linux Enterprise Server but not installed by default (see below for installation instructions). If these packages do not contain suitable drivers for your printer, get PPD les directly from your printer vendor or from the driver CD of a PostScript printer. For details, see Section 24.8.2, “No suitable PPD file available for a PostScript printer”. Alternatively, nd PPD les at https://www.openprinting.org/printers , the “OpenPrinting.org printer database”. When using PPD les from OpenPrinting, keep in mind that they may not be supported by SUSE Linux Enterprise Server. PROCEDURE 34.3: ADDING A PPD FILE FOR POSTSCRIPT PRINTERS 1. Start the YaST printer module with Hardware Printer. 2. In the Printer Configurations screen, click Add. 3. In the Find and Assign a Driver section, click Driver Packages. 4. Enter the full path to the PPD le into the text box under Make a Printer Description File Available . 5. Click OK to return to the Add New Printer Configuration screen. 6. To directly use this PPD le, proceed as described in Procedure 34.1, “Adding a new printer”. 465 Adding drivers with YaST SLES 15 SP634.1.2 Editing a local printer configuration By editing an existing configuration for a printer you can change basic settings such as connec- tion type and driver. It is also possible to adjust the default settings for paper size, resolution, media source, etc. You can change identifiers of the printer by altering the printer description or location. 1. Start the YaST printer module with Hardware Printer. 2. In the Printer Configurations screen, choose a local printer configuration from the list and click Edit. 3. Change the connection type or the driver as described in Procedure 34.1, “Adding a new printer”. This should only be necessary in case you have problems with the current con- figuration. 4. Optionally, make this printer the default by checking Default Printer. 5. Adjust default settings by clicking All Options for the Current Driver. To change a setting, expand the list of options by clicking the + sign. Change the default by clicking an option. Apply your changes with OK. 34.2 Configuring printing via the network with YaST Network printers are not detected automatically. They must be configured manually using the YaST printer module. Depending on your network setup, you can print to a print server (CUPS, LPD, SMB or IPX) or directly to a network printer (preferably via TCP). Access the configuration view for network printing by choosing Printing via Network from the left pane in the YaST printer module. 34.2.1 Using CUPS In a Linux environment CUPS is used to print via the network. The simplest setup is to only print via a single CUPS server which can directly be accessed by all clients. Printing via more than one CUPS server requires a running local CUPS daemon that communicates with the remote CUPS servers. 466 Editing a local printer configuration SLES 15 SP6Important: Browsing network print queues CUPS servers announce their print queues over the network either via the tradition- al CUPS browsing protocol or via Bonjour/DNS-SD. Clients need to browse these lists so users can select specific printers to send their print jobs to. To browse network print queues, the service cups-browsed provided by the package cups-filters-cups- browsed must run on all clients that print via CUPS servers. cups-browsed is started automatically when configuring network printing with YaST. If browsing does not work after starting cups-browsed , the CUPS servers may announce the network print queues via Bonjour/DNS-SD. In this case you need to additionally install the package avahi and start the associated service with sudo systemctl start avahi- daemon on all clients. PROCEDURE 34.4: PRINTING VIA A SINGLE CUPS SERVER 1. Start the YaST printer module with Hardware Printer. 2. From the left pane, select Print via Network. 3. Check Do All Your Printing Directly via One Single CUPS Server and specify the name or IP address of the server. 4. Click Test Server to make sure you have chosen the correct name or IP address. 5. Click OK to return to the Printer Configurations screen. All printers available via the CUPS server are now listed. PROCEDURE 34.5: PRINTING VIA MULTIPLE CUPS SERVERS 1. Start the YaST printer module with Hardware Printer. 2. From the left pane, select Print via Network. 3. Check Accept Printer Announcements from CUPS Servers. 4. Under General Settings specify which servers to use. You may accept connections from all networks available or from specific hosts. If you choose the latter option, you need to specify the host names or IP addresses. 5. Click OK and then Yes when prompted to start a local CUPS server. After the server has started, YaST returns to the Printer Configurations screen. Click Refresh list to see the printers detected so far. 467 Using CUPS SLES 15 SP634.2.2 Using print servers other than CUPS If your network offers print services via print servers other than CUPS, start the YaST printer module with Hardware Printer and select Print via Network from the left pane. Start the Con- nection Wizard and choose the appropriate Connection Type. Ask your network administrator for details on configuring a network printer in your environment. 34.3 Sharing printers over the network Printers managed by a local CUPS daemon can be shared over the network, effectively turning your machine into a CUPS server. You share a printer by enabling so-called “browsing mode” in CUPS. If browsing is enabled, the local print queues are made available on the network for listening to remote CUPS daemons. It is also possible to set up a dedicated CUPS server that manages all print queues and can be accessed by remote clients directly. In this case, enabling browsing is not required. PROCEDURE 34.6: SHARING PRINTERS 1. Start the YaST printer module with Hardware Printer. 2. Select Share Printers from the left pane. 3. Select Allow Remote Access. Also check For computers within the local network and enable browsing mode by also checking Publish printers by default within the local network. 4. Click OK to restart the CUPS server and to return to the Printer Configurations screen. 5. Regarding CUPS and firewall settings, see https://en.opensuse.org/SD- B:CUPS_and_SANE_Firewall_settings . 468 Using print servers other than CUPS SLES 15 SP635 Power management IBM Z The features and hardware described in this chapter do not exist on IBM Z, making this chapter irrelevant for these platforms. Power management is especially important on laptop computers, but is also useful on other sys- tems. ACPI (Advanced Configuration and Power Interface) is available on all modern computers (laptops, desktops and servers). Power management technologies require suitable hardware and BIOS routines. Most laptops and many modern desktops and servers meet these requirements. It is also possible to control CPU frequency scaling to save power or decrease noise. 35.1 Power saving functions Power saving functions are not only significant for the mobile use of laptops, but also for desktop systems. The main functions and their use in ACPI are: Standby Not supported. Suspend (to memory) This mode writes the entire system state to the RAM. Subsequently, the entire system except the RAM is put to sleep. In this state, the computer consumes little power. The advantage of this state is the possibility of resuming work at the same point within a few seconds without having to boot and restart applications. This function corresponds to the ACPI state S3 . Hibernation (suspend to disk) In this operating mode, the entire system state is written to the hard disk and the system is powered o. There must be a swap partition at least as big as the RAM to write all the active data. Reactivation from this state takes about 30 to 90 seconds. The state before the suspend is restored. Several manufacturers offer useful hybrid variants of this mode, such as RediSafe in IBM Thinkpads. The corresponding ACPI state is S4 . In Linux, suspend to disk is performed by kernel routines that are independent from ACPI. 469 Power saving functions SLES 15 SP6Note: Changed UUID for swap partitions when formatting via mkswap Do not reformat existing swap partitions with mkswap if possible. Reformatting with mkswap will change the UUID value of the swap partition. Either reformat via YaST (which will update /etc/fstab ) or adjust /etc/fstab manually. Battery monitor ACPI checks the battery charge status and provides information about it. Additionally, it coordinates actions to perform when a critical charge status is reached. Automatic power-off Following a shutdown, the computer is powered o. This is especially important when an automatic shutdown is performed shortly before the battery is empty. Processor speed control In connection with the CPU, energy can be saved in three different ways: frequency and voltage scaling (also known as PowerNow! or Speedstep), throttling and putting the proces- sor to sleep (C-states). Depending on the operating mode of the computer, these methods can also be combined. 35.2 Advanced configuration and power interface (ACPI) ACPI was designed to enable the operating system to set up and control the individual hard- ware components. ACPI supersedes both Power Management Plug and Play (PnP) and Advanced Power Management (APM). It delivers information about the battery, AC adapter, temperature, fan and system events, like “close lid” or “battery low.” The BIOS provides tables containing information about the individual components and hardware access methods. The operating system uses this information for tasks like assigning interrupts or activating and deactivating components. Because the operating system executes commands stored into the BIOS, the functionality depends on the BIOS implementation. The tables ACPI can detect and load are reported in journald. See Chapter 21, journalctl: query the systemd journal for more information on viewing the journal log messages. See Section 35.2.2, “Troubleshooting” for more information about troubleshooting ACPI problems. 470 Advanced configuration and power interface (ACPI) SLES 15 SP635.2.1 Controlling the CPU performance The CPU can save energy in three ways: Frequency and Voltage Scaling Throttling the Clock Frequency (T-states) Putting the Processor to Sleep (C-states) Depending on the operating mode of the computer, these methods can be combined. Saving energy also means that the system heats up less and the fans are activated less frequently. Frequency scaling and throttling are only relevant if the processor is busy, because the most economic C-state is applied anyway when the processor is idle. If the CPU is busy, frequency scaling is the recommended power saving method. Often the processor only works with a partial load. In this case, it can be run with a lower frequency. Dynamic frequency scaling controlled by the kernel on-demand governor is the best approach. Throttling should be used as the last resort, for example, to extend the battery operation time despite a high system load. However, certain systems do not run smoothly when they are throt- tled too much. Moreover, CPU throttling does not make sense if the CPU has little to do. For in-depth information, refer to Book “System Analysis and Tuning Guide”, Chapter 12 “Power man- agement”. 35.2.2 Troubleshooting There are two different types of problems. On one hand, the ACPI code of the kernel may contain bugs that were not detected in time. In this case, a solution will be made available for download. More often, the problems are caused by the BIOS. Sometimes, deviations from the ACPI speci- fication are purposely integrated in the BIOS to circumvent errors in the ACPI implementation of other widespread operating systems. Hardware components that have serious errors in the ACPI implementation are recorded in a blacklist that prevents the Linux kernel from using ACPI for these components. The rst thing to do when problems are encountered is to update the BIOS. If the computer does not boot, one of the following boot parameters may be helpful: pci=noacpi Do not use ACPI for configuring the PCI devices. 471 Controlling the CPU performance SLES 15 SP6acpi=ht Only perform a simple resource configuration. Do not use ACPI for other purposes. acpi=off Disable ACPI. Warning: Problems booting without ACPI Certain newer machines (especially SMP systems and AMD64 systems) need ACPI for con- figuring the hardware correctly. On these machines, disabling ACPI can cause problems. Sometimes, the machine is confused by hardware that is attached over USB or FireWire. If a machine refuses to boot, unplug all unneeded hardware and try again. Monitor the boot messages of the system with the command dmesg -T | grep -2i acpi (or all messages, because the problem may not be caused by ACPI) after booting. If an error occurs while parsing an ACPI table, the most important table—the DSDT (Differentiated System Description Table)—can be replaced with an improved version. In this case, the faulty DSDT of the BIOS is ignored. The procedure is described in Section 35.4, “Troubleshooting”. In the kernel configuration, there is a switch for activating ACPI debug messages. If a kernel with ACPI debugging is compiled and installed, detailed information is issued. If you experience BIOS or hardware problems, it is always advisable to contact the manufactur- ers. Especially if they do not always provide assistance for Linux, they should be confronted with the problems. Manufacturers only take the issue seriously if they realize that an adequate number of their customers use Linux. 35.2.2.1 More information https://tldp.org/HOWTO/ACPI-HOWTO/ (detailed ACPI HOWTO, contains DSDT patches) https://uefi.org/specifications (Advanced Configuration & Power Interface Specification) 472 Troubleshooting SLES 15 SP635.3 Rest for the hard disk In Linux, the hard disk can be put to sleep entirely if it is not needed or it can be run in a more economic or quieter mode. On modern laptops, you do not need to switch o the hard disks manually, because they automatically enter an economic operating mode whenever they are not needed. However, if you want to maximize power savings, test the following methods, using the hdparm command. It can be used to modify hard disk settings. The option -y instantly switches the hard disk to the standby mode. -Y puts it to sleep. hdparm -S X causes the hard disk to be spun down after a certain period of inactivity. Replace X as follows: 0 disables this mechanism, causing the hard disk to run continuously. Values from 1 to 240 are multiplied by 5 seconds. Values from 241 to 251 correspond to 1 to 11 times 30 minutes. Internal power saving options of the hard disk can be controlled with the option -B . Select a value from 0 to 255 for maximum saving to maximum throughput. The result depends on the hard disk used and is difficult to assess. To make a hard disk quieter, use the option -M . Select a value from 128 to 254 for quiet to fast. Often, it is not so easy to put the hard disk to sleep. In Linux, multiple processes write to the hard disk, waking it up repeatedly. Therefore, it is important to understand how Linux handles data that needs to be written to the hard disk. First, all data is buered in the RAM. This buer is monitored by the pdflush daemon. When the data reaches a certain age limit or when the buer is lled to a certain degree, the buer content is ushed to the hard disk. The buer size is dynamic and depends on the size of the memory and the system load. By default, pdush is set to short intervals to achieve maximum data integrity. It checks the buer every 5 seconds and writes the data to the hard disk. The following variables are interesting: /proc/sys/vm/dirty_writeback_centisecs Contains the delay until a pdush thread wakes up (in hundredths of a second). /proc/sys/vm/dirty_expire_centisecs Defines after which timeframe a dirty page should be written at latest. Default is 3000 , which means 30 seconds. /proc/sys/vm/dirty_background_ratio Maximum percentage of dirty pages until pdush begins to write them. Default is 5%. /proc/sys/vm/dirty_ratio When the dirty pages exceed this percentage of the total memory, processes are forced to write dirty buers during their time slice instead of continuing to write. 473 Rest for the hard disk SLES 15 SP6Warning: Data integrity risk Changes to the pdflush daemon settings can compromise data integrity. Apart from these processes, journaling le systems, like Btrfs , Ext3 , Ext4 and others write their metadata independently from pdflush , which also prevents the hard disk from spinning down. Another important factor is the way active programs behave. For example, good editors regularly write hidden backups of the currently modified le to the hard disk, causing the disk to wake up. Features like this can be disabled at the expense of data integrity. In this connection, the mail daemon postfix uses the variable POSTFIX_LAPTOP . If this variable is set to yes , postfix accesses the hard disk far less frequently. 35.4 Troubleshooting All error messages and alerts are logged in the system journal, which can be queried with the command journalctl (see Chapter 21, journalctl: query the systemd journal for more infor- mation). The following sections cover the most common problems. 35.4.1 CPU frequency does not work Refer to the kernel sources to see if your processor is supported. You may need a special kernel module or module option to activate CPU frequency control. If the kernel-source package is installed, this information is available in /usr/src/linux/Documentation/cpu-freq/* . 474 Troubleshooting SLES 15 SP636 Persistent memory This chapter contains additional information about using SUSE Linux Enterprise Server with non-volatile main memory, also known as Persistent Memory, comprising one or more NVDIMMs. 36.1 Introduction Persistent memory is a new type of computer storage, combining speeds approaching those of dynamic RAM (DRAM) along with RAM''s byte-by-byte addressability, plus the permanence of solid-state drives (SSDs). SUSE currently supports the use of persistent memory with SUSE Linux Enterprise Server on machines with the AMD64/Intel 64 and POWER architectures. Like conventional RAM, persistent memory is installed directly into mainboard memory slots. As such, it is supplied in the same physical form factor as RAM—as DIMMs. These are known as NVDIMMs: non-volatile dual inline memory modules. Unlike RAM, though, persistent memory is also similar to ash-based SSDs in several ways. Both are based on forms of solid-state memory circuitry, but despite this, both provide non-volatile storage: Their contents are retained when the system is powered o or restarted. For both forms of medium, writing data is slower than reading it, and both support a limited number of rewrite cycles. Finally, also like SSDs, sector-level access to persistent memory is possible if that is more suitable for a particular application. Different models use different forms of electronic storage medium, such as Intel 3D XPoint, or a combination of NAND-ash and DRAM. New forms of non-volatile RAM are also in develop- ment. This means that different vendors and models of NVDIMM offer different performance and durability characteristics. Because the storage technologies involved are in an early stage of development, different ven- dors'' hardware may impose different limitations. Thus, the following statements are generaliza- tions. Persistent memory is up to ten times slower than DRAM, but around a thousand times faster than ash storage. It can be rewritten on a byte-by-byte basis rather than ash memory''s whole-sector erase-and-rewrite process. Finally, while rewrite cycles are limited, most forms of persistent memory can handle millions of rewrites, compared to the thousands of cycles of ash storage. 475 Introduction SLES 15 SP6This has two important consequences: It is not possible with current technology to run a system with only persistent memory and thus achieve non-volatile main memory. You must use a mixture of both conventional RAM and NVDIMMs. The operating system and applications will execute in conventional RAM, with the NVDIMMs providing fast supplementary storage. The performance characteristics of different vendors'' persistent memory mean that it may be necessary for programmers to be aware of the hardware specifications of the NVDIMMs in a particular server, including how many NVDIMMs there are and in which memory slots they are fitted. This will impact hypervisor use, migration of software between different host machines, and so on. This new storage subsystem is defined in version 6 of the ACPI standard. However, libnvdimm supports pre-standard NVDIMMs and they can be used in the same way. Tip: Intel Optane DC Persistent Memory Intel Optane DIMMs memory can be used in specific modes: In App Direct Mode, the Intel Optane memory is used as fast persistent storage, an alternative to SSDs and NVMe devices. Data in this mode is kept when the system is powered o. App Direct Mode has been supported since SLES 12 SP4. In Memory Mode, the Intel Optane memory serves as a cost-effective, high-capaci- ty alternative to DRAM. In this mode, separate DRAM DIMMs act as a cache for the most frequently accessed data while the Optane DIMMs memory provides large memory capacity. However, compared with DRAM-only systems, this mode is slow- er under random access workloads. If you run applications without Optane-specif- ic enhancements that take advantage of this mode, memory performance may de- crease. Data in this mode is lost when the system is powered o. Memory Mode has been supported since SLES 15 SP1. In Mixed Mode, the Intel Optane memory is partitioned, so it can serve in both modes simultaneously. Mixed Mode has been supported since SLES 15 SP1. 476 Introduction SLES 15 SP636.2 Terms Region A region is a block of persistent memory that can be divided up into one or more name- spaces. You cannot access the persistent memory of a region without rst allocating it to a namespace. Namespace A single contiguously addressed range of non-volatile storage, comparable to NVM Express SSD namespaces, or to SCSI Logical Units (LUNs). Namespaces appear in the server''s / dev directory as separate block devices. Depending on the method of access required, namespaces can either amalgamate storage from multiple NVDIMMs into larger volumes, or allow it to be partitioned into smaller volumes. Mode Each namespace also has a mode that defines which NVDIMM features are enabled for that namespace. Sibling namespaces of the same parent region always have the same type, but might be configured to have different modes. Namespace modes include: devdax Device-DAX mode. Creates a single-character device le ( /dev/daxX.Y ). Does not require le system creation. fsdax File system-DAX mode. Default if no other mode is specified. Creates a block device ( /dev/pmemX [.Y] ) which supports DAX for ext4 or XFS . sector For legacy le systems which do not checksum metadata. Suitable for small boot volumes. Compatible with other operating systems. raw A memory disk without a label or metadata. Does not support DAX. Compatible with other operating systems. Note raw mode is not supported by SUSE. It is not possible to mount le systems on raw namespaces. 477 Terms SLES 15 SP6Type Each namespace and region has a type that defines how the persistent memory associated with that namespace or region can be accessed. A namespace always has the same type as its parent region. There are two different types: Persistent Memory, which can be config- ured in two different ways, and the deprecated Block Mode. Persistent memory (PMEM) PMEM storage offers byte-level access, similar to RAM. Using PMEM, a single name- space can include multiple interleaved NVDIMMs, allowing them all to be used as a single device. There are two ways to configure a PMEM namespace. PMEM with DAX A PMEM namespace configured for Direct Access (DAX) means that accessing the memory bypasses the kernel''s page cache and goes direct to the medium. Software can directly read or write every byte of the namespace separately. PMEM with block translation table (BTT) A PMEM namespace configured to operate in BTT mode is accessed on a sec- tor-by-sector basis, like a conventional disk drive, rather than the more RAM- like byte-addressable model. A translation table mechanism batches accesses into sector-sized units. The advantage of BTT is data protection. The storage subsystem ensures that each sector is completely written to the underlying medium. If a sector cannot be completely written (that is, if the write operation fails for some reason), then the whole sector will be rolled back to its previous state. Thus a given sector cannot be partially written. Additionally, access to BTT namespaces is cached by the kernel. The drawback is that DAX is not possible for BTT namespaces. Block mode (BLK) Block mode storage addresses each NVDIMM as a separate device. Its use is depre- cated and no longer supported. Apart from devdax namespaces, all other types must be formatted with a le system, just as with a conventional drive. SUSE Linux Enterprise Server supports the ext2 , ext4 and XFS le systems for this. 478 Terms SLES 15 SP6Direct access (DAX) DAX allows persistent memory to be directly mapped into a process''s address space, for example, using the mmap system call. DIMM physical address (DPA) A memory address as an offset into a single DIMM''s memory; that is, starting from zero as the lowest addressable byte on that DIMM. Label Metadata stored on the NVDIMM, such as namespace definitions. This can be accessed using DSMs. Device-specific method (DSM) ACPI method to access the rmware on an NVDIMM. 36.3 Use cases 36.3.1 PMEM with DAX This form of memory access is not transactional. In the event of a power outage or other system failure, data may not be written into storage. PMEM storage is only suitable if the application can handle the situation of partially written data. 36.3.1.1 Applications that benefit from large amounts of byte-addressable storage If the server will host an application that can directly use large amounts of fast storage on a byte-by-byte basis, the programmer can use the mmap system call to place blocks of persistent memory directly into the application''s address space, without using any additional system RAM. 36.3.1.2 Avoiding use of the kernel page cache Avoid using the kernel page cache to conserve the use of RAM for the page cache, and instead give it to your applications. For instance, non-volatile memory could be dedicated to holding virtual machine (VM) images. As these would not be cached, this would reduce the cache usage on the host, allowing more VMs per host. 479 Use cases SLES 15 SP636.3.2 PMEM with BTT This is useful when you want to use the persistent memory on a set of NVDIMMs as a disk-like pool of fast storage. For example, placing the le system journal on PMEM with BTT increases the reliability of le system recovery after a power failure or other sudden interruption (see Section 36.5.3, “Creating a PMEM namespace with BTT”). To applications, such devices appear as fast SSDs and can be used like any other storage device. For example, LVM can be layered on top of the persistent memory and will work as normal. The advantage of BTT is that sector write atomicity is guaranteed, so even sophisticated appli- cations that depend on data integrity will keep working. Media error reporting works through standard error-reporting channels. 36.4 Tools for managing persistent memory To manage persistent memory, it is necessary to install the ndctl package. This also installs the libndctl package, which provides a set of user space libraries to configure NVDIMMs. These tools work via the libnvdimm library, which supports three types of NVDIMM: PMEM BLK Simultaneous PMEM and BLK The ndctl utility has a helpful set of man pages, accessible with the command: > ndctl help subcommand To see a list of available subcommands, use: > ndctl --list-cmds The available subcommands include: version Displays the current version of the NVDIMM support tools. enable-namespace Makes the specified namespace available for use. 480 PMEM with BTT SLES 15 SP6disable-namespace Prevents the specified namespace from being used. create-namespace Creates a new namespace from the specified storage devices. destroy-namespace Removes the specified namespace. enable-region Makes the specified region available for use. disable-region Prevents the specified region from being used. zero-labels Erases the metadata from a device. read-labels Retrieves the metadata of the specified device. list Displays available devices. help Displays information about using the tool. 36.5 Setting up persistent memory 36.5.1 Viewing available NVDIMM storage The ndctl list command can be used to list all available NVDIMMs in a system. In the following example, the system has three NVDIMMs, which are in a single, triple-channel interleaved set. # ndctl list --dimms [ { "dev":"nmem2", 481 Setting up persistent memory SLES 15 SP6"id":"8089-00-0000-12325476" }, { "dev":"nmem1", "id":"8089-00-0000-11325476" }, { "dev":"nmem0", "id":"8089-00-0000-10325476" } ] With a different parameter, ndctl list will also list the available regions. Note Regions may not appear in numerical order. Note that although there are only three NVDIMMs, they appear as four regions. # ndctl list --regions [ { "dev":"region1", "size":68182605824, "available_size":68182605824, "type":"blk" }, { "dev":"region3", "size":202937204736, "available_size":202937204736, "type":"pmem", "iset_id":5903239628671731251 }, { "dev":"region0", "size":68182605824, "available_size":68182605824, "type":"blk" }, { "dev":"region2", "size":68182605824, "available_size":68182605824, 482 Viewing available NVDIMM storage SLES 15 SP6"type":"blk" } ] The space is available in two different forms: either as three separate 64 regions of type BLK, or as one combined 189 GB region of type PMEM which presents all the space on the three interleaved NVDIMMs as a single volume. Note that the displayed value for available_size is the same as that for size . This means that none of the space has been allocated yet. 36.5.2 Configuring the storage as a single PMEM namespace with DAX For the rst example, we will configure our three NVDIMMs into a single PMEM namespace with Direct Access (DAX). The rst step is to create a new namespace. # ndctl create-namespace --type=pmem --mode=fsdax --map=memory { "dev":"namespace3.0", "mode":"memory", "size":199764213760, "uuid":"dc8ebb84-c564-4248-9e8d-e18543c39b69", "blockdev":"pmem3" } This creates a block device /dev/pmem3 , which supports DAX. The 3 in the device name is inherited from the parent region number, in this case region3 . The --map=memory option sets aside part of the PMEM storage space on the NVDIMMs so that it can be used to allocate internal kernel data structures called struct pages . This allows the new PMEM namespace to be used with features such as O_DIRECT I/O and RDMA . The reservation of some persistent memory for kernel data structures is why the resulting PMEM namespace has a smaller capacity than the parent PMEM region. Next, we verify that the new block device is available to the operating system: # fdisk -l /dev/pmem3 Disk /dev/pmem3: 186 GiB, 199764213760 bytes, 390164480 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes 483 Configuring the storage as a single PMEM namespace with DAX SLES 15 SP6Before it can be used, like any other drive, it must be formatted. In this example, we format it with XFS: # mkfs.xfs /dev/pmem3 meta-data=/dev/pmem3 isize=256 agcount=4, agsize=12192640 blks = sectsz=4096 attr=2, projid32bit=1 = crc=0 finobt=0, sparse=0 data = bsize=4096 blocks=48770560, imaxpct=25 = sunit=0 swidth=0 blks naming =version 2 bsize=4096 ascii-ci=0 ftype=1 log =internal log bsize=4096 blocks=23813, version=2 = sectsz=4096 sunit=1 blks, lazy-count=1 realtime =none extsz=4096 blocks=0, rtextents=0 Next, we can mount the new drive onto a directory: # mount -o dax /dev/pmem3 /mnt/pmem3 Then we can verify that we now have a DAX-capable device: # mount | grep dax /dev/pmem3 on /mnt/pmem3 type xfs (rw,relatime,attr2,dax,inode64,noquota) The result is that we now have a PMEM namespace formatted with the XFS le system and mounted with DAX. Any mmap() calls to les in that le system will return virtual addresses that directly map to the persistent memory on our NVDIMMs, bypassing the page cache. Any fsync or msync calls on les in that le system will still ensure that modified data has been fully written to the NVDIMMs. These calls ush the processor cache lines associated with any pages that have been modified in user space via mmap mappings. 36.5.2.1 Removing a namespace Before creating any other type of volume that uses the same storage, we must unmount and then remove this PMEM volume. First, unmount it: # umount /mnt/pmem3 Then disable the namespace: # ndctl disable-namespace namespace3.0 disabled 1 namespace 484 Configuring the storage as a single PMEM namespace with DAX SLES 15 SP6Then delete it: # ndctl destroy-namespace namespace3.0 destroyed 1 namespace 36.5.3 Creating a PMEM namespace with BTT BTT provides sector write atomicity, which makes it a good choice when you need data protec- tion, , for Ext4 and XFS journals. If there is a power failure, the journals are protected and should be recoverable. The following examples show how to create a PMEM namespace with BTT in sector mode, and how to place the le system journal in this namespace. # ndctl create-namespace --type=pmem --mode=sector { "dev":"namespace3.0", "mode":"sector", "uuid":"51ab652d-7f20-44ea-b51d-5670454f8b9b", "sector_size":4096, "blockdev":"pmem3s" } Next, verify that the new device is present: # fdisk -l /dev/pmem3s Disk /dev/pmem3s: 188.8 GiB, 202738135040 bytes, 49496615 sectors Units: sectors of 1 * 4096 = 4096 bytes Sector size (logical/physical): 4096 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Like the DAX-capable PMEM namespace we previously configured, this BTT-capable PMEM namespace consumes all the available storage on the NVDIMMs. Note The trailing s in the device name ( /dev/pmem3s ) stands for sector and can be used to easily distinguish namespaces that are configured to use the BTT. The volume can be formatted and mounted as in the previous example. The PMEM namespace shown here cannot use DAX. Instead it uses the BTT to provide sector write atomicity. On each sector write through the PMEM block driver, the BTT will allocate a new sector to receive the new data. The BTT atomically updates its internal mapping structures 485 Creating a PMEM namespace with BTT SLES 15 SP6after the new data is fully written so the newly written data will be available to applications. If the power fails at any point during this process, the write will be lost and the application will have access to its old data, still intact. This prevents the condition known as “torn sectors”. This BTT-enabled PMEM namespace can be formatted and used with a le system same as any other standard block device. It cannot be used with DAX. However, mmap mappings for les on this block device will use the page cache. 36.5.4 Placing the file system journal on PMEM/BTT When you place the le system journal on a separate device, it must use the same le system block size as the le system. Most likely this is 4096, and you can nd the block size with this command: # blockdev --getbsz /dev/sda3 The following example creates a new Ext4 journal on a separate NVDIMM device, creates the le system on a SATA device, then attaches the new le system to the journal: # mke2fs -b 4096 -O journal_dev /dev/pmem3s # mkfs.ext4 -J device=/dev/pmem3s /dev/sda3 The following example creates a new XFS le system on a SATA drive, and creates the journal on a separate NVDIMM device: # mkfs.xfs -l logdev=/dev/pmem3s /dev/sda3 See man 8 mkfs.ext4 and man 8 mkfs.ext4 for detailed information about options. 36.6 More information More about this topic can be found in the following list: Persistent Memory Wiki (https://nvdimm.wiki.kernel.org/) Contains instructions for configuring NVDIMM systems, information about testing, and links to specifications related to NVDIMM enabling. This site is developing as NVDIMM support in Linux is developing. Persistent Memory Programming (https://pmem.io/) 486 Placing the file system journal on PMEM/BTT SLES 15 SP6Information about configuring, using and programming systems with non-volatile memory under Linux and other operating systems. Covers the NVM Library (NVML), which aims to provide useful APIs for programming with persistent memory in user space. LIBNVDIMM: Non-Volatile Devices (https://www.kernel.org/doc/Documentation/nvdimm/ nvdimm.txt) Aimed at kernel developers, this is part of the Documentation directory in the current Linux kernel tree. It talks about the different kernel modules involved in NVDIMM enablement, lays out technical details of the kernel implementation, and talks about the sysfs interface to the kernel that is used by the ndctl tool. GitHub: pmem/ndctl (https://github.com/pmem/ndctl) Utility library for managing the libnvdimm subsystem in the Linux kernel. Also contains user space libraries, as well as unit tests and documentation. 487 More information SLES 15 SP6V Services 37 Service management with YaST 489 38 Time synchronization with NTP 491 39 The domain name system 498 40 DHCP 523 41 SLP 539 42 The Apache HTTP server 543 43 Setting up an FTP server with YaST 586 44 Squid caching proxy server 590 45 Web Based Enterprise Management using SFCB 61037 Service management with YaST YaST provides a service manager for controlling the default system target, services, displaying service status, and reading the log le. New in SUSE Linux Enterprise Server 15 SP6 is YaST support for systemd socket-based services activation, which configures services to start on demand. systemd supports starting services with socket-based activation, for starting services on de- mand. These services have two unit types: service and socket. For example, CUPS is controlled by cups.service and cups.socket . YaST allows you to select the type of service start-up you want to use. Figure 37.1, “YaST service manager” shows the options in the Start Mode drop-down box: On Boot, On Demand, and Manually. Select On Demand for socket-based activation. This opens a listening network socket, and the service starts when there is a request. 489 SLES 15 SP6FIGURE 37.1: YAST SERVICE MANAGER The On Demand option is visible only for services that support it. Currently this is a small subset of services, such as CUPS, dbus, iscsid, iscsiuio, multipathd, pcscd, rpcbind, TFTP, virtlockd, virtlogd. See man 5 systemd.socket for detailed information on how socket activation works. 490 SLES 15 SP638 Time synchronization with NTP The NTP (network time protocol) mechanism is a protocol for synchronizing the system time over the network. First, a machine can obtain the time from a server that is a reliable time source. Second, a machine can itself act as a time source for other computers in the network. The goal is twofold—maintaining the absolute time and synchronizing the system time of all machines within a network. Maintaining an exact system time is important in many situations. The built-in hardware clock does often not meet the requirements of applications such as databases or clusters. Manual correction of the system time would lead to severe problems because, for example, a backward leap can cause malfunction of critical applications. Within a network, it is usually necessary to synchronize the system time of all machines, but manual time adjustment is a bad approach. NTP provides a mechanism to solve these problems. The NTP service continuously adjusts the system time with reliable time servers in the network. It further enables the management of local reference clocks, such as radio-controlled clocks. Since SUSE Linux Enterprise Server 15, chrony is the default implementation of NTP. chrony includes two parts; chronyd is a daemon that can be started at boot time and chronyc is a command line interface program to monitor the performance of chronyd , and to change operating parameters at runtime. Starting with SUSE Linux Enterprise Server 15.2, the YaST module for NTP client configuration configures the systemd-timer instead of the cron daemon to execute chrony , when it is not configured to run as a daemon. 38.1 Configuring an NTP client with YaST The NTP daemon ( chronyd ) coming with the chrony package is preset to use the local com- puter hardware clock as a time reference. The precision of the hardware clock heavily depends on its time source. For example, an atomic clock or GPS receiver is a precise time source, while a common RTC chip is not a reliable time source. YaST simplifies the configuration of an NTP client. In the YaST NTP client configuration (Network Services NTP Configuration) window, you can specify when to start the NTP daemon, the type of the configuration source, and add custom time servers. 491 Configuring an NTP client with YaST SLES 15 SP6FIGURE 38.1: NTP CONFIGURATION WINDOW 38.1.1 NTP daemon start You can choose from three options for when to start the NTP daemon: Only manually Select Only Manually to manually start the chrony daemon. Synchronize without daemon Select Synchronize without Daemon to set the system time periodically without a perma- nently running chrony . You can set the Interval of the Synchronization in Minutes. Now and on boot Select Now and On Boot to start chronyd automatically when the system is booted. This setting is recommended. 38.1.2 Type of the configuration source In the Configuration Source drop-down box, select either Dynamic or Static. Set Static if your server uses only a xed set of (public) NTP servers, while Dynamic is better if your internal network offers NTP servers via DHCP. 492 NTP daemon start SLES 15 SP638.1.3 Configure time servers Time servers for the client to query are listed in the lower part of the NTP Configuration window. Modify this list as needed with Add, Edit, and Delete. Click Add to add a new time server: FIGURE 38.2: ADDING A TIME SERVER 1. In the Address eld, type the URL of the time server or pool of time servers with which you want to synchronize the machine time. After the URL is complete, click Test to verify that it points to a valid time source. 2. Activate Quick Initial Sync to speed up the time synchronization by sending more requests at the chronyd daemon start. 3. Activate Start Offline to speed up the boot time on systems that start the chronyd daemon automatically and may not have an Internet connection at boot time. This option is useful, for example, for laptops with network connections managed by NetworkManager. 4. Confirm with OK. 493 Configure time servers SLES 15 SP638.2 Manually configuring NTP in the network chrony reads its configuration from the /etc/chrony.conf le. To keep the computer clock synchronized, you need to tell chrony what time servers to use. You can use specific server names or IP addresses, for example: 0.suse.pool.ntp.org 1.suse.pool.ntp.org 2.suse.pool.ntp.org 3.suse.pool.ntp.org You can also specify a pool name. Pool name resolves to several IP addresses: pool pool.ntp.org Tip: Computers on the same network To synchronize time on multiple computers on the same network, we do not recommend to synchronize them all with an external server. A good practice is to make one computer the time server which is synchronized with an external time server, and the other com- puters act as its clients. Add a local directive to the server''s /etc/chrony.conf to distinguish it from an authoritative time server: local stratum 10 To start chrony , run: systemctl start chronyd.service After initializing chronyd , it takes a while before the time is stabilized and the drift le for correcting the local computer clock is created. With the drift le, the systematic error of the hardware clock can be computed when the computer is powered on. The correction is used immediately, resulting in a higher stability of the system time. To enable the service so that chrony starts automatically at boot time, run: systemctl enable chronyd.service 494 Manually configuring NTP in the network SLES 15 SP6Warning: Conflicting yast-timesync.service service Besides the chronyd.service service, SLES includes yast-timesync.service . yast- timesync.service is triggered by a timer every 5 minutes and runs chronyd with the -q option to set the system time and exit. Because only one instance of chronyd can be running at any given time, do not enable or start both chronyd -related services at the same time. 38.3 Configure chronyd at runtime using chronyc You can use chronyc to change the behavior of chronyd at runtime. It also generates status reports about the operation of chronyd . You can run chronyc either in interactive or non-interactive mode. To run chronyc interac- tively, enter chronyc on the command line. It displays a prompt and waits for your command input. For example, to check how many NTP sources are online or offline, run: # chronyc chronyc> activity 200 OK 4 sources online 2 sources offline 1 sources doing burst (return to online) 1 sources doing burst (return to offline) 0 sources with unknown address To exit chronyc ''s prompt, enter quit or exit . If you do not need to use the interactive prompt, enter the command directly: # chronyc activity Note: Temporary changes Changes made using chronyc are not permanent. They will be lost after the next chronyd restart. For permanent changes, modify /etc/chrony.conf . For a complete list of chronyc commands, see its man page ( man 1 chronyc ). 495 Configure chronyd at runtime using chronyc SLES 15 SP638.4 Dynamic time synchronization at runtime Although chronyd starts up normally on a system that boots without a network connection, the tool cannot resolve the DNS names of the time servers specified in the configuration le. chronyd keeps trying to resolve the time server names specified by the server , pool , and peer directives in an increasing time interval until it succeeds. If the time server will not be reachable when chronyd is started, you can specify the offline option: server server_address offline chronyd will then not try to poll the server until it is enabled using the following command: # chronyc online server_address When the auto_offline option is set, chronyd assumes that the time server has gone offline when two requests have been sent to it without receiving a response. This option avoids the need to run the offline command from chronyc when disconnecting the network link. 38.5 Setting up a local reference clock The software package chrony relies on other programs (such as gpsd ) to access the timing data via the SHM or SOCK driver. Use the refclock directive in /etc/chrony.conf to specify a hardware reference clock to be used as a time source. It has two mandatory parameters: a driver name and a driver-specific parameter. The two parameters are followed by zero or more refclock options. chronyd includes the following drivers: PPS - driver for the kernel pulse per second API. For example: refclock PPS /dev/pps0 lock NMEA refid GPS SHM - NTP shared memory driver. For example: refclock SHM 0 poll 3 refid GPS1 refclock SHM 1:perm=0644 refid GPS2 496 Dynamic time synchronization at runtime SLES 15 SP6SOCK - Unix domain socket driver. For example: refclock SOCK /var/run/chrony.ttyS0.sock PHC - PTP hardware clock driver. For example: refclock PHC /dev/ptp0 poll 0 dpoll -2 offset -37 refclock PHC /dev/ptp1:nocrossts poll 3 pps For more information on individual drivers'' options, see man 8 chrony.conf . 38.6 Clock synchronization to an external time reference (ETR) Support for clock synchronization to an external time reference (ETR) is available. The external time reference sends an oscillator signal and a synchronization signal every 2**20 (2 to the power of 20) microseconds to keep TOD clocks of all connected servers synchronized. For availability two ETR units can be connected to a machine. If the clock deviates for more than the sync-check tolerance all CPUs get a machine check that indicates that the clock is not synchronized. If this happens, all DASD I/O to XRC enabled devices is stopped until the clock is synchronized again. The ETR support is activated via two sysfs attributes; run the following commands as root : echo 1 > /sys/devices/system/etr/etr0/online echo 1 > /sys/devices/system/etr/etr1/online 497 Clock synchronization to an external time reference (ETR) SLES 15 SP639 The domain name system DNS (domain name system) is needed to resolve the domain names and host names into IP addresses. In this way, the IP address 192.168.2.100 is assigned to the host name jupiter , for example. Before setting up your own name server, read the gen- eral information about DNS in Section 23.3, “Name resolution”. The following configu- ration examples refer to BIND, the default DNS server. 39.1 DNS terminology Zone The domain namespace is divided into regions called zones. For example, if you have example.com , you have the example section (or zone) of the com domain. DNS server The DNS server is a server that maintains the name and IP information for a domain. You can have a primary DNS server for primary zone, a secondary server for secondary zone, or a secondary server without any zones for caching. Primary zone DNS server The primary zone includes all hosts from your network and a DNS server primary zone stores up-to-date records for all the hosts in your domain. Secondary zone DNS server A secondary zone is a copy of the primary zone. The secondary zone DNS server obtains its zone data with zone transfer operations from its primary server. The sec- ondary zone DNS server responds authoritatively for the zone if it has valid (not ex- pired) zone data. If the secondary server cannot obtain a new copy of the zone data, it stops responding for the zone. Forwarder Forwarders are DNS servers to which your DNS server should send queries it cannot an- swer. To enable different configuration sources in one configuration, netconfig is used (see also man 8 netconfig ). 498 DNS terminology SLES 15 SP6Record The record is information about name and IP address. Supported records and their syntax are described in BIND documentation. Several special records are: NS record An NS record tells name servers which machines are in charge of a given domain zone. MX record The MX (mail exchange) records describe the machines to contact for directing mail across the Internet. SOA record SOA (Start of Authority) record is the rst record in a zone le. The SOA record is used when using DNS to synchronize data between multiple computers. 39.2 Installation To install a DNS server, start YaST and select Software Software Management. Choose View Pat- terns and select DHCP and DNS Server. Confirm the installation of the dependent packages to finish the installation process. Alternatively use the following command on the command line: > sudo zypper in -t pattern dhcp_dns_server 39.3 Configuration with YaST Use the YaST DNS module to configure a DNS server for the local network. When starting the module for the rst time, a wizard starts, prompting you to make a few decisions concerning administration of the server. Completing this initial setup produces a basic server configuration. Use the expert mode to deal with more advanced configuration tasks, such as setting up ACLs, logging, TSIG keys, and other options. 39.3.1 Wizard configuration The wizard consists of three steps or dialogs. At the appropriate places in the dialogs, you can enter the expert configuration mode. 499 Installation SLES 15 SP61. When starting the module for the rst time, the Forwarder Settings dialog, shown in Fig- ure 39.1, “DNS server installation: forwarder settings”, opens. The Local DNS Resolution Policy allows to set the following options: Merging forwarders is disabled Automatic merging Merging forwarders is enabled Custom configuration—If Custom configuration is selected, Custom policy can be speci- fied; by default (with Automatic merging selected), Custom policy is set to auto , but here you can either set interface names or select from the two special policy names STATIC and STATIC_FALLBACK . In Local DNS Resolution Forwarder, specify which service to use: Using system name servers, This name server (bind), or Local dnsmasq server. For more information about all these settings, see man 8 netconfig . FIGURE 39.1: DNS SERVER INSTALLATION: FORWARDER SETTINGS Forwarders are DNS servers to which your DNS server sends queries it cannot answer itself. Enter their IP address and click Add. 500 Wizard configuration SLES 15 SP62. The DNS Zones dialog consists of several parts and is responsible for the management of zone les, described in Section 39.6, “Zone files”. For a new zone, provide a name for it in Name. To add a reverse zone, the name must end in .in-addr.arpa . Finally, select the Type (primary, secondary, or forward). See Figure 39.2, “DNS server installation: DNS zones”. Click Edit to configure other settings of an existing zone. To remove a zone, click Delete. FIGURE 39.2: DNS SERVER INSTALLATION: DNS ZONES 3. In the final dialog, you can open the DNS port in the firewall by clicking Open Port in Firewall. Then decide whether to start the DNS server when booting (On or O). You can also activate LDAP support. See Figure 39.3, “DNS server installation: finish wizard”. 501 Wizard configuration SLES 15 SP6FIGURE 39.3: DNS SERVER INSTALLATION: FINISH WIZARD 39.3.2 Expert configuration After starting the module, YaST opens a window displaying several configuration options. Com- pleting it results in a DNS server configuration with the basic functions in place: 39.3.2.1 Start-up Under Start-Up, define whether the DNS server should be started when the booting the system or manually. To start the DNS server immediately, click Start DNS Server Now. To stop the DNS server, click Stop DNS Server Now. To save the current settings, select Save Settings and Reload DNS Server Now. You can open the DNS port in the firewall with Open Port in Firewall and modify the firewall settings with Firewall Details. By selecting LDAP Support Active, the zone les are managed by an LDAP database. Any changes to zone data written to the LDAP database are picked up by the DNS server when it is restarted or prompted to reload its configuration. 502 Expert configuration SLES 15 SP639.3.2.2 Forwarders If your local DNS server cannot answer a request, it tries to forward the request to a Forwarder, if configured so. This forwarder may be added manually to the Forwarder List. If the forwarder is not static like in dial-up connections, netconfig handles the configuration. For more information about netconfig, see man 8 netconfig . 39.3.2.3 Basic options In this section, set basic server options. From the Option menu, select the desired item then specify the value in the corresponding text box. Include the new entry by selecting Add. 39.3.2.4 Logging To set what the DNS server should log and how, select Logging. Under Log Type, specify where the DNS server should write the log data. Use the system-wide log by selecting System Log or specify a different le by selecting File. In the latter case, additionally specify a name, the maximum le size in megabytes and the number of log le versions to store. Further options are available under Additional Logging. Enabling Log All DNS Queries causes every query to be logged, in which case the log le could grow large. For this reason, it is not a good idea to enable this option for other than debugging purposes. To log the data traffic during zone updates between DHCP and DNS server, enable Log Zone Updates. To log the data traffic during a zone transfer from primary to secondary server, enable Log Zone Transfer. See Figure 39.4, “DNS server: logging”. 503 Expert configuration SLES 15 SP6FIGURE 39.4: DNS SERVER: LOGGING 39.3.2.5 ACLs Use this dialog to define ACLs (access control lists) to enforce access restrictions. After providing a distinct name under Name, specify an IP address (with or without netmask) under Value in the following fashion: { 192.168.1/24; } The syntax of the configuration le requires that the address ends with a semicolon and is put into curly braces. 39.3.2.6 TSIG keys The main purpose of TSIGs (transaction signatures) is to secure communications between DHCP and DNS servers. They are described in Section 39.8, “Secure transactions”. To generate a TSIG key, enter a distinctive name in the eld labeled Key ID and specify the le where the key should be stored (Filename). Confirm your choices with Generate. To use a previously created key, leave the Key ID eld blank and select the le where it is stored under Filename. After that, confirm with Add. 504 Expert configuration SLES 15 SP639.3.2.7 DNS zones (adding a secondary zone) To add a secondary zone, select DNS Zones, choose the zone type Secondary, write the name of the new zone, and click Add. In the Zone Editor sub-dialog under Primary DNS Server IP, specify the primary server from which the secondary server should pull its data. To limit access to the server, select one of the ACLs from the list. 39.3.2.8 DNS zones (adding a primary zone) To add a primary zone, select DNS Zones, choose the zone type Primary, write the name of the new zone, and click Add. When adding a primary zone, a reverse zone is also needed. For example, when adding the zone example.com that points to hosts in a subnet 192.168.1.0/24 , you should also add a reverse zone for the IP-address range covered. By definition, this should be named 1.168.192.in-addr.arpa . 39.3.2.9 DNS zones (editing a primary zone) To edit a primary zone, select DNS Zones, select the primary zone from the table and click Edit. The dialog consists of several pages: Basics (the one opened rst), NS Records, MX Records, SOA, and Records. The basic dialog, shown in Figure 39.5, “DNS server: Zone Editor (Basics)”, lets you define settings for dynamic DNS and access options for zone transfers to clients and secondary name servers. To permit the dynamic updating of zones, select Allow Dynamic Updates and the corresponding TSIG key. The key must have been defined before the update action starts. To enable zone transfers, select the corresponding ACLs. ACLs must have been defined already. In the Basics dialog, select whether to enable zone transfers. Use the listed ACLs to define who can download zones. 505 Expert configuration SLES 15 SP6FIGURE 39.5: DNS SERVER: ZONE EDITOR (BASICS) Zone Editor (NS Records) The NS Records dialog allows you to define alternative name servers for the zones specified. Make sure that your own name server is included in the list. To add a record, enter its name under Name Server to Add then confirm with Add. See Figure 39.6, “DNS server: Zone Editor (NS Records)”. FIGURE 39.6: DNS SERVER: ZONE EDITOR (NS RECORDS) 506 Expert configuration SLES 15 SP6Zone Editor (MX Records) To add a mail server for the current zone to the existing list, enter the corresponding address and priority value. After doing so, confirm by selecting Add. See Figure 39.7, “DNS server: Zone Editor (MX Records)”. FIGURE 39.7: DNS SERVER: ZONE EDITOR (MX RECORDS) Zone Editor (SOA) This page allows you to create SOA (start of authority) records. For an explanation of the individual options, refer to Example 39.6, “The /var/lib/named/example.com.zone file”. Chang- ing SOA records is not supported for dynamic zones managed via LDAP. 507 Expert configuration SLES 15 SP6FIGURE 39.8: DNS SERVER: ZONE EDITOR (SOA) Zone Editor (Records) This dialog manages name resolution. In Record Key, enter the host name then select its type. The A type represents the main entry. The value for this should be an IP address (IPv4). Use AAAA for IPv6 addresses. CNAME is an alias. Use the types NS and MX for detailed or partial records that expand on the information provided in the NS Records and MX Records tabs. These three types resolve to an existing A record. PTR is for reverse zones. It is the opposite of an A record, for example: hostname.example.com. IN A 192.168.0.1 1.0.168.192.in-addr.arpa IN PTR hostname.example.com. 39.3.2.9.1 Adding reverse zones To add a reverse zone, follow this procedure: 1. Start YaST DNS Server DNS Zones. 2. If you have not added a primary forward zone, add it and Edit it. 3. In the Records tab, ll the corresponding Record Key and Value, then add the record with Add and confirm with OK. If YaST complains about a non-existing record for a name server, add it in the NS Records tab. 508 Expert configuration SLES 15 SP6FIGURE 39.9: ADDING A RECORD FOR A PRIMARY ZONE 4. Back in the DNS Zones window, add a reverse primary zone. FIGURE 39.10: ADDING A REVERSE ZONE 5. Edit the reverse zone, and in the Records tab, you can see the PTR: Reverse translation record type. Add the corresponding Record Key and Value, then click Add and confirm with OK. 509 Expert configuration SLES 15 SP6FIGURE 39.11: ADDING A REVERSE RECORD Add a name server record if needed. Tip: Editing the reverse zone After adding a forward zone, go back to the main menu and select the reverse zone for editing. There in the tab Basics activate the check box Automatically Generate Records From and select your forward zone. That way, all changes to the forward zone are automatically updated in the reverse zone. 39.4 Starting the BIND name server On a SUSE® Linux Enterprise Server system, the name server BIND (Berkeley Internet Name Do- main) comes preconfigured, so it can be started right after installation without any problems. Normally, if you already have an Internet connection and entered 127.0.0.1 as the name serv- er address for localhost in /var/run/netconfig/resolv.conf , you already have a working name resolution without needing to know the DNS of the provider. BIND carries out name res- olution via the root name server, a notably slower process. Normally, the DNS of the provider should be entered with its IP address in the configuration le /etc/named.conf under for- 510 Starting the BIND name server SLES 15 SP6warders to ensure effective and secure name resolution. If this works so far, the name server runs as a pure caching-only name server. Only when you configure its own zones it becomes a proper DNS. Find a simple example documented in /usr/share/doc/packages/bind/config . Tip: Automatic adaptation of the name server information Depending on the type of Internet connection or the network connection, the name serv- er information can automatically be adapted to the current conditions. To do this, set the NETCONFIG_DNS_POLICY variable in the /etc/sysconfig/network/config le to auto . However, do not set up an official domain until one is assigned to you by the responsible insti- tution. Even if you have your own domain and it is managed by the provider, you are better o not using it, because BIND would otherwise not forward requests for this domain. The Web server at the provider, for example, would not be accessible for this domain. To start the name server, enter the command systemctl start named as root . Check with systemctl status named whether named (as the name server process is called) has been started successfully. Test the name server immediately on the local system with the host or dig programs, which should return localhost as the default server with the address 127.0.0.1 . If this is not the case, /var/run/netconfig/resolv.conf may contain an incorrect name server entry or the le does not exist. For the rst test, enter host   127.0.0.1 , which should always work. If you get an error message, use systemctl status named to see whether the server is running. If the name server does not start or behaves unexpectedly, check the output of jour- nalctl -e . To use the name server of the provider (or one already running on your network) as the for- warder, enter the corresponding IP address or addresses in the options section under for- warders . The addresses included in Example 39.1, “Forwarding options in named.conf” are examples only. Adjust these entries to your own setup. EXAMPLE 39.1: FORWARDING OPTIONS IN NAMED.CONF options { directory "/var/lib/named"; forwarders { 10.11.12.13; 10.11.12.14; }; listen-on { 127.0.0.1; 192.168.1.116; }; allow-query { 127/8; 192.168/16 }; notify no; }; 511 Starting the BIND name server SLES 15 SP6The options entry is followed by entries for the zone, localhost , and 0.0.127.in-ad- dr.arpa . The type hint entry under “.” should always be present. The corresponding les do not need to be modified and should work as they are. Also make sure that each entry is closed with a “;” and that the curly braces are in the correct places. After changing the configuration le /etc/named.conf or the zone les, tell BIND to reread them with systemctl reload named . Achieve the same by stopping and restarting the name server with systemctl restart named . Stop the server at any time by entering systemctl stop named . 39.5 The /etc/named.conf configuration file All the settings for the BIND name server itself are stored in the /etc/named.conf le. How- ever, the zone data for the domains to handle (consisting of the host names, IP addresses, and so on) are stored in separate les in the /var/lib/named directory. The details of this are described later. /etc/named.conf is roughly divided into two areas. One is the options section for general settings and the other consists of zone entries for the individual domains. A logging section and acl (access control list) entries are optional. Comment lines begin with a # sign or // . A minimal /etc/named.conf is shown in Example 39.2, “A basic /etc/named.conf”. EXAMPLE 39.2: A BASIC /ETC/NAMED.CONF options { directory "/var/lib/named"; forwarders { 10.0.0.1; }; notify no; }; zone "localhost" in { type master; file "localhost.zone"; }; zone "0.0.127.in-addr.arpa" in { type master; file "127.0.0.zone"; }; zone "." in { type hint; file "root.hint"; }; 512 The /etc/named.conf configuration file SLES 15 SP639.5.1 Important configuration options directory " FILENAME "; Specifies the directory in which BIND can nd the les containing the zone data. Usually, this is /var/lib/named . forwarders { IP-ADDRESS ; }; Specifies the name servers (of the provider) to which DNS requests should be forward- ed if they cannot be resolved directly. Replace IP-ADDRESS with an IP address like 192.168.1.116 . forward first; Causes DNS requests to be forwarded before an attempt is made to resolve them via the root name servers. Instead of forward first , forward only can be written to have all requests forwarded and none sent to the root name servers. This makes sense for firewall configurations. listen-on port 53 { 127.0.0.1; IP-ADDRESS ; }; Tells BIND on which network interfaces and port to accept client queries. port 53 does not need to be specified explicitly, because 53 is the default port. Enter 127.0.0.1 to permit requests from the local host. If you omit this entry entirely, all interfaces are used by default. listen-on-v6 port 53 {any; }; Tells BIND on which port it should listen for IPv6 client requests. The only alternative to any is none . As far as IPv6 is concerned, the server only accepts wild card addresses. query-source address * port 53; This entry is necessary if a firewall is blocking outgoing DNS requests. This tells BIND to post requests externally from port 53 and not from any of the high ports above 1024. query-source-v6 address * port 53; Tells BIND which port to use for IPv6 queries. allow-query { 127.0.0.1; NET ; }; Defines the networks from which clients can post DNS requests. Replace NET with address information like 192.168.2.0/24 . The /24 at the end is an abbreviated expression for the netmask (in this case 255.255.255.0 ). 513 Important configuration options SLES 15 SP6allow-transfer ! *;; Controls which hosts can request zone transfers. In the example, such requests are denied with ! * . Without this entry, zone transfers can be requested from anywhere without restrictions. statistics-interval 0; Without this entry, BIND generates several lines of statistical information per hour in the system''s journal. Set it to 0 to suppress these statistics or set an interval in minutes. cleaning-interval 720; This option defines at which time intervals BIND clears its cache. This triggers an entry in the system''s journal each time it occurs. The time specification is in minutes. The default is 60 minutes. interface-interval 0; BIND regularly searches the network interfaces for new or nonexistent interfaces. If this value is set to 0 , this is not done and BIND only listens at the interfaces detected at start- up. Otherwise, the interval can be defined in minutes. The default is sixty minutes. notify no; no prevents other name servers from being informed when changes are made to the zone data or when the name server is restarted. For a list of available options, read the man page man 5 named.conf . 39.5.2 Logging What, how and where logging takes place can be extensively configured in BIND. Normally, the default settings should be sufficient. Example 39.3, “Entry to disable logging”, shows the simplest form of such an entry and suppresses any logging. EXAMPLE 39.3: ENTRY TO DISABLE LOGGING logging { category default { null; }; }; 514 Logging SLES 15 SP639.5.3 Zone entries EXAMPLE 39.4: ZONE ENTRY FOR EXAMPLE.COM zone "example.com" in { type master; file "example.com.zone"; notify no; }; After zone , specify the name of the domain to administer ( example.com ) followed by in and a block of relevant options enclosed in curly braces, as shown in Example 39.4, “Zone entry for example.com”. To define a secondary zone, switch the type to secondary and specify a name server that administers this zone as primary (which, in turn, may be a secondary server of another primary server), as shown in Example 39.5, “Zone entry for example.net”. EXAMPLE 39.5: ZONE ENTRY FOR EXAMPLE.NET zone "example.net" in { type secondary; file "secondary/example.net.zone"; masters { 10.0.0.1; }; }; The zone options: type primary; By specifying primary , tell BIND that the zone is handled by the local name server. This assumes that a zone le has been created in the correct format. type secondary; This zone is transferred from another name server. It must be used together with prima- ry_servers . type hint; The zone . of the hint type is used to set the root name servers. This zone definition can be left as is. file example.com.zone or file “secondary/example.net.zone”; This entry specifies the le where zone data for the domain is located. This le is not required for a secondary server, because this data is pulled from another name server. To differentiate les of the primary and secondary server, use the directory secondary for the secondary les. 515 Zone entries SLES 15 SP6primary_servers { SERVER_IP_ADDRESS ; }; This entry is only needed for secondary zones. It specifies from which name server the zone le should be transferred. allow-update {! *; }; This option controls external write access, which would allow clients to make a DNS en- try—something not normally desirable for security reasons. Without this entry, zone up- dates are not allowed. The above entry achieves the same because ! * effectively bans any such activity. 39.6 Zone files Two types of zone les are needed. One assigns IP addresses to host names and the other does the reverse: it supplies a host name for an IP address. Tip: Using the dot (period, full stop) in zone files The "." has an important meaning in the zone les. If host names are given without a final dot ( . ), the zone is appended. Complete host names specified with a full domain name must end with a dot ( . ) to avoid having the domain added to it again. A missing or wrongly placed "." is the most frequent cause of name server configuration errors. The rst case to consider is the zone le example.com.zone , responsible for the domain ex- ample.com , shown in Example 39.6, “The /var/lib/named/example.com.zone file”. EXAMPLE 39.6: THE /VAR/LIB/NAMED/EXAMPLE.COM.ZONE FILE $TTL 2D 1 example.com. IN SOA dns root.example.com. ( 2 2003072441 ; serial 3 1D ; refresh 4 2H ; retry 5 1W ; expiry 6 2D ) ; minimum 7 IN NS dns 8 IN MX 10 mail dns 9 gate IN A 192.168.5.1 10 IN A 10.0.0.1 516 Zone files SLES 15 SP6dns IN A 192.168.1.116 mail IN A 192.168.3.108 jupiter IN A 192.168.2.100 venus IN A 192.168.2.101 saturn IN A 192.168.2.102 mercury IN A 192.168.2.103 ntp IN CNAME dns 11 dns6 IN A6 0 2002:c0a8:174:: 1 $TTL defines the default time to live that should apply to all the entries in this le. In this example, entries are valid for a period of two days ( 2 D ). 2 This is where the SOA (start of authority) control record begins: The name of the domain to administer is example.com in the rst position. This ends with "." , because otherwise the zone would be appended a second time. Alterna- tively, @ can be entered here, in which case the zone would be extracted from the corresponding entry in /etc/named.conf . After IN SOA is the name of the name server in charge as a primary server for this zone. The name is expanded from dns to dns.example.com , because it does not end with a "." . An e-mail address of the person in charge of this name server follows. Because the @ sign already has a special meaning, "." is entered here instead. For root@exam- ple.com the entry must read root.example.com. . The "." must be included at the end to prevent the zone from being added. The ( includes all lines up to ) into the SOA record. 3 The serial number is a 10-digit number. It must be changed each time this le is changed. It is needed to inform the secondary name servers (secondary servers) of changes. For this, a 10-digit number of the date and run number, written as YYYYMMDDNN, has become the customary format (YYYY = year, MM = month and DD = day. NN is a sequence number in case you update it more than once on the given day). 4 The refresh rate specifies the time interval at which the secondary name servers verify the zone serial number . In this case, one day. 5 The retry rate specifies the time interval at which a secondary name server, in case of error, attempts to contact the primary server again. Here, two hours. 6 The expiration time specifies the time frame after which a secondary name server dis- cards the cached data if it has not regained contact to the primary server. Here, a week. 517 Zone files SLES 15 SP67 The last entry in the SOA record specifies the negative caching TTL—the time for which results of unresolved DNS queries from other servers may be cached. 8 The IN NS specifies the name server responsible for this domain. dns is extended to dns.example.com because it does not end with a "." . There can be several lines like this—one for the primary and one for each secondary name server. If notify is not set to no in /etc/named.conf , all the name servers listed here are informed of the changes made to the zone data. 9 The MX record specifies the mail server that accepts, processes, and forwards e-mails for the domain example.com . In this example, this is the host mail.example.com . The number in front of the host name is the preference value. If there are multiple MX entries, the mail server with the smallest value is taken rst. If mail delivery to this server fails, the entry with the next-smallest value is used. 10 This and the following lines are the actual address records where one or more IP addresses are assigned to host names. The names are listed here without a "." because they do not include their domain, so example.com is added to them all. Two IP addresses are assigned to the host gate , as it has two network cards. Wherever the host address is a traditional one (IPv4), the record is marked with A . If the address is an IPv6 address, the entry is marked with AAAA . Note: IPv6 syntax The IPv6 record has a slightly different syntax than IPv4. Because of the fragmenta- tion possibility, it is necessary to provide information about missed bits before the address. To ll up the IPv6 address with the needed number of “0”, add two colons at the correct place in the address. pluto AAAA 2345:00C1:CA11::1234:5678:9ABC:DEF0 pluto AAAA 2345:00D2:DA11::1234:5678:9ABC:DEF0 11 The alias ntp can be used to address dns ( CNAME means canonical name). The pseudo domain in-addr.arpa is used for the reverse lookup of IP addresses into host names. It is appended to the network part of the address in reverse notation. So 192.168 is resolved into 168.192.in-addr.arpa . See Example 39.7, “Reverse lookup”. EXAMPLE 39.7: REVERSE LOOKUP $TTL 2D 1 518 Zone files SLES 15 SP6168.192.in-addr.arpa. IN SOA dns.example.com. root.example.com. ( 2 2003072441 ; serial 1D ; refresh 2H ; retry 1W ; expiry 2D ) ; minimum IN NS dns.example.com. 3 1.5 IN PTR gate.example.com. 4 100.3 IN PTR www.example.com. 253.2 IN PTR cups.example.com. 1 $TTL defines the standard TTL that applies to all entries here. 2 The configuration le should activate reverse lookup for the network 192.168 . Given that the zone is called 168.192.in-addr.arpa , it should not be added to the host names. Therefore, all host names are entered in their complete form—with their domain and with a "." at the end. The remaining entries correspond to those described for the previous example.com example. See Example 39.6, “The /var/lib/named/example.com.zone file” for detail on the entries within this record. 3 This line specifies the name server responsible for this zone. This time, however, the name is entered in its complete form with the domain and a "." at the end. 4 This, and the following lines, are the pointer records hinting at the IP addresses on the respective hosts. Only the last part of the IP address is entered at the beginning of the line, without the "." at the end. Appending the zone to this (without the .in-addr.arpa ) results in the complete IP address in reverse order. Normally, zone transfers between different versions of BIND should be possible without any problems. 39.7 Dynamic update of zone data The term dynamic update refers to operations by which entries in the zone les of a primary server are added, changed or deleted. This mechanism is described in RFC 2136. Dynamic up- date is configured individually for each zone entry by adding an optional allow-update or update-policy rule. Zones to update dynamically should not be edited by hand. 519 Dynamic update of zone data SLES 15 SP6Transmit the entries to update to the server with the command nsupdate . For the exact syntax of this command, check the man page for nsupdate ( man   8 nsupdate ). For security reasons, any such update should be performed using TSIG keys as described in Section 39.8, “Secure trans- actions”. 39.8 Secure transactions Secure transactions can be made with transaction signatures (TSIGs) based on shared secret keys (also called TSIG keys). This section describes how to generate and use such keys. Secure transactions are needed for communication between different servers and for the dynamic update of zone data. Making the access control dependent on keys is much more secure than merely relying on IP addresses. Generate a TSIG key with the following command (for details, see man   tsig-keygen ): > sudo tsig-keygen -a hmac-md5 host1-host2 > host1-host2.key This creates a le with the name host1-host2.key with contents that may look as follows: key "host1-host2" { | algorithm hmac-md5; secret "oHpBLgtcZso6wxnRTWdJMA=="; }; The le must be transferred to the remote host, preferably in a secure way (using scp, for exam- ple). To enable a secure communication between host1 and host2 , the key must be included in the /etc/named.conf le on both the local and the remote server. key host1-host2 { algorithm hmac-md5; secret "ejIkuCyyGJwwuN3xAteKgg=="; }; Warning: File permissions of /etc/named.conf Make sure that the permissions of /etc/named.conf are properly restricted. The default for this le is 0640 , with the owner being root and the group named . As an alternative, move the keys to an extra le with specially limited permissions, which is then included from /etc/named.conf . To include an external le, use: include "filename" 520 Secure transactions SLES 15 SP6Replace filename with an absolute path to your le with keys. To enable the server host1 to use the key for host2 (which has the address 10.1.2.3 in this example), the server''s /etc/named.conf must include the following rule: server 10.1.2.3 { keys { host1-host2. ;}; }; Analogous entries must be included in the configuration les of host2 . Add TSIG keys for any ACLs (access control lists, not to be confused with le system ACLs) that are defined for IP addresses and address ranges to enable transaction security. The corresponding entry could look like this: allow-update { key host1-host2. ;}; This topic is discussed in more detail in the BIND Administrator Reference Manual under up- date-policy . 39.9 DNS security DNSSEC, or DNS security, is described in RFC 2535. The tools available for DNSSEC are discussed in the BIND Manual. A zone considered secure must have one or several zone keys associated with it. These are generated with dnssec-keygen , as are the host keys. The DSA encryption algorithm is currently used to generate these keys. The public keys generated should be included in the corresponding zone le with an $INCLUDE rule. With the command dnssec-signzone , you can create sets of generated keys ( keyset- les), transfer them to the parent zone in a secure manner, and sign them. This generates the les to include for each zone in /etc/named.conf . 521 DNS security SLES 15 SP639.10 More information For more information, see the BIND Administrator Reference Manual from the bind-doc package, which is installed under /usr/share/doc/packages/bind/arm . Consider additionally consult- ing the RFCs referenced by the manual and the manual pages included with BIND. /usr/share/ doc/packages/bind/README.SUSE contains up-to-date information about BIND in SUSE Linux Enterprise Server. 522 More information SLES 15 SP640 DHCP The purpose of the Dynamic Host Configuration Protocol (DHCP) is to assign network settings centrally (from a server) rather than configuring them locally on every workstation. A host configured to use DHCP does not have control over its own sta- tic address. It is enabled to configure itself automatically according to directions from the server. If you use the NetworkManager on the client side, you do not need to configure the client. This is useful if you have changing environments and only one interface active at a time. Never use NetworkManager on a machine that runs a DHCP server. Tip: IBM Z: DHCP support On IBM Z platforms, DHCP only works on interfaces using the OSA and OSA Express network cards. These cards are the only ones with a MAC, which is required for the DHCP autoconfiguration features. One way to configure a DHCP server is to identify each client using the hardware address of its network card (which should usually be xed), then supply that client with identical settings each time it connects to the server. DHCP can also be configured to assign addresses to each relevant client dynamically from an address pool set up for this purpose. In the latter case, the DHCP server tries to assign the same address to the client each time it receives a request, even over extended periods. This works only if the network does not have more clients than addresses. DHCP makes life easier for system administrators. Any changes, even bigger ones, related to addresses and the network configuration can be implemented centrally by editing the server''s configuration le. This is much more convenient than reconfiguring multiple workstations. It is also much easier to integrate machines, particularly new machines, into the network, because they can be given an IP address from the pool. Retrieving the appropriate network settings from a DHCP server is especially useful in case of laptops regularly used in different networks. In this chapter, the DHCP server runs in the same subnet as the workstations, 192.168.2.0/24 with 192.168.2.1 as gateway. It has the xed IP address 192.168.2.254 and serves two address ranges, 192.168.2.10 to 192.168.2.20 and 192.168.2.100 to 192.168.2.200 . 523 SLES 15 SP6A DHCP server supplies not only the IP address and the netmask, but also the host name, domain name, gateway and name server addresses for the client to use. Besides that, DHCP allows several parameters to be configured in a centralized way, for example, a time server from which clients may poll the current time or even a print server. 40.1 Configuring a DHCP server with YaST To install a DHCP server, start YaST and select Software Software Management. Choose Fil- ter Patterns and select DHCP and DNS Server. Confirm the installation of the dependent pack- ages to finish the installation process. Important: LDAP support The YaST DHCP module can be set up to store the server configuration locally (on the host that runs the DHCP server) or to have its configuration data managed by an LDAP server. To use LDAP, set up your LDAP environment before configuring the DHCP server. For more information about LDAP, see Book “Security and Hardening Guide”, Chapter 5 “LDAP with 389 Directory Server”. The YaST DHCP module ( yast2-dhcp-server ) allows you to set up your own DHCP server for the local network. The module can run in wizard mode or expert configuration mode. 40.1.1 Initial configuration (wizard) When the module is started for the rst time, a wizard starts, prompting you to make a few basic decisions concerning server administration. Completing this initial setup produces a basic server configuration that should function in its essential aspects. The expert mode can be used to deal with more advanced configuration tasks. Proceed as follows: 1. Select the interface from the list to which the DHCP server should listen and click Select and then Next. See Figure 40.1, “DHCP server: card selection”. Note: DHCP and firewalld The option Open Firewall for Selected Interfaces does not (yet) support firewalld in SUSE Linux Enterprise Server 15 SP6. To manually open the DHCP port, run 524 Configuring a DHCP server with YaST SLES 15 SP6> sudo firewall-cmd --zone=public --permanent --add-service=dhcp > sudo firewall-cmd --reload FIGURE 40.1: DHCP SERVER: CARD SELECTION 2. Use the check box to determine whether your DHCP settings should be automatically stored by an LDAP server. In the text boxes, provide the network specics for all clients the DHCP server should manage. These specics are the domain name, address of a time server, addresses of the primary and secondary name server, addresses of a print and a WINS server (for a mixed network with both Windows and Linux clients), gateway address, and lease time. See Figure 40.2, “DHCP server: global settings”. 525 Initial configuration (wizard) SLES 15 SP6FIGURE 40.2: DHCP SERVER: GLOBAL SETTINGS 3. Configure how dynamic IP addresses should be assigned to clients. To do so, specify an IP range from which the server can assign addresses to DHCP clients. All these addresses must be covered by the same netmask. Also specify the lease time during which a client may keep its IP address without needing to request an extension of the lease. Optionally, specify the maximum lease time—the period during which the server reserves an IP address for a particular client. See Figure 40.3, “DHCP server: dynamic DHCP”. 526 Initial configuration (wizard) SLES 15 SP6FIGURE 40.3: DHCP SERVER: DYNAMIC DHCP 4. Define how the DHCP server should be started. Specify whether to start the DHCP server automatically when the system is booted or manually when needed (for example, for testing purposes). Click Finish to complete the configuration of the server. See Figure 40.4, “DHCP server: start-up”. 527 Initial configuration (wizard) SLES 15 SP6FIGURE 40.4: DHCP SERVER: START-UP 5. Instead of using dynamic DHCP in the way described in the preceding steps, you can also configure the server to assign addresses in quasi-static fashion. Use the text boxes provided in the lower part to specify a list of the clients to manage in this way. Specifically, provide the Name and the IP Address to give to such a client, the Hardware Address, and the Network Type (token ring or Ethernet). Modify the list of clients, which is shown in the upper part with Add, Edit, and Delete from List. See Figure 40.5, “DHCP server: host management”. 528 Initial configuration (wizard) SLES 15 SP6FIGURE 40.5: DHCP SERVER: HOST MANAGEMENT 40.1.2 DHCP server configuration (expert) Besides the configuration method discussed earlier, there is also an expert configuration mode that allows you to change the DHCP server setup in every detail. Start the expert configuration by clicking DHCP Server Expert Configuration in the Start-Up dialog (see Figure 40.4, “DHCP server: start-up”). Chroot environment and declarations In this rst dialog, make the existing configuration editable by selecting Start DHCP Server. An important feature of the behavior of the DHCP server is its ability to run in a chroot environment, or chroot jail, to secure the server host. If the DHCP server is compromised by an outside attack, the attacker is still in the chroot jail, which prevents them from accessing the rest of the system. The lower part of the dialog displays a tree view with the declarations that have already been defined. Modify these with Add, Delete and Edit. Selecting Advanced takes you to additional expert dialogs. See Figure 40.6, “DHCP server: chroot jail and declarations”. After selecting Add, define the type of declaration to add. With Advanced, view the log le of the server, configure TSIG key management, and adjust the configuration of the firewall according to the setup of the DHCP server. 529 DHCP server configuration (expert) SLES 15 SP6FIGURE 40.6: DHCP SERVER: CHROOT JAIL AND DECLARATIONS Selecting the declaration type The Global Options of the DHCP server are made up of several declarations. This dialog lets you set the declaration types Subnet, Host, Shared Network, Group, Pool of Addresses, and Class. This example shows the selection of a new subnet (see Figure 40.7, “DHCP server: selecting a declaration type”). 530 DHCP server configuration (expert) SLES 15 SP6FIGURE 40.7: DHCP SERVER: SELECTING A DECLARATION TYPE Subnet configuration This dialog allows you specify a new subnet with its IP address and netmask. In the middle part of the dialog, modify the DHCP server start options for the selected subnet using Add, Edit, and Delete. To set up dynamic DNS for the subnet, select Dynamic DNS. FIGURE 40.8: DHCP SERVER: CONFIGURING SUBNETS 531 DHCP server configuration (expert) SLES 15 SP6TSIG key management If you chose to configure dynamic DNS in the previous dialog, you can now configure the key management for a secure zone transfer. Selecting OK takes you to another dialog in which to configure the interface for dynamic DNS (see Figure 40.10, “DHCP server: interface configuration for dynamic DNS”). FIGURE 40.9: DHCP SERVER: TSIG CONFIGURATION Dynamic DNS: interface configuration You can now activate dynamic DNS for the subnet by selecting Enable Dynamic DNS for This Subnet. After doing so, use the drop-down box to activate the TSIG keys for forward and reverse zones, making sure that the keys are the same for the DNS and the DHCP server. With Update Global Dynamic DNS Settings, enable the automatic update and adjustment of the global DHCP server settings according to the dynamic DNS environment. Finally, define which forward and reverse zones should be updated per dynamic DNS, specifying the name of the primary name server for each of the two zones. Selecting OK returns to the subnet configuration dialog (see Figure 40.8, “DHCP server: configuring subnets”). Selecting OK again returns to the original expert configuration dialog. 532 DHCP server configuration (expert) SLES 15 SP6FIGURE 40.10: DHCP SERVER: INTERFACE CONFIGURATION FOR DYNAMIC DNS Note: ignore client-updates option When enabling Dynamic DNS for a zone, YaST automatically adds the ignore client-updates option to improve client compatibility. The option can be disabled if it is not required. Network interface configuration To define the interfaces the DHCP server should listen to and to adjust the firewall con- figuration, select Advanced Interface Configuration from the expert configuration dialog. From the list of interfaces displayed, select one or more that should be attended by the DHCP server. If clients in all subnets need to be able to communicate with the server and the server host also runs a firewall, adjust the firewall accordingly. Note: DHCP and firewalld The option Open Firewall for Selected Interfaces does not (yet) support firewalld in SUSE Linux Enterprise Server 15 SP6. To manually open the DHCP port, run > sudo firewall-cmd --zone=public --permanent --add-service=dhcp > sudo firewall-cmd --reload 533 DHCP server configuration (expert) SLES 15 SP6FIGURE 40.11: DHCP SERVER: NETWORK INTERFACE AND FIREWALL After completing all configuration steps, close the dialog with OK. The server is now started with its new configuration. 40.2 DHCP software packages Both the DHCP server and the DHCP clients are available for SUSE Linux Enterprise Server. The DHCP server available is dhcpd (published by the Internet Systems Consortium). On the client side, there is dhcp-client (also from ISC) and tools coming with the wicked package. By default, the wicked tools are installed with the services wickedd-dhcp4 and wickedd- dhcp6 . Both are launched automatically on each system boot to watch for a DHCP server. They do not need a configuration le to do their job and work out of the box in most standard setups. For more complex situations, use the ISC dhcp-client , which is controlled by the configuration les /etc/dhclient.conf and /etc/dhclient6.conf . 534 DHCP software packages SLES 15 SP640.3 The DHCP server dhcpd The core of any DHCP system is the dynamic host configuration protocol daemon. This server leases addresses and watches how they are used, according to the settings defined in the con- figuration le /etc/dhcpd.conf . By changing the parameters and values in this le, a system administrator can influence the program''s behavior in many ways. Look at the basic sample / etc/dhcpd.conf le in Example 40.1, “The configuration file /etc/dhcpd.conf”. EXAMPLE 40.1: THE CONFIGURATION FILE /ETC/DHCPD.CONF default-lease-time 600; # 10 minutes max-lease-time 7200; # 2 hours option domain-name "example.com"; option domain-name-servers 192.168.1.116; option broadcast-address 192.168.2.255; option routers 192.168.2.1; option subnet-mask 255.255.255.0; subnet 192.168.2.0 netmask 255.255.255.0 { range 192.168.2.10 192.168.2.20; range 192.168.2.100 192.168.2.200; } This simple configuration le should be sufficient to get the DHCP server to assign IP addresses in the network. Make sure that a semicolon is inserted at the end of each line, because otherwise dhcpd is not started. The sample le can be divided into three sections. The rst one defines how many seconds an IP address is leased to a requesting client by default ( default-lease-time ) before it should apply for renewal. This section also includes a statement of the maximum period for which a machine may keep an IP address assigned by the DHCP server without applying for renewal ( max-lease-time ). In the second part, certain basic network parameters are defined on a global level: The line option domain-name defines the default domain of your network. With the entry option domain-name-servers , specify up to three values for the DNS servers used to resolve IP addresses into host names and vice versa. Ideally, configure a name server on your machine or somewhere else in your network before setting up DHCP. That name server should also define a host name for each dynamic address and vice versa. To learn how to configure your own name server, read Chapter 39, The domain name system. 535 The DHCP server dhcpd SLES 15 SP6The line option broadcast-address defines the broadcast address the requesting client should use. With option routers , set where the server should send data packets that cannot be delivered to a host on the local network (according to the source and target host address and the subnet mask provided). Especially in smaller networks, this router is identical to the Internet gateway. With option subnet-mask , specify the netmask assigned to clients. The last section of the le defines a network, including a subnet mask. To finish, specify the address range that the DHCP daemon should use to assign IP addresses to interested clients. In Example 40.1, “The configuration file /etc/dhcpd.conf”, clients may be given any address between 192.168.2.10 and 192.168.2.20 or 192.168.2.100 and 192.168.2.200 . After editing these few lines, you should be able to activate the DHCP daemon with the com- mand systemctl start dhcpd . It will be ready for use immediately. Use the command rcd- hcpd  check-syntax to perform a brief syntax check. If you encounter any unexpected problems with your configuration (the server aborts with an error or does not return done on start), you should be able to nd out what has gone wrong by looking for information either in the main system log that can be queried with the command journalctl (see Chapter 21, journalctl: query the systemd journal for more information). On a default SUSE Linux Enterprise Server system, the DHCP daemon is started in a chroot environment for security reasons. The configuration les must be copied to the chroot environ- ment so the daemon can nd them. Normally, there is no need to worry about this because the command systemctl start dhcpd automatically copies the les. 40.3.1 Clients with fixed IP addresses DHCP can also be used to assign a predefined, static address to a specific client. Addresses as- signed explicitly always take priority over dynamic addresses from the pool. A static address never expires in the way a dynamic address would, for example, if there were not enough ad- dresses available and the server needed to redistribute them among clients. To identify a client configured with a static address, dhcpd uses the hardware address (which is a globally unique, xed numerical code consisting of six octet pairs) for the identification of all network devices (for example, 00:30:6E:08:EC:80 ). If the respective lines, like the ones in 536 Clients with fixed IP addresses SLES 15 SP6Example 40.2, “Additions to the configuration file”, are added to the configuration le of Example 40.1, “The configuration file /etc/dhcpd.conf”, the DHCP daemon always assigns the same set of data to the corresponding client. EXAMPLE 40.2: ADDITIONS TO THE CONFIGURATION FILE host jupiter { hardware ethernet 00:30:6E:08:EC:80; fixed-address 192.168.2.100; } The name of the respective client ( host HOSTNAME , here jupiter ) is entered in the rst line and the MAC address in the second line. On Linux hosts, nd the MAC address with the command ip link show followed by the network device (for example, eth0 ). The output should contain something like link/ether 00:30:6E:08:EC:80 In the preceding example, a client with a network card having the MAC address 00:30:6E:08:EC:80 is assigned the IP address 192.168.2.100 and the host name jupiter automatically. The type of hardware to enter is ethernet in nearly all cases, although to- ken-ring , which is often found on IBM systems, is also supported. 40.3.2 The SUSE Linux Enterprise Server version To improve security, the SUSE Linux Enterprise Server version of the ISC''s DHCP server comes with the non-root/chroot patch by Ari Edelkind applied. This enables dhcpd to run with the user ID nobody and run in a chroot environment ( /var/lib/dhcp ). To make this possible, the configuration le dhcpd.conf must be located in /var/lib/dhcp/etc . The init script automatically copies the le to this directory when starting. Control the server''s behavior regarding this feature via entries in the le /etc/syscon- fig/dhcpd . To run dhcpd without the chroot environment, set the variable DHCPD_RUN_CH- ROOTED in /etc/sysconfig/dhcpd to “no”. To enable dhcpd to resolve host names even from within the chroot environment, the following configuration les must be copied as well: /etc/localtime /etc/host.conf 537 The SUSE Linux Enterprise Server version SLES 15 SP6/etc/hosts /var/run/netconfig/resolv.conf These les are copied to /var/lib/dhcp/etc/ when starting the init script. Take these copies into account for any changes that they require if they are dynamically modified by scripts like /etc/ppp/ip-up . However, there should be no need to worry about this if the configuration le only specifies IP addresses (instead of host names). If your configuration includes additional les that should be copied into the chroot environment, set these under the variable DHCPD_CONF_INCLUDE_FILES in the le /etc/sysconfig/dhcpd . To ensure that the DHCP logging facility keeps working even after a restart of the syslog dae- mon, there is an additional entry SYSLOGD_ADDITIONAL_SOCKET_DHCP in the le /etc/syscon- fig/syslog . 40.4 More information More information about DHCP is available at the Web site of the Internet Systems Consor- tium (https://www.isc.org/dhcp/ ). Information is also available in the dhcpd , dhcpd.conf , dhcpd.leases , and dhcp-options man pages. 538 More information SLES 15 SP641 SLP Configuring a network client requires detailed knowledge about services provided over the network (such as printing or LDAP, for example). To make it easier to con- figure such services on a network client, the “service location protocol” (SLP) was developed. SLP makes the availability and configuration data of selected services known to all clients in the local network. Applications that support SLP can use this information to be configured automatically. SUSE® Linux Enterprise Server supports installation using installation sources provided with SLP and contains many system services with integrated support for SLP. You can use SLP to provide networked clients with central functions, such as an installation server, le server, or print server on your system. Services that offer SLP support include cupsd, login, ntp, openl- dap2-client, postfix, rpasswd, rsyncd, saned, sshd (via sh), vnc, and ypserv. All packages necessary to use SLP services on a network client are installed by default. However, to provide services via SLP, check that the openslp-server package is installed. 41.1 The SLP front-end slptool slptool is a command line tool to query and register SLP services. The query functions are useful for diagnostic purposes. The most important slptool subcommands are listed below. slptool   --help lists all available options and functions. findsrvtypes List all service types available on the network. > slptool findsrvtypes service:install.suse:nfs service:install.suse:ftp service:install.suse:http service:install.suse:smb service:ssh service:fish service:YaST.installation.suse:vnc service:smtp service:domain service:management-software.IBM:hardware-management-console service:rsync 539 The SLP front-end slptool SLES 15 SP6service:ntp service:ypserv findsrvs SERVICE_TYPE List all servers providing SERVICE_TYPE > slptool findsrvs service:ntp service:ntp://ntp.example.com:123,57810 service:ntp://ntp2.example.com:123,57810 findattrs SERVICE_TYPE // HOST List attributes for SERVICE_TYPE on HOST > slptool findattrs service:ntp://ntp.example.com (owner=tux),(email=tux@example.com) register SERVICE type // HOST : PORT "( ATTRIBUTE=VALUE ),( ATTRIBUTE=VALUE )" Registers SERVICE_TYPE on HOST with an optional list of attributes slptool register service:ntp://ntp.example.com:57810 \ "(owner=tux),(email=tux@example.com)" deregister SERVICE_TYPE // host Deregisters SERVICE_TYPE on HOST slptool deregister service:ntp://ntp.example.com For more information run slptool --help . 41.2 Providing services via SLP To provide SLP services, the SLP daemon ( slpd ) must be running. Like most system services in SUSE Linux Enterprise Server, slpd is controlled by a separate start script. After the installation, the daemon is inactive by default. To activate it for the current session, run sudo systemctl start slpd . If slpd should be activated on system start-up, run sudo systemctl enable slpd . 540 Providing services via SLP SLES 15 SP6Many applications in SUSE Linux Enterprise Server have integrated SLP support via the libslp library. If a service has not been compiled with SLP support, use one of the following methods to make it available via SLP: Static registration with /etc/slp.reg.d Create a separate registration le for each new service. The following example registers a scanner service: ## Register a saned service on this system ## en means english language ## 65535 disables the timeout, so the service registration does ## not need refreshes service:scanner.sane://$HOSTNAME:6566,en,65535 watch-port-tcp=6566 description=SANE scanner daemon The most important line in this le is the service URL, which begins with service: . This contains the service type ( scanner.sane ) and the address under which the service is available on the server. $HOSTNAME is automatically replaced with the full host name. The name of the TCP port on which the relevant service can be found follows, separated by a colon. Then enter the language in which the service should appear and the duration of registration in seconds. These should be separated from the service URL by commas. Set the value for the duration of registration between 0 and 65535 . 0 prevents registration. 65535 removes all restrictions. The registration le also contains the two variables watch-port-tcp and description . watch-port-tcp links the SLP service announcement to whether the relevant service is active by having slpd check the status of the service. The second variable contains a more precise description of the service that is displayed in suitable browsers. Tip: YaST and SLP Specific services brokered by YaST, such as an installation server or YOU server, perform this registration automatically when you activate SLP in the module dialogs. YaST then creates registration les for these services. Static registration with /etc/slp.reg The only difference between this method and the procedure with /etc/slp.reg.d is that all services are grouped within a central le. 541 Providing services via SLP SLES 15 SP6Dynamic registration with slptool If a service needs to be registered dynamically without the need of configuration les, use the slptool command line utility. The same utility can also be used to deregister an existing service offering without restarting slpd . See Section 41.1, “The SLP front-end slptool” for details. 41.2.1 Setting up an SLP installation server Announcing the installation data via SLP within your network makes the network installation much easier, since the installation data such as IP address of the server or the path to the installation media are automatically required via SLP query. Refer to Book “Deployment Guide”, Chapter 17 “Setting up a network installation source” for instructions. 41.3 More information RFC 2608, 2609, 2610 RFC 2608 generally deals with the definition of SLP. RFC 2609 deals with the syntax of the service URLs used in greater detail and RFC 2610 deals with DHCP via SLP. http://www.openslp.org The home page of the OpenSLP project. /usr/share/doc/packages/openslp This directory contains the documentation for SLP coming with the openslp-server package, including a README.SUSE containing the SUSE Linux Enterprise Server details, the RFCs, and two introductory HTML documents. Programmers who want to use the SLP functions nd more information in the Programmers Guide that is included in the openslp- devel package that is provided with the SUSE Software Development Kit. 542 Setting up an SLP installation server SLES 15 SP642 The Apache HTTP server According to the surveys from https://www.netcraft.com/ and https://w3tech- s.com/ , the Apache HTTP Server (Apache) is one of the world''s most popular Web servers. Developed by the Apache Software Foundation (https://www.apache.org/ ), it is available for most operating systems. SUSE® Linux Enterprise Server includes Apache version 2.4. This chapter describes how to install, configure and operate Apache. It also shows how to use additional modules, such as SSL, and how to trou- bleshoot Apache. 42.1 Quick start This section helps you quickly configure and start Apache. You must be root to install and configure Apache. 42.1.1 Requirements Make sure the following requirements are met before trying to set up the Apache Web server: 1. The machine''s network is configured properly. For more information about this topic, refer to Chapter 23, Basic networking. 2. The machine''s exact system time is maintained by synchronizing with a time server. This is necessary because parts of the HTTP protocol depend on the correct time. See Chapter 38, Time synchronization with NTP to learn more about this topic. 3. The latest security updates are installed. If in doubt, run a YaST Online Update. 4. The default Web server port ( 80 ) is opened in the firewall. For this, configure firewalld to allow the service http in the public zone. See Book “Security and Hardening Guide”, Chap- ter 23 “Masquerading and firewalls”, Section 23.4.3 “Configuring the firewall on the command line” for details. 543 Quick start SLES 15 SP642.1.2 Installation Apache on SUSE Linux Enterprise Server is not installed by default. To install it with a standard, predefined configuration that runs “out of the box”, proceed as follows: PROCEDURE 42.1: INSTALLING APACHE WITH THE DEFAULT CONFIGURATION 1. Start YaST and select Software Software Management. 2. Choose Filter Patterns and select Web and LAMP Server. 3. Confirm the installation of the dependent packages to finish the installation process. 42.1.3 Start You can start Apache automatically at boot time or start it manually. To make sure that Apache is automatically started during boot in the targets multi-user.tar- get and graphical.target , execute the following command: > sudo systemctl enable apache2.service For more information about the systemd targets in SUSE Linux Enterprise Server and a descrip- tion of the YaST Services Manager, refer to Section 19.4, “Managing services with YaST”. To manually start Apache using the shell, run systemctl start apache2.service . PROCEDURE 42.2: CHECKING IF APACHE IS RUNNING If you do not receive error messages when starting Apache, this usually indicates that the Web server is running. To test this: 1. Start a browser and open http://localhost/ . If Apache is up and running, you get a test page stating “It works!”. 2. If you do not see this page, refer to Section 42.9, “Troubleshooting”. Now that the Web server is running, you can add your own documents, adjust the configuration according to your needs, or add functionality by installing modules. 544 Installation SLES 15 SP642.2 Configuring Apache SUSE Linux Enterprise Server offers two configuration options: Configuring Apache manually Configuring Apache with YaST Manual configuration offers a higher level of detail, but lacks the convenience of the YaST GUI. Important: Reload or restart Apache after configuration changes Most configuration changes require a reload or a restart of Apache to take effect. Manually reload Apache with systemctl reload apache2.service or use one of the restart options as described in Section 42.3, “Starting and stopping Apache”. If you configure Apache with YaST, this can be taken care of automatically if you set HTTP Service to Enabled as described in Section 42.2.3.2, “HTTP server configuration”. 42.2.1 Apache configuration files This section gives an overview of the Apache configuration les. If you use YaST for configura- tion, you do not need to touch these les—however, the information might be useful for you to switch to manual configuration later on. Apache configuration les can be found in two different locations: /etc/sysconfig/apache2 /etc/apache2/ 42.2.1.1 /etc/sysconfig/apache2 /etc/sysconfig/apache2 controls global Apache settings, like modules to load, additional configuration les to include, ags with which the server should be started, and ags that should be added to the command line. Every configuration option in this le is extensively documented and therefore not mentioned here. For a general-purpose Web server, the settings in /etc/ sysconfig/apache2 should be sufficient for any configuration needs. 545 Configuring Apache SLES 15 SP642.2.1.2 /etc/apache2/ /etc/apache2/ hosts all configuration les for Apache. In the following, the purpose of each le is explained. Each le includes several configuration options (also called directives). Every configuration option in these les is extensively documented and therefore not mentioned here. The Apache configuration les are organized as follows: /etc/apache2/ | |- charset.conv |- conf.d/ | | | |- *.conf | |- default-server.conf |- errors.conf |- global.conf |- httpd.conf |- listen.conf |- loadmodule.conf |- magic |- mime.types |- mod_*.conf |- protocols.conf |- server-tuning.conf |- ssl-global.conf |- ssl.* |- sysconfig.d | | | |- global.conf | |- include.conf | |- loadmodule.conf . . | |- uid.conf |- vhosts.d | |- *.conf APACHE CONFIGURATION FILES IN /ETC/APACHE2/ charset.conv Specifies which character sets to use for different languages. Do not edit this le. 546 Apache configuration files SLES 15 SP6conf.d/*.conf Configuration les added by other modules. These configuration les can be included into your virtual host configuration where needed. See vhosts.d/vhost.template for exam- ples. By doing so, you can provide different module sets for different virtual hosts. default-server.conf Global configuration for all virtual hosts with reasonable defaults. Instead of changing the values, overwrite them with a virtual host configuration. errors.conf Defines how Apache responds to errors. To customize these messages for all virtual hosts, edit this le. Otherwise overwrite these directives in your virtual host configurations. global.conf General configuration of the main Web server process, such as the access path, error logs, or the level of logging. httpd.conf The main Apache server configuration le. Avoid changing this le. It primarily contains include statements and global settings. Overwrite global settings in the pertinent configu- ration les listed here. Change host-specific settings (such as document root) in your vir- tual host configuration. listen.conf Binds Apache to specific IP addresses and ports. Name-based virtual hosting is also con- figured here. For details, see Section 42.2.2.1.1, “Name-based virtual hosts”. magic Data for the mime_magic module that helps Apache automatically determine the MIME type of an unknown le. Do not change this le. mime.types MIME types known by the system (this is a link to /etc/mime.types ). Do not edit this le. If you need to add MIME types not listed here, add them to mod_mime-defaults.conf . mod_*.conf Configuration les for the modules that are installed by default. Refer to Section 42.4, “In- stalling, activating and configuring modules” for details. Configuration les for optional mod- ules reside in the directory conf.d . 547 Apache configuration files SLES 15 SP6protocols.conf Configuration directives for serving pages over HTTP2 connection. server-tuning.conf Contains configuration directives for the different MPMs (see Section 42.4.4, “Multiprocessing modules”) and general configuration options that control Apache''s performance. Properly test your Web server when making changes here. ssl-global.conf and ssl.* Global SSL configuration and SSL certificate data. Refer to Section 42.6, “Setting up a secure Web server with SSL” for details. sysconfig.d/*.conf Configuration les automatically generated from /etc/sysconfig/apache2 . Do not change any of these les—edit /etc/sysconfig/apache2 instead. Do not put other con- figuration les in this directory. uid.conf Specifies under which user and group ID Apache runs. Do not change this le. vhosts.d/*.conf Your virtual host configuration should be located here. The directory contains template les for virtual hosts with and without SSL. Every le in this directory ending with .conf is automatically included in the Apache configuration. Refer to Section 42.2.2.1, “Virtual host configuration” for details. 42.2.2 Configuring Apache manually Configuring Apache manually involves editing plain text configuration les as user root . 42.2.2.1 Virtual host configuration The term virtual host refers to Apache''s ability to serve multiple universal resource identifiers (URIs) from the same physical machine. This means that several domains, such as www.exam- ple.com and www.example.net, are run by a single Web server on one physical machine. It is common practice to use virtual hosts to save administrative effort (only a single Web server needs to be maintained) and hardware expenses (each domain does not require a dedicated server). Virtual hosts can be name based, IP based, or port based. 548 Configuring Apache manually SLES 15 SP6To list all existing virtual hosts, use the command apache2ctl -S . This outputs a list showing the default server and all virtual hosts together with their IP addresses and listening ports. Furthermore, the list also contains an entry for each virtual host showing its location in the configuration les. Virtual hosts can be configured via YaST as described in Section 42.2.3.1.4, “Virtual hosts” or by manually editing a configuration le. By default, Apache in SUSE Linux Enterprise Server is prepared for one configuration le per virtual host in /etc/apache2/vhosts.d/ . All les in this directory with the extension .conf are automatically included to the configuration. A basic template for a virtual host is provided in this directory ( vhost.template or vhost- ssl.template for a virtual host with SSL support). Tip: Always create a virtual host configuration It is recommended to always create a virtual host configuration le, even if your Web server only hosts one domain. By doing so, you not only have the domain-specific con- figuration in one le, but you can always fall back to a working basic configuration by simply moving, deleting or renaming the configuration le for the virtual host. For the same reason, you should also create separate configuration les for each virtual host. When using name-based virtual hosts, it is recommended to set up a default configura- tion that is used when a domain name does not match a virtual host configuration. The default virtual host is the one whose configuration is loaded rst. Since the order of the configuration les is determined by le name, start the le name of the default virtual host configuration with an underscore character ( _ ) to make sure it is loaded rst (for example: _default_vhost.conf ). The block holds the information that applies to a particu- lar domain. When Apache receives a client request for a defined virtual host, it uses the di- rectives enclosed in this section. Almost all directives can be used in a virtual host context. See https://httpd.apache.org/docs/2.4/mod/quickreference.html for further information about Apache''s configuration directives. 549 Configuring Apache manually SLES 15 SP642.2.2.1.1 Name-based virtual hosts With name-based virtual hosts, more than one Web site is served per IP address. Apache uses the host eld in the HTTP header that is sent by the client to connect the request to a matching ServerName entry of one of the virtual host declarations. If no matching ServerName is found, the rst specified virtual host is used as a default. The rst step is to create a block for each different name-based host that you want to serve. Inside each block, you will need at minimum a ServerName directive to designate which host is served and a DocumentRoot directive to show where in the le system the content for that host resides. EXAMPLE 42.1: BASIC EXAMPLES OF NAME-BASED VirtualHost ENTRIES # This first-listed virtual host is also the default for *:80 ServerName www.example.com ServerAlias example.com DocumentRoot /srv/www/htdocs/domain ServerName other.example.com DocumentRoot /srv/www/htdocs/otherdomain The opening VirtualHost tag takes the IP address (or fully qualified domain name) as an argument in a name-based virtual host configuration. A port number directive is optional. The wild card * is also allowed as a substitute for the IP address. When using IPv6 addresses, the address must be included in square brackets. EXAMPLE 42.2: NAME-BASED VirtualHost DIRECTIVES ... ... ... 550 Configuring Apache manually SLES 15 SP6 ... ... 42.2.2.1.2 IP-based virtual hosts This alternative virtual host configuration requires the setup of multiple IP addresses for a ma- chine. One instance of Apache hosts several domains, each of which is assigned a different IP. The physical server must have one IP address for each IP-based virtual host. If the machine does not have multiple network cards, virtual network interfaces (IP aliasing) can also be used. The following example shows Apache running on a machine with the IP 192.168.3.100 , host- ing two domains on the additional IP addresses 192.168.3.101 and 192.168.3.102 . A sepa- rate VirtualHost block is needed for every virtual server. EXAMPLE 42.3: IP-BASED VirtualHost DIRECTIVES ... ... Here, VirtualHost directives are only specified for interfaces other than 192.168.3.100 . When a Listen directive is also configured for 192.168.3.100 , a separate IP-based virtual host must be created to answer HTTP requests to that interface—otherwise the directives found in the default server configuration ( /etc/apache2/default-server.conf ) are applied. 42.2.2.1.3 Basic virtual host configuration At least the following directives should be in each virtual host configuration to set up a virtual host. See /etc/apache2/vhosts.d/vhost.template for more options. 551 Configuring Apache manually SLES 15 SP6ServerName The fully qualified domain name under which the host should be addressed. DocumentRoot Path to the directory from which Apache should serve les for this host. For security rea- sons, access to the entire le system is forbidden by default, so you must explicitly unlock this directory within a Directory container. ServerAdmin E-mail address of the server administrator. This address is, for example, shown on error pages Apache creates. ErrorLog The error log le for this virtual host. Although it is not necessary to create separate error log les for each virtual host, it is common practice to do so, because it makes the debug- ging of errors much easier. /var/log/apache2/ is the default directory for Apache''s log les. CustomLog The access log le for this virtual host. Although it is not necessary to create separate access log les for each virtual host, it is common practice to do so, because it allows the separate analysis of access statistics for each host. /var/log/apache2/ is the default directory for Apache''s log les. As mentioned above, access to the whole le system is forbidden by default for security reasons. Therefore, explicitly unlock the directories in which you have placed the les Apache should serve, for example, the DocumentRoot : Require all granted Note: Require all granted In previous versions of Apache, the statement Require all granted was expressed as: Order allow,deny Allow from all This old syntax is still supported by the mod_access_compat module. 552 Configuring Apache manually SLES 15 SP6The complete configuration le looks like this: EXAMPLE 42.4: BASIC VirtualHost CONFIGURATION ServerName www.example.com DocumentRoot /srv/www/www.example.com/htdocs ServerAdmin webmaster@example.com ErrorLog /var/log/apache2/www.example.com_log CustomLog /var/log/apache2/www.example.com-access_log common Require all granted 42.2.3 Configuring Apache with YaST To configure your Web server with YaST, start YaST and select Network Services HTTP Server. When starting the module for the rst time, the HTTP Server Wizard starts, prompting you to make a few basic decisions concerning administration of the server. After having finished the wizard, the HTTP Server Configuration dialog starts each time you call the HTTP Server module. For more information, see Section 42.2.3.2, “HTTP server configuration”. 42.2.3.1 HTTP server wizard The HTTP Server Wizard consists of ve steps. In the last step of the dialog, you may enter the expert configuration mode to make even more specific settings. 42.2.3.1.1 Network device selection Here, specify the network interfaces and ports Apache uses to listen for incoming requests. You can select any combination of existing network interfaces and their respective IP addresses. Ports from all three ranges (well-known ports, registered ports, and dynamic or private ports) that are not reserved by other services can be used. The default setting is to listen on all network interfaces (IP addresses) on port 80 . 553 Configuring Apache with YaST SLES 15 SP6Check Open Port In Firewall to open the ports in the firewall that the Web server listens on. This is necessary to make the Web server available on the network, which can be a LAN, WAN, or the public Internet. Keeping the port closed is only useful in test situations where no external access to the Web server is necessary. If you have multiple network interfaces, click Firewall Details to specify on which interface(s) the port(s) should be opened. Click Next to continue with the configuration. 42.2.3.1.2 Modules The Modules configuration option allows for the activation or deactivation of the script languages that the Web server should support. For the activation or deactivation of other modules, refer to Section 42.2.3.2.2, “Server modules”. Click Next to advance to the next dialog. 42.2.3.1.3 Default host This option pertains to the default Web server. As explained in Section 42.2.2.1, “Virtual host con- figuration”, Apache can serve multiple virtual hosts from a single physical machine. The rst declared virtual host in the configuration le is commonly called the default host. Each virtual host inherits the default host''s configuration. To edit the host settings (also called directives), select the appropriate entry in the table then click Edit. To add new directives, click Add. To delete a directive, select it and click Delete. 554 Configuring Apache with YaST SLES 15 SP6FIGURE 42.1: HTTP SERVER WIZARD: DEFAULT HOST Here is list of the default settings of the server: Document Root Path to the directory from which Apache serves les for this host. /srv/www/htdocs is the default location. Alias Using Alias directives, URLs can be mapped to physical le system locations. This means that a certain path even outside the Document Root in the le system can be accessed via a URL aliasing that path. The default SUSE Linux Enterprise Server Alias /icons points to /usr/share/apache2/ icons for the Apache icons displayed in the directory index view. ScriptAlias Similar to the Alias directive, the ScriptAlias directive maps a URL to a le system location. The difference is that ScriptAlias designates the target directory as a CGI location, meaning that CGI scripts should be executed in that location. Directory With Directory settings, you can enclose a group of configuration options that will only apply to the specified directory. 555 Configuring Apache with YaST SLES 15 SP6Access and display options for the directories /srv/www/htdocs , /usr/share/apache2/ icons and /srv/www/cgi-bin are configured here. It should not be necessary to change the defaults. Include With include, additional configuration les can be specified. Two Include directives are already preconfigured: /etc/apache2/conf.d/ is the directory containing the configura- tion les that come with external modules. With this directive, all les in this directory end- ing in .conf are included. With the second directive, /etc/apache2/conf.d/apache2- manual.conf , the apache2-manual configuration le is included. Server Name This specifies the default URL used by clients to contact the Web server. Use a fully qualified domain name (FQDN) to reach the Web server at http://FQDN/ or its IP address. You cannot choose an arbitrary name here—the server must be “known” under this name. Server Administrator E-Mail E-mail address of the server administrator. This address is, for example, shown on error pages Apache creates. After finishing with the Default Host step, click Next to continue with the configuration. 42.2.3.1.4 Virtual hosts In this step, the wizard displays a list of already configured virtual hosts (see Section 42.2.2.1, “Virtual host configuration”). If you have not made manual changes prior to starting the YaST HTTP wizard, no virtual host is present. To add a host, click Add to open a dialog in which to enter basic information about the host, such as Server Name, Server Contents Root ( DocumentRoot ), and the Administrator E-Mail. Server Resolution is used to determine how a host is identified (name based or IP based). Specify the name or IP address with Change Virtual Host ID Clicking Next advances to the second part of the virtual host configuration dialog. In part two of the virtual host configuration you can specify whether to enable CGI scripts and which directory to use for these scripts. It is also possible to enable SSL. If you do so, you must specify the path to the certificate as well. See Section 42.6.2, “Configuring Apache with SSL” for details on SSL and certificates. With the Directory Index option, you can specify which le to display when the client requests a directory (by default, index.html ). Add one or more le 556 Configuring Apache with YaST SLES 15 SP6names (space-separated) to change this. With Enable Public HTML, the content of the users public directories ( ~USER/public_html/ ) is made available on the server under http://www.exam- ple.com/~USER . Important: Creating virtual hosts It is not possible to add virtual hosts at will. If using name-based virtual hosts, each host name must be resolved on the network. If using IP-based virtual hosts, you can assign only one host to each IP address available. 42.2.3.1.5 Summary This is the final step of the wizard. Here, determine how and when the Apache server is started: when booting or manually. Also see a short summary of the configuration made so far. If you are satisfied with your settings, click Finish to complete configuration. To change something, click Back until you have reached the desired dialog. Clicking HTTP Server Expert Configuration opens the dialog described in Section 42.2.3.2, “HTTP server configuration”. FIGURE 42.2: HTTP SERVER WIZARD: SUMMARY 557 Configuring Apache with YaST SLES 15 SP642.2.3.2 HTTP server configuration The HTTP Server Configuration dialog also lets you make even more adjustments to the config- uration than the wizard (which only runs if you configure your Web server for the rst time). It consists of four tabs described in the following. No configuration option you change here is effective immediately—you always must confirm your changes with Finish to make them effec- tive. Clicking Abort leaves the configuration module and discards your changes. 42.2.3.2.1 Listen ports and addresses In HTTP Service, select whether Apache should be running (Enabled) or stopped (Disabled). In Listen on Ports, Add, Edit, or Delete addresses and ports on which the server should be available. The default is to listen on all interfaces on port 80 . You should always check Open Port In Firewall, because otherwise the Web server is not reachable from outside. Keeping the port closed is only useful in test situations where no external access to the Web server is necessary. If you have multiple network interfaces, click Firewall Details to specify on which interface(s) the port(s) should be opened. With Log Files, watch either the access log le or the error log le. This is useful if you want to test your configuration. The log le opens in a separate window from which you can also restart or reload the Web server. For details, see Section 42.3, “Starting and stopping Apache”. These commands are effective immediately and their log messages are also displayed immediately. 558 Configuring Apache with YaST SLES 15 SP6FIGURE 42.3: HTTP SERVER CONFIGURATION: LISTEN PORTS AND ADDRESSES 42.2.3.2.2 Server modules You can change the status (enabled or disabled) of Apache2 modules by clicking Toggle Status. Click Add Module to add a new module that is already installed but not yet listed. Learn more about modules in Section 42.4, “Installing, activating and configuring modules”. 559 Configuring Apache with YaST SLES 15 SP6FIGURE 42.4: HTTP SERVER CONFIGURATION: SERVER MODULES 42.2.3.2.3 Main host or hosts These dialogs are identical to the ones already described. Refer to Section 42.2.3.1.3, “Default host” and Section 42.2.3.1.4, “Virtual hosts”. 42.3 Starting and stopping Apache If configured with YaST as described in Section 42.2.3, “Configuring Apache with YaST”, Apache is started at boot time in the multi-user.target and graphical.target . You can change this behavior using YaST''s Services Manager or with the systemctl command line tool ( systemctl enable or systemctl disable ). To start, stop or manipulate Apache on a running system, use either the systemctl or the apachectl commands as described below. For general information about systemctl commands, refer to Section 19.2.1, “Managing services in a running system”. systemctl status apache2.service Checks if Apache is started. 560 Starting and stopping Apache SLES 15 SP6systemctl start apache2.service Starts Apache if it is not already running. systemctl stop apache2.service Stops Apache by terminating the parent process. systemctl restart apache2.service Stops and then restarts Apache. Starts the Web server if it was not running before. systemctl try-restart apache2.service Stops then restarts Apache only if it is already running. systemctl reload apache2.service Stops the Web server by advising all forked Apache processes to rst finish their requests before shutting down. As each process dies, it is replaced by a newly started one, resulting in a complete “restart” of Apache. Tip: Restarting Apache in production environments This command allows activating changes in the Apache configuration without caus- ing connection break-os. systemctl stop apache2.service Stops the Web server after a defined period of time configured with GracefulShutdown- Timeout to ensure that existing requests can be finished. apachectl configtest Checks the syntax of the configuration les without affecting a running Web server. Be- cause this check is forced every time the server is started, reloaded or restarted, it is usually not necessary to run the test explicitly (if a configuration error is found, the Web server is not started, reloaded or restarted). apachectl status and apachectl fullstatus Dumps a short or full status screen, respectively. Requires the module mod_status to be enabled and a text-based browser (such as links or w3m ) to be installed. Besides that, STATUS must be added to APACHE_SERVER_FLAGS in the le /etc/sysconfig/apache2 . 561 Starting and stopping Apache SLES 15 SP6Tip: Additional flags If you specify additional ags to the commands, these are passed through to the Web server. 42.4 Installing, activating and configuring modules The Apache software is built in a modular fashion: all functionality except certain core tasks are handled by modules. This has progressed so far that even HTTP is processed by a module ( http_core ). Apache modules can be compiled into the Apache binary at build time or be dynamically loaded at runtime. Refer to Section 42.4.2, “Activation and deactivation” for details of how to load modules dynamically. Apache modules are organized into the following categories: Base modules Base modules are compiled into Apache by default. Apache in SUSE Linux Enterprise Server has only mod_so (needed to load other modules) and http_core compiled in. All others are available as shared objects: rather than being included in the server binary itself, they can be included at runtime. Extension modules Modules labeled as extensions are included in the Apache software package, but are usually not compiled into the server statically. In SUSE Linux Enterprise Server, they are available as shared objects that can be loaded into Apache at runtime. External modules Modules labeled external are not included in the official Apache distribution. However, SUSE Linux Enterprise Server provides several of them. Multiprocessing modules (MPMs) MPMs are responsible for accepting and handling requests to the Web server, representing the core of the Web server software. 562 Installing, activating and configuring modules SLES 15 SP642.4.1 Module installation If you have done a default installation as described in Section 42.1.2, “Installation”, the following modules are already installed: all base and extension modules, the multiprocessing module Pre- fork MPM, and the external module mod_python . You can install additional external modules by starting YaST and choosing Software Software Management. Now choose View Search and search for apache . Among other packages, the results list contains all available external Apache modules. 42.4.2 Activation and deactivation Activate or deactivate particular modules either manually or with YaST. In YaST, script language modules (PHP 8 and Python) need to be enabled or disabled with the module configuration described in Section 42.2.3.1, “HTTP server wizard”. All other modules can be enabled or disabled as described in Section 42.2.3.2.2, “Server modules”. If you prefer to activate or deactivate the modules manually, use the commands a2enmod MOD- ULE or a2dismod MODULE , respectively. a2enmod -l outputs a list of all currently active mod- ules. Important: Including configuration files for external modules If you have activated external modules manually, make sure to load their configuration les in all virtual host configurations. Configuration les for external modules are lo- cated under /etc/apache2/conf.d/ and are loaded in /etc/apache2/default-serv- er.conf by default. For more ne-grained control you can comment out the inclusion in /etc/apache2/default-server.conf and add it to specific virtual hosts only. See / etc/apache2/vhosts.d/vhost.template for examples. 42.4.3 Base and extension modules All base and extension modules are described in detail in the Apache documentation. Only a brief description of the most important modules is available here. Refer to http://httpd.a- pache.org/docs/2.4/mod/ (https://httpd.apache.org/docs/2.4/mod/) to learn details about each module. 563 Module installation SLES 15 SP6mod_actions Provides methods to execute a script whenever a certain MIME type (such as applica- tion/pdf ), a le with a specific extension (like .rpm ), or a certain request method (such as GET ) is requested. This module is enabled by default. mod_alias Provides Alias and Redirect directives with which you can map a URL to a specific directory ( Alias ) or redirect a requested URL to another location. This module is enabled by default. mod_auth* The authentication modules provide different authentication methods: basic authentica- tion with mod_auth_basic or digest authentication with mod_auth_digest . mod_auth_basic and mod_auth_digest must be combined with an authentication provider module, mod_authn_* (for example, mod_authn_file for text le–based au- thentication) and with an authorization module mod_authz_* (for example, mod_au- thz_user for user authorization). More information about this topic is available in the Authentication HOWTO at https:// httpd.apache.org/docs/2.4/howto/auth.html . mod_auth_openidc mod_auth_openidc the only certified way to use OpenID Connect with the Apache HTTP server. (See https://openid.net/developers/certified-openid-connect-implementations/ .) mod_autoindex Autoindex generates directory listings when no index le (for example, index.html ) is present. The look and feel of these indexes is configurable. This module is enabled by default. However, directory listings are disabled by default via the Options directive— overwrite this setting in your virtual host configuration. The default configuration le for this module is located at /etc/apache2/mod_autoindex-defaults.conf . mod_cgi mod_cgi is needed to execute CGI scripts. This module is enabled by default. mod_deflate Using this module, Apache can be configured to compress given le types on the y before delivering them. 564 Base and extension modules SLES 15 SP6mod_dir mod_dir provides the DirectoryIndex directive with which you can configure which les are automatically delivered when a directory is requested ( index.html by default). It also provides an automatic redirect to the correct URL when a directory request does not contain a trailing slash. This module is enabled by default. mod_env Controls the environment that is passed to CGI scripts or SSI pages. Environment variables can be set or unset or passed from the shell that invoked the httpd process. This module is enabled by default. mod_expires With mod_expires , you can control how often proxy and browser caches refresh your documents by sending an Expires header. This module is enabled by default. mod_http2 With mod_http2 , Apache gains support for the HTTP/2 protocol. It can be enabled by specifying Protocols h2 http/1.1 in a VirtualHost . mod_include mod_include lets you use Server Side Includes (SSI), which provide a basic functionality to generate HTML pages dynamically. This module is enabled by default. mod_info Provides a comprehensive overview of the server configuration under http://local- host/server-info/. For security reasons, you should always limit access to this URL. By default only localhost is allowed to access this URL. mod_info is configured at /etc/ apache2/mod_info.conf . mod_log_config With this module, you can configure the look of the Apache log les. This module is enabled by default. mod_mime The mime module ensures that a le is delivered with the correct MIME header based on the le name''s extension (for example text/html for HTML documents). This module is enabled by default. 565 Base and extension modules SLES 15 SP6mod_negotiation Necessary for content negotiation. See http://httpd.apache.org/docs/2.4/content-negotia- tion.html (https://httpd.apache.org/docs/2.4/content-negotiation.html) for more informa- tion. This module is enabled by default. mod_rewrite Provides the functionality of mod_alias , but offers more features and flexibility. With mod_rewrite , you can redirect URLs based on multiple rules, request headers, and more. mod_setenvif Sets environment variables based on details of the client''s request, such as the browser string the client sends, or the client''s IP address. This module is enabled by default. mod_spelling mod_spelling attempts to automatically correct typographical errors in URLs, such as capitalization errors. mod_ssl Enables encrypted connections between Web server and clients. See Section 42.6, “Setting up a secure Web server with SSL” for details. This module is enabled by default. mod_status Provides information on server activity and performance under http://localhost/serv- er-status/. For security reasons, you should always limit access to this URL. By default, only localhost is allowed to access this URL. mod_status is configured at /etc/apache2/ mod_status.conf . mod_suexec mod_suexec lets you run CGI scripts under a different user and group. This module is enabled by default. mod_userdir Enables user-specific directories available under ~USER/ . The UserDir directive must be specified in the configuration. This module is enabled by default. 566 Base and extension modules SLES 15 SP642.4.4 Multiprocessing modules SUSE Linux Enterprise Server provides two different multiprocessing modules (MPMs) for use with Apache: Prefork MPM Worker MPM 42.4.4.1 Prefork MPM The prefork MPM implements a non-threaded, preforking Web server. It makes the Web server behave similarly to Apache version 1.x. In this version it isolates each request and handles it by forking a separate child process. Thus problematic requests cannot affect others, avoiding a lockup of the Web server. While providing stability with this process-based approach, the prefork MPM consumes more system resources than its counterpart, the worker MPM. The prefork MPM is considered the default MPM for Unix-based operating systems. Important: MPMs in this document This document assumes Apache is used with the prefork MPM. 42.4.4.2 Worker MPM The worker MPM provides a multi-threaded Web server. A thread is a “lighter” form of a process. The advantage of a thread over a process is its lower resource consumption. Instead of only forking child processes, the worker MPM serves requests by using threads with server processes. The preforked child processes are multi-threaded. This approach makes Apache perform better by consuming fewer system resources than the prefork MPM. One major disadvantage is the stability of the worker MPM: if a thread becomes corrupt, all threads of a process can be affected. In the worst case, this may result in a server crash. Especially when using the Common Gateway Interface (CGI) with Apache under heavy load, internal server errors might occur because of threads being unable to communicate with system resources. Another argument against using the worker MPM with Apache is that not all available Apache modules are thread-safe and thus cannot be used with the worker MPM. 567 Multiprocessing modules SLES 15 SP6Warning: Using PHP modules with MPMs Not all available PHP modules are thread-safe. Using the worker MPM with mod_php is strongly discouraged. 42.4.5 External modules Find a list of all external modules shipped with SUSE Linux Enterprise Server here. Find the module''s documentation in the listed directory. mod_apparmor Adds support to Apache to provide AppArmor confinement to individual CGI scripts han- dled by modules like mod_php8 . Package Name: apache2-mod_apparmor More Information: Book “Security and Hardening Guide” mod_php8 PHP is a server-side, cross-platform HTML embedded scripting language. Package Name: apache2-mod_php8 Configuration File: /etc/apache2/conf.d/php8.conf mod_python mod_python allows embedding Python within the Apache HTTP server for a considerable boost in performance and added flexibility in designing Web-based applications. Package Name: apache2-mod_python More Information: /usr/share/doc/packages/apache2-mod_python mod_security mod_security provides a Web application firewall to protect Web applications from a range of attacks. It also enables HTTP traffic monitoring and real-time analysis. Package Name: apache2-mod_security2 Configuration File: /etc/apache2/conf.d/mod_security2.conf More Information: /usr/share/doc/packages/apache2-mod_security2 Documentation: https://github.com/owasp-modsecurity/ModSecurity 568 External modules SLES 15 SP642.4.6 Compilation Apache can be extended by advanced users by writing custom modules. To develop modules for Apache or compile third-party modules, the package apache2-devel is required along with the corresponding development tools. apache2-devel also contains the apxs2 tools, which are necessary for compiling additional modules for Apache. apxs2 enables the compilation and installation of modules from source code (including the required changes to the configuration les), which creates dynamic shared objects (DSOs) that can be loaded into Apache at runtime. The apxs2 binaries are located under /usr/sbin : /usr/sbin/apxs2—suitable for building an extension module that works with any MPM. The installation location is /usr/lib64/apache2 . /usr/sbin/apxs2-prefork—suitable for prefork MPM modules. The installation loca- tion is /usr/lib64/apache2-prefork . /usr/sbin/apxs2-worker—suitable for worker MPM modules. The installation location is /usr/lib64/apache2-worker . Install and activate a module from source code with the following commands: > sudo cd /path/to/module/source > sudo apxs2 -cia MODULE.c where -c compiles the module, -i installs it, and -a activates it. Other options of apxs2 are described in the apxs2(1) man page. 42.5 Enabling CGI scripts Apache''s Common Gateway Interface (CGI) lets you create dynamic content with programs or scripts (CGI scripts). CGI scripts can be written in any programming language. To enable Apache to deliver content created by CGI scripts, mod_cgi needs to be activated. mod_alias is also needed. Both modules are enabled by default. Refer to Section 42.4.2, “Activation and deactivation” for details on activating modules. 569 Compilation SLES 15 SP6Warning: CGI security Allowing the server to execute CGI scripts is a potential security hole. Refer to Section 42.8, “Avoiding security problems” for additional information. 42.5.1 Apache configuration In SUSE Linux Enterprise Server, the execution of CGI scripts is only allowed in the directory /srv/www/cgi-bin/ . This location is already configured to execute CGI scripts. If you have created a virtual host configuration (see Section 42.2.2.1, “Virtual host configuration”) and want to place your scripts in a host-specific directory, you must unlock and configure this directory. EXAMPLE 42.5: VIRTUALHOST CGI CONFIGURATION ScriptAlias /cgi-bin/ "/srv/www/www.example.com/cgi-bin/" 1 Options +ExecCGI 2 AddHandler cgi-script .cgi .pl 3 Require all granted 4 1 Tells Apache to handle all les within this directory as CGI scripts. 2 Enables CGI script execution 3 Tells the server to treat les with the extensions .pl and .cgi as CGI scripts. Adjust according to your needs. 4 The Require directive controls the default access state. In this case, access is granted to the specified directory without limitation. For more information on authentication and authorization, see https://httpd.apache.org/docs/2.4/howto/auth.html . 42.5.2 Running an example script CGI programming differs from “regular” programming in that the CGI programs and scripts must be preceded by a MIME-Type header such as Content-type: text/html . This header is sent to the client, so it understands what kind of content it receives. Secondly, the script''s output must be something the client, usually a Web browser, understands—HTML or plain text or images, for example. 570 Apache configuration SLES 15 SP6A simple test script available under /usr/share/doc/packages/apache2/test-cgi is part of the Apache package. It outputs the content of certain environment variables as plain text. Copy this script to either /srv/www/cgi-bin/ or the script directory of your virtual host ( /srv/ www/www.example.com/cgi-bin/ ) and name it test.cgi . Edit the le to have #!/bin/sh as the rst line. Files accessible by the Web server should be owned by the user root . For additional information see Section 42.8, “Avoiding security problems”. Because the Web server runs with a different user, the CGI scripts must be world-executable and world-readable. Change into the CGI directory and use the command chmod 755 test.cgi to apply the proper permissions. Now call http://localhost/cgi-bin/test.cgi or http://www.example.com/cgi-bin/ test.cgi . You should see the “CGI/1.0 test script report”. 42.5.3 CGI troubleshooting If you do not see the output of the test program but an error message instead, check the following: CGI TROUBLESHOOTING Have you reloaded the server after having changed the configuration? If not, reload with sys- temctl reload apache2.service . If you have configured your custom CGI directory, is it configured properly? If in doubt, try the script within the default CGI directory /srv/www/cgi-bin/ and call it with http:// localhost/cgi-bin/test.cgi . Are the le permissions correct? Change into the CGI directory and execute ls -l test.cgi . The output should start with -rwxr-xr-x 1 root root Make sure that the script does not contain programming errors. If you have not changed test.cgi , this should not be the case, but if you are using your own programs, always make sure that they do not contain programming errors. 571 CGI troubleshooting SLES 15 SP642.6 Setting up a secure Web server with SSL Whenever sensitive data, such as credit card information, is transferred between Web server and client, it is desirable to have a secure, encrypted connection with authentication. mod_ssl provides strong encryption using the secure sockets layer (SSL) and transport layer security (TLS) protocols for HTTP communication between a client and the Web server. Using TLS/SSL, a private connection between Web server and client is established. Data integrity is ensured and client and server can authenticate each other. For this purpose, the server sends an SSL certificate that holds information proving the server''s valid identity before any request to a URL is answered. In turn, this guarantees that the server is the uniquely correct end point for the communication. Additionally, the certificate generates an encrypted connection between client and server that can transport information without the risk of exposing sensitive, plain-text content. mod_ssl does not implement the TLS/SSL protocols itself, but acts as an interface between Apache and an SSL library. In SUSE Linux Enterprise Server, the OpenSSL library is used. OpenSSL is automatically installed with Apache. The most visible effect of using mod_ssl with Apache is that URLs are prefixed with https:// instead of http:// . 42.6.1 Creating an SSL certificate To use TLS/SSL with the Web server, you need to create an SSL certificate. This certificate is needed for the authorization between Web server and client, so that each party can identify the other party. To ensure the integrity of the certificate, it must be signed by a party every user trusts. There are three types of certificates you can create: a “test” certificate for testing purposes only, a self-signed certificate for a defined circle of users that trust you, and a certificate signed by an independent, publicly known certificate authority (CA). Creating a certificate is a two step process. First, a private key for the certificate authority is generated then the server certificate is signed with this key. Tip: More information To learn more about concepts and definitions of TLS/SSL, refer to https://httpd.a- pache.org/docs/2.4/ssl/ssl_intro.html . 572 Setting up a secure Web server with SSL SLES 15 SP642.6.1.1 Creating a “test” certificate To generate a test certificate, call the script /usr/bin/gensslcert . It creates or overwrites the les listed below. Use gensslcert ''s optional switches to ne-tune the certificate. Call /usr/ bin/gensslcert -h for more information. /etc/apache2/ssl.crt/ca.crt /etc/apache2/ssl.crt/server.crt /etc/apache2/ssl.key/server.key /etc/apache2/ssl.csr/server.csr A copy of ca.crt is also placed at /srv/www/htdocs/CA.crt for download. Important: For testing purposes only A test certificate should never be used on a production system. Only use it for testing purposes. 42.6.1.2 Creating a self-signed certificate If you are setting up a secure Web server for an intranet or for a defined circle of users, it is sufficient to sign a certificate with your own certificate authority (CA). Visitors to such a site will see a warning like “this is an untrusted site”, as Web browsers do not recognize self-signed certificates. Important: Self-signed certificates Only use a self-signed certificate on a Web server that is accessed by people who know and trust you as a certificate authority. It is not recommended to use such a certificate for a public shop, for example. First you need to generate a certificate signing request (CSR). You are going to use openssl , with PEM as the certificate format. During this step, you will be asked for a passphrase, and to answer several questions. Remember the passphrase you enter as you will need it in the future. > sudo openssl req -new > new.cert.csr Generating a 1024 bit RSA private key ..++++++ 573 Creating an SSL certificate SLES 15 SP6.........++++++ writing new private key to ''privkey.pem'' Enter PEM pass phrase: 1 Verifying - Enter PEM pass phrase: 2 ----- You are about to be asked to enter information that will be incorporated into your certificate request. What you are about to enter is what is called a Distinguished Name or a DN. There are quite a few fields but you can leave some blank For some fields there will be a default value, If you enter ''.'', the field will be left blank. ----- Country Name (2 letter code) [AU]: 3 State or Province Name (full name) [Some-State]: 4 Locality Name (eg, city) []: 5 Organization Name (eg, company) [Internet Widgits Pty Ltd]: 6 Organizational Unit Name (eg, section) []: 7 Common Name (for example server FQDN, or YOUR name) []: 8 Email Address []: 9 Please enter the following ''extra'' attributes to be sent with your certificate request A challenge password []: 10 An optional company name []: 11 1 Fill in your passphrase. 2 Fill it in once more (and remember it). 3 Fill in your 2 letter country code, such as GB or CZ . 4 Fill in the name of the state where you live. 5 Fill in the city name, such as Prague . 6 Fill in the name of the organization you work for. 7 Fill in your organization unit, or leave blank if you have none. 8 Fill in either the domain name of the server, or your rst and last name. 9 Fill in your work e-mail address. 10 Leave the challenge password empty, otherwise you need to enter it every time you restart the Apache Web server. 11 Fill in the optional company name, or leave blank. Now you can generate the certificate. You are going to use openssl again, and the format of the certificate is the default PEM . 574 Creating an SSL certificate SLES 15 SP6PROCEDURE 42.3: GENERATING THE CERTIFICATE 1. Export the private part of the key to new.cert.key . You will be prompted for the passphrase you entered when creating the certificate signing request (CSR). > sudo openssl rsa -in privkey.pem -out new.cert.key 2. Generate the public part of the certificate according to the information you lled out in the signing request. The -days option specifies the length of time before the certificate expires. You can revoke a certificate, or replace one before it expires. > sudo openssl x509 -in new.cert.csr -out new.cert.cert -req \ -signkey new.cert.key -days 365 3. Copy the certificate les to the relevant directories, so that the Apache server can read them. Make sure that the private key /etc/apache2/ssl.key/server.key is not world- readable, while the public PEM certificate /etc/apache2/ssl.crt/server.crt is. > sudo cp new.cert.cert /etc/apache2/ssl.crt/server.crt > sudo cp new.cert.key /etc/apache2/ssl.key/server.key Tip: Public certificate location The last step is to copy the public certificate le from /etc/apache2/ssl.crt/serv- er.crt to a location where your users can access it to incorporate it into the list of known and trusted CAs in their Web browsers. Otherwise a browser complains that the certificate was issued by an unknown authority. 42.6.1.3 Getting an officially signed certificate There are several official certificate authorities that sign your certificates. The certificate is signed by a trustworthy third party, so can be fully trusted. Publicly operating secure Web servers usually have an officially signed certificate. A list of the most used Certificate Authorities (CAs) is available at https://en.wikipedia.org/wiki/Certificate_authority#Providers . When requesting an officially signed certificate, you do not send a certificate to the CA. Instead, issue a Certificate Signing Request (CSR). To create a CSR, run the following command: > openssl req -new -newkey rsa:2048 -nodes -keyout newkey.pem -out newreq.pem 575 Creating an SSL certificate SLES 15 SP6You are asked to enter a distinguished name. This requires you to answer a few questions, such as country name or organization name. Enter valid data—everything you enter here later shows up in the certificate and is checked. You do not need to answer every question. If one does not apply to you or you want to leave it blank, use “.”. Common name is the name of the CA itself—choose a significant name, such as My company CA. Last, a challenge password and an alternative company name must be entered. Find the CSR in the directory from which you called the script. The le is named newreq.pem . 42.6.2 Configuring Apache with SSL The default port for TLS/SSL requests on the Web server side is 443. There is no conflict between a “regular” Apache listening on port 80 and an TLS/SSL-enabled Apache listening on port 443. In fact, HTTP and HTTPS can be run with the same Apache instance. Usually separate virtual hosts are used to dispatch requests to port 80 and port 443 to separate virtual servers. Important: Firewall configuration Do not forget to open the firewall for SSL-enabled Apache on port 443. This can be done with firewalld as described in Book “Security and Hardening Guide”, Chapter 23 “Masquerad- ing and firewalls”, Section 23.4.3 “Configuring the firewall on the command line”. The SSL module is enabled by default in the global server configuration. In case it has been disabled on your host, activate it with the following command: a2enmod ssl . To finally enable SSL, the server needs to be started with the ag “SSL”. To do so, call a2enflag SSL (case- sensitive!). If you have chosen to encrypt your server certificate with a password, you should also increase the value for APACHE_TIMEOUT in /etc/sysconfig/apache2 , so you have enough time to enter the passphrase when Apache starts. Restart the server to make these changes active. A reload is not sufficient. The virtual host configuration directory contains a template /etc/apache2/vhosts.d/vhost- ssl.template with SSL-specific directives that are extensively documented. Refer to Sec- tion 42.2.2.1, “Virtual host configuration” for the general virtual host configuration. 576 Configuring Apache with SSL SLES 15 SP6To get started, copy the template to /etc/apache2/vhosts.d/MYSSL-HOST.conf and edit it. Adjusting the values for the following directives should be sufficient: DocumentRoot ServerName ServerAdmin ErrorLog TransferLog 42.6.2.1 Name-based virtual hosts and SSL By default it is not possible to run multiple SSL-enabled virtual hosts on a server with only one IP address. Name-based virtual hosting requires that Apache knows which server name has been requested. The problem with SSL connections is, that such a request can only be read after the SSL connection has already been established (by using the default virtual host). As a result, users will receive a warning message stating that the certificate does not match the server name. SUSE Linux Enterprise Server comes with an extension to the SSL protocol called Server Name Indication (SNI) addresses this issue by sending the name of the virtual domain as part of the SSL negotiation. This enables the server to “switch” to the correct virtual domain early and present the browser the correct certificate. SNI is enabled by default on SUSE Linux Enterprise Server. To enable Name-Based Virtual Hosts for SSL, configure the server as described in Section 42.2.2.1.1, “Name-based virtual hosts” (you need to use port 443 rather than port 80 with SSL). Important: SNI browser support SNI must also be supported on the client side. However, SNI is supported by most browsers, except for certain older browsers. For more information, see https://en.wikipedi- a.org/wiki/Server_Name_Indication#Support . To configure handling of non-SNI capable browsers, use the directive SSLStric- tSNIVHostCheck . When set to on in the server configuration, non-SNI capable browser will be rejected for all virtual hosts. When set to on within a VirtualHost directive, access to this particular host will be rejected. 577 Configuring Apache with SSL SLES 15 SP6When set to off in the server configuration, the server will behave as if not having SNI support. SSL requests will be handled by the rst virtual host defined (for port 443). 42.7 Running multiple Apache instances on the same server Running multiple Apache instances on the same server has several advantages over running multiple virtual hosts (see Section 42.2.2.1, “Virtual host configuration”): When a virtual host needs to be disabled for a period of time, you need to change the Web server configuration and restart it so that the change takes effect. In case of problems with one virtual host, you need to restart them all. You can run the default Apache instance as usual: > sudo systemctl start apache2.service It reads the default /etc/sysconfig/apache2 le. If the le is not present, or it is present but it does not set the APACHE_HTTPD_CONF variable, it reads /etc/apache2/httpd.conf . To activate another Apache instance, run: > sudo systemctl start apache2@INSTANCE_NAME For example: > sudo systemctl start apache2@example_web.org By default, the instance uses /etc/apache2@example_web.org/httpd.conf as a main con- figuration le, which can be overwritten by setting APACHE_HTTPD_CONF in /etc/syscon- fig/apache2@example_web.org . An example to set up an additional instance of Apache follows. You need to execute all the commands as root . 578 Running multiple Apache instances on the same server SLES 15 SP6PROCEDURE 42.4: CONFIGURING AN ADDITIONAL APACHE INSTANCE 1. Create a new configuration le based on /etc/sysconfig/apache2 , for example /etc/ sysconfig/apache2@example_web.org : > sudo cp /etc/sysconfig/apache2 /etc/sysconfig/apache2@example_web.org 2. Edit the le /etc/sysconfig/apache2@example_web.org and change the line contain- ing APACHE_HTTPD_CONF to APACHE_HTTPD_CONF="/etc/apache2/httpd@example_web.org.conf" 3. Create the le /etc/apache2/httpd@example_web.org.conf based on /etc/apache2/ httpd.conf . > sudo cp /etc/apache2/httpd.conf /etc/apache2/httpd@example_web.org.conf 4. Edit /etc/apache2/httpd@example_web.org.conf and change Include /etc/apache2/listen.conf to Include /etc/apache2/listen@example_web.org.conf Review all the directives and change them to t your needs. You may want to change Include /etc/apache2/global.conf and create new global@example_web.org.conf for each instance. We suggest to change ErrorLog /var/log/apache2/error_log to ErrorLog /var/log/apache2/error@example_web.org_log to have separate logs for each instance. 5. Create /etc/apache2/listen@example_web.org.conf based on /etc/apache2/lis- ten.conf . 579 Running multiple Apache instances on the same server SLES 15 SP6> sudo cp /etc/apache2/listen.conf /etc/apache2/listen@example_web.org.conf 6. Edit /etc/apache2/listen@example_web.org.conf and change Listen 80 to the port number you want the new instance to run on, for example, 82: Listen 82 To run the new Apache instance over a secured protocol (see Section 42.6, “Setting up a secure Web server with SSL”), change also the line Listen 443 for example, to Listen 445 7. Start the new Apache instance: > sudo systemctl start apache2@example_web.org 8. Check if the server is running by pointing your Web browser at http://server_name:82 . If you previously changed the name of the error log le for the new instance, you can check it: > sudo tail -f /var/log/apache2/error@example_web.org_log Here are several points to consider when setting up more Apache instances on the same server: The le /etc/sysconfig/apache2@INSTANCE_NAME can include the same variables as / etc/sysconfig/apache2 , including module loading and MPM setting. The default Apache instance does not need to be running while other instances run. The Apache helper utilities a2enmod , a2dismod and apachectl operate on the default Apache instance if not specified otherwise with the HTTPD_INSTANCE environment vari- able. The following example > sudo export HTTPD_INSTANCE=example_web.org > sudo a2enmod access_compat > sudo a2enmod status 580 Running multiple Apache instances on the same server SLES 15 SP6> sudo apachectl start will add access_compat and status modules to the APACHE_MODULES variable of /etc/ sysconfig/apache2@example_web.org , and then start the example_web.org instance. 42.8 Avoiding security problems A Web server exposed to the public Internet requires an ongoing administrative effort. It is in- evitable that security issues appear, both related to the software and to accidental misconfigu- ration. Here are several tips for how to deal with them. 42.8.1 Up-to-date software If there are vulnerabilities found in the Apache software, a security advisory will be issued by SUSE. It contains instructions for fixing the vulnerabilities, which in turn should be applied when possible. The SUSE security announcements are available from the following locations: Web page.  https://www.suse.com/support/security/ Mailing list archive.  https://lists.opensuse.org/archives/list/security-announce@lists.open- suse.org/ List of security announcements.  https://www.suse.com/support/update/ 42.8.2 DocumentRoot permissions By default in SUSE Linux Enterprise Server, the DocumentRoot directory /srv/www/htdocs and the CGI directory /srv/www/cgi-bin belong to the user and group root . You should not change these permissions. If the directories are writable for all, any user can place les into them. These les might then be executed by Apache with the permissions of wwwrun , which may give the user unintended access to le system resources. Use subdirectories of /srv/www to place the DocumentRoot and CGI directories for your virtual hosts and make sure that directories and les belong to user and group root . 581 Avoiding security problems SLES 15 SP642.8.3 File system access By default, access to the whole le system is denied in /etc/apache2/httpd.conf . You should never overwrite these directives, but specifically enable access to all directories Apache should be able to read. For details, see Section 42.2.2.1.3, “Basic virtual host configuration”. In doing so, ensure that no critical les, such as password or system configuration les, can be read from the outside. 42.8.4 CGI scripts Interactive scripts in PHP, SSI or any other programming language can run arbitrary commands and therefore present a general security issue. Scripts that will be executed from the server should only be installed from sources the server administrator trusts—allowing users to run their own scripts is generally not a good idea. It is also recommended to do security audits for all scripts. To make the administration of scripts as easy as possible, it is common practice to limit the execution of CGI scripts to specific directories instead of globally allowing them. The directives ScriptAlias and Option ExecCGI are used for configuration. The SUSE Linux Enterprise Server default configuration does not allow execution of CGI scripts from everywhere. All CGI scripts run as the same user, so different scripts can potentially conflict with each other. The module suEXEC lets you run CGI scripts under a different user and group. 42.8.5 User directories When enabling user directories (with mod_userdir or mod_rewrite ) you should strongly con- sider not allowing .htaccess les, which would allow users to overwrite security settings. At least you should limit the user''s engagement by using the directive AllowOverRide . In SUSE Linux Enterprise Server, .htaccess les are enabled by default, but the user is not al- lowed to overwrite any Option directives when using mod_userdir (see the /etc/apache2/ mod_userdir.conf configuration le). 582 File system access SLES 15 SP642.9 Troubleshooting If Apache does not start, the Web page is not accessible, or users cannot connect to the Web server, it is important to nd the cause of the problem. Here are typical places to look for error explanations and important things to check: Output of the apache2.service subcommand: Instead of starting and stopping the Web server with the binary /usr/sbin/apache2ctl , rather use the systemctl commands instead (described in Section 42.3, “Starting and stop- ping Apache”). systemctl status apache2.service is verbose about errors, and it even provides tips and hints for fixing configuration errors. Log files and verbosity In case of both fatal and nonfatal errors, check the Apache log les for causes, mainly the error log le located at /var/log/apache2/error_log by default. Additionally, you can control the verbosity of the logged messages with the LogLevel directive if more detail is needed in the log les. Tip: A simple test Watch the Apache log messages with the command tail -F /var/log/ apache2/MY_ERROR_LOG . Then run systemctl restart apache2.service . Now, try to connect with a browser and check the output. Firewall and ports A common mistake is to not open the ports for Apache in the firewall configuration of the server. If you configure Apache with YaST, there is a separate option available to take care of this specific issue (see Section 42.2.3, “Configuring Apache with YaST”). If you are configuring Apache manually, open firewall ports for HTTP and HTTPS via YaST''s firewall module. If the error cannot be tracked down with any of these, check the online Apache bug database at https://httpd.apache.org/bug_report.html . Additionally, the Apache user community can be reached via a mailing list available at https://httpd.apache.org/userslist.html . 583 Troubleshooting SLES 15 SP642.10 More information The package apache2-doc contains the complete Apache manual in multiple localizations for local installation and reference. It is not installed by default—the quickest way to install it is to use the command zypper in apache2-doc . Having been installed, the Apache manual is available at http://localhost/manual/ . You may also access it on the Web at https://httpd.a- pache.org/docs/2.4/ . SUSE-specific configuration hints are available in the directory /usr/ share/doc/packages/apache2/README.* . 42.10.1 Apache 2.4 For a list of new features in Apache 2.4, refer to https://httpd.apache.org/docs/2.4/new_fea- tures_2_4.html . Information about upgrading from version 2.2 to 2.4 is available at https:// httpd.apache.org/docs/2.4/upgrading.html . 42.10.2 Apache modules More information about external Apache modules that are briey described in Section 42.4.5, “External modules” is available at the following locations: mod_apparmor https://en.opensuse.org/SDB:AppArmor mod_php8 https://www.php.net/manual/en/install.unix.apache2.php You can obtain detailed information about mod_php8 configuration in its well-commented main configuration le /etc/php8/apache2/php.ini . mod_python https://modpython.org/ mod_security https://github.com/owasp-modsecurity/ModSecurity 584 More information SLES 15 SP642.10.3 Development More information about developing Apache modules or about getting involved in the Apache Web server project are available at the following locations: Apache developer information https://httpd.apache.org/dev/ Apache developer documentation https://httpd.apache.org/docs/2.4/developer/ 42.10.4 Miscellaneous sources If you experience difficulties specific to Apache in SUSE Linux Enterprise Server, take a look at the Technical Information Search at https://www.suse.com/support/ . The history of Apache is provided at https://httpd.apache.org/ABOUT_APACHE.html . This page also explains why the server is called Apache. 585 Development SLES 15 SP643 Setting up an FTP server with YaST Using the YaST FTP Server module, you can configure your machine to function as an FTP (File Transfer Protocol) server. Anonymous and/or authenticated users can connect to your machine and download les using the FTP protocol. Depending on the configuration, they can also upload les to the FTP server. YaST uses vsftpd (Very Secure FTP Daemon). If the YaST FTP Server module is not available in your system, install the yast2-ftp-server package. (For managing the FTP server from the command line, see Section 4.4.3.7, “yast ftp- server”.) To configure the FTP server using YaST, follow these steps: 1. Open the YaST control center and choose Network Services FTP Server or run the yast2 ftp-server command as root . 2. If there is not any FTP server installed in your system, you are asked which server to install when the YaST FTP Server module starts. Choose the vsftpd server and confirm the dialog. 3. In the Start-Up dialog, configure the options for starting of the FTP server. For more infor- mation, see Section 43.1, “Starting the FTP server”. In the General dialog, configure FTP directories, welcome message, le creation masks and other parameters. For more information, see Section 43.2, “FTP general settings”. In the Performance dialog, set the parameters that affect the load on the FTP server. For more information, see Section 43.3, “FTP performance settings”. In the Authentication dialog, set whether the FTP server should be available for anonymous and/or authenticated users. For more information, see Section 43.4, “Authentication”. In the Expert Settings dialog, configure the operation mode of the FTP server, SSL connec- tions and firewall settings. For more information, see Section 43.5, “Expert settings”. 4. Click Finish to save the configurations. 586 SLES 15 SP643.1 Starting the FTP server In the Service Start frame of the FTP Start-Up dialog set the way the FTP server is started up. You can choose between starting the server automatically during the system boot and starting it manually. If the FTP server should be started only after an FTP connection request, choose Via socket. The current status of the FTP server is shown in the Switch On and O frame of the FTP Start-Up dialog. Start the FTP server by clicking Start FTP Now. To stop the server, click Stop FTP Now. After having changed the settings of the server click Save Settings and Restart FTP Now. Your configurations will be saved by leaving the configuration module with Finish. FIGURE 43.1: FTP SERVER CONFIGURATION — START-UP 43.2 FTP general settings In the General Settings frame of the FTP General Settings dialog you can set the Welcome message which is shown after connecting to the FTP server. If you check the Chroot Everyone option, all local users are placed in a chroot jail in their home directory after login. This option has security implications, especially if the users have upload permission or shell access, so be careful enabling this option. 587 Starting the FTP server SLES 15 SP6If you check the Verbose Logging option, all FTP requests and responses are logged. You can limit permissions of les created by anonymous and/or authenticated users with umask. Set the le creation mask for anonymous users in Umask for Anonymous and the le creation mask for authenticated users in Umask for Authenticated Users. The masks should be entered as octal numbers with a leading zero. For more information about umask, see the umask man page ( man 1p umask ). In the FTP Directories frame set the directories used for anonymous and authorized users. With Browse, you can select a directory to be used from the local le system. The default FTP directory for anonymous users is /srv/ftp . vsftpd does not allow this directory to be writable for all users. The subdirectory upload with write permissions for anonymous users is created instead. 43.3 FTP performance settings In the Performance dialog set the parameters which affect the load on the FTP server. Max Idle Time is the maximum time (in minutes) the remote client may spend between FTP commands. In case of longer inactivity, the remote client is disconnected. Max Clients for One IP determines the maximum number of clients that can be connected from a single IP address. Max Clients determines the maximum number of clients that may be connected. Any additional clients are refused. The maximum data transfer rate (in KB/s) is set in Local Max Rate for local authenticated users, and in Anonymous Max Rate for anonymous clients respectively. The default value for the rate settings is 0 , which means unlimited data transfer rate. 43.4 Authentication In the Enable/Disable Anonymous and Local Users frame of the Authentication dialog, you can set which users are allowed to access your FTP server. You can choose between the following options: granting access to anonymous users only, to authenticated users only (with accounts on the system) or to both types of users. To allow users to upload les to the FTP server, check Enable Upload in the Uploading frame of the Authentication dialog. Here you can allow uploading or creating directories even for anonymous users by checking the respective box. 588 FTP performance settings SLES 15 SP6Note: vsftp—allowing file upload for anonymous users If a vsftpd server is used and you want anonymous users to be able to upload les or create directories, a subdirectory with writing permissions for all users needs to be created in the anonymous FTP directory. 43.5 Expert settings An FTP server can run in active or in passive mode. By default the server runs in passive mode. To switch into active mode, deselect the Enable Passive Mode option in the Expert Settings dialog. You can also change the range of ports on the server used for the data stream by tweaking the Min Port for Pas. Mode and Max Port for Pas. Mode options. If you want encrypted communication between clients and the server, you can Enable SSL and, additionally, Enable TLS. Specify the RSA certificate to be used for SSL encrypted connections. Important By default, new versions of the vsftpd daemon have the TLS protocol older than version 1.2 disabled. If you use an FTP client that requires an older version of the TLS protocol, you need to add the following configuration to the /etc/vsftpd.conf le: ssl_tlsv1 = YES ssl_tlsv1_1 = YES Then restart the vsftpd daemon to reread the configuration: > sudo systemctl restart vsftpd.service If your system is protected by a firewall, check Open Port in Firewall to enable a connection to the FTP server. 43.6 More information For more information about the FTP server read the manual pages of vsftpd and vsftpd.conf . 589 Expert settings SLES 15 SP644 Squid caching proxy server Squid is a widely used caching proxy server for Linux and Unix platforms. This means that it stores requested Internet objects, such as data on a Web or FTP server, on a machine that is closer to the requesting workstation than the server. It can be set up in multiple hierarchies to assure optimal response times and low bandwidth usage, even in modes that are transparent to end users. Squid acts as a caching proxy server. It redirects object requests from clients (in this case, from Web browsers) to the server. When the requested objects arrive from the server, it delivers the objects to the client and keeps a copy of them in the hard disk cache. An advantage of caching is that several clients requesting the same object can be served from the hard disk cache. This enables clients to receive the data much faster than from the Internet. This procedure also reduces the network traffic. Along with actual caching, Squid offers a wide range of features: Distributing load over intercommunicating hierarchies of proxy servers Defining strict access control lists for all clients accessing the proxy server Allowing or denying access to specific Web pages using other applications Generating statistics about frequently visited Web pages for the assessment of surfing habits Squid is not a generic proxy server. It normally proxies only HTTP connections. It supports the protocols FTP, Gopher, SSL and WAIS, but it does not support other Internet protocols, such as the news protocol, or video conferencing protocols. Because Squid only supports the UDP protocol to provide communication between different caches, many multimedia programs are not supported. 44.1 Facts about proxy servers As a caching proxy server, Squid can be used in several ways. When combined with a firewall, it can help with security. Multiple proxies can be used together. It can also determine what types of objects should be cached and for how long. 590 Facts about proxy servers SLES 15 SP644.1.1 Squid and security It is possible to use Squid together with a firewall to secure internal networks from the outside. The firewall denies all clients access to external services except Squid. All Web connections must be established by the proxy server. With this configuration, Squid fully controls Web access. If the firewall configuration includes a demilitarized zone (DMZ), the proxy server should oper- ate within this zone. Section 44.6, “Configuring a transparent proxy” describes how to implement a transparent proxy. This simplifies the configuration of the clients, because in this case, they do not need any information about the proxy server. 44.1.2 Multiple caches Several instances of Squid can be configured to exchange objects between them. This reduces the total system load and increases the chances of retrieving an object from the local network. It is also possible to configure cache hierarchies, so a cache can forward object requests to sibling caches or to a parent cache—causing it to request objects from another cache in the local network, or directly from the source. Choosing the appropriate topology for the cache hierarchy is important, because it is not desir- able to increase the overall traffic on the network. For a large network, it would make sense to configure a proxy server for every subnet and connect them to a parent proxy server, which in turn is connected to the caching proxy server of the ISP. All this communication is handled by ICP (Internet cache protocol) running on top of the UDP protocol. Data transfers between caches are handled using HTTP (hypertext transmission pro- tocol) based on TCP. To nd the most appropriate server from which to request objects, a cache sends an ICP request to all sibling proxies. The sibling proxies answer these requests via ICP responses. If the object was detected, they use the code HIT , if not, they use MISS . If multiple HIT responses were found, the proxy server decides from which server to download, depending on factors such as which cache sent the fastest answer or which one is closer. If no satisfactory responses are received, the request is sent to the parent cache. 591 Squid and security SLES 15 SP6Note: How Squid avoids duplication of objects To avoid duplication of objects in different caches in the network, other ICP protocols are used, such as CARP (cache array routing protocol) or HTCP (hypertext cache protocol). The more objects maintained in the network, the greater the possibility of finding the desired object. 44.1.3 Caching Internet objects Many objects available in the network are not static, such as dynamically generated pages and TLS/SSL-encrypted content. Objects like these are not cached because they change each time they are accessed. To determine how long objects should remain in the cache, objects are assigned one of several states. Web and proxy servers nd out the status of an object by adding headers to these objects, such as “Last modified” or “Expires” and the corresponding date. Other headers specifying that objects must not be cached can be used as well. Objects in the cache are normally replaced, because of a lack of free disk space, using algorithms such as LRU (last recently used). This means that the proxy expunges those objects that have not been requested for the longest time. 44.2 System requirements System requirements depend on the maximum network load that the system must bear. There- fore, examine load peaks, as during those times, load might be more than four times the day''s average. When in doubt, slightly overestimate the system''s requirements. Having Squid working close to the limit of its capabilities can lead to a severe loss in quality of service. The following sections point to system factors in order of significance: 1. RAM size 2. CPU speed/physical CPU cores 3. Size of the disk cache 4. Hard disks/SSDs and their architecture 592 Caching Internet objects SLES 15 SP644.2.1 RAM The amount of memory (RAM) required by Squid directly correlates with the number of ob- jects in the cache. Random access memory is much faster than a hard disk/SSD. Therefore, it is important to have sufficient memory for the Squid process, because system performance is dramatically reduced if the swap disk is used. Squid also stores cache object references and frequently requested objects in the main memory to speed up retrieval of this data. Besides that, there is other data that Squid needs to keep in memory, such as a table with all the IP addresses handled, an exact domain name cache, the most frequently requested objects, access control lists, buers and more. 44.2.2 CPU Squid is tuned to work best with lower processor core counts (4–8 physical cores), with each providing high performance. Technologies providing virtual cores such as hyperthreading can hurt performance. To make the best use of multiple CPU cores, it is necessary to set up multiple worker threads writing to different caching devices. By default, multi-core support is disabled. 44.2.3 Size of the disk cache In a small cache, the probability of a HIT (finding the requested object already located there) is small, because the cache is easily lled and less requested objects are replaced by newer ones. If, for example, 1 GB is available for the cache and the users use up only 10 MB per day surfing, it would take more than one hundred days to ll the cache. The easiest way to determine the necessary cache size is to consider the maximum transfer rate of the connection. With a 1 Mbit/s connection, the maximum transfer rate is 128 KB/s. If all this traffic ended up in the cache, in one hour it would add up to 460 MB. Assuming that all this traffic is generated in only eight working hours, it would reach 3.6 GB in one day. Because the connection is normally not used to its upper volume limit, it can be assumed that the total data volume handled by the cache is approximately 2 GB. Hence, in this example, 2 GB of disk space is required for Squid to keep one day''s worth of browsing data cached. 593 RAM SLES 15 SP644.2.4 Hard disk/SSD architecture Speed plays an important role in the caching process, so this factor deserves special attention. For hard disks/SSDs, this parameter is described as random seek time or random read performance, measured in milliseconds. Because the data blocks that Squid reads from or writes to the hard disk/SSD tend to be small, the seek time/read performance of the hard disk/SSD is more impor- tant than its data throughput. For use as a proxy server, hard disks with high rotation speeds or SSDs are the best choice. When using hard disks, it can be better to use multiple smaller hard disks, each with a single cache directory to avoid excessive read times. Using a RAID system allows increasing reliability at expense of speed. However, for performance reasons, avoid (software) RAID5 and similar settings. In most cases, the choice of le system choice does not matter. However, using the mount option noatime can improve performance—Squid provides its own time stamps, so it does not need the le system to track access times. 44.3 Basic usage of Squid Since squid is not installed by default on SUSE® Linux Enterprise Server, make sure the pack- age is installed on your system. As Squid is preconfigured in SUSE Linux Enterprise Server, you can start it immediately after the installation. To avoid problems during the start-up, make sure that the network is connected to the Internet connection and has at least one name server. Using a dial-up connection with a dynamic DNS configuration may cause problems. In this case, specify at least the name server, as Squid does not start if it does not detect a DNS server in /var/run/netconfig/resolv.conf . 44.3.1 Starting Squid To start Squid, run the following command: > sudo systemctl start squid To start Squid on system boot, enable the service with systemctl enable squid . 594 Hard disk/SSD architecture SLES 15 SP644.3.2 Checking whether Squid is working There are several ways to check whether Squid is running: Using systemctl : > systemctl status squid The output should indicate that Squid is loaded and active (running) . Using Squid itself: > sudo squid -k check | echo $? The output should be 0 , but it can also contain additional messages, such as warnings. To test the functionality of Squid on the local system, choose one of the following options: Use squidclient , a command-line tool that outputs the response to a Web request, similar to wget or curl . Unlike wget or curl , squidclient automatically connects to the default proxy setup of Squid, localhost:3128 . However, if you modified the configuration of Squid, you must configure squidclient accordingly. For more information, see squidclient --help . EXAMPLE 44.1: A REQUEST WITH squidclient > squidclient http://www.example.org HTTP/1.1 200 OK Cache-Control: max-age=604800 Content-Type: text/html Date: Fri, 22 Jun 2016 12:00:00 GMT Expires: Fri, 29 Jun 2016 12:00:00 GMT Last-Modified: Fri, 09 Aug 2013 23:54:35 GMT Server: ECS (iad/182A) Vary: Accept-Encoding X-Cache: HIT x-ec-custom-error: 1 Content-Length: 1270 X-Cache: MISS from moon 1 X-Cache-Lookup: MISS from moon:3128 Via: 1.1 moon (squid/3.5.16) 2 Connection: close 595 Checking whether Squid is working SLES 15 SP6 [...] The output shown in Example 44.1, “A request with squidclient” consists of two parts: 1. The protocol headers of the response (the lines before the blank line). 2. The actual content of the response (the lines after the blank line). To verify that Squid is used, refer to the selected header lines: 1 The value of the header X-Cache shows that the requested document was not in the Squid cache ( MISS ) of the computer moon . The example above contains two X-Cache lines. The rst X-Cache header can be safely ignored, as it is produced by the internal caching software of the originating Web server. 2 The value of the header Via shows the HTTP version, the name of the computer, and the version of Squid in use. Using a browser: set up localhost as the proxy and 3128 as the port. Then load a page and check the response headers in the Network panel of the browser''s Inspector or Developer Tools. The headers should be reproduced similarly to the way shown in Example 44.1, “A request with squidclient”. To allow users from the local system and other systems to access Squid and the Internet, change the entry in the configuration les /etc/squid/squid.conf from http_access deny all to http_access allow all . However, keep in mind that this makes Squid fully accessible to anyone. Therefore, define ACLs (access control lists) that control access to the proxy server. After modifying the configuration le, Squid must be reloaded or restarted. For more information on ACLs, see Section 44.5.2, “Options for access controls”. If Squid stops working after a short period of time, check whether there is an incorrect name server entry or whether the /var/run/netconfig/resolv.conf le is missing. Squid logs the cause of a start-up failure in the le /var/log/squid/cache.log . 596 Checking whether Squid is working SLES 15 SP644.3.3 Stopping, reloading, and restarting Squid There are two ways to reload Squid: Using systemctl : > sudo systemctl reload squid or > sudo systemctl restart squid Using YaST: In the Squid module, click the Save Settings and Restart Squid Now button. To stop Squid, use one of the following options: Using systemctl : > sudo systemctl stop squid Using YaST In the Squid module click the Stop Squid Now. button. Shutting down Squid can take a while, because Squid waits up to half a minute before dropping the connections to the clients and writing its data to the disk (see shutdown_lifetime option in /etc/squid/squid.conf ), Warning: Terminating Squid Terminating Squid with kill or killall can damage the cache. To be able to restart Squid, damaged caches must be deleted. 44.3.4 Removing Squid Removing Squid from the system does not remove the cache hierarchy and log les. To remove them, delete the /var/cache/squid directory manually. 597 Stopping, reloading, and restarting Squid SLES 15 SP644.3.5 Local DNS server Setting up a local DNS server makes sense even if it does not manage its own domain. In that case, it acts as a caching-only name server, and it can also resolve DNS requests via the root name servers without requiring any special configuration (see Section 39.4, “Starting the BIND name server”). How this can be done depends on whether you chose dynamic DNS during the configuration of the Internet connection. Dynamic DNS Normally, with dynamic DNS, the DNS server is set by the provider when establishing the Internet connection and the local /var/run/netconfig/resolv.conf le is adjusted automatically. This behavior is specified in the /etc/sysconfig/network/config le using the NETCONFIG_DNS_POLICY sysconfig variable. Set NETCONFIG_DNS_POLICY to "" with the YaST sysconfig editor. Then add the local DNS server in the /var/run/netconfig/resolv.conf le with the IP address 127.0.0.1 for localhost . This way, Squid can always nd the local name server when it starts. To make the provider''s name server accessible, specify it in the configuration le /etc/ named.conf under forwarders along with its IP address. With dynamic DNS, this can be done automatically when establishing the connection by setting the sysconfig variable NETCONFIG_DNS_POLICY to auto . Static DNS With static DNS, no automatic DNS adjustments take place while establishing a connection, so there is no need to change any sysconfig variables. However, you must specify the local DNS server in the le /var/run/netconfig/resolv.conf as described in Dynamic DNS. Additionally, the provider''s static name server must be specified manually in the /etc/ named.conf le under forwarders along with its IP address. Tip: DNS and firewall If you have a firewall running, make sure DNS requests can pass through it. 598 Local DNS server SLES 15 SP644.4 The YaST Squid module The YaST Squid module contains the following tabs: Start-Up Specifies how Squid is started and which firewall port is open in which interfaces. HTTP Ports Define all ports for Squid to listen for HTTP requests from clients. Refresh Patterns Defines how Squid treats objects in the cache. Cache Settings Defines settings related to cache memory, maximum and minimum object size, and more. Cache Directory Defines the top-level directory for Squid to store cache swap les. Access Control Controls the access to the Squid server via ACL groups. Logging and Timeout Define paths to access, cache and cache store log les and connection timeouts and client lifetime. Miscellaneous Specifies language and mail address of administrator. 44.5 The Squid configuration file Squid proxy server settings are stored in the /etc/squid/squid.conf le. Although starting Squid for the rst time does not require any changes to the le, external clients are initially denied access. The proxy is available for localhost . The default port is 3128 . The preinstalled configuration le /etc/squid/squid.conf provides detailed information about the options and many examples. Many entries are disabled using the comment character # . The relevant specifications can be found at the end of the line. The given values usually correlate with the default values, so removing the comment signs without changing any of the parameters usually has no effect. If 599 The YaST Squid module SLES 15 SP6possible, leave the commented lines as they are and insert the options along with the modified values in the line below. This way, the default values may easily be recovered and compared with the changes. Tip: Adapting the configuration file after an update If you have updated from an earlier Squid version, it is recommended to edit the new / etc/squid/squid.conf and only apply the changes made in the previous le. Sometimes, Squid options are added, removed or modified. Therefore, if you try to use the old squid.conf , Squid might stop working properly. 44.5.1 General configuration options The following is a list of a selection of configuration options for Squid. It is not exhaustive. The Squid package contains a full, lightly documented list of options in /etc/squid/squid.con- f.documented . http_port PORT This is the port on which Squid listens for client requests. The default port is 3128 , but 8080 is also common. cache_peer HOST_NAME TYPE PROXY_PORT ICP_PORT This option allows creating a network of caches that work together. The cache peer is a computer that also hosts a network cache and stands in a relationship to your own. The type of relationship is specified as the TYPE . The type can either be parent or sibling . As the HOST_NAME , specify the name or IP address of the proxy server to use. For PROX- Y_PORT , specify the port number for use in a browser (usually 8080 ). Set ICP_PORT to 7 or, if the ICP port of the parent is not known and its use is irrelevant to the provider, to 0 . To make Squid behave like a Web browser instead of a proxy server, disable the use of the ICP protocol by appending the options default and no-query . cache_mem SIZE This option defines the amount of memory Squid can use for the most frequent replies. The default is 8 MB . This does not specify the memory usage of Squid and may be exceeded. 600 General configuration options SLES 15 SP6cache_dir STORAGE_TYPE CACHE_DIRECTORY CACHE_SIZE LEVEL_1_DIRECTORIES LEV- EL_2_DIRECTORIES The option cache_dir defines the directory for the disk cache. In the default configuration on SUSE Linux Enterprise Server, Squid does not create a disk cache. The placeholder STORAGE_TYPE can be one of the following: Directory-based storage types: ufs , aufs (the default), diskd . All three are varia- tions of the storage format ufs . However, while ufs runs as part of the core Squid thread, aufs runs in a separate thread, and diskd uses a separate process. This means that the latter two types avoid blocking Squid because of disk I/O. Database-based storage systems: rock . This storage format relies on a single database le, in which each object takes up one or more memory units of a xed size (“slots”). In the following, only the parameters for storage types based on ufs are discussed. rock has different parameters. The CACHE_DIRECTORY is the directory for the disk cache. By default, that is /var/cache/ squid . CACHE_SIZE is the maximum size of that directory in megabytes; by default, this is set to 100 MB. Set it to between 50% and a maximum of 80% of available disk space. The LEVEL_1_DIRECTORIES and LEVEL_2_DIRECTORIES values specify how many subdi- rectories are created in the CACHE_DIRECTORY . By default, 16 subdirectories are created at the rst level below CACHE_DIRECTORY and 256 within each of these. These values should only be increased with caution, because creating too many directories can lead to performance problems. If you have several disks that share a cache, specify several cache_dir lines. cache_access_log LOG_FILE , cache_log LOG_FILE , cache_store_log LOG_FILE These three options specify the paths where Squid logs all its actions. Normally, nothing needs to be changed here. If Squid is under heavy load, it might make sense to distribute the cache and the log les over several disks. client_netmask NETMASK This option allows masking IP addresses of clients in the log les by applying a subnet mask. For example, to set the last digit of the IP address to 0 , specify 255.255.255.0 . 601 General configuration options SLES 15 SP6ftp_user E-MAIL This option allows setting the password that Squid should use for anonymous FTP login. Specify a valid e-mail address here, as FTP servers check these for validity. cache_mgr E-MAIL When Squid crashes, it sends a message to the specified e-mail address. The default is webmaster. logfile_rotate VALUE When used with squid   -k rotate , squid rotates log les. The les are numbered and, after reaching the specified value, the oldest le is overwritten. The default value is 10 which rotates log les with the numbers 0 to 9. However, on SUSE Linux Enterprise Server, rotating log les is performed automatically using logrotate and the configuration le /etc/logrotate.d/squid . append_domain DOMAIN Use append_domain to specify which domain to append automatically when none is given. Usually, your own domain is specified here, so pointing the browser to www navigates to your own Web server. forwarded_for STATE If this option is set to on , it adds a line to the header similar to this: X-Forwarded-For: 192.168.0.1 If you set this option to off , Squid removes the IP address and the system name of the client from HTTP requests. negative_ttl TIME , negative_dns_ttl TIME If these options are configured, Squid caches certain types of failures, such as 404 respons- es. It then refuses to issue new requests, even if the resource becomes available. By default, negative_ttl is set to 0 , negative_dns_ttl is set to 1 minutes . This means that negative responses to Web requests are not cached by default, while negative responses to DNS requests are cached for 1 minute. 602 General configuration options SLES 15 SP6never_direct allow ACL_NAME To prevent Squid from accepting requests directly from the Internet, use the option nev- er_direct to force connection to another proxy server. This must have previously been specified in cache_peer . If all is specified as the ACL_NAME , all requests are forwarded directly to the parent . This can be necessary, for example, if you are using a provider that dictates the use of its proxies or denies its firewall direct Internet access. 44.5.2 Options for access controls Squid can control the access to the proxy server through Access Control Lists (ACL), lists with rules that are processed sequentially. ACLs must be defined before they can be used. Squid includes default ACLs, such as all and localhost . However, for an ACL to take effect, it must have a corresponding http_access rule. The syntax for the option acl is as follows: acl ACL_NAME TYPE DATA The placeholders within this syntax stand for the following: ACL_NAME can be any name. For TYPE , select from the options available in the ACCESS CONTROLS section of the /etc/ squid/squid.conf le. The specification for DATA depends on the individual ACL type, for example, host names, IP addresses, or URLs. To add rules in the YaST Squid module, open the module and click the Access Control tab. Click Add under the ACL Groups list and enter the name of your rule, the type, and its parameters. For more information on types of ACL rules, see the Squid documentation at https://www.squid- cache.org/Versions/v3/3.5/cfgman/acl.html . EXAMPLE 44.2: DEFINING ACL RULES acl mysurfers srcdomain .example.com 1 acl teachers src 192.168.1.0/255.255.255.0 2 acl students src 192.168.7.0-192.168.9.0/255.255.255.0 3 acl lunch time MTWHF 12:00-15:00 4 1 This ACL defines mysurfers as all users coming from within .example.com (as deter- mined by a reverse lookup for the IP). 603 Options for access controls SLES 15 SP62 This ACL defines teachers as the users of computers with IP addresses starting with 192.168.1. . 3 This ACL defines students as the users of the computer with IP addresses starting with 192.168.7. , 192.168.8. , or 192.168.9. . 4 This ACL defines lunch as a time on the days Monday through Friday between noon and 3 p.m. http_access allow ACL_NAME http_access defines who is allowed to use the proxy server and who can access what on the Internet. You need to define ACLs for this. The localhost and all ACLs have already been defined above, and you can deny or allow access to them via deny or allow . A list containing any number of http_access entries can be created, processed from top to bottom. Depending on which occurs rst, access is allowed or denied to the respective URL. The last entry should always be http_access deny all . In the following example, localhost has free access to everything, while all other hosts are denied access: http_access allow localhost http_access deny all In another example using these rules, the group teachers always has access to the Inter- net. The group students only has access between Monday and Friday during lunch time: http_access deny localhost http_access allow teachers http_access allow students lunch time http_access deny all For better readability, specify all http_access options as a block in the configuration le /etc/squid/squid.conf . url_rewrite_program PATH Use this option to specify a URL rewriter. auth_param basic program PATH If users must be authenticated on the proxy server, set a corresponding program, such as /usr/sbin/pam_auth . When accessing pam_auth for the rst time, the user is prompted to provide a user name and a password. Besides that, you need an ACL, so only clients with a valid login can use the Internet: acl password proxy_auth REQUIRED http_access allow password 604 Options for access controls SLES 15 SP6http_access deny all In the acl proxy_auth option, using REQUIRED means that all valid user names are accepted. REQUIRED can also be replaced with a list of permitted user names. ident_lookup_access allow ACL_NAME Use this option to enable an ident request action to nd each user''s identity for all clients defined by an ACL of the type src . To enable this for all clients, apply the predefined ACL all as the ACL_NAME . All clients specified by ident_lookup_access must run an ident daemon. On Linux, you can use pidentd (package pidentd ) as the ident daemon. To ensure that only clients with a successful ident lookup are permitted, define a corresponding ACL: acl identhosts ident REQUIRED http_access allow identhosts http_access deny all Setting the acl identhosts ident option to REQUIRED ensures that all valid user names are accepted. REQUIRED can also be replaced with a list of permitted user names. Using ident can slow down access time, because ident lookups are repeated for each request. 44.6 Configuring a transparent proxy A transparent proxy intercepts and answers the requests of the Web browser, so the Web brows- er receives the requested pages without knowing where they are coming from. As the name indicates, the entire process is transparent to the user. The standard way of working with proxy servers is as follows: the Web browser sends requests to a certain port of the proxy server and the proxy always provides these required objects, regardless of whether they are in its cache. However, in the following cases using the transparent proxy mode of Squid makes sense: When for security reasons it is desirable for all clients to use a proxy server to access the Internet. When all clients must use a proxy server, regardless of whether they are aware of it. When the proxy server in a network is moved, but the existing clients need to retain their old configuration. 605 Configuring a transparent proxy SLES 15 SP6PROCEDURE 44.1: SQUID AS A TRANSPARENT PROXY SERVER (COMMAND LINE) 1. In /etc/squid/squid.conf , add the parameter transparent to the line http_port . You should then have 2 lines: http_port 3128# http_port 3128 transparent 2. Restart Squid: > sudo systemctl restart squid 3. Set up the firewall to redirect HTTP traffic to the port given in http_proxy (in the ex- ample above, it is port 3128). Then reload the firewall configuration. This assumes that the zone internal is assigned to your LAN interface. > sudo firewall-cmd --permanent --zone=internal \ --add-forward-port=port=80:proto=tcp:toport=3128:toaddr=LAN_IP > sudo firewall-cmd --permanent --zone=internal --add-port=3128/tcp > sudo firewall-cmd --reload Replace LAN_IP with the IP address of your LAN interface or the interface Squid is lis- tening on. 4. To verify that everything is working properly, check the Squid log les in /var/log/ squid/access.log . 44.7 Using the Squid cache manager CGI interface (cachemgr.cgi) The Squid cache manager CGI interface ( cachemgr.cgi ) is a CGI utility for displaying statistics about the memory usage of a running Squid process. It also provides a convenient way to manage the cache and view statistics without logging the server. PROCEDURE 44.2: SETTING UP cachemgr.cgi 1. Make sure the Apache Web server is running on your system. Configure Apache as de- scribed in Chapter 42, The Apache HTTP server. In particular, see Section 42.5, “Enabling CGI scripts”. To check whether Apache is already running, use: > sudo systemctl status apache2 606 Using the Squid cache manager CGI interface (cachemgr.cgi) SLES 15 SP6If the status is inactive , start Apache with the SUSE Linux Enterprise Server default settings: > sudo systemctl start apache2 2. Now enable cachemgr.cgi in Apache. To do this, create a configuration le for a Scrip- tAlias . Create the le in the directory /etc/apache2/conf.d and name it cachemgr.conf . Add the following to the le: ScriptAlias /squid/cgi-bin/ /usr/lib64/squid/ Options +ExecCGI AddHandler cgi-script .cgi Require host HOST_NAME Replace HOST_NAME with the host name of the computer you want to access cachemgr.c- gi from. This allows only your computer to access cachemgr.cgi . To allow access from anywhere, use Require all granted instead. 3. If Squid and the Apache Web server run on the same computer, the /etc/squid/ squid.conf configuration le requires no modifications. However, verify that the le contains the following lines: http_access allow manager localhost http_access deny manager This allows you to access the manager interface from your computer ( localhost ) only. If Squid and the Apache Web server run on different computers, you need to add extra rules to allow access from the CGI script to Squid. Define an ACL for the server (replace WEB_SERVER_IP with the IP address of the Web server): acl webserver src WEB_SERVER_IP/255.255.255.255 Make sure the following rules are in the configuration le. Keep in mind that the order is important. http_access allow manager localhost 607 Using the Squid cache manager CGI interface (cachemgr.cgi) SLES 15 SP6http_access allow manager webserver http_access deny manager 4. (Optional) Optionally, you can configure one or more passwords for cachemgr.cgi . This also gives you access to more actions such as closing the cache remotely or viewing more information about the cache. To enable access, configure the options cache_mgr and cachemgr_passwd with one or more password for the manager and a list of allowed actions. The following example configuration enables viewing the index page, the menu, and 60- minute average of counters without authentication. The configuration also enables tog- gling offline mode using the password secretpassword and to disable everything else. cache_mgr user cachemgr_passwd none index menu 60min cachemgr_passwd secretpassword offline_toggle cachemgr_passwd disable all cache_mgr defines a user name. cache_mgr defines which actions are allowed using which password. The keywords none and disable are special: none removes the need for a password, disable disables functionality outright. The full list of actions can be best seen after logging in to cachemgr.cgi . To nd out how the operation needs to be referenced in the configuration le, see the string after &operation= in the URL of the action page. all is a special keyword meaning all actions. 5. Reload Squid and Apache to enable the changes: > sudo systemctl reload squid 6. To view the statistics, go to the cachemgr.cgi page that you set up before. For example, it could be http://webserver.example.org/squid/cgi-bin/cachemgr.cgi . Choose the right server. If a user name and password are configured, specify them. Click Continue and browse through the available statistics. 608 Using the Squid cache manager CGI interface (cachemgr.cgi) SLES 15 SP644.8 Cache report generation with Calamaris Calamaris is a Perl script for generating reports of cache activity in ASCII or HTML format. It works with Squid access log les. This tool does not belong to the SUSE Linux Enterprise Server default installation scope—to use it, install the calamaris package. Further info on Calamaris is available at https://cord.de/calamaris-english . Log in as root , then enter: # cat access1.log [access2.log access3.log] | calamaris OPTIONS > reportfile When using more than one log le, make sure they are ordered chronologically, with older les listed rst. This can be done either by listing the les one after the other as in the example above or by using access{1..3}.log . calamaris accepts the following options: -a output all available reports -w output as HTML report -l include a message or logo in report header Further information about options can be found in the program''s man page with man   cala- maris . A typical example is: # cat access.log.{10..1} access.log | calamaris -a -w \ > /usr/local/httpd/htdocs/Squid/squidreport.html This saves the report in the directory of the Web server. Apache is required to view the reports. 44.9 More Information Visit the home page of Squid at https://www.squid-cache.org/ . Here, nd the “Squid User Guide” and an extensive collection of FAQs on Squid. Squid mailing lists are available at https://www.squid-cache.org/Support/mailing-lists.html . 609 Cache report generation with Calamaris SLES 15 SP645 Web Based Enterprise Management using SFCB 45.1 Introduction and basic concept SUSE® Linux Enterprise Server (SLES) provides a collection of open standards based tools for the unified management of disparate computing systems and environments. Our enterprise solutions implement the standards proposed by the Distributed Management Task Force. The following paragraphs describe their basic components. Distributed Management Task Force, Inc (DMTF) is the industry organization which leads the development of management standards for enterprise and Internet environments. Their goal is to unify management standards and initiatives, and to enable more integrated, cost effective and interoperable management solutions. DMTF standards provide common system management components for control and communication. Their solutions are independent of platforms and technologies. Web Based Enterprise Management and the Common Information Model are two of their key technologies. Web Based Enterprise Management (WBEM) is a set of management and Internet standard tech- nologies. WBEM was developed to unify the management of enterprise computing environments. It provides the ability for the industry to deliver a well-integrated collection of management tools using Web technologies. WBEM consists of the following standards: A data model: the Common Information Model (CIM) standard An encoding specification: CIM-XML Encoding Specification A transport mechanism: CIM operations over HTTP The Common Information Model is a conceptual information model that describes system man- agement. It is not bound to a particular implementation and enables the interchange of man- agement information between management systems, networks, services and applications. There are two parts to CIM: the CIM Specification and the CIM Schema. 610 Introduction and basic concept SLES 15 SP6The CIM Specification describes the language, naming and meta schema. The meta schema is a formal definition of the model. It defines the terms used to express the model and their usage and semantics. The elements of the meta schema are classes, properties, and methods. The meta schema also supports indications and associations as types of classes, and references as types of properties. The CIM Schema provides the actual model descriptions. It supplies a set of classes with properties and associations that provide a well understood conceptual framework within which it is possible to organize the available information about the managed environment. The Common Information Model Object Manager (CIMOM) is a CIM object manager or, more specifically, an application that manages objects according to the CIM standard. CIMOM man- ages communication between CIMOM providers and a CIM client, where the administrator man- ages the system. CIMOM providers are software performing specific tasks within the CIMOM that are requested by client applications. Each provider instruments one or more aspects of the CIMOM''s schema. These providers interact directly with the hardware. Standards Based Linux Instrumentation for Manageability (SBLIM) is a collection of tools designed to support Web-Based Enterprise Management (WBEM). SUSE® Linux Enterprise Server uses the open source CIMOM (or CIM server) from the SBLIM project called Small Footprint CIM Broker . Small Footprint CIM Broker is a CIM server intended for use in resource-limited or embedded envi- ronments. It is designed to be modular and lightweight at the same time. Its based on open stan- dards and it supports CMPI providers, CIM-XML encoding, and Managed Object Format (MOF). It is highly configurable and performs stability even if the provider crashes. It is also easily ac- cessible as it supports multiple transport protocols, such as HTTP, HTTPS, Unix domain sockets, Service Location Protocol (SLP), and Java Database Connectivity (JDBC). 611 Introduction and basic concept SLES 15 SP645.2 Setting up SFCB To set up the Small Footprint CIM Broker (SFCB) environment, make sure the Web-Based Enter- prise Management pattern in YaST is selected during SUSE Linux Enterprise Server installation. Alternatively, select it as a component to install on a server that is already running. Make sure the following packages are installed on your system: cim-schema, Common Information Model (CIM) schema Contains the Common Information Model (CIM). CIM is a model for describing overall management information in a network or enterprise environments. CIM consists of a spec- ification and a schema. The specification defines the details for integration with other management models. The schema provides the actual model descriptions. python2-pywbem Contains a Python module for making CIM operation calls through the WBEM protocol to query and update managed objects. cmpi-provider-register, CIMOM neutral provider registration utility Contains a utility allowing CMPI provider packages to register with whatever CIMOM happens to be present on the system. sblim-sfcb, small footprint CIM broker Contains Small Footprint CIM Broker. It is a CIM server conforming to the CIM Operations over HTTP protocol. It is robust, with low resource consumption and, therefore, specifical- ly suited for embedded and resource constrained environments. SFCB supports providers written against the Common Manageability Programming Interface (CMPI). sblim-sfcc Contains Small Footprint CIM Client library runtime libraries. sblim-wbemcli Contains WBEM command line interface. It is a stand-alone command line WBEM client especially suited for basic systems management tasks. 45.2.1 Starting, stopping and checking status for SFCB CIM server sfcbd daemon is installed together with Web-Based Enterprise Management software and is started by default at system start-up. The following table explains how to start, stop and check status for sfcbd. 612 Setting up SFCB SLES 15 SP6TABLE 45.1: COMMANDS FOR MANAGING SFCBD Task Linux Command Start sfcbd Enter systemctl start sblim-sfcb.ser- vice as root in the command line. Stop sfcbd Enter systemctl stop sblim-sfcb.ser- vice as root in the command line. Check sfcbd status Enter systemctl status sblim-sfcb.ser- vice as root in the command line. 45.2.2 Ensuring secure access The default setup of SFCB is secure. However, check that the access to SFCB components is as secure as required for your organization. 45.2.2.1 Certificates Secure Sockets Layers (SSL) transports require a certificate for secure communication to occur. When SFCB is installed, it has a self-signed certificate generated. You can replace the path to the default certificate with a path to a commercial or self-signed one by changing the sslCertificateFilePath: PATH_FILENAME setting in /etc/sfcb/ sfcb.cfg . The le must be in PEM format. By default, SFCB expects a server certificate in the following location: /etc/sfcb/server.pem To generate a new certificate, run the following command: > sudo sh /usr/share/sfcb/genSslCert.sh Generating SSL certificates in . Generating a 2048 bit RSA private key ...................................................................+++ .+++ writing new private key to ''/var/tmp/sfcb.0Bjt69/key.pem'' ----- 613 Ensuring secure access SLES 15 SP6By default, the script generates certificates client.pem , file.pem and server.pem in the current working directory. If you want the script to generate the certificates in /etc/sfcb directory, you need to append the path to the command. If these les already exist, a warning message is displayed, and the old certificates are not overwritten. > sudo sh /usr/share/sfcb/genSslCert.sh /etc/sfcb Generating SSL certificates in . WARNING: server.pem SSL Certificate file already exists. old file will be kept intact. WARNING: client.pem SSL Certificate trust store already exists. old file will be kept intact. You must remove the old certificates from the le system and run the command again. To change the way SFCB uses certificates, see Section 45.2.2.3, “Authentication”. 45.2.2.2 Ports By default, SFCB is configured to accept all communications through the secure port 5989. The following paragraphs explain the communication port setup and recommended configuration. Port 5989 (secure) The secure port that SFCB communications use via HTTPS services. This is the default. With this setting, all communications between the CIMOM and client applications are encrypted when sent over the Internet between servers and workstations. Users must authenticate with the client application to reach SFCB server. We recommend that you keep this setting. For the SFCB CIMOM to communicate with the necessary applications, this port must be open on routers and firewall rules if they are present between the client application and the nodes being monitored. Port 5988 (insecure) The insecure port that SFCB communications use via HTTP services. This setting is disabled by default. With this setting, all communications between the CIMOM and client applica- tions are open for review when sent over the Internet between servers and workstations by anyone, without any authentication. We recommend that you use this setting only when attempting to debug a problem with the CIMOM. When the problem is resolved, disable the non-secure port option back. For the SFCB CIMOM to communicate with the necessary applications that require non-secure access, this port must be open in routers and firewall rules between the client application and the nodes being monitored. 614 Ensuring secure access SLES 15 SP6To change the default port assignments, see Section 45.2.2.2, “Ports”. 45.2.2.3 Authentication SFCB supports HTTP basic authentication and authentication based on client certificates (HTTP over SSL connections). Basic HTTP authentication is enabled by specifying doBasicAuth=true in the SFCB configuration le ( /etc/sfcb/sfcb.cfg by default). SUSE® Linux Enterprise Server installation of SFCB supports Pluggable Authentication Modules (PAM) approach; there- fore the local root user can authenticate to the SFCB CIMOM with local root user credentials. If the sslClientCertificate configuration property is set to accept or require , the SFCB HTTP adapter will request a certificate from clients when connecting via HTTP over SSL (HTTPS). If require is specified, the client must provide a valid certificate (according to the client trust store specified via sslClientTrustStore ). If the client fails to do so, the connec- tion will be rejected by the CIM server. The setting sslClientCertificate=accept may not be obvious. It is useful if both basic and client certificate authentication are allowed. If the client can provide a valid certificate, HTTPS connection will be established and the basic authentication procedure will not be executed. If this function cannot verify the certificate, the HTTP basic authentication will take place instead. 45.3 SFCB CIMOM configuration SFCB is a lightweight implementation of the CIM server, but it is also highly configurable. Several options can control its behavior. You can control the SFCB server in three ways: by setting appropriate environment variables by using command line options by changing its configuration le 45.3.1 Environment variables Several environment variables directly affect the behavior of SFCB. You need to restart the SFCB daemon by systemctl restart sfcb for these changes to take effect. PATH Specifies the path to the sfcbd daemon and utilities. 615 SFCB CIMOM configuration SLES 15 SP6LD_LIBRARY_PATH Specifies the path to the sfcb runtime libraries. Alternatively, you can add this path to the system-wide dynamic loader configuration le /etc/ld.so.conf . SFCB_PAUSE_PROVIDER Specifies the provider name. The SFCB server pauses after the provider is loaded for the rst time. You can then attach a runtime debugger to the provider''s process for debugging purposes. SFCB_PAUSE_CODEC Specifies the name of the SFCB codec (currently supports only http . The SFCB server pauses after the codec is loaded for the rst time. You can then attach a runtime debugger to the process. SFCB_TRACE Specifies the level of debug messages for SFCB. Valid values are 0 (no debug messages), or 1 (key debug messages) to 4 (all debug messages). Default is 1. SFCB_TRACE_FILE By default, SFCB outputs its debug messages to standard error output (STDERR). Setting this variable causes the debug messages to be written to a specified le instead. SBLIM_TRACE Specifies the level of debug messages for SBLIM providers. Valid values are 0 (no debug messages), or 1 (key debug messages) to 4 (all debug messages). SBLIM_TRACE_FILE By default, SBLIM provider outputs its trace messages to STDERR. Setting this variable causes the trace messages to be written to a specified le instead. 45.3.2 Command line options sfcbd , the SFCB daemon, has several command line options that switch particular runtime features on or o. Enter these options when SFCB daemon starts. -c, --config-file = FILE When SFCB daemon starts, it reads its configuration from /etc/sfcb/sfcb.cfg by de- fault. With this option, you can specify an alternative configuration le. 616 Command line options SLES 15 SP6-d, --daemon Forces sfcbd and its child processes to run in the background. -s, --collect-stats Turns on runtime statistics collecting. sfcbd runtime statistics will be written to the sfcbS- tat le in the current working directory. By default, no statistics are collected. -l, --syslog-level = LOGLEVEL Specifies the level of verbosity for the system logging facility. LOGLEVEL can be one of LOG_INFO, LOG_DEBUG or LOG_ERR, which is the default. -k, --color-trace = LOGLEVEL Prints trace output in a different color per process for easier debugging. -t, --trace-components = NUM Activates component-level tracing messages, where NUM is an OR-ed bitmask integer that defines which component to trace. After you specify -t ? , it lists all the components and their associated integer bitmask: > sfcbd -t ? --- Traceable Components: Int Hex --- providerMgr: 1 0x0000001 --- providerDrv: 2 0x0000002 --- cimxmlProc: 4 0x0000004 --- httpDaemon: 8 0x0000008 --- upCalls: 16 0x0000010 --- encCalls: 32 0x0000020 --- ProviderInstMgr: 64 0x0000040 --- providerAssocMgr: 128 0x0000080 --- providers: 256 0x0000100 --- indProvider: 512 0x0000200 --- internalProvider: 1024 0x0000400 --- objectImpl: 2048 0x0000800 --- xmlIn: 4096 0x0001000 --- xmlOut: 8192 0x0002000 --- sockets: 16384 0x0004000 --- memoryMgr: 32768 0x0008000 --- msgQueue: 65536 0x0010000 --- xmlParsing: 131072 0x0020000 --- responseTiming: 262144 0x0040000 --- dbpdaemon: 524288 0x0080000 --- slp: 1048576 0x0100000 A useful value that reveals the internal functions of sfcbd but does not generate too many messages, is -t 2019 . 617 Command line options SLES 15 SP645.3.3 SFCB configuration file SFCB reads its runtime configuration from configuration le /etc/sfcb/sfcb.cfg after start- ing up. This behavior can be overridden using -c option at start-up. The configuration le contains option : VALUE pairs, one per line. Any setting that has the options commented out with a number sign (#) uses the default setting. The following list of options may not be complete. See the content of /etc/sfcb/sfcb.cfg and /usr/share/doc/packages/sblim-sfcb/README for their complete list. 45.3.3.1 httpPort Purpose Specifies the local port value that sfcbd should listen to receive HTTP (insecure) requests from CIM clients. Default is 5988 . Syntax httpPort: PORT_NUMBER 45.3.3.2 enableHttp Purpose Specifies whether SFCB should accept HTTP client connections. Default is false . Syntax enableHttp: OPTION Option Description true Enables HTTP connections. false Disables HTTP connections. 618 SFCB configuration file SLES 15 SP645.3.3.3 httpProcs Purpose Specifies the maximum number of simultaneous HTTP client connections before new incoming HTTP requests are blocked. Default is 8 . Syntax httpProcs: MAX_NUMBER_OF_CONNECTIONS 45.3.3.4 httpUserSFCB, httpUser Purpose These options control what user the HTTP server will run under. If httpUserSFCB is true , HTTP will run under the same user as the SFCB main process. If it is false the user name specified for httpUser will be used. This setting is used for both HTTP and HTTPS servers. httpUser must be specified if httpUserSFCB is set to false . the default is true . Syntax httpUserSFCB: true 45.3.3.5 httpLocalOnly Purpose Specifies whether to limit HTTP requests to localhost only. Default is false . Syntax httpLocalOnly: false 619 SFCB configuration file SLES 15 SP645.3.3.6 httpsPort Purpose Specifies the local port value where sfcbd listens for HTTPS requests from CIM clients. Default is 5989 . Syntax httpsPort: port_number 45.3.3.7 enableHttps Purpose Specifies if SFCB will accept HTTPS client connections. Default is true . Syntax enableHttps: option Option Description true Enables HTTPS connections. false Disables HTTPS connections. 45.3.3.8 httpsProcs Purpose Specifies the maximum number of simultaneous HTTPS client connections before new incoming HTTPS requests are blocked. Default is 8 . 620 SFCB configuration file SLES 15 SP6Syntax httpsProcs:   MAX_NUMBER_OF_CONNECTIONS 45.3.3.9 enableInterOp Purpose Specifies if SFCB will provide the interop namespace for indication support. Default is true . Syntax enableInterOp:   OPTION Option Description true Enables interop namespace. false Disables interop namespace. 45.3.3.10 provProcs Purpose Specifies the maximum number of simultaneous provider processes. After this point, if a new incoming request requires loading a new provider, then one of the existing providers will rst be automatically unloaded. Default is 32 . Syntax provProcs:   MAX_NUMBER_OF_PROCS 621 SFCB configuration file SLES 15 SP645.3.3.11 doBasicAuth Purpose Switches basic authentication on or o based on the client user identifier before it accepts the request. Default value is true which means that basic client authentication is performed. Syntax doBasicAuth:   OPTION Option Description true Enables basic authentication. false Disables basic authentication. 45.3.3.12 basicAuthLib Purpose Specifies the local library name. The SFCB server loads the library to authenticate the client user identifier. Default is sfcBasicPAMAuthentication . Syntax provProcs:   MAX_NUMBER_OF_PROCS 45.3.3.13 useChunking Purpose This option switches the use of HTTP/HTTPS “chunking” on or o. If switched on, the server will return large volumes of response data to the client in smaller “chunks”, rather than buer the data and send it back all in one chunk. Default is true . 622 SFCB configuration file SLES 15 SP6Syntax useChunking:   OPTION Option Description true Enables HTTP/HTTPS data chunking. false Disables HTTP/HTTPS data chunking. 45.3.3.14 keepaliveTimeout Purpose Specifies the maximum time in seconds that SFCB HTTP process waits between two requests on one connection before it terminates. Setting it to 0 disables HTTP keep-alive. Default is 0 . Syntax keepaliveTimeout:   SECS 45.3.3.15 keepaliveMaxRequest Purpose Specifies the maximum number of consecutive requests on one connection. Setting it to 0 dis- ables HTTP keep-alive. Default value is 10 . Syntax keepaliveMaxRequest:   NUMBER_OF_CONNECTIONS 623 SFCB configuration file SLES 15 SP645.3.3.16 registrationDir Purpose Specifies the registration directory, which contains the provider registration data, the staging area, and the static repository. Default is /var/lib/sfcb/registration . Syntax registrationDir:   DIR 45.3.3.17 providerDirs Purpose Specifies a space-separated list of directories where SFCB is searching for provider libraries. Default is /usr/lib64 /usr/lib64 /usr/lib64/cmpi . Syntax providerDirs:   DIR 45.3.3.18 providerSampleInterval Purpose Specifies the interval in seconds at which the provider manager is checking for idle providers. Default is 30 . Syntax providerSampleInterval:   SECS 624 SFCB configuration file SLES 15 SP645.3.3.19 providerTimeoutInterval Purpose Specifies the interval in seconds before an idle provider gets unloaded by the provider manager. Default is 60 . Syntax providerTimeoutInterval:   SECS 45.3.3.20 providerAutoGroup Purpose If the provider registration le does not specify any other group, and the option is set to true , all providers in the same shared library are executed in the same process. Syntax providerAutoGroup:   OPTION Option Description true Enables grouping of providers. false Disables grouping of providers. 45.3.3.21 sslCertificateFilePath Purpose Specifies the name of the le that contains the server certificate. The le must be in PEM (Privacy Enhanced Mail, RFC 1421 and RFC 1424) format. This le is only required if enableHttps is set to true . Default is /etc/sfcb/server.pem . 625 SFCB configuration file SLES 15 SP6Syntax sslCertificateFilePath:   PATH 45.3.3.22 sslKeyFilePath Purpose Specifies the name of the le that contains the private key for the server certificate. The le must be in PEM format and may not be protected by passphrase. This le is only required if enableHttps is set to true . Default is /etc/sfcb/file.pem . Syntax sslKeyFilePath:   PATH 45.3.3.23 sslClientTrustStore Purpose Specifies the name of the le that contains either the CA or self-signed certificates of the clients. This le must be in PEM format and is only required if sslClientCertificate is set to accept or require . Default is /etc/sfcb/client.pem . Syntax sslClientTrustStore:   PATH 626 SFCB configuration file SLES 15 SP645.3.3.24 sslClientCertificate Purpose Specifies the way SFCB handles client certificate based authentication. If set to ignore , it will not request a certificate from the client. If set to accept it will request a certificate from the client but will not fail if the client does not present one. If set to require , it will refuse the client connection if the client does not present a certificate. Default value is ignore . Syntax sslClientCertificate:   OPTION Option Description ignore Disables requesting a client certificate. accept Disables requesting a client certificate. Will not fail if no certificate is present. require Refuses the client connection without a valid certificate. 45.3.3.25 certificateAuthLib Purpose Specifies the name of the local library to request for the user authentication based on client certificate. This is only requested if sslClientCertificate is not set to ignore . Default value is sfcCertificateAuthentication . Syntax certificateAuthLib:   FILE 627 SFCB configuration file SLES 15 SP645.3.3.26 traceLevel Purpose Specifies the trace level for SFCB. You can override it by setting environment variable SFCB_TRACE_LEVEL . Default value is 0 . Syntax traceLevel:   NUM_LEVEL 45.3.3.27 traceMask Purpose Specifies the trace mask for SFCB. you can override it by the command line option --trace- components . Default value is 0 . Syntax traceMask:   MASK 45.3.3.28 traceFile Purpose Specifies the trace le for SFCB. You can override it by setting environment variable SFCB_TRACE_FILE . Default value is stderr (standard error output). Syntax traceFile:   OUTPUT 628 SFCB configuration file SLES 15 SP645.4 Advanced SFCB tasks This chapter covers more advanced topics related to SFCB usage. To understand them, you need to have basic knowledge of the Linux le system and experience with the Linux command line. This chapter includes the following tasks: Installing CMPI providers Testing SFCB Using wbemcli CIM client 45.4.1 Installing CMPI providers To install a CMPI provider, you need to make sure that its shared library is copied into one of the directories specified by providerDirs configuration option, see Section 45.3.3.17, “providerDirs”. The provider must also be properly registered using sfcbstage and sfcbrepos commands. The provider package is prepared for SFCB, so that its installation takes care of the proper registration. Most SBLIM providers are prepared for SFCB. 45.4.1.1 Class repository Class repository is a place where SFCB stores information about CIM classes. It consists of a directory tree with namespace components. Typical CIM namespaces are root/cimv2 or root/ interop , which respectively translate to the class repository directory path on the le system /var/lib/sfcb/registration/repository/root/cimv2 and /var/lib/sfcb/registration/repository/root/interop Each namespace directory contains the le classSchemas . The le has a compiled binary rep- resentation of all the CIM classes registered under that namespace. It also contains necessary information about their CIM superclasses. Each namespace directory may contain a le qualifiers which contains all qualifiers for the namespace. When sfcbd restarts, the class provider will scan the directory /var/lib/sfcb/ registration/repository/ and all its subdirectories to determine the registered namespaces. Then classSchemas les are decoded and the class hierarchy for each namespace is built. 629 Advanced SFCB tasks SLES 15 SP645.4.1.2 Adding new classes SFCB cannot make live CIM class manipulations. You need to add, change or remove classes offline and restart SFCB service with systemctl restart sfcb to register the changes. To store providers class and registration information, SFCB uses a place called staging area. On SUSE® Linux Enterprise Server systems, it is the directory structure under /var/lib/sfcb/ stage/ . To add a new provider, you need to: Copy the provider class definition les to the ./mofs subdirectory of staging area directory ( /var/lib/sfcb/stage/mofs ). Copy a registration le which contains the name of the class or classes and type of provider, and the name of the executable library le into the ./regs subdirectory. There are two default “mof” (class definition) les in the staging directory: indication.mof and interop.mof . MOF les under the root stage directory /var/lib/sfcb/stage/mofs will be copied into each namespace after running sfcbrepos command. The interop.mof will only be compiled into the interop namespace. The directory layout may look like the following example: > ls /var/lib/sfcb/stage default.reg mofs regs > ls /var/lib/sfcb/stage/mofs indication.mof root > ls /var/lib/sfcb/stage/mofs/root cimv2 interop suse virt > ls -1 /var/lib/sfcb/stage/mofs/root/cimv2 | less Linux_ABIParameter.mof Linux_BaseIndication.mof Linux_Base.mof Linux_DHCPElementConformsToProfile.mof Linux_DHCPEntity.mof [..] OMC_StorageSettingWithHints.mof OMC_StorageVolumeDevice.mof OMC_StorageVolume.mof OMC_StorageVolumeStorageSynchronized.mof OMC_SystemStorageCapabilities.mof 630 Installing CMPI providers SLES 15 SP6> ls -1 /var/lib/sfcb/stage/mofs/root/interop ComputerSystem.mof ElementConformsToProfile.mof HostSystem.mof interop.mof Linux_DHCPElementConformsToProfile.mof [..] OMC_SMIElementSoftwareIdentity.mof OMC_SMISubProfileRequiresProfile.mof OMC_SMIVolumeManagementSoftware.mof ReferencedProfile.mof RegisteredProfile.mof > ls -1 /var/lib/sfcb/stage/regs AllocationCapabilities.reg Linux_ABIParameter.reg Linux_BaseIndication.reg Linux_DHCPGlobal.reg Linux_DHCPRegisteredProfile.reg [..] OMC_Base.sfcb.reg OMC_CopyServices.sfcb.reg OMC_PowerManagement.sfcb.reg OMC_Server.sfcb.reg RegisteredProfile.reg > cat /var/lib/sfcb/stage/regs/Linux_DHCPRegisteredProfile.reg [Linux_DHCPRegisteredProfile] provider: Linux_DHCPRegisteredProfileProvider location: cmpiLinux_DHCPRegisteredProfile type: instance namespace: root/interop # [Linux_DHCPElementConformsToProfile] provider: Linux_DHCPElementConformsToProfileProvider location: cmpiLinux_DHCPElementConformsToProfile type: instance association namespace: root/cimv2 # [Linux_DHCPElementConformsToProfile] provider: Linux_DHCPElementConformsToProfileProvider location: cmpiLinux_DHCPElementConformsToProfile type: instance association namespace: root/interop SFCB uses a custom provider registration le for each provider. 631 Installing CMPI providers SLES 15 SP6Note: SBLIM providers registration files All SBLIM providers on the SBLIM Web site already include a registration le that is used to generate the .reg le for SFCB. The format of SFCB registration le is: [ ] provider: location: type: [instance] [association] [method] [indication] group: unload: never namespace: ... where: The CIM class name (required) The CMPI provider name (required) The name of the provider library (required) type The type of the provider (required). This can be any combination of: instance , associ- ation , method or indication . Multiple providers can be grouped together and run under a single process to further min- imize runtime resources. All providers registered under the same will be executed under the same process. By default each provider will be run as a separate process. unload Specifies the unload policy for the provider. Currently the only supported option is never , which specifies that the provider will not be monitored for idle times and will never be unloaded. By default each provider will be unloaded when its idle times exceed the value specified in the configuration le. 632 Installing CMPI providers SLES 15 SP6namespace List of namespaces for which this provider can be executed. This is required, although for most providers this will be root/cimv2 . Once all the class definitions and provider registration les are stored in the staging area, you need to rebuild the SFCB class repository with the command sfcbrepos -f . You can add, change or remove classes this way. After rebuilding the class repository, restart SFCB with command systemctl restart sfcb . Alternatively, the SFCB package contains a utility that will copy provider class mof les and registration les to the correct locations in the staging area. sfcbstage -r [provider.reg] [class1.mof] [class2.mof] ... After running this command you still need to rebuild the class repository and restart SFCB service. 45.4.2 Testing SFCB The SFCB package includes two testing scripts: wbemcat and xmltest . wbemcat sends raw CIM-XML data via HTTP protocol to the specified SFCB host (localhost by default) listening on port 5988. Then it displays the returned results. The following le contains the CIM-XML representation of a standard EnumerateClasses request: TRUE FALSE 633 Testing SFCB SLES 15 SP6 FALSE TRUE Sending this request to SFCB CIMOM returns a list of all supported classes for which there is a registered provider. Suppose you save the le as cim_xml_test.xml . > wbemcat cim_xml_test.xml | less HTTP/1.1 200 OK Content-Type: application/xml; charset="utf-8" Content-Length: 337565 Cache-Control: no-cache CIMOperation: MethodResponse [..] The classes listed will vary depending on what providers are installed on your system. The second script xmltest is also used to send a raw CIM-XML test le to the SFCB CIMOM. It then compares the returned results against a previously saved “OK” result le. If there does not yet exist a corresponding “OK” le, it will be created for later use: > xmltest cim_xml_test.xml Running test cim_xml_test.xml ... OK Saving response as cim_xml_test.OK 634 Testing SFCB SLES 15 SP6# xmltest cim_xml_test.xml Running test cim_xml_test.xml ... Passed 45.4.3 Command line CIM client: wbemcli Besides wbemcat and xmltest , the SBLIM project includes a more advanced command line CIM client wbemcli . The client is used to send CIM requests to SFCB server and display returned results. It is independent of CIMOM library and can be used with all WBEM compliant imple- mentations. For example, if you need to list all the classes implemented by SBLIM providers registered to your SFCB, send the “EnumerateClasses” (ec) request to SFCB: > wbemcli -dx ec http://localhost/root/cimv2 To server: \ \ TRUE \ FALSE FALSE \ TRUE \ From server: Content-Type: application/xml; charset="utf-8" From server: Content-Length: 337565 From server: Cache-Control: no-cache From server: CIMOperation: MethodResponse From server: 635 Command line CIM client: wbemcli SLES 15 SP6 [..] 0 0 [..] The -dx option shows you the actual XML sent to SFCB by wbemcli and the actual XML re- ceived. In the above example, the rst of many returned classes was CIM_ResourcePool fol- lowed by Linux_Ext4FileSystem . Similar entries will appear for all other registered classes. If you omit the -dx option, wbemcli will display only a compact representation of the returned data: > wbemcli ec http://localhost/root/cimv2 localhost:5988/root/cimv2:CIM_ResourcePool Generation=,ElementName=, \ Description=,Caption=,InstallDate=,Name=,OperationalStatus=, \ StatusDescriptions=,Status=,HealthState=,PrimaryStatus=, \ DetailedStatus=,OperatingStatus=,CommunicationStatus=,InstanceID=, \ PoolID=,Primordial=,Capacity=,Reserved=,ResourceType=, \ OtherResourceType=,ResourceSubType=, \AllocationUnits= localhost:5988/root/cimv2:Linux_Ext4FileSystem FSReservedCapacity=, \ TotalInodes=,FreeInodes=,ResizeIncrement=,IsFixedSize=,NumberOfFiles=, \ OtherPersistenceType=,PersistenceType=,FileSystemType=,ClusterSize=, \ MaxFileNameLength=,CodeSet=,CasePreserved=,CaseSensitive=, \ CompressionMethod=,EncryptionMethod=,ReadOnly=,AvailableSpace=, \ FileSystemSize=,BlockSize=,Root=,Name=,CreationClassName=,CSName=, \ CSCreationClassName=,Generation=,ElementName=,Description=,Caption=, \ InstanceID=,InstallDate=,OperationalStatus=,StatusDescriptions=, \ Status=,HealthState=,PrimaryStatus=,DetailedStatus=,OperatingStatus= \ ,CommunicationStatus=,EnabledState=,OtherEnabledState=,RequestedState= \ ,EnabledDefault=,TimeOfLastStateChange=,AvailableRequestedStates=, \ TransitioningToState=,PercentageSpaceUse= 636 Command line CIM client: wbemcli SLES 15 SP6[..] 45.5 More information FOR MORE DETAILS ABOUT WBEM AND SFCB, SEE THE FOLLOWING SOURCES: https://www.dmtf.org Distributed Management Task Force Web site https://www.dmtf.org/standards/wbem/ Web-Based Enterprise Management (WBEM) Web site https://www.dmtf.org/standards/cim/ Common Information Model (CIM) Web site 637 More information SLES 15 SP6VI Troubleshooting 46 Help and documentation 639 47 Gathering system information for support 644 48 Common problems and their solutions 67446 Help and documentation SUSE® Linux Enterprise Server comes with several sources of information and documentation, available online or integrated into your installed system. Product Documentation Extensive documentation for SUSE Linux Enterprise Server is available at https://documen- tation.suse.com/#sles . Topics covered range from deployment, upgrade and system ad- ministration to virtualization, system tuning and security, among others. At https://documentation.suse.com/sbp-supported.html , you can nd SUSE''s best practice series of documents covering hands-on documentation on implementation scenarios. At https://documentation.suse.com/trd-supported.html , our technical reference documenta- tion series provides guides on deploying solution components from SUSE and its partners. Documentation in /usr/share/doc This directory holds release notes for your system (in the subdirectory release-notes ). It also contains information of installed packages in the subdirectory packages . Find more detailed information in Section 46.1, “Documentation directory”. Man pages and info pages for shell commands When working with the shell, you do not need to know the options of the commands by heart. Traditionally, the shell provides integrated help by means of man pages and info pages. Read more in Section 46.2, “Man pages” and Section 46.3, “Info pages”. Desktop help center The help center of the GNOME desktop (Help) provides central access to the GNOME desktop documentation. Separate help packages for certain applications When installing new software with YaST, the software documentation is normally installed automatically and appears in the help center of your desktop. However, certain applica- tions, such as GIMP, may have different online help packages that can be installed sepa- rately with YaST and do not integrate into the help centers. 639 SLES 15 SP646.1 Documentation directory The traditional directory to nd documentation on your installed Linux system is /usr/share/ doc . The directory contains the release notes and information about the packages installed on your system, plus manuals and more. Note: Contents depend on installed packages In the Linux world, manuals and other kinds of documentation are available in the form of packages, like software. How much and which information you nd in /usr/share/ doc also depends on the (documentation) packages installed. If you cannot nd the sub- directories mentioned here, check if the respective packages are installed on your system and add them with YaST, if needed. 46.1.1 Release notes We provide HTML, PDF, RTF and text versions of SUSE Linux Enterprise Server release notes. They are available on your installed system under /usr/share/doc/release-notes/ or online at your product-specific Web page at https://www.suse.com/releasenotes/index.html . 46.1.2 Package documentation Under packages , nd the documentation that is included in the software packages installed on your system. For every package, a subdirectory /usr/share/doc/packages/PACKAGENAME is created. It often contains README les for the package and sometimes examples, configuration les, or additional scripts. The following list introduces typical les to be found under /usr/ share/doc/packages . None of these entries are mandatory and many packages only include a few of them. AUTHORS List of the main developers. BUGS Known bugs or malfunctions. May also contain a link to a Bugzilla Web page where you can search all bugs. 640 Documentation directory SLES 15 SP6CHANGES , ChangeLog Summary of changes from version to version. It is interesting for developers, because it is detailed. COPYING , LICENSE Licensing information. FAQ Question and answers collected from mailing lists or newsgroups. INSTALL How to install this package on your system. As the package is already installed by the time you get to read this le, you can safely ignore the contents of this le. README , README.* General information on the software. For example, for what purpose and how to use it. TODO Features planned for the future. MANIFEST List of les with a brief summary. NEWS Description of what is new in this version. 46.2 Man pages Man pages are an essential part of any Linux system. They explain the usage of a command and all available options and parameters. Man pages can be accessed with man followed by the name of the command, for example, man ls . Man pages are displayed directly in the shell. To navigate them, move up and down with Page ↑ and Page ↓ . Move between the beginning and the end of a document with Home and End . End this viewing mode by pressing Q . Learn more about the man command itself with man man . Man pages are sorted in categories as shown in Table 46.1, “Man pages—categories and descriptions” (taken from the man page for man itself). 641 Man pages SLES 15 SP6TABLE 46.1: MAN PAGES—CATEGORIES AND DESCRIPTIONS Number Description 1 Executable programs or shell commands 2 System calls (functions provided by the ker- nel) 3 Library calls (functions within program li- braries) 4 Special les (normally found in /dev ) 5 File formats and conventions ( /etc/fstab ) 6 Games 7 Miscellaneous (including macro packages and conventions), for example, man(7), gro(7) 8 System administration commands (normally only for root ) 9 Kernel routines (nonstandard) Each man page consists of several parts labeled NAME, SYNOPSIS, DESCRIPTION, SEE ALSO, LICENSING, and AUTHOR. There may be additional sections available depending on the type of command. 46.3 Info pages Info pages are another important source of information on your system. normally, they are more detailed than man pages. They consist of more than command line options and contain sometimes whole tutorials or reference documentation. To view the info page for a certain command, enter info followed by the name of the command, for example, info ls . You can browse an info page with a viewer directly in the shell and display the different sections, called “nodes”. Use Space to move forward and <— to move backward. Within a node, you can also 642 Info pages SLES 15 SP6browse with Page ↑ and Page ↓ but only Space and <— takes you also to the previous or subsequent node. Press Q to end the viewing mode. Not every command comes with an info page and vice versa. 46.4 Online resources For an overview of all documentation available for SUSE Linux Enterprise Server check out the product-specific documentation Web pages at https://documentation.suse.com/ . If you are searching for additional product-related information, you can also refer to the follow- ing Web sites: SUSE technical support The SUSE Technical Support can be found at https://www.suse.com/support/ if you have questions or need solutions for technical problems. User community SUSE and Rancher Community (https://www.rancher.com/community) SUSE blog The SUSE blog offers articles, tips, Q and A: https://www.suse.com/c/blog/ GNOME documentation Documentation for GNOME users, administrators and developers is available at https:// help.gnome.org/ . The Linux documentation project The Linux Documentation Project (TLDP) is run by a team of volunteers who write Lin- ux-related documentation (see https://tldp.org/ ). It is a comprehensive documentation resource for Linux. The set of documents contains tutorials for beginners, but is mainly fo- cused on experienced users and professional system administrators. TLDP publishes HOW- TOs, FAQs and guides (handbooks) under a free license. Parts of the documentation from TLDP are also available on SUSE Linux Enterprise Server. 643 Online resources SLES 15 SP647 Gathering system information for support For a quick overview of all relevant system information of a machine, SUSE Linux Enterprise Server offers the hostinfo package. It also helps system administrators to check for tainted kernels (that are not supported) or any third-party packages in- stalled on a machine. In case of problems, a detailed system report may be created with either the sup- portconfig command line tool or the YaST Support module. Both collect informa- tion about the system such as: current kernel version, hardware, installed packages, partition setup, and much more. The result is a TAR archive of les. After opening a Service Request (SR), you can upload the TAR archive to Global Technical Support. It helps to locate the issue you reported and to assist you in solving the problem. Additionally, you can analyze the supportconfig output for known issues to help resolve problems faster. For this purpose, SUSE Linux Enterprise Server provides both an appliance and a command line tool for Supportconfig Analysis (SCA). 47.1 Displaying current system information For a quick and easy overview of all relevant system information when logging in to a server, use the package hostinfo . After it has been installed on a machine, the console displays the following information to any root user that logs in to this machine: EXAMPLE 47.1: OUTPUT OF hostinfo WHEN LOGGING IN AS root Welcome to SUSE Linux Enterprise Server 15 SP2 Snapshot8 (x86_64) - Kernel \r (\l). Distribution: SUSE Linux Enterprise Server 15 SP6 Current As Of: Mon 11 March 2024 10:11:51 AM CET Hostname: localhost Kernel Version: 6.4.0-150600.9-default Architecture: x86_64 Installed: Fri 08 March 2024 04:45:50 PM CET Status: Not Tainted Last Installed Package: Mon 11 March 2024 10:02:13 AM CET Patches Needed: 0 Security: 0 3rd Party Packages: 6 644 Displaying current system information SLES 15 SP6Network Interfaces eth0: 192.168.2/24 2002:c0a8:20a::/64 Memory Total/Free/Avail: 7.4Gi/6.4Gi/6.8Gi (91% Avail) CPU Load Average: 7 (3%) with 2 CPUs In case the output shows a tainted kernel status, see Section 47.6, “Support of kernel modules” for more details. 47.2 Collecting system information with supportconfig To create a TAR archive with detailed system information that you can hand over to Global Technical Support, use either: the command supportconfig or, the YaST Support module. The command line tool is provided by the package supportutils which is installed by default. The YaST Support module is also based on the command line tool. Certain packages integrate Supportconfig plug-ins. When Supportconfig is executed, all plug-ins are executed as well and create one or more result les for the archive. The benefit is that only topics with a specific plug-in are checked. Supportconfig plug-ins are stored in the directory / usr/lib/supportconfig/plugins/ . 47.2.1 Creating a service request number Supportconfig archives can be generated at any time. However, for handing over the Support- config data to Global Technical Support, you need to generate a service request number rst. You need it to upload the archive to support. To create a service request, go to https://scc.suse.com/support/requests and follow the instruc- tions on the screen. Write down the service request number. Note: Privacy statement SUSE treats system reports as confidential data. For details about our privacy commit- ment, see https://www.suse.com/company/policies/privacy/ . 645 Collecting system information with supportconfig SLES 15 SP647.2.2 Upload targets After having created a service request number, you can upload your Supportconfig archives to Global Technical Support as described in Procedure 47.1, “Submitting information to support with YaST” or Procedure 47.2, “Submitting information to support from command line”. Use one of the fol- lowing upload targets: North America: FTP ftp://support-ftp.us.suse.com/incoming/ EMEA, Europe, the Middle East and Africa: FTP ftp://support-ftp.emea.suse.com/incom- ing Alternatively, you can manually attach the TAR archive to your service request using the service request URL: https://scc.suse.com/support/requests . 47.2.3 Creating a supportconfig archive with YaST To use YaST to gather your system information, proceed as follows: 1. Start YaST and open the Support module. 2. Click Create report tarball. 646 Upload targets SLES 15 SP63. In the next window, select one of the Supportconfig options from the radio button list. Use Custom (Expert) Settings is preselected by default. To test the report function rst, use Only gather a minimum amount of info. For additional information on the other options, refer to the supportconfig man page. Click Next. 4. Enter your contact information. It is saved in the basic-environment.txt le and in- cluded in the created archive. 5. To submit the archive to Global Technical Support, provide the required Upload Informa- tion. YaST automatically suggests an upload server. To modify it, refer to Section 47.2.2, “Upload targets” for details of which upload servers are available. To submit the archive later, leave the Upload Information empty. 6. Click Next to start the information collection process. After the process is finished, click Next. 7. To review the collected data, select the desired le from File Name to view its contents in YaST. To remove a le from the TAR archive before submitting it to support, use Remove from Data. Press Next. 647 Creating a supportconfig archive with YaST SLES 15 SP68. Save the TAR archive. If you started the YaST module as root user, YaST prompts to save the archive to /var/log (otherwise, to your home directory). The le name format is scc_HOST_DATE_TIME.tbz . 9. To upload the archive to support directly, make sure Upload log les tarball to URL is acti- vated. The Upload Target shown here is the one that YaST suggests in Step 5. To modify the upload target, check which upload servers are available in Section 47.2.2, “Upload targets”. 10. To skip the upload, deactivate Upload log les tarball to URL. 11. Confirm the changes to close the YaST module. 47.2.4 Creating a supportconfig archive from command line The following procedure shows how to create a Supportconfig archive, but without submitting it to support directly. For uploading it, you need to run the command with certain options as described in Procedure 47.2, “Submitting information to support from command line”. 1. Open a shell and become root . 2. Run supportconfig . It is enough to run this tool without any options. However, the most common options are displayed in the following list: -E MAIL , -N NAME , -O COMPANY , -P PHONE Sets your contact data: e-mail address ( -E ), company name ( -O ), your name ( -N ), and your phone number ( -P ). -i KEYWORDS , -F Limits the features to check. The placeholder KEYWORDS is a comma separated list of case-sensitive keywords. Get a list of all keywords with supportconfig -F . -r SRNUMBER Defines your service request number when uploading the generated TAR archive. 3. Wait for the tool to complete the operation. 648 Creating a supportconfig archive from command line SLES 15 SP64. The default archive location is /var/log , with the le name format being sc- c_HOST_DATE_TIME.tbz 47.2.5 Understanding the output of supportconfig Whether you run supportconfig through YaST or directly, the script gives you a summary of what it did. Support Utilities - Supportconfig Script Version: 3.0-98 Script Date: 2017 06 01 [...] Gathering system information Data Directory: /var/log/scc_d251_180201_1525 1 Basic Server Health Check... Done 2 RPM Database... Done 2 Basic Environment... Done 2 System Modules... Done 2 [...] File System List... Skipped 3 [...] Command History... Excluded 4 [...] Supportconfig Plugins: 1 5 Plugin: pstree... Done [...] Creating Tar Ball ==[ DONE ]=================================================================== Log file tar ball: /var/log/scc_d251_180201_1525.txz 6 Log file size: 732K Log file md5sum: bf23e0e15e9382c49f92cbce46000d8b ============================================================================= 1 The temporary data directory to store the results. This directory is archived as tar le, see 6 . 2 The feature was enabled (either by default or selected manually) and executed successfully. The result is stored in a le (see Table 47.1, “Comparison of features and file names in the TAR archive”). 3 The feature was skipped because les of one or more RPM packages were changed. 4 The feature was excluded because it was deselected via the -x option. 649 Understanding the output of supportconfig SLES 15 SP65 The script found one plug-in and executes the plug-in pstree . The plug-in was found in the directory /usr/lib/supportconfig/plugins/ . See the man page for details. 6 The tar le name of the archive, by default compressed with xz . 47.2.6 Common supportconfig options The supportconfig utility is usually called without any options. Display a list of all options with supportconfig -h or refer to the man page. The following list gives a brief overview of common use cases: Reducing the size of the information being gathered Use the minimal option ( -m ): > sudo supportconfig -m Limiting the information to a specific topic If you have already localized a problem that relates to a specific area or feature set only, you should limit the collected information to the specific area for the next supportconfig run. For example, if you detected problems with LVM and want to test a recent change that you did to the LVM configuration. In that case it makes sense to gather the minimum Supportconfig information around LVM only: > sudo supportconfig -i LVM Additional keywords can be separated through commas. For example, an additional disk test: > sudo supportconfig -i LVM,DISK For a complete list of feature keywords that you can use for limiting the collected infor- mation to a specific area, run: > sudo supportconfig -F Including additional contact information in the output: > sudo supportconfig -E tux@example.org -N "Tux Penguin" -O "Penguin Inc." ... (all in one line) Collecting already rotated log files > sudo supportconfig -l 650 Common supportconfig options SLES 15 SP6This is especially useful in high logging environments or after a kernel crash when syslog rotates the log les after a reboot. 47.2.7 Overview of the archive content The TAR archive contains all the results from the features. The set of features can be limited through the -i option (see Section 47.2.6, “Common supportconfig options”). To list the content of the archive, use the following tar command: # tar xf /var/log/scc_earth_180131_1545.tbz The following le names are always available inside the TAR archive: MINIMUM FILES IN ARCHIVE basic-environment.txt Contains the date when this script was executed and system information like version of the distribution, hypervisor information, and more. basic-health-check.txt Contains basic health checks like uptime, virtual memory statistics, free memory and hard disk, checks for zombie processes, and more. hardware.txt Contains basic hardware checks like information about the CPU architecture, list of all connected hardware, interrupts, I/O ports, kernel boot messages, and more. messages.txt Contains log messages from the system journal. rpm.txt Contains a list of all installed RPM packages, the name, where they are coming from, and their versions. summary.xml Contains information in XML format like distribution, the version, and product specific fragments. supportconfig.txt Contains information about the supportconfig script itself. y2log.txt Contains YaST specific information like specific packages, configuration les, and log les. 651 Overview of the archive content SLES 15 SP6Table 47.1, “Comparison of features and file names in the TAR archive” lists all available features and their le names. Further service packs can extend the list, as can plug-ins. TABLE 47.1: COMPARISON OF FEATURES AND FILE NAMES IN THE TAR ARCHIVE Feature File name APPARMOR security-apparmor.txt AUDIT security-audit.txt AUTOFS fs-autofs.txt BOOT boot.txt BTRFS fs-btrfs.txt DAEMONS systemd.txt CIMOM cimom.txt CRASH crash.txt CRON cron.txt DHCP dhcp.txt DISK fs-diskio.txt DNS dns.txt DOCKER docker.txt DRBD drbd.txt ENV env.txt ETC etc.txt HA ha.txt HAPROXY haproxy.txt HISTORY shell_history.txt IB ib.txt IMAN novell-iman.txt 652 Overview of the archive content SLES 15 SP6Feature File name ISCSI fs-iscsi.txt LDAP ldap.txt LIVEPATCH kernel-livepatch.txt LVM lvm.txt MEM memory.txt MOD modules.txt MPIO mpio.txt NET network-*.txt NFS nfs.txt NTP ntp.txt NVME nvme.txt OCFS2 ocfs2.txt OFILES open-files.txt PRINT print.txt PROC proc.txt SAR sar.txt SLERT slert.txt SLP slp.txt SMT smt.txt SMART fs-smartmon.txt SMB samba.txt SRAID fs-softraid.txt SSH ssh.txt 653 Overview of the archive content SLES 15 SP6Feature File name SSSD sssd.txt SYSCONFIG sysconfig.txt SYSFS sysfs.txt TRANSACTIONAL transactional-update.txt TUNED tuned.txt UDEV udev.txt UFILES fs-files-additional.txt UP updates.txt WEB web.txt X x.txt 47.3 Submitting information to Global Technical Support Use the YaST Support module or the supportconfig command line utility to submit system information to the Global Technical Support. When you experience a server issue and want the support''s assistance, you will need to open a service request rst. For details, see Section 47.2.1, “Creating a service request number”. The following examples use 12345678901 as a placeholder for your service request number. Replace 12345678901 with the service request number you created in Section 47.2.1, “Creating a service request number”. PROCEDURE 47.1: SUBMITTING INFORMATION TO SUPPORT WITH YAST The following procedure assumes that you have already created a Supportconfig archive, but have not uploaded it yet. Make sure to have included your contact information in the archive as described in Section 47.2.3, “Creating a supportconfig archive with YaST”, Step 4. For instructions on how to generate and submit a Supportconfig archive in one go, see Section 47.2.3, “Creating a supportconfig archive with YaST”. 654 Submitting information to Global Technical Support SLES 15 SP61. Start YaST and open the Support module. 2. Click Upload. 3. In Package with log les specify the path to the existing Supportconfig archive or Browse for it. 4. YaST automatically proposes an upload server. To modify it, refer to Section 47.2.2, “Upload targets” for details of which upload servers are available. Proceed with Next. 5. Click Finish. PROCEDURE 47.2: SUBMITTING INFORMATION TO SUPPORT FROM COMMAND LINE The following procedure assumes that you have already created a Supportconfig archive, but have not uploaded it yet. For instructions on how to generate and submit a Support- config archive in one go, see Section 47.2.3, “Creating a supportconfig archive with YaST”. 1. Servers with Internet connectivity: a. To use the default upload target, run: > sudo supportconfig -ur 12345678901 655 Submitting information to Global Technical Support SLES 15 SP6b. For the secure upload target, use the following: > sudo supportconfig -ar 12345678901 2. Servers without Internet connectivity a. Run the following: > sudo supportconfig -r 12345678901 b. Manually upload the /var/log/scc_SR12345678901*tbz archive to one of our FTP servers. Which one to use depends on your location in the world. For an overview, see Section 47.2.2, “Upload targets”. 3. After the TAR archive arrives in the incoming directory of our FTP server, it becomes automatically attached to your service request. 47.4 Analyzing system information System reports created with supportconfig can be analyzed for known issues to help resolve problems faster. For this purpose, SUSE Linux Enterprise Server provides both an appliance and a command line tool for Supportconfig Analysis (SCA). The SCA appliance is a serv- er-side tool which is non-interactive. The SCA tool ( scatool provided by the package sca- server-report ) runs on the client-side and is executed from command line. Both tools analyze Supportconfig archives from affected servers. The initial server analysis takes place on the SCA appliance or the workstation on which scatool is running. No analysis cycles happen on the production server. Both the appliance and the command line tool additionally need product-specific patterns that enable them to analyze the Supportconfig output for the associated products. Each pattern is a script that parses and evaluates a Supportconfig archive for one known issue. The patterns are available as RPM packages. You can also develop your own patterns as briey described in Section 47.4.3, “Developing custom analysis patterns”. 656 Analyzing system information SLES 15 SP647.4.1 SCA command line tool The SCA command line tool lets you analyze a local machine using both supportconfig and the analysis patterns for the specific product that is installed on the local machine. The tool creates an HTML report showing its analysis results. For an example, see Figure 47.1, “HTML report generated by SCA tool”. FIGURE 47.1: HTML REPORT GENERATED BY SCA TOOL The scatool command is provided by the sca-server-report package. It is not installed by default. Additionally, you need the sca-patterns-base package and any of the product-spe- cific sca-patterns-* packages that matches the product installed on the machine where you want to run the scatool command. Execute the scatool command either as root user or with sudo . When calling the SCA tool, either analyze an existing supportconfig TAR archive or let it generate and analyze a new archive in one go. The tool also provides an interactive console with tab completion. It is possible to run supportconfig on an external machine and to execute the subsequent analysis on the local machine. 657 SCA command line tool SLES 15 SP6Find a few example commands below: sudo scatool -s Calls supportconfig and generates a new Supportconfig archive on the local machine. Analyzes the archive for known issues by applying the SCA analysis patterns that match the installed product. Displays the path to the HTML report that is generated from the results of the analysis. It is written to the same directory where the Supportconfig archive can be found. sudo scatool  -s   -o   /opt/sca/reports/ Same as sudo scatool -s , only that the HTML report is written to the path specified with -o . sudo scatool  -a   PATH_TO_TARBALL_OR_DIR Analyzes the specified Supportconfig archive le (or the specified directory to where the Supportconfig archive has been extracted). The generated HTML report is saved in the same location as the Supportconfig archive or directory. sudo scatool  -a   SLES_SERVER.COMPANY.COM Establishes an SSH connection to an external server SLES_SERVER.COMPANY.COM and runs supportconfig on the server. The Supportconfig archive is then copied back to the lo- cal machine and is analyzed there. The generated HTML report is saved to the default / var/log directory. (Only the Supportconfig archive is created on SLES_SERVER.COMPA- NY.COM ). sudo scatool -c Starts the interactive console for scatool . Press →| twice to see the available commands. For further options and information, run sudo scatool -h or see the scatool man page. 47.4.2 SCA appliance If you decide to use the SCA appliance for analyzing the Supportconfig archives, configure a dedicated server (or virtual machine) as the SCA appliance server. The SCA appliance server can then be used to analyze Supportconfig archives from all machines in your enterprise running SUSE Linux Enterprise Server or SUSE Linux Enterprise Desktop. You can simply upload Sup- portconfig archives to the appliance server for analysis. Interaction is not required. In a MariaDB database, the SCA appliance keeps track of all Supportconfig archives that have been analyzed . 658 SCA appliance SLES 15 SP6You can read the SCA reports directly from the appliance Web interface. Alternatively, you can have the appliance send the HTML report to any administrative user via e-mail. For details, see Section 47.4.2.5.4, “Sending SCA reports via e-mail”. 47.4.2.1 Installation quick start To install and set up the SCA appliance in a fast way from the command line, follow the in- structions here. The procedure is intended for experts and focuses on the bare installation and setup commands. For more information, refer to the more detailed description in Section 47.4.2.2, “Prerequisites” to Section 47.4.2.3, “Installation and basic setup”. PREREQUISITES Web and LAMP Pattern Web and Scripting Module (you must register the machine to be able to select this module). Note: root privileges required All commands in the following procedure must be run as root . PROCEDURE 47.3: INSTALLATION USING ANONYMOUS FTP FOR UPLOAD After the appliance is set up and running, no more manual interaction is required. This way of setting up the appliance is therefore ideal for using cron jobs to create and upload Supportconfig archives. 1. On the machine on which to install the appliance, log in to a console and execute the following commands (make sure to accept the recommended packages): > sudo zypper install sca-appliance-* sca-patterns-* \ vsftpd yast2 yast2-ftp-server > sudo systemctl enable apache2 > sudo systemctl start apache2 > sudo systemctl enable vsftpd > sudo systemctl start vsftpd > sudo yast ftp-server 2. In YaST FTP Server, select Authentication Enable Upload Anonymous Can Upload Fin- ish Yes to Create /srv/ftp/upload. 659 SCA appliance SLES 15 SP63. Execute the following commands: > sudo systemctl enable mysql > sudo systemctl start mysql > sudo mysql_secure_installation > sudo setup-sca -f The mysql_secure_installation will create a MariaDB root password. PROCEDURE 47.4: INSTALLATION USING SCP/TMP FOR UPLOAD This way of setting up the appliance requires manual interaction when typing the SSH password. 1. On the machine on which to install the appliance, log in to a console. 2. Execute the following commands: > sudo zypper install sca-appliance-* sca-patterns-* > sudo systemctl enable apache2 > sudo systemctl start apache2 > sudo sudo systemctl enable mysql > sudo systemctl start mysql > sudo mysql_secure_installation > sudo setup-sca 47.4.2.2 Prerequisites To run an SCA appliance server, you need the following prerequisites: All sca-appliance-* packages. The sca-patterns-base package. Additionally, any of the product-specific sca-pat- terns-* for the type of Supportconfig archives that you want to analyze with the appli- ance. Apache PHP MariaDB anonymous FTP server (optional) 660 SCA appliance SLES 15 SP647.4.2.3 Installation and basic setup As listed in Section 47.4.2.2, “Prerequisites”, the SCA appliance has several dependencies on other packages. Therefore, you need to take preparatory steps before installing and setting up the SCA appliance server: 1. For Apache and MariaDB, install the Web and LAMP installation patterns. 2. Set up Apache, MariaDB, and optionally an anonymous FTP server. For more information, see Chapter 42, The Apache HTTP server and Chapter 43, Setting up an FTP server with YaST. 3. Configure Apache and MariaDB to start at boot time: > sudo systemctl enable apache2 mysql 4. Start both services: > sudo systemctl start apache2 mysql Now you can install the SCA appliance and set it up as described in Procedure 47.5, “Installing and configuring the SCA appliance”. PROCEDURE 47.5: INSTALLING AND CONFIGURING THE SCA APPLIANCE After installing the packages, use the setup-sca script for the basic configuration of the MariaDB administration and report database that is used by the SCA appliance. It can be used to configure the following options you have for uploading the Supportconfig archives from your machines to the SCA appliance: scp anonymous FTP server 1. Install the appliance and the SCA base-pattern library: > sudo zypper install sca-appliance-* sca-patterns-base 2. Additionally, install the pattern packages for the types of Supportconfig archives you want to analyze. For example, if you have SUSE Linux Enterprise Server 12 and SUSE Linux Enterprise Server 15 servers in your environment, install both the sca-patterns-sle12 and sca-patterns-sle15 packages. To install all available patterns: > sudo zypper install sca-patterns-* 661 SCA appliance SLES 15 SP63. For basic setup of the SCA appliance, use the setup-sca script. How to call it depends on how you want to upload the Supportconfig archives to the SCA appliance server: If you have configured an anonymous FTP server that uses the /srv/ftp/upload directory, execute the setup script with the -f option. Follow the instructions on the screen: > sudo setup-sca -f Note: FTP server using another directory If your FTP server uses another directory than /srv/ftp/upload , adjust the following configuration les rst to make them point to the correct directory: /etc/sca/sdagent.conf and /etc/sca/sdbroker.conf . To upload Supportconfig les to the /tmp directory of the SCA appliance server via scp , call the setup script without any parameters. Follow the instructions on the screen: > sudo setup-sca The setup script runs a few checks regarding its requirements and configures the needed components. It will prompt you for two passwords: the MySQL root password of the MariaDB that you have set up, and a Web user password with which to log in to the Web interface of the SCA appliance. 4. Enter the existing MariaDB root password. It will allow the SCA appliance to connect to the MariaDB. 5. Define a password for the Web user. It will be written to /srv/www/htdocs/sca/web- config.php and will be set as the password for the user scdiag . Both user name and password can be changed at any time later, see Section 47.4.2.5.1, “Password for the Web interface”. After successful installation and setup, the SCA appliance is ready for use, see Section 47.4.2.4, “Using the SCA appliance”. However, you should modify options such as changing the password for the Web interface, changing the source for the SCA pattern updates, enabling archiving mode or configuring e-mail notifications. For details on that, see Section 47.4.2.5, “Customizing the SCA appliance”. 662 SCA appliance SLES 15 SP6Warning: Data protection As the reports on the SCA appliance server contain security-relevant information, make sure to protect the data on the SCA appliance server against unauthorized access. 47.4.2.4 Using the SCA appliance You can upload existing Supportconfig archives to the SCA appliance manually or create new Supportconfig archives and upload them to the SCA appliance in one step. Uploading can be done via FTP or SCP. For both, you need to know the URL where the SCA appliance can be reached. For upload via FTP, an FTP server needs to be configured for the SCA appliance, see Procedure 47.5, “Installing and configuring the SCA appliance”. 47.4.2.4.1 Uploading supportconfig archives to the SCA appliance For creating a Supportconfig archive and uploading it via (anonymous) FTP: > sudo supportconfig -U “ftp://SCA-APPLIANCE.COMPANY.COM/upload” For creating a Supportconfig archive and uploading it via SCP: > sudo supportconfig -U “scp://SCA-APPLIANCE.COMPANY.COM/tmp” You will be prompted for the root user password of the server running the SCA appliance. To manually upload one or multiple archives, copy the existing archive les (located at / var/log/scc_*.tbz ) to the SCA appliance. As target, use either the appliance server''s / tmp directory or the /srv/ftp/upload directory (if FTP is configured for the SCA appli- ance server). 47.4.2.4.2 Viewing SCA reports SCA reports can be viewed from any machine that has a browser installed and can access the report index page of the SCA appliance. 1. Start a Web browser and make sure that JavaScript and cookies are enabled. 2. As a URL, enter the report index page of the SCA appliance. 663 SCA appliance SLES 15 SP6https://sca-appliance.company.com/sca If in doubt, ask your system administrator. 3. You will be prompted for a user name and a password to log in. FIGURE 47.2: HTML REPORT GENERATED BY SCA APPLIANCE 4. After logging in, click the date of the report you want to read. 5. Click the Basic Health category rst to expand it. 6. In the Message column, click an individual entry. This opens the corresponding article in the SUSE Knowledge base. Read the proposed solution and follow the instructions. 7. If the Solutions column of the Supportconfig Analysis Report shows any additional entries, click them. Read the proposed solution and follow the instructions. 8. Check the SUSE Knowledge base (https://www.suse.com/support/kb/ ) for results that di- rectly relate to the problem identified by SCA. Work at resolving them. 9. Check for results that can be addressed proactively to avoid future problems. 664 SCA appliance SLES 15 SP647.4.2.5 Customizing the SCA appliance The following sections show how to change the password for the Web interface, how to change the source for the SCA pattern updates, how to enable archiving mode, and how to configure e-mail notifications. 47.4.2.5.1 Password for the Web interface The SCA Appliance Web interface requires a user name and password for logging in. The default user name is scdiag and the default password is linux (if not specified otherwise, see Proce- dure 47.5, “Installing and configuring the SCA appliance”). Change the default password to a secure password at the earliest possibility. You can also modify the user name. PROCEDURE 47.6: CHANGING USER NAME OR PASSWORD FOR THE WEB INTERFACE 1. Log in as root user at the system console of the SCA appliance server. 2. Open /srv/www/htdocs/sca/web-config.php in an editor. 3. Change the values of $username and $password as desired. 4. Save the le and exit. 47.4.2.5.2 Updates of SCA patterns By default, all sca-patterns-* packages are updated regularly by a root cron job that ex- ecutes the sdagent-patterns script nightly, which in turn runs zypper update sca-pat- terns-* . A regular system update will update all SCA appliance and pattern packages. To up- date the SCA appliance and patterns manually, run: > sudo zypper update sca-* The updates are installed from the SUSE Linux Enterprise 15 SP6 update repository by default. You can change the source for the updates to an RMT server, if desired. When sdagent-pat- terns runs zypper update sca-patterns-* , it gets the updates from the currently config- ured update channel. If that channel is located on an RMT server, the packages will be pulled from there. PROCEDURE 47.7: DISABLING AUTOMATIC UPDATES OF SCA PATTERNS 1. Log in as root user at the system console of the SCA appliance server. 665 SCA appliance SLES 15 SP62. Open /etc/sca/sdagent-patterns.conf in an editor. 3. Change the entry UPDATE_FROM_PATTERN_REPO=1 to UPDATE_FROM_PATTERN_REPO=0 4. Save the le and exit. The machine does not require any restart to apply the change. 47.4.2.5.3 Archiving mode All Supportconfig archives are deleted from the SCA appliance after they have been analyzed and their results have been stored in the MariaDB database. However, for troubleshooting purposes it can be useful to keep copies of Supportconfig archives from a machine. By default, archiving mode is disabled. PROCEDURE 47.8: ENABLING ARCHIVING MODE IN THE SCA APPLIANCE 1. Log in as root user at the system console of the SCA appliance server. 2. Open /etc/sca/sdagent.conf in an editor. 3. Change the entry ARCHIVE_MODE=0 to ARCHIVE_MODE=1 4. Save the le and exit. The machine does not require any restart to apply the change. After having enabled archive mode, the SCA appliance will save the Supportconfig les to the /var/log/archives/saved directory, instead of deleting them. 666 SCA appliance SLES 15 SP647.4.2.5.4 Sending SCA reports via e-mail The SCA appliance can e-mail a report HTML le for each Supportconfig analyzed. This feature is disabled by default. When enabling it, you can define a list of e-mail addresses to which the reports should be sent. Define a level of status messages that trigger the sending of reports ( STATUS_NOTIFY_LEVEL ). POSSIBLE VALUES FOR STATUS_NOTIFY_LEVEL $STATUS_OFF Deactivate sending of HTML reports. $STATUS_CRITICAL Send only SCA reports that include a CRITICAL. $STATUS_WARNING Send only SCA reports that include a WARNING or CRITICAL. $STATUS_RECOMMEND Send only SCA reports that include a RECOMMEND, WARNING or CRITICAL. $STATUS_SUCCESS Send SCA reports that include a SUCCESS, RECOMMEND, WARNING or CRITICAL. PROCEDURE 47.9: CONFIGURING E-MAIL NOTIFICATIONS FOR SCA REPORTS 1. Log in as root user at the system console of the SCA appliance server. 2. Open /etc/sca/sdagent.conf in an editor. 3. Search for the entry STATUS_NOTIFY_LEVEL . By default, it is set to $STATUS_OFF (e-mail notifications are disabled). 4. To enable e-mail notifications, change $STATUS_OFF to the level of status messages that you want to have e-mail reports for, for example: STATUS_NOTIFY_LEVEL=$STATUS_SUCCESS For details, see Possible values for STATUS_NOTIFY_LEVEL. 5. To define the list of recipients to which the reports should be sent: a. Search for the entry EMAIL_REPORT=''root'' . 667 SCA appliance SLES 15 SP6b. Replace root with a list of e-mail addresses to which SCA reports should be sent. The e-mail addresses must be separated by spaces. For example: EMAIL_REPORT=''tux@my.company.com wilber@your.company.com'' 6. Save the le and exit. The machine does not require any restart to apply the changes. All future SCA reports will be e-mailed to the specified addresses. 47.4.2.6 Backing up and restoring the database To back up and restore the MariaDB database that stores the SCA reports, use the scadb com- mand as described below. scadb is provided by the package sca-appliance-broker . PROCEDURE 47.10: BACKING UP THE DATABASE 1. Log in as root user at the system console of the server running the SCA appliance. 2. Put the appliance into maintenance mode by executing: # scadb maint 3. Start the backup with: # scadb backup The data is saved to a TAR archive: sca-backup-*sql.gz . 4. If you are using the pattern creation database to develop your own patterns (see Sec- tion 47.4.3, “Developing custom analysis patterns”), back up this data, too: # sdpdb backup The data is saved to a TAR archive: sdp-backup-*sql.gz . 5. Copy the following data to another machine or an external storage medium: sca-backup-*sql.gz sdp-backup-*sql.gz /usr/lib/sca/patterns/local (only needed if you have created custom patterns) 668 SCA appliance SLES 15 SP66. Reactivate the SCA appliance with: # scadb reset agents PROCEDURE 47.11: RESTORING THE DATABASE To restore the database from your backup, proceed as follows: 1. Log in as root user at the system console of the server running the SCA appliance. 2. Copy the newest sca-backup-*sql.gz and sdp-backup-*sql.gz TAR archives to the SCA appliance server. 3. To decompress the les, run: # gzip -d *-backup-*sql.gz 4. To import the data into the database, execute: # scadb import sca-backup-*sql 5. If you are using the pattern creation database to create your own patterns, also import the following data with: # sdpdb import sdp-backup-*sql 6. If you are using custom patterns, also restore /usr/lib/sca/patterns/local from your backup data. 7. Reactivate the SCA appliance with: # scadb reset agents 8. Update the pattern modules in the database with: # sdagent-patterns -u 47.4.3 Developing custom analysis patterns The SCA appliance comes with a complete pattern development environment (the SCA Pattern Database) that enables you to develop your own, custom patterns. Patterns can be written in any programming language. To make them available for the Supportconfig analysis process, they need to be saved to /usr/lib/sca/patterns/local and to be made executable. Both the 669 Developing custom analysis patterns SLES 15 SP6SCA appliance and the SCA tool will then run the custom patterns against new Supportconfig archives as part of the analysis report. For detailed instructions on how to create (and test) your own patterns, see https://www.suse.com/c/sca-pattern-development/ . 47.5 Gathering information during the installation During the installation, supportconfig is not available. However, you can collect log les from YaST by using save_y2logs . This command will create a .tar.xz archive in the directory /tmp . If issues appear early during installation, you may be able to gather information from the log le created by linuxrc . linuxrc is a small command that runs before YaST starts. This log le is available at /var/log/linuxrc.log . Important: Installation log files not available in the installed system The log les available during the installation are not available in the installed system anymore. Properly save the installation log les while the installer is still running. 47.6 Support of kernel modules An important requirement for every enterprise operating system is the level of support you re- ceive for your environment. Kernel modules are the most relevant connector between hardware (“controllers”) and the operating system. Every kernel module in SUSE Linux Enterprise has a supported ag that can take three possible values: “yes”, thus supported “external”, thus supported (empty, not set), thus unsupported The following rules apply: All modules of a self-recompiled kernel are by default marked as unsupported. Kernel modules supported by SUSE partners and delivered using SUSE SolidDriver Pro- gram are marked “external”. 670 Gathering information during the installation SLES 15 SP6If the supported ag is not set, loading this module will taint the kernel. Tainted ker- nels are not supported. Unsupported Kernel modules are included in an extra RPM pack- age ( kernel-FLAVOR-extra ). That package is only available for SUSE Linux Enterprise Desktop and the SUSE Linux Enterprise Workstation Extension. Those kernels will not be loaded by default ( FLAVOR= default | xen |...). Besides, these unsupported modules are not available in the installer, and the kernel-FLAVOR-extra package is not part of the SUSE Linux Enterprise media. Kernel modules not provided under a license compatible to the license of the Linux kernel also taint the kernel. For details, see the state of /proc/sys/kernel/tainted . 47.6.1 Technical background Linux kernel: The value of /proc/sys/kernel/unsupported defaults to 2 on SUSE Linux Enterprise 15 SP6 ( do not warn in syslog when loading unsupported modules ). This default is used in the installer and in the installed system. modprobe : The modprobe utility for checking module dependencies and loading modules appropriately checks for the value of the supported ag. If the value is “yes” or “external” the module will be loaded, otherwise it will not. For information on how to override this behavior, see Section 47.6.2, “Working with unsupported modules”. Note: Support SUSE does not generally support the removal of storage modules via modprobe -r . 47.6.2 Working with unsupported modules While general supportability is important, situations can occur where loading an unsupported module is required. For example, for testing or debugging purposes, or if your hardware vendor provides a hotfix. To override the default, copy /lib/modprobe.d/10-unsupported-modules.conf to / etc/modprobe.d/10-unsupported-modules.conf and change the value of the variable allow_unsupported_modules from 0 to 1 . Do not edit /lib/modprobe.d/10-unsup- ported-modules.conf directly; any changes will be overwritten whenever the suse- module-tools package is updated. 671 Technical background SLES 15 SP6If an unsupported module is needed in the initrd, do not forget to run dracut -f to update the initrd. If you only want to try loading a module once, you can use the --allow-unsupport- ed-modules option with modprobe . For more information, see the comments in /lib/ modprobe.d/10-unsupported-modules.conf and the modprobe man page. During installation, unsupported modules may be added through driver update disks, and they will be loaded. To enforce loading of unsupported modules during boot and after- ward, use the kernel command line option oem-modules . While installing and initializ- ing the suse-module-tools package, the kernel ag TAINT_NO_SUPPORT ( /proc/sys/ kernel/tainted ) will be evaluated. If the kernel is already tainted, allow_unsupport- ed_modules will be enabled. This will prevent unsupported modules from failing in the system being installed. If no unsupported modules are present during installation and the other special kernel command line option ( oem-modules=1 ) is not used, the default still is to disallow unsupported modules. Remember that loading and running unsupported modules will make the kernel and the whole system unsupported by SUSE. 47.7 More information man supportconfig—The supportconfig man page. man supportconfig.conf—The man page of the Supportconfig configuration le. man scatool—The scatool man page. man scadb—The scadb man page. man setup-sca—The setup-sca man page. https://mariadb.com/kb/en/ —The MariaDB documentation. https://httpd.apache.org/docs/ and Chapter  42, The Apache HTTP server—Documentation about the Apache Web server. Chapter 43, Setting up an FTP server with YaST—Documentation of how to set up an FTP server. https://www.suse.com/c/sca-pattern-development/ —Instructions on how to create (and test) your own SCA patterns. 672 More information SLES 15 SP6https://www.suse.com/c/basic-server-health-check-supportconfig/ —A Basic Server Health Check with Supportconfig. https://community.microfocus.com/img/gw/groupwise/w/tips/34308/create-your-own- supportconfig-plugin —Create Your Own Supportconfig Plugin. https://www.suse.com/c/creating-a-central-supportconfig-repository/ —Creating a Central Supportconfig Repository. 673 More information SLES 15 SP648 Common problems and their solutions This chapter describes a range of potential problems and their solutions. Even if your situation is not precisely listed, there may be one similar enough to offer hints to the solution of your problem. 48.1 Finding and gathering information Linux reports things in a detailed way. There are several places to look when you encounter problems with your system. Most of them are standard to Linux systems, and several are rele- vant to SUSE Linux Enterprise Server systems. Most log les can be viewed with YaST (Miscel- laneous Start-Up Log). YaST offers the possibility to collect all system information needed by the support team. Use Other Support and select the problem category. When all information is gathered, attach it to your support request. A list of the most frequently checked log les follows with the description of their typical pur- pose. Paths containing ~ refer to the current user''s home directory. TABLE 48.1: LOG FILES Log File Description ~/.xsession-errors Messages from the desktop applications cur- rently running. /var/log/apparmor/ Log les from AppArmor, see Book “Securi- ty and Hardening Guide” for detailed informa- tion. /var/log/audit/audit.log Log le from Audit to track any access to les, directories, or resources of your system, and trace system calls. See Book “Security and Hardening Guide” for detailed information. /var/log/mail.* Messages from the mail system. /var/log/NetworkManager Log le from NetworkManager to collect problems with network connectivity 674 Finding and gathering information SLES 15 SP6Log File Description /var/log/samba/ Directory containing Samba server and client log messages. /var/log/warn All messages from the kernel and system log daemon with the “warning” level or higher. /var/log/wtmp Binary le containing user login records for the current machine session. View it with last . /var/log/Xorg.*.log Start-up and runtime log les from the X Window System. It is useful for debugging failed X start-ups. /var/log/YaST2/ Directory containing YaST''s actions and their results. /var/log/zypper.log Log le of Zypper. Apart from log les, your machine also supplies you with information about the running system. See Table 48.2: System information with the /proc file system TABLE 48.2: SYSTEM INFORMATION WITH THE /proc FILE SYSTEM File Description /proc/cpuinfo Contains processor information, including its type, make, model, and performance. /proc/dma Shows which DMA channels are currently being used. /proc/interrupts Shows which interrupts are in use, and how many of each have been in use. /proc/iomem Displays the status of I/O (input/output) memory. 675 Finding and gathering information SLES 15 SP6File Description /proc/ioports Shows which I/O ports are in use at the mo- ment. /proc/meminfo Displays memory status. /proc/modules Displays the individual modules. /proc/mounts Displays devices currently mounted. /proc/partitions Shows the partitioning of all hard disks. /proc/version Displays the current version of Linux. Apart from the /proc le system, the Linux kernel exports information with the sysfs module, an in-memory le system. This module represents kernel objects, their attributes and relation- ships. For more information about sysfs , see the context of udev in Chapter 29, Dynamic kernel device management with udev. Table 48.3 contains an overview of the most common directories under /sys . TABLE 48.3: SYSTEM INFORMATION WITH THE /sys FILE SYSTEM File Description /sys/block Contains subdirectories for each block device discovered in the system. Generally, these are mostly disk type devices. /sys/bus Contains subdirectories for each physical bus type. /sys/class Contains subdirectories grouped together as a functional types of devices (like graphics, net, printer, etc.) /sys/device Contains the global device hierarchy. Linux comes with several tools for system analysis and monitoring. See Book “System Analysis and Tuning Guide”, Chapter 2 “System monitoring utilities” for a selection of the most important ones used in system diagnostics. 676 Finding and gathering information SLES 15 SP6Each of the following scenarios begins with a header describing the problem followed by a paragraph or two offering suggested solutions, available references for more detailed solutions, and cross-references to other scenarios that are related. 48.2 Boot problems Boot problems are situations when your system does not boot properly (does not boot to the expected target and login screen). 48.2.1 The GRUB 2 boot loader fails to load If the hardware is functioning properly, it is possible that the boot loader is corrupted and Linux cannot start on the machine. In this case, it is necessary to repair the boot loader. To do so, you need to start the Rescue System as described in Section 48.5.2, “Using the rescue system” and follow the instructions in Section 48.5.2.4, “Modifying and re-installing the boot loader”. Alternatively, you can use the Rescue System to x the boot loader as follows. Boot your machine from the installation media. In the boot screen, choose More Boot Linux System. Select the disk containing the installed system and kernel with the default kernel options. When the system is booted, start YaST and switch to System Boot Loader. Make sure that the Write generic Boot Code to MBR option is enabled, and click OK. This fixes the corrupted boot loader by overwriting it, or installs the boot loader if it is missing. Other reasons for the machine not booting may be BIOS-related: BIOS settings Check your BIOS for references to your hard disk. GRUB 2 may simply not be started if the hard disk itself cannot be found with the current BIOS settings. BIOS boot order Check whether your system''s boot order includes the hard disk. If the hard disk option was not enabled, your system may install properly, but fails to boot when access to the hard disk is required. 677 Boot problems SLES 15 SP648.2.2 No graphical login If the machine starts, but does not boot into the graphical login manager, anticipate problems either with the choice of the default systemd target or the configuration of the X Window System. To check the current systemd default target run the command sudo systemctl get-default . If the value returned is not graphical.target , run the command sudo systemctl isolate graphical.target . If the graphical login screen starts, log in and start YaST System Services Manager and set the Default System Target to Graphical Interface. From now on the system should boot into the graphical login screen. If the graphical login screen does not start even if having booted or switched to the graphical target, your desktop or X Window software may be misconfigured or corrupted. Examine the log les at /var/log/Xorg.*.log for detailed messages from the X server as it attempted to start. If the desktop fails during start, it may log error messages to the system journal that can be queried with the command journalctl (see Chapter 21, journalctl: query the systemd journal for more information). If these error messages hint at a configuration problem in the X server, try to x these issues. If the graphical system still does not come up, consider reinstalling the graphical desktop. 48.2.3 Root Btrfs partition cannot be mounted If a btrfs root partition becomes corrupted, try the following options: Mount the partition with the -o recovery option. If that fails, run btrfs-zero-log on your root partition. 48.2.4 Force checking root partitions If the root partition becomes corrupted, use the parameter forcefsck on the boot prompt. This passes the option -f (force) to the fsck command. 678 No graphical login SLES 15 SP648.2.5 Disable swap to enable booting When a swap device is not available and the system cannot enable it during boot, booting may fail. Try disabling all swap devices by appending the following options to the kernel command line: systemd.device_wants_unit=off systemd.mask=swap.target You may also try disabling specific swap devices: systemd.mask=dev-sda1.swap 48.2.6 GRUB 2 fails during reboot on a dual-boot system If GRUB 2 fails during reboot, disable the Fast Boot setting in the BIOS. 48.3 Login problems Login problems occur when your system refuses to accept the user name and password, or accepts them but then fails to start the graphic desktop, produces errors, or drops to a command line, for example. 48.3.1 Valid user name and password combinations fail This often occurs when the system is configured to use network authentication or directory services and cannot retrieve results from its configured servers. The root user is the only local user that can still log in to these machines. The following are common reasons a machine appears functional but cannot process logins correctly: The network is not working. For further directions on this, turn to Section 48.4, “Network problems”. DNS is not working at the moment (which prevents GNOME from working and the system from making validated requests to secure servers). One indication that this is the case is that the machine takes a long time to respond to any action. Find more information about this topic in Section 48.4, “Network problems”. 679 Disable swap to enable booting SLES 15 SP6If the system is configured to use Kerberos, the system''s local time may have drifted past the accepted variance with the Kerberos server time (this is typically 300 seconds). If NTP (network time protocol) is not working properly or local NTP servers are not working, Kerberos authentication ceases to function because it depends on common clock synchro- nization across the network. The system''s authentication configuration is misconfigured. Check the PAM configuration les involved for any typographical errors or misordering of directives. For additional background information about PAM and the syntax of the configuration les involved, refer to Book “Security and Hardening Guide”, Chapter 2 “Authentication with PAM”. The home partition is encrypted. Find more information about this topic in Section 48.3.3, “Login to encrypted home partition fails”. In cases that do not involve external network problems, the solution is to log in as root and repair the configuration. If you cannot log in to the running system, reboot it into the rescue mode as outlined in Procedure 18.3, “Entering rescue mode”. 48.3.2 Valid user name and password not accepted This is by far the most common problem users encounter, because there are many reasons this can occur. Depending on whether you use local user management and authentication or network authentication, login failures occur for different reasons. Local user management can fail for the following reasons: The user may have entered the wrong password. The user''s home directory containing the desktop configuration les is corrupted or write protected. There may be problems with the X Window System authenticating this particular user, especially if the user''s home directory has been used with another Linux distribution before installing the current one. To locate the reason for a local login failure, proceed as follows: 1. Check whether the user remembered their password correctly before you start debugging the whole authentication mechanism. If the user may have not have remembered their password correctly, use the YaST User Management module to change the user''s password. Pay attention to the Caps Lock key and unlock it, if necessary. 680 Valid user name and password not accepted SLES 15 SP62. Log in as root and check the system journal with journalctl -e for error messages of the login process and of PAM. 3. Try to log in from a console (using Ctrl – Alt – F1 ). If this is successful, the blame cannot be put on PAM, because it is possible to authenticate this user on this machine. Try to locate any problems with the X Window System or the GNOME desktop. For more information, refer to Section 48.3.4, “GNOME desktop has issues”. 4. If the user''s home directory has been used with another Linux distribution, remove the Xauthority le in the user''s home. Use a console login via Ctrl – Alt – F1 and run rm .Xauthority as this user. This should eliminate X authentication problems for this user. Try graphical login again. 5. If the desktop could not start because of corrupt configuration les, proceed with Sec- tion 48.3.4, “GNOME desktop has issues”. In the following, common reasons a network authentication for a particular user may fail on a specific machine are listed: The user may have entered the wrong password. The user name exists in the machine''s local authentication les and is also provided by a network authentication system, causing conflicts. The home directory exists but is corrupt or unavailable. Perhaps it is write protected or is on a server that is inaccessible at the moment. The user does not have permission to log in to that particular host in the authentication system. The machine has changed host names, for whatever reason, and the user does not have permission to log in to that host. The machine cannot reach the authentication server or directory server that contains that user''s information. There may be problems with the X Window System authenticating this particular user, especially if the user''s home has been used with another Linux distribution before installing the current one. 681 Valid user name and password not accepted SLES 15 SP6To locate the cause of the login failures with network authentication, proceed as follows: 1. Check whether the user remembered their password correctly before you start debugging the whole authentication mechanism. 2. Determine the directory server which the machine relies on for authentication and make sure that it is up and running and properly communicating with the other machines. 3. Determine that the user''s user name and password work on other machines to make sure that their authentication data exists and is properly distributed. 4. See if another user can log in to the misbehaving machine. If another user can log in without difficulty or if root can log in, log in and examine the system journal with the journalctl -e > le. Locate the time stamps that correspond to the login attempts and determine if PAM has produced any error messages. 5. Try to log in from a console (using Ctrl – Alt – F1 ). If this is successful, the problem is not with PAM or the directory server on which the user''s home is hosted, because it is possible to authenticate this user on this machine. Try to locate any problems with the X Window System or the GNOME desktop. For more information, refer to Section 48.3.4, “GNOME desktop has issues”. 6. If the user''s home directory has been used with another Linux distribution, remove the Xauthority le in the user''s home. Use a console login via Ctrl – Alt – F1 and run rm .Xauthority as this user. This should eliminate X authentication problems for this user. Try graphical login again. 7. If the desktop could not start because of corrupt configuration les, proceed with Sec- tion 48.3.4, “GNOME desktop has issues”. 48.3.3 Login to encrypted home partition fails It is recommended to use an encrypted home partition for laptops. If you cannot log in to your laptop, the reason might be that your partition could not be unlocked. During the boot time, you need to enter the passphrase to unlock your encrypted partition. If you do not enter it, the boot process continues, leaving the partition locked. To unlock your encrypted partition, proceed as follows: 1. Switch to the text console with Ctrl – Alt – F1 . 682 Login to encrypted home partition fails SLES 15 SP62. Become root . 3. Restart the unlocking process again with: # systemctl restart home.mount 4. Enter your passphrase to unlock your encrypted partition. 5. Exit the text console and switch back to the login screen with Alt – F7 . 6. Log in as usual. 48.3.4 GNOME desktop has issues If you are experiencing issues with the GNOME desktop, there are several ways to troubleshoot the misbehaving graphical desktop environment. The recommended procedure described below offers the safest option to x a broken GNOME desktop. PROCEDURE 48.1: TROUBLESHOOTING GNOME 1. Launch YaST and switch to Security and Users. 2. Open the User and Group Management dialog and click Add. 3. Fill out the required elds and click OK to create a new user. 4. Log out and log in as the new user. This gives you a fresh GNOME environment. 5. Copy individual subdirectories from the ~/.local/ and ~/.config/ directories of the old user account to the respective directories of the new user account. Log out and log in again as the new user after every copy operation to check whether GNOME still works correctly. 6. Repeat the previous step until you nd the configuration le that breaks GNOME. 7. Log in as the old user, and move the offending configuration le to a different location. Log out and log in again as the old user. 8. Delete the previously created user. 683 GNOME desktop has issues SLES 15 SP648.4 Network problems Many problems of your system may be network-related, although the symptoms look different. For example, the reason for a system not allowing users to log in may be a network problem. This section introduces a simple checklist you can apply to identify the cause of any network problem encountered. PROCEDURE 48.2: HOW TO IDENTIFY NETWORK PROBLEMS When checking the network connection of your machine, proceed as follows: 1. If you use an Ethernet connection, check the hardware rst. Make sure that your network cable is properly plugged into your computer and router (or hub, etc.). The control lights next to your Ethernet connector are normally both be active. If the connection fails, check whether your network cable works with another machine. If it does, your network card causes the failure. If hubs or switches are included in your network setup, they may be faulty, as well. 2. If using a wireless connection, check whether the wireless link can be established by other machines. If not, contact the wireless network''s administrator. 3. When you have checked your basic network connectivity, try to nd out which service is not responding. Gather the address information of all network servers needed in your setup. Either look them up in the appropriate YaST module or ask your system adminis- trator. The following list gives typical network servers involved in a setup together with the symptoms of an outage. DNS (name service) A broken or malfunctioning name service affects the network''s functionality in many ways. If the local machine relies on any network servers for authentication and these servers cannot be found because of name resolution issues, users would not even be able to log in. Machines in the network managed by a broken name server would not be able to “see” each other and communicate. NTP (time service) A malfunctioning or broken NTP service could affect Kerberos authentication and X server functionality. 684 Network problems SLES 15 SP6NFS (file service) If any application needs data stored in an NFS mounted directory, it cannot start or function properly if this service was down or misconfigured. In the worst case scenario, a user''s personal desktop configuration would not come up if their home directory containing the .gconf subdirectory could not be found because of a faulty NFS server. Samba (file service) If any application needs data stored in a directory on a faulty Samba server, it cannot start or function properly. NIS (user management) If your SUSE Linux Enterprise Server system relies on a faulty NIS server to provide the user data, users cannot log in to this machine. LDAP (user management) If your SUSE Linux Enterprise Server system relies on a faulty LDAP server to provide the user data, users cannot log in to this machine. Kerberos (authentication) Authentication does not work and login to any machine fails. CUPS (network printing) Users cannot print. 4. Check whether the network servers are running and whether your network setup allows you to establish a connection: Important: Limitations The debugging procedure described below only applies to a simple network serv- er/client setup that does not involve any internal routing. It assumes both server and client are members of the same subnet without the need for additional routing. a. Use ping IP_ADDRESS/HOSTNAME (replace with the host name or IP address of the server) to check whether each one of them is up and responding to the network. If this command is successful, it tells you that the host you were looking for is up and running and that the name service for your network is configured correctly. 685 Network problems SLES 15 SP6If ping fails with destination host unreachable , either your system or the desired server is not properly configured or down. Check whether your system is reachable by running ping IP address or YOUR_HOSTNAME from another machine. If you can reach your machine from another machine, it is the server that is not running or not configured correctly. If ping fails with unknown host , the name service is not configured correctly or the host name used was incorrect. For further checks on this matter, refer to Step 4.b. If ping still fails, either your network card is not configured correctly or your network hardware is faulty. b. Use host HOSTNAME to check whether the host name of the server you are trying to connect to is properly translated into an IP address and vice versa. If this command returns the IP address of this host, the name service is up and running. If the host command fails, check all network configuration les relating to name and address resolution on your host: /var/run/netconfig/resolv.conf This le is used to keep track of the name server and domain you are currently using. It is a symbolic link to /run/netconfig/resolv.conf and is usually automatically adjusted by YaST or DHCP. Make sure that this le has the fol- lowing structure and all network addresses and domain names are correct: search FULLY_QUALIFIED_DOMAIN_NAME nameserver IPADDRESS_OF_NAMESERVER This le can contain more than one name server address, but at least one of them must be correct to provide name resolution to your host. If needed, adjust this le using the YaST Network Settings module (Hostname/DNS tab). If your network connection is handled via DHCP, enable DHCP to change host name and name service information by selecting Set Hostname via DHCP (can be set globally for any interface or per interface) and Update Name Servers and Search List via DHCP in the YaST Network Settings module (Hostname/DNS tab). /etc/nsswitch.conf This le tells Linux where to look for name service information. It should look like this: ... 686 Network problems SLES 15 SP6hosts: files dns networks: files dns ... The dns entry is vital. It tells Linux to use an external name server. Normally, these entries are automatically managed by YaST, but it would be prudent to check. If all the relevant entries on the host are correct, let your system administra- tor check the DNS server configuration for the correct zone information. For detailed information about DNS, refer to Chapter 39, The domain name system. If you have made sure that the DNS configuration of your host and the DNS server are correct, proceed with checking the configuration of your network and network device. c. If your system cannot establish a connection to a network server and you have ex- cluded name service problems from the list of possible culprits, check the configu- ration of your network card. Use the command ip addr show NETWORK_DEVICE to check whether this device was properly configured. Make sure that the inet address with the netmask ( /MASK ) is configured correctly. An error in the IP address or a missing bit in your network mask would render your network configuration unusable. If necessary, perform this check on the server as well. d. If the name service and network hardware are properly configured and running, but certain external network connections still get long timeouts or fail entirely, use traceroute FULLY_QUALIFIED_DOMAIN_NAME (executed as root ) to track the net- work route these requests are taking. This command lists any gateway (hop) that a request from your machine passes on its way to its destination. It lists the response time of each hop and whether this hop is reachable. Use a combination of traceroute and ping to track down the culprit and let the administrators know. When you have identified the cause of your network trouble, you can resolve it yourself (if the problem is located on your machine) or let the system administrators of your network know about your findings so they can reconfigure the services or repair the necessary systems. 687 Network problems SLES 15 SP648.4.1 NetworkManager problems If you have a problem with network connectivity, narrow it down as described in Procedure 48.2, “How to identify network problems”. If NetworkManager looks suspicious, proceed as follows to get logs providing hints on why NetworkManager fails: 1. Open a shell and log in as root . 2. Restart the NetworkManager: > sudo systemctl restart NetworkManager 3. Open a Web page, for example, https://www.opensuse.org as normal user to see, if you can connect. 4. Collect any information about the state of NetworkManager in /var/log/NetworkMan- ager . For more information about NetworkManager, refer to Chapter 31, Using NetworkManager. 48.5 Data problems Data problems are when the machine may or may not boot properly but, in either case, it is clear that there is data corruption on the system and that the system needs to be recovered. These situations call for a backup of your critical data, enabling you to recover the system state from before your system failed. 48.5.1 Managing partition images Sometimes you need to perform a backup from an entire partition or even hard disk. Linux comes with the dd tool which can create an exact copy of your disk. Combined with gzip you save space. PROCEDURE 48.3: BACKING UP AND RESTORING HARD DISKS 1. Start a Shell as user root . 2. Select your source device. Typically this is something like /dev/sda (labeled as SOURCE ). 688 NetworkManager problems SLES 15 SP63. Decide where you want to store your image (labeled as BACKUP_PATH ). It must be different from your source device. In other words: if you make a backup from /dev/sda , your image le must not to be stored under /dev/sda . 4. Run the commands to create a compressed image le: # dd if=/dev/SOURCE | gzip > /BACKUP_PATH/image.gz 5. Restore the hard disk with the following commands: # gzip -dc /BACKUP_PATH/image.gz | dd of=/dev/SOURCE If you only need to back up a partition, replace the SOURCE placeholder with your respective partition. In this case, your image le can lie on the same hard disk, but on a different partition. 48.5.2 Using the rescue system There are several reasons a system could fail to come up and run properly. A corrupted le system following a system crash, corrupted configuration les, or a corrupted boot loader con- figuration are the most common ones. To help you to resolve these situations, SUSE Linux Enterprise Server contains a rescue system that you can boot. The rescue system is a small Linux system that can be loaded into a RAM disk and mounted as root le system, allowing you to access your Linux partitions from the outside. Using the rescue system, you can recover or modify any important aspect of your system. Manipulate any type of configuration le. Check the le system for defects and start automatic repair processes. Access the installed system in a “change root” environment. Check, modify, and re-install the boot loader configuration. Recover from a badly installed device driver or unusable kernel. Resize partitions using the parted command. Find more information about this tool at the GNU Parted Web site https://www.gnu.org/software/parted/parted.html . The rescue system can be loaded from various sources and locations. The simplest option is to boot the rescue system from the original installation medium. 689 Using the rescue system SLES 15 SP6Note: IBM Z: starting the rescue system On IBM Z the installation system can be used for rescue purposes. To start the rescue system follow the instructions in Section 48.6, “IBM Z: using initrd as a rescue system”. 1. Insert the installation medium into your DVD drive. 2. Reboot the system. 3. At the boot screen, press F4 and choose DVD-ROM. Then choose Rescue System from the main menu. 4. Enter root at the Rescue: prompt. A password is not required. If your hardware setup does not include a DVD drive, you can boot the rescue system from a network source. The following example applies to a remote boot scenario—if using another boot medium, such as a DVD, modify the info le accordingly and boot as you would for a normal installation. 1. Enter the configuration of your PXE boot setup and add the lines install=PROTO- COL://INSTSOURCE and rescue=1 . If you need to start the repair system, use repair=1 instead. As with a normal installation, PROTOCOL stands for any of the supported network protocols (NFS, HTTP, FTP, etc.) and INSTSOURCE for the path to your network installa- tion source. 2. Boot the system using “Wake on LAN”, as described in Book “Deployment Guide”, Chapter 18 “Preparing network boot environment”, Section 18.5 “Using wake-on-LAN for remote wakeups”. 3. Enter root at the Rescue: prompt. A password is not required. When you have entered the rescue system, you can use the virtual consoles that can be reached with Alt – F1 to Alt – F6 . A shell and other useful utilities, such as the mount program, are available in the /bin directo- ry. The /sbin directory contains important le and network utilities for reviewing and repair- ing the le system. This directory also contains the most important binaries for system mainte- nance, such as fdisk , mkfs , mkswap , mount , and shutdown , ip and ss for maintaining the network. The directory /usr/bin contains the vi editor, nd, less, and SSH. To see the system messages, either use the command dmesg or view the system log with jour- nalctl . 690 Using the rescue system SLES 15 SP648.5.2.1 Checking and manipulating configuration files As an example for a configuration that might be xed using the rescue system, imagine you have a broken configuration le that prevents the system from booting properly. You can x this using the rescue system. To manipulate a configuration le, proceed as follows: 1. Start the rescue system using one of the methods described above. 2. To mount a root le system located under /dev/sda6 to the rescue system, use the fol- lowing command: > sudo mount /dev/sda6 /mnt All directories of the system are now located under /mnt 3. Change the directory to the mounted root le system: > sudo cd /mnt 4. Open the problematic configuration le in the vi editor. Adjust and save the configuration. 5. Unmount the root le system from the rescue system: > sudo umount /mnt 6. Reboot the machine. 48.5.2.2 Repairing and checking file systems Generally, le systems cannot be repaired on a running system. If you encounter serious prob- lems, you may not even be able to mount your root le system and the system boot may end with a “kernel panic”. In this case, the only way is to repair the system from the outside. The system contains the fsck utility to check and repair multiple le system types, such as ext2 , ext3 , ext4 , msdos , and vfat . Use the -t option to specify which le system to check. The following command checks all ext4 le systems found in the /etc/fstab specification: > sudo fsck -t ext4 -A Tip For Btrfs, you can use the btrfs check command found in the btrfsprogs package. 691 Using the rescue system SLES 15 SP6Find topics about the Btrfs le system in the following places: The Storage Administration Guide includes https://documentation.suse.com/sles/ html/SLES-all/cha-filesystems.html#sec-filesystems-major-btrfs and https://doc- umentation.suse.com/sles/html/SLES-all/cha-resize-fs.html#sec-resize-fs-btrfs sec- tions. The following article describes how to recover from Btrfs errors https:// www.suse.com/support/kb/doc/?id=000018769 . The following article includes links to multiple Btrfs-related topics https:// www.suse.com/support/kb/doc/?id=000018779 . The man 8 btrfs-check man page details all options of the btrfs check com- mand. 48.5.2.3 Accessing the installed system If you need to access the installed system from the rescue system, you need to do this in a change root environment. For example, to modify the boot loader configuration, or to execute a hardware configuration utility. To set up a change root environment based on the installed system, proceed as follows: 1. Tip: Import LVM volume groups If you are using an LVM setup (refer to Book “Storage Administration Guide” for more general details), import all existing volume groups to be able to nd and mount the device(s): rootvgimport -a Run lsblk to check which node corresponds to the root partition. It is /dev/sda2 in our example: > lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sda 8:0 0 149,1G 0 disk ├─sda1 8:1 0 2G 0 part [SWAP] 692 Using the rescue system SLES 15 SP6├─sda2 8:2 0 20G 0 part / └─sda3 8:3 0 127G 0 part └─cr_home 254:0 0 127G 0 crypt /home 2. Mount the root partition from the installed system: > sudo mount /dev/sda2 /mnt 3. Mount /proc , /dev , and /sys partitions: > sudo mount -t proc none /mnt/proc > sudo mount --rbind /dev /mnt/dev > sudo mount --rbind /sys /mnt/sys 4. Now you can “change root” into the new environment, keeping the bash shell: > chroot /mnt /bin/bash 5. Finally, mount the remaining partitions from the installed system: > mount -a 6. Now you have access to the installed system. Before rebooting the system, unmount the partitions with umount -a and leave the “change root” environment with exit . Warning: Limitations Although you have full access to the les and applications of the installed system, there are some limitations. The kernel that is running is the one that was booted with the res- cue system, not with the change root environment. It only supports essential hardware and it is not possible to add kernel modules from the installed system unless the kernel versions are identical. Always check the version of the currently running (rescue) kernel with uname -r and then nd out if a matching subdirectory exists in the /lib/modules directory in the change root environment. If yes, you can use the installed modules, oth- erwise you need to supply their correct versions on other media, such as a ash disk. Most often the rescue kernel version differs from the installed one — then you cannot simply access a sound card, for example. It is also not possible to start a graphical user interface. Also note that you leave the “change root” environment when you switch the console with Alt – F1 to Alt – F6 . 693 Using the rescue system SLES 15 SP648.5.2.4 Modifying and re-installing the boot loader Sometimes a system cannot boot because the boot loader configuration is corrupted. The start- up routines cannot, for example, translate physical drives to the actual locations in the Linux le system without a working boot loader. To check the boot loader configuration and re-install the boot loader, proceed as follows: 1. Perform the necessary steps to access the installed system as described in Section 48.5.2.3, “Accessing the installed system”. 2. Check that the GRUB 2 boot loader is installed on the system. If not, install the package grub2 and run > sudo grub2-install /dev/sda 3. Check whether the following les are correctly configured according to the GRUB 2 con- figuration principles outlined in Chapter 18, The boot loader GRUB 2 and apply fixes if nec- essary. /etc/default/grub /boot/grub2/device.map /boot/grub2/grub.cfg (this le is generated, do not edit) /etc/sysconfig/bootloader 4. Re-install the boot loader using the following command sequence: > sudo grub2-mkconfig -o /boot/grub2/grub.cfg 5. Unmount the partitions, log out of the “change root” environment, and reboot the system: > umount -a exit reboot 694 Using the rescue system SLES 15 SP648.5.2.5 Fixing kernel installation A kernel update may introduce a new bug which can impact the operation of your system. For example a driver for a piece of hardware in your system may be faulty, which prevents you from accessing and using it. In this case, revert to the last working kernel (if available on the system) or install the original kernel from the installation media. Tip: How to keep last kernels after update To prevent failures to boot after a faulty kernel update, use the kernel multiversion feature and tell libzypp which kernels you want to keep after the update. For example to always keep the last two kernels and the currently running one, add multiversion.kernels = latest,latest-1,running to the /etc/zypp/zypp.conf le. See Chapter 27, Installing multiple kernel versions for more information. A similar case is when you need to re-install or update a broken driver for a device not sup- ported by SUSE Linux Enterprise Server. For example when a hardware vendor uses a specific device, such as a hardware RAID controller, which needs a binary driver to be recognized by the operating system. The vendor typically releases a Driver Update Disk (DUD) with the xed or updated version of the required driver. In both cases you need to access the installed system in the rescue mode and x the kernel related problem, otherwise the system may fail to boot correctly: 1. Boot from the SUSE Linux Enterprise Server installation media. 2. If you are recovering after a faulty kernel update, skip this step. If you need to use a driver update disk (DUD), press F6 to load the driver update after the boot menu appears, and choose the path or URL to the driver update and confirm with Yes. 3. Choose Rescue System from the boot menu and press Enter . If you chose to use DUD, you will be asked to specify where the driver update is stored. 4. Enter root at the Rescue: prompt. A password is not required. 5. Manually mount the target system and “change root” into the new environment. For more information, see Section 48.5.2.3, “Accessing the installed system”. 695 Using the rescue system SLES 15 SP66. If using DUD, install/re-install/update the faulty device driver package. Always make sure the installed kernel version exactly matches the version of the driver you are installing. If fixing faulty kernel update installation, you can install the original kernel from the installation media with the following procedure. a. Identify your DVD device with hwinfo --cdrom and mount it with mount /dev/ sr0 /mnt . b. Navigate to the directory where your kernel les are stored on the DVD, for example cd /mnt/suse/x86_64/ . c. Install required kernel-* , kernel-*-base , and kernel-*-extra packages of your flavor with the rpm -i command. 7. Update configuration les and reinitialize the boot loader if needed. For more information, see Section 48.5.2.4, “Modifying and re-installing the boot loader”. 8. Remove any bootable media from the system drive and reboot. 48.6 IBM Z: using initrd as a rescue system If the kernel of the SUSE® Linux Enterprise Server for IBM Z is upgraded or modified, it is possible to reboot the system accidentally in an inconsistent state, so standard procedures of IPLing the installed system fail. In such a case, you may use the installation system for rescue purposes. IPL the SUSE Linux Enterprise Server for IBM Z installation system as described in Book “Deploy- ment Guide”, Chapter 5 “Installation on IBM Z and LinuxONE”, Section 5.3 “Preparing for installation”. Choose Start Installation and enter all required parameters. After the installation system has loaded and you are asked which display type to use to control the installation, select SSH . Now you can log in to the system with SSH as root without a password. In this state, no disks are configured. You need to configure them before you can proceed. PROCEDURE 48.4: CONFIGURING DASDS 1. Configure DASDs with the following command: dasd_configure 0.0.0150 1 0 696 IBM Z: using initrd as a rescue system SLES 15 SP60.0.0150 is the channel to which the DASD is connected. The 1 means activate the disk (a 0 at this place would deactivate the disk). The 0 stands for “no DIAG mode” for the disk (a 1 here would enable DAIG access to the disk). 2. Now the DASD is online (check with cat /proc/partitions ) and can used for subse- quent commands. PROCEDURE 48.5: CONFIGURING A ZFCP DISK 1. To configure a zFCP disk, it is necessary to rst configure the zFCP adapter. Do this with the following command: zfcp_host_configure 0.0.4000 1 0.0.4000 is the channel to which the adapter is attached and 1 stands for activate (a 0 here would deactivate the adapter). 2. After the adapter is activated, a disk can be configured. Do this with the following com- mand: zfcp_disk_configure 0.0.4000 1234567887654321 8765432100000000 1 0.0.4000 is the previously-used channel ID, 1234567887654321 is the WWPN (World wide Port Number), and 8765432100000000 is the LUN (logical unit number). The 1 stands for activating the disk (a 0 here would deactivate the disk). 3. Now the zFCP disk is online (check with cat /proc/partitions ) and can used for sub- sequent commands. Now the rescue system is fully set up and you can start repairing the installed system. See Section 48.5.2, “Using the rescue system” for instructions on how to repair the most common issues. 48.7 IBM Z: After a kernel update the system boots into the previous kernel Installing a new kernel version on an IBM Z system does not automatically update the stage 1 zipl loader. This means that after a restart the system boots into the old kernel. And if secure boot is enabled, booting fails when the old kernel is signed with a signing key that has been retracted by, for example, a shim update at the same time. 697 IBM Z: After a kernel update the system boots into the previous kernel SLES 15 SP6To solve the problem, refresh zipl to make it aware of the new kernel version. To do this, run the following command after you install the new kernel: grub2-emu --kexec In the grub2 boot menu, choose the new kernel to reboot. Run the command above the second time for the changes to take effect. Finally, run the following command to reinstall the boot loader: update-bootloader --reinit 698 IBM Z: After a kernel update the system boots into the previous kernel SLES 15 SP6A An example network This example network is used across all network-related chapters of the SUSE® Linux Enterprise Server documentation. 699 SLES 15 SP6B GNU licenses formats that can be read and edited only by proprietary word processors, SGML or XML for This appendix contains the GNU Free Docu- which the DTD and/or processing tools are not generally available, and the machine-generat- ed HTML, PostScript or PDF produced by some word processors for output purposes only. mentation License version 1.2. The "Title Page" means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, "Title Page" means the text near the GNU Free Documentation License most prominent appearance of the work''s title, preceding the beginning of the body of the text. A section "Entitled XYZ" means a named subunit of the Document whose title either is precisely Copyright (C) 2000, 2001, 2002 Free Software Foundation, Inc. 51 Franklin St, Fifth Floor, XYZ or contains XYZ in parentheses following text that translates XYZ in another language. Boston, MA 02110-1301 USA. Everyone is permitted to copy and distribute verbatim copies (Here XYZ stands for a specific section name mentioned below, such as "Acknowledgements", of this license document, but changing it is not allowed. "Dedications", "Endorsements", or "History".) To "Preserve the Title" of such a section when you modify the Document means that it remains a section "Entitled XYZ" according to this 0. PREAMBLE definition. The Document may include Warranty Disclaimers next to the notice which states that this The purpose of this License is to make a manual, textbook, or other functional and useful License applies to the Document. These Warranty Disclaimers are considered to be included document "free" in the sense of freedom: to assure everyone the effective freedom to copy by reference in this License, but only as regards disclaiming warranties: any other implication and redistribute it, with or without modifying it, either commercially or non-commercially. that these Warranty Disclaimers may have is void and has no effect on the meaning of this Secondarily, this License preserves for the author and publisher a way to get credit for their License. work, while not being considered responsible for modifications made by others. This License is a kind of "copyleft", which means that derivative works of the document must 2. VERBATIM COPYING themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software. You may copy and distribute the Document in any medium, either commercially or non- We have designed this License to use it for manuals for free software, because free software commercially, provided that this License, the copyright notices, and the license notice saying needs free documentation: a free program should come with manuals providing the same this License applies to the Document are reproduced in all copies, and that you add no other freedoms that the software does. But this License is not limited to software manuals; it can conditions whatsoever to those of this License. You may not use technical measures to obstruct be used for any textual work, regardless of subject matter or whether it is published as a or control the reading or further copying of the copies you make or distribute. However, you printed book. We recommend this License principally for works whose purpose is instruction may accept compensation in exchange for copies. If you distribute a large enough number of or reference. copies you must also follow the conditions in section 3. You may also lend copies, under the same conditions stated above, and you may publicly 1. APPLICABILITY AND DEFINITIONS display copies. This License applies to any manual or other work, in any medium, that contains a notice placed 3. COPYING IN QUANTITY by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under If you publish printed copies (or copies in media that commonly have printed covers) of the the conditions stated herein. The "Document", below, refers to any such manual or work. Any Document, numbering more than 100, and the Document''s license notice requires Cover Texts, member of the public is a licensee, and is addressed as "you". You accept the license if you you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: copy, modify or distribute the work in a way requiring permission under copyright law. Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers A "Modified Version" of the Document means any work containing the Document or a portion must also clearly and legibly identify you as the publisher of these copies. The front cover of it, either copied verbatim, or with modifications and/or translated into another language. must present the full title with all words of the title equally prominent and visible. You may A "Secondary Section" is a named appendix or a front-matter section of the Document that add other material on the covers in addition. Copying with changes limited to the covers, as deals exclusively with the relationship of the publishers or authors of the Document to the long as they preserve the title of the Document and satisfy these conditions, can be treated Document''s overall subject (or to related matters) and contains nothing that could fall directly as verbatim copying in other respects. within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a If the required texts for either cover are too voluminous to t legibly, you should put the Secondary Section may not explain any mathematics.) The relationship could be a matter rst ones listed (as many as t reasonably) on the actual cover, and continue the rest onto of historical connection with the subject or with related matters, or of legal, commercial, adjacent pages. philosophical, ethical or political position regarding them. If you publish or distribute Opaque copies of the Document numbering more than 100, you The "Invariant Sections" are certain Secondary Sections whose titles are designated, as being must either include a machine-readable Transparent copy along with each Opaque copy, or those of Invariant Sections, in the notice that says that the Document is released under this state in or with each Opaque copy a computer-network location from which the general net- License. If a section does not t the above definition of Secondary then it is not allowed to be work-using public has access to download using public-standard network protocols a complete designated as Invariant. The Document may contain zero Invariant Sections. If the Document Transparent copy of the Document, free of added material. If you use the latter option, you does not identify any Invariant Sections then there are none. must take reasonably prudent steps, when you begin distribution of Opaque copies in quanti- The "Cover Texts" are certain short passages of text that are listed, as Front-Cover Texts or ty, to ensure that this Transparent copy will remain thus accessible at the stated location until Back-Cover Texts, in the notice that says that the Document is released under this License. A at least one year after the last time you distribute an Opaque copy (directly or through your Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words. agents or retailers) of that edition to the public. A "Transparent" copy of the Document means a machine-readable copy, represented in a for- It is requested, but not required, that you contact the authors of the Document well before mat whose specification is available to the general public, that is suitable for revising the doc- redistributing any large number of copies, to give them a chance to provide you with an ument straightforwardly with generic text editors or (for images composed of pixels) generic updated version of the Document. paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent le format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not "Transparent" is called "Opaque". Examples of suitable formats for Transparent copies include plain ASCII without markup, Tex- info input format, LaTeX input format, SGML or XML using a publicly available DTD, and stan- dard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary 700 SLES 15 SP64. MODIFICATIONS The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version. You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this 5. COMBINING DOCUMENTS License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you You may combine the Document with other documents released under this License, under must do these things in the Modified Version: the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and A. Use in the Title Page (and on the covers, if any) a title distinct from that of the list them all as Invariant Sections of your combined work in its license notice, and that you Document, and from those of previous versions (which should, if there were any, preserve all their Warranty Disclaimers. be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission. The combined work need only contain one copy of this License, and multiple identical Invari- ant Sections may be replaced with a single copy. If there are multiple Invariant Sections with B. List on the Title Page, as authors, one or more persons or entities responsible for the same name but different contents, make the title of each such section unique by adding authorship of the modifications in the Modified Version, together with at least ve at the end of it, in parentheses, the name of the original author or publisher of that section if of the principal authors of the Document (all of its principal authors, if it has fewer known, or else a unique number. Make the same adjustment to the section titles in the list of than ve), unless they release you from this requirement. Invariant Sections in the license notice of the combined work. C. State on the Title page the name of the publisher of the Modified Version, as the In the combination, you must combine any sections Entitled "History" in the various original publisher. documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections D. Preserve all the copyright notices of the Document. Entitled "Endorsements". E. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices. 6. COLLECTIONS OF DOCUMENTS F. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form You may make a collection consisting of the Document and other documents released under shown in the Addendum below. this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License G. Preserve in that license notice the full lists of Invariant Sections and required Cover for verbatim copying of each of the documents in all other respects. Texts given in the Document''s license notice. You may extract a single document from such a collection, and distribute it individually under H. Include an unaltered copy of this License. this License, provided you insert a copy of this License into the extracted document, and follow I. Preserve the section Entitled "History", Preserve its Title, and add to it an item this License in all other respects regarding verbatim copying of that document. stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled "History" in the Document, 7. AGGREGATION WITH INDEPENDENT WORKS create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in A compilation of the Document or its derivatives with other separate and independent docu- the previous sentence. ments or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the com- J. Preserve the network location, if any, given in the Document for public access to pilation''s users beyond what the individual works permit. When the Document is included in a Transparent copy of the Document, and likewise the network locations given in an aggregate, this License does not apply to the other works in the aggregate which are not the Document for previous versions it was based on. These may be placed in the themselves derivative works of the Document. "History" section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the If the Cover Text requirement of section 3 is applicable to these copies of the Document, then version it refers to gives permission. if the Document is less than one half of the entire aggregate, the Document''s Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic K. For any section Entitled "Acknowledgements" or "Dedications", Preserve the Title equivalent of covers if the Document is in electronic form. Otherwise they must appear on of the section, and preserve in the section all the substance and tone of each of the printed covers that bracket the whole aggregate. contributor acknowledgements and/or dedications given therein. L. Preserve all the Invariant Sections of the Document, unaltered in their text and 8. TRANSLATION in their titles. Section numbers or the equivalent are not considered part of the section titles. Translation is considered a kind of modification, so you may distribute translations of the M. Delete any section Entitled "Endorsements". Such a section may not be included Document under the terms of section 4. Replacing Invariant Sections with translations requires in the Modified Version. special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You N. Do not retitle any existing section to be Entitled "Endorsements" or to conflict in may include a translation of this License, and all the license notices in the Document, and title with any Invariant Section. any Warranty Disclaimers, provided that you also include the original English version of this O. Preserve any Warranty Disclaimers. License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the If the Modified Version includes new front-matter sections or appendices that qualify as Se- original version will prevail. condary Sections and contain no material copied from the Document, you may at your option If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the designate some or all of these sections as invariant. To do this, add their titles to the list of requirement (section 4) to Preserve its Title (section 1) will typically require changing the Invariant Sections in the Modified Version''s license notice. These titles must be distinct from actual title. any other section titles. You may add a section Entitled "Endorsements", provided it contains nothing but endorse- ments of your Modified Version by various parties--for example, statements of peer review 9. TERMINATION or that the text has been approved by an organization as the authoritative definition of a You may not copy, modify, sublicense, or distribute the Document except as expressly pro- standard. vided for under this License. Any other attempt to copy, modify, sublicense or distribute the You may add a passage of up to ve words as a Front-Cover Text, and a passage of up to 25 Document is void, and will automatically terminate your rights under this License. However, words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only parties who have received copies, or rights, from you under this License will not have their one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through licenses terminated so long as such parties remain in full compliance. arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one. 701 SLES 15 SP610. FUTURE REVISIONS OF THIS LICENSE The Free Software Foundation may publish new, revised versions of the GNU Free Documen- tation License from time to time. Such new versions will be similar in spirit to the present ver- sion, but may differ in detail to address new problems or concerns. See https://www.gnu.org/ copyleft/ . Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. ADDENDUM: How to use this License for your documents Copyright (c) YEAR YOUR NAME. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”. If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this: with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation. If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software. 702 SLES 15 SP6">