SUSE Linux Enterprise Server for Global Commercialization

chmod +x ~/bin/hello.sh 9 Writing shell scripts SLES 15 SP3If you have fullled all of 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 something, 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, an existing le will be deleted. For example, the ls command writes its output into the le listing.txt : tux > ls > listing.txt Command >> File Appends the output of the command to a le. For example, the ls command appends its output to the le listing.txt : tux > 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: tux > read a < foo Command1 | Command2 10 Redirecting command events SLES 15 SP3Redirects 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 lter only those lines which contain cpu : tux > 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 : tux > find / -name "foo*" 2>/dev/null 1.4 Using aliases An alias is a shortcut denition of one or more commands. The syntax for an alias is: alias NAME=DEFINITION For example, the following line denes an alias lt that outputs a long listing (option -l ), sorts it by modication time ( -t ), and prints it in reverse sorted order ( -r ): tux > alias lt=''ls -ltr'' To view all alias denitions, use alias . Remove your alias with unalias and the corresponding alias name. 1.5 Using variables in Bash A shell variable can be global or local. Global variables, or environment variables, can be accessed 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: tux > printenv PATH A variable, be it global or local, can also be viewed with echo : tux > echo $PATH 11 Using aliases SLES 15 SP3To set a local variable, use a variable name followed by the equal sign, followed by the value: tux > PROJECT="SLED" Do not insert spaces around the equal sign, otherwise you get an error. To set an environment variable, use export : tux > export NAME="tux" To remove a variable, use unset : tux > unset NAME The following table contains some common environment variables which can be used 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 directories separated by colon PS1 species the normal prompt printed before each command PS2 species the secondary prompt printed when you execute a multi-line command PWD current working directory USER the current user 12 Using variables in Bash SLES 15 SP31.5.1 Using argument variables For example, if you have the script foo.sh you can execute it like this: tux > 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: tux > file=/home/tux/book/book.tar.bz2 tux > echo ${file#*/} home/tux/book/book.tar.bz2 ${VAR##pattern} removes the longest possible match from the left: tux > file=/home/tux/book/book.tar.bz2 tux > echo ${file##*/} book.tar.bz2 ${VAR%pattern} removes the shortest possible match from the right: tux > file=/home/tux/book/book.tar.bz2 tux > echo ${file%.*} /home/tux/book/book.tar 13 Using argument variables SLES 15 SP3${VAR%%pattern} removes the longest possible match from the right: tux > file=/home/tux/book/book.tar.bz2 tux > echo ${file%%.*} /home/tux/book/book ${VAR/pattern_1/pattern_2} substitutes the content of VAR from the PATTERN_1 with PATTERN_2 : tux > file=/home/tux/book/book.tar.bz2 tux > 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 specic 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: tux > cat filelist.txt ; ls -l filelist.txt Command1 && 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): tux > 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: tux > mkdir /home/tux/foo || mkdir /home/wilber/bar 14 Grouping and combining commands SLES 15 SP3funcname(){ ... } creates a shell function. You can use the positional parameters to access its arguments. The following line denes the function hello to print a short message: tux > hello() { echo "Hello $1"; } You can call this function like this: tux > 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." else 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 15 Working with common flow constructs SLES 15 SP3Find 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 some 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: http://tldp.org/LDP/Bash-Beginners-Guide/html/index.html —Bash Guide for Beginners http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO.html —BASH Programming - Introduction HOW-TO http://tldp.org/LDP/abs/html/index.html —Advanced Bash-Scripting Guide http://www.grymoire.com/Unix/Sh.html —Sh - the Bourne Shell 16 Creating loops with the for command SLES 15 SP32 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 congured to work similarly to su . However, sudo provides a exible mechanism that allows users to run commands with privileges of any other user. This can be used to assign roles with specic 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 congured to authenticate with your own credentials. This means that the users do not have 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 : tux > id -un 1 tux tux > sudo id -un root''s password: 2 root tux > id -un tux 3 tux > 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 SP34 The elevated privileges persist for a certain period of time, so you do not have to provide the root again. password again. Tip: I/O redirection When using sudo , I/O redirection does not work: tux > sudo echo s > /proc/sysrq-trigger bash: /proc/sysrq-trigger: Permission denied tux > 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 specied by the SHELL environment variable or the target user''s default shell. If a command is specied, 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 SP3tux:~ > 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 congurable 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 . 2.2.1 Editing the configuration files The main policy conguration le for sudo is /etc/sudoers . As it is possible to lock yourself out of the system if the le is malformed, it is strongly recommended to use visudo for editing. It prevents editing conicts and checks for syntax errors before saving the modications. You can use another editor instead of vi by setting the EDITOR environment variable, for example: sudo EDITOR=/usr/bin/nano visudo Keep in mind that the /etc/sudoers le is supplied by the system packages, and modications done directly in the le may break updates. Therefore, it is recommended to put custom conguration into les in the /etc/sudoers.d/ directory. Use the following command to create or edit a le: sudo visudo -f /etc/sudoers.d/NAME The command bellow opens the le using a dierent editor (in this case, nano ): sudo EDITOR=/usr/bin/nano visudo -f /etc/sudoers.d/NAME 19 Configuring sudo SLES 15 SP3Note: Ignored files in /etc/sudoers.d The #includedir directive in /etc/sudoers ignores les that end with the ~ (tilde) character or contain the . (dot) character. For more information on the visudo command, run man 8 visudo . 2.2.2 Basic sudoers configuration syntax The sudoers conguration 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 conguration 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 tux 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 2.2.3, “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. 20 Basic sudoers configuration syntax SLES 15 SP3Defaults 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 specic set of users. For detailed information about the /etc/sudoers conguration le, consult man 5 sudoers . 2.2.3 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) identiers: either a user name, a group in the format %GROUPNAME , or a user ID in the format #UID . Negation can be specied with the ! prex. Host_List One or several (separated by comma) identiers: either a (fully qualied) host name or an IP address. Negation can be specied with the ! prex. ALL is a common choice for Host_List . NOPASSWD:|PASSWD: 21 Basic sudoers rules SLES 15 SP3The user is not prompted for a password when running commands matching Cmd_List after NOPASSWD: . PASSWD is the default. It only needs to be specied 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) speciers: 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 A 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 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 separator option in the smb.conf le. By default, it is \ . If it is changed, for example, to + , then the account format in sudoers le must be DOMAIN+GROUP_NAME . 22 Basic sudoers rules SLES 15 SP32.3 sudo use cases While the default conguration works for standard usage scenarios, you can customize the default conguration to meet your specic needs. 2.3.1 Using sudo without root password By design, members of the group wheel can run all commands with sudo as root. The following procedure explains how to add a user account to the wheel group. 1. Add your user account to the group wheel . If your user account is not already a member of the wheel group, add it using the sudo usermod -a -G wheel USERNAME command. Log out and log in again to enable the change. Verify that the change was successful by running the groups USERNAME command. 2. Authenticate with the user account''s normal password. Create the le /etc/sudoers.d/userpw using the visudo command (see Section 2.2.1, “Editing the configuration files”) and add the following: Defaults !targetpw 3. Select a new default rule. Depending on whether you want users to re-enter their passwords, uncomment the appropriate line in /etc/sudoers and comment out the default rule. ## Uncomment to allow members of group wheel to execute any command # %wheel ALL=(ALL) ALL ## Same thing without a password # %wheel ALL=(ALL) NOPASSWD: ALL 4. Make the default rule more restrictive. Comment out or remove the allow-everything rule in /etc/sudoers : ALL ALL=(ALL) ALL # WARNING! Only use this together with ''Defaults targetpw''! Warning: Dangerous rule in sudoers Do not skip this step. Otherwise any user can execute any command as root ! 23 sudo use cases SLES 15 SP35. Test the conguration. Run sudo as member and non-member of wheel . tux:~ > groups users wheel tux:~ > sudo id -un tux''s password: root wilber:~ > groups users wilber:~ > sudo id -un wilber is not in the sudoers file. This incident will be reported. 2.3.2 Using sudo with X.Org applications Starting graphical applications with sudo usually results in the following error: tux > 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 Warning: Potential security issue Running graphical applications with root privileges has security implications. It is recommended 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. 24 Using sudo with X.Org applications SLES 15 SP32.4 More information The sudo --help command oers a brief overview of the available command line options, while the man sudoers command provides detailed information about sudoers and its conguration. 25 More information SLES 15 SP33 YaST YaST is a SUSE Linux Enterprise Server tool that provides a graphical interface for all essential installation and system conguration tasks. Whether you need to update packages, congure a printer, modify rewall 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 ocial Web site at https:// yast.opensuse.org/ . 3.1 YaST topics Detailed information on using specic YaST modules and functionality is covered throughout the documentation. Administration Guide Chapter 5: “YaST online update” Section 35.2.3: “Configuring Apache with YaST” Section 14.3: “Configuring the boot loader with YaST” Section 19.4: “Configuring a network connection with YaST” Chapter 36: “Setting up an FTP server with YaST” Chapter 30: “Service management with YaST” Deployment Guide Chapter 25: “Changing language and country settings with YaST” Section 20.3: “Setting up a printer” Section 20.2: “Setting up sound cards” Chapter 22: “Installing modules, extensions, and third party add-on products” Section 21.4: “Managing software repositories and services” 26 YaST topics SLES 15 SP3Chapter 21: “Installing or removing software” Chapter 24: “Managing users with YaST” Chapter 20: “Setting up hardware components with YaST” Section 20.1: “Setting up your system keyboard layout” Security and Hardening Guide Chapter 34: “Building and managing profiles with YaST” Section 26.4: “Setting up a VPN server or client using YaST” Chapter 18: “Configuring security settings with YaST” 3.2 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 navigation 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 specic module, enter its name into the search eld, and you should see the modules that match the entered string as you type. 3.3 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. Shift – F7 Enable/disable logging of debug messages. 27 YaST interface overview SLES 15 SP3Shift – F8 Open a le dialog to save log les to a user-dened location. Ctrl – Shift – Alt – D Send a DebugEvent. YaST modules can react to this by executing special debugging actions. The result depends on the specic YaST module. Ctrl – Shift – Alt – M Start and stop macro recorder. Ctrl – Shift – Alt – P Replay macro. Ctrl – Shift – Alt – S Show style sheet 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. 28 Useful key combinations SLES 15 SP34 YaST in text mode The ncurses-based pseudo-graphical YaST interface is designed primarily to help system administrators to manage systems without an X server. The interface oers several advantages compared 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 command. Use the Tab 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 . 29 SLES 15 SP3Tip: 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 dierent 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 conrm 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 various buttons. Available function key combinations ( FX ) are shown in the bottom line of the YaST screen. Which function keys are actually mapped to which buttons depend on the active YaST module, because the dierent modules oer dierent buttons (Details, Info, Add, Delete, etc.). Use F10 for Accept, OK, Next, and Finish. Press F1 to access the YaST help. Using the navigation tree 30 Navigation in modules SLES 15 SP3Some YaST modules use a navigation tree in the left part of the window to select conguration 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 lters on the left side to list packages matching the specied 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 oers several advanced key combinations. Shift – F1 List advanced hotkeys. Shift – F4 Change color schema. 31 Advanced key combinations SLES 15 SP3Ctrl – 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 might 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 terminal, 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 might 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: tux > sudo yast -h 32 Restriction of key combinations SLES 15 SP34.4.1 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: tux > sudo yast -i package_name or tux > sudo yast --install -i package_name package_name can be a single short package name (for example gvim ) installed with dependency checking, or the full path to an RPM package, which is installed without dependency checking. While YaST oers 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 6.1, “Using Zypper”. 4.4.2 Working with individual modules To save time, you can start individual YaST modules using the following command: tux > 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 modules. However, not all modules have command line support. To display the available options of a module, use the following command: tux > 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. 33 Installing packages from the command line SLES 15 SP34.4.3.1 Common YaST module commands All YaST modules support the following commands: help Lists all the module''s supported commands with their description: tux > sudo yast lan help longhelp Same as help , but adds a detailed list of all command''s options and their descriptions: tux > sudo yast lan longhelp xmlhelp Same as longhelp , but the output is structured as an XML document and redirected to a le: tux > sudo yast lan xmlhelp xmlfile=/tmp/yast_lan.xml interactive Enters the interactive mode. This lets you run the module''s commands without prexing 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 specied path: tux > 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 congures the Linux Audit Framework. Refer to the Book “Security and Hardening Guide” for more details. yast audit-laf accepts the following commands: set 34 Command line parameters of YaST modules SLES 15 SP3Sets an option: tux > sudo yast audit-laf set log_file=/tmp/audit.log For a complete list of options, run yast audit-laf set help . show Displays settings of an option: tux > 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 congures its settings. yast dhcp-server accepts the following commands: disable Disables the DHCP server service. enable Enables the DHCP server service. host Congures settings for individual hosts. interface Species to which network interface to listen to: tux > 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 35 Command line parameters of YaST modules SLES 15 SP3Manages global DHCP options. For a complete list of options, run yast dhcp-server options help . status 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 conguration. yast dns-server accepts the following commands: acls Displays access control list settings: tux > sudo yast dns-server acls show ACLs: ----- Name Type Value ---------------------------- any Predefined localips Predefined localnets Predefined none Predefined dnsrecord Congures zone resource records: tux > 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 Congures DNS forwarders: tux > sudo yast dns-server forwarders add ip=10.0.0.100 tux > sudo yast dns-server forwarders show [...] Forwarder IP ------------ 36 Command line parameters of YaST modules SLES 15 SP310.0.0.100 For a complete list of options, run yast dns-server forwarders help . host Handles ''A'' and its related ''PTR'' record at once: tux > sudo yast dns-server host show zone=example.org For a complete list of options, run yast dns-server host help . logging Congures logging settings: tux > sudo yast dns-server logging set updates=no transfers=yes For a complete list of options, run yast dns-server logging help . mailserver Congures zone mail servers: tux > 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 Congures zone name servers: tux > sudo yast dns-server nameserver add zone=example.com ns=ns1 For a complete list of options, run yast dns-server nameserver help . soa Congures the start of authority (SOA) record: tux > 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: tux > sudo yast dns-server startup atboot For a complete list of options, run yast dns-server startup help . transport 37 Command line parameters of YaST modules SLES 15 SP3Congures zone transport rules. For a complete list of options, run yast dns-server transport help . zones Manages DNS zones: tux > 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 congured disks in the system: tux > 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: tux > 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 Congures FTP server settings. yast ftp-server accepts the following options: SSL, TLS 38 Command line parameters of YaST modules SLES 15 SP3Controls secure connections via SSL and TLS. SSL options are valid for the vsftpd only. tux > sudo yast ftp-server SSL enable tux > sudo yast ftp-server TLS disable access Congures access permissions: tux > sudo yast ftp-server access authen_only For a complete list of options, run yast ftp-server access help . anon_access Congures access permissions for anonymous users: tux > sudo yast ftp-server anon_access can_upload For a complete list of options, run yast ftp-server anon_access help . anon_dir Species the directory for anonymous users. The directory must already exist on the server: tux > 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): tux > sudo yast ftp-server chroot enable tux > sudo yast ftp-server chroot disable idle-time Sets the maximum idle time in minutes before FTP server terminates the current connection: tux > sudo yast ftp-server idle-time set_idle_time=15 logging Determines whether to save the log messages into a log le: tux > sudo yast ftp-server logging enable tux > sudo yast ftp-server logging disable max_clients 39 Command line parameters of YaST modules SLES 15 SP3Species the maximum number of concurrently connected clients: tux > sudo yast ftp-server max_clients set_max_clients=1500 max_clients_ip Species the maximum number of concurrently connected clients via IP: tux > sudo yast ftp-server max_clients_ip set_max_clients=20 max_rate_anon Species the maximum data transfer rate permitted for anonymous clients (KB/s): tux > sudo yast ftp-server max_rate_anon set_max_rate=10000 max_rate_authen Species the maximum data transfer rate permitted for locally authenticated users (KB/s): tux > sudo yast ftp-server max_rate_authen set_max_rate=10000 port_range Species the port range for passive connection replies: tux > 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: tux > sudo yast ftp-server startup atboot For a complete list of options, run yast ftp-server startup help . umask Species the le umask for authenticated:anonymous users: tux > sudo yast ftp-server umask set_umask=177:077 welcome_message Species the text to display when someone connects to the FTP server: tux > sudo yast ftp-server welcome_message set_message="hello everybody" 40 Command line parameters of YaST modules SLES 15 SP34.4.3.8 yast http-server Congures the HTTP server (Apache2). yast http-server accepts the following commands: configure Congures the HTTP server host settings: tux > sudo yast http-server configure host=main servername=www.example.com \ serveradmin=admin@example.com For a complete list of options, run yast http-server configure help . hosts Congures virtual hosts: tux > 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 Species the ports and network addresses where the HTTP server should listen: tux > sudo yast http-server listen add=81 tux > sudo yast http-server listen list Listen Statements: ================== :80 :81 tux > 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: tux > sudo yast http-server mode wizard=on modules Controls the Apache2 server modules: tux > sudo yast http-server modules enable=php5,rewrite tux > sudo yast http-server modules disable=ssl tux > sudo http-server modules list [...] 41 Command line parameters of YaST modules SLES 15 SP3Enabled rewrite Disabled ssl Enabled php5 [...] 4.4.3.9 yast kdump Congures kdump settings. For more information on kdump , refer to the Book “System Analysis and Tuning Guide”, Chapter 18 “Kexec and Kdump”, Section 18.7 “Basic Kdump configuration”. yast kdump accepts the following commands: copykernel Copies the kernel into the dump directory. customkernel Species the kernel_string part of the name of the custom kernel. The naming scheme is /boot/vmlinu[zx]-kernel_string[.gz] . tux > sudo yast kdump customkernel kernel=kdump For a complete list of options, run yast kdump customkernel help . dumpformat Species the (compression) format of the dump kernel image. Available formats are ''none'', ''ELF'', ''compressed'', or ''lzo'': tux > sudo yast kdump dumpformat dump_format=ELF dumplevel Species the dump level number in the range from 0 to 31: tux > sudo yast kdump dumplevel dump_level=24 dumptarget Species the destination for saving dump images: tux > sudo kdump dumptarget taget=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 42 Command line parameters of YaST modules SLES 15 SP3Controls whether the system should reboot immediately after saving the core in the kdump kernel: tux > sudo yast kdump immediatereboot enable tux > sudo yast kdump immediatereboot disable keepolddumps Species how many old dump images are kept. Specify zero to keep them all: tux > sudo yast kdump keepolddumps no=5 kernelcommandline Species the command line that needs to be passed o to the kdump kernel: tux > sudo yast kdump kernelcommandline command="ro root=LABEL=/" kernelcommandlineappend Species the command line that you need to append to the default command line string: tux > sudo yast kdump kernelcommandlineappend command="ro root=LABEL=/" notificationcc Species an e-mail address for sending copies of notication messages: tux > sudo yast kdump notificationcc email="user1@example.com user2@example.com" notificationto Species an e-mail address for sending notication messages: tux > sudo yast kdump notificationto email="user1@example.com user2@example.com" show Displays kdump settings: tux > 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 43 Command line parameters of YaST modules SLES 15 SP3Species the le with the plain text SMTP password used for sending notication messages: tux > sudo yast kdump smtppass pass=/path/to/file smtpserver Species the SMTP server host name used for sending notication messages: tux > sudo yast kdump smtpserver server=smtp.server.com smtpuser Species the SMTP user name used for sending notication messages: tux > sudo yast kdump smtpuser user=smtp_user startup Enables or disables start-up options: tux > sudo yast kdump startup enable alloc_mem=128,256 tux > sudo yast kdump startup disable 4.4.3.10 yast keyboard Congures the system keyboard for virtual consoles. It does not aect 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: tux > sudo yast keyboard set layout=czech summary Displays the current keyboard conguration. 4.4.3.11 yast lan Congures network cards. yast lan accepts the following commands: add 44 Command line parameters of YaST modules SLES 15 SP3Congures a new network card: tux > 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: tux > sudo yast lan delete id=0 edit Changes the conguration of an existing network card: tux > sudo yast lan edit id=0 bootproto=dhcp list Displays a summary of network card conguration: tux > sudo yast lan list id name, bootproto 0 Ethernet Card 0, NONE 1 Network Bridge, DHCP 4.4.3.12 yast language Congures system languages. yast language accepts the following commands: list Lists all available languages. set Species the main system languages and secondary languages: tux > sudo yast language set lang=cs_CZ languages=en_US,es_ES no_packages 4.4.3.13 yast mail Displays the conguration of the mail system: tux > sudo yast mail summary 45 Command line parameters of YaST modules SLES 15 SP34.4.3.14 yast nfs Controls the NFS client. yast nfs accepts the following commands: add Adds a new NFS mount: tux > sudo yast nfs add spec=remote_host:/path/to/nfs/share file=/local/mount/point For a complete list of options, run yast nfs add help . delete Deletes an existing NFS mount: tux > 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: tux > 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: tux > 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 Congures the NFS server. yast nfs-server accepts the following commands: add Adds a directory to export: tux > sudo yast nfs-server add mountpoint=/nfs/export hosts=*.allowed_hosts.com 46 Command line parameters of YaST modules SLES 15 SP3For a complete list of options, run yast nfs-server add help . delete Deletes a directory from the NFS export: tux > sudo yast nfs-server delete mountpoint=/nfs/export set Species additional parameters for the NFS server: tux > 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: tux > sudo yast nfs-server start stop Stops the NFS server service: tux > sudo yast nfs-server stop summary Displays a summary of the NFS server conguration: tux > 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 Congures the NIS client. yast nis accepts the following commands: configure 47 Command line parameters of YaST modules SLES 15 SP3Changes global settings of a NIS client: tux > 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: tux > sudo yast nis disable enable Enables your machine as NIS client: tux > 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: tux > sudo yast nis find domain=nisdomain.com summary Displays a conguration summary of a NIS client. 4.4.3.17 yast nis-server Congures a NIS server. yast nis-server accepts the following commands: master Congures a NIS master server: tux > sudo yast nis-server master domain=nisdomain.com yppasswd=yes For a complete list of options, run yast nis-server master help . slave Congures a NIS slave server: tux > 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 . 48 Command line parameters of YaST modules SLES 15 SP3stop Stops a NIS server: tux > sudo yast nis-server stop summary Displays a conguration summary of a NIS server: tux > sudo yast nis-server summary 4.4.3.18 yast proxy Congures proxy settings. yast proxy accepts the following commands: authentication Species the authentication options for proxy: tux > 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: tux > 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: tux > sudo yast rdp allow set=yes 49 Command line parameters of YaST modules SLES 15 SP3list Displays the remote desktop conguration summary. 4.4.3.20 yast samba-client Congures the Samba client settings. yast samba-client accepts the following commands: configure Changes global settings of Samba: tux > sudo yast samba-client configure workgroup=FAMILY isdomainmember Checks whether the machine is a member of a domain: tux > sudo yast samba-client isdomainmember domain=SMB_DOMAIN joindomain Makes the machine a member of a domain: tux > sudo yast samba-client joindomain domain=SMB_DOMAIN user=username password=pwd winbind Enables or disables Winbind services (the winbindd daemon): tux > sudo yast samba-client winbind enable tux > sudo yast samba-client winbind disable 4.4.3.21 yast samba-server Congures Samba server settings. yast samba-server accepts the following commands: backend Species the back-end for storing user information: tux > sudo yast samba-server backend smbpasswd For a complete list of options, run yast samba-server backend help . configure 50 Command line parameters of YaST modules SLES 15 SP3Congures global settings of the Samba server: tux > 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: tux > sudo yast samba-server list Status Type Name ============================== Disabled Disk profiles Enabled Disk print$ Enabled Disk homes Disabled Disk groups Enabled Disk movies Enabled Printer printers role Species the role of the Samba server: tux > 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 ): tux > sudo yast samba-server service enable tux > sudo yast samba-server service disable share Manipulates a single Samba share: tux > 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 51 Command line parameters of YaST modules SLES 15 SP3Species the security level of the host: tux > sudo yast security level server For a complete list of options, run yast security level help . set Sets the value of a specic option: tux > sudo yast security set passwd=sha512 crack=yes For a complete list of options, run yast security set help . summary Displays a summary of the current security conguration: sudoyast security summary 4.4.3.23 yast sound Congures sound card settings. yast sound accepts the following commands: add Congures a new sound card. Without any parameters, the command adds the rst detected card. tux > 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: tux > sudo yast sound channels card=0 Master 75 PCM 100 modules Lists all available sound kernel modules: tux > sudo yast sound modules 52 Command line parameters of YaST modules SLES 15 SP3snd-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: tux > sudo yast sound playtest card=0 remove Removes a congured sound card: tux > sudo yast sound remove card=0 tux > sudo yast sound remove all set Species new values for a sound card: tux > sudo yast sound set card=0 volume=80 show Displays detailed information about a sound card: tux > 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 conguration summary for all sound cards on the system: tux > sudo yast sound summary volume 53 Command line parameters of YaST modules SLES 15 SP3Species 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: tux > sudo yast sysconfig clear=POSTFIX_LISTEN Tip: Variable in multiple files If the variable is available in several les, use the VARIABLE_NAME $ FILE_NAME syntax: tux > sudo yast sysconfig clear=CONFIG_TYPE$/etc/sysconfig/mail details Displays detailed information about a variable: tux > 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 modied variables. Use all to list all variables and their values: tux > sudo yast sysconfig list all AOU_AUTO_AGREE_WITH_LICENSES="false" AOU_ENABLE_CRONJOB="true" 54 Command line parameters of YaST modules SLES 15 SP3AOU_INCLUDE_RECOMMENDS="false" [...] set Sets a value for a variable: tux > 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: tux > sudo yast sysconfig set CONFIG_TYPE$/etc/sysconfig/mail=advanced 4.4.3.25 yast tftp-server Congures a TFTP server. yast tftp-server accepts the following commands: directory Species the directory of the TFTP server: tux > sudo yast tftp-server directory path=/srv/tftp tux > sudo yast tftp-server directory list Directory Path: /srv/tftp status Controls the status of the TFTP server service: tux > sudo yast tftp-server status disable tux > sudo yast tftp-server status show Service Status: false tux > sudo yast tftp-server status enable 4.4.3.26 yast timezone Congures the time zone. yast timezone accepts the following commands: list 55 Command line parameters of YaST modules SLES 15 SP3Lists all available time zones grouped by region: tux > sudo yast timezone list Region: Africa Africa/Abidjan (Abidjan) Africa/Accra (Accra) Africa/Addis_Ababa (Addis Ababa) [...] set Species new values for the time zone conguration: tux > sudo yast timezone set timezone=Europe/Prague hwclock=local summary Displays the time zone conguration summary: tux > sudo yast timezone summary Current Time Zone: Europe/Prague Hardware 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: tux > 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: tux > 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: tux > sudo yast users edit username=user1 password=new_secret 56 Command line parameters of YaST modules SLES 15 SP3For a complete list of options, run yast users edit help . list Lists existing users ltered by user type: tux > sudo yast users list system For a complete list of options, run yast users list help . show Displays details about a user: tux > 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 Login Name: wwwrun UID: 456 For a complete list of options, run yast users show help . 57 Command line parameters of YaST modules SLES 15 SP35 YaST online update SUSE oers 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 Book “Deployment Guide”, Chapter 21 “Installing or removing software”, Section 21.5 “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 congured. 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 repository 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 Book “Deployment Guide”, Chapter  21 “Installing or removing software”, Section  21.4 “Managing software repositories and services”. Note: Error on accessing the update catalog If you are not able to access the update catalog, this might be 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 will 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// . SUSE provides updates with dierent relevance levels: Security updates Fix severe security hazards and should always be installed. Recommended updates Fix issues that could compromise your computer. Optional updates Fix non-security relevant issues or provide enhancements. 58 SLES 15 SP35.1 The online update dialog To open the YaST Online Update dialog, start YaST and select Software Online Update. Alternatively, start it from the command line with yast2 online_update . The Online Update window consists of four sections. FIGURE 5.1: 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. Unneeded patches Patches that either apply to packages not installed on your system, or patches that have requirements which have already have been fullled (because the relevant packages have already been updated from another source). All patches All patches available for SUSE Linux Enterprise Server. 59 The online update dialog SLES 15 SP3Each 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 fullled with this installation. In this case a check mark is displayed in front of the patch summary. The patch will be visible in the list until you mark it for installation. This will in fact 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. 5.2 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 notied 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 5.1: APPLYING PATCHES WITH YAST ONLINE UPDATE 1. Start YaST and select Software Online Update. 2. To automatically apply all new patches (except optional ones) that are currently available for your system, click Apply or Accept. 3. First modify the selection of patches that you want to apply: a. Use the respective lters and views that the interface provides. For details, refer to Section 5.1, “The online update dialog”. 60 Installing patches SLES 15 SP3b. 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 very good reason. These patches x severe security hazards and prevent your system from being exploited. c. Most patches include updates for several packages. To change actions for single packages, right-click a package in the package view and choose an action. d. To conrm 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. 5.3 Automatic online update You may congure 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 congurations might require you to disable the use of delta RPMs for the sake of performance. Some patches, such as kernel updates or packages requiring license agreements, require user interaction, which would cause the automatic update procedure to stop. You can congure 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 5.2: CONFIGURING THE AUTOMATIC ONLINE UPDATE 1. After installation, start YaST and select Software Online Update. Choose Conguration Online Update. If the yast2-online-update-configuration is not installed, you will be prompted to do that. 61 Automatic online update SLES 15 SP3FIGURE 5.2: 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 conrm the installation of the patch. Such patches are called “Interactive Patches”. When installing patches automatically, it is assumed that you have accepted the installation 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 automated 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. 62 Automatic online update SLES 15 SP37. To lter the patches by category (such as security or recommended), check Filter by Category 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 usually 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 features and modules. Security patches provide crucial updates and bugxes. Recommended patches are optional bugxes and enhancements. Optional are new packages. Other is equivalent to miscellaneous. Document is unused. 8. Conrm your conguration 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. 63 Automatic online update SLES 15 SP36 Managing software with command line tools This chapter describes Zypper and RPM, two command line tools for managing software. For a denition of the terminology used in this context (for example, repository , patch , or update ) refer to Book “Deployment Guide”, Chapter 21 “Installing or removing software”, Section 21.1 “Definition of terms”. 6.1 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. 6.1.1 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 specic 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: tux > sudo zypper patch Global options Additionally, you can choose from one or more global options by typing them immediately before the command: tux > 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). 64 Using Zypper SLES 15 SP3Command-specific options To use options that are specic to a particular command, type them immediately after the command: tux > 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 conrm any licenses. Instead, license 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: tux > sudo zypper install mplayer Some options also require a single argument. The following command will list all known patterns: tux > 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: tux > sudo zypper -v install --from factory mc vim The --from option keeps all repositories enabled (for solving any dependencies) while requesting the package from the specied 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. tux > 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. tux > sudo zypper --userdata STRING patch 65 General usage SLES 15 SP36.1.2 Using Zypper subcommands Zypper subcommands are executables that are stored in the zypper_execdir, /usr/lib/zypper/ commands . If a subcommand is not found in the zypper_execdir, Zypper automatically searches the rest of your $PATH for it. This enables writing your own local extensions and storing them in userspace. Executing subcommands in the Zypper shell, and using global Zypper options are not supported. List your available subcommands: tux > 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 View the help screen for a subcommand: tux > zypper help appstream-cache 6.1.3 Installing and removing software with Zypper To install or remove packages, use the following commands: tux > sudo zypper install PACKAGE_NAME tux > 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. 66 Using Zypper subcommands SLES 15 SP36.1.3.1 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 tux > sudo zypper install MozillaFirefox By exact package name and version number tux > sudo zypper install MozillaFirefox-52.2 By repository alias and package name tux > 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”: tux > 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 nishes and you need to clean the environment, run the following: tux > 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 : tux > sudo zypper install firefox 67 Installing and removing software with Zypper SLES 15 SP3By 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: tux > 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). tux > sudo zypper install ''firefox>=74.2'' You can also combine a hardware architecture and version requirement: tux > 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: tux > sudo zypper install /tmp/install/MozillaFirefox.rpm tux > sudo zypper install http://download.example.com/MozillaFirefox.rpm 6.1.3.2 Combining installation and removal of packages To install and remove packages simultaneously, use the +/- modiers. To install emacs and simultaneously remove vim , use: tux > sudo zypper install emacs -vim To remove emacs and simultaneously install vim , use: tux > 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 -- : tux > sudo zypper install -emacs +vim # Wrong tux > sudo zypper install vim -emacs # Correct 68 Installing and removing software with Zypper SLES 15 SP3tux > sudo zypper install -- -emacs +vim # Correct tux > sudo zypper remove emacs +vim # Correct 6.1.3.3 Cleaning up dependencies of removed packages If (together with a certain package), you automatically want to remove any packages that become unneeded after removing the specied package, use the --clean-deps option: tux > sudo zypper rm --clean-deps PACKAGE_NAME 6.1.3.4 Using Zypper in scripts By default, Zypper asks for a conrmation 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: tux > sudo zypper --non-interactive install PACKAGE_NAME This option allows the use of Zypper in scripts and cron jobs. 6.1.3.5 Installing or downloading source packages To install the corresponding source package of a package, use: tux > 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 conguration. This command will also install the build dependencies of the specied package. If you do not want this, add the switch -D : tux > sudo zypper source-install -D PACKAGE_NAME To install only the build dependencies use -d . tux > sudo zypper source-install -d PACKAGE_NAME 69 Installing and removing software with Zypper SLES 15 SP3Of 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 6.1.6, “Managing repositories with Zypper” for details on repository management. A list of all source packages available in your repositories can be obtained with: tux > zypper search -t srcpackage You can also download source packages for all installed packages to a local directory. To download source packages, use: tux > 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 downloading or deleting anything, use the --status option. To delete extraneous source packages, use the --delete option. To disable deleting, use the --no-delete option. 6.1.3.6 Installing packages from disabled repositories Normally you can only install or refresh packages from enabled repositories. The --plus- content 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 specic -debuginfo package, use the option as follows: tux > 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 congured 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. 70 Installing and removing software with Zypper SLES 15 SP36.1.3.7 Utilities To verify whether all dependencies are still fullled and to repair missing dependencies, use: tux > zypper verify In addition to dependencies that must be fullled, 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: tux > 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 fullled. 6.1.4 Updating software with Zypper There are three dierent ways to update software using Zypper: by installing patches, by installing 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 “Upgrade Guide”, Chapter 1 “Upgrade paths and methods”. 6.1.4.1 Installing all needed patches To install all ocially released patches that apply to your system, run: tux > sudo zypper patch All patches available from repositories congured on your computer are checked for their relevance to your installation. If they are relevant (and not classied as optional or feature ), they are installed immediately. Note that the ocial 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: tux > sudo zypper patch --with-update 71 Updating software with Zypper SLES 15 SP3To install also optional patches, use: tux > sudo zypper patch --with-optional To install all patches relating to a specic Bugzilla issue, use: tux > sudo zypper patch --bugzilla=NUMBER To install all patches relating to a specic CVE database entry, use: tux > sudo zypper patch --cve=NUMBER For example, to install a security patch with the CVE number CVE-2010-2713 , execute: tux > sudo zypper patch --cve=CVE-2010-2713 To install only patches which aect Zypper and the package management itself, use: tux > 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. 6.1.4.2 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 : tux > 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 aect 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 72 Updating software with Zypper SLES 15 SP3To list all patches available for SUSE Linux Enterprise Server, regardless of whether they are already installed or apply to your installation, use zypper patches . It is also possible to list and install patches relevant to specic issues. To list specic 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 specic 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: tux > zypper list-patches --bugzilla=972197,956917 By CVE number To list all needed patches that relate to an entry in the CVE database (Common Vulnerabilities and Exposures), use the option --cve . To list patches for a specic 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: tux > zypper list-patches --bugzilla=CVE-2016-2315,CVE-2016-2324 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: tux > 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 [...] 6.1.4.3 Installing new package versions If a repository contains only new packages, but does not provide patches, zypper patch does not show any eect. To update all installed packages with newer available versions (while maintaining system integrity), use: tux > sudo zypper update 73 Updating software with Zypper SLES 15 SP3To update individual packages, specify the package with either the update or install command: tux > sudo zypper update PACKAGE_NAME tux > sudo zypper install PACKAGE_NAME A list of all new installable packages can be obtained with the command: tux > 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 package, is installable (all dependencies are satised). A list of all new available packages (regardless whether installable or not) can be obtained with: tux > 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. 6.1.4.4 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: tux > sudo zypper packages --orphaned With this list, you can decide if a package is still needed or can be removed safely. 6.1.5 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: tux > zypper ps 74 Identifying processes and services using deleted files SLES 15 SP3PID | 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. tux > 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. 75 Identifying processes and services using deleted files SLES 15 SP3avahi-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 15, The systemd daemon. 6.1.6 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: tux > zypper repos The result will look similar to the following output: EXAMPLE 6.1: ZYPPER—LIST OF KNOWN REPOSITORIES tux > 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: tux > zypper repos -d 76 Managing repositories with Zypper SLES 15 SP36.1.6.1 Adding repositories To add a repository, run tux > 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 identier 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. 6.1.6.2 Refreshing repositories zypper enables you to fetch changes in packages from congured repositories. To fetch the changes, run: tux > 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: tux > sudo zypper --plus-content refresh This option fetches changes in repositories, but keeps the disabled repositories in the same state —disabled. 6.1.6.3 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 6.1, “Zypper—list of known repositories”, use one of the following commands: tux > sudo zypper removerepo 1 tux > sudo zypper removerepo "SLEHA-12-GEO" 77 Managing repositories with Zypper SLES 15 SP36.1.6.4 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: tux > 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 : tux > sudo zypper renamerepo ''Mozilla Firefox'' firefox 6.1.7 Querying repositories and packages with Zypper Zypper oers various methods to query repositories or packages. To get lists of all products, patterns, packages or patches available, use the following commands: tux > zypper products tux > zypper patterns tux > zypper packages tux > zypper patches To query all repositories for certain packages, use search . To get information regarding particular packages, use the info command. 6.1.7.1 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. 78 Querying repositories and packages with Zypper SLES 15 SP3Simple search for a package name containing fire tux > zypper search "fire" Simple search for the exact package MozillaFirefox tux > zypper search --match-exact "MozillaFirefox" Also search in package descriptions and summaries tux > zypper search -d fire Only display packages not already installed tux > zypper search -u fire Display packages containing the string fir not followed be e tux > zypper se "/fir[^e]/" 6.1.7.2 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: tux > 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 6.1.7.3 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: tux > zypper what-provides ''perl(SVN::Core)'' 79 Querying repositories and packages with Zypper SLES 15 SP3The 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. 6.1.7.4 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 specic 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 : tux > zypper info --requires MozillaFirefox 6.1.8 Showing lifecycle information SUSE products are generally supported for 10 years. Often, you can extend that standard lifecycle by using the extended support oerings 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: root # 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* 80 Showing lifecycle information SLES 15 SP3Package end of support if different from product: autofs Now, installed 5.1.3-7.3.1, update available 5.1.3-7.6.1 6.1.9 Configuring Zypper Zypper now comes with a conguration le, allowing you to permanently change Zypper''s behavior (either system-wide or user-specic). For system-wide changes, edit /etc/zypp/ zypper.conf . For user-specic 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. 6.1.10 Troubleshooting If you have trouble accessing packages from congured 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: tux > sudo zypper refresh If that does not help, try tux > sudo zypper refresh -fdb This forces a complete refresh and rebuild of the database, including a forced download of raw metadata. 6.1.11 Zypper rollback feature on Btrfs file system If the Btrfs le system is used on the root partition and snapper is installed, Zypper automatically 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 7, System recovery and snapshot management with Snapper for more information. 81 Configuring Zypper SLES 15 SP36.1.12 More information For more information on managing software from the command line, enter zypper help , zypper help  COMMAND or refer to the zypper(8) man page. For a complete and detailed command 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 . 6.2 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 administrators 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 congure 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, headers, 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 identied by the name extension -devel , such as the packages alsa-devel and gimp-devel . 82 More information SLES 15 SP36.2.1 Verifying package authenticity RPM packages have a GPG signature. To verify the signature of an RPM package, use the command 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 xing 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: tux > 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. 6.2.2 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 fullled and if there are no conicts 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 conicts arise—a specic le can only belong to one package. By choosing dierent 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 example, rpm -F PACKAGE .rpm). This command removes the les of the old version and immediately installs the new les. The dierence between the two versions is that -U installs 83 Verifying package authenticity SLES 15 SP3packages that previously did not exist in the system, while -F merely updates previously installed packages. When updating, rpm updates conguration les carefully using the following strategy: If a conguration 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 conguration 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 the newer version are dierent. 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 conguration le already exists and if the noreplace label was specied 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 conguration le. A list of these les is available in /var/adm/rpmconfigcheck . Some conguration les (like /etc/httpd/httpd.conf ) are not overwritten to allow continued operation. 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 database. 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 . 84 Managing packages: install, update, and uninstall SLES 15 SP36.2.3 Delta RPM packages Delta RPM packages contain the dierence 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. The 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: tux > 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: tux > sudo applydeltarpm new.delta.rpm new.rpm To derive it from the old RPM without accessing the le system, use the -r option: tux > sudo applydeltarpm -r old.rpm new.delta.rpm new.rpm See /usr/share/doc/packages/deltarpm/README for technical details. 6.2.4 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 6.1, “Essential RPM query options”. TABLE 6.1: 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 specied with FILE ) 85 Delta RPM packages SLES 15 SP3-s File list with status information (implies -l ) -d List only documentation les (implies -l ) -c List only conguration les (implies -l ) --dump File list with complete details (to be used with -l , -c , or -d ) --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 6.2, “rpm -q -i wget”. EXAMPLE 6.2: 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 86 RPM queries SLES 15 SP3The option -f only works if you specify the complete le name with its full path. Provide as many le names as desired. For example: tux > 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 6.3, “Script to search for packages”. Pass the partial le name to the script shown as a parameter when running it. EXAMPLE 6.3: 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 specic package, sorted by date. With the installed RPM database, verication 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 6.2: RPM VERIFY OPTIONS 5 MD5 check sum S File size L Symbolic link T Modication time D Major and minor device numbers U Owner G Group M Mode (permissions and le type) 87 RPM queries SLES 15 SP3In the case of conguration les, the letter c is printed. For example, for changes to /etc/ wgetrc ( wget package): tux > 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 . Before 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 . 6.2.5 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 unpacked 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 specied custom settings in a le like /etc/rpmrc ): SOURCES for the original sources ( .tar.bz2 or .tar.gz les, etc.) and for distribution-specic adjustments (mostly .diff or .patch les) SPECS for the .spec les, similar to a meta Makele, which control the build process BUILD all the sources are unpacked, patched and compiled in this directory RPMS 88 Installing and compiling source packages SLES 15 SP3where 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 . Warning: 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 conguration 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 . 89 Installing and compiling source packages SLES 15 SP3--short-circuit Skip some steps. The binary RPM created can now be installed with rpm -i or, preferably, with rpm -U . Installation 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. 6.2.6 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 dened 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 : root # cd /usr/src/packages/SOURCES/ root # mv ../SPECS/wget.spec . root # 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 oers 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. 6.2.7 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, oering all usual menu options of Midnight Commander. Display the HEADER with F3 . View the archive structure with the cursor keys and Enter . Copy archive components with F5 . 90 Compiling RPM packages with build SLES 15 SP3A full-featured package manager is available as a YaST module. For details, see Book “Deployment Guide”, Chapter 21 “Installing or removing software”. 91 Tools for RPM archives and the RPM database SLES 15 SP37 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. However, 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 partition.) You can also boot from Btrfs snapshots. For more information, see Section 7.3, “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 7.2, “Using Snapper to undo changes” for details. Restore les from previous snapshots. See Section 7.2.2, “Using Snapper to restore files” for details. Do a system rollback by booting from a snapshot. See Section 7.3, “System rollback by booting from snapshots” for details. Manually create and manage snapshots, within the running system. See Section  7.6, “Manually creating and managing snapshots” for details. 92 SLES 15 SP37.1 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 conguration for the root le system by running: tux > sudo snapper -c root create-config / Afterward enable the dierent snapshot types as described in Section 7.1.4.1, “Disabling/ enabling snapshots”. Note that on a Btrfs root le system, snapshots require a le system with subvolumes set up 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 modied, 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 modied. 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 dierent 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 modications. 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 7.1.4.4, “Controlling snapshot archiving” for details. 93 Default setup SLES 15 SP37.1.1 Default settings Disks larger than 16 GB Conguration le: /etc/snapper/configs/root USE_SNAPPER=yes TIMELINE_CREATE=no Disks smaller than 16 GB Conguration le: not created USE_SNAPPER=no TIMELINE_CREATE=yes 7.1.2 Types of snapshots Although snapshots themselves do not dier 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. Old snapshots are automatically deleted. By default, the rst snapshot of the last ten days, months, and years are kept. Timeline snapshots are disabled by default. Installation snapshots Whenever one or more packages are installed with YaST or Zypper, a pair of snapshots is created: one before the installation starts (“Pre”) and another one after the installation has nished (“Post”). In case an important system component such as the kernel has been installed, the snapshot pair is marked as important ( important=yes ). Old snapshots are automatically deleted. By default the last ten important snapshots and the last ten “regular” (including administration snapshots) snapshots are kept. Installation snapshots are enabled by default. Administration snapshots 94 Default settings SLES 15 SP3Whenever you administrate the system with YaST, a pair of snapshots is created: one when a YaST module is started (“Pre”) and another when the module is closed (“Post”). Old snapshots are automatically deleted. By default the last ten important snapshots and the last ten “regular” snapshots (including installation snapshots) are kept. Administration snapshots are enabled by default. 7.1.3 Directories that are excluded from snapshots Some directories need to be excluded from snapshots for dierent 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 conguration is not supported. The directories listed above are architecture-specic. The rst two directories are present on AMD64/Intel 64 machines, 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 rollbacks. /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 uninstalling 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 databases. Therefore this subvolume is created to exclude all of this variable data from snapshots and has Copy-On-Write disabled. 95 Directories that are excluded from snapshots SLES 15 SP37.1.4 Customizing the setup SUSE Linux Enterprise Server comes with a reasonable default setup, which should be sucient for most use cases. However, all aspects of taking automatic snapshots and snapshot keeping can be congured according to your needs. 7.1.4.1 Disabling/enabling snapshots Each of the three snapshot types (timeline, installation, administration) can be enabled or disabled independently. Disabling/enabling timeline snapshots Enabling. snapper -c root set-config "TIMELINE_CREATE=yes" Disabling. snapper -c root set-config "TIMELINE_CREATE=no" Timeline snapshots are enabled by default, except for the root partition. 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. 7.1.4.2 Controlling installation snapshots Taking snapshot pairs upon installing packages with YaST or Zypper is handled by the snapper- zypp-plugin . An XML conguration le, /etc/snapper/zypp-plugin.conf denes, when to make snapshots. By default the le looks like the following: 1 2 3 4 kernel-* 3 5 dracut 96 Customizing the setup SLES 15 SP36 glibc 7 systemd* 8 udev 9 * 4 10 11 1 The match attribute denes 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 will also be 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 conguration 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 snapshot pair will also be 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 7.1.4.3 Creating and mounting new subvolumes Creating a new subvolume underneath the / hierarchy and permanently mounting it is supported. Such a subvolume will be 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. 97 Customizing the setup SLES 15 SP3SUSE Linux Enterprise Server is congured with the /@/ subvolume which serves as an independent root for permanent subvolumes such as /opt , /srv , /home and others. Any new subvolumes 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 . tux > sudo mount /dev/sda2 -o subvol=@ /mnt tux > sudo btrfs subvolume create /mnt/usr/important tux > 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 . 7.1.4.4 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 will be deleted. A minimum of four important and two regular snapshots are always kept. Refer to Section 7.5.1, “Managing existing configurations” for instructions on how to change these values. 98 Customizing the setup SLES 15 SP37.1.4.5 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 10 “Expert Partitioner”, Section 10.2 “LVM configuration”. To use Snapper on a thinly-provisioned LVM volume you need to create a Snapper conguration 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: tux > sudo snapper -c lvm create-config --fstype="lvm(xfs)" /thin_lvm You can adjust this conguration according to your needs as described in Section 7.5.1, “Managing existing configurations”. 7.2 Using Snapper to undo changes Snapper on SUSE Linux Enterprise Server is precongured to serve as a tool that lets you undo changes made by zypper and YaST. For this purpose, Snapper is congured 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 modied. Timeline snapshots for the root partition need to be enabled for this purpose—see Section 7.1.4.1, “Disabling/enabling snapshots” for details. By default, automatic snapshots as described above are congured for the root partition and its subvolumes. To make snapshots available for other partitions such as /home for example, you can create custom congurations. Important: Undoing changes compared to rollback When working with snapshots to restore data, it is important to know that there are two fundamentally dierent scenarios Snapper can handle: Undoing changes When undoing changes as described in the following, two snapshots are being compared 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 99 Using Snapper to undo changes SLES 15 SP3When doing rollbacks as described in Section  7.3, “System rollback by booting from snapshots”, the system is reset to the state at which the snapshot was taken. When 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 7.3, “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, some 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. 7.2.1 Undoing YaST and Zypper changes If you set up the root partition with Btrfs during the installation, Snapper—precongured 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 nished. 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 dierences between two versions of a le (di). PROCEDURE 7.1: 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 Conguration is set to root. This is always the case unless you have manually added own Snapper congurations. 100 Undoing YaST and Zypper changes SLES 15 SP33. 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 dier between the two snapshots. 101 Undoing YaST and Zypper changes SLES 15 SP35. 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 respective check box. Click Restore Selected and conrm the action by clicking Yes. To restore a single le, activate its di view by clicking its name. Click Restore From First and conrm your choice with Yes. 102 Undoing YaST and Zypper changes SLES 15 SP3PROCEDURE 7.2: 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) . tux > 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 -. tux > 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. tux > sudo snapper diff 350..351 /usr/share/fonts/truetype/fonts.scale 103 Undoing YaST and Zypper changes SLES 15 SP3--- /.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. tux > 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 104 Undoing YaST and Zypper changes SLES 15 SP3Warning: 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. 7.2.2 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 modications 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 directories, for example, create a separate Snapper conguration for /home doing automatic timeline snapshots. See Section 7.5, “Creating and modifying Snapper configurations” for instructions. Warning: Restoring files compared to rollback Snapshots taken from the root le system (dened by Snapper''s root conguration), 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 7.3, “System rollback by booting 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 conguration le from the /etc directory, but not the complete list of les from the snapshot. This restriction only aects snapshots taken from the root le system! PROCEDURE 7.3: 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 Conguration from which to choose a snapshot. 105 Using Snapper to restore files SLES 15 SP33. 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 dierence between the snapshot 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 conrm the action by clicking Yes. PROCEDURE 7.4: RESTORING FILES USING THE snapper COMMAND 1. Get a list of timeline snapshots for a specic conguration by running the following command: tux > sudo snapper -c CONFIG list -t single | grep timeline CONFIG needs to be replaced by an existing Snapper conguration. Use snapper list- configs to display a list. 2. Get a list of changed les for a given snapshot by running the following command: tux > sudo snapper -c CONFIG status SNAPSHOT_ID..0 Replace SNAPSHOT_ID by the ID for the snapshot from which you want to restore the le(s). 3. Optionally list the dierences between the current le version and the one from the snapshot by running tux > sudo snapper -c CONFIG diff SNAPSHOT_ID..0 FILE NAME If you do not specify , the dierence for all les are shown. 4. To restore one or more les, run tux > sudo snapper -c CONFIG -v undochange SNAPSHOT_ID..0 FILENAME1 FILENAME2 If you do not specify le names, all changed les will be restored. 106 Using Snapper to restore files SLES 15 SP37.3 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 miscongured system. Only snapshots created for the default Snapper conguration ( root ) are bootable. Important: Supported configuration As of SUSE Linux Enterprise Server 15 SP3 system rollbacks are only supported if the default subvolume conguration 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 modied. Important: Undoing changes compared to rollback When working with snapshots to restore data, it is important to know that there are two fundamentally dierent scenarios Snapper can handle: Undoing changes When undoing changes as described in Section 7.2, “Using Snapper to undo changes”, two snapshots are compared and the changes between these two snapshots are reverted. 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 supported. 107 System rollback by booting from snapshots SLES 15 SP3The root le system needs to be on a single device, a single partition and a single subvolume. Directories that are excluded from snapshots such as /srv (see Section 7.1.3, “Directories that are excluded from snapshots” for a full list) may reside on separate partitions. The system needs to be bootable via the installed boot loader. 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 dierent snapshot, or start the rescue system. b. To perform the rollback, run tux > 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 7.3.1, “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 Tip: 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 identied by the description after installation . 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). 108 System rollback by booting from snapshots SLES 15 SP37.3.1 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 7.7, “Automatic snapshot clean-up” for details. If the snapshot contains important data, extract the data from the snapshot before it is removed. 7.3.1.1 Example of rollback snapshot For example, after a fresh installation the following snapshots are available on the system: root # 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. root # snapper --iso list Type | # | | Cleanup | Description | Userdata -------+---+ ... +---------+-----------------------+-------------- single | 0 | | | current | single | 1 | | number | first root filesystem | single | 2 | | number | after installation | important=yes single | 3 | | number | rollback backup of #1 | important=yes single | 4 | | | | 7.3.2 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. 109 Snapshots after rollback SLES 15 SP3FIGURE 7.1: BOOT LOADER: SNAPSHOTS 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 ) 1 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. 110 Accessing and identifying snapshot boot entries SLES 15 SP3Tip: 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 sucient, or a user-provided description is too long. To set a custom string STRING for snapshot NUMBER , use the following command: tux > 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. 7.3.3 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. 7.3.3.1 Directories excluded from snapshots Root le system snapshots do not contain all directories. See Section 7.1.3, “Directories that are excluded from snapshots” for details and reasons. As a general consequence, data from these directories is not restored, resulting in the following limitations. Add-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 others 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 aected les after the rollback. Incompatible data formats 111 Limitations SLES 15 SP3If 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 aected 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. 7.3.3.2 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 . 7.4 Enabling Snapper in user home directories You may enable snapshots for users'' /home directories, which supports a number of 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 conguration 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 7.4.3, “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 conguration. pam_snapper provides integration with the useradd command, pluggable authentication modules (PAM), and Snapper. By default it creates snapshots at user login and logout, and also creates time-based snapshots as some users remain logged in for extended periods of time. You may change the defaults using the normal Snapper commands and conguration les. 112 Enabling Snapper in user home directories SLES 15 SP37.4.1 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 : root # 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: root # /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. The les from /etc/skel will be copied into the user''s home directory at their rst login. Verify that the user''s conguration was created by listing your Snapper congurations: root # 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. 7.4.2 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 conguration, and deletes all snapshots. root # /usr/lib/pam_snapper/pam_snapper_userdel.sh username 113 Installing pam_snapper and creating users SLES 15 SP37.4.3 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. root # btrfs subvol create /home/username root # snapper -c home_username create-config /home/username root # sed -i -e "s/ALLOW_USERS=\"\"/ALLOW_USERS=\"username\"/g" \ /etc/snapper/configs/home_username root # yast users add username=username home=/home/username password=password root # chown username.group /home/username root # chmod 755 /home/username/.snapshots 7.5 Creating and modifying Snapper configurations The way Snapper behaves is dened in a conguration le that is specic for each partition or Btrfs subvolume. These conguration les reside under /etc/snapper/configs/ . In 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 conguration is named root . It creates and manages the YaST and Zypper snapshot. See Section  7.5.1.1, “Configuration data” for a list of the default values. Note: Minimum root file system size for enabling snapshots As explained in Section 7.1, “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_INCREASE_PERCENTAGE /100) 114 Manually enabling snapshots in home directories SLES 15 SP3Keep 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 congurations for other partitions formatted with Btrfs or existing subvolumes on a Btrfs partition. In the following example we will set up a Snapper conguration for backing up the Web server data residing on a separate, Btrfs -formatted partition mounted at /srv/www . After a conguration 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 Conguration, while you need to specify your conguration for snapper with the global switch -c (for example, snapper -c myconfig list ). To create a new Snapper conguration, run snapper create-config : tux > sudo snapper -c www-data 1 create-config /srv/www 2 1 Name of conguration le. 2 Mount point of the partition or Btrfs subvolume on which to take snapshots. This command will create a new conguration le /etc/snapper/configs/www-data with reasonable default values (taken from /etc/snapper/config-templates/default ). Refer to Section 7.5.1, “Managing existing configurations” for instructions on how to adjust these defaults. Tip: Configuration defaults Default values for a new conguration are taken from /etc/snapper/config- templates/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g command: tux > sudo snapper -c www-data create-config -t MY_DEFAULTS /srv/www 115 Creating and modifying Snapper configurations SLES 15 SP37.5.1 Managing existing configurations The snapper command oers several subcommands for managing existing congurations. You can list, show, delete and modify them: Listing configurations Use the subcommand snapper list-configs to get all existing congurations: tux > 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 specied conguration. Replace CONFIG with one of the conguration names shown by snapper list-configs . For more information about the conguration options, see Section 7.5.1.1, “Configuration data”. To display the default conguration, run: tux > sudo snapper -c root get-config Modifying a configuration Use the subcommand snapper -c CONFIG set-config OPTION=VALUE to modify an option in the specied conguration. Replace CONFIG with one of the conguration names shown by snapper list-configs . Possible values for OPTION and VALUE are listed in Section 7.5.1.1, “Configuration data”. Deleting a configuration Use the subcommand snapper -c CONFIG delete-config to delete a conguration. Replace CONFIG with one of the conguration names shown by snapper list-configs . 7.5.1.1 Configuration data Each conguration contains a list of options that can be modied 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 116 Managing existing configurations SLES 15 SP3Granting permissions to use snapshots to regular users. See Section 7.5.1.2, “Using Snapper as regular user” for more information. The default value is "" . BACKGROUND_COMPARISON Denes whether pre and post snapshots should be compared in the background after creation. The default value is "yes" . EMPTY_* Denes the clean-up algorithm for snapshots pairs with identical pre and post snapshots. See Section 7.7.3, “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_* Denes the clean-up algorithm for installation and admin snapshots. See Section  7.7.1, “Cleaning up numbered snapshots” for details. QGROUP / SPACE_LIMIT Adds quota support to the clean-up algorithms. See Section 7.7.5, “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 7.5.1.2, “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_* 117 Managing existing configurations SLES 15 SP3Denes the clean-up algorithm for timeline snapshots. See Section 7.7.2, “Cleaning up timeline snapshots” for details. 7.5.1.2 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 congurations that grant permissions to users or/ and groups. The corresponding .snapshots directory needs to be readable and accessible by the specied users. The easiest way to achieve this is to set the SYNC_ACL option to yes . PROCEDURE 7.5: ENABLING REGULAR USERS TO USE SNAPPER Note that all steps in this procedure need to be run by root . 1. If a Snapper conguration does not exist yet, create one for the partition or subvolume on which the user should be able to use Snapper. Refer to Section 7.5, “Creating and modifying Snapper configurations” for instructions. Example: tux > sudo snapper --config web_data create /srv/www 2. The conguration le is created under /etc/snapper/configs/CONFIG , where CONFIG is the value you specied 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 7.5.1, “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: tux > sudo snapper -c web_data set-config "ALLOW_USERS=www_admin" SYNC_ACL="yes" 4. The given Snapper conguration can now be used by the specied user(s) and/or group(s). You can test it with the list command, for example: www_admin:~ > snapper -c web_data list 118 Managing existing configurations SLES 15 SP37.6 Manually creating and managing snapshots Snapper is not restricted to creating and managing snapshots automatically by conguration; 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 conguration (see Section 7.5, “Creating and modifying Snapper configurations” for details). You can only take snapshots of partitions or volumes for which a conguration exists. By default the system conguration ( root ) is used. To create or manage snapshots for your own conguration you need to explicitly choose it. Use the Current Conguration drop-down box in YaST or specify the -c on the command line ( snapper -c MYCONFIG COMMAND ). 7.6.1 Snapshot metadata Each snapshot consists of the snapshot itself and some 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 conguration home . To list snapshots for the default conguration (root), use snapper -c root list or snapper list . snapper list -a Lists snapshots for all existing congurations. snapper list -t pre-post Lists all pre and post snapshot pairs for the default ( root ) conguration. snapper list -t single Lists all snapshots of the type single for the default ( root ) conguration. The following metadata is available for each snapshot: Type: Snapshot type, see Section 7.6.1.1, “Snapshot types” for details. This data cannot be changed. Number: Unique number of the snapshot. This data cannot be changed. Pre Number: Species the number of the corresponding pre snapshot. For snapshots of type post only. This data cannot be changed. 119 Manually creating and managing snapshots SLES 15 SP3Description: 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  7.7, “Automatic snapshot clean-up” for details. 7.6.1.1 Snapshot types Snapper knows three dierent types of snapshots: pre, post, and single. Physically they do not dier, but Snapper handles them dierently. pre Snapshot of a le system before a modication. 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 modication. 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. 7.6.1.2 Cleanup algorithms Snapper provides three algorithms to clean up old snapshots. The algorithms are executed in a daily cron job. It is possible to dene the number of dierent types of snapshots to keep in the Snapper conguration (see Section 7.5.1, “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. 120 Snapshot metadata SLES 15 SP3empty-pre-post Deletes pre/post snapshot pairs with empty dis. 7.6.2 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 . snapper create --from 17 --description "with package2" Creates a stand-alone snapshot (type single) from an existing snapshot, which is specied 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 ) conguration with a description. Because no cleanup-algorithm is specied, 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 conguration named home with a description. Because no cleanup-algorithm is specied, the snapshot will never be deleted automatically. snapper --config home create --description "Daily data backup" --cleanup- algorithm timeline > Creates a stand-alone snapshot (type single) for a custom conguration named home with a description. The snapshot will automatically be deleted when it meets the criteria specied for the timeline cleanup-algorithm in the conguration. snapper create --type pre --print-number --description "Before the Apache config cleanup" --userdata "important=yes" 121 Creating snapshots SLES 15 SP3Creates 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. 7.6.3 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 modify 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 Modies the metadata of snapshot 10 for the default ( root ) conguration. The cleanup algorithm is set to timeline . snapper --config home modify --description "daily backup" -cleanup-algorithm "timeline" 120 Modies the metadata of snapshot 120 for a custom conguration named home . A new description is set and the cleanup algorithm is unset. 7.6.4 Deleting snapshots To delete a snapshot with the YaST Snapper module, choose a snapshot from the list and click Delete. 122 Modifying snapshot metadata SLES 15 SP3To 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 snapshot (and vice versa). snapper delete 65 Deletes snapshot 65 for the default ( root ) conguration. snapper -c home delete 89 90 Deletes snapshots 89 and 90 for a custom conguration named home . snapper delete --sync 23 Deletes snapshot 23 for the default ( root ) conguration and makes the freed space available 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. 123 Deleting snapshots SLES 15 SP3Snapshots are also automatically deleted by a daily cron job. Refer to Section 7.6.1.2, “Cleanup algorithms” for details. 7.7 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 oers algorithms to automatically delete old snapshots. These algorithms dierentiate between timeline snapshots and numbered snapshots (administration plus installation snapshot pairs). You can specify the number of snapshots to keep for each type. In addition to that, you can optionally specify a disk space quota, dening 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 dier. A clean-up algorithm is always bound to a single Snapper conguration, so you need to congure algorithms for each conguration. To prevent certain snapshots from being automatically deleted, refer to Q:. The default setup ( root ) is congured 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. 7.7.1 Cleaning up numbered snapshots Cleaning up numbered snapshots—administration plus installation snapshot pairs—is controlled by the following parameters of a Snapper conguration. NUMBER_CLEANUP Enables or disables clean-up of installation and admin snapshot pairs. If enabled, snapshot pairs are deleted when the total snapshot count exceeds a number specied with NUMBER_LIMIT and/or NUMBER_LIMIT_IMPORTANT and an age specied with NUMBER_MIN_AGE . Valid values: yes (enable), no (disable). The default value is "yes" . Example command to change or set: tux > sudo snapper -c CONFIG set-config "NUMBER_CLEANUP=no" 124 Automatic snapshot clean-up SLES 15 SP3NUMBER_LIMIT / NUMBER_LIMIT_IMPORTANT Denes 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_IMPORTANT . The cleaning algorithms delete snapshots above the specied maximum value, without 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: tux > sudo snapper -c CONFIG set-config "NUMBER_LIMIT=10" Important: Ranged compared to constant values In case quota support is enabled (see Section 7.7.5, “Adding disk quota support”) the limit needs to be specied as a minimum-maximum range, for example 2-10 . If quota support is disabled, a constant value, for example 10 , needs to be provided, otherwise cleaning-up will fail with an error. NUMBER_MIN_AGE Denes the minimum age in seconds a snapshot must have before it can automatically be deleted. Snapshots younger than the value specied here will not be deleted, regardless of how many exist. The default value is "1800" . Example command to change or set: tux > 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 dened with NUMBER_LIMIT* regardless of their age, set NUMBER_MIN_AGE to 0 . The following example shows a conguration to keep the last 10 important and regular snapshots regardless of age: NUMBER_CLEANUP=yes 125 Cleaning up numbered snapshots SLES 15 SP3NUMBER_LIMIT_IMPORTANT=10 NUMBER_LIMIT=10 NUMBER_MIN_AGE=0 On the other hand, 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 conguration to only keep snapshots younger than ten days: NUMBER_CLEANUP=yes NUMBER_LIMIT_IMPORTANT=0 NUMBER_LIMIT=0 NUMBER_MIN_AGE=864000 7.7.2 Cleaning up timeline snapshots Cleaning up timeline snapshots is controlled by the following parameters of a Snapper conguration. TIMELINE_CLEANUP Enables or disables clean-up of timeline snapshots. If enabled, snapshots are deleted when the total snapshot count exceeds a number specied with TIMELINE_LIMIT_* and an age specied with TIMELINE_MIN_AGE . Valid values: yes , no . The default value is "yes" . Example command to change or set: tux > 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 Denes the minimum age in seconds a snapshot must have before it can automatically be deleted. The default value is "1800" . 126 Cleaning up timeline snapshots SLES 15 SP3EXAMPLE 7.1: 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 conguration 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). Since 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. 7.7.3 Cleaning up snapshot pairs that do not differ As explained in Section 7.1.2, “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 dierence between the pre and post snapshots. Such “empty” snapshot pairs can be automatically be deleted by setting the following parameters in a Snapper conguration: EMPTY_PRE_POST_CLEANUP If set to yes , pre and post snapshot pairs that do not dier will be deleted. 127 Cleaning up snapshot pairs that do not differ SLES 15 SP3The default value is "yes" . EMPTY_PRE_POST_MIN_AGE Denes the minimum age in seconds a pre and post snapshot pair that does not dier must have before it can automatically be deleted. The default value is "1800" . 7.7.4 Cleaning up manually created snapshots Snapper does not oer 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 specied. 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) conguration and assigns the number clean-up algorithm. snapper modify --cleanup-algorithm "timeline" 25 Modies the snapshot with the number 25 and assigns the clean-up algorithm timeline . 7.7.5 Adding disk quota support In addition to the number and/or timeline clean-up algorithms described above, Snapper supports quotas. You can dene what percentage of the available space snapshots are allowed to occupy. This percentage value always applies to the Btrfs subvolume dened in the respective Snapper conguration. 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 conguration (see Section 7.5, “Creating and modifying Snapper configurations” for more information). Quota support is controlled by the following parameters of a Snapper conguration. QGROUP 128 Cleaning up manually created snapshots SLES 15 SP3The 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%, ...). The following limitations and guidelines apply: Quotas are only activated in addition to an existing number and/or timeline clean-up algorithm. 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 specied for number and timeline snapshots. Only if the quota is exceeded after this run, the quota-specic rules will be applied in a second run. Even if quota support is enabled, Snapper will always keep the number of snapshots specied 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 NUMBER_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. 7.8 Showing exclusive disk space used by snapshots Snapshots share data, for ecient use of storage space, so using ordinary commands like du and df won''t 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: root # snapper--iso list # | Type | Pre # | Date | User | Used Space | Cleanup | Description | Userdata 129 Showing exclusive disk space used by snapshots SLES 15 SP3----+--------+-------+---------------------+------+------------+--------- +-----------------------+-------------- 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 4 | 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: root # 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 identication number for each subvolume, assigning a qgroup level/ID combination. The rfer column displays the total amount of data referred to in the subvolume. 130 Showing exclusive disk space used by snapshots SLES 15 SP3The excl column displays the exclusive data in each subvolume. The parent column shows the parent qgroup of the subvolumes. The nal 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: root # btrfs subvolume list -st / ID gen top level path -- --- --------- ---- 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 7.6.4, “Deleting snapshots” for details. 7.9 Frequently asked questions Q: Why does Snapper never show changes in /var/log , /tmp and other directories? A: For some directories we decided to exclude them from snapshots. See Section  7.1.3, “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 7.3, “System rollback by booting from snapshots” for details. Q: Can a snapshot be protected from deletion? A: Currently Snapper does not oer means to prevent a snapshot from being deleted manually. However, you can prevent snapshots from being automatically deleted by clean-up algorithms. Manually created snapshots (see Section  7.6.2, “Creating snapshots”) 131 Frequently asked questions SLES 15 SP3have no clean-up algorithm assigned unless you specify one with --cleanup-algorithm . Automatically created snapshots always either have the number or timeline algorithm assigned. To remove such an assignment from one or more snapshots, proceed as follows: 1. List all available snapshots: tux > sudo snapper list -a 2. Memorize the number of the snapshot(s) you want to prevent from being deleted. 3. Run the following command and replace the number placeholders with the number(s) you memorized: tux > 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 modied. Q: Where can I get more information on Snapper? A: See the Snapper home page at http://snapper.io/ . 132 Frequently asked questions SLES 15 SP38 Live kernel patching with KLP This document describes the basic principles of the Kernel Live Patching (KLP) technology, 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. 8.1 Advantages of Kernel Live Patching KLP oers several benets. Keeping a large number of servers automatically up to date is essential for organizations obtaining or maintaining certain compliance certications. KLP can help achieve compliance, while reducing the need for costly maintenance windows. Companies that work with service-level agreement contracts must guarantee a specic 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. 8.2 Kernel Live Patching overview Kernel live patches are delivered as packages with modied code that are separate from the main kernel package. The live patches are cumulative, so the latest patch contains all xes 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 xes. 133 Advantages of Kernel Live Patching SLES 15 SP3Important: Live patches vs. kernel updates Live patches contain only critical xes, 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. It is possible to have multiple versions of the kernel package installed along with their live patches. These packages do not conict. 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 8.5.1, “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 xes and serves as a seed for future live patches for the corresponding kernel. These empty seed patches are called initial patches . 134 Kernel Live Patching overview SLES 15 SP38.2.1 Kernel Live Patching scope The scope of SLE Live Patching includes xes for SUSE Common Vulnerability Scoring System (CVSS; SUSE CVSS is based on the CVSS v3.0 system) level 7+ vulnerabilities and bug xes related to system stability or data corruption. However, it may not be technically feasible to create live patches for all xes that fall under the specied categories. SUSE therefore reserves the right to skip xes in situations where creating a kernel live patch is not possible for technical reasons. Currently, over 95% of qualifying xes are released as live patches. For more information on CVSS (the base for the SUSE CVSS rating), see Common Vulnerability Scoring System SIG (https://www.first.org/cvss/) . 8.2.2 Kernel Live Patching limitations KLP involves replacing functions and gracefully handling replacement of interdependent function sets. This is done by redirecting calls to old code to updated code in a dierent 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, some xes cannot be converted to live patches. In this situation, a system restart is the only way to apply the xes. 8.3 Activating Kernel Live Patching using YaST To activate KLP on your system, you need to have active SLES and SLE Live Patching subscriptions. Visit SUSE Customer Center (https://scc.suse.com/) to check the status of your subscriptions and obtain a registration code for the SLE Live Patching subscription. To 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. Conrm the license terms and click Next. 4. Enter your SLE Live Patching registration code and click Next. 135 Kernel Live Patching scope SLES 15 SP35. 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 will install the base Kernel Live Patching components on your system, the initial live patch, and the required dependencies. 8.4 Activating Kernel Live Patching from the command line To activate Kernel Live Patching, you need to have active SLES and SLES Live Patching subscriptions. Visit SUSE Customer Center (https://scc.suse.com/) to check the status of your subscriptions 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 SP3 x86_64 Activate with: SUSEConnect -p sle-module-live-patching/15.3/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/15.3/x86_64 \ -r LIVE_PATCHING_REGISTRATION_CODE 3. Install the required packages and dependencies using the command zypper install - t pattern lp_sles At 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 xes as part of the package installation. The kernel gets live-patched even before the product installation is complete. 136 Activating Kernel Live Patching from the command line SLES 15 SP38.5 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 kernel-default package is installed, the update manager prompts you to reboot the system. To prevent this message from appearing, you can lter out kernel updates from the patching operation. This can be done by adding package locks with Zypper. SUSE Manager also makes it possible to lter channel contents (see Live Patching with SUSE Manager (https://documentation.suse.com/external-tree/en-us/suma/4.1/ suse-manager/administration/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 xes applied, so there is no need to perform patching again. 8.5.1 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-patching/ current-patches/) page allows you to check expiration dates based on the running kernel version without installing the product extension. 137 Performing Kernel Live Patching SLES 15 SP38.6 Troubleshooting Kernel Live Patching issues 8.6.1 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 8.1: 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-5_3_18-24_29-default-2-2.1.x86_64 The 5_3_18-24_29-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 available 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 release lower than the current one. 3. Install the desired version with the command zypper in --oldpackage kernel- livepatch-RUNNING_KERNEL_VERSION-default=DESIRED_VERSION . 138 Troubleshooting Kernel Live Patching issues SLES 15 SP39 Transactional updates Transactional updates are available in SUSE Linux Enterprise Server as a technology preview, for updating SLES when the root le system is read-only. Transactional updates are atomic (all updates are applied only if all updates succeed) and support rollbacks. It does not aect a running system as no changes are activated until after the system is rebooted. As reboots are disruptive, the admin must decide if a reboot is more expensive than disturbing running services. If reboots are too expensive 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 snapshot of the root le system in the background, and then fetches updates from the release channels. After the new snapshot is completely updated, it is marked as active and will be the new default root le system after the next reboot of the system. When transactional-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 congurable. 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. 9.1 Limitations of technology preview As a technology preview, there are certain limitations in functionality. The following packages will not work with transactional-update : The nginx default index.html page may not be available tomcat-webapps and tomcat-admin-webapps phpMyAdmin sca-appliance-* 139 Limitations of technology preview SLES 15 SP3mpi-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: In general 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 will not work. Normal system operations only modifying conguration les in /etc will work. 140 Limitations of technology preview SLES 15 SP3For php7-fastcgi , you must manually create a symlink, /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 supported 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 transactional 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/sysconfig/ btrfsmaintenance must be changed from / to /.snapshots . For btrfs-scrub , the variable BTRFS_SCRUB_MOUNTPOINTS in /etc/sysconfig/ btrfsmaintenance must be changed from / to /.snapshots . 9.2 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. Note that changing the subvolume layout of the root partition, or putting sub-directories or subvolumes of the root partition on their own partitions (except /home , /var , /srv , and / opt ) is not supported, and will most likely break the system. 9.3 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: root # systemctl --now disable transactional-update.timer 141 Enabling transactional-update SLES 15 SP39.4 The transactional-update command The transactional-update command enables atomic installation or removal of updates; updates are applied only if all of them 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 current 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 nal snapshot includes everything you want reboot the system, and your nal 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 transactional-update to install a new package in a snapshot based on snapshot 13, and then running it again to install another package: root # transactional-update pkg install package_1 root # transactional-update --continue 13 pkg install package_2 The --continue [num] option calls snapper create --from , see Section 7.6.2, “Creating snapshots”. cleanup If the current root lesystem is identical to the active root lesystem (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 142 The transactional-update command SLES 15 SP3will be 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 : root # transactional-update cleanup pkg in/install Installs individual packages from the available channels using the zypper install command. This command can also be used to install Program Temporary Fix (PTF) RPM les. root # transactional-update pkg install package_name or root # transactional-update pkg install rpm1 rpm2 pkg rm/remove Removes individual packages from the active snapshot using the zypper remove command. This command can also be used to remove PTF RPM les. root # transactional-update pkg remove package_name pkg up/update Updates individual packages from the active snapshot using the zypper update command. Only packages that are part of the snapshot of the base le system can be updated. root # transactional-update pkg remove package_name up/update If there are new updates available, a new snapshot is created and zypper up/update updates the snapshot. root # 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. root # transactional-update dup 143 The transactional-update command SLES 15 SP3patch If there are new updates available, a new snapshot is created and zypper patch updates the snapshot. root # transactional-update patch rollback This sets the default subvolume. On systems with a read-write le system snapper rollback 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. root # transactional-update rollback snapshot_number grub.cfg This creates a new GRUB2 conguration. Sometimes it is necessary to adjust the boot conguration, 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 conguration will be overwritten with the default by the next transactional-update. root # transactional-update grub.cfg reboot This parameter triggers a reboot after the action is completed. root # transactional-update dup reboot --help This prints a help screen with options and subcommands. root # transactional-update --help 9.5 Troubleshooting If the upgrade fails, run supportconfig to collect log data. Provide the resulting les, including /var/log/transactional-update.log to SUSE Support. 144 Troubleshooting SLES 15 SP310 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- independent 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 dierent kinds of VNC sessions: One- time sessions that “live” as long as the VNC connection from the client is kept up, and persistent sessions that “live” until they are explicitly terminated. A VNC server can oer both kinds of sessions simultaneously on dierent ports, but an open session cannot be converted from one type to the other. 10.1 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. 10.1.1 Connecting using the vncviewer CLI To start your VNC viewer and initiate a session with the server, use the command: tux > vncviewer jupiter.example.com:1 Instead of the VNC display number you can also specify the port number with two colons: tux > 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 picked by the vncserver command on the target machine. See Section 10.4, “Configuring persistent VNC server sessions” for further info. 145 The vncviewer client SLES 15 SP310.1.2 Connecting using the vncviewer GUI By running vncviewer without specifying --listen or a host to connect to, it will show a window to ask for connection details. Enter the host into the VNC server eld like in Section 10.1.1, “Connecting using the vncviewer CLI” and click Connect. FIGURE 10.1: VNCVIEWER 10.1.3 Notification of unencrypted connections The VNC protocol supports dierent kinds of encrypted connections, not to be confused with password authentication. If a connection does not use TLS, the text “(Connection not encrypted!)” can be seen in the window title of the VNC viewer. 10.2 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. 10.2.1 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: root # zypper in remmina remmina-plugin-vnc 146 Connecting using the vncviewer GUI SLES 15 SP310.2.2 Main window Run Remmina by entering the remmina command. FIGURE 10.2: 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. 10.2.3 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. 147 Main window SLES 15 SP3FIGURE 10.3: REMOTE DESKTOP PREFERENCE Complete the elds that specify your newly added remote session prole. The most important are: Name Name of the prole. 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 specic settings. 148 Adding remote sessions SLES 15 SP3Tip: 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. Conrm with Save. Your new prole will be listed in the main window. 10.2.4 Starting remote sessions You can either start a previously saved session, or quick-start a remote session without saving the connection details. 10.2.4.1 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 10.4: QUICK-STARTING Select the communication protocol from the drop-down box, for example ''VNC'', then enter the VNC server DNS or IP address followed by a colon and a display number, and conrm with Enter . 10.2.4.2 Opening saved remote sessions To open a specic remote session, double-click it from the list of sessions. 10.2.4.3 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, such as toggle fullscreen mode, resize the window to match the display size of the session, send specic keystrokes to the session, take screenshots of the session, or set the image quality. 149 Starting remote sessions SLES 15 SP3FIGURE 10.5: REMMINA VIEWING REMOTE SESSION 10.2.5 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 10.2.3, “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 prole, optionally adjust relevant options, and conrm with Save. To Delete a saved remote session, right-click its name in Remmina''s main window and select Delete. Conrm with Yes in the next dialog. 10.2.6 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: tux > remmina -c profile_name.remmina 150 Editing, copying, and deleting saved sessions SLES 15 SP3Remmina''s prole les are stored in the .local/share/remmina/ directory in your home directory. To determine which prole 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 prole le in the window''s status line at the bottom. FIGURE 10.6: READING PATH TO THE PROFILE FILE While Remmina is not running, you can rename the prole le to a more reasonable le name, such as sle15.remmina . You can even copy the prole le to your custom directory and run it using the remmina -c command from there. 10.3 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 terminate the client connection to such a VNC session, all applications started within that session will be 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 10.1: 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. 151 Configuring one-time sessions on the VNC server SLES 15 SP34. If necessary, also check Open Port in Firewall (for example, when your network interface is congured to be in the External Zone). If you have more than one network interface, restrict opening the rewall ports to a specic interface via Firewall Details. 5. Conrm 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 eect. FIGURE 10.7: REMOTE ADMINISTRATION 10.3.1 Available configurations The default conguration 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. 152 Available configurations SLES 15 SP3Other congurations can be made available on dierent ports, see Section 10.3.3, “Configuring one- time VNC sessions”. VNC display numbers and X display numbers are independent in one-time sessions. A VNC display number is manually assigned to every conguration that the server supports (:1 in the example above). Whenever a VNC session is initiated with one of the congurations, it automatically gets a free X display number. By default, both the VNC client and server try to communicate securely via a self-signed SSL certicate, which is generated after installation. You can either use the default one, or replace it with your own. When using the self-signed certicate, you need to conrm its signature before the rst connection—both in the VNC viewer and the Web browser. 10.3.2 Initiating a one-time VNC session To connect to a one-time VNC session, a VNC viewer must be installed, see also Section 10.1, “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 10.3.3 Configuring one-time VNC sessions You can skip this section, if you do not need or want to modify the default conguration. One-time VNC sessions are started via the systemd socket xvnc.socket . By default it oers six conguration 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: tux > sudo systemctl enable xvnc.socket To start the socket immediately, run: tux > sudo systemctl start xvnc.socket The Xvnc server can be congured via the server_args option. For a list of options, see Xvnc --help . When adding custom congurations, make sure they are not using ports that are already in use by other congurations, other services, or existing persistent VNC sessions on the same host. 153 Initiating a one-time VNC session SLES 15 SP3Activate conguration changes by entering the following command: tux > sudo systemctl reload xvnc.socket Important: Firewall and VNC ports When activating Remote Administration as described in Procedure 10.1, “Enabling one-time VNC sessions”, the ports 5801 and 5901 are opened in the rewall. If the network interface serving the VNC sessions is protected by a rewall, you need to manually open the respective ports when activating additional ports for VNC sessions. See Book “Security and Hardening Guide”, Chapter 25 “Masquerading and firewalls” for instructions. 10.4 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 might 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 Section  10.1, “The vncviewer client” for more details. Alternatively use a JavaScript- capable Web browser to view the VNC session by entering the following URL: http:// jupiter.example.com:5801 There are two types of persistent VNC sessions: VNC session initiated using vncserver VNC session initiated using vncmanager 154 Configuring persistent VNC server sessions SLES 15 SP310.4.1 VNC session initiated using vncserver This type of persistent VNC session is initiated on the server. The session and all applications started in this session run regardless of client connections until the session is terminated. Access to persistent sessions is protected by two possible types of passwords: a regular password that grants full access or an optional view-only password that grants a non-interactive (view-only) access. A session can have multiple client connections of both kinds at once. PROCEDURE 10.2: STARTING A PERSISTENT VNC SESSION USING vncserver 1. Open a shell and make sure you are logged in as the user that should own the VNC session. 2. If the network interface serving the VNC sessions is protected by a rewall, you need to manually open the port used by your session in the rewall. If starting multiple sessions you may alternatively open a range of ports. See Book “Security and Hardening Guide”, Chapter 25 “Masquerading and firewalls” for details on how to congure the rewall. vncserver uses the ports 5901 for display :1 , 5902 for display :2 , and so on. For persistent sessions, the VNC display and the X display usually have the same number. 3. To start a session with a resolution of 1024x768 pixel and with a color depth of 16-bit, enter the following command: vncserver -alwaysshared -geometry 1024x768 -depth 16 The vncserver command picks an unused display number when none is given and prints its choice. See man 1 vncserver for more options. When running vncserver for the rst time, it asks for a password for full access to the session. If needed, you can also provide a password for view-only access to the session. The password(s) you are providing here are also used for future sessions started by the same user. They can be changed with the vncpasswd command. Important: Security considerations Make sure to use strong passwords of signicant length (eight or more characters). Do not share these passwords. 155 VNC session initiated using vncserver SLES 15 SP3To terminate the session shut down the desktop environment that runs inside the VNC session from the VNC viewer as you would shut it down if it was a regular local X session. If you prefer to manually terminate a session, open a shell on the VNC server and make sure you are logged in as the user that owns the VNC session you want to terminate. Run the following command to terminate the session that runs on display :1 : vncserver -kill :1 10.4.1.1 Configuring persistent VNC sessions Persistent VNC sessions can be congured by editing $HOME/.vnc/xstartup . By default this shell script starts the same GUI/window manager it was started from. In SUSE Linux Enterprise Server this will either be GNOME or IceWM. If you want to start your session with a window manager of your choice, set the variable WINDOWMANAGER : WINDOWMANAGER=gnome vncserver -geometry 1024x768 WINDOWMANAGER=icewm vncserver -geometry 1024x768 Note: One configuration for each user Persistent VNC sessions are congured in a single per-user conguration. Multiple sessions started by the same user will all use the same start-up and password les. 10.4.2 VNC session initiated using vncmanager PROCEDURE 10.3: 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 congured to be in the External Zone). If you have more than one network interface, restrict opening the rewall ports to a specic interface via Firewall Details. 5. Conrm your settings with Next. 156 VNC session initiated using vncmanager SLES 15 SP36. 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 eect. 10.4.2.1 Configuring persistent VNC sessions After you enable the VNC session management as described in Procedure 10.3, “Enabling persistent VNC sessions”, you can normally connect to the remote session with your favorite VNC viewer, such as vncviewer or Remmina. You will be presented with the login screen. After you log in, the ''VNC'' icon will appear in the system tray of your desktop environment. Click the icon to open the VNC Session window. If it does not appear or if your desktop environment does not support icons in the system tray, run vncmanager-controller manually. FIGURE 10.8: VNC SESSION SETTINGS 157 VNC session initiated using vncmanager SLES 15 SP3There are several settings that inuence the VNC session''s behavior: Non-persistent, private This is equivalent to a one-time session. It is not visible to others and will be terminated after you disconnect from it. Refer to Section 10.3, “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 Here you can specify the name of the persistent session so that it is easily identied when reconnecting. No password required The session will be 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. Allow 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. Conrm with OK. 158 VNC session initiated using vncmanager SLES 15 SP310.4.2.2 Joining persistent VNC sessions After you set up a persistent VNC session as described in Section 10.4.2.1, “Configuring persistent VNC sessions”, you can join it with your VNC viewer. After your VNC client connects to the server, you will be prompted to choose whether you want to create a new session, or join the existing one: FIGURE 10.9: JOINING A PERSISTENT VNC SESSION After you click the name of the existing session, you may be asked for login credentials, depending on the persistent session settings. 10.5 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. 159 Configuring encryption on the VNC server SLES 15 SP3Whether for a one-time or a persistent VNC session, security options are congured 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 verication 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 certicate. If you use a self-signed certicate, you will be asked to verify it on the rst connection. On subsequent connections you will be warned only if the certicate 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 certicate signed by a certicate authority matching the machine name, then you get full security (similar to typical HTTPS usage). Tip: Path to certificate and key With X509 based encryption, you need to specify the path to the X509 certicate and the key with -X509Cert and -X509Key options. 160 Configuring encryption on the VNC server SLES 15 SP3If you select multiple security types separated by comma, the rst one supported and allowed by both client and server will be used. That way you can congure 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 will warn you with the "Connection not encrypted!" message in that case). 161 Configuring encryption on the VNC server SLES 15 SP311 File copying with RSync Today, a typical user has several computers: home and workplace machines, a laptop, 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. 11.1 Conceptual overview For synchronizing a large amount of data over a slow network connection, Rsync oers a reliable method of transmitting only changes within les. This applies not only to text les but also binary les. To detect the dierences between les, Rsync subdivides the les into blocks and computes check sums over them. Detecting changes requires some 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. 11.2 Basic syntax Rsync is a command-line tool that has the following basic syntax: rsync [OPTION] SOURCE [SOURCE]... DEST 162 Conceptual overview SLES 15 SP3You can use Rsync on any local or remote machine, provided you have access and write permissions. 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 trailing slash after the directory denotes the content of the directory. No trailing slash denotes the directory itself. 11.3 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: tux > rsync -avz backup.tar.xz /var/backup/ The le backup.tar.xz is copied to /var/backup/ ; the absolute path will be /var/backup/ backup.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/ : tux > rsync -avz tux /var/backup/ 163 Copying files and directories locally SLES 15 SP3Find the copy in the absolute path /var/backup/tux/ . 11.4 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: tux > rsync -avz file.tar.xz tux@192.168.1.1: Depending on what you prefer, these commands are also possible and equivalent: tux > rsync -avz file.tar.xz 192.168.1.1:~ tux > rsync -avz file.tar.xz 192.168.1.1:/home/tux In all cases with standard conguration, you will be prompted to enter your passphrase of the remote user. This command will copy file.tar.xz to the home directory of user tux (usually /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: tux > rsync -avz tux 192.168.1.1:/var/backup/ Assuming you have write permissions on the host 192.168.1.1 , you will nd the copy in the absolute path /var/backup/tux . 11.5 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”. 164 Copying files and directories remotely SLES 15 SP3The following description explains how to create an Rsync server on jupiter with a backup target. This target can be used to store your backups. To create an Rsync server, do the following: PROCEDURE 11.1: SETTING UP AN RSYNC SERVER 1. On jupiter, create a directory to store all your backup les. In this example, we use / var/backup : root # mkdir /var/backup 2. Specify ownership. In this case, the directory is owned by user tux in group users : root # chown tux.users /var/backup 3. Congure the rsyncd daemon. We will separate the conguration le into a main le and some “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/ : root # mkdir /etc/rsyncd.d/ b. In the main conguration 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 conguration 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 [backup] 1 165 Configuring and using an rsync server SLES 15 SP3uid = 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 Species the user name or group name that is used when the le transfer takes place. 3 Denes the path to store your backups (from Step 1). 4 Species a comma-separated list of allowed users. In its simplest form, it contains the user names that are allowed to connect to this module. In our case, only user tux is allowed. 5 Species the path of a le that contains lines with user names and plain passwords. 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 : root # chmod 0600 /etc/rsyncd.secrets 4. Start and enable the rsyncd daemon with: root # systemctl enable rsyncd root # systemctl start rsyncd 5. Test the access to your Rsync server: tux > rsync jupiter:: You should see a response that looks like this: backup Our backup target 166 Configuring and using an rsync server SLES 15 SP3Otherwise, check your conguration le, rewall 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 if you want to debug your transfers. To list the content of your backup target, use the following command: tux > 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: tux > 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 conicts that arise must be resolved manually. 11.6 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:// www.seas.upenn.edu/~bcpierce/unison/ . Rear A disaster recovery framework, see the Administration Guide of the SUSE Linux Enterprise High Availability Extension, chapter Disaster Recovery with Rear (Relax-and-Recover) (https:// documentation.suse.com/sle-ha-15/html/SLE-HA-all/cha-ha-rear.html) . 167 More information SLES 15 SP3II Booting a Linux system 12 Introduction to the boot process 169 13 UEFI (Unified Extensible Firmware Interface) 177 14 The boot loader GRUB 2 186 15 The systemd daemon 20712 Introduction to the boot process Booting a Linux system involves dierent components and tasks. After a rmware and hardware initialization process, which depends on the machine''s architecture, the kernel is started by means of the boot loader GRUB 2. After this point, the boot process is completely controlled by the operating system and handled by systemd . systemd provides a set of “targets” that boot congurations for everyday usage, maintenance or emergencies. 12.1 Terminology This chapter uses terms that can be interpreted ambiguously. To understand how they are used here, read the denitions below: init Two dierent 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. Once 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 Enterprise 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 . 169 Terminology SLES 15 SP312.2 The Linux boot process The Linux boot process consists of several stages, each represented by a dierent component: 1. Section 12.2.1, “The initialization and boot loader phase” 2. Section 12.2.2, “The kernel phase” 3. Section 12.2.3, “The init on initramfs phase” 4. Section 12.2.4, “The systemd phase” 12.2.1 The initialization and boot loader phase During the initialization phase the machine''s hardware is set up and the devices are prepared. This process diers signicantly between 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 14, The boot loader GRUB 2. 12.2.1.1 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. Once it has access to this partition, GRUB 2 loads the kernel and the initramfs image into memory and hands control over to the kernel. 170 The Linux boot process SLES 15 SP3When 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 congure 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. This is completely independent of local hard disks. 12.2.1.2 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 various 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 conguration from /boot/grub2/grub.cfg and loads the nal kernel and initramfs from /boot . The new kernel now gets loaded via Kexec. 12.2.2 The kernel phase When the boot loader has passed on system control, the boot process is the same on all architectures. The boot loader loads both the kernel and an initial RAM-based le system ( initramfs ) into memory and the kernel takes over. 171 The kernel phase SLES 15 SP3After 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 . 12.2.2.1 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 specic hardware requirements other than sucient 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 . 12.2.2.1.1 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 will inform you about this by showing the output of the command that generates the initramfs . However, there are some occasions when you need to regenerate an initramfs manually: Adding drivers because of hardware changes Moving system directories to a RAID or LVM Adding disks to an LVM group or Btrfs RAID containing the root file system Changing kernel variables 172 The kernel phase SLES 15 SP3Adding drivers because of hardware changes If you need to change hardware (for example, hard disks), and this hardware requires dierent drivers to be in the kernel at boot time, you must update the initramfs le. Open or create /etc/dracut.conf.d/10-DRIVER.conf and add the following line (mind the leading whitespace): 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 12.1, “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 12.1, “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 containing the root le system, you need to create an initramfs that contains support for the enlarged volume. Follow the instructions at Procedure 12.1, “Generate an initramfs”. Proceed with Procedure 12.1, “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 12.1, “Generate an initramfs”. PROCEDURE 12.1: GENERATE AN INITRAMFS Note that all commands in the following procedure need to be executed as user root . 1. Generate a new initramfs le by running 173 The kernel phase SLES 15 SP3dracut MY_INITRAMFS Replace MY_INITRAMFS with a le name of your choice. The new initramfs will be created as /boot/MY_INITRAMFS . Alternatively, run dracut -f . This will overwrite the currently used, existing le. 2. (Skip this step if you ran dracut -f in the previous step.) Create a link to the initramfs le you created in the previous step: (cd /boot && ln -sf MY_INITRAMFS initrd) 3. On the IBM Z architecture, additionally run grub2-install . 12.2.3 The init on initramfs phase The temporary root le system mounted by the kernel from the initramfs contains the executable systemd (which is called init on initramfs in the following, also see Section 12.1, “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 conguration, init on initramfs is responsible for the following tasks. Loading kernel modules Depending on your hardware conguration, special drivers may be needed to access the hardware components of your computer (the most important component being your hard disk). To access the nal root le system, the kernel needs to load the proper le system drivers. Providing 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 congured 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. 174 The init on initramfs phase SLES 15 SP3Managing the network configuration If you congured 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 conguration 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 automatically 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. 12.2.3.1 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 dier from those mentioned above. Note that the installation system also does not start systemd from initramfs—these tasks are performed by linuxrc . Finding 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  12.2.2.1, “The initramfs file”, the boot process starts with a minimum set of drivers that can be used with most hardware congurations. On AArch64, POWER, and AMD64/Intel  64 machines, linuxrc starts an initial hardware scanning 175 The init on initramfs phase SLES 15 SP3process that determines the set of drivers suitable for your hardware conguration. On IBM Z, a list of drivers and their parameters needs to be provided, for example via linuxrc or a parmle. 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 15.6.4, “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guration. 12.2.4 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 15, The systemd daemon for details. 176 The systemd phase SLES 15 SP313 UEFI (Unified Extensible Firmware Interface) UEFI (Unied 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 oers 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 oers 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 http://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 some features are implemented in SUSE Linux Enterprise Server. 13.1 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 Platform Key (PK) into the rmware, representing the root of trust. The trust relationship with operating 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, some driver located in the ash memory of some PCI Express card or on disk, or be it an update of the rmware itself. 177 Secure boot SLES 15 SP3To 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 certicates, as long as they are signed with the private part of the PK. 13.1.1 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 13.1: 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 installation, it will try to create a GPT partition. UEFI expects to nd the EFI programs on a FAT-formatted EFI System Partition (ESP). 178 Implementation on SUSE Linux Enterprise Server SLES 15 SP3Supporting 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 endorse a SUSE key, which SUSE then signs the boot loader with. The other way is to go through Microsoft’s Windows Logo Certication program to have the boot loader certied and have Microsoft 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 13.2: 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 simplies the certication and signing step considerably. 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. SUSE provides this functionality since SLE11 SP3 on fresh installations with UEFI Secure Boot enabled. 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 congure UEFI. 179 Implementation on SUSE Linux Enterprise Server SLES 15 SP3UEFI oers two types of variables to fulll 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. The various UEFI key lists are of the rst type, as this allows online updating, adding, and blacklisting of keys, drivers, and rmware ngerprints. 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 certicate 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. 13.1.2 MOK (Machine Owner Key) To replace specic kernels, drivers, or other components that are part of the boot process, you have 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 bootloader 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. 180 MOK (Machine Owner Key) SLES 15 SP3Enrolling a key from disk is usually 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. 13.1.3 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 certicate and make that certicate known to the rmware or MOK. 1. Create a custom X.509 key and certicate 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 certicates, see https://en.opensuse.org/ openSUSE:UEFI_Image_File_Sign_Tools#Create_Your_Own_Certificate . 2. Package the key and the certicate as a PKCS#12 structure: tux > openssl pkcs12 -export -inkey key.asc -in cert.pem \ -name kernel_cert -out cert.p12 3. Generate an NSS database for use with pesign : tux > certutil -d . -N 4. Import the key and the certicate contained in PKCS#12 into the NSS database: tux > pk12util -d . -i cert.p12 5. “Bless” the kernel with the new signature using pesign : tux > pesign -n . -c kernel_cert -i arch/x86/boot/bzImage \ -o vmlinuz.signed -s 6. List the signatures on the kernel image: tux > pesign -n . -S -i vmlinuz.signed 181 Booting a custom kernel SLES 15 SP3At that point, you can install the kernel in /boot as usual. Because the kernel now has a custom signature the certicate used for signing needs to be imported into the UEFI rmware or MOK. 7. Convert the certicate to the DER format for import into the rmware or MOK: tux > openssl x509 -in cert.pem -outform der -out cert.der 8. Copy the certicate to the ESP for easier access: tux > sudo cp cert.der /boot/efi/ 9. Use mokutil to launch the MOK list automatically. • a. Import the certicate to MOK: tux > mokutil --root-pw --import cert.der The --root-pw option enables usage of the root user directly. b. Check the list of certicates that are prepared to be enrolled: tux > mokutil --list-new c. Reboot the system; shim should launch MokManager. You need to enter the root password to conrm the import of the certicate to the MOK list. d. Check if the newly imported key was enrolled: tux > mokutil --list-enrolled • a. Alternatively, this is the procedure if you want 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 . 182 Booting a custom kernel SLES 15 SP3f. Follow the instructions to enroll the key. Normally this should be pressing '' 0 '' and then '' y '' to conrm. Alternatively, the rmware menu may provide ways to add a new key to the Signature Database. 13.1.4 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 dierent 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 specic 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 . 183 Using non-inbox drivers SLES 15 SP313.1.5 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 videomode support, the kernel can retrieve video mode from UEFI to congure KMS mode with the same parameters. UEFI booting from USB devices is supported. When booting in Secure Boot mode, the following limitations apply: To ensure that Secure Boot cannot be easily circumvented, some kernel features are disabled when running under Secure Boot. Boot loader, kernel, and kernel modules must be signed. Kexec and Kdump are disabled. 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 eect on the kernel. 184 Features and limitations SLES 15 SP313.2 More information https://www.uefi.org —UEFI home page where you can nd the current UEFI specications. 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. 185 More information SLES 15 SP314 The boot loader GRUB 2 This chapter describes how to congure 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 conguring the most important settings. The boot procedure as a whole is outlined in Chapter 12, Introduction to the boot process. For details on Secure Boot support for UEFI machines, see Chapter 13, UEFI (Unified Extensible Firmware Interface). 14.1 Main differences between GRUB legacy and GRUB 2 The conguration is stored in dierent 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 systems, such as Windows. Includes a minimal Bash-like console. 14.2 Configuration file structure The conguration of GRUB 2 is based on the following les: /boot/grub2/grub.cfg This le contains the conguration 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 . 186 Main differences between GRUB legacy and GRUB 2 SLES 15 SP3/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 will also be parsed when using grub-once . /etc/default/grub This le controls the user settings of GRUB 2 and usually includes additional environmental 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 conguration le /boot/grub/grub.cfg . /etc/sysconfig/bootloader This conguration le holds some 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 conguration les contain architecture-specic options. GRUB 2 can be controlled in various ways. Boot entries from an existing conguration can be selected from the graphical menu (splash screen). The conguration is loaded from the le /boot/grub2/grub.cfg which is compiled from other conguration les (see below). All GRUB 2 conguration les are considered system les, and you need root privileges to edit them. Note: Activating configuration changes After having manually edited GRUB  2 conguration les, you need to run grub2- mkconfig -o /boot/grub2/grub.cfg to activate the changes. However, this is not necessary when changing the conguration with YaST, because YaST will automatically run this command. 14.2.1 The file /boot/grub2/grub.cfg The graphical splash screen with the boot menu is based on the GRUB 2 conguration le / boot/grub2/grub.cfg , which contains information about all partitions or operating systems that can be booted by the menu. 187 The file /boot/grub2/grub.cfg SLES 15 SP3Every 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 conguration 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 conguration as described in Section 14.3, “Configuring the boot loader with YaST”. 14.2.2 The file /etc/default/grub More general options of GRUB 2 belong here, 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: tux > grep "export GRUB_DEFAULT" -A50 /usr/sbin/grub2-mkconfig | grep GRUB_ In addition to already dened variables, the user may introduce their own variables, and use them later in the scripts found in the /etc/grub.d directory. After having edited /etc/default/grub , update the main conguration le with grub2- mkconfig -o /boot/grub2/grub.cfg . Note: Scope All options set in this le are general options that aect all boot entries. Specic options for Xen kernels or the Xen hypervisor can be set via the GRUB_*_XEN_* conguration options. See below for details. 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”. GRUB_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 “Example boot menu entry”. 188 The file /etc/default/grub SLES 15 SP3GRUB_DEFAULT=saved boots the entry specied by the grub2-once or grub2-set- default commands. While grub2-reboot sets the default boot entry for the next reboot only, grub2-set-default sets the default boot entry until changed. grub2-editenv list lists the next boot entry. GRUB_HIDDEN_TIMEOUT Waits the specied 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 specied, 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 identied by GRUB 2. GRUB_HIDDEN_TIMEOUT_QUIET If false is specied, 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 will cause 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 mode. 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 will completely replace the GRUB_CMDLINE_LINUX parameters for all Xen boot entries. GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT Same as GRUB_CMDLINE_LINUX_XEN_REPLACE but it will only replace parameters of GRUB_CMDLINE_LINUX_DEFAULT . GRUB_CMDLINE_XEN 189 The file /etc/default/grub SLES 15 SP3This entry species the kernel parameters for the Xen guest kernel only—the operation principle is the same as for GRUB_CMDLINE_LINUX . GRUB_CMDLINE_XEN_DEFAULT Same as GRUB_CMDLINE_XEN—the operation principle is the same as for GRUB_CMDLINE_LINUX_DEFAULT . GRUB_TERMINAL Enables and species 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. Note that you can only use modes supported by your graphics card (VBE). The default is ‘auto’, which tries to select a preferred resolution. You can display the screen resolutions available to GRUB 2 by typing videoinfo 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 sux. If necessary, the image will be scaled to t the screen. GRUB_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 7.3, “System rollback by booting from snapshots”. For a complete list of options, see the GNU GRUB manual (http://www.gnu.org/software/grub/ manual/grub.html#Simple-configuration) . 190 The file /etc/default/grub SLES 15 SP314.2.3 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 alphabetic 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. If you want 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 will be preserved. A list of the most important scripts follows: 00_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 Identies 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 191 Scripts in /etc/grub.d SLES 15 SP3This 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 specic 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 will be automatically included into /boot/grub2/grub.cfg just after 40_custom at boot time. 14.2.4 Mapping between BIOS drives and Linux devices In GRUB Legacy, the device.map conguration 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 conguration. 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 usually sucient, particularly in the case of single-disk systems. However, 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 mapping to make DISK 3 the boot disk. Note that GRUB 2 partition numbers start with 1 and not with 0 as in GRUB Legacy. (hd1) /dev/disk-by-id/DISK3 ID (hd2) /dev/disk-by-id/DISK1 ID (hd3) /dev/disk-by-id/DISK2 ID 192 Mapping between BIOS drives and Linux devices SLES 15 SP314.2.5 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 conguration. It can also be used to test new settings without altering the system conguration. 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 14.1: GRUB 2 BOOT EDITOR Now you have two options: a. Add space-separated parameters to the end of the line starting with linux or linuxefi 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. 193 Editing menu entries during the boot procedure SLES 15 SP3Important: Keyboard layout during the boot procedure The US keyboard layout is the only one available when booting. See Book “Deployment Guide”, Chapter  12 “Troubleshooting”, Section  12.3 “Booting from installation media fails”, US keyboard 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 will be permanently saved in the installed system. Note: Editing GRUB 2 menu entries on IBM Z Cursor movement and editing commands on IBM Z dier—see Section 14.4, “Differences in terminal usage on IBM Z” for details. 14.2.6 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. Important: Booting requires 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 Password ). 1. Encrypt the password using grub2-mkpasswd-pbkdf2: tux > sudo grub2-mkpasswd-pbkdf2 Password: **** 194 Setting a boot password SLES 15 SP3Reenter 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 conguration le, run: tux > sudo grub2-mkconfig -o /boot/grub2/grub.cfg After you reboot, you will be prompted 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 will boot the selected boot entry. For more information, see https://www.gnu.org/software/grub/manual/grub.html#Security . 14.3 Configuring the boot loader with YaST The easiest way to congure 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 conguration 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. 195 Configuring the boot loader with YaST SLES 15 SP3FIGURE 14.2: BOOT CODE OPTIONS 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. 196 Configuring the boot loader with YaST SLES 15 SP314.3.1 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 14.1: 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 dierent 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 14.3: CODE OPTIONS 197 Boot loader location and boot code options SLES 15 SP3The 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, operating system independent code. If you deactivate this option, the system may become unbootable. Enable Trusted Boot Support Starts TrustedGRUB2, which supports trusted computing functionality (Trusted Platform Module (TPM)). For more information refer to https://github.com/Sirrix-AG/ TrustedGRUB2 . 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. 14.3.2 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 14.2.4, “Mapping between BIOS drives and Linux devices”). 198 Adjusting the disk order SLES 15 SP3Warning: 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 14.2: 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. 14.3.3 Configuring advanced options Advanced boot parameters can be congured via the Boot Loader Options tab. 199 Configuring advanced options SLES 15 SP314.3.3.1 Boot Loader Options tab FIGURE 14.4: BOOT LOADER OPTIONS Boot Loader Time-Out Change the value of Time-Out in Seconds by typing in a new value and clicking the appropriate 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 manual conguration, see Section 14.2.6, “Setting a boot password”. If this option is activated, the boot password is required on every boot, which means the system does not boot automatically. However, if you prefer the behavior of GRUB 1, additionally enable Protect 200 Configuring advanced options SLES 15 SP3Entry Modication 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. 14.3.3.2 Kernel Parameters tab FIGURE 14.5: 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 mitigations 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. Auto + No SMT. Provides the full set of available security mitigations. Enables all mitigations required for your CPU model. In addition, it disables Simultaneous 201 Configuring advanced options SLES 15 SP3Multithreading (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, depending 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 manually set it via Console resolution. The graphical theme denition le can be specied 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 http://www.gnu.org/software/grub/ manual/grub.html#Serial-terminal 14.4 Differences in terminal usage on IBM Z On 3215 and 3270 terminals there are some dierences and limitations on how to move the cursor and how to issue editing commands within GRUB 2. 14.4.1 Limitations Interactivity Interactivity is strongly limited. Typing often does not result in visual feedback. To see where the cursor is, type an underscore ( _ ). Note: 3270 compared to 3215 The 3270 terminal is much better at displaying and refreshing screens than the 3215 terminal. 202 Differences in terminal usage on IBM Z SLES 15 SP3Cursor 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 14.4.2, “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. 14.4.2 Key combinations Common Substitutes: ^ – J engage (“Enter”) ^ – L abort, 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 ^ – F boot selected entry or enter submenu (same as ^ – J ) E edit selected entry 203 Key combinations SLES 15 SP3C 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 kill 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 ^ – E end of line ^ – B backward char ^ – F forward char 204 Key combinations SLES 15 SP3^ – H backspace ^ – D delete ^ – K kill line ^ – U discard line ^ – Y yank 14.5 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 14.1: USAGE OF GRUB2-MKCONFIG grub2-mkconfig -o /boot/grub2/grub.cfg Tip: Syntax check Running grub2-mkconfig without any parameters prints the conguration to STDOUT where it can be reviewed. Use grub2-script-check after /boot/grub2/ grub.cfg has been written to check its syntax. Important: 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: root # shim-install --config-file=/boot/grub2/grub.cfg grub2-mkrescue 205 Helpful GRUB 2 commands SLES 15 SP3Creates a bootable rescue image of your installed GRUB 2 conguration. EXAMPLE 14.2: USAGE OF GRUB2-MKRESCUE grub2-mkrescue -o save_path/name.iso iso grub2-script-check Checks the given le for syntax errors. EXAMPLE 14.3: 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 14.4: 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. 14.6 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. 206 More information SLES 15 SP315 The systemd daemon systemd is responsible for initializing the system, and 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 either started directly by systemd or by one of its child processes. systemd is a replacement for the System V init daemon and 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 http://www.freedesktop.org/wiki/Software/systemd/ . 15.1 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 on-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 15.1.1 Unit file A unit conguration 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. 207 The systemd concept SLES 15 SP3“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 .service 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 socket- 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. Usually auto-generated by the fstab generator; le ends with .mount Automount point. Information about a le system automount point; le ends with .automount Swap. Information about a swap device or le for memory paging; le ends with .swap Device. 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 http://www.freedesktop.org/software/ systemd/man/systemd.unit.html 15.2 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, since there is only one command to memorize for the majority of service-handling tasks: systemctl . It uses the “command plus subcommand” notation like git or zypper : systemctl GENERAL OPTIONS SUBCOMMAND SUBCOMMAND OPTIONS See man 1 systemctl for a complete manual. 208 Basic usage SLES 15 SP3Tip: 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 subcommand and then press →| . This feature is only available in the bash shell and requires the installation of the package bash-completion . 15.2.1 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) System 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: tux > sudo systemctl start MY_1ST_SERVICE MY_2ND_SERVICE To list all services available on the system: tux > sudo systemctl list-unit-files --type=service The following table lists the most important service management commands for systemd and System V init: TABLE 15.1: SERVICE MANAGEMENT COMMANDS Task systemd Command System V init Command Starting. start start Stopping. stop stop 209 Managing services in a running system SLES 15 SP3Task systemd Command System V init Command Restarting. Shuts down services and starts restart restart them afterward. If a service is not yet running it will be 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 reload reload conguration les without interrupting operation. Use case: Tell Apache to reload a modied httpd.conf conguration le. Note that not all services support reloading. Reloading or restarting. Reloads services reload-or-restart n/a if reloading is supported, otherwise restarts them. If a service is not yet running it will be started. Reloading or restarting conditionally. reload-or-try-restart n/a Reloads services if reloading is supported, otherwise restarts them if currently running. Does nothing for services that are not running. Getting detailed status information. Lists status status information about the status of services. The systemd command shows details such as description, executable, status, cgroup, and messages last issued by a service (see Section 15.6.9, “Debugging services”). The level of details displayed with the System V init diers from service to service. Getting short status information. Shows is-active status whether services are active or not. 210 Managing services in a running system SLES 15 SP315.2.2 Permanently enabling/disabling services The service management commands mentioned in the previous section let you manipulate services 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. 15.2.2.1 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 scheduled to be started with the next system start-up or runlevel/target change. To immediately start a service after having enabled it, explicitly run systemctl start MY_SERVICE or rc MY_SERVICE start . TABLE 15.2: COMMANDS FOR ENABLING AND DISABLING SERVICES Task systemd Command System V init Command 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 211 Permanently enabling/disabling services SLES 15 SP3Task systemd Command System V init Command command rst disables and then enables a service. Useful 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 completely disable 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. 15.3 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. 15.3.1 Targets compared to runlevels With System V init the system was booted into a so-called “Runlevel”. A runlevel denes 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 specic purposes. For example, the targets local-fs.target and swap.target mount local le systems and swap spaces. 212 System start and target management SLES 15 SP3The 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 oers great exibility. The following list shows the most important systemd target units. For a full list refer to man 7 systemd.special . SELECTED systemd TARGET UNITS default.target The target that is booted by default. Not a “real” target, but rather a symbolic link to another target like graphic.target . Can be permanently changed via YaST (see Section  15.4, “Managing services with YaST”). To change it for a session, use the kernel parameter systemd.unit=MY_TARGET.target at the boot prompt. emergency.target Starts an emergency 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 system without network. To remain compatible with the System V init runlevel system, systemd provides special targets named runlevelX.target mapping the corresponding runlevels numbered X . If you want to know the current target, use the command: systemctl get-default 213 Targets compared to runlevels SLES 15 SP3TABLE 15.3: SYSTEM V RUNLEVELS AND systemd TARGET UNITS System V systemd target Purpose runlevel 0 runlevel0.target , System shutdown halt.target , poweroff.target 1, S runlevel1.target , Single-user mode rescue.target , 2 runlevel2.target , multi- Local multiuser without remote user.target , network 3 runlevel3.target , multi- Full multiuser with network user.target , 4 runlevel4.target Unused/User-dened 5 runlevel5.target , Full multiuser with network and graphical.target , display manager 6 runlevel6.target , System reboot reboot.target , Important: systemd ignores /etc/inittab The runlevels in a System V init system are congured in /etc/inittab . systemd does not use this conguration. Refer to Section 15.5.4, “Creating custom targets” for instructions on how to create your own bootable target. 214 Targets compared to runlevels SLES 15 SP315.3.1.1 Commands to change targets Use the following commands to operate with target units: Task systemd Command System V init Command Change the systemctl isolate MY_TARGET .target telinit X current target/ runlevel Change to the systemctl default n/a default target/ 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 runlevel currently active targets. persistently Use the Services Manager or run the Use the Services Manager change the following command: or change the line default runlevel ln -sf /usr/lib/systemd/system/ id: X :initdefault: MY_TARGET .target /etc/systemd/system/ in /etc/inittab default.target Change the Enter the following option at the boot Enter the desired runlevel default runlevel prompt number at the boot for the current systemd.unit= MY_TARGET .target prompt. boot process Show a target''s/ systemctl show -p "Requires" n/a runlevel''s MY_TARGET .target dependencies systemctl show -p "Wants" MY_TARGET .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). 215 Targets compared to runlevels SLES 15 SP315.3.2 Debugging system start-up systemd oers 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. 15.3.2.1 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 specic service, use systemctl status MY_SERVICE . EXAMPLE 15.1: LIST ACTIVE SERVICES root # 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 15.2: LIST FAILED SERVICES root # systemctl --failed UNIT LOAD ACTIVE SUB JOB DESCRIPTION apache2.service loaded failed failed apache NetworkManager.service loaded failed failed Network Manager 216 Debugging system start-up SLES 15 SP3plymouth-start.service loaded failed failed Show Plymouth Boot Screen [...] 15.3.2.2 Debug start-up time To debug system start-up time, systemd oers 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. Listing the system start-up time root # systemd-analyze Startup finished in 2666ms (kernel) + 21961ms (userspace) = 24628ms Listing the services start-up time root # 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 root # systemd-analyze plot > jupiter.example.com-startup.svg 217 Debugging system start-up SLES 15 SP315.3.2.3 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 : tux > dmesg -T | less 218 Debugging system start-up SLES 15 SP315.3.3 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 dierent user via su or sudo in init scripts will result 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 terminated after the init script is nished. As a consequence, the service that has been started by the init script will also be 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.target . If it should only be started when booting into the display manager, user graphical.target here. 2. Start the daemon with systemctl start APPLICATION . 219 System V compatibility SLES 15 SP315.4 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 15.1: 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. 220 Managing services with YaST SLES 15 SP3To 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 you will see is identical to the one generated by the command systemctl - l status MY_SERVICE . 15.5 Customizing systemd The following sections contain some examples for systemd customization. Warning: Preventing your customization from being overwritten When customizing systemd , always use the directory /etc/systemd/ , never use / usr/lib/systemd/ . Otherwise your changes will be overwritten by the next update of systemd . 15.5.1 Customizing unit files The recommended way to customize unit les is to use the systemctl edit SERVICE command. This command starts the default text editor and creates a directory with the override.conf le in /etc/systemd/system/NAME.service.d/ . The command also ensures that the running systemd process is notied about the changes. Alternatively, you can open a copy of the original le for editing instead of a blank le by running systemctl edit --full SERVICE . When editing the le, make sure that you do not remove any of the existing sections. As an exercise, change how long the system waits for MariaDB to start. As root, run systemctl edit --full mariadb.service . The le opened will look similar to the following: [Unit] Description=MySQL server Wants=basic.target Conflicts=mariadb.target After=basic.target network.target 221 Customizing systemd SLES 15 SP3[Install] WantedBy=multi-user.target Alias=mysql.service [Service] Restart=on-abort Type=notify ExecStartPre=/usr/lib/mysql/mysql-systemd-helper install ExecStartPre=/usr/lib/mysql/mysql-systemd-helper upgrade ExecStart=/usr/lib/mysql/mysql-systemd-helper start # Configures the time to wait for start-up/stop TimeoutSec=300 # Prevent writes to /usr, /boot, and /etc ProtectSystem=full # Prevent accessing /home, /root and /run/user ProtectHome=true UMask=007 Adjust the TimeoutSec value and save the changes. To enable the changes, as root, run systemctl daemon-reload . For further information, refer to the man pages that can be evoked with the man 1 systemctl command. 15.5.2 Creating drop-in files For minor changes of a conguration le, use so-called drop-in les. Drop-in les let you extend the conguration of unit les without having to edit or override the unit les themselves. For example, to change a single value for the FOOBAR service located in /usr/lib/systemd/ system/FOOBAR.SERVICE , proceed as follows: 1. Create a directory called /etc/systemd/system/FOOBAR.service.d/ . Note the .d sux. The directory must otherwise be named like the service that you want to patch with the drop-in le. 2. In that directory, create a le your_modification.conf . Make sure it only contains the line with the value that you want to modify. 3. Save your changes to the le. 222 Creating drop-in files SLES 15 SP3Note: Avoiding name conflicts To avoid name conicts between your drop-in les and les shipped by SUSE, it is recommended to prex all drop-in lenames 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 20-25 is reserved for systemd shipped by SUSE 26-29 is reserved for SUSE packages (other than systemd) 50 is reserved for drop-in les created with systemctl set-property . Use a two-digit number above this range to ensure that none of the drop-in les shipped by SUSE will override your own drop-in les. You can use systemctl cat $UNIT to list and verify which les are taken into account in the units conguration. 15.5.3 Converting xinetd services to systemd Since the release of SUSE Linux Enterprise Server 15, the xinetd infrastructure has been removed. 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 ( *.socket ) 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: root # cat /etc/xinetd.d/example service example { socket_type = stream protocol = tcp port = 10085 wait = no user = user group = users groups = yes 223 Converting xinetd services to systemd SLES 15 SP3server = /usr/libexec/example/exampled server_args = -auth=bsdtcp exampledump disable = no } To convert it to systemd , you need the following two matching les: root # cat /usr/lib/systemd/system/example.socket [Socket] ListenStream=0.0.0.0:10085 Accept=false [Install] WantedBy=sockets.target root # 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 ). 15.5.4 Creating custom targets On System V init SUSE systems, runlevel 4 is unused to allow administrators to create their own runlevel conguration. 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 conguration le /usr/lib/systemd/system/graphical.target to /etc/ systemd/system/MY_TARGET.target and adjust it according to your needs. 2. The conguration 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 . 3. For each wanted service, create a symbolic link from /usr/lib/systemd/system into / etc/systemd/system/MY_TARGET.target.wants . 224 Creating custom targets SLES 15 SP34. When you have nished setting up the target, reload the systemd conguration to make the new target available: tux > sudo systemctl daemon-reload 15.6 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 http://0pointer.de/blog/projects . 15.6.1 Cleaning temporary directories systemd supports cleaning temporary directories regularly. The conguration from the previous system version is automatically migrated and active. tmpfiles.d—which is responsible for managing temporary les—reads its conguration from /etc/tmpfiles.d/ *.conf , /run/tmpfiles.d/*.conf , and /usr/lib/tmpfiles.d/*.conf les. Conguration placed in /etc/tmpfiles.d/*.conf overrides related congurations from the other two directories ( /usr/lib/tmpfiles.d/*.conf is where packages store their conguration les). The conguration 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 tmple timer: tux > 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. For more information on temporary les handling, see man 5 tmpfiles.d . 225 Advanced usage SLES 15 SP315.6.2 System log Section  15.6.9, “Debugging services” explains how to view log messages for a given service. However, 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 journalctl to display the complete log messages starting with the oldest entries. Refer to man 1 journalctl for options such as applying lters or changing the output format. 15.6.3 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 dened 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 tux > sudo systemctl snapshot MY_SNAPSHOT.snapshot Delete a snapshot tux > sudo systemctl delete MY_SNAPSHOT.snapshot View a snapshot tux > sudo systemctl show MY_SNAPSHOT.snapshot Activate a snapshot tux > sudo systemctl isolate MY_SNAPSHOT.snapshot 15.6.4 Loading kernel modules With systemd , kernel modules can automatically be loaded at boot time via a conguration le in /etc/modules-load.d . The le should be named MODULE .conf and have the following content: # load module MODULE at boot time MODULE 226 System log SLES 15 SP3In case a package installs a conguration le for loading a kernel module, the le gets installed to /usr/lib/modules-load.d . If two conguration 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. 15.6.5 Performing actions before loading a service With System V init actions that need to be performed before loading a service, needed to be specied in /etc/init.d/before.local . This procedure is no longer supported with systemd . 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 ): tux > sudo systemctl daemon-reload tux > sudo systemctl enable before Every time you modify the service le, you need to run: tux > sudo systemctl daemon-reload 227 Performing actions before loading a service SLES 15 SP315.6.6 Kernel control groups (cgroups) On a traditional System V init system it is not always possible to clearly assign a process to the service that spawned it. Some 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 dicult or even impossible. Additionally, a service may not terminate correctly, leaving some children alive. systemd solves this problem by placing each service into its own cgroup. cgroups are a kernel 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 allowed to “leave” its cgroup, this provides an eective 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 . The result will look like the following (shortened) example: EXAMPLE 15.3: LIST ALL PROCESSES BELONGING TO A SERVICE root # 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 │ └─1436 /usr/sbin/sshd -D [...] 228 Kernel control groups (cgroups) SLES 15 SP3See Book “System Analysis and Tuning Guide”, Chapter 9 “Kernel control groups” for more information about cgroups. 15.6.7 Terminating services (sending signals) As explained in Section 15.6.6, “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 dicult to terminate a service and all of its children. Child processes that have not been terminated will remain as zombie processes. systemd ''s concept of conning each service into a cgroup makes it possible to clearly 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. tux > sudo systemctl kill MY_SERVICE Sending SIGNAL to a service Use the -s option to specify the signal that should be sent. tux > sudo systemctl kill -s SIGNAL MY_SERVICE Selecting processes By default the kill command sends the signal to all processes of the specied 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 conguration by sending SIGHUP : tux > sudo systemctl kill -s SIGHUP --kill-who=main MY_SERVICE 15.6.8 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. 229 Terminating services (sending signals) SLES 15 SP3Terminating dbus or restarting it in the running system is similar to an attempt to terminate or restart pid 1. It will break systemd client/server communication and make 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 congured to skip the packages that require reboot. 15.6.9 Debugging services By default, systemd is not overly verbose. If a service was started successfully, no output will be produced. In case of a failure, a short error message will be displayed. However, systemctl status provides means to debug 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 dierent 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: root # systemctl start apache2 Job failed. See system journal and ''systemctl status'' for details. root # 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> Show last N service messages 230 Debugging services SLES 15 SP3The 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: tux > sudo systemctl status chronyd tux > 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 : tux > sudo systemctl --follow status chronyd Messages output format The --output=MODE parameter allows you to change the output format of service messages. 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. 15.7 systemd timer units Similar to cron, systemd timer units provide a mechanism for scheduling jobs on Linux. Although systemd timer units serve the same purpose as cron, they oer 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 troubleshoot them. systemd timer units are identied by the .timer le name extension. 231 systemd timer units SLES 15 SP315.7.1 systemd timer types Timer units can use monotonic and realtime timers. Similar to cronjobs, realtime timers are triggered on calendar events. Realtime timers are dened using the option OnCalendar . Monotonic timers are triggered at a specied time elapsed from a certain starting point. The latter could be a system boot or system unit activation event. There are several options for dening monotonic timers including OnBootSec , OnUnitActiveSec , and OnTypeSec . Monotonic timers are not persistent, and they are reset after each reboot. 15.7.2 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. 15.7.3 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 denition: [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 denition: [Unit] Description="Run foo shell script" [Timer] 232 systemd timer types SLES 15 SP3OnBootSec=5min OnUnitActiveSec=24h Unit=foo.service [Install] WantedBy=multi-user.target The [Timer] section in the example above species what service to trigger ( foo.service ) and when to trigger it. In this case, the option OnBootSec species 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 will trigger the service once a day). Finally the option WantedBy species that the timer should start when the system has reached the multi-user target. Instead of a monotonic timer, you can specify a realtime one using the option OnCalendar . The following realtime timer denition 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 will be triggered immediately after the timer activation if the timer missed the last start time (for example, due to the system being powered o). The option OnCalendar can also be used to dene specic 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 dierent 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. 233 Practical example SLES 15 SP3When 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: tux > sudo systemd-analyze verify /etc/systemd/system/foo.* If the command returns no output, the les have passed the verication 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 . 15.7.4 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. In addition to that, 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 . 15.8 More information For more information on systemd refer to the following online resources: Homepage http://www.freedesktop.org/wiki/Software/systemd 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 http://0pointer.de/blog/projects . 234 Managing systemd timers SLES 15 SP3III System 16 32-bit and 64-bit applications in a 64-bit system environment 236 17 journalctl: Query the systemd journal 238 18 update-alternatives: Managing multiple versions of commands and files 246 19 Basic networking 254 20 Printer operation 326 21 Graphical user interface 341 22 Accessing file systems with FUSE 358 23 Managing kernel modules 360 24 Dynamic kernel device management with udev 363 25 Special system features 375 26 Using NetworkManager 387 27 Power management 399 28 VM guest 405 29 Persistent memory 40616 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 oers 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 oers runtime support for 32-bit binaries. 16.1 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 Enterprise 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. Unfortunately, the names are identical for the 32-bit and 64-bit versions of these libraries. They must be dierentiated from each other in another way. 236 Runtime support SLES 15 SP3To 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 (File System Hierarchy Standard). 16.2 Kernel specifications The 64-bit kernels for AMD64/Intel 64, POWER and IBM Z oer 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 specically for 64-bit kernels. It is not possible to use 32-bit kernel modules with 64-bit kernels. Tip: Kernel-loadable modules Some 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. 237 Kernel specifications SLES 15 SP317 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- journald.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 system service errors. The systemd-journald service is on by default: tux > 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 [...] 17.1 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, the directory / var/log/journal/ must exist with correct ownership and permissions so the systemd-journald service can store its data. systemd will create the directory for you—and switch to persistent logging—if you do the following: 1. As root , open /etc/systemd/journald.conf for editing. root # vi /etc/systemd/journald.conf 2. Uncomment the line containing Storage= and change it to [...] [Journal] Storage=persistent #Compress=yes [...] 238 Making the journal persistent SLES 15 SP33. Save the le and restart systemd-journald: root # systemctl restart systemd-journald 17.2 journalctl: Useful switches This section introduces several common useful options to enhance the default journalctl behavior. All switches are described in the journalctl manual page, man 1 journalctl . Tip: Messages related to a specific executable To show all journal messages related to a specic executable, specify the full path to the executable: tux > 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 17.3.3, “Filtering based on fields”). -u Shows only messages for the specied systemd unit. This is equivalent to the eld match _SYSTEMD_UNIT=UNIT (see Section 17.3.3, “Filtering based on fields”). tux > 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. 239 journalctl: Useful switches SLES 15 SP317.3 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 ltered by specic switches and elds. 17.3.1 Filtering based on a boot number journalctl can lter messages based on a specic system boot. To list all available boots, run tux > 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 oset: 0 for the current boot, -1 for the previous one, -2 for the one prior to that, etc. The second column contains the boot ID followed by the limiting time stamps of the specic boot. Show all messages from the current boot: tux > sudo journalctl -b If you need to see journal messages from the previous boot, add an oset parameter. The following example outputs the previous boot messages: tux > sudo journalctl -b -1 Another way is to list boot messages based on the boot ID. For this purpose, use the _BOOT_ID eld: tux > sudo journalctl _BOOT_ID=156019a44a774a0bb0148a92df4af81b 17.3.2 Filtering based on time interval You can lter the output of journalctl by specifying the starting and/or ending date. The date specication 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", 240 Filtering the journal output SLES 15 SP3or "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 prexed with - or + , referring to times before or after the current time. Show only new messages since now, and update the output continuously: tux > sudo journalctl --since "now" -f Show all messages since last midnight till 3:20am: tux > sudo journalctl --since "today" --until "3:20" 17.3.3 Filtering based on fields You can lter the output of the journal by specic elds. The syntax of a eld to be matched is FIELD_NAME=MATCHED_VALUE , such as _SYSTEMD_UNIT=httpd.service . You can specify multiple matches in a single query to lter the output messages even more. See man 7 systemd.journal-fields for a list of default elds. Show messages produced by a specic process ID: tux > sudo journalctl _PID=1039 Show messages belonging to a specic user ID: # journalctl _UID=1000 Show messages from the kernel ring buer (the same as dmesg produces): tux > sudo journalctl _TRANSPORT=kernel Show messages from the service''s standard or error output: tux > sudo journalctl _TRANSPORT=stdout Show messages produced by a specied service only: tux > sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service If two dierent elds are specied, only entries that match both expressions at the same time are shown: tux > sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1488 If two matches refer to the same eld, all entries matching either expression are shown: tux > sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service _SYSTEMD_UNIT=dbus.service 241 Filtering based on fields SLES 15 SP3You 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: tux > sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1480 + _SYSTEMD_UNIT=dbus.service 17.4 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. 1. 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: tux > 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: tux > 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: tux > sudo systemctl start apache2 && systemctl status apache2 apache2.service - The Apache Webserver 242 Investigating systemd errors SLES 15 SP3Loaded: 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 [...] 17.5 Journald configuration The behavior of the systemd-journald service can be adjusted by modifying /etc/systemd/ journald.conf . This section introduces only basic option settings. For a complete le description, see man 5 journald.conf . Note that you need to restart the journal for the changes to take eect with tux > sudo systemctl restart systemd-journald 17.5.1 Changing the journal size limit If the journal log data is saved to a persistent location (see Section  17.1, “Making the journal persistent”), 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 17.5.2 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 243 Journald configuration SLES 15 SP317.5.3 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. tux > sudo rpm -q rsyslog rsyslog-7.4.8-2.16.x86_64 rsyslog service is enabled. tux > sudo systemctl is-enabled rsyslog enabled Forwarding to syslog is enabled in /etc/systemd/journald.conf . ForwardToSyslog=yes 17.6 Using YaST to filter the systemd journal For an easy way of ltering 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 17.1: YAST SYSTEMD JOURNAL 244 Forwarding the journal to syslog facility SLES 15 SP3The 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 lter the entries by date and time, unit, le, or priority, click Change lters and set the respective options. 17.7 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 . 245 Viewing logs in GNOME SLES 15 SP318 update-alternatives: Managing multiple versions of commands and files Often, there are several versions of the same tool installed on a system. To give administrators a choice and to make it possible to install and use dierent versions side by side, the alternatives system allows managing such versions consistently. 18.1 Overview On SUSE Linux Enterprise Server, some programs perform the same or similar tasks. For example, 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 administrator 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 current state of alternatives. Alternative The name of a specic 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 246 Overview SLES 15 SP3The link in a link group that determines how the other links in the group are congured. Slave 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 modied by the administrator through the update-alternatives command. The alternatives system provides the update-alternatives command to create, remove, maintain, and show information about symbolic links. While these symbolic links usually 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. Usually, 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 18.1: 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. 247 Overview SLES 15 SP318.2 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. 18.3 Getting an overview of alternatives To retrieve the names of all congured alternatives, use: tux > ls /var/lib/alternatives To get an overview of all congured alternatives and their values, use tux > 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 [...] 18.4 Viewing details on specific alternatives The easiest way to check the alternatives is to follow the symbolic links of your command. For example, if you want to know what the java command is referring to, use the following command: tux > 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 available for this command. To see the full alternatives (including slaves), use the --display option: tux > sudo update-alternatives --display java 248 Use cases SLES 15 SP3java - 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 [...] 18.5 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: tux > 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: tux > 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 dierent. After you have selected 1 , java shows the following version number: tux > 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) OpenJDK 64-Bit Server VM (build 25.171-b11, mixed mode) 249 Setting the default version of alternatives SLES 15 SP3Also, 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 18.4, “Viewing details on specific alternatives”). To check the master-slave relationships, use: tux > sudo update-alternatives --display java 18.6 Installing custom alternatives This section describes how to set up custom alternatives on a system. 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 conicts 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: tux > sudo chmod +x /usr/local/bin/foo-{2,3} 3. Run update-alternatives for both scripts: tux > sudo update-alternatives --install \ /usr/local/bin/foo 1 \ foo 2 \ /usr/local/bin/foo-2 3 \ 200 4 tux > sudo update-alternatives --install \ /usr/local/bin/foo 1 \ foo 2 \ /usr/local/bin/foo-3 3 \ 300 4 250 Installing custom alternatives SLES 15 SP3The options after --install have the following meanings: 1 The generic name. To avoid confusion, this is usually the script name without any version numbers. 2 The name of the master link. Must be the same. 3 The path to the original script(s) 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 signicant number increase to separate priorities. For example, a priority of 200 for foo-2 and 300 for foo-3 . 4. Check the master link: tux > 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: tux > 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: tux > 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-3 - priority 300 18.7 Defining dependent alternatives If you have alternatives, the script itself is not enough. Most commands are not completely stand- alone: They usually ship with additional les, such as extensions, congurations, or man pages. To create alternatives which are dependent on a master link, use slave alternatives. 251 Defining dependent alternatives SLES 15 SP3Let us assume we want to extend our example in Section 18.6, “Installing custom alternatives” and provide man pages and conguration les: Two man pages, foo-2.1.gz and foo-3.1.gz stored in the /usr/local/man/man1 directory. Two conguration 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 conguration les into /etc : tux > sudo cp foo-{2,3}.conf /etc 2. Copy the man pages into the /usr/local/man/man1 directory: tux > sudo cp foo-{2,3}.1.gz /usr/local/man/man1/ 3. Add the slave links to the main scripts with the --slave option: tux > 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 tux > 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 \ --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 200 252 Defining dependent alternatives SLES 15 SP3slave 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. 253 Defining dependent alternatives SLES 15 SP319 Basic networking Linux oers the necessary networking tools and features for integration into all types of network structures. Network access using a network card can be congured with YaST. Manual conguration is also possible. In this chapter only the fundamental mechanisms and the relevant network conguration 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 oer various 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 various 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 http:// www.ietf.org/rfc.html . 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 254 SLES 15 SP3Internet 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 participating in TCP/IP data transfer. In addition, it provides a special echo mode that can be viewed using the program ping. IGMP Internet Group Management Protocol: This protocol controls machine behavior when implementing IP multicast. As shown in Figure 19.1, “Simplified layer model for TCP/IP”, data exchange takes place in dierent 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 19.1: SIMPLIFIED LAYER MODEL FOR TCP/IP 255 SLES 15 SP3The diagram provides one or two examples for each layer. The layers are ordered according to abstraction levels. The lowest layer is very 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 mostly 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 approximately 64 KB. Packets are normally quite smaller, as the network hardware can be a limiting factor. The maximum size of a data packet on an Ethernet is about fteen hundred bytes. The size of a TCP/IP packet is limited to this amount when the data is sent over an 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 19.2, “TCP/ IP ethernet packet”. The proof sum is located at the end of the packet, not at the beginning. This simplies things for the network hardware. FIGURE 19.2: TCP/IP ETHERNET PACKET When an application sends data over the network, the data passes through each layer, all implemented in the Linux kernel except the physical layer. Each layer is responsible for 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 is responsible for 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 irrelevant for the data line which kind of data is transmitted, as long as packets are in the correct format. 256 SLES 15 SP319.1 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 19.2, “IPv6—the next generation Internet”. 19.1.1 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 19.1, “Writing IP addresses”. EXAMPLE 19.1: 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 inexible and was discontinued. Now, classless routing (CIDR, classless interdomain routing) is used. 19.1.2 Netmasks and routing Netmasks are used to dene 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 trac 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 dierences, 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 19.2, “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 19.2, “Linking IP addresses to the netmask” the rst net with 24 bits could also be written as 192.168.0.0/24 . 257 IP addresses and routing SLES 15 SP3EXAMPLE 19.2: 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 usually located in the same subnet and are directly accessible. Even when the subnet is physically divided 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 congured for the target network. In the most common case, there is only one gateway that handles all trac that is external. However, it is also possible to congure several gateways for dierent subnets. If a gateway has been congured, 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 19.2, “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 netmask 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 dened with IPv4. With IPv6 there is only one loopback address ( ::1 ). 258 Netmasks and routing SLES 15 SP3Because IP addresses must be unique all over the world, you cannot select random addresses. There are three address domains to use if you want 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 specied in RFC 1597 and listed in Table 19.1, “Private IP address domains”. TABLE 19.1: 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 19.2 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 explosive growth, with an increasing number of computers communicating via TCP/IP in the past fteen years. Since Tim Berners-Lee at CERN (http://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, quite a few IP addresses are lost —they cannot be used because of the way in which 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 259 IPv6—the next generation Internet SLES 15 SP3shortage. The problem with them lies in their conguration, which is a chore to set up and a burden to maintain. 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 conguration should be a thing of the past. The following sections tell more about the improvements and benets brought by IPv6 and about the transition from the old protocol to the new one. 19.2.1 Advantages The most important and most visible improvement brought by the newer 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 dierent from their predecessors with regard to their length. They also have a dierent internal structure that may contain more specic information about the systems and the networks to which they belong. More details about this are found in Section 19.2.2, “Address types and structure”. The following is a list of other advantages of the newer protocol: Autoconfiguration IPv6 makes the network “plug and play” capable, which means that a newly set up system integrates into the (local) network without any manual conguration. The new host uses its automatic conguration mechanism to derive its own address from the information made available by the neighboring routers, relying on a protocol called the neighbor discovery (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 advertisements 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 oered by mobile phone companies. When you take 260 Advantages SLES 15 SP3your 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 19.2.3, “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 completely separate, such that there is no interference between the two protocol versions. Custom tailored services through multicasting With IPv4, some 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 dierent 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 some predened groups to address all name servers (the all name servers multicast group), for example, or all routers (the all routers multicast group). 19.2.2 Address types and structure As mentioned, the current IP protocol has two major limitations: there is an increasing shortage of IP addresses, and conguring 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). When dealing with IPv6, it is useful to know about three dierent types of addresses: Unicast 261 Address types and structure SLES 15 SP3Addresses 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 oering 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 for some reason, 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 hexadecimal 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 19.3, “Sample IPv6 address”, where all three lines represent the same address. EXAMPLE 19.3: 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 dened function. The rst bytes form the prex 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 dened by indicating the length of the prex after a slash at the end of the address. An address, as shown in Example 19.4, “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 262 Address types and structure SLES 15 SP3the 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 19.4: IPV6 ADDRESS SPECIFYING THE PREFIX LENGTH fe80::10:1000:1a4/64 IPv6 knows about several predened types of prexes. Some are shown in Various IPv6 prefixes. VARIOUS 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 prex as well. 2 or 3 as the first digit Aggregatable global unicast addresses. As is the case with IPv4, an interface can be assigned 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 prex 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 eect, 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 prexes mentioned above) is used to route packets through the public Internet. It includes information about the company or institution that provides the Internet access. Site topology 263 Address types and structure SLES 15 SP3The second part contains routing information about the subnet to which to deliver the packet. Interface ID The third part identies 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 identier coded into the device by the hardware maker, the conguration procedure is substantially simplied. 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 PPP. On top of this basic structure, IPv6 distinguishes between ve dierent types of unicast addresses: :: (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 prex consisting of 96 zero bits. This type of compatibility address is used for tunneling (see Section 19.2.3, “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 species 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 prex ( fe80::/10 ) and the interface ID of the network card, with the middle part consisting of zero bytes. Addresses of this type are used during automatic conguration to communicate with other hosts belonging to the same subnet. 264 Address types and structure SLES 15 SP3site-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 dened by IPv4. They contain a special prex ( fec0::/10 ), the interface ID, and a 16 bit eld specifying the subnet ID. Again, the rest is lled with zero bytes. As a completely new feature introduced with IPv6, each network interface normally gets several IP addresses, with the advantage that several networks can be accessed through the same interface. One of these networks can be congured completely automatically using the MAC and a known prex 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 dierent networks, it needs at least two addresses. One of them, the home address, not only contains the interface ID but also an identier of the home network to which it normally belongs (and the corresponding prex). 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 the completely new features introduced with IPv6, such as stateless autoconguration 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. On the other hand, those packets destined to the care-of address are directly transferred to the mobile host without any special detours. 19.2.3 Coexistence of IPv4 and IPv6 The migration of all hosts connected to the Internet from IPv4 to IPv6 is a gradual process. Both protocols will coexist for some 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 how 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 oer tunneling and compatibility addresses (see Section 19.2.2, “Address types and structure”). 265 Coexistence of IPv4 and IPv6 SLES 15 SP3IPv6 hosts that are more or less 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 prex) and the IPv4 address of the remote host at the receiving end of the tunnel. A basic tunnel can be congured manually according to an agreement between the hosts'' administrators. This is also called static tunneling. However, the conguration and maintenance of static tunnels is often too labor-intensive to use them for daily communication needs. Therefore, IPv6 provides for three dierent 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 huge local area network (LAN). This makes it possible to determine the receiving end of the IPv4 tunnel automatically. However, this method does not scale very 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 specications for this method are laid down in RFC 2529. 6to4 With this method, IPv4 addresses are automatically generated from IPv6 addresses, enabling isolated IPv6 hosts to communicate over an IPv4 network. However, several problems 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. 19.2.4 Configuring IPv6 To congure IPv6, you normally do not need to make any changes on the individual workstations. 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. 266 Configuring IPv6 SLES 15 SP3Because of the autoconguration 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 prex and gateways should be implemented. The radvd program can be used to set up an IPv6 router. This program informs the workstations which prex to use for the IPv6 addresses and which routers. Alternatively, use zebra/quagga for automatic conguration of both addresses and routing. For information about how to set up various types of tunnels using the /etc/sysconfig/ network les, see the man page of ifcfg-tunnel ( man ifcfg-tunnel ). 19.2.5 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: http://www.ipv6.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. http://www.bieringer.de/linux/IPv6/ Here, nd the Linux IPv6-HOWTO and many links related to the topic. RFC 2460 The fundamental RFC about IPv6. IPv6 essentials A book describing all the important aspects of the topic is IPv6 Essentials by Silvia Hagen (ISBN 0-596-00125-8). 267 More information SLES 15 SP319.3 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 usually 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 hostname.domain . A full name, called a fully qualied 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 quite 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. In addition to that, 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 readily 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 http://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 conguration of name server access with SUSE® Linux Enterprise Server is described in Section 19.4.1.4, “Configuring host name and DNS”. Setting up your own name server is described in Chapter 32, The domain name system. The protocol whois is closely related to DNS. With this program, quickly nd out who is responsible for a given domain. 268 Name resolution SLES 15 SP3Note: MDNS and .local domain names The .local top level domain is treated as link-local domain by the resolver. DNS requests are send as multicast DNS requests instead of normal DNS requests. If you already use the .local domain in your name server conguration, you must switch this option o in /etc/host.conf . For more information, see the host.conf manual 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 . 19.4 Configuring a network connection with YaST There are many supported networking types on Linux. Most of them use dierent device names and the conguration les are spread over several locations in the le system. For a detailed overview of the aspects of manual network conguration, see Section 19.5, “Configuring a network connection manually”. All network interfaces with link up (with a network cable connected) are automatically congured. Additional hardware can be congured any time on the installed system. The following sections describe the network conguration 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 congure the interface. 19.4.1 Configuring the network card with YaST To congure 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 Options, Overview, Hostname/DNS and Routing. The 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 19.4.1.1, “Configuring global networking options”. 269 Configuring a network connection with YaST SLES 15 SP3The Overview tab contains information about installed network interfaces and congurations. Any properly detected network card is listed with its name. You can manually congure new cards, remove or change their conguration in this dialog. To manually congure a card that was not automatically detected, see Section 19.4.1.3, “Configuring an undetected network card”. To change the conguration of an already congured card, see Section 19.4.1.2, “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 19.4.1.4, “Configuring host name and DNS”. The Routing tab is used for the conguration of routing. See Section 19.4.1.5, “Configuring routing” for more information. FIGURE 19.3: CONFIGURING NETWORK SETTINGS 19.4.1.1 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. 270 Configuring the network card with YaST SLES 15 SP3Note: 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 NetworkManager 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 congure 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 congure options for the DHCP client. The DHCP Client Identier must be dierent 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 identier here. The Hostname to Send species 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 the Hostname to Send option eld to contain a specic string in the DHCP messages from clients. Leave AUTO to send the current host name (that is the one dened 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, deactivate Change Default Route via DHCP. 271 Configuring the network card with YaST SLES 15 SP319.4.1.2 Changing the configuration of a network card To change the conguration 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 conguration using the General, Address and Hardware tabs. 19.4.1.2.1 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 automatically congured to use automatic address setup via DHCP. Note: IBM Z and DHCP On IBM Z platforms, DHCP-based address conguration 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, congure the details in DHCP Client Options in the Global Options tab of the Network Settings dialog of the YaST network card conguration module. If you have a virtual host setup where dierent hosts communicate through the same interface, an DHCP Client Identier is necessary to distinguish them. DHCP is a good choice for client conguration but it is not ideal for server conguration. 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 conguration 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 prex length in format /64 . 272 Configuring the network card with YaST SLES 15 SP3Optionally, you can enter a fully qualied Hostname for this address, which will be written to the /etc/hosts conguration le. 4. Click Next. 5. To activate the conguration, click OK. Note: Interface activation and link detection During activation of a network interface, wicked checks for a carrier and only applies the IP conguration when a link has been detected. If you need to apply the conguration 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 conguration 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-* conguration les, refer to Section 19.5.2.5, “/ etc/sysconfig/network/ifcfg-*” and man 5 ifcfg . If you use the static address, the name servers and default gateway are not congured automatically. To congure name servers, proceed as described in Section 19.4.1.4, “Configuring host name and DNS”. To congure a gateway, proceed as described in Section 19.4.1.5, “Configuring routing”. 19.4.1.2.2 Configuring multiple addresses One network device can have multiple IP addresses. Note: Aliases are a compatibility feature These so-called aliases or labels, respectively, work with IPv4 only. With IPv6 they will be ignored. Using iproute2 network interfaces can have one or more addresses. Using YaST to set additional addresses for your network card, 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. 273 Configuring the network card with YaST SLES 15 SP32. 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 conguration, conrm the settings. 19.4.1.2.3 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 identied 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 conguration, conrm the settings. 19.4.1.2.4 Changing network card kernel driver For some network cards, several kernel drivers may be available. If the card is already congured, YaST allows you to select a kernel driver to be used from a list of available suitable drivers. 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. 274 Configuring the network card with YaST SLES 15 SP34. To activate the conguration, conrm the settings. 19.4.1.2.5 Activating the network device If you use the method with wicked , you can congure 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 interface is set when available. It is similar to the At Boot Time option, and only diers 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 conguration, conrm the settings. Tip: 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 conguring 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 conguration tab as described in Section  19.4.1.2.5, “Activating the network device” and choose On NFSroot in the Device Activation pane. 275 Configuring the network card with YaST SLES 15 SP319.4.1.2.6 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 eciency. 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 conguration, conrm the settings. 19.4.1.2.7 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 conguration. 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”. 19.4.1.2.8 Infiniband configuration for IP-over-InfiniBand (IPoIB) 1. In YaST select the InniBand device in System Network Settings and click Edit. 2. In the General tab, select one of the IP-over-InniBand (IPoIB) modes: connected (default) or datagram. 3. To activate the conguration, conrm the settings. For more information about InniBand, see /usr/src/linux/Documentation/infiniband/ ipoib.txt . 276 Configuring the network card with YaST SLES 15 SP319.4.1.2.9 Configuring the firewall Without having to perform the detailed rewall setup as described in Book “Security and Hardening Guide”, Chapter  25 “Masquerading and firewalls”, Section  25.4 “firewalld”, you can determine the basic rewall conguration 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 rewall is disabled and the rewall does not run. Only use this option if your machine is part of a greater network that is protected by an outer rewall. Automatically assign zone This option is available only if the rewall is enabled. The rewall is running and the interface is automatically assigned to a rewall zone. The zone which contains the keyword any or the external zone will be used for such an interface. Internal zone (unprotected) The rewall 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 rewall. It is also useful for the interfaces connected to the internal network, when the machine has more network interfaces. Demilitarized 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 internal network and from the Internet, but cannot access the internal network. External zone The rewall is running on this interface and fully protects it against other— presumably hostile—network trac. This is the default option. 4. To activate the conguration, conrm the settings. 277 Configuring the network card with YaST SLES 15 SP319.4.1.3 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 congure it manually. You can also congure special network device types, such as bridge, bond, TUN or TAP. To congure 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 Conguration Name. If the network card is a USB device, activate the respective check box and exit this dialog with Next. Otherwise, you can dene 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 information 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. Congure any needed options, such as the IP address, device activation or rewall zone for the interface in the General, Address, and Hardware tabs. For more information about the conguration options, see Section 19.4.1.2, “Changing the configuration of a network card”. 5. If you selected Wireless as the device type of the interface, congure the wireless connection in the next dialog. 6. To activate the new network conguration, conrm the settings. 19.4.1.4 Configuring host name and DNS If you did not change the network conguration 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. 278 Configuring the network card with YaST SLES 15 SP3To 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 dierent networks, because they may assign dierent 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 Conguration, select the way the DNS conguration (name servers, search list, the content of the /run/netconfig/resolv.conf le) is modied. If the Use Default Policy option is selected, the conguration is handled by the netconfig script which merges the data dened statically (with YaST or in the conguration les) with data obtained dynamically (from the DHCP client or NetworkManager). This default policy is usually sucient. 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 dening the merge policy should be specied. 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 dened in the /etc/sysconfig/network/config le: STATIC The static settings need to be merged together with the dynamic settings. STATIC_FALLBACK The static settings are used only when no dynamic conguration 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 specied by IP addresses, such as 192.168.1.116, not by host names. Names specied in the Domain Search tab are domain names used for resolving host names without a specied domain. If more than one Domain Search is used, separate domains with commas or white space. 5. To activate the conguration, conrm the settings. 279 Configuring the network card with YaST SLES 15 SP3It is also possible to edit the host name using YaST from the command line. The changes made by YaST take eect immediately (which is not the case when editing the /etc/HOSTNAME le manually). To change the host name, use the following command: root # yast dns edit hostname=HOSTNAME To change the name servers, use the following commands: root # yast dns edit nameserver1=192.168.1.116 root # yast dns edit nameserver2=192.168.1.117 root # yast dns edit nameserver3=192.168.1.118 19.4.1.5 Configuring routing To make your machine communicate with other machines and other networks, routing information must be given to make network trac take the correct path. If DHCP is used, this information 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 trac to the dened 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. Note: Route prioritization If more default routes are used, it is possible to specify the metric option to determine which route has a higher priority. To specify the metric option, enter - metric NUMBER in Options. The route with the highest metric is used as default. If the network device is disconnected, 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. 280 Configuring the network card with YaST SLES 15 SP35. To activate the conguration, conrm the settings. 19.4.2 IBM Z: configuring network devices SUSE Linux Enterprise Server for IBM Z supports several types of network interfaces. YaST can be used to congure all of them. 19.4.2.1 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 (example 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 conguration by clicking Next and OK. 19.4.2.2 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 conguration with Next and OK. 19.4.2.3 The ctc device To add a ctc (IBM parallel CTC Adapter) interface to the installed system, start the System Network Settings module in YaST. Select one of the devices marked IBM Parallel CTC Adapter to use as your read channel and click Congure. 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 conguration with Next and OK. 281 IBM Z: configuring network devices SLES 15 SP3Warning: 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. 19.4.2.4 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 Congure. Enter the needed port number, some additional options, your IP address and an appropriate netmask. Leave the network conguration with Next and OK. 19.4.2.5 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 conguration 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. 19.5 Configuring a network connection manually Manual conguration of the network software should be the last alternative. Using YaST is recommended. However, this background information about the network conguration can also assist your work with YaST. 19.5.1 The wicked network configuration The tool and library called wicked provides a new framework for network conguration. 282 Configuring a network connection manually SLES 15 SP3One of the challenges with traditional network interface management is that dierent layers of network management get jumbled together into one single script, or at most two dierent scripts. These scripts interact with each other in a way that is not well dened. This leads to unpredictable issues, obscure constraints and conventions, etc. Several layers of special hacks for a variety of dierent scenarios increase the maintenance burden. Address conguration 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 identication 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 dierent projects together is hopefully going to create a better solution overall. One approach is to use a client/server model. This allows wicked to dene standardized facilities for things like address conguration that are well integrated with the overall framework. For example, using a specic address conguration, the administrator may request that an interface should be congured via DHCP or IPv4 zeroconf. In this case, the address conguration 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 dene a dbus service that congures the network interface''s device layer—a VLAN, a bridge, a bonding, or a paravirtualized device. Common functionality, such as address conguration, is implemented by joint services that are layered on top of these device specic services without having to implement them specically. 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. Each network interface is represented via a child object of /org/opensuse/Network/ Interfaces . The name of the child object is given by its index. For example, the loopback interface, which usually gets index 1, is /org/opensuse/Network/Interfaces/1 , the rst Ethernet interface 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 283 The wicked network configuration SLES 15 SP3Generic 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 conguration services for DHCP, IPv4 zeroconf, etc. Beyond this, network interfaces may require or oer special conguration mechanisms. For an Ethernet device, for example, you should be able to control the link speed, ooading of checksumming, etc. To achieve this, Ethernet devices have a class of their own, called netif-ethernet , which is a subclass of netif . As a consequence, the dbus interfaces assigned to an Ethernet 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 innibands. 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 denes factory interfaces, such as org.opensuse.Network.VLAN.Factory . Such a factory interface oers 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. 19.5.1.1 wicked architecture and features The wicked service comprises several parts as depicted in Figure 19.4, “wicked architecture”. 284 The wicked network configuration SLES 15 SP3FIGURE 19.4: wicked ARCHITECTURE wicked currently supports the following: Conguration le back-ends to parse SUSE style /etc/sysconfig/network les. An internal conguration back-end to represent network interface conguration in XML. Bring up and shutdown of “normal” network interfaces such as Ethernet or InniBand, 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 congured interfaces when the device is available (interface hotplugging) and set up the IP conguration when a link (carrier) is detected. See Section  19.5.1.3, “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 . 19.5.1.2 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 285 The wicked network configuration SLES 15 SP3If 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 dierent 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 conguration sources as dened 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" 286 The wicked network configuration SLES 15 SP3Use the client utility to display interface information for all interfaces or the interface specied 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 conguration source specied, the wicked client checks its default sources of conguration dened 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. 19.5.1.3 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 dened by the current policy set. Nanny continues to set up even if ifup already exited because of specied timeout constraints. By default, the nanny daemon is active on the system. It is enabled in the /etc/wicked/ common.xml conguration le: ... 287 The wicked network configuration SLES 15 SP3true This setting causes ifup and ifreload to apply a policy with the eective conguration to the nanny daemon; then, nanny congures wickedd and thus ensures hotplug support. It waits in the background for events or changes (such as new devices or carrier on). 19.5.1.4 Bringing up multiple interfaces For bonds and bridges, it may make sense to dene the entire device topology in one le (ifcfg- bondX), and bring it up in one go. wicked then can bring up the whole conguration 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 19.5.1.5 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 . 19.5.1.6 Handling incremental changes With wicked , there is no need to actually take down an interface to recongure it (unless it is required by the kernel). For example, to add another IP address or route to a statically congured network interface, add the IP address to the interface denition, and do another 288 The wicked network configuration SLES 15 SP3“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 conguration mode (for example, when moving from a static conguration 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. 19.5.1.7 Wicked extensions: address configuration wicked is designed to be extensible with shell scripts. These extensions can be dened in the config.xml le. Currently, several classes of extensions are supported: link conguration: these are scripts responsible for setting up a device''s link layer according to the conguration provided by the client, and for tearing it down again. address conguration: these are scripts responsible for managing a device''s address conguration. Usually address conguration and DHCP are managed by wicked itself, but can be implemented by means of extensions. rewall extension: these scripts can apply rewall 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 rewall extension dened in etc/ server.xml : 289 The wicked network configuration SLES 15 SP3The extension is attached to the tag and denes commands to execute for the actions of this interface. Further, the declaration can dene and initialize environment variables passed to the actions. 19.5.1.8 Wicked extensions: configuration files You can extend the handling of conguration les with scripts as well. For example, DNS updates from leases are ultimately handled by the extensions/resolver script, with behavior congured in server.xml : When an update arrives in wickedd , the system updater routines parse the lease and call the appropriate commands ( backup , install , etc.) in the resolver script. This in turn congures the DNS settings using /sbin/netconfig , or by manually writing /run/netconfig/ resolv.conf as a fallback. 19.5.2 Configuration files This section provides an overview of the network conguration les and explains their purpose and the format used. 19.5.2.1 /etc/wicked/common.xml The /etc/wicked/common.xml le contains common denitions that should be used by all applications. It is sourced/included by the other conguration 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 . 290 Configuration files SLES 15 SP3In case you want to disable nanny by setting the to false , restart the wickedd.service and then run the following command to apply all congurations and policies: tux > sudo wicked ifup all Note: Configuration files The wickedd , wicked , or nanny programs try to read /etc/wicked/common.xml if their own conguration les do not exist. 19.5.2.2 /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 congures 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/server- local.xml , that gets included by /etc/wicked/server.xml . By using a separate le you avoid overwriting of your changes during maintenance updates. 19.5.2.3 /etc/wicked/client.xml The /etc/wicked/client.xml is used by the wicked command. The le species the location of a script used when discovering devices managed by ibft and congures locations of network interface congurations. 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. 19.5.2.4 /etc/wicked/nanny.xml The /etc/wicked/nanny.xml congures types of link layers. We recommend to add specic conguration into a separate le: /etc/wicked/nanny-local.xml to avoid losing the changes during maintenance updates. 291 Configuration files SLES 15 SP319.5.2.5 /etc/sysconfig/network/ifcfg-* These les contain the traditional congurations for network interfaces. Note: wicked and the ifcfg-* files wicked reads these les if you specify the compat: prex. According to the SUSE Linux Enterprise Server default conguration in /etc/wicked/client.xml , wicked tries these les before the XML conguration les in /etc/wicked/ifconfig . The --ifconfig switch is provided mostly for testing only. If specied, default conguration sources dened 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 conguring macvlan and macvtab interfaces, see the ifcfg-macvlan and ifcfg- macvtap 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  19.5.2.6, “/etc/sysconfig/network/config, /etc/ sysconfig/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-specic elements like qeth . 19.5.2.6 /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 conguration 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/sysconfig/ 292 Configuration files SLES 15 SP3network/ifcfg.template le lists variables that can be specied 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 congured properly. Starting withSUSE Linux Enterprise 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 congured 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 installation system: ifcfg=eth0=dhcp6,DHCLIENT6_MODE=managed 19.5.2.7 /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 specied 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 routing, dene an additional conguration le: /etc/sysconfig/network/ifroute-* . Replace the wild card ( * ) with the name of the interface. The entries in the routing conguration 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 qualied network or host name. The network should be written in CIDR notation (address with the associated routing prex-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. 293 Configuration files SLES 15 SP3The 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 prex-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 19.5: 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 19.5.2.8 /var/run/netconfig/resolv.conf The domain to which the host belongs is specied in /var/run/netconfig/resolv.conf (keyword search ). Up to six domains with a total of 256 characters can be specied with the search option. When resolving a name that is not fully qualied, an attempt is made to generate one by attaching the individual search entries. Up to three name servers can be 294 Configuration files SLES 15 SP3specied 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 19.6, “/var/run/netconfig/ resolv.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 dene static DNS conguration without using YaST, edit the appropriate variables manually in the /etc/ sysconfig/network/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 congured, for example bind or resolver 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 conguration using netcong, set NETCONFIG_DNS_POLICY='''' . For more information about netconfig , see the netconfig(8) man page ( man 8 netconfig ). EXAMPLE 19.6: /var/run/netconfig/resolv.conf # Our domain search example.com # # We use dns.example.com (192.168.1.116) as nameserver 295 Configuration files SLES 15 SP3nameserver 192.168.1.116 19.5.2.9 /sbin/netconfig netconfig is a modular tool to manage additional network conguration settings. It merges statically dened settings with settings provided by autoconguration mechanisms as DHCP or PPP according to a predened policy. The required changes are applied to the system by calling the netcong modules that are responsible for modifying a conguration 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 netcong. Only the netconfig update command is available for the user: modify The netconfig modify command modies the current interface and service specic dynamic settings and updates the network conguration. Netcong reads settings from standard input or from a le specied with the --lease-file FILENAME option and internally 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 interface is specied by the -i INTERFACE_NAME parameter. The service is specied by the -s SERVICE_NAME parameter. remove The netconfig remove command removes the dynamic settings provided by an editing action for the specied interface and service combination and updates the network conguration. The interface is specied by the -i INTERFACE_NAME parameter. The service is specied by the -s SERVICE_NAME parameter. update The netconfig update command updates the network conguration using current settings. This is useful when the policy or the static conguration has changed. Use the - m MODULE_TYPE parameter to update a specied service only ( dns , nis , or ntp ). The netcong policy and the static conguration settings are dened either manually or using YaST in the /etc/sysconfig/network/config le. The dynamic conguration settings provided by autoconguration tools such as DHCP or PPP are delivered directly by these tools with the netconfig modify and netconfig remove actions. When NetworkManager is enabled, netcong (in policy mode auto ) uses only NetworkManager settings, ignoring settings 296 Configuration files SLES 15 SP3from any other interfaces congured 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 . 19.5.2.10 /etc/hosts In this le, shown in Example 19.7, “/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 qualied 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 19.7: /etc/hosts 127.0.0.1 localhost 192.168.2.100 jupiter.example.com jupiter 192.168.2.101 venus.example.com venus 19.5.2.11 /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 19.8, “/etc/networks”. EXAMPLE 19.8: /etc/networks loopback 127.0.0.0 localnet 192.168.0.0 19.5.2.12 /etc/host.conf Name resolution—the translation of host and network names via the resolver library—is controlled 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 entered on a separate line. Comments are preceded by a # sign. Table 19.2, “Parameters for /etc/ host.conf” shows the parameters available. A sample /etc/host.conf is shown in Example 19.9, “/etc/host.conf”. 297 Configuration files SLES 15 SP3TABLE 19.2: PARAMETERS FOR /ETC/HOST.CONF order hosts, bind Species in which order the services are accessed for the name resolution. Available arguments are (separated by blank spaces or commas): hosts: searches the /etc/hosts le bind: accesses a name server nis: uses NIS multi on/o Denes if a host entered in /etc/hosts can have multiple IP addresses. nospoof on spoofalert on/o These parameters inuence the name server spoong but do not exert any inuence on the network conguration. trim domainname The specied domain name is separated from the host name after host name resolution (as long as the host name includes the domain name). This option is useful only if names from the local domain are in the /etc/ hosts le, but should still be recognized with the attached domain names. EXAMPLE 19.9: /etc/host.conf # We have named running order hosts bind # Allow multiple address multi on 19.5.2.13 /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. 298 Configuration files SLES 15 SP3The order for queries is dened in the le /etc/nsswitch.conf . A sample nsswitch.conf is shown in Example 19.10, “/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 32, The domain name system). EXAMPLE 19.10: /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  19.3, “Databases available via /etc/ nsswitch.conf”. The conguration options for NSS databases are listed in Table 19.4, “Configuration options for NSS “databases””. TABLE 19.3: 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. Only needed, if you use subnetting. group User groups used by getgrent . See also the man page for group . 299 Configuration files SLES 15 SP3hosts Host names and IP addresses, used by gethostbyname and similar functions. netgroup Valid host and user lists in the network for controlling access permissions; see the netgroup(5) man page. networks Network names and addresses, used by getnetent . 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 addresses, used by getrpcbyname and similar functions. services Network services, used by getservent . shadow Shadow passwords of users, used by getspnam ; see the shadow(5) man page. TABLE 19.4: 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 4 “Using NIS” dns can only be used as an extension for hosts and networks 300 Configuration files SLES 15 SP3compat can only be used as an extension for passwd , shadow and group 19.5.2.14 /etc/nscd.conf This le is used to congure 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 fteen seconds until a newly added local user is recognized. Reduce this waiting time by restarting nscd with: tux > sudo systemctl restart nscd 19.5.2.15 /etc/HOSTNAME /etc/HOSTNAME contains the fully qualied host name (FQHN). The fully qualied 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. 19.5.3 Testing the configuration Before you write your conguration to the conguration les, you can test it. To set up a test conguration, use the ip command. To test the connection, use the ping command. The command ip changes the network conguration directly without saving it in the conguration le. Unless you enter your conguration in the correct conguration les, the changed network conguration 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. 301 Testing the configuration SLES 15 SP319.5.3.1 Configuring a network interface with ip ip is a tool to show and congure 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: tux > sudo ip link set DEV_NAME For example, to deactivate device eth0, enter tux > sudo ip link set eth0 down To activate it again, use tux > sudo ip link set eth0 up 302 Testing the configuration SLES 15 SP3Tip: Disconnecting NIC device If you deactivate a device with tux > 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 connected switch is turned o, run tux > 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 tux > sudo ip link set DEV_NAME carrier on After activating a device, you can congure it. To set the IP address, use tux > 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 broadcast (option brd ), enter tux > sudo ip addr add 192.168.12.154/30 brd + dev eth0 To have a working connection, you must also congure the default gateway. To set a gateway for your system, enter tux > sudo ip route add default via gateway_ip_address To display all devices, use tux > sudo ip link ls To display the running interfaces only, use tux > sudo ip link ls up To print interface statistics for a device, enter tux > sudo ip -s link ls DEV_NAME 303 Testing the configuration SLES 15 SP3To view additional useful information, specically about virtual network devices, enter tux > sudo ip -d link ls DEV_NAME Moreover, to view network layer (IPv4, IPv6) addresses of your devices, enter tux > sudo ip addr In the output, you can nd information about MAC addresses of your devices. To show all routes, use tux > 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: tux > sudo ip addr help Find the ip manual in /usr/share/doc/packages/iproute2/ip-cref.pdf . 19.5.3.2 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 eect. 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 19.11, “Output of the command ping”, you can see an example of the ping output. The second-to-last line contains 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 19.11: OUTPUT OF THE COMMAND PING ping -c 3 example.com PING example.com (192.168.3.100) 56(84) bytes of data. 304 Testing the configuration SLES 15 SP364 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 specic 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 19.5.4 Unit files and start-up scripts Apart from the conguration 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 15, 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 settings provided by the system administrator. 305 Unit files and start-up scripts SLES 15 SP3For more information, see http://www.freedesktop.org/wiki/Software/systemd/ NetworkTarget/ . multi-user.target multi-user.target is the systemd target for a multiuser system with all required network 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 postx process. 19.6 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 rewalling. 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 disables several mechanisms, for example IPv6 does not accept an IPv6 RA (router advertisement) anymore, which also prevents the creation of a default route. 306 Basic router setup SLES 15 SP32. 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 lter (this feature does not currently exist for IPv6): net.ipv4.conf.all.rp_filter = 0 You can also lter with rewall 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 specic) 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 congure 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 prefered 1/2 h } } Congure the rewall to masquerade trac with NAT from the LAN into the WAN and to block inbound trac on the WAN interface: tux > sudo firewall-cmd --permanent --zone=external --change-interface=WAN_INTERFACE 307 Basic router setup SLES 15 SP3tux > sudo firewall-cmd --permanent --zone=external --add-masquerade tux > sudo firewall-cmd --permanent --zone=internal --change-interface=LAN_INTERFACE tux > sudo firewall-cmd --reload 19.7 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 conguration of the bonding device is done by means of bonding module options. The behavior is mainly aected by the mode of the bonding device. By default, this is active- backup which means that a dierent slave device will become active if the active slave 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 dierent interface becomes active. This setting is the default for SUSE Linux Enterprise Server. Provides fault tolerance. 2 (balance-xor) Trac is split between all available interfaces based on the following policy: [(source MAC address XOR''d with destination MAC address XOR packet type ID) modulo slave count] Requires support from the switch. Provides fault tolerance and load balancing. 3 (broadcast) All trac 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 congured for IEEE 802.3ad Dynamic link aggregation. Provides fault tolerance and load balancing. 5 (balance-tlb) 308 Setting up bonding devices SLES 15 SP3Adaptive transmit load balancing. Requires ethtool support in the interface drivers but not switch support. Provides fault tolerance and load balancing. 6 (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/Documentation/ networking/bonding.txt . Tip: Bonding and Xen Using bonding devices is only of interest for machines where you have multiple real network cards available. In most congurations, this means that you should use the bonding conguration 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 conict with the tlb/alb bonding conguration 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 congure 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. 309 Setting up bonding devices SLES 15 SP33. 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 Slaves 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. 310 Setting up bonding devices SLES 15 SP319.7.1 Hotplugging of bonding slaves In specic network environments (such as High Availability), there are cases when you need to replace a bonding slave interface with another one. The reason may be a constantly failing network device. The solution is to set up hotplugging of bonding slaves. The bond is congured 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 slaves are specied 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 slave interface is controlled by the bond master. STARTMODE=hotplug causes the slave 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 hwinfo --netcard ) instead of by MAC address. This allows replacement of defective hardware (a network card in the same slot but with a dierent MAC) and prevents confusion when the bond changes the MAC address of all its slaves. For example: SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", KERNELS=="0000:00:19.0", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0" 311 Hotplugging of bonding slaves SLES 15 SP3At boot time, the systemd network.service does not wait for the hotplug slaves, but for the bond to become ready, which requires at least one available slave. When one of the slave 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 slave, and calls ifup for it. The ifup call automatically joins it into the bond. 19.8 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 truncating”, 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 19.7, “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 dierence 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 dierent from the original bonding implementation which contains all of its functionality exclusively in the kernel. For a comparison refer to Table 19.5, “Feature comparison between bonding and team”. TABLE 19.5: 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) 312 Setting up team devices for Network Teaming SLES 15 SP3Feature Bonding Team TX load-balancing support no yes for LACP Ethtool link monitoring yes yes ARP link monitoring yes yes NS/NA (IPV6) link no yes monitoring RCU locking on TX/RX paths no yes port prio and stickiness no yes separate per-port link no yes monitoring setup multiple link monitoring limited yes setup VLAN support yes yes multiple device stacking yes yes Source: http://libteam.org/files/teamdev.pp.pdf Both implementations, bonding and Network Teaming, can be used in parallel. Network Teaming is an alternative to the existing bonding implementation. It does not replace bonding. Network Teaming can be used for dierent use cases. The two most important use cases are explained later and involve: Load balancing between dierent network devices. Failover from one network device to another in case one of the devices should fail. Currently, there is no YaST module to support creating a teaming device. You need to congure Network Teaming manually. The general procedure is shown below which can be applied for all your Network Teaming congurations: PROCEDURE 19.1: GENERAL PROCEDURE 1. Make sure you have all the necessary packages installed. Install the packages libteam- tools , libteamdctl0 , and python-libteam . 313 Setting up team devices for Network Teaming SLES 15 SP32. Create a conguration 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 conguration le contains several variables which are explained in the man pages (see man ifcfg and man ifcfg-team ). An example conguration can be found in your system in the le /etc/sysconfig/network/ifcfg.template . 3. Remove the conguration 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 conguration les with the necessary parameters for teaming. 4. Optionally, check if everything is included in Wicked''s conguration le: tux > sudo wicked show-config 5. Start the Network Teaming device team0 : tux > sudo wicked ifup all team0 In case you need additional debug information, use the option --debug all after the all subcommand. 6. Check the status of the Network Teaming device. This can be done by the following commands: Get the state of the teamd instance from Wicked: tux > sudo wicked ifstatus --verbose team0 Get the state of the entire instance: tux > sudo teamdctl team0 state Get the systemd state of the teamd instance: tux > sudo systemctl status teamd@team0 Each of them shows a slightly dierent view depending on your needs. 7. In case you need to change something in the ifcfg-team0 le afterward, reload its conguration with: tux > sudo wicked ifreload team0 314 Setting up team devices for Network Teaming SLES 15 SP3Do 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 19.2: REMOVING A TEAM DEVICE 1. Stop the Network Teaming device team0 : tux > sudo wicked ifdown team0 2. Rename the le /etc/sysconfig/network/ifcfg-team0 to /etc/sysconfig/ network/.ifcfg-team0 . Inserting a dot in front of the le name makes it “invisible” for wicked. If you really do not need the conguration anymore, you can also remove the le. 3. Reload the conguration: tux > sudo wicked ifreload all 19.8.1 Use case: load balancing with Network Teaming Load balancing is used to improve bandwidth. Use the following conguration le to create a Network Teaming device with load balancing capabilities. Proceed with Procedure 19.1, “General procedure” to set up the device. Check the output with teamdctl . EXAMPLE 19.12: 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" 6 315 Use case: load balancing with Network Teaming SLES 15 SP31 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 Species one or more devices which should be aggregated to create the Network Teaming device. 5 Denes a link watcher to monitor the state of subordinate devices. The default value ethtool 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 condence in the connection, use the arp_ping option. This sends pings to an arbitrary host (congured in the TEAM_LW_ARP_PING_TARGET_HOST variable). The Network Teaming device is considered to be up only if the replies are received. 6 Denes the delay in milliseconds between the link coming up (or down) and the runner being notied. 19.8.2 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 conguration le to create a Network Teaming device with failover capabilities. Proceed with Procedure 19.1, “General procedure” to set up the device. Check the output with teamdctl . EXAMPLE 19.13: 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" 4 316 Use case: failover with Network Teaming SLES 15 SP3TEAM_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 Species one or more devices which should be aggregated to create the Network Teaming device. 5 Denes a link watcher to monitor the state of subordinate devices. The default value ethtool 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 condence in the connection, use the arp_ping option. This sends pings to an arbitrary host (congured 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 Denes the delay in milliseconds between the link coming up (or down) and the runner being notied. 19.8.3 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 dierent 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 192.168.20.1 317 Use case: VLAN over team device SLES 15 SP3Proceed 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 19.8.1, “Use case: load balancing with Network Teaming” or Section 19.8.2, “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'' 1 Denes a xed IP address, specied in IPADDR . 2 Denes the IP address, here with its netmask. 3 Contains the real interface to use for the VLAN interface, here our team device ( team0 ). 4 Species a unique ID for the VLAN. Preferably, the le name and the VLAN_ID corresponds 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/network/ 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: root # wicked ifup vlan0 vlan1 6. Check the output of ifconfig : root # ifconfig -a [...] 318 Use case: VLAN over team device SLES 15 SP3vlan0 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) 19.9 Software-defined networking with Open vSwitch Software-dened networking (SDN) means separating the system that controls where trac is sent (the control plane) from the underlying system that forwards trac to the selected destination (the data plane, also called the forwarding plane). This means that the functions previously fullled by a single, usually inexible 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 exible and adapt quickly to changing network conditions. Open vSwitch is software that implements a distributed virtual multilayer switch that is compatible with the OpenFlow protocol. OpenFlow allows a controller application to modify the conguration 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 dierent switches. 19.9.1 Advantages of Open vSwitch Software-dened networking with Open vSwitch brings several advantages with it, especially when you used together with virtual machines: Networking states can be identied easily. Networks and their live state can be moved from one host to another. 319 Software-defined networking with Open vSwitch SLES 15 SP3Network 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 congured 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 hardware and can control hardware switches. 19.9.2 Installing Open vSwitch 1. Install Open vSwitch and supplementary packages: root # zypper install openvswitch openvswitch-switch If 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: root # systemctl enable openvswitch 3. Either restart the computer or use systemctl to start the Open vSwitch service immediately: root # systemctl start openvswitch 4. To check whether Open vSwitch was activated correctly, use: root # systemctl status openvswitch 19.9.3 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. 320 Installing Open vSwitch SLES 15 SP319.9.3.1 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 conguration and state of Open vSwitch. 19.9.3.2 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. ovsdb-tool Create, upgrade, compact, and query Open vSwitch databases. Do transactions on Open vSwitch databases. ovs-appctl Congure 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 diagnostics 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 conguration database. It can be used to query and modify the database. In eect, it shows the status of ovs-vswitchd and can be used to congure it. 321 Overview of Open vSwitch daemons and utilities SLES 15 SP319.9.4 Creating a bridge with Open vSwitch The following example conguration uses the Wicked network service that is used by default on SUSE Linux Enterprise Server. To learn more about Wicked, see Section 19.5, “Configuring a network connection manually”. When you have installed and started Open vSwitch, proceed as follows: 1. To congure 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 conguring the IP address. 3 Mark the conguration as an Open vSwitch bridge. 4 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 previous denition, 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: root # wicked ifup br0 When Wicked is done, it should output the name of the bridge and next to it the state up . 322 Creating a bridge with Open vSwitch SLES 15 SP319.9.5 Using Open vSwitch directly with KVM After having created the bridge as described in Section 19.9.4, “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 congured 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 congured in the next step. 2. Now add a conguration 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 323 Using Open vSwitch directly with KVM SLES 15 SP33. Finally, open the conguration for the device dened as the rst OVS_BRIDGE_PORT_DEVICE . 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: root # wicked ifreload br0 This will also trigger a reload of the newly dened bridge port devices. 5. To start a virtual machine, use, for example: root # 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. For further information on the usage of KVM/QEMU, see Book “Virtualization Guide”. 19.9.6 Using Open vSwitch with libvirt After having created the bridge as described before in Section 19.9.4, “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 19.9.4, “Creating a bridge with Open vSwitch” without further changes to the networking conguration. 1. Open the domain XML le for the intended virtual machine: root # virsh edit VM_NAME Replace VM_NAME with the name of the desired virtual machine. This will open your default text editor. 324 Using Open vSwitch with libvirt SLES 15 SP32. 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 conguration 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”. 19.9.7 More information https://docs.openvswitch.org/en/latest/#documentation The documentation section of the Open vSwitch project Web site https://www.opennetworking.org/images/stories/downloads/sdn-resources/white-papers/wp- sdn-newnorm.pdf Whitepaper by the Open Networking Foundation about software-dened networking and the OpenFlow protocol 325 More information SLES 15 SP320 Printer operation SUSE® Linux Enterprise Server supports printing with many types of printers, including remote network printers. Printers can be congured manually or with YaST. For conguration instructions, refer to Book “Deployment Guide”, Chapter 20 “Setting up hardware components with YaST”, Section 20.3 “Setting up a printer”. Both graphical and command line utilities are available for starting and managing print jobs. If your printer does not work as expected, refer to Section 20.8, “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 generated 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 workow. Standard printers (languages like PCL and ESC/p) In the case of 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 mostly used by HP printers and their clones) and ESC/P (which is used by Epson printers). These printer languages are usually supported by Linux and produce an adequate print result. Linux may not be able to address some 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. Proprietary printers (also called GDI printers) 326 SLES 15 SP3These 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. Usually only Windows drivers are available for these printers. See Section 20.8.1, “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: http://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. http://pages.cs.wisc.edu/~ghost/ The Ghostscript Web page. /usr/share/doc/packages/ghostscript/catalog.devices List of built-in Ghostscript drivers. 20.1 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 lter, such as printer-specic 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 lter and back-end to the printer. The lter converts the data generated by the application that is printing (usually PostScript or PDF, but also ASCII, JPEG, etc.) into printer-specic data (PostScript, PCL, ESC/P, etc.). The features of the printer are described in the PPD les. A PPD le contains printer-specic options with the parameters needed to enable them on the printer. The lter system makes sure that options selected by the user are enabled. 327 The CUPS workflow SLES 15 SP3If you use a PostScript printer, the lter system converts the data into printer-specic PostScript. This does not require a printer driver. If you use a non-PostScript printer, the lter system converts the data into printer-specic data. This requires a printer driver suitable for your printer. The back-end receives the printer-specic data from the lter then passes it to the printer. 20.2 Methods and protocols for connecting printers There are various possibilities for connecting a printer to the system. The conguration 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. 20.3 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 various printer options in CUPS. Without a PPD le, the print data would be forwarded to the printer in a “raw” state, which is usually not desired. To congure 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 20.7.3, “PPD files in various packages” and Section 20.8.2, “No suitable PPD file available for a PostScript printer”. 328 Methods and protocols for connecting printers SLES 15 SP3New PPD les can be stored in the directory /usr/share/cups/model/ or added to the print system with YaST as described in Book “Deployment Guide”, Chapter  20 “Setting up hardware components with YaST”, Section 20.3.1.1 “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 dierently 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. 20.4 Network printers A network printer can support various protocols, some even concurrently. Although most of the supported protocols are standardized, some manufacturers modify the standard. Manufacturers then provide drivers for only a few operating systems. Unfortunately, Linux drivers are rarely provided. The current situation is such that you cannot act on the assumption that every protocol works smoothly in Linux. Therefore, you may need to experiment with various options to achieve a functional conguration. 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. Some socket port numbers that are commonly used are 9100 or 35 . The device URI (uniform resource identier) syntax is: socket:// IP.OF.THE.PRINTER : PORT , for example: socket://192.168.2.202:9100/ . LPD (line printer daemon) The LPD protocol is described in RFC 1179. Under this protocol, some 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 specied when conguring the LPD protocol. The implementations of diverse printer manufacturers are exible 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 . IPP (Internet printing protocol) 329 Network printers SLES 15 SP3IPP 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 congure 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 device 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 conguration. If the manufacturer 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: tux > nmap -p 35,137-139,515,631,9100-10000 IP.OF.THE.PRINTER 20.5 Configuring CUPS with command line tools CUPS can be congured 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 ":/" : tux > 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: tux > sudo lpadmin -p QUEUE -v DEVICE-URI -P PPD-FILE -E Then the device ( -v ) is available as QUEUE ( -p ), using the specied PPD le ( -P ). This means that you must know the PPD le and the device URI to congure the printer manually. 330 Configuring CUPS with command line tools SLES 15 SP3Do 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: tux > sudo lpadmin -p ps -v usb://ACME/FunPrinter%20XL -P \ /usr/share/cups/model/Postscript.ppd.gz -E The following example congures a network printer: tux > 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 modied 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: tux > sudo lpoptions -p QUEUE -l Example: Resolution/Output Resolution: 150dpi *300dpi 600dpi The activated default option is identied by a preceding asterisk ( * ). 2. Change the option with lpadmin : tux > sudo lpadmin -p QUEUE -o Resolution=600dpi 3. Check the new setting: tux > sudo lpoptions -p QUEUE -l Resolution/Output Resolution: 150dpi 300dpi *600dpi When a normal user runs lpoptions , the settings are written to ~/.cups/lpoptions . However, root settings are written to /etc/cups/lpoptions . 331 Configuring CUPS with command line tools SLES 15 SP320.6 Printing from the command line To print from the command line, enter lp -d QUEUENAME FILENAME , substituting the corresponding names for QUEUENAME and FILENAME . Some applications rely on the lp command for printing. In this case, enter the correct command in the application''s print dialog, usually without specifying FILENAME , for example, lp -d QUEUENAME . 20.7 Special features in SUSE Linux Enterprise Server Several CUPS features have been adapted for SUSE Linux Enterprise Server. Some of the most important changes are covered here. 20.7.1 CUPS and firewall After completing a default installation of SUSE Linux Enterprise Server, firewalld is active and the network interfaces are congured to be in the public zone, which blocks incoming trac. When firewalld is active, you may need to congure 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 conguration is available in Book “Security and Hardening Guide”, Chapter 25 “Masquerading and firewalls”, Section 25.4 “firewalld” and at https:// en.opensuse.org/SDB:CUPS_and_SANE_Firewall_settings .) 20.7.1.1 CUPS client Normally, a CUPS client runs on a regular workstation located in a trusted network environment behind a rewall. In this case it is recommended to congure the network interface to be in the Internal Zone , so the workstation is reachable from within the network. 332 Printing from the command line SLES 15 SP320.7.1.2 CUPS server If the CUPS server is part of a trusted network environment protected by a rewall, the network interface should be congured to be in the Internal Zone of the rewall. It is not recommended to set up a CUPS server in an untrusted network environment unless you ensure that it is protected by special rewall rules and secure settings in the CUPS conguration. 20.7.2 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 service 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 server(s) probably 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  20.7.1, “CUPS and firewall” for information on allowing printer browsing through firewalld . 20.7.3 PPD files in various packages The YaST printer conguration 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 conguration generates a database from the vendor and model information extracted from the PPD les. 333 Browsing for network printers SLES 15 SP3The conguration using only PPD les and no other information sources has the advantage that the PPD les in /usr/share/cups/model can be modied 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 conguration 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 20.8 Troubleshooting The following sections cover some of 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 conguration. Common network printer problems, defective printouts, and queue handling are also addressed. 20.8.1 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 addressed with the proprietary printer language of the respective printer model. Some GDI printers can be switched to operate either in GDI mode or in one of the standard printer languages. See the manual of the printer whether this is possible. Some models require special Windows software to do the switch (note that 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. 334 Troubleshooting SLES 15 SP3Some manufacturers provide proprietary drivers for their printers. The disadvantage of proprietary printer drivers is that there is no guarantee that these work with the installed print system or that they are suitable for the various 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-eective 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gure special driver software and obtain driver updates that may be required because of new developments in the print system. 20.8.2 No suitable PPD file available for a PostScript printer If the manufacturer-PPDs or OpenPrintingPPDs-postscript packages do not contain a suitable 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 Specication, version 4.3.” If the utility returns “FAIL,” the errors in the PPD les are serious and are likely to cause major problems. The problem spots reported by cupstestppd should be eliminated. If necessary, ask the printer manufacturer for a suitable PPD le. 20.8.3 Network printer connections Identifying network problems Connect the printer directly to the computer. For test purposes, congure 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. Checking a remote lpd 335 No suitable PPD file available for a PostScript printer SLES 15 SP3Use the following command to test if a TCP connection can be established to lpd (port 515 ) on HOST : tux > 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 : root # 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 20.1, “Error message from lpd”, the problem is caused by the remote lpd . EXAMPLE 20.1: 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. tux > netcat -u -l -p 631 & PID=$! ; sleep 40 ; kill $PID If a broadcasting CUPS network server exists, the output appears as shown in Example 20.2, “Broadcast from the CUPS network server”. EXAMPLE 20.2: 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. 336 Network printer connections SLES 15 SP3The following command can be used to test if a TCP connection can be established to cupsd (port 631 ) on HOST : tux > 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 (possibly very long) 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. Possibly, a blank page may be ejected. tux > 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 20.4, “Network printers”. In this way, the print server machine is reduced to a converter between the various 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 usually be determined with the nmap utility from the nmap package some 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 addressed 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 . This may take some time. For further information, refer to the man page of nmap . 337 Network printer connections SLES 15 SP3Enter a command like tux > 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. 20.8.4 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-specic data) the print system does not notice this. If the printer cannot print the printer-specic data, select a PPD le that is more suitable for the printer. 20.8.5 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 . 20.8.6 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 dierent 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 . 338 Defective printouts without error message SLES 15 SP3To 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 (that is, sent it completely to the printer). Use the obtained job number to delete the print job on the server as follows: tux > cancel -h cups.example.com QUEUE-JOBNUMBER 20.8.7 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 completely 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. Some 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 terminate it. 4. Reset the printer completely by switching it o for some time. Then insert the paper and turn on the printer. 20.8.8 Debugging CUPS Use the following generic procedure to locate problems in CUPS: 1. Set LogLevel debug in /etc/cups/cupsd.conf . 2. Stop cupsd . 339 Defective print jobs and data transfer errors SLES 15 SP33. Remove /var/log/cups/error_log* to avoid having to search through very 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. 20.8.9 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 specic problems are presented in the SUSE Knowledgebase (https://www.suse.com/support/ ). Locate the relevant articles with a text search for CUPS . 340 More information SLES 15 SP321 Graphical user interface SUSE Linux Enterprise Server includes the X.org server and the GNOME desktop. This chapter describes the conguration of the graphical user interface for all users. 21.1 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). Usually, the X Window System needs no conguration. The hardware is dynamically detected 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 conguration 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 conguration 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 conguration (if needed). More information on the X11 development can be found on the project''s home page at http://www.x.org . Drivers are found in xf86-video-* packages, for example xf86-video-ati . Many of the drivers delivered with these packages are described in detail in the related manual page. For example, 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. 341 X window system SLES 15 SP321.2 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 specic 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 dierent 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 inuenced 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 subjective, some defaults need to be created. Linux font rendering systems consist of several libraries with dierent relations. The basic font rendering library is FreeType (http://www.freetype.org/) , which converts font glyphs of supported formats into optimized bitmap glyphs. The rendering process is controlled by an algorithm and its parameters (which may be subject to patent issues). Every program or library which uses FreeType should consult the Fontconfig (http:// www.fontconfig.org/) library. This library gathers font conguration from users and from the system. When a user amends their Fontcong setting, this change will result in Fontcong-aware applications. 342 Installing and configuring fonts SLES 15 SP3More sophisticated OpenType shaping needed for scripts such as Arabic, Han or Phags-Pa and other higher level text processing is done using Harfbuzz (http://www.harfbuzz.org/) or Pango (http://www.pango.org/) . 21.2.1 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 dierent list depending on system and user conguration: rpm Invoke rpm to see which software packages containing fonts are installed on your system: tux > 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: tux > fc-list '':'' family Note: Command fc-list The command fc-list is a wrapper to the Fontcong library. It is possible to query a lot of interesting information from Fontcong—or, to be more precise, from its cache. See man 1 fc-list for more details. 21.2.2 Viewing fonts If you want to know what an installed font family looks like, either use the command ftview (package ft2demos ) or visit http://fontinfo.opensuse.org/ . For example, to display the FreeMono font in 14 point, use ftview like this: tux > ftview 14 /usr/share/fonts/truetype/FreeMono.ttf 343 Showing installed fonts SLES 15 SP3If you need further information, go to http://fontinfo.opensuse.org/ to nd out which styles (regular, bold, italic, etc.) and languages are supported. 21.2.3 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: tux > fc-match ''Liberation Serif'' LiberationSerif-Regular.ttf: "Liberation Serif" "Regular" If the desired font does not exist on your system, Fontcong''s matching rules take place and try to nd the most similar fonts available. This means, your request is substituted: tux > fc-match ''Foo Family'' DejaVuSans.ttf: "DejaVu Sans" "Book" Fontcong 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: tux > 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 Fontcong always returns a real family (if at least one is installed) according to the given request, as similar as possible. “Similarity” depends on Fontcong''s internal metrics and on the user''s or administrator''s Fontcong settings. 344 Querying fonts SLES 15 SP321.2.4 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, Fontcong allows you to choose another one. Let Fontcong know by using the element, see Section 21.2.5.2, “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 (http://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 SP3: tux > sudo zypper ar https://download.opensuse.org/repositories/M17N:/fonts/SLE_15/ To search for your FONT_FAMILY_NAME use this command: tux > zypper se ''FONT_FAMILY_NAME*fonts'' 21.2.5 Configuring the appearance of fonts Depending on the rendering medium, and font size, the result may be unsatisfactory. For example, 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 (tting to the grid), or subpixel rendering (tripling resolution in one direction). These algorithms can also dier from one font format to another. Important: Patent issues with subpixel rendering Subpixel rendering is not used in SUSE distributions. Although FreeType2 has support for this algorithm, it is covered by several patents expiring at the end of the year 2019. Therefore, setting subpixel rendering options in Fontcong has no eect unless the system has a FreeType2 library with subpixel rendering compiled in. 345 Installing fonts SLES 15 SP3Via Fontcong, it is possible to select a rendering algorithms for every font individually or for a set of fonts. 21.2.5.1 Configuring fonts via sysconfig SUSE Linux Enterprise Server comes with a sysconfig layer above Fontcong. This is a good starting point for experimenting with font conguration. To change the default settings, edit the conguration le /etc/sysconfig/fonts-config . (or use the YaST syscong module). After you have edited the le, run fonts-config : tux > sudo /usr/sbin/fonts-config Restart the application to make the eect visible. Keep in mind the following issues: A few applications do need not to be restarted. For example, Firefox re-reads Fontcong conguration from time to time. Newly created or reloaded tabs get new font congurations later. The fonts-config script is called automatically after every package installation or removal (if not, it is a bug of the font software package). Every syscong variable can be temporarily overridden by the fonts-config command line option. See fonts-config --help for details. There are several syscong variables which can be altered. See man 1 fonts-config or the help page of the YaST syscong 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 conguration examples, sorted from the “most readable” fonts (more contrast) to “most beautiful” (more smoothed). Bitmap fonts 346 Configuring the appearance of fonts SLES 15 SP3Prefer 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. Scalable 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 syscong 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" 347 Configuring the appearance of fonts SLES 15 SP3Use FORCE_HINTSTYLE to control the level of hinting. 21.2.5.2 Diving into fontconfig XML Fontcong''s conguration 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/ . The central Fontcong conguration le is /etc/fonts/fonts.conf , which—along other work —includes the whole /etc/fonts/conf.d/ directory. To customize Fontcong, 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g conguration les in the ~/.config/fontconfig/conf.d/ directory. User-specic 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 conguration 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 Fontcong searches recursively for fonts. 348 Configuring the appearance of fonts SLES 15 SP3Font-rendering algorithms can be chosen with following Fontcong snippet (see Example 21.1, “Specifying rendering algorithms”): EXAMPLE 21.1: SPECIFYING RENDERING ALGORITHMS FAMILY_NAME 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 21.2: ALIASES AND FAMILY NAME SUBSTITUTIONS Rule 1 Alegreya SC serif Rule 2 serif Droid Serif 349 Configuring the appearance of fonts SLES 15 SP3 Rule 3 serif STIXGeneral The rules from Example 21.2, “Aliases and family name substitutions” create a prioritized family list (PFL). Depending on the element, dierent 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 21.1, “Generating PFL from fontconfig rules”. TABLE 21.1: 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 Fontcong''s metrics, the family name has the highest priority over other patterns, like style, size, etc. Fontcong checks which family is currently installed on the system. If “Alegreya SC” is installed, then Fontcong returns it. If not, it asks for “Droid Serif”, etc. 350 Configuring the appearance of fonts SLES 15 SP3Be careful. When the order of Fontcong snippets is changed, Fontcong can return dierent results, as depicted in Table  21.2, “Results from generating PFL from fontconfig rules with changed order”. TABLE 21.2: RESULTS FROM GENERATING PFL FROM FONTCONFIG RULES WITH CHANGED ORDER Order Current PFL Note Request Alegreya SC Same request performed. 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 performed Note: Implication Think of the alias as a classication or inclusion of this group (if not installed). As the example shows, should always precede the and aliases of that group. classication 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 Fontcong snippet in Example 21.3, “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 21.3: ALIASES AND FAMILY NAME SUBSTITUTIONS Alegreya SC serif 351 Configuring the appearance of fonts SLES 15 SP3 Droid Serif serif STIXGeneral serif serif Droid Serif STIXGeneral Alegreya SC Priority is given by the order in the alias. Similarly, stronger aliases can be used. Example 21.2, “Aliases and family name substitutions” is expanded by Example 21.4, “Aliases and family names substitutions”. EXAMPLE 21.4: ALIASES AND FAMILY NAMES SUBSTITUTIONS Rule 4 serif Liberation Serif Rule 5 serif DejaVu Serif 352 Configuring the appearance of fonts SLES 15 SP3 The expanded conguration from Example 21.4, “Aliases and family names substitutions” would lead to the following PFL evolution: TABLE 21.3: RESULTS FROM 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 Rule 4 Alegreya SC , Droid Serif , serif , Liberation Serif , STIXGeneral 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 declaration that is parsed last “wins”. If possible, do not use after user ( /etc/fonts/conf.d/*-user.conf ) when creating a system-wide conguration. In case multiple before user in the system-wide conguration. Every declaration overwrites declarations for the same generic name. If the administrator wants to allow the user to use and not only , the administrator should not use in the system- wide conguration. On the other hand, as users mostly use , this should not have any detrimental eect. We also see the use of in system-wide congurations. 353 Configuring the appearance of fonts SLES 15 SP321.3 GNOME configuration for administrators 21.3.1 The dconf system Conguration 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 administrators 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 conguration options with the command line. The GNOME Tweaks tool provides an easy-to-use user interface for additional conguration options beyond the normal GNOME conguration. The tool can be started from the GNOME application menu or from the command line with gnome-tweak-tool . 21.3.2 System-wide configuration Global dconf conguration parameters can be set in the /etc/dconf/db/ directory. This includes the conguration for GDM or locking certain conguration options for users. Use the following procedure as an example to create a system-wide conguration: 1. Create a new directory that ends with a .d in /etc/dconf/db/ . This directory can contain an arbitrary amount of text les with conguration 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 conguration directives into the dconf database format: tux > sudo dconf update 3. Add the new network conguration database to the default user prole, by creating the le /etc/dconf/profiles/user . Then add the following content: system-db:network 354 GNOME configuration for administrators SLES 15 SP3The le /etc/dconf/profiles/user is a GNOME default that will be used. Other proles can be dened in the environment variable DCONF_PROFILE . 4. Optional: To lock the proxy conguration for users, create the le /etc/dconf/db/ network/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 prole with one user and then use dconf dump / to list all conguration options. The conguration options can then be stored in a global prole. A detailed description of the global conguration is available at https://wiki.gnome.org/Projects/ dconf/SystemAdministrators . 21.3.3 More information For more information, see http://help.gnome.org/admin/ . 21.4 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 if you wish to to use SUSE Prime (see Section 21.4.1, “Prerequisites”). 21.4.1 Prerequisites There must not be a /etc/X11/xorg.conf le, and no conguration les with active "ServerLayout", "Device", or "Screen" sections in the /etc/X11/xorg.conf.d directory. 355 More information SLES 15 SP3SUSE Prime works only with X11. Use the loginctl command to see if your system is using X11 or Wayland: tux > loginctl SESSION UID USER SEAT TTY 2 1000 tux seat0 tux > 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. 21.4.2 Installing and using SUSE Prime Your NVIDIA graphics card should already be installed and working. If it is not, see Section 21.4.3, “Installing NVIDIA drivers”. Install the suse-prime package: tux > sudo zypper install suse-prime To switch your GPU run one of the following commands, then log out and log back in: tux > sudo prime-select intel tux > sudo prime-select intel2 tux > 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 : tux > 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? tux > sudo /usr/sbin/prime-select get-current Driver configured: intel 356 Installing and using SUSE Prime SLES 15 SP321.4.3 Installing NVIDIA drivers If you need to identify your NVIDIA card so you know which driver to use, run the following command: tux > /sbin/lspci | grep VGA Follow these steps to install the drivers with Zypper. List the available driver packages: tux > sudo zypper se nvidia Then install the drivers for your NVIDIA graphics card: tux > sudo zypper se packagename 357 Installing NVIDIA drivers SLES 15 SP322 Accessing file systems with FUSE FUSE is the acronym for le system in user space. This means you can congure 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 extend FUSE to access almost all le systems like remote SSH connections, ISO images, and more. 22.1 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 congure 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 dierent le systems there. 22.2 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. 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 . 4. Mount the partition in read-write mode. Replace the placeholder DEVICE with your respective Windows partition: tux > ntfs-3g /dev/DEVICE MOUNT POINT 358 Configuring FUSE SLES 15 SP3To use your Windows partition in read-only mode, append -o ro : tux > 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. If you want to set the write permissions to a dierent user, use the command id USER to get the output of the UID and GID values. Set it with: root # 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 . 22.3 More information For more information, see the home page of FUSE at https://github.com/libfuse/libfuse . 359 More information SLES 15 SP323 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. 23.1 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: tux > 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. Note that this list may be incomplete. To view detailed information about a specic kernel module, use the modinfo MODULE_NAME command, where MODULE_NAME is the name of the desired kernel module. Note that 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: tux > /sbin/modinfo kvm filename: /lib/modules/5.3.18-57-default/kernel/arch/x86/kvm/kvm.ko.xz license: GPL author: Qumranet suserelease: SLE15-SP3 srcversion: 3D8FBA9060D4537359A06FC depends: irqbypass supported: yes retpoline: Y 360 Listing loaded modules with lsmod and modinfo SLES 15 SP3intree: Y name: kvm vermagic: 5.3.18-57-default SMP mod_unload modversions 23.2 Adding and removing kernel modules While it is possible to use insmod and rmmod to add and remove kernel modules, it is recommended to use the modprobe tool instead. modprobe oers several important advantages, including automatic dependency resolution and blacklisting. When used without any parameters, the modprobe command installs a specied kernel module. modprobe must be run with root privileges: tux > sudo modprobe acpi To remove a kernel module, use the -r parameter: tux > sudo modprobe -r acpi 23.2.1 Loading kernel modules automatically on boot Instead of loading kernel modules manually, you can load them automatically during the boot process using the system-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 conguration le the same name as the module, for example: /etc/modules-load.d/rt2800usb.conf The conguration 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 specic options, add a conguration 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-thinkfan.conf . The conguration le must contain the name of the kernel module and the desired parameters. You can use the example command below to create a conguration le containing the name of the kernel module and its parameters: tux > echo "options thinkpad_acpi fan_control=1" | sudo tee /etc/modprobe.d/thinkfan.conf 361 Adding and removing kernel modules SLES 15 SP3Note: Loading kernel modules Most kernel modules are loaded by the system automatically when a device is detected or user space requests specic functionality. Thus, adding modules manually to /etc/ modules-load.d/ is rarely required. 23.2.2 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. Note that you can still load blacklisted kernel modules manually using the insmod or modprobe tools. To blacklist a module, add the blacklist MODULE_NAME line to the /etc/modprobe.d/50- blacklist.conf le. For example: blacklist nouveau Run the mkinitrd command as root to generate a new initrd image, then reboot your machine. These steps can be performed using the following command: tux > su echo "blacklist nouveau" >> /etc/modprobe.d/50-blacklist.conf && mkinitrd && 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 specied conguration. 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_CMD_LINUX command. Then run the sudo grub2-mkconfig -o /boot/grub2/grub.cfg command to enable the changes. 362 Blacklisting kernel modules with modprobe SLES 15 SP324 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 congured 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 processing. 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. 24.1 The /dev directory The device nodes in the /dev directory provide access to the corresponding kernel devices. With udev , the /dev directory reects 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 modied 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-tmples. The conguration les are found in /usr/lib/tmpfiles.d/ and /etc/tmpfiles.d/ ; for more information, see the systemd-tmpfiles(8) man page. 24.2 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-specic 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 363 The /dev directory SLES 15 SP3changed, 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 24.6, “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 specic 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. 24.3 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. Usually these IDs consist of vendor and product ID and other subsystem-specic 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 . 24.4 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. 364 Drivers, kernel modules and devices SLES 15 SP3As 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 dierence between a device coldplug sequence and a device discovery during runtime. In both cases, the same rules are used to match and the same congured programs are run. 24.5 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 nished 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 nish, because the partition events may rely on the data that the main disk event has queried from the hardware. 365 Monitoring the running udev daemon SLES 15 SP3udevadm 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 specied in the udev conguration le /etc/udev/udev.conf . The log priority of the running daemon can be changed with udevadm control --log_priority= LEVEL/ NUMBER . 24.6 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-specic conguration). 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 specied value. A matching rule may specify the name of the device node, add symbolic links pointing to the node or run a specied 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 24.1: EXAMPLE udev RULES # console 366 Influencing kernel device event handling with udev rules SLES 15 SP3KERNEL=="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 eect. 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. 367 Influencing kernel device event handling with udev rules SLES 15 SP3Some general 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 dierent lines as you would do in shell syntax. udev rules support a shell-style pattern that matches the * , ? , and [] patterns. udev rules support substitutions. 24.6.1 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 nal value. Disallow any later change by later rules. 368 Using operators in udev rules SLES 15 SP324.6.2 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 (specied by ATTRIBUTE ). %E{VARIABLE} , $env{VARIABLE} The value of an environment variable (specied by VARIABLE ). %c , $result The output of PROGRAM . %% The % character. $$ The $ character. 369 Using substitutions in udev rules SLES 15 SP324.6.3 Using udev match keys Match keys describe conditions that must be met before a udev rule can be applied. The following 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. PROGRAM 370 Using udev match keys SLES 15 SP3Let 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. 24.6.4 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 specied 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 very short tasks to avoid blocking further events for this device. LABEL Add a label where a GOTO can jump to. 371 Using udev assign keys SLES 15 SP3GOTO 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 specied, 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 specied 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 completely. 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. 24.7 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 with 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 372 Persistent device naming SLES 15 SP3|-- 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 24.8 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-tmples; 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 conguration le. /etc/udev/rules.d/* System-specic udev event matching rules. You can add custom rules here to modify or override the default rules from /usr/lib/udev/rules.d/* . 373 Files used by udev SLES 15 SP3Files 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. 24.9 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 conguration 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. 374 More information SLES 15 SP325 Special system features This chapter starts with information about various 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 release 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 country-specic settings (I18N and L10N). 25.1 Information about special software packages The following chapter provides basic information about the following tools: bash , cron , logrotate , locate , ulimit and free . 25.1.1 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 personal adjustments: tux > mv ~/.bashrc ~/.bashrc.old 375 Information about special software packages SLES 15 SP3tux > cp /etc/skel/.bashrc ~/.bashrc tux > mv ~/.profile ~/.profile.old tux > cp /etc/skel/.profile ~/.profile Then copy personal adjustments back from the *.old les. 25.1.2 The cron package Use cron to automatically run commands in the background at predened 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 25.1, “Entry in /etc/crontab”, root is entered. Package-specic tables, located in /etc/cron.d , have the same format. See the cron man page ( man cron ). EXAMPLE 25.1: 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 modied 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 25.2, “/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 25.2: /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 376 The cron package SLES 15 SP344 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 specied DAILY_TIME for a longer time. The maximum value of MAX_NOT_RUN is 14 days. The daily system maintenance jobs are distributed to various scripts for reasons of clarity. They are contained in the package aaa_base . /etc/cron.daily contains, for example, the components suse.de-backup-rpmdb , suse.de-clean-tmp or suse.de-cron-local . 25.1.3 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 documented in the cron man page. In the update case it is recommended to set these values according to your needs. 25.1.4 Log files: package logrotate There are several system services (daemons) that, along with the kernel itself, regularly record the system status and specic 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 specied 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 “Analyzing and managing system log files”, Section 3.3 “Managing log files with logrotate”. 25.1.5 The locate command locate , a command for quickly nding les, is not included in the standard scope of installed software. If desired, install the package mlocate , the successor of the package findutils- locate . The updatedb process is started automatically every night or about 15 minutes after booting the system. 377 Stopping cron status messages SLES 15 SP325.1.6 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 25.1, “ulimit: Setting resources for the user”. TABLE 25.1: 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 recommended, because changes will be overwritten during system upgrades. To customize systemwide prole settings, use /etc/profile.local . Per-user settings should be made in ~USER/.profile . EXAMPLE 25.3: 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 specied in KB. For more detailed information, see man bash . Important: ulimit support Not all shells support ulimit directives. PAM (for example, pam_limits ) oers comprehensive adjustment possibilities as an alternative to ulimit . 378 The ulimit command SLES 15 SP325.1.7 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 unied memory management. The slogan free memory is bad memory applies well to Linux. As a result, Linux has always made the eort to balance out caches without actually allowing free or unused memory. The 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 dierences 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 . 25.1.8 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. 25.1.9 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 dierent 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 initialization le such as ~/.bashrc . 379 The free command SLES 15 SP325.1.10 Settings for GNU Emacs GNU Emacs is a complex work environment. The following sections cover the conguration les processed when GNU Emacs is started. More information is available at http://www.gnu.org/ software/emacs/ . On start-up, Emacs reads several les containing the settings of the user, system administrator and distributor for customization or preconguration. The initialization le ~/.emacs is installed 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 directory (with cp /etc/skel/.gnu-emacs ~/.gnu-emacs ) and make the desired settings there. .gnu-emacs denes 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 initialization le ~/.emacs . Among other things, site-start.el ensures that special conguration les distributed with Emacs add-on packages, such as psgml , are loaded automatically. Conguration 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: info:/ 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. 380 Settings for GNU Emacs SLES 15 SP325.2 Virtual consoles Linux is a multiuser and multitasking system. The advantages of these features can be appreciated 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. To 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 . 25.3 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 aect applications that use terminfo entries or whose conguration 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/ packages/xkeyboard-config (part of the xkeyboard-config package). 381 Virtual consoles SLES 15 SP325.4 Language and country-specific settings The system is, to a very large extent, internationalized and can be modied for local needs. Internationalization (I18N) allows specic 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. Settings are made with LC_ variables dened 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 dened 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_LC_MONETARY These variables are passed to the shell without the RC_ prex and represent the listed categories. The shell proles 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-specic settings, otherwise the system administrator always works in a POSIX environment. The variables can be set with the YaST syscong editor. The value of such a variable contains the language code, country code, encoding and modier. The individual components are joined by special characters: LANG=[[_].[@]] 382 Language and country-specific settings SLES 15 SP325.4.1 System-wide locale settings systemd reads /etc/locale.conf at early boot. The locale settings congured in this le are inherited by every service or user, unless there are individual settings. Note: 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/ sysconfig/language , /etc/sysconfig/keyboard , and /etc/sysconfig/console . Starting with SUSE Linux Enterprise Server 15 GA, these les are considered obsolete. systemd does not read settings from these les anymore. Instead, systemd reads /etc/ locale.conf . However, variables dened in /etc/sysconfig/language will still be used: They override the system-wide locale and can be used to dene dierent locale settings for user shells (see Section 25.4.2, “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 assignment (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 : root # 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 syscong to their nal destinations if they are not already dened there. 383 System-wide locale settings SLES 15 SP325.4.2 Some examples You should always set the language and country codes together. Language settings follow the standard ISO 639 available at http://www.evertype.com/standards/iso639/iso639-en.html and http://www.loc.gov/standards/iso639-2/ . Country codes are listed in ISO 3166, see http:// en.wikipedia.org/wiki/ISO_3166 . It 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 sometimes for programs that have not been updated to support UTF-8 . The string dening 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. 384 Some examples SLES 15 SP3Users can override the system defaults by editing their ~/.bashrc accordingly. For example, 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. 25.4.3 Locale settings in ~/.i18n If you are not satised with locale system defaults, change the settings in ~/.i18n according to the Bash scripting syntax. Entries in ~/.i18n override system defaults from /etc/sysconfig/ language . Use the same variable names but without the RC_ namespace prexes. For example, use LANG instead of RC_LANG : LANG=cs_CZ.UTF-8 LC_COLLATE=C 25.4.4 Settings for language support Files in the category Messages are, as a rule, only stored in the corresponding language directory (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 dened, 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" Note that in Norwegian, LC_TIME is also treated dierently. 385 Locale settings in ~/.i18n SLES 15 SP3One 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 denition 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 denition visible to the system. 25.4.5 More information The GNU C Library Reference Manual, Chapter “Locales and Internationalization”. It is included 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 . 386 More information SLES 15 SP326 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 conguring 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 connection. Important: NetworkManager is only supported by SUSE for desktop workloads with SLED or the Workstation extension. All server certications are done with wicked as the network conguration tool, and using NetworkManager may invalidate them. NetworkManager is not supported by SUSE for server workloads. 26.1 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 example, it is a DHCP or DNS server. Your computer is a Xen server or your system is a virtual system inside Xen. 387 Use cases for NetworkManager SLES 15 SP326.2 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 congure 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. Congure your network connections with NetworkManager as described in Section 26.3, “Configuring network connections”. 4. To deactivate NetworkManager and control the network with your own conguration: a. In the Network Setup Method eld, choose Controlled by wicked. b. Click OK. c. Set up your network card with YaST using automatic conguration via DHCP or a static IP address. Find a detailed description of the network conguration with YaST in Section 19.4, “Configuring a network connection with YaST”. 26.3 Configuring network connections After enabling NetworkManager in YaST, congure your network connections with the NetworkManager front-end available in GNOME. It shows tabs for all types of network connections, such as wired, wireless, mobile broadband, DSL, and VPN connections. Tip: NetworkManager connection editor In previous SUSE Linux Enterprise Server releases, network connections were congured using an application called NetworkManager Connection Editor. This is no longer installed by default, because GNOME Control Center has fully replaced its conguration capabilities. 388 Enabling or disabling NetworkManager SLES 15 SP3If you still need to use NetworkManager Connection Editor to congure network connections, install the NetworkManager-connection-editor package manually: tux > sudo zypper install NetworkManager-connection-editor To open the network conguration dialog in GNOME, open the settings menu via the status menu and click the Network entry. Note: Availability of options Depending on your system setup, you may not be allowed to congure connections. In a secured environment, some options may be locked or require root permission. Ask your system administrator for details. FIGURE 26.1: GNOME NETWORK CONNECTIONS DIALOG PROCEDURE 26.1: ADDING AND EDITING CONNECTIONS 1. Open the NetworkManager conguration dialog. 2. To add a Connection: a. Click the + icon in the lower left corner. b. Select your preferred connection type and follow the instructions. 389 Configuring network connections SLES 15 SP3c. When you are nished click Add. d. After conrming your changes, the newly-congured network connection appears in the list of available networks in the Status Menu. 3. To edit a connection: a. Select the entry to edit. b. Click the gear icon to open the Connection Settings dialog. c. Insert your changes and click Apply to save them. d. To make your connection available as a system connection go to the Identity tab and set the check box Make available to other users. For more information about user and system connections, see Section 26.4.1, “User and system connections”. 26.3.1 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 change the connection details or to switch it o. 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. 26.3.2 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 26.2: 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. 390 Managing wired network connections SLES 15 SP34. If the network is encrypted, a conguration dialog opens. It shows the type of encryption the network uses and text boxes for entering the login credentials. PROCEDURE 26.3: CONNECTING TO AN INVISIBLE WIRELESS NETWORK 1. To connect to a network that does not broadcast its service set identier (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. 4. 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 will remain 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. 26.3.3 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 conguration. 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. 26.3.4 NetworkManager and VPN NetworkManager supports several Virtual Private Network (VPN) technologies. For each technology, SUSE Linux Enterprise Server comes with a base package providing the generic support for NetworkManager. In addition to that, you also need to install the respective desktop- specic package for your applet. OpenVPN 391 Configuring your Wi-Fi/Bluetooth card as an access point SLES 15 SP3To use this VPN technology, install: NetworkManager-openvpn NetworkManager-openvpn-gnome OpenConnect To use this VPN technology, install: NetworkManager-openconnect NetworkManager-openconnect-gnome PPTP (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 26.4: 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 Certicates (TLS) or Password with Certicates (TLS). 5. Insert the necessary values into the respective text boxes. For our example conguration, these are: Gateway The remote endpoint of the VPN server User name The user (only available when you have selected Password with Certicates (TLS)) 392 NetworkManager and VPN SLES 15 SP3Password The password for the user (only available when you have selected Password with Certicates (TLS)) User Certicate /etc/openvpn/client1.crt CA Certicate /etc/openvpn/ca.crt Private Key /etc/openvpn/client1.key 6. Finish the conguration with Add. 7. 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. 26.4 NetworkManager and security NetworkManager distinguishes two types of wireless connections: trusted and untrusted. A trusted connection is any network that you explicitly selected in the past. All others are untrusted. Trusted connections are identied by the name and MAC address of the access point. Using the MAC address ensures that you cannot use a dierent 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, NetworkManager attempts to connect, but rst you are asked to conrm the new encryption settings and provide any updates, such as a new key. If you switch from using a wireless connection to oine mode, NetworkManager blanks the SSID or ESSID. This ensures that the card is disconnected. 26.4.1 User and system connections NetworkManager knows two types of connections: user and system connections. 393 NetworkManager and security SLES 15 SP3User connections require every user to authenticate in NetworkManager, which stores the user''s credentials in their local GNOME keyring so they don''t have to re-enter them every time they connect. System connections are available to all users automatically. The rst user to create the connection enters any necessary credentials, and then all other users have access without needing to know the credentials. The dierence in conguring a user or system connection is a single checkbox, Make available to other users. For information on how to congure user or system connections with NetworkManager, refer to Section 26.3, “Configuring network connections”. 26.4.2 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. NetworkManager can also retrieve its certicates for secure connections (for example, encrypted wired, wireless or VPN connections) from the certicate store. For more information, refer to Book “Security and Hardening Guide”, Chapter 21 “Certificate store”. 26.4.3 Firewall zones FIGURE 26.2: firewalld ZONES IN NETWORKMANAGER 394 Storing passwords and credentials SLES 15 SP3The rewall zones set general rules about which network connections are allowed. To congure the zone of rewalld for a wired connection, go to the Identity tab of the connection settings. To congure the zone of rewalld for a WiFi 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 rewalld, see Book “Security and Hardening Guide”, Chapter 25 “Masquerading and firewalls”, Section 25.4 “firewalld”. 26.5 Frequently asked questions In the following, nd some frequently asked questions about conguring special network options with NetworkManager. Q: 1. How to tie a connection to a specific device? By default, connections in NetworkManager are device type-specic: 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 conguring network connections and choose the connection you want to modify. On the Wired or Wireless tab, enter the MAC Address of the device and conrm your changes. Q: 2. How to specify a certain access point in case multiple access points with the same ESSID are detected? When multiple access points with dierent 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 conguring wireless connections. The Basic Service Set Identier (BSSID) uniquely identies 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. 395 Frequently asked questions SLES 15 SP3Start the dialog for conguring network connections as described in Section  26.3, “Configuring network connections”. Choose the wireless connection you want to modify and click Edit. On the Wireless tab, enter the BSSID. Q: 3. How to share network connections with other computers? The primary device (the device which is connected to the Internet) does not need any special conguration. However, you need to congure the device that is connected to the local hub or machine as follows: 1. Start the dialog for conguring network connections as described in Section 26.3, “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 box, activate Shared to other computers. That will enable IP trac forwarding and run a DHCP server on the device. Conrm your changes in NetworkManager. 2. As the DCHP server uses port 67 , make sure that it is not blocked by the rewall: On the machine sharing the connections, start YaST and select Security and Users Firewall. Switch to the Allowed Services category. If DCHP Server is not already shown as Allowed Service, select DCHP Server from Services to Allow and click Add. Conrm your changes in YaST. Q: 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 override it. Start the dialog for conguring network connections as described in Section  26.3, “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 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. Conrm your changes. Q: 5. How to make NetworkManager connect to password protected networks before a user logs in? Dene a system connection that can be used for such purposes. For more information, refer to Section 26.4.1, “User and system connections”. 396 Frequently asked questions SLES 15 SP326.6 Troubleshooting Connection problems can occur. Some common problems related to NetworkManager include the applet not starting or a missing VPN option. Methods for resolving and preventing these problems depend on the tool used. NetworkManager 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 26.2, “Enabling or disabling NetworkManager”. Then make sure that the NetworkManager-gnome package is also installed. If the desktop applet is installed but is not running for some reason, 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 separate 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 26.3.4, “NetworkManager and VPN”. No network connection available If you have congured 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 . 26.7 More information More information about NetworkManager can be found on the following Web sites and directories: NetworkManager project page https://gitlab.freedesktop.org/NetworkManager/NetworkManager Package documentation 397 Troubleshooting SLES 15 SP3Also 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/ . 398 More information SLES 15 SP327 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 systems. ACPI (Advanced Conguration 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. 27.1 Power saving functions Power saving functions are not only signicant 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 very 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 prior to the suspend is restored. Some manufacturers oer 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. 399 Power saving functions SLES 15 SP3Note: 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 dierent ways: frequency and voltage scaling (also known as PowerNow! or Speedstep), throttling and putting the processor to sleep (C-states). Depending on the operating mode of the computer, these methods can also be combined. 27.2 Advanced configuration and power interface (ACPI) ACPI was designed to enable the operating system to set up and control the individual hardware 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 17, journalctl: Query the systemd journal for more information on viewing the journal log messages. See Section 27.2.2, “Troubleshooting” for more information about troubleshooting ACPI problems. 400 Advanced configuration and power interface (ACPI) SLES 15 SP327.2.1 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. Usually, 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, some systems do not run smoothly when they are throttled 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 11 “Power management”. 27.2.2 Troubleshooting There are two dierent 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cation 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 conguring the PCI devices. 401 Controlling the CPU performance SLES 15 SP3acpi=ht Only perform a simple resource conguration. Do not use ACPI for other purposes. acpi=off Disable ACPI. Warning: Problems booting without ACPI Some newer machines (especially SMP systems and AMD64 systems) need ACPI for conguring 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 (Dierentiated 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 27.4, “Troubleshooting”. In the kernel conguration, 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 manufacturers. Especially if they do not always provide assistance for Linux, they should be confronted with the problems. Manufacturers will only take the issue seriously if they realize that an adequate number of their customers use Linux. 27.2.2.1 More information https://tldp.org/HOWTO/ACPI-HOWTO/ (detailed ACPI HOWTO, contains DSDT patches) https://uefi.org/specifications (Advanced Conguration & Power Interface Specication) https://01.org/linux-acpi (the Linux ACPI project) 402 Troubleshooting SLES 15 SP327.3 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 some of the following methods, using the hdparm command. It can be used to modify various 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 dicult 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, numerous 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 Denes 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. 403 Rest for the hard disk SLES 15 SP3Warning: 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 modied 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 postx uses the variable POSTFIX_LAPTOP . If this variable is set to yes , postx accesses the hard disk far less frequently. 27.4 Troubleshooting All error messages and alerts are logged in the system journal, which can be queried with the command journalctl (see Chapter 17, journalctl: Query the systemd journal for more information). The following sections cover the most common problems. 27.4.1 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/* . 404 Troubleshooting SLES 15 SP328 VM guest This chapter contains additional information on when SUSE Linux Enterprise Server is used in a virtual machine. 28.1 Adding and removing CPUs Some virtualization environments allow adding or removing CPUs while the virtual machine is running. For safe removal of CPUs, rst deactivate them by executing root # echo 0 > /sys/devices/system/cpu/cpuX/online Replace X with the CPU number. To bring a CPU back online, execute root # echo 1 > /sys/devices/system/cpu/cpuX/online 405 Adding and removing CPUs SLES 15 SP329 Persistent memory This chapter contains additional information about using SUSE Linux Enterprise with non-volatile main memory, also known as Persistent Memory, comprising one or more NVDIMMs. 29.1 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 disks (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 motherboard 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. Dierent models use dierent 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 development. This means that dierent vendors and models of NVDIMM oer dierent performance and durability characteristics. Because the storage technologies involved are in an early stage of development, dierent vendors'' hardware may impose dierent limitations. Thus, the following statements are generalizations. 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. 406 Introduction SLES 15 SP3This has two important consequences: It is not possible with current technology to run a system with only persistent memory and thus achieve completely 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 very fast supplementary storage. The performance characteristics of dierent vendors'' persistent memory mean that it may be necessary for programmers to be aware of the hardware specications of the NVDIMMs in a particular server, including how many NVDIMMs there are and in which memory slots they are tted. This will obviously impact hypervisor use, migration of software between dierent host machines, and so on. This new storage subsystem is dened in version 6 of the ACPI standard. However, libnvdimm supports pre-standard NVDIMMs and they can be used in the same way. 29.2 Terms Region A region is a block of persistent memory that can be divided up into one or more namespaces. 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 denes which NVDIMM features are enabled for that namespace. Sibling namespaces of the same parent region will always have the same type, but might be congured to have dierent modes. Namespace modes include: devdax Device-DAX mode. Creates a single-character device le ( /dev/daxX.Y ). Does not require le system creation. 407 Terms SLES 15 SP3fsdax File system-DAX mode. Default if no other mode is specied. 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. Type Each namespace and region has a type that denes the way in which 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 dierent types: Persistent Memory, which can be congured in two dierent ways, and the deprecated Block Mode. Persistent memory (PMEM) PMEM storage oers byte-level access, just like RAM. Using PMEM, a single namespace can include multiple interleaved NVDIMMs, allowing them all to be used as a single device. There are two ways to congure a PMEM namespace. PMEM with DAX A PMEM namespace congured 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 congured to operate in BTT mode is accessed on a sector- 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. 408 Terms SLES 15 SP3The 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 deprecated 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. Direct 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 oset 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 denitions. This can be accessed using DSMs. Device-specific method (DSM) ACPI method to access the rmware on an NVDIMM. 29.3 Use cases 29.3.1 PMEM with DAX It is important to note that this form of memory access is not transactional. In the event of a power outage or other system failure, data may not be completely written into storage. PMEM storage is only suitable if the application can handle the situation of partially-written data. 409 Use cases SLES 15 SP329.3.1.1 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. 29.3.1.2 Avoiding use of the kernel page cache Avoid using the kernel page cache if you wish 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. 29.3.2 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 very 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 29.5.3, “Creating a PMEM namespace with BTT”). To applications, such devices just appear as very 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 applications that depend on data integrity will keep working. Media error reporting works through standard error-reporting channels. 29.4 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 congure NVDIMMs. 410 PMEM with BTT SLES 15 SP3These 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: tux > ndctl help subcommand To see a list of available subcommands, use: tux > ndctl --list-cmds The available subcommands include: version Displays the current version of the NVDIMM support tools. enable-namespace Makes the specied namespace available for use. disable-namespace Prevents the specied namespace from being used. create-namespace Creates a new namespace from the specied storage devices. destroy-namespace Removes the specied namespace. enable-region Makes the specied region available for use. disable-region Prevents the specied region from being used. zero-labels Erases the metadata from a device. read-labels Retrieves the metadata of the specied device. 411 Tools for managing persistent memory SLES 15 SP3list Displays available devices. help Displays information about using the tool. 29.5 Setting up persistent memory 29.5.1 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. root # ndctl list --dimms [ { "dev":"nmem2", "id":"8089-00-0000-12325476" }, { "dev":"nmem1", "id":"8089-00-0000-11325476" }, { "dev":"nmem0", "id":"8089-00-0000-10325476" } ] With a dierent 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. root # ndctl list --regions 412 Setting up persistent memory SLES 15 SP3[ { "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, "type":"blk" } ] The space is available in two dierent forms: either as three separate 64 GB 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. 29.5.2 Configuring the storage as a single PMEM namespace with DAX For the rst example, we will congure our three NVDIMMs into a single PMEM namespace with Direct Access (DAX). The rst step is to create a new namespace. root # ndctl create-namespace --type=pmem --mode=fsdax --map=memory 413 Configuring the storage as a single PMEM namespace with DAX SLES 15 SP3{ "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: root # 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 Before it can be used, like any other drive, it must be formatted. In this example, we format it with XFS: root # 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: root # mount -o dax /dev/pmem3 /mnt/pmem3 Then we can verify that we now have a DAX-capable device: root # mount | grep dax 414 Configuring the storage as a single PMEM namespace with DAX SLES 15 SP3/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, completely bypassing the page cache. Any fsync or msync calls on les in that le system will still ensure that modied data has been fully written to the NVDIMMs. These calls ush the processor cache lines associated with any pages that have been modied in user space via mmap mappings. 29.5.2.1 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: root # umount /mnt/pmem3 Then disable the namespace: root # ndctl disable-namespace namespace3.0 disabled 1 namespace Then delete it: root # ndctl destroy-namespace namespace3.0 destroyed 1 namespace 29.5.3 Creating a PMEM namespace with BTT BTT provides sector write atomicity, which makes it a good choice when you need data protection, for example 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. root # ndctl create-namespace --type=pmem --mode=sector { "dev":"namespace3.0", "mode":"sector", 415 Creating a PMEM namespace with BTT SLES 15 SP3"uuid":"51ab652d-7f20-44ea-b51d-5670454f8b9b", "sector_size":4096, "blockdev":"pmem3s" } Next, verify that the new device is present: root # 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 congured, 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 congured 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 after 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 completely 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 just like 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. 29.5.4 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: root # blockdev --getbsz /dev/sda3 416 Placing the file system journal on PMEM/BTT SLES 15 SP3The 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: root # mke2fs -b 4096 -O journal_dev /dev/pmem3s root # 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: root # mkfs.xfs -l logdev=/dev/pmem3s /dev/sda3 See man 8 mkfs.ext4 and man 8 mkfs.ext4 for detailed information about options. 29.6 More information More about this topic can be found in the following list: Persistent Memory Wiki (https://nvdimm.wiki.kernel.org/) Contains instructions for conguring NVDIMM systems, information about testing, and links to specications related to NVDIMM enabling. This site is developing as NVDIMM support in Linux is developing. Persistent Memory Programming (http://pmem.io/) Information about conguring, 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 folder in the current Linux kernel tree. It talks about the dierent kernel modules involved in NVDIMM enablement, lays out some 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. 417 More information SLES 15 SP3IV Services 30 Service management with YaST 419 31 Time synchronization with NTP 421 32 The domain name system 428 33 DHCP 453 34 SLP 468 35 The Apache HTTP server 472 36 Setting up an FTP server with YaST 514 37 Squid caching proxy server 518 38 Web Based Enterprise Management using SFCB 53830 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 SP3 is YaST support for Systemd socket-based services activation, which congures services to start on demand. Systemd supports starting services with socket-based activation, for starting services on demand. 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 startup you want to use. Figure 30.1, “YaST service manager” shows the options in the Start Mode drop-down menu: 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. FIGURE 30.1: YAST SERVICE MANAGER 419 SLES 15 SP3The 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. 420 SLES 15 SP331 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 various operating parameters at runtime. Starting with SUSE Linux Enterprise Server 15.2, the YaST module for NTP client conguration congures the systemd-timer instead of the cron daemon to execute chrony , when it is not congured to run as a daemon. 31.1 Configuring an NTP client with YaST The NTP daemon ( chronyd ) coming with the chrony package is preset to use the local computer hardware clock as a time reference. The precision of a hardware clock heavily depends on its time source. For example, an atomic clock or GPS receiver is a very precise time source, while a common RTC chip is not a reliable time source. YaST simplies the conguration of an NTP client. In the YaST NTP client conguration (Network Services NTP Conguration) window, you can specify when to start the NTP daemon, the type of the conguration source, and add custom time servers. 421 Configuring an NTP client with YaST SLES 15 SP3FIGURE 31.1: NTP CONFIGURATION WINDOW 31.1.1 NTP daemon start You can choose from three options for when to start the NTP daemon: Only manually Select Only Manually, if you want to manually start the chrony daemon. Synchronize without daemon Select Synchronize without Daemon to set the system time periodically without a permanently 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. 31.1.2 Type of the configuration source In the Conguration 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 oers NTP servers via DHCP. 422 NTP daemon start SLES 15 SP331.1.3 Configure time servers Time servers for the client to query are listed in the lower part of the NTP Conguration window. Modify this list as needed with Add, Edit, and Delete. Click Add to add a new time server: FIGURE 31.2: 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 Oine 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. Conrm with OK. 423 Configure time servers SLES 15 SP331.2 Manually configuring NTP in the network chrony reads its conguration 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 specic server names or IP addresses, for example: server 0.europe.pool.ntp.org server 1.europe.pool.ntp.org server 2.europe.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 all of them 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 computers 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 some time 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 424 Manually configuring NTP in the network SLES 15 SP331.3 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 interactively, 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 oine, run: root # 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: root # 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 manual page ( man 1 chronyc ). 31.4 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 specied in the conguration le. chronyd keeps trying to resolve the time server names specied 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 425 Configure chronyd at runtime using chronyc SLES 15 SP3chronyd will then not try to poll the server until it is enabled using the following command: root # chronyc online server_address When the auto_offline option is set, chronyd assumes that the time server has gone oine when two requests have been sent to it without receiving a response. This option avoids the need to run the ''oine'' command from chronyc when disconnecting the network link. 31.5 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-specic 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 SOCK - 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 . 426 Setting up a local reference clock SLES 15 SP331.6 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 427 Clock synchronization to an external time reference (ETR) SLES 15 SP332 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 general information about DNS in Section 19.3, “Name resolution”. The following conguration examples refer to BIND, the default DNS server. 32.1 DNS terminology Zone The domain name space 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 master zone, a secondary server for slave zone, or a slave server without any zones for caching. Master zone DNS server The master zone includes all hosts from your network and a DNS server master zone stores up-to-date records for all the hosts in your domain. Slave zone DNS server A slave zone is a copy of the master zone. The slave zone DNS server obtains its zone data with zone transfer operations from its master server. The slave zone DNS server responds authoritatively for the zone as long as it has valid (not expired) zone data. If the slave 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 answer. To enable dierent conguration sources in one conguration, netconfig is used (see also man 8 netconfig ). Record 428 DNS terminology SLES 15 SP3The record is information about name and IP address. Supported records and their syntax are described in BIND documentation. Some 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. 32.2 Installation To install a DNS server, start YaST and select Software Software Management. Choose View Patterns and select DHCP and DNS Server. Conrm the installation of the dependent packages to nish the installation process. Alternatively use the following command on the command line: tux > sudo zypper in -t pattern dhcp_dns_server 32.3 Configuration with YaST Use the YaST DNS module to congure 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 conguration. Use the expert mode to deal with more advanced conguration tasks, such as setting up ACLs, logging, TSIG keys, and other options. 32.3.1 Wizard configuration The wizard consists of three steps or dialogs. At the appropriate places in the dialogs, you can enter the expert conguration mode. 429 Installation SLES 15 SP31. When starting the module for the rst time, the Forwarder Settings dialog, shown in Figure 32.1, “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 conguration—If Custom conguration is selected, Custom policy can be specied; 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 32.1: 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. 430 Wizard configuration SLES 15 SP32. The DNS Zones dialog consists of several parts and is responsible for the management of zone les, described in Section 32.6, “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 (master, slave, or forward). See Figure 32.2, “DNS server installation: DNS zones”. Click Edit to congure other settings of an existing zone. To remove a zone, click Delete. FIGURE 32.2: DNS SERVER INSTALLATION: DNS ZONES 3. In the nal dialog, you can open the DNS port in the rewall 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 32.3, “DNS server installation: finish wizard”. 431 Wizard configuration SLES 15 SP3FIGURE 32.3: DNS SERVER INSTALLATION: FINISH WIZARD 32.3.2 Expert configuration After starting the module, YaST opens a window displaying several conguration options. Completing it results in a DNS server conguration with the basic functions in place: 32.3.2.1 Start-up Under Start-Up, dene 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 rewall with Open Port in Firewall and modify the rewall 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 conguration. 432 Expert configuration SLES 15 SP332.3.2.2 Forwarders If your local DNS server cannot answer a request, it tries to forward the request to a Forwarder, if congured so. This forwarder may be added manually to the Forwarder List. If the forwarder is not static like in dial-up connections, netcong handles the conguration. For more information about netcong, see man 8 netconfig . 32.3.2.3 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. 32.3.2.4 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 dierent 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 extremely large. For this reason, it is not a good idea to enable this option for other than debugging purposes. To log the data trac during zone updates between DHCP and DNS server, enable Log Zone Updates. To log the data trac during a zone transfer from master to slave, enable Log Zone Transfer. See Figure 32.4, “DNS server: logging”. 433 Expert configuration SLES 15 SP3FIGURE 32.4: DNS SERVER: LOGGING 32.3.2.5 ACLs Use this dialog to dene 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 conguration le requires that the address ends with a semicolon and is put into curly braces. 32.3.2.6 TSIG keys The main purpose of TSIGs (transaction signatures) is to secure communications between DHCP and DNS servers. They are described in Section 32.8, “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). Conrm 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, conrm with Add. 434 Expert configuration SLES 15 SP332.3.2.7 DNS zones (adding a slave zone) To add a slave zone, select DNS Zones, choose the zone type Slave, write the name of the new zone, and click Add. In the Zone Editor sub-dialog under Master DNS Server IP, specify the master from which the slave should pull its data. To limit access to the server, select one of the ACLs from the list. 32.3.2.8 DNS zones (adding a master zone) To add a master zone, select DNS Zones, choose the zone type Master, write the name of the new zone, and click Add. When adding a master 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 denition, this should be named 1.168.192.in-addr.arpa . 32.3.2.9 DNS zones (editing a master zone) To edit a master zone, select DNS Zones, select the master 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 32.5, “DNS server: Zone Editor (Basics)”, lets you dene settings for dynamic DNS and access options for zone transfers to clients and slave name servers. To permit the dynamic updating of zones, select Allow Dynamic Updates and the corresponding TSIG key. The key must have been dened before the update action starts. To enable zone transfers, select the corresponding ACLs. ACLs must have been dened already. In the Basics dialog, select whether to enable zone transfers. Use the listed ACLs to dene who can download zones. 435 Expert configuration SLES 15 SP3FIGURE 32.5: DNS SERVER: ZONE EDITOR (BASICS) Zone Editor (NS Records) The NS Records dialog allows you to dene alternative name servers for the zones specied. 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 conrm with Add. See Figure 32.6, “DNS server: Zone Editor (NS Records)”. FIGURE 32.6: DNS SERVER: ZONE EDITOR (NS RECORDS) Zone Editor (MX Records) 436 Expert configuration SLES 15 SP3To add a mail server for the current zone to the existing list, enter the corresponding address and priority value. After doing so, conrm by selecting Add. See Figure 32.7, “DNS server: Zone Editor (MX Records)”. FIGURE 32.7: 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 32.6, “The /var/lib/named/example.com.zone file”. Changing SOA records is not supported for dynamic zones managed via LDAP. 437 Expert configuration SLES 15 SP3FIGURE 32.8: 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. 32.3.2.9.1 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 master 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 conrm with OK. If YaST complains about a non-existing record for a name server, add it in the NS Records tab. 438 Expert configuration SLES 15 SP3FIGURE 32.9: ADDING A RECORD FOR A MASTER ZONE 4. Back in the DNS Zones window, add a reverse master zone. FIGURE 32.10: 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 conrm with OK. 439 Expert configuration SLES 15 SP3FIGURE 32.11: 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. 32.4 Starting the BIND name server On a SUSE® Linux Enterprise Server system, the name server BIND (Berkeley Internet Name Domain) comes precongured, 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 server 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 resolution via the root name server, a notably slower process. Normally, the DNS of the provider should be entered with its IP address in the conguration le /etc/named.conf under 440 Starting the BIND name server SLES 15 SP3forwarders to ensure eective and secure name resolution. If this works so far, the name server runs as a pure caching-only name server. Only when you congure 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 server 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 ocial domain until one is assigned to you by the responsible institution. 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 probably contains 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 actually running. If the name server does not start or behaves unexpectedly, check the output of journalctl -e . To use the name server of the provider (or one already running on your network) as the forwarder, enter the corresponding IP address or addresses in the options section under forwarders . The addresses included in Example  32.1, “Forwarding options in named.conf” are examples only. Adjust these entries to your own setup. EXAMPLE 32.1: 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; }; 441 Starting the BIND name server SLES 15 SP3The options entry is followed by entries for the zone, localhost , and 0.0.127.in- addr.arpa . The type hint entry under “.” should always be present. The corresponding les do not need to be modied 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 conguration 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 . 32.5 The /etc/named.conf configuration file All the settings for the BIND name server itself are stored in the /etc/named.conf le. However, 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 32.2, “A basic /etc/named.conf”. EXAMPLE 32.2: 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"; }; 442 The /etc/named.conf configuration file SLES 15 SP332.5.1 Important configuration options directory " FILENAME "; Species the directory in which BIND can nd the les containing the zone data. Usually, this is /var/lib/named . forwarders { IP-ADDRESS ; }; Species the name servers (mostly of the provider) to which DNS requests should be forwarded 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 rewall congurations. 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 specied 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 rewall 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 ; }; Denes 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 ). allow-transfer ! *;; 443 Important configuration options SLES 15 SP3Controls which hosts can request zone transfers. In the example, such requests are completely denied with ! * . Without this entry, zone transfers can be requested from anywhere without restrictions. statistics-interval 0; In the absence of this entry, BIND generates several lines of statistical information per hour in the system''s journal. Set it to 0 to suppress these statistics completely or set an interval in minutes. cleaning-interval 720; This option denes at which time intervals BIND clears its cache. This triggers an entry in the system''s journal each time it occurs. The time specication 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 dened 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 manual page man 5 named.conf . 32.5.2 Logging What, how, and where logging takes place can be extensively congured in BIND. Normally, the default settings should be sucient. Example 32.3, “Entry to disable logging”, shows the simplest form of such an entry and completely suppresses any logging. EXAMPLE 32.3: ENTRY TO DISABLE LOGGING logging { category default { null; }; }; 444 Logging SLES 15 SP332.5.3 Zone entries EXAMPLE 32.4: 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 32.4, “Zone entry for example.com”. To dene a slave zone, switch the type to slave and specify a name server that administers this zone as master (which, in turn, may be a slave of another master), as shown in Example 32.5, “Zone entry for example.net”. EXAMPLE 32.5: ZONE ENTRY FOR EXAMPLE.NET zone "example.net" in { type slave; file "slave/example.net.zone"; masters { 10.0.0.1; }; }; The zone options: type master; By specifying master , 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 slave; This zone is transferred from another name server. It must be used together with masters . type hint; The zone . of the hint type is used to set the root name servers. This zone denition can be left as is. file example.com.zone or file “slave/example.net.zone”; This entry species the le where zone data for the domain is located. This le is not required for a slave, because this data is pulled from another name server. To dierentiate master and slave les, use the directory slave for the slave les. 445 Zone entries SLES 15 SP3masters { SERVER_IP_ADDRESS ; }; This entry is only needed for slave zones. It species 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 entry —something not normally desirable for security reasons. Without this entry, zone updates are not allowed. The above entry achieves the same because ! * eectively bans any such activity. 32.6 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 nal dot ( . ), the zone is appended. Complete host names specied 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 probably the most frequent cause of name server conguration errors. The rst case to consider is the zone le example.com.zone , responsible for the domain example.com , shown in Example 32.6, “The /var/lib/named/example.com.zone file”. EXAMPLE 32.6: 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 10.0.0.1 446 Zone files SLES 15 SP3dns 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 denes 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. Alternatively, @ 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 master 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@example.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 (slave 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 species the time interval at which the secondary name servers verify the zone serial number . In this case, one day. 5 The retry rate species 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 species the time frame after which a secondary name server discards the cached data if it has not regained contact to the primary server. Here, a week. 447 Zone files SLES 15 SP37 The last entry in the SOA record species the negative caching TTL—the time for which results of unresolved DNS queries from other servers may be cached. 8 The IN NS species 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 species 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 all of them. 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 dierent syntax than IPv4. Because of the fragmentation 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 32.7, “Reverse lookup”. EXAMPLE 32.7: REVERSE LOOKUP $TTL 2D 1 448 Zone files SLES 15 SP3168.192.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 denes the standard TTL that applies to all entries here. 2 The conguration 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 32.6, “The /var/lib/named/example.com.zone file” for detail on the entries within this record. 3 This line species 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 dierent versions of BIND should be possible without any problems. 32.7 Dynamic update of zone data The term dynamic update refers to operations by which entries in the zone les of a master server are added, changed, or deleted. This mechanism is described in RFC 2136. Dynamic update is congured 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. 449 Dynamic update of zone data SLES 15 SP3Transmit the entries to update to the server with the command nsupdate . For the exact syntax of this command, check the manual page for nsupdate ( man  8 nsupdate ). For security reasons, any such update should be performed using TSIG keys as described in Section  32.8, “Secure transactions”. 32.8 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 dierent 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 ): tux > 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 example). 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" 450 Secure transactions SLES 15 SP3Replace 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 conguration les of host2 . Add TSIG keys for any ACLs (access control lists, not to be confused with le system ACLs) that are dened 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 update- policy . 32.9 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 . 451 DNS security SLES 15 SP332.10 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 consulting 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. 452 More information SLES 15 SP333 DHCP The purpose of the Dynamic Host Conguration Protocol (DHCP) is to assign network settings centrally (from a server) rather than conguring them locally on every workstation. A host congured to use DHCP does not have control over its own static address. It is enabled to congure itself completely and automatically according to directions from the server. If you use the NetworkManager on the client side, you do not need to congure 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 autoconguration features. One way to congure 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 congured 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 conguration in general can be implemented centrally by editing the server''s conguration le. This is much more convenient than reconguring numerous 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 dierent networks. In this chapter, the DHCP server will run 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 . 453 SLES 15 SP3A 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. In addition to that, DHCP allows several parameters to be congured in a centralized way, for example, a time server from which clients may poll the current time or even a print server. 33.1 Configuring a DHCP server with YaST To install a DHCP server, start YaST and select Software Software Management. Choose Filter Patterns and select DHCP and DNS Server. Conrm the installation of the dependent packages to nish the installation process. Important: LDAP support The YaST DHCP module can be set up to store the server conguration locally (on the host that runs the DHCP server) or to have its conguration data managed by an LDAP server. To use LDAP, set up your LDAP environment before conguring the DHCP server. For more information about LDAP, see Book “Security and Hardening Guide”, Chapter 6 “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 conguration mode. 33.1.1 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 very basic server conguration that should function in its essential aspects. The expert mode can be used to deal with more advanced conguration 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 33.1, “DHCP server: card selection”. 454 Configuring a DHCP server with YaST SLES 15 SP3Note: DHCP and firewalld Please note that the option Open Firewall for Selected Interfaces does not (yet) support firewalld in SUSE Linux Enterprise Server 15 SP3. To manually open the DHCP port, run tux > sudo firewall-cmd --zone=public --permanent --add-service=dhcp tux > sudo firewall-cmd --reload FIGURE 33.1: 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 33.2, “DHCP server: global settings”. 455 Initial configuration (wizard) SLES 15 SP3FIGURE 33.2: DHCP SERVER: GLOBAL SETTINGS 3. Congure 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 33.3, “DHCP server: dynamic DHCP”. 456 Initial configuration (wizard) SLES 15 SP3FIGURE 33.3: DHCP SERVER: DYNAMIC DHCP 4. Dene 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 conguration of the server. See Figure 33.4, “DHCP server: start-up”. FIGURE 33.4: DHCP SERVER: START-UP 457 Initial configuration (wizard) SLES 15 SP35. Instead of using dynamic DHCP in the way described in the preceding steps, you can also congure 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. Specically, 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 33.5, “DHCP server: host management”. FIGURE 33.5: DHCP SERVER: HOST MANAGEMENT 33.1.2 DHCP server configuration (expert) In addition to the conguration method discussed earlier, there is also an expert conguration mode that allows you to change the DHCP server setup in every detail. Start the expert conguration by clicking DHCP Server Expert Conguration in the Start-Up dialog (see Figure 33.4, “DHCP server: start-up”). Chroot environment and declarations In this rst dialog, make the existing conguration 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 should ever be compromised by an outside attack, the attacker will still be in the chroot jail, which prevents them from accessing the rest of the system. The lower part of the dialog displays 458 DHCP server configuration (expert) SLES 15 SP3a tree view with the declarations that have already been dened. Modify these with Add, Delete, and Edit. Selecting Advanced takes you to additional expert dialogs. See Figure 33.6, “DHCP server: chroot jail and declarations”. After selecting Add, dene the type of declaration to add. With Advanced, view the log le of the server, congure TSIG key management, and adjust the conguration of the rewall according to the setup of the DHCP server. FIGURE 33.6: 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 33.7, “DHCP server: selecting a declaration type”). 459 DHCP server configuration (expert) SLES 15 SP3FIGURE 33.7: 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 33.8: DHCP SERVER: CONFIGURING SUBNETS 460 DHCP server configuration (expert) SLES 15 SP3TSIG key management If you chose to congure dynamic DNS in the previous dialog, you can now congure the key management for a secure zone transfer. Selecting OK takes you to another dialog in which to congure the interface for dynamic DNS (see Figure 33.10, “DHCP server: interface configuration for dynamic DNS”). FIGURE 33.9: 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, dene 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 conguration dialog (see Figure 33.8, “DHCP server: configuring subnets”). Selecting OK again returns to the original expert conguration dialog. 461 DHCP server configuration (expert) SLES 15 SP3FIGURE 33.10: 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 dene the interfaces the DHCP server should listen to and to adjust the rewall conguration, select Advanced Interface Conguration from the expert conguration 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 rewall, adjust the rewall accordingly. Note: DHCP and firewalld Please note that the option Open Firewall for Selected Interfaces does not (yet) support firewalld in SUSE Linux Enterprise Server 15 SP3. To manually open the DHCP port, run tux > sudo firewall-cmd --zone=public --permanent --add-service=dhcp 462 DHCP server configuration (expert) SLES 15 SP3tux > sudo firewall-cmd --reload FIGURE 33.11: DHCP SERVER: NETWORK INTERFACE AND FIREWALL After completing all conguration steps, close the dialog with OK. The server is now started with its new conguration. 33.2 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 conguration 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 means of the conguration les /etc/dhclient.conf and /etc/dhclient6.conf . 463 DHCP software packages SLES 15 SP333.3 The DHCP server dhcpd The core of any DHCP system is the dynamic host conguration protocol daemon. This server leases addresses and watches how they are used, according to the settings dened in the conguration le /etc/dhcpd.conf . By changing the parameters and values in this le, a system administrator can inuence the program''s behavior in numerous ways. Look at the basic sample /etc/dhcpd.conf le in Example 33.1, “The configuration file /etc/dhcpd.conf”. EXAMPLE 33.1: 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 conguration le should be sucient 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 denes 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, some basic network parameters are dened on a global level: The line option domain-name denes 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, congure a name server on your machine or somewhere else in your network before setting up DHCP. That name server should also dene a host name for each dynamic address and vice versa. To learn how to congure your own name server, read Chapter 32, The domain name system. 464 The DHCP server dhcpd SLES 15 SP3The line option broadcast-address denes 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). Usually, 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 denes a network, including a subnet mask. To nish, specify the address range that the DHCP daemon should use to assign IP addresses to interested clients. In Example 33.1, “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 command systemctl start dhcpd . It will be ready for use immediately. Use the command rcdhcpd   check-syntax to perform a brief syntax check. If you encounter any unexpected problems with your conguration (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 17, 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 conguration les must be copied to the chroot environment 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. 33.3.1 Clients with fixed IP addresses DHCP can also be used to assign a predened, static address to a specic client. Addresses assigned 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 addresses available and the server needed to redistribute them among clients. To identify a client congured with a static address, dhcpd uses the hardware address (which is a globally unique, xed numerical code consisting of six octet pairs) for the identication of all network devices (for example, 00:30:6E:08:EC:80 ). If the respective lines, like the ones in 465 Clients with fixed IP addresses SLES 15 SP3Example 33.2, “Additions to the configuration file”, are added to the conguration le of Example 33.1, “The configuration file /etc/dhcpd.conf”, the DHCP daemon always assigns the same set of data to the corresponding client. EXAMPLE 33.2: 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 token- ring , which is often found on IBM systems, is also supported. 33.3.2 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 conguration 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 by means of entries in the le / etc/sysconfig/dhcpd . To run dhcpd without the chroot environment, set the variable DHCPD_RUN_CHROOTED in /etc/sysconfig/dhcpd to “no”. To enable dhcpd to resolve host names even from within the chroot environment, some other conguration les must be copied as well: /etc/localtime /etc/host.conf 466 The SUSE Linux Enterprise Server version SLES 15 SP3/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 modied by scripts like /etc/ppp/ip-up . However, there should be no need to worry about this if the conguration le only species IP addresses (instead of host names). If your conguration 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 daemon, there is an additional entry SYSLOGD_ADDITIONAL_SOCKET_DHCP in the le /etc/sysconfig/ syslog . 33.4 More information More information about DHCP is available at the Web site of the Internet Systems Consortium (https://www.isc.org/dhcp/ ). Information is also available in the dhcpd , dhcpd.conf , dhcpd.leases , and dhcp-options man pages. 467 More information SLES 15 SP334 SLP Conguring 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gure such services on a network client, the “service location protocol” (SLP) was developed. SLP makes the availability and conguration data of selected services known to all clients in the local network. Applications that support SLP can use this information to be congured 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 oer SLP support include cupsd, login, ntp, openldap2- client, postx, 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, if you want to provide services via SLP, check that the openslp-server package is installed. 34.1 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. tux > 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 468 The SLP front-end slptool SLES 15 SP3service:ntp service:ypserv findsrvs SERVICE_TYPE List all servers providing SERVICE_TYPE tux > 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 tux > 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 . 34.2 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 means of 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 . Many 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 469 Providing services via SLP SLES 15 SP3Create 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 Some 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 dierence between this method and the procedure with /etc/slp.reg.d is that all services are grouped within a central le. Dynamic registration with slptool If a service needs to be registered dynamically without the need of conguration les, use the slptool command line utility. The same utility can also be used to deregister an existing service oering without restarting slpd . See Section 34.1, “The SLP front-end slptool” for details. 470 Providing services via SLP SLES 15 SP334.2.1 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 16 “Setting up a network installation source” for instructions. 34.3 More information RFC 2608, 2609, 2610 RFC 2608 generally deals with the denition 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 will nd more information in the Programmers Guide that is included in the openslp-devel package that is provided with the SUSE Software Development Kit. 471 Setting up an SLP installation server SLES 15 SP335 The Apache HTTP server According to the survey from http://www.netcraft.com/ , the Apache HTTP Server (Apache) is the world''s most widely-used Web server. Developed by the Apache Software Foundation (http://www.apache.org/ ), it is available for most operating systems. SUSE® Linux Enterprise Server includes Apache version 2.4. In this chapter, learn how to install, congure and set up a Web server; how to use SSL, CGI, and additional modules; and how to troubleshoot Apache. 35.1 Quick start With this section, quickly set up and start Apache. You must be root to install and congure Apache. 35.1.1 Requirements Make sure the following requirements are met before trying to set up the Apache Web server: 1. The machine''s network is congured properly. For more information about this topic, refer to Chapter 19, 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 31, 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 rewall. For this, congure firewalld to allow the service http in the public zone. See Book “Security and Hardening Guide”, Chapter 25 “Masquerading and firewalls”, Section 25.4.3 “Configuring the firewall on the command line” for details. 472 Quick start SLES 15 SP335.1.2 Installation Apache on SUSE Linux Enterprise Server is not installed by default. To install it with a standard, predened conguration that runs “out of the box”, proceed as follows: PROCEDURE 35.1: INSTALLING APACHE WITH THE DEFAULT CONFIGURATION 1. Start YaST and select Software Software Management. 2. Choose View Patterns and select Web and LAMP Server. 3. Conrm the installation of the dependent packages to nish the installation process. 35.1.3 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.target and graphical.target , execute the following command: tux > sudo systemctl enable apache2 For more information about the systemd targets in SUSE Linux Enterprise Server and a description of the YaST Services Manager, refer to Section 15.4, “Managing services with YaST”. To manually start Apache using the shell, run systemctl start apache2 . PROCEDURE 35.2: 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 35.9, “Troubleshooting”. Now that the Web server is running, you can add your own documents, adjust the conguration according to your needs, or add functionality by installing modules. 473 Installation SLES 15 SP335.2 Configuring Apache SUSE Linux Enterprise Server oers two conguration options: Configuring Apache manually Configuring Apache with YaST Manual conguration oers a higher level of detail, but lacks the convenience of the YaST GUI. Important: Reload or restart Apache after configuration changes Most conguration changes require a reload (some also a restart) of Apache to take eect. Manually reload Apache with systemctl reload apache2 or use one of the restart options as described in Section 35.3, “Starting and stopping Apache”. If you congure Apache with YaST, this can be taken care of automatically if you set HTTP Service to Enabled as described in Section 35.2.3.2, “HTTP server configuration”. 35.2.1 Apache configuration files This section gives an overview of the Apache conguration les. If you use YaST for conguration, you do not need to touch these les—however, the information might be useful for you to switch to manual conguration later on. Apache conguration les can be found in two dierent locations: /etc/sysconfig/apache2 /etc/apache2/ 35.2.1.1 /etc/sysconfig/apache2 /etc/sysconfig/apache2 controls some global settings of Apache, like modules to load, additional conguration les to include, ags with which the server should be started, and ags that should be added to the command line. Every conguration 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 sucient for any conguration needs. 474 Configuring Apache SLES 15 SP335.2.1.2 /etc/apache2/ /etc/apache2/ hosts all conguration les for Apache. In the following, the purpose of each le is explained. Each le includes several conguration options (also called directives). Every conguration option in these les is extensively documented and therefore not mentioned here. The Apache conguration les are organized as follows: /etc/apache2/ | |- charset.conv |- conf.d/ | | | |- *.conf | |- default-server.conf |- errors.conf |- httpd.conf |- listen.conf |- magic |- mime.types |- mod_*.conf |- server-tuning.conf |- ssl.* |- ssl-global.conf |- sysconfig.d | | | |- global.conf | |- include.conf | |- loadmodule.conf . . | |- uid.conf |- vhosts.d | |- *.conf APACHE CONFIGURATION FILES IN /ETC/APACHE2/ charset.conv Species which character sets to use for dierent languages. Do not edit this le. conf.d/*.conf Conguration les added by other modules. These conguration les can be included into your virtual host conguration where needed. See vhosts.d/vhost.template for examples. By doing so, you can provide dierent module sets for dierent virtual hosts. default-server.conf 475 Apache configuration files SLES 15 SP3Global conguration for all virtual hosts with reasonable defaults. Instead of changing the values, overwrite them with a virtual host conguration. errors.conf Denes how Apache responds to errors. To customize these messages for all virtual hosts, edit this le. Otherwise overwrite these directives in your virtual host congurations. httpd.conf The main Apache server conguration le. Avoid changing this le. It primarily contains include statements and global settings. Overwrite global settings in the pertinent conguration les listed here. Change host-specic settings (such as document root) in your virtual host conguration. listen.conf Binds Apache to specic IP addresses and ports. Name-based virtual hosting is also congured here. For details, see Section 35.2.2.1.1, “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 actually 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 Conguration les for the modules that are installed by default. Refer to Section  35.4, “Installing, activating, and configuring modules” for details. Note that conguration les for optional modules reside in the directory conf.d . server-tuning.conf Contains conguration directives for the dierent MPMs (see Section 35.4.4, “Multiprocessing modules”) and general conguration options that control Apache''s performance. Properly test your Web server when making changes here. ssl-global.conf and ssl.* Global SSL conguration and SSL certicate data. Refer to Section 35.6, “Setting up a secure Web server with SSL” for details. sysconfig.d/*.conf 476 Apache configuration files SLES 15 SP3Conguration les automatically generated from /etc/sysconfig/apache2 . Do not change any of these les—edit /etc/sysconfig/apache2 instead. Do not put other conguration les in this directory. uid.conf Species under which user and group ID Apache runs. Do not change this le. vhosts.d/*.conf Your virtual host conguration 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 conguration. Refer to Section 35.2.2.1, “Virtual host configuration” for details. 35.2.2 Configuring Apache manually Conguring Apache manually involves editing plain text conguration les as user root . 35.2.2.1 Virtual host configuration The term virtual host refers to Apache''s ability to serve multiple universal resource identiers (URIs) from the same physical machine. This means that several domains, such as www.example.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 eort (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. To 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 conguration les. Virtual hosts can be congured via YaST as described in Section 35.2.3.1.4, “Virtual hosts” or by manually editing a conguration le. By default, Apache in SUSE Linux Enterprise Server is prepared for one conguration le per virtual host in /etc/apache2/vhosts.d/ . All les in this directory with the extension .conf are automatically included to the conguration. 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). 477 Configuring Apache manually SLES 15 SP3Tip: Always create a virtual host configuration It is recommended to always create a virtual host conguration le, even if your Web server only hosts one domain. By doing so, you not only have the domain-specic conguration in one le, but you can always fall back to a working basic conguration by simply moving, deleting, or renaming the conguration le for the virtual host. For the same reason, you should also create separate conguration les for each virtual host. When using name-based virtual hosts it is recommended to set up a default conguration that will be used when a domain name does not match a virtual host conguration. The default virtual host is the one whose conguration is loaded rst. Since the order of the conguration les is determined by le name, start the le name of the default virtual host conguration 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 particular domain. When Apache receives a client request for a dened virtual host, it uses the directives enclosed in this section. Almost all directives can be used in a virtual host context. See http:// httpd.apache.org/docs/2.4/mod/quickreference.html for further information about Apache''s conguration directives. 35.2.2.1.1 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 specied virtual host is used as a default. The rst step is to create a block for each dierent 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 35.1: 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 478 Configuring Apache manually SLES 15 SP3 ServerName other.example.com DocumentRoot /srv/www/htdocs/otherdomain The opening VirtualHost tag takes the IP address (or fully qualied domain name) as an argument in a name-based virtual host conguration. 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 35.2: NAME-BASED VirtualHost DIRECTIVES ... ... ... ... ... 35.2.2.1.2 IP-based virtual hosts This alternative virtual host conguration requires the setup of multiple IP addresses for a machine. One instance of Apache hosts several domains, each of which is assigned a dierent 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 , hosting two domains on the additional IP addresses 192.168.3.101 and 192.168.3.102 . A separate VirtualHost block is needed for every virtual server. 479 Configuring Apache manually SLES 15 SP3EXAMPLE 35.3: IP-BASED VirtualHost DIRECTIVES ... ... Here, VirtualHost directives are only specied for interfaces other than 192.168.3.100 . When a Listen directive is also congured 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 conguration ( /etc/apache2/default-server.conf ) are applied. 35.2.2.1.3 Basic virtual host configuration At least the following directives should be in each virtual host conguration to set up a virtual host. See /etc/apache2/vhosts.d/vhost.template for more options. ServerName The fully qualied 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 reasons, 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 debugging of errors much easier. /var/log/apache2/ is the default directory for Apache''s log les. CustomLog 480 Configuring Apache manually SLES 15 SP3The 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. The complete conguration le looks like this: EXAMPLE 35.4: 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 481 Configuring Apache manually SLES 15 SP335.2.3 Configuring Apache with YaST To congure 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 nished the wizard, the HTTP Server Conguration dialog starts each time you call the HTTP Server module. For more information, see Section 35.2.3.2, “HTTP server configuration”. 35.2.3.1 HTTP server wizard The HTTP Server Wizard consists of ve steps. In the last step of the dialog, you may enter the expert conguration mode to make even more specic settings. 35.2.3.1.1 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 . Check Open Port In Firewall to open the ports in the rewall 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 conguration. 35.2.3.1.2 Modules The Modules conguration 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 35.2.3.2.2, “Server modules”. Click Next to advance to the next dialog. 482 Configuring Apache with YaST SLES 15 SP335.2.3.1.3 Default host This option pertains to the default Web server. As explained in Section  35.2.2.1, “Virtual host configuration”, Apache can serve multiple virtual hosts from a single physical machine. The rst declared virtual host in the conguration le is commonly called the default host. Each virtual host inherits the default host''s conguration. 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. FIGURE 35.1: 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. 483 Configuring Apache with YaST SLES 15 SP3ScriptAlias Similar to the Alias directive, the ScriptAlias directive maps a URL to a le system location. The dierence 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 conguration options that will only apply to the specied directory. Access and display options for the directories /srv/www/htdocs , /usr/share/apache2/ icons and /srv/www/cgi-bin are congured here. It should not be necessary to change the defaults. Include With include, additional conguration les can be specied. Two Include directives are already precongured: /etc/apache2/conf.d/ is the directory containing the conguration les that come with external modules. With this directive, all les in this directory ending in .conf are included. With the second directive, /etc/apache2/ conf.d/apache2-manual.conf , the apache2-manual conguration le is included. Server Name This species the default URL used by clients to contact the Web server. Use a fully qualied 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 nishing with the Default Host step, click Next to continue with the conguration. 35.2.3.1.4 Virtual hosts In this step, the wizard displays a list of already congured virtual hosts (see Section 35.2.2.1, “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 identied (name based or IP based). Specify the name or IP address with Change Virtual Host ID 484 Configuring Apache with YaST SLES 15 SP3Clicking Next advances to the second part of the virtual host conguration dialog. In part two of the virtual host conguration 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 certicate as well. See Section 35.6.2, “Configuring Apache with SSL” for details on SSL and certicates. 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 names (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.example.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. 35.2.3.1.5 Summary This is the nal 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 conguration made so far. If you are satised with your settings, click Finish to complete conguration. To change something, click Back until you have reached the desired dialog. Clicking HTTP Server Expert Conguration opens the dialog described in Section 35.2.3.2, “HTTP server configuration”. 485 Configuring Apache with YaST SLES 15 SP3FIGURE 35.2: HTTP SERVER WIZARD: SUMMARY 35.2.3.2 HTTP server configuration The HTTP Server Conguration dialog also lets you make even more adjustments to the conguration than the wizard (which only runs if you congure your Web server for the rst time). It consists of four tabs described in the following. No conguration option you change here is eective immediately—you always must conrm your changes with Finish to make them eective. Clicking Abort leaves the conguration module and discards your changes. 35.2.3.2.1 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. 486 Configuring Apache with YaST SLES 15 SP3With Log Files, watch either the access log le or the error log le. This is useful if you want to test your conguration. The log le opens in a separate window from which you can also restart or reload the Web server. For details, see Section 35.3, “Starting and stopping Apache”. These commands are eective immediately and their log messages are also displayed immediately. FIGURE 35.3: HTTP SERVER CONFIGURATION: LISTEN PORTS AND ADDRESSES 35.2.3.2.2 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 35.4, “Installing, activating, and configuring modules”. 487 Configuring Apache with YaST SLES 15 SP3FIGURE 35.4: HTTP SERVER CONFIGURATION: SERVER MODULES 35.2.3.2.3 Main host or hosts These dialogs are identical to the ones already described. Refer to Section 35.2.3.1.3, “Default host” and Section 35.2.3.1.4, “Virtual hosts”. 35.3 Starting and stopping Apache If congured with YaST as described in Section 35.2.3, “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 15.2.1, “Managing services in a running system”. systemctl status apache2 Checks if Apache is started. 488 Starting and stopping Apache SLES 15 SP3systemctl start apache2 Starts Apache if it is not already running. systemctl stop apache2 Stops Apache by terminating the parent process. systemctl restart apache2 Stops and then restarts Apache. Starts the Web server if it was not running before. systemctl try-restart apache2 Stops then restarts Apache only if it is already running. systemctl reload apache2 Stops the Web server by advising all forked Apache processes to rst nish 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 conguration without causing connection break-os. systemctl stop apache2 Stops the Web server after a dened period of time congured with GracefulShutdownTimeout to ensure that existing requests can be nished. apachectl configtest Checks the syntax of the conguration les without aecting a running Web server. Because 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 conguration 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. In addition to that, STATUS must be added to APACHE_SERVER_FLAGS in the le /etc/sysconfig/ apache2 . 489 Starting and stopping Apache SLES 15 SP3Tip: Additional flags If you specify additional ags to the commands, these are passed through to the Web server. 35.4 Installing, activating, and configuring modules The Apache software is built in a modular fashion: all functionality except some 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 35.4.2, “Activation and deactivation” for details of how to load modules dynamically. Apache modules can be divided into four dierent 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 In general, 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 ocial 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. 490 Installing, activating, and configuring modules SLES 15 SP335.4.1 Module installation If you have done a default installation as described in Section 35.1.2, “Installation”, the following modules are already installed: all base and extension modules, the multiprocessing module Prefork 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. 35.4.2 Activation and deactivation Activate or deactivate particular modules either manually or with YaST. In YaST, script language modules (PHP 5 and Python) need to be enabled or disabled with the module conguration described in Section 35.2.3.1, “HTTP server wizard”. All other modules can be enabled or disabled as described in Section 35.2.3.2.2, “Server modules”. If you prefer to activate or deactivate the modules manually, use the commands a2enmod MODULE or a2dismod MODULE , respectively. a2enmod -l outputs a list of all currently active modules. Important: Including configuration files for external modules If you have activated external modules manually, make sure to load their conguration les in all virtual host congurations. Conguration les for external modules are located under /etc/apache2/conf.d/ and are loaded in /etc/apache2/default- server.conf by default. For more ne-grained control you can comment out the inclusion in /etc/apache2/default-server.conf and add it to specic virtual hosts only. See /etc/apache2/vhosts.d/vhost.template for examples. 35.4.3 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.apache.org/ docs/2.4/mod/ to learn details about each module. mod_actions 491 Module installation SLES 15 SP3Provides methods to execute a script whenever a certain MIME type (such as application/pdf ), a le with a specic 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 specic directory ( Alias ) or redirect a requested URL to another location. This module is enabled by default. mod_auth* The authentication modules provide dierent authentication methods: basic authentication 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 authentication) and with an authorization module mod_authz_* (for example, mod_authz_user for user authorization). More information about this topic is available in the Authentication HOWTO at http:// httpd.apache.org/docs/2.4/howto/auth.html . mod_auth_openidc mod_auth_openidc the only certied way to use OpenID Connect with the Apache HTTP server. (See https://openid.net/developers/certified/ .) mod_autoindex Autoindex generates directory listings when no index le (for example, index.html ) is present. The look and feel of these indexes is congurable. This module is enabled by default. However, directory listings are disabled by default via the Options directive— overwrite this setting in your virtual host conguration. The default conguration 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 congured to compress given le types on the y before delivering them. mod_dir 492 Base and extension modules SLES 15 SP3mod_dir provides the DirectoryIndex directive with which you can congure 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 conguration under http://localhost/ 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 congured at /etc/apache2/ mod_info.conf . mod_log_config With this module, you can congure 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. mod_negotiation Necessary for content negotiation. See http://httpd.apache.org/docs/2.4/content- negotiation.html for more information. This module is enabled by default. 493 Base and extension modules SLES 15 SP3mod_rewrite Provides the functionality of mod_alias , but oers more features and exibility. 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 35.6, “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/server- 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 congured at /etc/apache2/ mod_status.conf . mod_suexec mod_suexec lets you run CGI scripts under a dierent user and group. This module is enabled by default. mod_userdir Enables user-specic directories available under ~USER/ . The UserDir directive must be specied in the conguration. This module is enabled by default. 35.4.4 Multiprocessing modules SUSE Linux Enterprise Server provides two dierent multiprocessing modules (MPMs) for use with Apache: Prefork MPM Worker MPM 494 Multiprocessing modules SLES 15 SP335.4.4.1 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 aect 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. 35.4.4.2 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 aected. 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. Warning: Using PHP modules with MPMs Not all available PHP modules are thread-safe. Using the worker MPM with mod_php is strongly discouraged. 495 Multiprocessing modules SLES 15 SP335.4.5 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 connement to individual CGI scripts handled by modules like mod_php5 . Package Name: apache2-mod_apparmor More Information: Book “Security and Hardening Guide” mod_php5 PHP is a server-side, cross-platform HTML embedded scripting language. Package Name: apache2-mod_php5 Conguration File: /etc/apache2/conf.d/php5.conf More Information: /usr/share/doc/packages/apache2-mod_php5 mod_python mod_python allows embedding Python within the Apache HTTP server for a considerable boost in performance and added exibility 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 rewall to protect Web applications from a range of attacks. It also enables HTTP trac monitoring and real-time analysis. Package Name: apache2-mod_security2 Conguration File: /etc/apache2/conf.d/mod_security2.conf More Information: /usr/share/doc/packages/apache2-mod_security2 Documentation: http://modsecurity.org/documentation/ 496 External modules SLES 15 SP335.4.6 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 conguration 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 location 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: tux > sudo cd /path/to/module/source tux > 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. 35.5 Enabling CGI scripts Apache''s Common Gateway Interface (CGI) lets you create dynamic content with programs or scripts usually called CGI scripts. CGI scripts can be written in any programming language. Usually, script languages such as PHP are used. 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 35.4.2, “Activation and deactivation” for details on activating modules. 497 Compilation SLES 15 SP3Warning: CGI security Allowing the server to execute CGI scripts is a potential security hole. Refer to Section 35.8, “Avoiding security problems” for additional information. 35.5.1 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 congured to execute CGI scripts. If you have created a virtual host conguration (see Section 35.2.2.1, “Virtual host configuration”) and want to place your scripts in a host-specic directory, you must unlock and congure this directory. EXAMPLE 35.5: 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 specied directory without limitation. For more information on authentication and authorization, see http://httpd.apache.org/docs/2.4/howto/auth.html . 35.5.2 Running an example script CGI programming diers 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 usually, or plain text or images, for example. 498 Apache configuration SLES 15 SP3A simple test script available under /usr/share/doc/packages/apache2/test-cgi is part of the Apache package. It outputs the content of some 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 35.8, “Avoiding security problems”. Because the Web server runs with a dierent 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”. 35.5.3 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 conguration? If not, reload with systemctl reload apache2 . If you have congured your custom CGI directory, is it congured 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. 499 CGI troubleshooting SLES 15 SP335.6 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 certicate 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 certicate 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 eect of using mod_ssl with Apache is that URLs are prexed with https:// instead of http:// . 35.6.1 Creating an SSL certificate To use TLS/SSL with the Web server, you need to create an SSL certicate. This certicate is needed for the authorization between Web server and client, so that each party can clearly identify the other party. To ensure the integrity of the certicate, it must be signed by a party every user trusts. There are three types of certicates you can create: a “dummy” certicate for testing purposes only, a self-signed certicate for a dened circle of users that trust you, and a certicate signed by an independent, publicly-known certicate authority (CA). Creating a certicate is a two step process. First, a private key for the certicate authority is generated then the server certicate is signed with this key. Tip: More information To learn more about concepts and denitions of TLS/SSL, refer to http://httpd.apache.org/ docs/2.4/ssl/ssl_intro.html . 500 Setting up a secure Web server with SSL SLES 15 SP335.6.1.1 Creating a “dummy” certificate To generate a dummy certicate, call the script /usr/bin/gensslcert . It creates or overwrites the les listed below. Use gensslcert ''s optional switches to ne-tune the certicate. 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 dummy certicate should never be used on a production system. Only use it for testing purposes. 35.6.1.2 Creating a self-signed certificate If you are setting up a secure Web server for an intranet or for a dened circle of users, it is probably sucient if you sign a certicate with your own certicate authority (CA). Note that visitors to such a site will see a warning like “this is an untrusted site”, as Web browsers do not recognize self-signed certicates. Important: Self-signed certificates Only use a self-signed certicate on a Web server that is accessed by people who know and trust you as a certicate authority. It is not recommended to use such a certicate for a public shop, for example. First you need to generate a certicate signing request (CSR). You are going to use openssl , with PEM as the certicate 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. tux > sudo openssl req -new > new.cert.csr Generating a 1024 bit RSA private key ..++++++ 501 Creating an SSL certificate SLES 15 SP3.........++++++ 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 will 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 certicate. You are going to use openssl again, and the format of the certicate is the default PEM . 502 Creating an SSL certificate SLES 15 SP3PROCEDURE 35.3: 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 certicate signing request (CSR). tux > sudo openssl rsa -in privkey.pem -out new.cert.key 2. Generate the public part of the certicate according to the information you lled out in the signing request. The -days option species the length of time before the certicate expires. You can revoke a certicate, or replace one before it expires. tux > sudo openssl x509 -in new.cert.csr -out new.cert.cert -req \ -signkey new.cert.key -days 365 3. Copy the certicate 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 certicate /etc/apache2/ssl.crt/server.crt is. tux > sudo cp new.cert.cert /etc/apache2/ssl.crt/server.crt tux > sudo cp new.cert.key /etc/apache2/ssl.key/server.key Tip: Public certificate location The last step is to copy the public certicate le from /etc/apache2/ssl.crt/ server.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 certicate was issued by an unknown authority. 35.6.1.3 Getting an officially signed certificate There are several ocial certicate authorities that sign your certicates. The certicate is signed by a trustworthy third party, so can be fully trusted. Publicly operating secure Web servers usually have an ocially signed certicate. A list of the most used Certicate Authorities (CAs) is available at https://en.wikipedia.org/wiki/Certificate_authority#Providers . When requesting an ocially signed certicate, you do not send a certicate to the CA. Instead, issue a Certicate Signing Request (CSR). To create a CSR, run the following command: tux > openssl req -new -newkey rsa:2048 -nodes -keyout newkey.pem -out newreq.pem 503 Creating an SSL certificate SLES 15 SP3You 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 certicate 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 signicant 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 . 35.6.2 Configuring Apache with SSL The default port for TLS/SSL requests on the Web server side is 443. There is no conict 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 rewall for SSL-enabled Apache on port 443. This can be done with firewalld as described in Book “Security and Hardening Guide”, Chapter 25 “Masquerading and firewalls”, Section 25.4.3 “Configuring the firewall on the command line”. The SSL module is enabled by default in the global server conguration. In case it has been disabled on your host, activate it with the following command: a2enmod ssl . To nally 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 certicate 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 sucient. The virtual host conguration directory contains a template /etc/apache2/vhosts.d/ vhost-ssl.template with SSL-specic directives that are extensively documented. Refer to Section 35.2.2.1, “Virtual host configuration” for the general virtual host conguration. 504 Configuring Apache with SSL SLES 15 SP3To 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 sucient: DocumentRoot ServerName ServerAdmin ErrorLog TransferLog 35.6.2.1 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 certicate 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 certicate. SNI is enabled by default on SUSE Linux Enterprise Server. To enable Name-Based Virtual Hosts for SSL, congure the server as described in Section 35.2.2.1.1, “Name-based virtual hosts” (note that 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.wikipedia.org/wiki/Server_Name_Indication#Support . To congure handling of non-SNI capable browsers, use the directive SSLStrictSNIVHostCheck . When set to on in the server conguration, 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. 505 Configuring Apache with SSL SLES 15 SP3When set to off in the server conguration, the server will behave as if not having SNI support. SSL requests will be handled by the rst virtual host dened (for port 443). 35.7 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 35.2.2.1, “Virtual host configuration”): When a virtual host needs to be disabled for some time, you need to change the Web server conguration and restart it so that the change takes eect. In case of problems with one virtual host, you need to restart all of them. You can run the default Apache instance as usual: tux > sudo systemctl start apache2 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: tux > sudo systemctl start apache2@INSTANCE_NAME For example: tux > sudo systemctl start apache2@example_web.org By default, the instance uses /etc/apache2@example_web.org/httpd.conf as a main conguration le, which can be overwritten by setting APACHE_HTTPD_CONF in /etc/ sysconfig/apache2@example_web.org . An example to set up an additional instance of Apache follows. Note that you need to execute all the commands as root . 506 Running multiple Apache instances on the same server SLES 15 SP3PROCEDURE 35.4: CONFIGURING AN ADDITIONAL APACHE INSTANCE 1. Create a new conguration le based on /etc/sysconfig/apache2 , for example /etc/ sysconfig/apache2@example_web.org : tux > 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 containing 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 . tux > 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 will probably 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. 507 Running multiple Apache instances on the same server SLES 15 SP35. Create /etc/apache2/listen@example_web.org.conf based on /etc/apache2/ listen.conf . tux > 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 35.6, “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: tux > 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: tux > 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 specied otherwise with the HTTPD_INSTANCE environment variable. The following example tux > sudo export HTTPD_INSTANCE=example_web.org 508 Running multiple Apache instances on the same server SLES 15 SP3tux > sudo a2enmod access_compat tux > sudo a2enmod status tux > 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. 35.8 Avoiding security problems A Web server exposed to the public Internet requires an ongoing administrative eort. It is inevitable that security issues appear, both related to the software and to accidental misconguration. Here are some tips for how to deal with them. 35.8.1 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 xing 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.opensuse.org/ List of security announcements. https://www.suse.com/support/update/ 35.8.2 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 . 509 Avoiding security problems SLES 15 SP335.8.3 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 specically enable access to all directories Apache should be able to read. For details, see Section 35.2.2.1.3, “Basic virtual host configuration”. In doing so, ensure that no critical les, such as password or system conguration les, can be read from the outside. 35.8.4 CGI scripts Interactive scripts in PHP, SSI, or any other programming language can essentially 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 specic directories instead of globally allowing them. The directives ScriptAlias and Option ExecCGI are used for conguration. The SUSE Linux Enterprise Server default conguration does not allow execution of CGI scripts from everywhere. All CGI scripts run as the same user, so dierent scripts can potentially conict with each other. The module suEXEC lets you run CGI scripts under a dierent user and group. 35.8.5 User directories When enabling user directories (with mod_userdir or mod_rewrite ) you should strongly consider 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 allowed to overwrite any Option directives when using mod_userdir (see the /etc/apache2/ mod_userdir.conf conguration le). 510 File system access SLES 15 SP335.9 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 some 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  35.3, “Starting and stopping Apache”). systemctl status apache2 is verbose about errors, and it even provides tips and hints for xing conguration 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 . 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 rewall conguration of the server. If you congure Apache with YaST, there is a separate option available to take care of this specic issue (see Section 35.2.3, “Configuring Apache with YaST”). If you are conguring Apache manually, open rewall ports for HTTP and HTTPS via YaST''s rewall module. If the error cannot be tracked down with any of these, check the online Apache bug database at http://httpd.apache.org/bug_report.html . Additionally, the Apache user community can be reached via a mailing list available at http://httpd.apache.org/userslist.html . 511 Troubleshooting SLES 15 SP335.10 More information The package apache2-doc contains the complete Apache manual in various 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 http:// httpd.apache.org/docs-2.4/ . SUSE-specic conguration hints are available in the directory / usr/share/doc/packages/apache2/README.* . 35.10.1 Apache 2.4 For a list of new features in Apache 2.4, refer to http://httpd.apache.org/docs/2.4/ new_features_2_4.html . Information about upgrading from version 2.2 to 2.4 is available at http://httpd.apache.org/docs-2.4/upgrading.html . 35.10.2 Apache modules More information about external Apache modules that are briey described in Section 35.4.5, “External modules” is available at the following locations: mod_apparmor https://en.opensuse.org/SDB:AppArmor mod_php5 http://www.php.net/manual/en/install.unix.apache2.php mod_python http://www.modpython.org/ mod_security http://modsecurity.org/ 35.10.3 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 512 More information SLES 15 SP3http://httpd.apache.org/dev/ Apache developer documentation http://httpd.apache.org/docs/2.4/developer/ 35.10.4 Miscellaneous sources If you experience diculties specic 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. 513 Miscellaneous sources SLES 15 SP336 Setting up an FTP server with YaST Using the YaST FTP Server module, you can congure 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 conguration, 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 congure 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 will be asked which server to install when the YaST FTP Server module starts. Choose the vsftpd server and conrm the dialog. 3. In the Start-Up dialog, congure the options for starting of the FTP server. For more information, see Section 36.1, “Starting the FTP server”. In the General dialog, congure FTP directories, welcome message, le creation masks and other parameters. For more information, see Section 36.2, “FTP general settings”. In the Performance dialog, set the parameters that aect the load on the FTP server. For more information, see Section 36.3, “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 36.4, “Authentication”. In the Expert Settings dialog, congure the operation mode of the FTP server, SSL connections and rewall settings. For more information, see Section 36.5, “Expert settings”. 4. Click Finish to save the congurations. 514 SLES 15 SP336.1 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 congurations will be saved by leaving the conguration module with Finish. FIGURE 36.1: FTP SERVER CONFIGURATION — START-UP 36.2 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 will be 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. 515 Starting the FTP server SLES 15 SP3If 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 . Note that vsftpd does not allow this directory to be writable for all users. The subdirectory upload with write permissions for anonymous users is created instead. 36.3 FTP performance settings In the Performance dialog set the parameters which aect 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 which can be connected from a single IP address. Max Clients determines the maximum number of clients which may be connected. Any additional clients will get an error message. 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. 36.4 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. 516 FTP performance settings SLES 15 SP3Note: 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. 36.5 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. Check the versions of the protocol to be supported and specify the RSA certicate to be used for SSL encrypted connections. If your system is protected by a rewall, check Open Port in Firewall to enable a connection to the FTP server. 36.6 More information For more information about the FTP server read the manual pages of vsftpd and vsftpd.conf . 517 Expert settings SLES 15 SP337 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 trac. Along with actual caching, Squid oers a wide range of features: Distributing load over intercommunicating hierarchies of proxy servers Dening strict access control lists for all clients accessing the proxy server Allowing or denying access to specic Web pages using other applications Generating statistics about frequently-visited Web pages for the assessment of surng 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 dierent caches, many multimedia programs are not supported. 37.1 Some facts about proxy servers As a caching proxy server, Squid can be used in several ways. When combined with a rewall, 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. 518 Some facts about proxy servers SLES 15 SP337.1.1 Squid and security It is possible to use Squid together with a rewall to secure internal networks from the outside. The rewall denies all clients access to external services except Squid. All Web connections must be established by the proxy server. With this conguration, Squid completely controls Web access. If the rewall conguration includes a demilitarized zone (DMZ), the proxy server should operate within this zone. Section 37.6, “Configuring a transparent proxy” describes how to implement a transparent proxy. This simplies the conguration of the clients, because in this case, they do not need any information about the proxy server. 37.1.2 Multiple caches Several instances of Squid can be congured 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 congure 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 very important, because it is not desirable to increase the overall trac on the network. For a very large network, it would make sense to congure 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 protocol) 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. 519 Squid and security SLES 15 SP3Note: How Squid avoids duplication of objects To avoid duplication of objects in dierent 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 nding the desired object. 37.1.3 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 modied” 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. 37.2 System requirements System requirements largely depend on the maximum network load that the system must bear. Therefore, 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 signicance: 1. RAM size 2. CPU speed/physical CPU cores 3. Size of the disk cache 4. Hard disks/SSDs and their architecture 520 Caching Internet objects SLES 15 SP337.2.1 RAM The amount of memory (RAM) required by Squid directly correlates with the number of objects in the cache. Random access memory is much faster than a hard disk/SSD. Therefore, it is very important to have sucient 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. In addition to 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. 37.2.2 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 dierent caching devices. By default, multi-core support is mostly disabled. 37.2.3 Size of the disk cache In a small cache, the probability of a HIT (nding 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 surng, 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 trac ended up in the cache, in one hour it would add up to 460 MB. Assuming that all this trac 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. 521 RAM SLES 15 SP337.2.4 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 important 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. File system choice is usually not decisive. However, using the mount option noatime can improve performance—Squid provides its own time stamps and thus does not need the le system to track access times. 37.3 Basic usage of Squid If not already installed, install the package squid . squid is not among the packages installed by default on SUSE® Linux Enterprise Server. Squid is already precongured in SUSE Linux Enterprise Server, you can start it directly after the installation. To ensure a smooth start-up, the network should be congured in a way that at least one name server and the Internet can be reached. Problems can arise if a dial-up connection is used with a dynamic DNS conguration. In this case, at least the name server should be specied, because Squid does not start if it does not detect a DNS server in /var/ run/netconfig/resolv.conf . 37.3.1 Starting Squid To start Squid, use: tux > sudo systemctl start squid If you want Squid to start when the system boots up, enable the service with systemctl enable squid . 522 Hard disk/SSD architecture SLES 15 SP337.3.2 Checking whether Squid is working To check whether Squid is running, choose one of the following ways: Using systemctl : tux > systemctl status squid The output of this command should indicate that Squid is loaded and active (running) . Using Squid itself: tux > sudo squid -k check | echo $? The output of this command should be 0 , but may contain additional warnings or messages. To test the functionality of Squid on the local system, choose one of the following ways: To test, you can use squidclient , a command-line tool that can output the response to a Web request, similar to wget or curl . Unlike those tools, squidclient will automatically connect to the default proxy setup of Squid, localhost:3128 . However, if you changed the conguration of Squid, you need to congure squidclient to use dierent settings using command line options. For more information, see squidclient --help . EXAMPLE 37.1: A REQUEST WITH squidclient tux > 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 523 Checking whether Squid is working SLES 15 SP3 [...] The output shown in Example 37.1, “A request with squidclient” can be split into 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 tells you that the requested document was not in the Squid cache ( MISS ) of the computer moon . The example above contains two X-Cache lines. You can ignore the rst X- Cache header. It is produced by the internal caching software of the originating Web server. 2 The value of the header Via tells you 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. You can 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 37.1, “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 conguration les /etc/squid/squid.conf from http_access deny all to http_access allow all . However, in doing so, consider that Squid is made completely accessible to anyone by this action. Therefore, dene ACLs (access control lists) that control access to the proxy server. After modifying the conguration le, Squid must be reloaded or restarted. For more information on ACLs, see Section 37.5.2, “Options for access controls”. If Squid quits after a short period of time even though it was started successfully, check whether there is a faulty 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 . 524 Checking whether Squid is working SLES 15 SP337.3.3 Stopping, reloading, and restarting Squid To reload Squid, choose one of the following ways: Using systemctl : tux > sudo systemctl reload squid or tux > sudo systemctl restart squid Using YaST: In the Squid module, click the Save Settings and Restart Squid Now button. To stop Squid, choose one of the following ways: Using systemctl : tux > 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. 37.3.4 Removing Squid Removing Squid from the system does not remove the cache hierarchy and log les. To remove these, delete the /var/cache/squid directory manually. 525 Stopping, reloading, and restarting Squid SLES 15 SP337.3.5 Local DNS server Setting up a local DNS server makes sense even if it does not manage its own domain. It then simply acts as a caching-only name server and is also able to resolve DNS requests via the root name servers without requiring any special conguration (see Section 32.4, “Starting the BIND name server”). How this can be done depends on whether you chose dynamic DNS during the conguration of the Internet connection. Dynamic DNS Normally, with dynamic DNS, the DNS server is set by the provider during the establishment of the Internet connection and the local /var/run/netconfig/ resolv.conf le is adjusted automatically. This behavior is controlled in the /etc/ sysconfig/network/config le with the NETCONFIG_DNS_POLICY syscong variable. Set NETCONFIG_DNS_POLICY to "" with the YaST syscong 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 conguration le /etc/ named.conf under forwarders along with its IP address. With dynamic DNS, this can be achieved automatically when establishing the connection by setting the syscong 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 syscong 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 specied manually in the /etc/ named.conf le under forwarders along with its IP address. Tip: DNS and firewall If you have a rewall running, make sure DNS requests can pass it. 526 Local DNS server SLES 15 SP337.4 The YaST Squid module The YaST Squid module contains the following tabs: Start-Up Species how Squid is started and which Firewall port is open on which interfaces. HTTP Ports Dene all ports where Squid will listen for HTTP requests from clients. Refresh Patterns Denes how Squid treats objects in the cache. Cache Settings Denes settings in regard to cache memory, maximum and minimum object size, and more. Cache Directory Denes the top-level directory where Squid stores all cache swap les. Access Control Controls the access to the Squid server via ACL groups. Logging and Timeout Dene paths to access, cache, and cache store log les in addition with connection timeouts and client lifetime. Miscellaneous Sets language and mail address of administrator. 37.5 The Squid configuration file All Squid proxy server settings are made in the /etc/squid/squid.conf le. To start Squid for the rst time, no changes are necessary in this le, but external clients are initially denied access. The proxy is available for localhost . The default port is 3128 . The preinstalled conguration le /etc/squid/squid.conf provides detailed information about the options and many examples. Many entries are commented and therefore begin with the comment character # . The relevant specications 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 527 The YaST Squid module SLES 15 SP3has no eect. If possible, leave the commented lines as they are and insert the options along with the modied 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 modied. Therefore, if you try to use the old squid.conf , Squid might stop working properly. 37.5.1 General configuration options The following is a list of a selection of conguration options for Squid. It is not exhaustive. The Squid package contains a full, lightly documented list of options in /etc/squid/ squid.conf.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 specied 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 PROXY_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 like a proxy server, prohibit the use of the ICP protocol. You can do so by appending the options default and no-query . cache_mem SIZE This option denes the amount of memory Squid can use for very popular replies. The default is 8 MB . This does not specify the memory usage of Squid and may be exceeded. cache_dir STORAGE_TYPE CACHE_DIRECTORY CACHE_SIZE LEVEL_1_DIRECTORIES LEVEL_2_DIRECTORIES 528 General configuration options SLES 15 SP3The option cache_dir denes the directory for the disk cache. In the default conguration 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 variations 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 will be discussed. rock has somewhat dierent 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 nal two values, LEVEL_1_DIRECTORIES and LEVEL_2_DIRECTORIES specify how many subdirectories 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 burdened by heavy usage, 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 . ftp_user E-MAIL This option allows setting the password that Squid should use for anonymous FTP login. Specify a valid e-mail address here, because some FTP servers check these for validity. cache_mgr E-MAIL 529 General configuration options SLES 15 SP3If it unexpectedly crashes, Squid sends a message to this e-mail address. The default is webmaster. logfile_rotate VALUE If you run squid   -k rotate , squid can rotate log les. The les are numbered in this process and, after reaching the specied 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 conguration 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 specied here, so specifying www in the browser accesses 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 set, Squid will cache some types of failures, such as 404 responses. It will then refuse to issue new requests, even if the resource would be available then. 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. never_direct allow ACL_NAME To prevent Squid from taking requests directly from the Internet, use the option never_direct to force connection to another proxy server. This must have previously been specied in cache_peer . If all is specied 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 rewall direct Internet access. 530 General configuration options SLES 15 SP337.5.2 Options for access controls Squid provides a detailed system for controlling the access to the proxy server. These Access Control Lists (ACL) are lists with rules that are processed sequentially. ACLs must be dened before they can be used. Some default ACLs, such as all and localhost , already exist. However, the mere denition of an ACL does not mean that it is actually applied. This only happens when there is 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: The name ACL_NAME can be chosen arbitrarily. For TYPE , select from a variety of dierent options which can be found in the ACCESS CONTROLS section in the /etc/squid/squid.conf le. The specication for DATA depends on the individual ACL type, for example host names, IP addresses, or URLs, and can also be read from a le. 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 http://www.squid- cache.org/Versions/v3/3.5/cfgman/acl.html . EXAMPLE 37.2: 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 denes mysurfers as all users coming from within .example.com (as determined by a reverse lookup for the IP). 2 This ACL denes teachers as the users of computers with IP addresses starting with 192.168.1. . 3 This ACL denes students as the users of the computer with IP addresses starting with 192.168.7. , 192.168.8. , or 192.168.9. . 531 Options for access controls SLES 15 SP34 This ACL denes lunch as a time on the days Monday through Friday between noon and 3 p.m. http_access allow ACL_NAME http_access denes who is allowed to use the proxy server and who can access what on the Internet. For this, ACLs must be dened. localhost and all have already been dened above for which you can deny or allow access 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 completely: http_access allow localhost http_access deny all In another example using these rules, the group teachers always has access to the Internet. 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 readability, within the conguration le /etc/squid/squid.conf , specify all http_access options as a block. url_rewrite_program PATH With this option, 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 sees a login window in which they need to specify a user name and a password. In addition, you need an ACL, so only clients with a valid login can use the Internet: acl password proxy_auth REQUIRED http_access allow password http_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. 532 Options for access controls SLES 15 SP3ident_lookup_access allow ACL_NAME With this option, have an ident request run to nd each user''s identity for all clients dened by an ACL of the type src . Alternatively, use this for all clients, apply the predened ACL all as the ACL_NAME . All clients covered by ident_lookup_access must run an ident daemon. On Linux, you can use pidentd (package pidentd ) as the ident daemon. For other operating systems, free software is usually available. To ensure that only clients with a successful ident lookup are permitted, dene a corresponding ACL: acl identhosts ident REQUIRED http_access allow identhosts http_access deny all In the acl identhosts ident option, using REQUIRED means 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. 37.6 Configuring a transparent proxy A transparent proxy intercepts and answers the requests of the Web browser, so the Web browser receives the requested pages without knowing where they are coming from. As the name indicates, the entire process is transparent to the user. The usual 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 some cases the transparent proxy mode of Squid makes sense: If, for security reasons, it is recommended that all clients use a proxy server to surf the Internet. If all clients must use a proxy server, regardless of whether they are aware of it. If the proxy server in a network is moved, but the existing clients need to retain their old conguration. 533 Configuring a transparent proxy SLES 15 SP3PROCEDURE 37.1: SQUID AS A TRANSPARENT PROXY SERVER (COMMAND LINE) 1. In /etc/squid/squid.conf , on the line of the option http_port add the parameter transparent . You should then have 2 lines: http_port 3128 http_port 3128 transparent 2. Restart Squid: tux > sudo systemctl restart squid 3. Set up the rewall to redirect HTTP trac to the port given in http_proxy . In the example above it is port 3128. Then reload the rewall conguration. This assumes that the zone internal is assigned to your LAN interface. tux > sudo firewall-cmd --permanent --zone=internal \ --add-forward-port=port=80:proto=tcp:toport=3128:toaddr=LAN_IP tux > sudo firewall-cmd --permanent --zone=internal --add-port=3128/tcp tux > sudo firewall-cmd --reload Replace LAN_IP with the IP address of your LAN interface or the interface Squid is listening on. 4. To verify that everything is working properly, check the Squid log les in /var/log/ squid/access.log . 37.7 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 is also a convenient way to manage the cache and view statistics without logging the server. PROCEDURE 37.2: SETTING UP cachemgr.cgi 1. Make sure the Apache Web server is running on your system. Congure Apache as described in Chapter 35, The Apache HTTP server. In particular, see Section 35.5, “Enabling CGI scripts”. To check whether Apache is already running, use: tux > sudo systemctl status apache2 534 Using the Squid cache manager CGI interface (cachemgr.cgi) SLES 15 SP3If inactive is shown, you can start Apache with the SUSE Linux Enterprise Server default settings: tux > sudo systemctl start apache2 2. Now enable cachemgr.cgi in Apache. To do so, create a conguration le for a ScriptAlias . Create the le in the directory /etc/apache2/conf.d and name it cachemgr.conf . In it, add the following: 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.cgi from. This allows only your computer to access cachemgr.cgi . To allow access from anywhere, use Require all granted instead. 3. If Squid and your Apache Web server run on the same computer, there should be no changes that need to be made to /etc/squid/squid.conf . However, verify that / etc/squid/squid.conf contains the following lines: http_access allow manager localhost http_access deny manager These lines allow you to access the manager interface from your own computer ( localhost ) but not from elsewhere. If Squid and your Apache Web server run on dierent computers, you need to add extra rules to allow access from the CGI script to Squid. Dene an ACL for your server (replace WEB_SERVER_IP with the IP address of your Web server): acl webserver src WEB_SERVER_IP/255.255.255.255 Make sure the following rules are in the conguration le. Compared to the default conguration, only the rule in the middle is new. However, the sequence is important. 535 Using the Squid cache manager CGI interface (cachemgr.cgi) SLES 15 SP3http_access allow manager localhost http_access allow manager webserver http_access deny manager 4. (Optional) Optionally, you can congure one or more passwords for cachemgr.cgi . This also allows access to more actions such as closing the cache remotely or viewing more information about the cache. For this, congure the options cache_mgr and cachemgr_passwd with one or more password for the manager and a list of allowed actions. For example, to explicitly enable viewing the index page, the menu, 60-minute average of counters without authentication, to enable toggling oine mode using the password secretpassword , and to completely disable everything else, use the following conguration: cache_mgr user cachemgr_passwd none index menu 60min cachemgr_passwd secretpassword offline_toggle cachemgr_passwd disable all cache_mgr denes a user name. cache_mgr denes 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 conguration 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 after the conguration le changes: tux > 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, and, if set, specify user name and password. Then click Continue and browse through the dierent statistics. 536 Using the Squid cache manager CGI interface (cachemgr.cgi) SLES 15 SP337.8 Cache report generation with Calamaris Calamaris is a Perl script used to generate reports of cache activity in ASCII or HTML format. It works with native Squid access log les. The Calamaris home page is located at http://cord.de/ calamaris-english . This tool does not belong to the SUSE Linux Enterprise Server default installation scope—to use it, install the calamaris package. Log in as root , then enter: root # cat access1.log [access2.log access3.log] | calamaris OPTIONS > reportfile When using more than one log le, make sure they are chronologically ordered, with older les listed rst. This can be achieved by either listing the les one after the other as in the example above, or by using access{1..3}.log . calamaris takes the following options: -a output all available reports -w output as HTML report -l include a message or logo in report header More information about the various options can be found in the program''s manual page with man   calamaris . A typical example is: root # cat access.log.{10..1} access.log | calamaris -a -w \ > /usr/local/httpd/htdocs/Squid/squidreport.html This puts the report in the directory of the Web server. Apache is required to view the reports. 37.9 More information Visit the home page of Squid at http://www.squid-cache.org/ . Here, nd the “Squid User Guide” and a very extensive collection of FAQs on Squid. In addition, mailing lists are available for Squid at http://www.squid-cache.org/Support/mailing- lists.html . 537 Cache report generation with Calamaris SLES 15 SP338 Web Based Enterprise Management using SFCB 38.1 Introduction and basic concept SUSE® Linux Enterprise Server (SLES) provides a collection of open standards based tools for the unied 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 eective 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 technologies. 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 specication: CIM-XML Encoding Specication A transport mechanism: CIM operations over HTTP The Common Information Model is a conceptual information model that describes system management. It is not bound to a particular implementation and enables the interchange of management information between management systems, networks, services and applications. There are two parts to CIM — the CIM Specication and the CIM Schema. 538 Introduction and basic concept SLES 15 SP3The CIM Specication describes the language, naming and meta schema. The meta schema is a formal denition of the model. It denes 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 specically, an application that manages objects according to the CIM standard. CIMOM manages communication between CIMOM providers and a CIM client, where the administrator manages the system. CIMOM providers are software performing specic 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 environments. It is designed to be modular and lightweight at the same time. Its based on open standards and it supports CMPI providers, CIM-XML encoding, and Managed Object Format (MOF). It is highly congurable and performs stability even if the provider crashes. It is also easily accessible as it supports various transport protocols, such as HTTP, HTTPS, Unix domain sockets, Service Location Protocol (SLP), and Java Database Connectivity (JDBC). 38.2 Setting up SFCB To set up the Small Footprint CIM Broker (SFCB) environment, make sure the Web-Based Enterprise 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 539 Setting up SFCB SLES 15 SP3Contains the Common Information Model (CIM). CIM is a model for describing overall management information in a network or enterprise environments. CIM consists of a specication and a schema. The specication denes 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, specically 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. 38.2.1 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. TABLE 38.1: COMMANDS FOR MANAGING SFCBD Task Linux Command Start sfcbd Enter systemctl start sfcb as root in the command line. Stop sfcbd Enter systemctl stop sfcb as root in the command line. 540 Starting, stopping and checking status for SFCB SLES 15 SP3Task Linux Command Check sfcbd status Enter systemctl status sfcb as root in the command line. 38.2.2 Ensuring secure access The default setup of SFCB is relatively secure. However, check that the access to SFCB components is as secure as required for your organization. 38.2.2.1 Certificates Secure Socket Layers (SSL) transports require a certicate for secure communication to occur. When SFCB is installed, it has a self-signed certicate generated. You can replace the path to the default certicate 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 certicate in the following location: /etc/sfcb/server.pem To generate a new certicate, run the following command: tux > 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'' ----- By default, the script generates certicates client.pem , file.pem and server.pem in the current working directory. If you want the script to generate the certicates 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 certicates are not overwritten. tux > sudo sh /usr/share/sfcb/genSslCert.sh /etc/sfcb Generating SSL certificates in . WARNING: server.pem SSL Certificate file already exists. 541 Ensuring secure access SLES 15 SP3old 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 certicates from the le system and run the command again. To change the way SFCB uses certicates, see Section 38.2.2.3, “Authentication”. 38.2.2.2 Ports By default, SFCB is congured to accept all communications through the secure port 5989. The following paragraphs explain the communication port setup and recommended conguration. 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 rewalls 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 applications 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 rewalls between the client application and the nodes being monitored. To change the default port assignments, see Section 38.2.2.2, “Ports”. 38.2.2.3 Authentication SFCB supports HTTP basic authentication and authentication based on client certicates (HTTP over SSL connections). Basic HTTP authentication is enabled by specifying doBasicAuth=true in the SFCB conguration le ( /etc/sfcb/sfcb.cfg by default). SUSE® Linux Enterprise 542 Ensuring secure access SLES 15 SP3Server installation of SFCB supports Pluggable Authentication Modules (PAM) approach; therefore the local root user can authenticate to the SFCB CIMOM with local root user credentials. If the sslClientCertificate conguration property is set to accept or require , the SFCB HTTP adapter will request a certicate from clients when connecting via HTTP over SSL (HTTPS). If require is specied, the client must provide a valid certicate (according to the client trust store specied via sslClientTrustStore ). If the client fails to do so, the connection will be rejected by the CIM server. The setting sslClientCertificate=accept may not be obvious. It is very useful if both basic and client certicate authentication are allowed. If the client can provide a valid certicate, HTTPS connection will be established and the basic authentication procedure will not be executed. If this function cannot verify the certicate, the HTTP basic authentication will take place instead. 38.3 SFCB CIMOM configuration SFCB is a lightweight implementation of the CIM server, but it is also highly congurable. 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 conguration le 38.3.1 Environment variables Several environment variables directly aect the behavior of SFCB. You need to restart the SFCB daemon by systemctl restart sfcb for these changes to take eect. PATH Species the path to the sfcbd daemon and utilities. LD_LIBRARY_PATH Species the path to the sfcb runtime libraries. Alternatively, you can add this path to the system-wide dynamic loader conguration le /etc/ld.so.conf . SFCB_PAUSE_PROVIDER 543 SFCB CIMOM configuration SLES 15 SP3Species 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 Species 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 Species 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 specied le instead. SBLIM_TRACE Species 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 specied le instead. 38.3.2 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 conguration from /etc/sfcb/sfcb.cfg by default. With this option, you can specify an alternative conguration le. -d, --daemon Forces sfcbd and its child processes to run in the background. -s, --collect-stats Turns on runtime statistics collecting. Various sfcbd runtime statistics will be written to the sfcbStat le in the current working directory. By default, no statistics are collected. 544 Command line options SLES 15 SP3-l, --syslog-level = LOGLEVEL Species 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 dierent color per process for easier debugging. -t, --trace-components = NUM Activates component-level tracing messages, where NUM is an OR-ed bitmask integer that denes which component to trace. After you specify -t ? , it lists all the components and their associated integer bitmask: tux > 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 . 38.3.3 SFCB configuration file SFCB reads its runtime conguration from conguration le /etc/sfcb/sfcb.cfg after starting up. This behavior can be overridden using -c option at start-up. 545 SFCB configuration file SLES 15 SP3The conguration le contains option : VALUE pairs, one per line. When making changes to this le, you can use any text editor that saves the le in a format that is native to the environment you are using. 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. 38.3.3.1 httpPort Purpose Species the local port value that sfcbd should listen to receive HTTP (insecure) requests from CIM clients. Default is 5988 . Syntax httpPort: PORT_NUMBER 38.3.3.2 enableHttp Purpose Species whether SFCB should accept HTTP client connections. Default is false . Syntax enableHttp: OPTION Option Description true Enables HTTP connections. false Disables HTTP connections. 546 SFCB configuration file SLES 15 SP338.3.3.3 httpProcs Purpose Species the maximum number of simultaneous HTTP client connections before new incoming HTTP requests are blocked. Default is 8 . Syntax httpProcs: MAX_NUMBER_OF_CONNECTIONS 38.3.3.4 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 specied for httpUser will be used. This setting is used for both HTTP and HTTPS servers. httpUser must be specied if httpUserSFCB is set to false . the default is true . Syntax httpUserSFCB: true 38.3.3.5 httpLocalOnly Purpose Species whether to limit HTTP requests to localhost only. Default is false . Syntax httpLocalOnly: false 547 SFCB configuration file SLES 15 SP338.3.3.6 httpsPort Purpose Species the local port value where sfcbd listens for HTTPS requests from CIM clients. Default is 5989 . Syntax httpsPort: port_number 38.3.3.7 enableHttps Purpose Species if SFCB will accept HTTPS client connections. Default is true . Syntax enableHttps: option Option Description true Enables HTTPS connections. false Disables HTTPS connections. 38.3.3.8 httpsProcs Purpose Species the maximum number of simultaneous HTTPS client connections before new incoming HTTPS requests are blocked. Default is 8 . 548 SFCB configuration file SLES 15 SP3Syntax httpsProcs:   MAX_NUMBER_OF_CONNECTIONS 38.3.3.9 enableInterOp Purpose Species 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. 38.3.3.10 provProcs Purpose Species 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 549 SFCB configuration file SLES 15 SP338.3.3.11 doBasicAuth Purpose Switches basic authentication on or o based on the client user identier 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. 38.3.3.12 basicAuthLib Purpose Species the local library name. The SFCB server loads the library to authenticate the client user identier. Default is sfcBasicPAMAuthentication . Syntax provProcs:   MAX_NUMBER_OF_PROCS 38.3.3.13 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 . 550 SFCB configuration file SLES 15 SP3Syntax useChunking:   OPTION Option Description true Enables HTTP/HTTPS data chunking. false Disables HTTP/HTTPS data chunking. 38.3.3.14 keepaliveTimeout Purpose Species 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 38.3.3.15 keepaliveMaxRequest Purpose Species the maximum number of consecutive requests on one connection. Setting it to 0 disables HTTP keep-alive. Default value is 10 . Syntax keepaliveMaxRequest:   NUMBER_OF_CONNECTIONS 551 SFCB configuration file SLES 15 SP338.3.3.16 registrationDir Purpose Species 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 38.3.3.17 providerDirs Purpose Species 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 38.3.3.18 providerSampleInterval Purpose Species the interval in seconds at which the provider manager is checking for idle providers. Default is 30 . Syntax providerSampleInterval:   SECS 552 SFCB configuration file SLES 15 SP338.3.3.19 providerTimeoutInterval Purpose Species the interval in seconds before an idle provider gets unloaded by the provider manager. Default is 60 . Syntax providerTimeoutInterval:   SECS 38.3.3.20 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. 38.3.3.21 sslCertificateFilePath Purpose Species the name of the le that contains the server certicate. 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 . 553 SFCB configuration file SLES 15 SP3Syntax sslCertificateFilePath:   PATH 38.3.3.22 sslKeyFilePath Purpose Species the name of the le that contains the private key for the server certicate. 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 38.3.3.23 sslClientTrustStore Purpose Species the name of the le that contains either the CA or self-signed certicates 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 554 SFCB configuration file SLES 15 SP338.3.3.24 sslClientCertificate Purpose Species the way SFCB handles client certicate based authentication. If set to ignore , it will not request a certicate from the client. If set to accept it will request a certicate 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 certicate. Default value is ignore . Syntax sslClientCertificate:   OPTION Option Description ignore Disables requesting a client certicate. accept Disables requesting a client certicate. Will not fail if no certicate is present. require Refuses the client connection without a valid certicate. 38.3.3.25 certificateAuthLib Purpose Species the name of the local library to request for the user authentication based on client certicate. This is only requested if sslClientCertificate is not set to ignore . Default value is sfcCertificateAuthentication . Syntax certificateAuthLib:   FILE 555 SFCB configuration file SLES 15 SP338.3.3.26 traceLevel Purpose Species the trace level for SFCB. You can override it by setting environment variable SFCB_TRACE_LEVEL . Default value is 0 . Syntax traceLevel:   NUM_LEVEL 38.3.3.27 traceMask Purpose Species the trace mask for SFCB. you can override it by the command line option --trace- components . Default value is 0 . Syntax traceMask:   MASK 38.3.3.28 traceFile Purpose Species 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 556 SFCB configuration file SLES 15 SP338.4 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 38.4.1 Installing CMPI providers To install a CMPI provider, you need to make sure that its shared library is copied into one of the directories specied by providerDirs conguration option, see Section 38.3.3.17, “providerDirs”. The provider must also be properly registered using sfcbstage and sfcbrepos commands. The provider package is usually prepared for SFCB, so that its installation takes care of the proper registration. Most SBLIM providers are prepared for SFCB. 38.4.1.1 Class repository Class repository is a place where SFCB stores information about CIM classes. It usually 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 representation of all the CIM classes registered under that namespace. It also contains necessary information about their CIM superclasses. 557 Advanced SFCB tasks SLES 15 SP3In addition, each namespace directory may contain a le qualifiers which contains all qualiers 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. 38.4.1.2 Adding new classes SFCB cannot make live CIM class manipulations. You need to add, change or remove classes oine 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 denition 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 denition) 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: tux > ls /var/lib/sfcb/stage default.reg mofs regs tux > ls /var/lib/sfcb/stage/mofs indication.mof root tux > ls /var/lib/sfcb/stage/mofs/root cimv2 interop suse virt tux > ls -1 /var/lib/sfcb/stage/mofs/root/cimv2 | less Linux_ABIParameter.mof 558 Installing CMPI providers SLES 15 SP3Linux_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 tux > 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 tux > 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 tux > 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 559 Installing CMPI providers SLES 15 SP3type: 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. Note: 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 , association , method or indication . 560 Installing CMPI providers SLES 15 SP3Multiple providers can be grouped together and run under a single process to further minimize 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 Species the unload policy for the provider. Currently the only supported option is never , which species 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 specied in the conguration le. namespace 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 denitions 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. 38.4.2 Testing SFCB The SFCB package includes two testing scripts: wbemcat and xmltest . wbemcat sends raw CIM-XML data via HTTP protocol to the specied 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: 561 Testing SFCB SLES 15 SP3 TRUE FALSE 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 . tux > 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 [..] 562 Testing SFCB SLES 15 SP3 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: tux > xmltest cim_xml_test.xml Running test cim_xml_test.xml ... OK Saving response as cim_xml_test.OK root # xmltest cim_xml_test.xml Running test cim_xml_test.xml ... Passed 38.4.3 Command line CIM client: wbemcli In addition to 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 implementations. 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: tux > 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 563 Command line CIM client: wbemcli SLES 15 SP3From server: Cache-Control: no-cache From server: CIMOperation: MethodResponse From server: [..] 0 0 [..] The -dx option shows you the actual XML sent to SFCB by wbemcli and the actual XML received. In the above example, the rst of many returned classes was CIM_ResourcePool followed by Linux_Ext4FileSystem . Similar entries will appear for all of the other registered classes. If you omit the -dx option, wbemcli will display only a compact representation of the returned data: tux > wbemcli ec http://localhost/root/cimv2 localhost:5988/root/cimv2:CIM_ResourcePool Generation=,ElementName=, \ Description=,Caption=,InstallDate=,Name=,OperationalStatus=, \ StatusDescriptions=,Status=,HealthState=,PrimaryStatus=, \ 564 Command line CIM client: wbemcli SLES 15 SP3DetailedStatus=,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= [..] 38.5 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 http://sblim.sourceforge.net/wiki/index.php/Main_Page Standards Based Linux Instrumentation (SBLIM) Web site 565 More information SLES 15 SP3V Troubleshooting 39 Help and documentation 567 40 Gathering system information for support 573 41 Common problems and their solutions 60439 Help and documentation SUSE® Linux Enterprise Server comes with various sources of information and documentation, many of which are already integrated into your installed system. Documentation in /usr/share/doc This traditional help directory holds various documentation les and release notes for your system. It contains also information of installed packages in the subdirectory packages . Find more detailed information in Section 39.1, “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 39.2, “Man pages” and Section 39.3, “Info pages”. Desktop help center The help center of the GNOME desktop (Help) provides central access to the most important documentation resources on your system in searchable form. These resources include online help for installed applications, man pages, info pages, and the SUSE manuals delivered with your product. Separate help packages for some applications When installing new software with YaST, the software documentation is usually installed automatically and appears in the help center of your desktop. However, some applications, such as GIMP, may have dierent online help packages that can be installed separately with YaST and do not integrate into the help centers. 39.1 Documentation directory The traditional directory to nd documentation on your installed Linux system is /usr/share/ doc . Usually, the directory contains information about the packages installed on your system, plus release notes, manuals, and more. 567 Documentation directory SLES 15 SP3Note: Contents depends on installed packages In the Linux world, many 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/docs also depends on the (documentation) packages installed. If you cannot nd the subdirectories mentioned here, check if the respective packages are installed on your system and add them with YaST, if needed. 39.1.1 SUSE manuals We provide HTML and PDF versions of our books in dierent languages. In the manual subdirectory, nd HTML versions of most of the SUSE manuals available for your product. For an overview of all documentation available for your product refer to the preface of the manuals. If more than one language is installed, /usr/share/doc/manual may contain dierent language versions of the manuals. The HTML versions of the SUSE manuals are also available in the help center of both desktops. For information on where to nd the PDF and HTML versions of the books on your installation media, refer to the SUSE Linux Enterprise Server Release Notes. They are available on your installed system under /usr/share/doc/release-notes/ or online at your product-specic Web page at https://www.suse.com/releasenotes// . 39.1.2 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, conguration 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 might only include a few of them. AUTHORS List of the main developers. BUGS Known bugs or malfunctions. Might also contain a link to a Bugzilla Web page where you can search all bugs. 568 SUSE manuals SLES 15 SP3CHANGES , ChangeLog Summary of changes from version to version. Usually interesting for developers, because it is very 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 Things that are not implemented yet, but probably will be in the future. MANIFEST List of les with a brief summary. NEWS Description of what is new in this version. 39.2 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 39.1, “Man pages—categories and descriptions” (taken from the man page for man itself). 569 Man pages SLES 15 SP3TABLE 39.1: MAN PAGES—CATEGORIES AND DESCRIPTIONS Number Description 1 Executable programs or shell commands 2 System calls (functions provided by the kernel) 3 Library calls (functions within program libraries) 4 Special les (usually 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 (usually 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. 39.3 Info pages Info pages are another important source of information on your system. Usually, 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 dierent sections, called “nodes”. Use Space to move forward and <— to move backward. Within a node, you can also 570 Info pages SLES 15 SP3browse with Page ↑ and Page ↓ but only Space and <— will take 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. 39.4 Online resources In addition to the online versions of the SUSE manuals installed under /usr/share/doc , you can also access the product-specic manuals and documentation on the Web. For an overview of all documentation available for SUSE Linux Enterprise Server check out your product-specic documentation Web page at https://documentation.suse.com/ . If you are searching for additional product-related information, you can also refer to the following 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. SUSE forums There are several forums where you can dive in on discussions about SUSE products. See https://forums.suse.com/ for a list. SUSE blog The SUSE blog oers articles, tips, Q and A: https://www.suse.com/c/blog/ GNOME documentation Documentation for GNOME users, administrators and developers is available at https:// library.gnome.org/ . The Linux documentation project The Linux Documentation Project (TLDP) is run by a team of volunteers who write Linux- related documentation (see https://www.tldp.org ). It is probably the most comprehensive documentation resource for Linux. The set of documents contains tutorials for beginners, but is mainly focused on experienced users and professional system administrators. TLDP publishes HOWTOs, FAQs, and guides (handbooks) under a free license. Parts of the documentation from TLDP are also available on SUSE Linux Enterprise Server. 571 Online resources SLES 15 SP3You can also try general-purpose search engines. For example, use the search terms Linux CD- RW help or OpenOffice file conversion problem if you have trouble with burning CDs or LibreOce le conversion. 572 Online resources SLES 15 SP340 Gathering system information for support For a quick overview of all relevant system information of a machine, SUSE Linux Enterprise Server oers the hostinfo package. It also helps system administrators to check for tainted kernels (that are not supported) or any third-party packages installed on a machine. In case of problems, a detailed system report may be created with either the supportconfig command line tool or the YaST Support module. Both will collect information 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 will help 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). 40.1 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 40.1: 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 SP2 Current As Of: Wed 25 Mar 2020 12:09:20 PM PDT Hostname: localhost Kernel Version: 5.3.18-8-default Architecture: x86_64 Installed: Thu 19 Mar 2020 11:25:13 AM PDT Status: Not Tainted Last Installed Package: Wed 25 Mar 2020 11:42:24 AM PDT 573 Displaying current system information SLES 15 SP3Patches Needed: 0 Security: 0 3rd Party Packages: 219 Network 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 40.6, “Support of kernel modules” for more details. 40.2 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. Depending on which packages are installed on your system, some of these packages integrate Supportcong plug-ins. When Supportcong is executed, all plug-ins are executed as well and create one or more result les for the archive. That has the benet that the only topics checked are those that contain a specic plug-in for them. Supportcong plug-ins are stored in the directory /usr/lib/supportconfig/plugins/ . 40.2.1 Creating a service request number Supportcong archives can be generated at any time. However, for handing over the Supportcong data to Global Technical Support, you need to generate a service request number rst. You will need it to upload the archive to support. To create a service request, go to https://scc.suse.com/support/requests and follow the instructions on the screen. Write down the service request number. 574 Collecting system information with supportconfig SLES 15 SP3Note: Privacy statement SUSE treats system reports as condential data. For details about our privacy commitment, see https://www.suse.com/company/policies/privacy/ . 40.2.2 Upload targets After having created a service request number, you can upload your Supportcong archives to Global Technical Support as described in Procedure  40.1, “Submitting information to support with YaST” or Procedure 40.2, “Submitting information to support from command line”. Use one of the following upload targets: North America: FTP ftp://support-ftp.us.suse.com/incoming/ , FTPS ftps://support- ftp.us.suse.com/incoming/ EMEA, Europe, the Middle East, and Africa: FTP ftp://support-ftp.emea.suse.com/ incoming , FTPS ftps://support-ftp.emea.suse.com/incoming Alternatively, you can manually attach the TAR archive to your service request using the service request URL: https://scc.suse.com/support/requests . 40.2.3 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. 575 Upload targets SLES 15 SP32. Click Create report tarball. 3. In the next window, select one of the Supportcong options from the radio button list. Use Custom (Expert) Settings is preselected by default. If you want 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. Press Next. 4. Enter your contact information. It is saved in the basic-environment.txt le and included in the created archive. 5. To submit the archive to Global Technical Support, provide the required Upload Information. YaST automatically suggests an upload server. To modify it, refer to Section 40.2.2, “Upload targets” for details of which upload servers are available. To submit the archive later, leave the Upload Information empty. 6. Press Next to start the information collection process. 576 Creating a supportconfig archive with YaST SLES 15 SP3After the process is nished, press 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. 8. 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 activated. 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 40.2.2, “Upload targets”. 10. To skip the upload, deactivate Upload log les tarball to URL. 11. Conrm the changes to close the YaST module. 577 Creating a supportconfig archive with YaST SLES 15 SP340.2.4 Creating a supportconfig archive from command line The following procedure shows how to create a Supportcong archive, but without submitting it to support directly. For uploading it, you need to run the command with certain options as described in Procedure 40.2, “Submitting information to support from command line”. 1. Open a shell and become root . 2. Run supportconfig . Usually, it is enough to run this tool without any options. Some options are very common and 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 Denes your service request number when uploading the generated TAR archive. 3. Wait for the tool to complete the operation. 4. The default archive location is /var/log , with the le name format being scc_HOST_DATE_TIME.tbz 40.2.5 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 578 Creating a supportconfig archive from command line SLES 15 SP3Data 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 40.1, “Comparison of features and file names in the TAR archive”). 3 The feature was skipped because some les of one or more RPM packages were changed. 4 The feature was excluded because it was deselected via the -x option. 5 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 . 40.2.6 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 some common use cases: Reducing the size of the information being gathered 579 Common supportconfig options SLES 15 SP3Use the minimal option ( -m ): tux > sudo supportconfig -m Limiting the information to a specific topic If you have already localized a problem that relates to a specic area or feature set only, you should limit the collected information to the specic 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 conguration. In that case it makes sense to gather the minimum Supportcong information around LVM only: tux > sudo supportconfig -i LVM Additional keywords can be separated through commas. For example, an additional disk test: tux > sudo supportconfig -i LVM,DISK For a complete list of feature keywords that you can use for limiting the collected information to a specic area, run: tux > sudo supportconfig -F Including additional contact information in the output: tux > sudo supportconfig -E tux@example.org -N "Tux Penguin" -O "Penguin Inc." ... (all in one line) Collecting already rotated log files tux > sudo supportconfig -l This is especially useful in high logging environments or after a kernel crash when syslog rotates the log les after a reboot. 40.2.7 Overview of the archive content The TAR archive contains all the results from the features. Depending on what you have selected (all or only a small set), the archive can contain more or less les. The set of features can be limited through the -i option (see Section 40.2.6, “Common supportconfig options”). To list the content of the archive, use the following tar command: root # tar xf /var/log/scc_earth_180131_1545.tbz 580 Overview of the archive content SLES 15 SP3The 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 some 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 some information in XML format like distribution, the version, and product specic fragments. supportconfig.txt Contains information about the supportconfig script itself. y2log.txt Contains YaST specic information like specic packages, conguration les, and log les. Table 40.1, “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 40.1: 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 581 Overview of the archive content SLES 15 SP3Feature File name 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 ISCSI fs-iscsi.txt LDAP ldap.txt LIVEPATCH kernel-livepatch.txt LVM lvm.txt MEM memory.txt 582 Overview of the archive content SLES 15 SP3Feature File name 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 SSSD sssd.txt SYSCONFIG sysconfig.txt SYSFS sysfs.txt TRANSACTIONAL transactional-update.txt TUNED tuned.txt 583 Overview of the archive content SLES 15 SP3Feature File name UDEV udev.txt UFILES fs-files-additional.txt UP updates.txt WEB web.txt X x.txt 40.3 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 40.2.1, “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 40.2.1, “Creating a service request number”. PROCEDURE 40.1: SUBMITTING INFORMATION TO SUPPORT WITH YAST The following procedure assumes that you have already created a Supportcong archive, but have not uploaded it yet. Make sure to have included your contact information in the archive as described in Section 40.2.3, “Creating a supportconfig archive with YaST”, Step 4. For instructions on how to generate and submit a Supportcong archive in one go, see Section 40.2.3, “Creating a supportconfig archive with YaST”. 1. Start YaST and open the Support module. 2. Click Upload. 3. In Package with log les specify the path to the existing Supportcong archive or Browse for it. 4. YaST automatically proposes an upload server. If you want to modify it, refer to Section 40.2.2, “Upload targets” for details of which upload servers are available. 584 Submitting information to Global Technical Support SLES 15 SP3Proceed with Next. 5. Click Finish. PROCEDURE 40.2: SUBMITTING INFORMATION TO SUPPORT FROM COMMAND LINE The following procedure assumes that you have already created a Supportcong archive, but have not uploaded it yet. For instructions on how to generate and submit a Supportcong archive in one go, see Section 40.2.3, “Creating a supportconfig archive with YaST”. 1. Servers with Internet connectivity: a. To use the default upload target, run: tux > sudo supportconfig -ur 12345678901 b. For the secure upload target, use the following: tux > sudo supportconfig -ar 12345678901 2. Servers without Internet connectivity a. Run the following: tux > sudo supportconfig -r 12345678901 585 Submitting information to Global Technical Support SLES 15 SP3b. 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 40.2.2, “Upload targets”. 3. After the TAR archive arrives in the incoming directory of our FTP server, it becomes automatically attached to your service request. 40.4 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 server- 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 Supportcong archives from aected 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-specic patterns that enable them to analyze the Supportcong output for the associated products. Each pattern is a script that parses and evaluates a Supportcong 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 40.4.3, “Developing custom analysis patterns”. 40.4.1 SCA command line tool The SCA command line tool lets you analyze a local machine using both supportconfig and the analysis patterns for the specic product that is installed on the local machine. The tool creates an HTML report showing its analysis results. For an example, see Figure 40.1, “HTML report generated by SCA tool”. 586 Analyzing system information SLES 15 SP3FIGURE 40.1: 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- specic 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. Find some example commands below: sudo scatool -s 587 SCA command line tool SLES 15 SP3Calls supportconfig and generates a new Supportcong 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 usually written to the same directory where the Supportcong 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 specied with -o . sudo scatool  -a   PATH_TO_TARBALL_OR_DIR Analyzes the specied Supportcong archive le (or the specied directory to where the Supportcong archive has been extracted). The generated HTML report is saved in the same location as the Supportcong 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 Supportcong archive is then copied back to the local machine and is analyzed there. The generated HTML report is saved to the default /var/log directory. (Only the Supportcong archive is created on SLES_SERVER.COMPANY.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. 40.4.2 SCA appliance If you decide to use the SCA appliance for analyzing the Supportcong archives, congure a dedicated server (or virtual machine) as the SCA appliance server. The SCA appliance server can then be used to analyze Supportcong archives from all machines in your enterprise running SUSE Linux Enterprise Server or SUSE Linux Enterprise Desktop. You can simply upload Supportcong archives to the appliance server for analysis. Interaction is not required. In a MariaDB database, the SCA appliance keeps track of all Supportcong archives that have been analyzed . You 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 40.4.2.5.4, “Sending SCA reports via e-mail”. 588 SCA appliance SLES 15 SP340.4.2.1 Installation quick start To install and set up the SCA appliance in a very fast way from the command line, follow the instructions 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 40.4.2.2, “Prerequisites” to Section 40.4.2.3, “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 40.3: 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 Supportcong 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): tux > sudo zypper install sca-appliance-* sca-patterns-* \ vsftpd yast2 yast2-ftp-server tux > sudo systemctl enable apache2 tux > sudo systemctl start apache2 tux > sudo systemctl enable vsftpd tux > sudo systemctl start vsftpd tux > sudo yast ftp-server 2. In YaST FTP Server, select Authentication Enable Upload Anonymous Can Upload Finish Yes to Create /srv/ftp/upload. 3. Execute the following commands: tux > sudo systemctl enable mysql tux > sudo systemctl start mysql tux > sudo mysql_secure_installation tux > sudo setup-sca -f The mysql_secure_installation will create a MariaDB root password. 589 SCA appliance SLES 15 SP3PROCEDURE 40.4: 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: tux > sudo zypper install sca-appliance-* sca-patterns-* tux > sudo systemctl enable apache2 tux > sudo systemctl start apache2 tux > sudo sudo systemctl enable mysql tux > sudo systemctl start mysql tux > sudo mysql_secure_installation tux > sudo setup-sca 40.4.2.2 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-specic sca- patterns-* for the type of Supportcong archives that you want to analyze with the appliance. Apache PHP MariaDB anonymous FTP server (optional) 40.4.2.3 Installation and basic setup As listed in Section 40.4.2.2, “Prerequisites”, the SCA appliance has several dependencies on other packages. Therefore you need do so some preparations before installing and setting up the SCA appliance server: 1. For Apache and MariaDB, install the Web and LAMP installation patterns. 590 SCA appliance SLES 15 SP32. Set up Apache, MariaDB, and optionally an anonymous FTP server. For more information, see Chapter 35, The Apache HTTP server and Chapter 36, Setting up an FTP server with YaST. 3. Congure Apache and MariaDB to start at boot time: tux > sudo systemctl enable apache2 mysql 4. Start both services: tux > sudo systemctl start apache2 mysql Now you can install the SCA appliance and set it up as described in Procedure 40.5, “Installing and configuring the SCA appliance”. PROCEDURE 40.5: INSTALLING AND CONFIGURING THE SCA APPLIANCE After installing the packages, use the setup-sca script for the basic conguration of the MariaDB administration and report database that is used by the SCA appliance. It can be used to congure the following options you have for uploading the Supportcong archives from your machines to the SCA appliance: scp anonymous FTP server 1. Install the appliance and the SCA base-pattern library: tux > sudo zypper install sca-appliance-* sca-patterns-base 2. Additionally, install the pattern packages for the types of Supportcong 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: tux > sudo zypper install sca-patterns-* 591 SCA appliance SLES 15 SP33. For basic setup of the SCA appliance, use the setup-sca script. How to call it depends on how you want to upload the Supportcong archives to the SCA appliance server: If you have congured 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: tux > sudo setup-sca -f Note: FTP server using another directory If your FTP server uses another directory than /srv/ftp/upload , adjust the following conguration les rst to make them point to the correct directory: /etc/sca/sdagent.conf and /etc/sca/sdbroker.conf . If you want to upload Supportcong 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: tux > sudo setup-sca The setup script runs a few checks regarding its requirements and congures 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. Dene 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 40.4.2.5.1, “Password for the Web interface”. After successful installation and setup, the SCA appliance is ready for use, see Section 40.4.2.4, “Using the SCA appliance”. However, you should modify some options such as changing the password for the Web interface, changing the source for the SCA pattern updates, enabling archiving mode or conguring e-mail notications. For details on that, see Section  40.4.2.5, “Customizing the SCA appliance”. 592 SCA appliance SLES 15 SP3Warning: 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. 40.4.2.4 Using the SCA appliance You can upload existing Supportcong archives to the SCA appliance manually or create new Supportcong 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 congured for the SCA appliance, see Procedure 40.5, “Installing and configuring the SCA appliance”. 40.4.2.4.1 Uploading supportconfig archives to the SCA appliance For creating a Supportcong archive and uploading it via (anonymous) FTP: tux > sudo supportconfig -U “ftp://SCA-APPLIANCE.COMPANY.COM/upload” For creating a Supportcong archive and uploading it via SCP: tux > 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. If you want to manually upload one or multiple archives, copy the existing archive les (usually 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 congured for the SCA appliance server). 40.4.2.4.2 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. 593 SCA appliance SLES 15 SP3https://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 40.2: 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 Supportcong 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 directly relate to the problem identied by SCA. Work at resolving them. 9. Check for results that can be addressed proactively to avoid future problems. 594 SCA appliance SLES 15 SP340.4.2.5 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 congure e-mail notications. 40.4.2.5.1 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 specied otherwise, see Procedure 40.5, “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 40.6: 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. 40.4.2.5.2 Updates of SCA patterns By default, all sca-patterns-* packages are updated regularly by a root cron job that executes the sdagent-patterns script nightly, which in turn runs zypper update sca- patterns-* . A regular system update will update all SCA appliance and pattern packages. To update the SCA appliance and patterns manually, run: tux > sudo zypper update sca-* The updates are installed from the SUSE Linux Enterprise 15 SP3 update repository by default. You can change the source for the updates to an RMT server, if desired. When sdagent- patterns runs zypper update sca-patterns-* , it gets the updates from the currently congured update channel. If that channel is located on an RMT server, the packages will be pulled from there. PROCEDURE 40.7: DISABLING AUTOMATIC UPDATES OF SCA PATTERNS 1. Log in as root user at the system console of the SCA appliance server. 595 SCA appliance SLES 15 SP32. 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. 40.4.2.5.3 Archiving mode All Supportcong 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 Supportcong archives from a machine. By default, archiving mode is disabled. PROCEDURE 40.8: 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 Supportcong les to the /var/log/archives/saved directory, instead of deleting them. 596 SCA appliance SLES 15 SP340.4.2.5.4 Sending SCA reports via e-mail The SCA appliance can e-mail a report HTML le for each Supportcong analyzed. This feature is disabled by default. When enabling it, you can dene a list of e-mail addresses to which the reports should be sent. Dene 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 40.9: 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 notications are disabled). 4. To enable e-mail notications, 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 dene the list of recipients to which the reports should be sent: a. Search for the entry EMAIL_REPORT=''root'' . 597 SCA appliance SLES 15 SP3b. 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 specied addresses. 40.4.2.6 Backing up and restoring the database To back up and restore the MariaDB database that stores the SCA reports, use the scadb command as described below. scadb is provided by the package sca-appliance-broker . PROCEDURE 40.10: 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: root # scadb maint 3. Start the backup with: root # 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 Section 40.4.3, “Developing custom analysis patterns”), back up this data, too: root # 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) 598 SCA appliance SLES 15 SP36. Reactivate the SCA appliance with: root # scadb reset agents PROCEDURE 40.11: 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: root # gzip -d *-backup-*sql.gz 4. To import the data into the database, execute: root # 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: root # 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: root # scadb reset agents 8. Update the pattern modules in the database with: root # sdagent-patterns -u 40.4.3 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 Supportcong analysis process, they need to be saved to /usr/lib/sca/patterns/local and to be made executable. Both the 599 Developing custom analysis patterns SLES 15 SP3SCA appliance and the SCA tool will then run the custom patterns against new Supportcong 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/blog/sca-pattern-development/ . 40.5 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 very 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. 40.6 Support of kernel modules An important requirement for every enterprise operating system is the level of support you receive 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 Program are marked “external”. 600 Gathering information during the installation SLES 15 SP3If the supported ag is not set, loading this module will taint the kernel. Tainted kernels are not supported. Unsupported Kernel modules are included in an extra RPM package ( 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 |...). In addition, 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 will also taint the kernel. For details, see /usr/src/linux/Documentation/sysctl/ kernel.txt and the state of /proc/sys/kernel/tainted . 40.6.1 Technical background Linux kernel: The value of /proc/sys/kernel/unsupported defaults to 2 on SUSE Linux Enterprise 15 SP3 ( do not warn in syslog when loading unsupported modules ). This default is used in the installer and in the installed system. See /usr/src/linux/ Documentation/sysctl/kernel.txt for more information. 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 40.6.2, “Working with unsupported modules”. Note: Support SUSE does not generally support the removal of storage modules via modprobe -r . 40.6.2 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 hotx. To override the default, edit /etc/modprobe.d/10-unsupported-modules.conf and change the value of the variable allow_unsupported_modules to 1 . If an unsupported module is needed in the initrd, do not forget to run dracut -f to update the initrd. 601 Technical background SLES 15 SP3If you only want to try loading a module once, you can use the --allow-unsupported- modules option with modprobe . For more information, see 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 afterward, use the kernel command line option oem-modules . While installing and initializing 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_unsupported_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. 40.7 More information man supportconfig—The supportconfig man page. man supportconfig.conf—The man page of the Supportcong conguration 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. http://httpd.apache.org/docs/ and Chapter  35, The Apache HTTP server—Documentation about the Apache Web server. Chapter 36, Setting up an FTP server with YaST—Documentation of how to set up an FTP server. https://www.suse.com/c/blog/sca-pattern-development/ —Instructions on how to create (and test) your own SCA patterns. https://www.suse.com/c/blog/basic-server-health-check-supportconfig/ —A Basic Server Health Check with Supportcong. 602 More information SLES 15 SP3https://community.microfocus.com/t5/GroupWise-Tips-Information/Create-Your-Own- Supportconfig-Plugin/ta-p/1783289 —Create Your Own Supportcong Plugin. https://www.suse.com/c/blog/creating-a-central-supportconfig-repository/ —Creating a Central Supportcong Repository. 603 More information SLES 15 SP341 Common problems and their solutions This chapter describes a range of potential problems and their solutions. Even if your situation is not precisely listed here, there may be one similar enough to oer hints to the solution of your problem. 41.1 Finding and gathering information Linux reports things in a very detailed way. There are several places to look when you encounter problems with your system, most of which are standard to Linux systems in general, and some are relevant to SUSE Linux Enterprise Server systems. Most log les can be viewed with YaST (Miscellaneous Start-Up Log). YaST oers 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 purpose. Paths containing ~ refer to the current user''s home directory. TABLE 41.1: LOG FILES Log File Description ~/.xsession-errors Messages from the desktop applications currently running. /var/log/apparmor/ Log les from AppArmor, see Book “Security and Hardening Guide” for detailed information. /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 604 Finding and gathering information SLES 15 SP3Log 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 Various 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 41.2: System information with the /proc file system TABLE 41.2: 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. 605 Finding and gathering information SLES 15 SP3File Description /proc/ioports Shows which I/O ports are in use at the moment. /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 relationships. For more information about sysfs , see the context of udev in Chapter 24, Dynamic kernel device management with udev. Table 41.3 contains an overview of the most common directories under /sys . TABLE 41.3: 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. 606 Finding and gathering information SLES 15 SP3Each of the following scenarios begins with a header describing the problem followed by a paragraph or two oering suggested solutions, available references for more detailed solutions, and cross-references to other scenarios that are related. 41.2 Boot problems Boot problems are situations when your system does not boot properly (does not boot to the expected target and login screen). 41.2.1 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 41.5.2, “Using the rescue system” and follow the instructions in Section 41.5.2.4, “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 xes 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. 607 Boot problems SLES 15 SP341.2.2 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 conguration 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 is probably miscongured 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 17, journalctl: Query the systemd journal for more information). If these error messages hint at a conguration problem in the X server, try to x these issues. If the graphical system still does not come up, consider reinstalling the graphical desktop. 41.2.3 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. 41.2.4 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. 608 No graphical login SLES 15 SP341.2.5 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 specic swap devices: systemd.mask=dev-sda1.swap 41.2.6 GRUB 2 fails during reboot on a dual-boot system If GRUB 2 fails during reboot, disable the Fast Boot setting in the BIOS. 41.3 Login problems Login problems occur when your machine does boot to the expected welcome screen or login prompt, but refuses to accept the user name and password, or accepts them but then does not behave properly (fails to start the graphic desktop, produces errors, drops to a command line, etc.). 41.3.1 Valid user name and password combinations fail This usually occurs when the system is congured to use network authentication or directory services and, for some reason, cannot retrieve results from its congured servers. The root user, as the only local user, is the only user that can still log in to these machines. The following are some common reasons a machine appears functional but cannot process logins correctly: The network is not working. For further directions on this, turn to Section 41.4, “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 an extremely long time to respond to any action. Find more information about this topic in Section 41.4, “Network problems”. 609 Disable swap to enable booting SLES 15 SP3If the system is congured 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 synchronization across the network. The system''s authentication conguration is miscongured. Check the PAM conguration les involved for any typographical errors or misordering of directives. For additional background information about PAM and the syntax of the conguration les involved, refer to Book “Security and Hardening Guide”, Chapter 3 “Authentication with PAM”. The home partition is encrypted. Find more information about this topic in Section 41.3.3, “Login to encrypted home partition fails”. In all cases that do not involve external network problems, the solution is to reboot the system into single-user mode and repair the conguration before booting again into operating mode and attempting to log in again. To boot into single-user mode: 1. Reboot the system. The boot screen appears, oering a prompt. 2. Press Esc to exit the splash screen and get to the GRUB 2 text-based menu. 3. Press B to enter the GRUB 2 editor. 4. Add the following parameter to the line containing the kernel parameters: systemd.unit=rescue.target 5. Press F10 . 6. Enter the user name and password for root . 7. Make all the necessary changes. 8. Boot into the full multiuser and network mode by entering systemctl isolate graphical.target at the command line. 41.3.2 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 dierent reasons. 610 Valid user name and password not accepted SLES 15 SP3Local user management can fail for the following reasons: The user may have entered the wrong password. The user''s home directory containing the desktop conguration 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 prior to 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. 2. 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 41.3.4, “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 conguration les, proceed with Section 41.3.4, “GNOME desktop has issues”. In the following, common reasons a network authentication for a particular user may fail on a specic 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 conicts. 611 Valid user name and password not accepted SLES 15 SP3The 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 prior to installing the current one. To 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 diculty or if root can log in, log in and examine the system journal with 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 41.3.4, “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. 612 Valid user name and password not accepted SLES 15 SP37. If the desktop could not start because of corrupt conguration les, proceed with Section 41.3.4, “GNOME desktop has issues”. 41.3.3 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 is usually simple: 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 . 2. Become root . 3. Restart the unlocking process again with: root # 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. 41.3.4 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 oers the safest option to x a broken GNOME desktop. PROCEDURE 41.1: 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. 613 Login to encrypted home partition fails SLES 15 SP35. 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 conguration le that breaks GNOME. 7. Log in as the old user, and move the oending conguration le to a dierent location. Log out and log in again as the old user. 8. Delete the previously created user. 41.4 Network problems Many problems of your system may be network-related, even though they do not seem to be at rst. For example, the reason for a system not allowing users to log in may be a network problem of some kind. This section introduces a simple checklist you can apply to identify the cause of any network problem encountered. PROCEDURE 41.2: 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 administrator. The following list gives some typical network servers involved in a setup together with the symptoms of an outage. DNS (name service) 614 Network problems SLES 15 SP3A broken or malfunctioning name service aects 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 completely broken NTP service could aect Kerberos authentication and X server functionality. NFS (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 miscongured. In the worst case scenario, a user''s personal desktop conguration 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 will not work and login to any machine fails. CUPS (network printing) Users cannot print. 615 Network problems SLES 15 SP34. 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 server/ 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 congured correctly. If ping fails with destination host unreachable , either your system or the desired server is not properly congured 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 congured correctly. If ping fails with unknown host , the name service is not congured 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 congured 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 conguration 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 following structure and all network addresses and domain names are correct: search FULLY_QUALIFIED_DOMAIN_NAME nameserver IPADDRESS_OF_NAMESERVER 616 Network problems SLES 15 SP3This 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: ... hosts: 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 administrator check the DNS server conguration for the correct zone information. For detailed information about DNS, refer to Chapter 32, The domain name system. If you have made sure that the DNS conguration of your host and the DNS server are correct, proceed with checking the conguration of your network and network device. c. If your system cannot establish a connection to a network server and you have excluded name service problems from the list of possible culprits, check the conguration of your network card. Use the command ip addr show NETWORK_DEVICE to check whether this device was properly congured. Make sure that the inet address with the netmask ( /MASK ) is congured correctly. An error in the IP address or a missing bit in your network mask would render your network conguration unusable. If necessary, perform this check on the server as well. 617 Network problems SLES 15 SP3d. If the name service and network hardware are properly congured and running, but some external network connections still get long time-outs or fail entirely, use traceroute FULLY_QUALIFIED_DOMAIN_NAME (executed as root ) to track the network 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 identied 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 ndings so they can recongure the services or repair the necessary systems. 41.4.1 NetworkManager problems If you have a problem with network connectivity, narrow it down as described in Procedure 41.2, “How to identify network problems”. If NetworkManager seems to be the culprit, 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: tux > sudo systemctl restart NetworkManager 3. Open a Web page, for example, http://www.opensuse.org as normal user to see, if you can connect. 4. Collect any information about the state of NetworkManager in /var/log/ NetworkManager . For more information about NetworkManager, refer to Chapter 26, Using NetworkManager. 41.5 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. 618 NetworkManager problems SLES 15 SP341.5.1 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 some space. PROCEDURE 41.3: 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 ). 3. Decide where you want to store your image (labeled as BACKUP_PATH ). It must be dierent 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: root # dd if=/dev/SOURCE | gzip > /BACKUP_PATH/image.gz 5. Restore the hard disk with the following commands: root # 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 dierent partition. 41.5.2 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 conguration les, or a corrupted boot loader conguration 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 conguration le. Check the le system for defects and start automatic repair processes. Access the installed system in a “change root” environment. 619 Managing partition images SLES 15 SP3Check, modify, and re-install the boot loader conguration. 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 http://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. Note: 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 41.6, “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 conguration of your PXE boot setup and add the lines install=PROTOCOL:// 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 installation source. 2. Boot the system using “Wake on LAN”, as described in Book “Deployment Guide”, Chapter 17 “Preparing network boot environment”, Section 17.5 “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 . 620 Using the rescue system SLES 15 SP3A shell and other useful utilities, such as the mount program, are available in the /bin directory. The /sbin directory contains important le and network utilities for reviewing and repairing the le system. This directory also contains the most important binaries for system maintenance, 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 journalctl . 41.5.2.1 Checking and manipulating configuration files As an example for a conguration that might be xed using the rescue system, imagine you have a broken conguration le that prevents the system from booting properly. You can x this using the rescue system. To manipulate a conguration 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 following command: tux > 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: tux > sudo cd /mnt 4. Open the problematic conguration le in the vi editor. Adjust and save the conguration. 5. Unmount the root le system from the rescue system: tux > sudo umount /mnt 6. Reboot the machine. 621 Using the rescue system SLES 15 SP341.5.2.2 Repairing and checking file systems Generally, le systems cannot be repaired on a running system. If you encounter serious problems, 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 utilities to check and repair the btrfs , ext2 , ext3 , ext4 , xfs , dosfs , and vfat le systems. Look for the command fsck.FILESYSTEM . For example, if you need a le system check for btrfs , use fsck.btrfs . 41.5.2.3 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 conguration, or to execute a hardware conguration 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: tux > 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] ├─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: tux > sudo mount /dev/sda2 /mnt 622 Using the rescue system SLES 15 SP33. Mount /proc , /dev , and /sys partitions: tux > sudo mount -t proc none /mnt/proc tux > sudo mount --rbind /dev /mnt/dev tux > sudo mount --rbind /sys /mnt/sys 4. Now you can “change root” into the new environment, keeping the bash shell: tux > chroot /mnt /bin/bash 5. Finally, mount the remaining partitions from the installed system: tux > 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 rescue 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, otherwise you need to supply their correct versions on other media, such as a ash disk. Most often the rescue kernel version diers 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 . 41.5.2.4 Modifying and re-installing the boot loader Sometimes a system cannot boot because the boot loader conguration 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. 623 Using the rescue system SLES 15 SP3To check the boot loader conguration and re-install the boot loader, proceed as follows: 1. Perform the necessary steps to access the installed system as described in Section 41.5.2.3, “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 tux > sudo grub2-install /dev/sda 3. Check whether the following les are correctly congured according to the GRUB  2 conguration principles outlined in Chapter 14, The boot loader GRUB 2 and apply xes if necessary. /etc/default/grub /boot/grub2/device.map (optional le, only present if created manually) /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: tux > sudo grub2-mkconfig -o /boot/grub2/grub.cfg 5. Unmount the partitions, log out from the “change root” environment, and reboot the system: tux > umount -a exit reboot 41.5.2.5 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. 624 Using the rescue system SLES 15 SP3Tip: 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 Book “Deployment Guide”, Chapter  23 “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 supported by SUSE Linux Enterprise Server. For example when a hardware vendor uses a specic 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 conrm 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 41.5.2.3, “Accessing the installed system”. 6. 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 xing 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 . 625 Using the rescue system SLES 15 SP3b. 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 avor with the rpm -i command. 7. Update conguration les and reinitialize the boot loader if needed. For more information, see Section 41.5.2.4, “Modifying and re-installing the boot loader”. 8. Remove any bootable media from the system drive and reboot. 41.6 IBM Z: using initrd as a rescue system If the kernel of the SUSE® Linux Enterprise Server for IBM Z is upgraded or modied, 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 “Deployment 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 congured. You need to congure them before you can proceed. PROCEDURE 41.4: CONFIGURING DASDS 1. Congure DASDs with the following command: dasd_configure 0.0.0150 1 0 0.0.0150 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 subsequent commands. 626 IBM Z: using initrd as a rescue system SLES 15 SP3PROCEDURE 41.5: CONFIGURING A ZFCP DISK 1. To congure a zFCP disk, it is necessary to rst congure 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 congured. Do this with the following command: 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 subsequent commands. Now the rescue system is fully set up and you can start repairing the installed system. See Section 41.5.2, “Using the rescue system” for instructions on how to repair the most common issues. 627 IBM Z: using initrd as a rescue system SLES 15 SP3A An example network This example network is used across all network-related chapters of the SUSE® Linux Enterprise Server documentation. 628 SLES 15 SP3B GNU licenses XML for which the DTD and/or processing tools are not generally available, and the machine- This appendix contains the GNU Free generated HTML, PostScript or PDF produced by some word processors for output purposes only. Documentation 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 sub-unit of the Document whose title either Copyright (C) 2000, 2001, 2002 Free Software Foundation, Inc. 51 Franklin St, Fifth Floor, is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in Boston, MA 02110-1301 USA. Everyone is permitted to copy and distribute verbatim copies another language. (Here XYZ stands for a specic section name mentioned below, such as of this license document, but changing it is not allowed. "Acknowledgements", "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" 0. PREAMBLE according to this denition. 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 eective 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 eect 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 modications 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 "Modied 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 modications 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, those of Invariant Sections, in the notice that says that the Document is released under this or state in or with each Opaque copy a computer-network location from which the general License. If a section does not t the above denition of Secondary then it is not allowed to be network-using public has access to download using public-standard network protocols a designated as Invariant. The Document may contain zero Invariant Sections. If the Document complete Transparent copy of the Document, free of added material. If you use the latter does not identify any Invariant Sections then there are none. option, you must take reasonably prudent steps, when you begin distribution of Opaque copies The "Cover Texts" are certain short passages of text that are listed, as Front-Cover Texts or in quantity, to ensure that this Transparent copy will remain thus accessible at the stated Back-Cover Texts, in the notice that says that the Document is released under this License. A location until at least one year after the last time you distribute an Opaque copy (directly or Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words. through your agents or retailers) of that edition to the public. A "Transparent" copy of the Document means a machine-readable copy, represented in a It is requested, but not required, that you contact the authors of the Document well before format whose specication is available to the general public, that is suitable for revising redistributing any large number of copies, to give them a chance to provide you with an the document straightforwardly with generic text editors or (for images composed of pixels) updated version of the Document. generic 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 modication 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, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modication. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or 629 SLES 15 SP34. 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 Modied Version. You may copy and distribute a Modied Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modied Version under precisely this 5. COMBINING DOCUMENTS License, with the Modied Version lling the role of the Document, thus licensing distribution and modication of the Modied 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 Modied Version: the terms dened in section 4 above for modied versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodied, 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 Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections B. List on the Title Page, as authors, one or more persons or entities responsible for with the same name but dierent contents, make the title of each such section unique by authorship of the modications in the Modied Version, together with at least ve adding at the end of it, in parentheses, the name of the original author or publisher of that of the principal authors of the Document (all of its principal authors, if it has fewer section if known, or else a unique number. Make the same adjustment to the section titles in than ve), unless they release you from this requirement. the list of Invariant Sections in the license notice of the combined work. C. State on the Title page the name of the publisher of the Modied 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 modications 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 Modied 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 Modied 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 Modied Version as stated in A compilation of the Document or its derivatives with other separate and independent the previous sentence. documents 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 J. Preserve the network location, if any, given in the Document for public access to of the compilation''s users beyond what the individual works permit. When the Document is a Transparent copy of the Document, and likewise the network locations given in included in an aggregate, this License does not apply to the other works in the aggregate the Document for previous versions it was based on. These may be placed in the which are not 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 modication, 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 Modied 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 conict 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 Modied Version includes new front-matter sections or appendices that qualify as original version will prevail. Secondary Sections and contain no material copied from the Document, you may at your If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the option designate some or all of these sections as invariant. To do this, add their titles to the requirement (section 4) to Preserve its Title (section 1) will typically require changing the list of Invariant Sections in the Modied Version''s license notice. These titles must be distinct actual title. from any other section titles. You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modied Version by various parties--for example, statements of peer 9. TERMINATION review or that the text has been approved by an organization as the authoritative denition You may not copy, modify, sublicense, or distribute the Document except as expressly of a standard. provided 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 Modied 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. 630 SLES 15 SP310. FUTURE REVISIONS OF THIS LICENSE The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may dier in detail to address new problems or concerns. See http:// www.gnu.org/copyleft/ . Each version of the License is given a distinguishing version number. If the Document species 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 specied 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. 631 SLES 15 SP3">