Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or (at your option) version 1.3; with the Invariant Section being this copyright notice and license. A copy of the license version 1.2 is included in the section entitled “GNU Free Documentation License”.

For SUSE trademarks, see https://www.suse.com/company/legal/. All other third-party trademarks are the property of their respective owners. Trademark symbols (®, ™ etc.) denote trademarks of SUSE and its affiliates. Asterisks (*) denote third-party trademarks.

All information found in this book has been compiled with utmost attention to detail. However, this does not guarantee complete accuracy. Neither SUSE LLC, its affiliates, the authors nor the translators shall be held liable for possible errors or the consequences thereof.

About This Guide #Edit source

Available Documentation
Giving Feedback
Documentation Conventions
Product Life Cycle and Support

This guide is intended for use by professional network and system administrators during the operation of SUSE® Linux Enterprise. As such, it is solely concerned with ensuring that SUSE Linux Enterprise is properly configured and that the required services on the network are available to allow it to function properly as initially installed. This guide does not cover the process of ensuring that SUSE Linux Enterprise offers proper compatibility with your enterprise's application software or that its core functionality meets those requirements. It assumes that a full requirements audit has been done and the installation has been requested, or that a test installation for such an audit has been requested.

This guide contains the following:

Support and Common Tasks: SUSE Linux Enterprise offers a wide range of tools to customize various aspects of the system. This part introduces a few of them. A breakdown of available device technologies, high availability configurations, and advanced administration possibilities introduces the system to the administrator.
System: Learn more about the underlying operating system by studying this part. SUSE Linux Enterprise supports several hardware architectures and you can use this to adapt your own applications to run on SUSE Linux Enterprise. The boot loader and boot procedure information assists you in understanding how your Linux system works and how your own custom scripts and applications may blend in with it.
Services: SUSE Linux Enterprise is designed to be a network operating system. It offers a wide range of network services, such as DNS, DHCP, Web, proxy, and authentication services. It also integrates well into heterogeneous environments, including MS Windows clients and servers.
Mobile Computers: Laptops, and the communication between mobile devices like PDAs, or cellular phones and SUSE Linux Enterprise need some special attention. Take care for power conservation and for the integration of different devices into a changing network environment. Also get in touch with the background technologies that provide the needed functionality.
Troubleshooting: Provides an overview of finding help and additional documentation when you need more information or want to perform specific tasks. There is also a list of the most frequent problems with explanations of how to fix them.

1 Available Documentation #Edit source

Note: Online Documentation and Latest Updates

Documentation for our products is available at https://documentation.suse.com/, where you can also find the latest updates, and browse or download the documentation in various formats. The latest documentation updates are usually available in the English version of the documentation.

The following documentation is available for this product:

Article “Installation Quick Start”: This Quick Start guides you step-by-step through the installation of SUSE® Linux Enterprise Server 15 SP1.
Book “Deployment Guide”: This guide details how to install single or multiple systems, and how to exploit the product-inherent capabilities for a deployment infrastructure. Choose from various approaches: local installation from physical installation media, customizing the standard installation images, network installation server, mass deployment using a remote-controlled, highly-customized, automated installation process, and initial system configuration.
Administration Guide: Covers system administration tasks like maintaining, monitoring and customizing an initially installed system.
Book “Virtualization Guide”: Describes virtualization technology in general, and introduces libvirt—the unified interface to virtualization—and detailed information on specific hypervisors.
Book “Storage Administration Guide”: Provides information about how to manage storage devices on a SUSE Linux Enterprise Server.
Book “AutoYaST Guide”: AutoYaST is a system for unattended mass deployment of SUSE Linux Enterprise Server systems using an AutoYaST profile containing installation and configuration data. The manual guides you through the basic steps of auto-installation: preparation, installation, and configuration.
Book “Security and Hardening Guide”: Introduces basic concepts of system security, covering both local and network security aspects. Shows how to use the product inherent security software like AppArmor, SELinux, or the auditing system that reliably collects information about any security-relevant events. Supports the administrator with security-related choices and decisions in installing and setting up a secure SUSE Linux Enterprise Server and additional processes to further secure and harden that installation.
Book “System Analysis and Tuning Guide”: An administrator's guide for problem detection, resolution and optimization. Find how to inspect and optimize your system by means of monitoring tools and how to efficiently manage resources. Also contains an overview of common problems and solutions and of additional help and documentation resources.
Book “Repository Mirroring Tool Guide”: An administrator's guide to Subscription Management Tool—a proxy system for SUSE Customer Center with repository and registration targets. Learn how to install and configure a local SMT server, mirror and manage repositories, manage client machines, and configure clients to use SMT.
Book “GNOME User Guide”: Introduces the GNOME desktop of SUSE Linux Enterprise Server. It guides you through using and configuring the desktop and helps you perform key tasks. It is intended mainly for end users who want to make efficient use of GNOME as their default desktop.

The release notes for this product are available at https://www.suse.com/releasenotes/.

2 Giving Feedback #Edit source

Your feedback and contribution to this documentation is welcome! Several channels are available:

Service Requests and Support

For services and support options available for your product, refer to https://www.suse.com/support/.

To open a service request, you need a subscription at SUSE Customer Center. Go to https://scc.suse.com/support/requests, log in, and click Create New.

Bug Reports

Report issues with the documentation at https://bugzilla.suse.com/. To simplify this process, you can use the Report Documentation Bug links next to headlines in the HTML version of this document. These preselect the right product and category in Bugzilla and add a link to the current section. You can start typing your bug report right away. A Bugzilla account is required.

Contributions

To contribute to this documentation, use the Edit Source links next to headlines in the HTML version of this document. They take you to the source code on GitHub, where you can open a pull request. A GitHub account is required.

For more information about the documentation environment used for this documentation, see the repository's README.

Mail

Alternatively, you can report errors and send feedback concerning the documentation to <doc-team@suse.com>. Make sure to include the document title, the product version and the publication date of the documentation. Refer to the relevant section number and title (or include the URL) and provide a concise description of the problem.

3 Documentation Conventions #Edit source

The following notices and typographical conventions are used in this documentation:

/etc/passwd: directory names and file names
PLACEHOLDER: replace PLACEHOLDER with the actual value
PATH: the environment variable PATH
ls, --help: commands, options, and parameters
user: users or groups
package name : name of a package
Alt, Alt–F1: a key to press or a key combination; keys are shown in uppercase as on a keyboard
File, File › Save As: menu items, buttons
AMD/Intel This paragraph is only relevant for the AMD64/Intel 64 architecture. The arrows mark the beginning and the end of the text block.
IBM Z, POWER This paragraph is only relevant for the architectures IBM Z and POWER. The arrows mark the beginning and the end of the text block.
Dancing Penguins (Chapter Penguins, ↑Another Manual): This is a reference to a chapter in another manual.
Commands that must be run with root privileges. Often you can also prefix these commands with the sudo command to run them as non-privileged user.
```
root # command
tux > sudo command
```
Commands that can be run by non-privileged users.
```
tux > command
```
Notices
Warning: Warning Notice
Vital information you must be aware of before proceeding. Warns you about security issues, potential loss of data, damage to hardware, or physical hazards.
Important: Important Notice
Important information you should be aware of before proceeding.
Note: Note Notice
Additional information, for example about differences in software versions.
Tip: Tip Notice
Helpful information, like a guideline or a piece of practical advice.

4 Product Life Cycle and Support #Edit source

SUSE products are supported for up to 13 years. To check the life cycle dates for your product, see https://www.suse.com/lifecycle/.

For SUSE Linux Enterprise, the following life cycles and release cycles apply:

SUSE Linux Enterprise Server has a 13-year life cycle: 10 years of general support and three years of extended support.
SUSE Linux Enterprise Desktop has a 10-year life cycle: seven years of general support and three years of extended support.
Major releases are published every four years. Service packs are published every 12-14 months.
SUSE supports previous SUSE Linux Enterprise service packs for six months after the release of a new service pack.

For some products, Long Term Service Pack Support (LTSS) is available. Find information about our support policy and options at https://www.suse.com/support/policy.html and https://www.suse.com/support/programs/long-term-service-pack-support.html.

Modules have a different life cycle, update policy, and update timeline than their base products. Modules contain software packages and are fully supported parts of SUSE Linux Enterprise Server. For more information, see the Article “Modules and Extensions Quick Start”.

4.1 Support Statement for SUSE Linux Enterprise Server #Edit source

To receive support, you need an appropriate subscription with SUSE. To view the specific support offerings available to you, go to https://www.suse.com/support/ and select your product.

The support levels are defined as follows:

L1: Problem determination, which means technical support designed to provide compatibility information, usage support, ongoing maintenance, information gathering and basic troubleshooting using available documentation.
L2: Problem isolation, which means technical support designed to analyze data, reproduce customer problems, isolate problem area and provide a resolution for problems not resolved by Level 1 or prepare for Level 3.
L3: Problem resolution, which means technical support designed to resolve problems by engaging engineering to resolve product defects which have been identified by Level 2 Support.

For contracted customers and partners, SUSE Linux Enterprise Server is delivered with L3 support for all packages, except for the following:

Technology Previews
Sound, graphics, fonts and artwork.
Packages that require an additional customer contract.
Some packages shipped as part of the module Workstation Extension are L2-supported only.
Packages with names ending in -devel (containing header files and similar developer resources) will only be supported together with their main packages.

SUSE will only support the usage of original packages. That is, packages that are unchanged and not recompiled.

4.2 Technology Previews #Edit source

Technology previews are packages, stacks, or features delivered by SUSE to provide glimpses into upcoming innovations. The previews are included for your convenience to give you the chance to test new technologies within your environment. We would appreciate your feedback! If you test a technology preview, please contact your SUSE representative and let them know about your experience and use cases. Your input is helpful for future development.

However, technology previews come with the following limitations:

Technology previews are still in development. Therefore, they may be functionally incomplete, unstable, or in other ways not suitable for production use.
Technology previews are not supported.
Technology previews may only be available for specific hardware architectures.
Details and functionality of technology previews are subject to change. As a result, upgrading to subsequent releases of a technology preview may be impossible and require a fresh installation.
Technology previews can be dropped at any time. For example, if SUSE discovers that a preview does not meet the customer or market needs, or does not prove to comply with enterprise standards. SUSE does not commit to providing a supported version of such technologies in the future.

For an overview of technology previews shipped with your product, see the release notes at https://www.suse.com/releasenotes/.

Part I Common Tasks #Edit source

1 Bash and Bash Scripts

Today, many people use computers with a graphical user interface (GUI) like GNOME. Although GUIs offer many features, they're limited when performing automated task execution. Shells complement GUIs well, and this chapter gives an overview of some aspects of shells, in this case the Bash shell.

2 sudo

Many commands and system utilities need to be run as root to modify files and/or perform tasks that only the super user is allowed to. For security reasons and to avoid accidentally running dangerous commands, it is generally advisable not to log in directly as root. Instead, it is recommended to wo…

3 YaST Online Update

SUSE offers a continuous stream of software security updates for your product. By default, the update applet is used to keep your system up-to-date. Refer to Book “Deployment Guide”, Chapter 20 “Installing or Removing Software”, Section 20.5 “The GNOME Package Updater” for further information on the…

4 YaST

YaST is the installation and configuration tool for SUSE Linux Enterprise Server. It has a graphical interface and the capability to customize your system quickly during and after the installation. It can be used to set up hardware, configure the network, system services, and tune your security sett…

5 YaST in Text Mode

This section is intended for system administrators and experts who do not run an X server on their systems and depend on the text-based installation tool. It provides basic information about starting and operating YaST in text mode.

6 Managing Software with Command Line Tools

This chapter describes Zypper and RPM, two command line tools for managing software. For a definition of the terminology used in this context (for example, repository, patch, or update) refer to Book “Deployment Guide”, Chapter 20 “Installing or Removing Software”, Section 20.1 “Definition of Terms”.

7 System Recovery and Snapshot Management with Snapper

Snapper allows creating and managing file system snapshots. File system snapshots allow keeping a copy of the state of a file 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 file system or thinly-provisioned LVM volumes with an XFS or Ext4 file system.

8 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.

9 Transactional Updates

Transactional updates are available in SUSE Linux Enterprise Server as a technology preview, for updating SLES when the root filesystem is read-only. Transactional updates are atomic (all updates are applied only if all updates succeed) and support rollbacks. It does not affect 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 file 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 file 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 configurable.

Only packages that are part of the snapshot of the root file system can be updated. If packages contain files 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.

10 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 different 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 offer both kinds of sessions simultaneously on different ports, but an open session cannot be converted from one type to the other.

11 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 files and documents in synchronization across multiple devices all the more important.

1 Bash and Bash Scripts #Edit source

1.1 What is “The Shell”?
1.2 Writing Shell Scripts
1.3 Redirecting Command Events
1.4 Using Aliases
1.5 Using Variables in Bash
1.6 Grouping and Combining Commands
1.7 Working with Common Flow Constructs
1.8 For More Information

1.1 What is “The Shell”? #Edit source

Traditionally, the Linux shell is Bash (Bourne again Shell). When this chapter speaks about “the shell” it means Bash. There are more shells available (ash, csh, ksh, zsh, …), each employing different features and characteristics. If you need further information about other shells, search for shell in YaST.

1.1.1 Bash Configuration Files #Edit source

A shell can be invoked as an:

Interactive login shell. This is used when logging in to a machine, invoking Bash with the --login option or when logging in to a remote machine with SSH.
“Ordinary” interactive shell. This is normally the case when starting xterm, konsole, gnome-terminal, or similar command-line interface (CLI) tools.
Non-interactive shell. This is invoked when invoking a shell script at the command line.

Depending on the type of shell you use, different configuration files will be read. The following tables show the login and non-login shell configuration files.

Table 1.1: Bash Configuration Files for Login Shells #

File	Description
`/etc/profile`	Do not modify this file, otherwise your modifications may be destroyed during your next update!
`/etc/profile.local`	Use this file if you extend `/etc/profile`
`/etc/profile.d/`	Contains system-wide configuration files for specific programs
`~/.profile`	Insert user specific configuration for login shells here

Note that the login shell also sources the configuration files listed under Table 1.2, “Bash Configuration Files for Non-Login Shells”.

Table 1.2: Bash Configuration Files for Non-Login Shells #

`/etc/bash.bashrc`	Do not modify this file, otherwise your modifications may be destroyed during your next update!
`/etc/bash.bashrc.local`	Use this file to insert your system-wide modifications for Bash only
`~/.bashrc`	Insert user specific configuration here

Additionally, Bash uses some more files:

Table 1.3: Special Files for Bash #

File	Description
`~/.bash_history`	Contains a list of all commands you have typed
`~/.bash_logout`	Executed when logging out
`~/.alias`	User defined aliases of frequently used commands. See `man 1 alias` for more details about defining aliases.

No-Login Shells#Edit source

There are special shells that block users from logging into the system: /bin/false and /sbin/nologin. Both fail silently when the user attempts to log into the system. This was intended as a security measure for system users, though modern Linux operating systems have more effective tools for controlling system access, such as PAM and AppArmor.

The default on SUSE Linux Enterprise Server is to assign /bin/bash to human users, and /bin/false or /sbin/nologin to system users. The nobody user has /bin/bash for historical reasons, as it is a minimally-privileged user that used to be the default for system users. However, whatever little bit of security gained by using nobody is lost when multiple system users use it. It should be possible to change it to /sbin/nologin; the fastest way to test it is change it and see if it breaks any services or applications.

Use the following command to list which shells are assigned to all users, system and human users, in /etc/passwd. The output varies according to the services and users on your system:

tux > sort -t: -k 7 /etc/passwd | awk -F: '{print $1"\t" $7}' | column -t
tux               /bin/bash
nobody            /bin/bash
root              /bin/bash
avahi             /bin/false
chrony            /bin/false
dhcpd             /bin/false
dnsmasq           /bin/false
ftpsecure         /bin/false
lightdm           /bin/false
mysql             /bin/false
postfix           /bin/false
rtkit             /bin/false
sshd              /bin/false
tftp              /bin/false
unbound           /bin/false
bin               /sbin/nologin
daemon            /sbin/nologin
ftp               /sbin/nologin
lp                /sbin/nologin
mail              /sbin/nologin
man               /sbin/nologin
nscd              /sbin/nologin
polkitd           /sbin/nologin
pulse             /sbin/nologin
qemu              /sbin/nologin
radvd             /sbin/nologin
rpc               /sbin/nologin
statd             /sbin/nologin
svn               /sbin/nologin
systemd-coredump  /sbin/nologin
systemd-network   /sbin/nologin
systemd-timesync  /sbin/nologin
usbmux            /sbin/nologin
vnc               /sbin/nologin
wwwrun            /sbin/nologin
messagebus        /usr/bin/false
scard             /usr/sbin/nologin

1.1.2 The Directory Structure #Edit source

The following table provides a short overview of the most important higher-level directories that you find on a Linux system. Find more detailed information about the directories and important subdirectories in the following list.

Table 1.4: Overview of a Standard Directory Tree #

Directory	Contents
`/`	Root directory—the starting point of the directory tree.
`/bin`	Essential binary files, such as commands that are needed by both the system administrator and normal users. Usually also contains the shells, such as Bash.
`/boot`	Static files of the boot loader.
`/dev`	Files needed to access host-specific devices.
`/etc`	Host-specific system configuration files.
`/home`	Holds the home directories of all users who have accounts on the system. However, `root`'s home directory is not located in `/home` but in `/root`.
`/lib`	Essential shared libraries and kernel modules.
`/media`	Mount points for removable media.
`/mnt`	Mount point for temporarily mounting a file system.
`/opt`	Add-on application software packages.
`/root`	Home directory for the superuser `root`.
`/sbin`	Essential system binaries.
`/srv`	Data for services provided by the system.
`/tmp`	Temporary files.
`/usr`	Secondary hierarchy with read-only data.
`/var`	Variable data such as log files.
`/windows`	Only available if you have both Microsoft Windows* and Linux installed on your system. Contains the Windows data.

The following list provides more detailed information and gives some examples of which files and subdirectories can be found in the directories:

/bin

Contains the basic shell commands that may be used both by root and by other users. These commands include ls, mkdir, cp, mv, rm and rmdir. /bin also contains Bash, the default shell in SUSE Linux Enterprise Server.

/boot

Contains data required for booting, such as the boot loader, the kernel, and other data that is used before the kernel begins executing user-mode programs.

/dev

Holds device files that represent hardware components.

/etc

Contains local configuration files that control the operation of programs like the X Window System. The /etc/init.d subdirectory contains LSB init scripts that can be executed during the boot process.

/home/USERNAME

Holds the private data of every user who has an account on the system. The files located here can only be modified by their owner or by the system administrator. By default, your e-mail directory and personal desktop configuration are located here in the form of hidden files and directories, such as .gconf/ and .config.

Note: Home Directory in a Network Environment

If you are working in a network environment, your home directory may be mapped to a directory in the file system other than /home.

/lib

Contains the essential shared libraries needed to boot the system and to run the commands in the root file system. The Windows equivalent for shared libraries are DLL files.

/media

Contains mount points for removable media, such as CD-ROMs, flash disks, and digital cameras (if they use USB). /media generally holds any type of drive except the hard disk of your system. When your removable medium has been inserted or connected to the system and has been mounted, you can access it from here.

/mnt

This directory provides a mount point for a temporarily mounted file system. root may mount file systems here.

/opt

Reserved for the installation of third-party software. Optional software and larger add-on program packages can be found here.

/root

Home directory for the root user. The personal data of root is located here.

/run

A tmpfs directory used by systemd and various components. /var/run is a symbolic link to /run.

/sbin

As the s indicates, this directory holds utilities for the superuser. /sbin contains the binaries essential for booting, restoring and recovering the system in addition to the binaries in /bin.

/srv

Holds data for services provided by the system, such as FTP and HTTP.

/tmp

This directory is used by programs that require temporary storage of files.

Important: Cleaning up `/tmp` at Boot Time

Data stored in /tmp is not guaranteed to survive a system reboot. It depends, for example, on settings made in /etc/tmpfiles.d/tmp.conf.

/usr

/usr has nothing to do with users, but is the acronym for Unix system resources. The data in /usr is static, read-only data that can be shared among various hosts compliant with the Filesystem Hierarchy Standard (FHS). This directory contains all application programs including the graphical desktops such as GNOME and establishes a secondary hierarchy in the file system. /usr holds several subdirectories, such as /usr/bin, /usr/sbin, /usr/local, and /usr/share/doc.

/usr/bin

Contains generally accessible programs.

/usr/sbin

Contains programs reserved for the system administrator, such as repair functions.

/usr/local

In this directory the system administrator can install local, distribution-independent extensions.

/usr/share/doc

Holds various documentation files and the release notes for your system. In the manual subdirectory find an online version of this manual. If more than one language is installed, this directory may contain versions of the manuals for different languages.

Under packages find the documentation included in the software packages installed on your system. For every package, a subdirectory /usr/share/doc/packages/PACKAGENAME is created that often holds README files for the package and sometimes examples, configuration files or additional scripts.

If HOWTOs are installed on your system /usr/share/doc also holds the howto subdirectory in which to find additional documentation on many tasks related to the setup and operation of Linux software.

/var

Whereas /usr holds static, read-only data, /var is for data which is written during system operation and thus is variable data, such as log files or spooling data. For an overview of the most important log files you can find under /var/log/, refer to Table 44.1, “Log Files”.

1.2 Writing Shell Scripts #Edit source

Shell scripts provide a convenient way to perform a wide range of tasks: collecting data, searching for a word or phrase in a text and other useful things. The following example shows a small shell script that prints a text:

Example 1.1: A Shell Script Printing a Text #

#!/bin/sh 1
# Output the following line: 2
echo "Hello World" 3

1	The first line begins with the Shebang characters (`#!`) which indicate that this file is a script. The interpreter, specified after the Shebang, executes the script. In this case, the specified interpreter is `/bin/sh`.
2	The second line is a comment beginning with the hash sign. We recommend that you comment difficult lines. With proper commenting, you can remember the purpose and function of the line. Also, other readers will hopefully understand your script. Commenting is considered good practice in the development community.
3	The third line uses the built-in command `echo` to print the corresponding text.

Before you can run this script, there are a few prerequisites:

Every script should contain a Shebang line (as in the example above). If the line is missing, you need to call the interpreter manually.
You can save the script wherever you want. However, it is a good idea to save it in a directory where the shell can find it. The search path in a shell is determined by the environment variable PATH. Usually a normal user does not have write access to /usr/bin. Therefore it is recommended to save your scripts in the users' directory ~/bin/. The above example gets the name hello.sh.
The script needs executable permissions. Set the permissions with the following command:
```
tux > chmod +x ~/bin/hello.sh
```

If you have fulfilled all of the above prerequisites, you can execute the script in the following ways:

As Absolute Path. The script can be executed with an absolute path. In our case, it is ~/bin/hello.sh.
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 #Edit source

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 file, an existing file will be deleted. For example, the ls command writes its output into the file listing.txt:

tux > ls > listing.txt

Command >> File

Appends the output of the command to a file. For example, the ls command appends its output to the file listing.txt:

tux > ls >> listing.txt

Command < File

Reads the file as input for the given command. For example, the read command reads in the content of the file into the variable:

tux > read a < foo

Command1 | Command2

Redirects the output of the left command as input for the right command. For example, the cat command outputs the content of the /proc/cpuinfo file. This output is used by grep to filter only those lines which contain cpu:

tux > cat /proc/cpuinfo | grep cpu

Every channel has a file descriptor: 0 (zero) for standard input, 1 for standard output and 2 for standard error. It is allowed to insert this file descriptor before a < or > character. For example, the following line searches for a file starting with foo, but suppresses its errors by redirecting it to /dev/null:

tux > find / -name "foo*" 2>/dev/null

1.4 Using Aliases #Edit source

An alias is a shortcut definition of one or more commands. The syntax for an alias is:

alias NAME=DEFINITION

For example, the following line defines an alias lt that outputs a long listing (option -l), sorts it by modification time (-t), and prints it in reverse sorted order (-r):

tux > alias lt='ls -ltr'

To view all alias definitions, use alias. Remove your alias with unalias and the corresponding alias name.

1.5 Using Variables in Bash #Edit source

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

To 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`	specifies the normal prompt printed before each command
`PS2`	specifies the secondary prompt printed when you execute a multi-line command
`PWD`	current working directory
`USER`	the current user

1.5.1 Using Argument Variables #Edit source

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 first 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 #Edit source

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

${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 #Edit source

Shells allow you to concatenate and group commands for conditional execution. Each command returns an exit code which determines the success or failure of its operation. If it is 0 (zero) the command was successful, everything else marks an error which is specific to the command.

The following list shows, how commands can be grouped:

Command1 ; Command2

executes the commands in sequential order. The exit code is not checked. The following line displays the content of the file with cat and then prints its file 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 file and prints its file 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

funcname(){ ... }

creates a shell function. You can use the positional parameters to access its arguments. The following line defines the function hello to print a short message:

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 #Edit source

To control the flow of your script, a shell has while, if, for and case constructs.

1.7.1 The if Control Command #Edit source

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 file foo.txt exists:

if test -e /tmp/foo.txt ; then
  echo "Found foo.txt"
fi

The test expression can also be abbreviated in square brackets:

if [ -e /tmp/foo.txt ] ; then
  echo "Found foo.txt"
fi

Find more useful expressions at https://bash.cyberciti.biz/guide/If..else..fi.

1.7.2 Creating Loops with the `for` Command #Edit source

The for loop allows you to execute commands to a list of entries. For example, the following code prints some information about PNG files in the current directory:

for i in *.png; do
 ls -l $i
done

1.8 For More Information #Edit source

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

Many commands and system utilities need to be run as root to modify files and/or perform tasks that only the super user is allowed to. For security reasons and to avoid accidentally running dangerous commands, it is generally advisable not to log in directly as root. Instead, it is recommended to work as a normal, unprivileged user and use the sudo command to run commands with elevated privileges.

On SUSE Linux Enterprise Server, sudo is configured by default to work similarly to su. However, sudo offers the possibility to allow users to run commands with privileges of any other user in a highly configurable manner. This can be used to assign roles with specific privileges to certain users and groups. It is for example possible to allow members of the group users to run a command with the privileges of wilber. Access to the command can be further restricted by, for example, forbidding to specify any command options. While su always requires the root password for authentication with PAM, sudo can be configured to authenticate with your own credentials. This increases security by not having to share the root password. For example, you can allow members of the group users to run a command frobnicate as wilber, with the restriction that no arguments are specified. This can be used to assign roles with specific abilities to certain users and groups.

2.1 Basic `sudo` Usage #Edit source

sudo is simple to use, yet very powerful.

2.1.1 Running a Single Command #Edit source

Logged in as normal user, you can run any command as root by adding sudo before it. It will prompt for the root password and, if authenticated successfully, run the command as root:

tux > id -un1
tux
tux > sudo id -un
root's password:2
root
tux > id -un
tux3
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 bullets.
3	Only commands started with `sudo` are run with elevated privileges. If you run the same command without the `sudo` prefix, it is run with the privileges of the current user again.
4	For a limited amount of time, you do not need to enter the `root` password again.

Tip: I/O Redirection

I/O redirection does not work as you would probably expect:

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

Only the echo/cat binary is run with elevated privileges, while the redirection is performed by the user's shell with user privileges. You can either start a shell like in Section 2.1.2, “Starting a Shell” or use the dd utility instead:

echo s | sudo dd of=/proc/sysrq-trigger
sudo dd if=/proc/1/maps | cat

2.1.2 Starting a Shell #Edit source

Having to add sudo before every command can be cumbersome. While you could specify a shell as a command sudo bash, it is recommended to rather use one of the built-in mechanisms to start a shell:

sudo -s (<command>)

Starts a shell specified by the SHELL environment variable or the target user's default shell. If a command is given, it is passed to the shell (with the -c option), else the shell is run in interactive mode.

tux:~ > sudo -i
root's password:
root:/home/tux # exit
tux:~ >

sudo -i (<command>)

Like -s, but starts the shell as login shell. This means that the shell's start-up files (.profile etc.) are processed and the current working directory is set to the target user's home directory.

tux:~ > sudo -i
root's password:
root:~ # exit
tux:~ >

2.1.3 Environment Variables #Edit source

By default, sudo does not propagate environment variables:

tux > ENVVAR=test env | grep ENVVAR
ENVVAR=test
tux > ENVVAR=test sudo env | grep ENVVAR
root's password:
1
tux >

1	The empty output shows that the environment variable `ENVVAR` did not exist in the context of the command run with `sudo`.

This behavior can be changed by the env_reset option, see Table 2.1, “Useful Flags and Options”.

2.2 Configuring `sudo` #Edit source

sudo is a very flexible tool with extensive configuration.

Note: Locked yourself out of sudo

If you accidentally locked yourself out of sudo, use su - and the root password to get a root shell. To fix the error, run visudo.

2.2.1 Editing the Configuration Files #Edit source

The main policy configuration file for sudo is /etc/sudoers. As it is possible to lock yourself out of the system because of errors in this file, it is strongly recommended to use visudo for editing. It will prevent simultaneous changes to the opened file and check for syntax errors before saving the modifications.

Despite its name, you can also use editors other than vi by setting the EDITOR environment variable, for example:

sudo EDITOR=/usr/bin/nano visudo

However, the /etc/sudoers file itself is supplied by the system packages and modifications may break on updates. Therefore, it is recommended to put custom configuration into files in the /etc/sudoers.d/ directory. Any file in there is automatically included. To create or edit a file in that subdirectory, run:

sudo visudo -f /etc/sudoers.d/NAME

Alternatively with a different editor (for example nano):

sudo EDITOR=/usr/bin/nano visudo -f /etc/sudoers.d/NAME

Note: Ignored Files in `/etc/sudoers.d`

The #includedir command in /etc/sudoers, used for /etc/sudoers.d, ignores files that end in ~ (tilde) or contain a . (dot).

For more information on the visudo command, run man 8 visudo.

2.2.2 Basic sudoers Configuration Syntax #Edit source

In the sudoers configuration files, there are two types of options: strings and flags. While strings can contain any value, flags can be turned either ON or OFF. The most important syntax constructs for sudoers configuration files are:

# Everything on a line after a # gets 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 normal commands. Followed by digits, it specifies a UID.
2	Remove the `!` to set the specified flag to ON.
3	See Section 2.2.3, “Rules in sudoers”.

Table 2.1: Useful Flags and Options #

Option name	Description	Example
`targetpw`	This flag 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` will prompt for the `root` password instead of the target user's or the user that invoked the command. The default is OFF.	Defaults !rootpw # Turn rootpw flag OFF
`env_reset`	If set, `sudo` constructs a minimal environment with only `TERM`, `PATH`, `HOME`, `MAIL`, `SHELL`, `LOGNAME`, `USER`, `USERNAME`, and `SUDO_*` set. Additionally, variables listed in `env_keep` get imported from the calling environment. The default is ON.	Defaults env_reset # Turn env_reset flag ON
`env_keep`	List of environment variables to keep when the `env_reset` flag 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` flag is OFF.	# Set env_delete to contain EDITOR and PROMPT Defaults env_delete = "EDITOR PROMPT" Defaults env_delete += "JRE_HOME" # Add JRE_HOME Defaults env_delete -= "JRE_HOME" # Remove JRE_HOME

The Defaults token can also be used to create aliases for a collection of users, hosts, and commands. Furthermore, it is possible to apply an option only to a specific set of users.

For detailed information about the /etc/sudoers configuration file, consult man 5 sudoers.

2.2.3 Rules in sudoers #Edit source

Rules in the sudoers configuration can be very complex, so this section will only cover the basics. Each rule follows the basic scheme ([] marks optional parts):

#Who      Where         As whom      Tag                What
User_List Host_List = [(User_List)] [NOPASSWD:|PASSWD:] Cmnd_List

Syntax for sudoers Rules #

User_List

One or more (separated by ,) identifiers: Either a user name, a group in the format %GROUPNAME or a user ID in the format #UID. Negation can be performed with a ! prefix.

Host_List

One or more (separated by ,) identifiers: Either a (fully qualified) host name or an IP address. Negation can be performed with a ! prefix. ALL is the usual choice for Host_List.

NOPASSWD:|PASSWD:

The user will not be prompted for a password when running commands matching CMDSPEC after NOPASSWD:.

PASSWD is the default, it only needs to be specified when both are on the same line:

tux ALL = PASSWD: /usr/bin/foo, NOPASSWD: /usr/bin/bar

Cmnd_List

One or more (separated by ,) specifiers: A path to an executable, followed by allowed arguments or nothing.

/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: Dangerous constructs

Constructs of the kind

ALL ALL = ALL

must not be used without Defaults targetpw, otherwise anyone can run commands as root.

2.3 Common Use Cases #Edit source

Although the default configuration is often sufficient for simple setups and desktop environments, custom configurations can be very useful.

2.3.1 Using `sudo` without `root` Password #Edit source

In cases with special restrictions (“user X can only run command Y as root”) it is not possible. In other cases, it is still favorable to have some kind of separation. By convention, members of the group wheel can run all commands with sudo as root.

Add yourself to the wheel group
If your user account is not already member of the wheel group, add it by running sudo usermod -a -G wheel USERNAME and logging out and in again. Verify that the change was successful by running groups USERNAME.
Make authentication with the invoking user's password the default.
Create the file /etc/sudoers.d/userpw with visudo (see Section 2.2.1, “Editing the Configuration Files”) and add:
```
Defaults !targetpw
```
Select a new default rule.
Depending on whether you want users to re-enter their passwords, uncomment the specific 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
```
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 forget this step, otherwise any user can execute any command as root!

Test the configuration

Try to 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 #Edit source

When starting graphical applications with sudo, you will encounter the following error:

tux > sudo xterm
xterm: Xt error: Can't open display: %s
xterm: DISPLAY is not set

YaST will pick the ncurses interface instead of the graphical one.

To use X.Org in applications started with sudo, the environment variables DISPLAY and XAUTHORITY need to be propagated. To configure this, create the file /etc/sudoers.d/xorg, (see Section 2.2.1, “Editing the Configuration Files”) and add the following line:

Defaults env_keep += "DISPLAY XAUTHORITY"

If not set already, set the XAUTHORITY variable as follows:

export XAUTHORITY=~/.Xauthority

Now X.Org applications can be run as usual:

sudo yast2

2.4 More Information #Edit source

A quick overview about the available command line switches can be retrieved by sudo --help. An explanation and other important information can be found in the man page: man 8 sudo, while the configuration is documented in man 5 sudoers.

3 YaST Online Update #Edit source

3.1 The Online Update Dialog
3.2 Installing Patches
3.3 Automatic Online Update

SUSE offers a continuous stream of software security updates for your product. By default, the update applet is used to keep your system up-to-date. Refer to Book “Deployment Guide”, Chapter 20 “Installing or Removing Software”, Section 20.5 “The GNOME Package Updater” for further information on the update applet. This chapter covers the alternative tool for updating software packages: YaST Online Update.

The current patches for SUSE® Linux Enterprise Server are available from an update software repository. If you have registered your product during the installation, an update repository is already configured. If you have not registered SUSE Linux Enterprise Server, you can do so by starting the Product Registration in YaST. Alternatively, you can manually add an update 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 20 “Installing or Removing Software”, Section 20.4 “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 different 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.

3.1 The Online Update Dialog #Edit source

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 3.1: 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 fulfilled (because the relevant packages have already been updated from another source).
All Patches: All patches available for SUSE Linux Enterprise Server.

Each list entry in the Summary section consists of a symbol and the patch name. For an overview of the possible symbols and their meaning, press Shift–F1. Actions required by Security and Recommended patches are automatically preset. These actions are Autoinstall, Autoupdate and Autodelete.

If you install an up-to-date package from a repository other than the update repository, the requirements of a patch for this package may be fulfilled with this installation. In this case a check mark is displayed in front of the patch summary. The patch 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.

3.2 Installing Patches #Edit source

The YaST Online Update dialog allows you to either install all available patches at once or manually select the desired patches. You may also revert patches that have been applied to the system.

By default, all new patches (except optional ones) that are currently available for your system are already marked for installation. They will be applied automatically once you click Accept or Apply. If one or multiple patches require a system reboot, you will be notified about this before the patch installation starts. You can then either decide to continue with the installation of the selected patches, skip the installation of all patches that need rebooting and install the rest, or go back to the manual patch selection.

Procedure 3.1: Applying Patches with YaST Online Update #

Start YaST and select Software › Online Update.
To automatically apply all new patches (except optional ones) that are currently available for your system, click Apply or Accept.
First modify the selection of patches that you want to apply:
1. Use the respective filters and views that the interface provides. For details, refer to Section 3.1, “The Online Update Dialog”.
2. 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 fix severe security hazards and prevent your system from being exploited.
3. 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.
4. To confirm your selection and apply the selected patches, proceed with Apply or Accept.
After the installation is complete, click Finish to leave the YaST Online Update. Your system is now up-to-date.

3.3 Automatic Online Update #Edit source

You may configure automatic updates with a daily, weekly, or monthly schedule with YaST. Install the yast2-online-update-configuration package.

By default, updates are downloaded as delta RPMs. Since rebuilding RPM packages from delta RPMs is a memory- and processor-intensive task, certain setups or hardware configurations 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 configure skipping patches that require user interaction.

Use the Patches tab in the YaST Software module to review available and installed patches, including references to bug reports and CVE bulletins.

Procedure 3.2: Configuring the Automatic Online Update #

After installation, start YaST and select Software › Online Update. Choose Configuration › Online Update. If the yast2-online-update-configuration is not installed, you will be prompted to do that.
Figure 3.2: YaST Online Update Configuration #
Alternatively, start the module with yast2 online_update_configuration from the command line.
Choose the update interval: Daily, Weekly, or Monthly.
Sometimes patches may require the attention of the administrator, for example when restarting critical services. For example, this might be an update for Docker Open Source Engine that requires all containers to be restarted. Before these patches are installed, the user is informed about the consequences and is asked to confirm the installation of the patch. Such patches are called “Interactive Patches”.
When installing patches automatically, it is assumed that you have accepted the 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.
To automatically accept any license agreements, activate Agree with Licenses.
To automatically install all packages recommended by updated packages, activate Include Recommended Packages.
To disable the use of delta RPMs (for performance reasons), un-check Use Delta RPMs.
To filter 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 bugfixes.
- Recommended patches are optional bugfixes and enhancements.
- Optional are new packages.
- Other is equivalent to miscellaneous.
- Document is unused.
Confirm your configuration by clicking OK.

The automatic online update does not automatically restart the system afterward. If there are package updates that require a system reboot, you need to do this manually.

4 YaST #Edit source

4.1 Advanced Key Combinations

4.1 Advanced Key Combinations #Edit source

YaST has a set of advanced key combinations.

Print Screen: Take and save a screenshot. May not be available when YaST is running under some desktop environments.
Shift–F4: Enable/disable the color palette optimized for vision impaired users.
Shift–F7: Enable/disable logging of debug messages.
Shift–F8: Open a file dialog to save log files to a non-standard location.
Ctrl–Shift–Alt–D: Send a DebugEvent. YaST modules can react to this by executing special debugging actions. The result depends on the specific YaST module.
Ctrl–Shift–Alt–M: Start/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 file.
Ctrl–Shift–Alt–X: Open a terminal window (xterm). Useful for installation process via VNC.
Ctrl–Shift–Alt–Y: Show widget tree browser.

5 YaST in Text Mode #Edit source

5.1 Navigation in Modules
5.2 Advanced Key Combinations
5.3 Restriction of Key Combinations
5.4 YaST Command Line Options

YaST in text mode uses the ncurses library to provide an easy pseudo-graphical user interface. The ncurses library is installed by default. The minimum supported size of the terminal emulator in which to run YaST is 80x25 characters.

Figure 5.1: Main Window of YaST in Text Mode #

When you start YaST in text mode, the YaST control center appears (see Figure 5.1). The main window consists of three areas. The left frame features the categories to which the various modules belong. This frame is active when YaST is started and therefore it is marked by a bold white border. The active category is selected. The right frame provides an overview of the modules available in the active category. The bottom frame contains the buttons for Help and Quit.

When you start the YaST control center, the category Software is selected automatically. Use ↓ and ↑ to change the category. To select a module from the category, activate the right frame with → and then use ↓ and ↑ to select the module. Keep the arrow keys pressed to scroll through the list of available modules. After selecting a module, press Enter to start it.

Various buttons or selection fields in the module contain a highlighted letter (yellow by default). Use Alt–highlighted_letter to select a button directly instead of navigating there with →|. Exit the YaST control center by pressing Alt–Q or by selecting Quit and pressing Enter.

Tip: 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.

5.1 Navigation in Modules #Edit source

The following description of the control elements in the YaST modules assumes that all function keys and Alt key combinations work and are not assigned to different global functions. Read Section 5.3, “Restriction of Key Combinations” for information about possible exceptions.

Navigation among Buttons and Selection Lists: Use →| to navigate among the buttons and frames containing selection lists. To navigate in reverse order, use Alt–→| or Shift–→| combinations.
Navigation in Selection Lists: Use the arrow keys (↑ and ↓) to navigate among the individual elements in an active frame containing a selection list. If individual entries within a frame exceed its width, use Shift–→ or Shift–← to scroll horizontally to the right and left. Alternatively, use Ctrl–E or Ctrl–A. This combination can also be used if using → or ← results in changing the active frame or the current selection list, as in the control center.
Buttons, Radio Buttons, and Check Boxes: To select buttons with empty square brackets (check boxes) or empty parentheses (radio buttons), press Space or Enter. Alternatively, radio buttons and check boxes can be selected directly with Alt–highlighted_letter. In this case, you do not need to confirm with Enter. If you navigate to an item with →|, press Enter to execute the selected action or activate the respective menu item.
Function Keys: The function keys (F1 ... 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 different modules offer different buttons (Details, Info, Add, Delete, etc.). Use F10 for Accept, OK, Next, and Finish. Press F1 to access the YaST help.
Using Navigation Tree in ncurses Mode: Some YaST modules use a navigation tree in the left part of the window to select configuration dialogs. Use the arrow keys (↑ and ↓) to navigate in the tree. Use Space to open or close tree items. In ncurses mode, Enter must be pressed after a selection in the navigation tree to show the selected dialog. This is an intentional behavior to save time consuming redraws when browsing through the navigation tree.
Selecting Software in the Software Installation Module: Use the filters on the left side to limit the amount of displayed packages. 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 5.2: The Software Installation Module #

5.2 Advanced Key Combinations #Edit source

YaST in text mode has a set of advanced key combinations.

Shift–F1: List advanced hotkeys.
Shift–F4: Change color schema.
Ctrl–\: Quit the application.
Ctrl–L: Refresh screen.
Ctrl–DF1: List advanced hotkeys.
Ctrl–DShift–D: Dump dialog to the log file as a screenshot.
Ctrl–DShift–Y: Open YDialogSpy to see the widget hierarchy.

5.3 Restriction of Key Combinations #Edit source

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.

Replacing Alt with Esc: Alt shortcuts can be executed with Esc instead of Alt. For example, Esc–H replaces Alt–H. (First press Esc, then press H.)
Backward and Forward Navigation with Ctrl–F and Ctrl–B: If the Alt and Shift combinations are occupied 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 occupied 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 pure text console.

5.4 YaST Command Line Options #Edit source

Besides the text mode interface, YaST provides a pure command line interface. To get a list of YaST command line options, enter:

tux > sudo yast -h

5.4.1 Installing Packages from the Command Line #Edit source

If you know the package name and the package is provided by any of your active installation repositories, you can use the command line option -i to install the package:

tux > sudo yast -i package_name

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.

If you need a command line based software management utility with functionality beyond what YaST provides, consider using Zypper. This utility uses the same software management library that is also the foundation for the YaST package manager. The basic usage of Zypper is covered in Section 6.1, “Using Zypper”.

5.4.2 Starting Individual Modules #Edit source

To save time, you can start individual YaST modules directly. To start a module, enter:

tux > sudo yast module_name

View a list of all module names available on your system with yast -l or yast --list. Start the network module, for example, with yast lan.

5.4.3 Command Line Parameters of YaST Modules #Edit source

To use YaST functionality in scripts, YaST provides command line support for individual modules. Not all modules have command line support. To display the available options of a module, enter:

tux > sudo yast module_name help

If a module does not provide command line support, it is started in a text mode and the following message appears:

This YaST module does not support the command line interface.

The following sections describe all YaST modules with command line support, together with a brief explanation of all their commands and available options.

5.4.3.1 Common YaST Module Commands #Edit source

All YaST modules support the following commands:

help

Lists all the module's supported commands together with their description:

tux > sudo yast lan help

longhelp

Same as help, but adds a detailed list of each command's options together with their description:

tux > sudo yast lan longhelp

xmlhelp

Same as longhelp, but the output is structured as an XML document and redirected to a file:

tux > sudo yast lan xmlhelp xmlfile=/tmp/yast_lan.xml

interactive

If you need to spend more time querying a module's settings, run the interactive mode. The YaST shell opens, where you can enter all the module's commands without the sudo yast ... prefix. To leave the interactive mode, enter exit.

5.4.3.2 yast add-on #Edit source

Adds a new add-on product from the specified 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://.

5.4.3.3 yast audit-laf #Edit source

Displays and configures the Linux Audit Framework. Refer to the Book “Security and Hardening Guide” for more details. yast audit-laf accepts the following commands:

set

Sets an option:

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.

5.4.3.4 yast dhcp-server #Edit source

Manages the DHCP server and configures its settings. yast dhcp-server accepts the following commands:

disable

Disables the DHCP server service.

enable

Enables the DHCP server service.

host

Configures settings for individual hosts.

interface

Specifies to which network interface to listen to:

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

Manages 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.

5.4.3.5 yast dns-server #Edit source

Manages the DNS server configuration. 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

Configures 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

Configures DNS forwarders:

tux > sudo yast dns-server forwarders add ip=10.0.0.100
tux > sudo yast dns-server forwarders show
[...]
Forwarder IP
------------
10.0.0.100

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

Configures 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

Configures 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

Configures 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

Configures 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

Configures 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.

5.4.3.6 yast disk #Edit source

Prints information about all disks or partitions. The only supported command is list followed by either of the following options:

disks

Lists all configured disks in the system:

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    | /           |       |
[...]

5.4.3.7 yast ftp-server #Edit source

Configures FTP server settings. yast ftp-server accepts the following options:

SSL, TLS

Controls secure connections via SSL and TLS. SSL options are valid for the vsftpd only.

tux > sudo yast ftp-server SSL enable
tux > sudo yast ftp-server TLS disable

access

Configures access permissions:

tux > sudo yast ftp-server access authen_only

For a complete list of options, run yast ftp-server access help.

anon_access

Configures access permissions for anonymous users:

tux > sudo yast ftp-server anon_access can_upload

For a complete list of options, run yast ftp-server anon_access help.

anon_dir

Specifies the directory for anonymous users. The directory must already exist on the server:

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

Controls whether to save the log messages into a log file:

tux > sudo yast ftp-server logging enable
tux > sudo yast ftp-server logging disable

max_clients

Specifies the maximum number of concurrently connected clients:

tux > sudo yast ftp-server max_clients set_max_clients=1500

max_clients_ip

Specifies the maximum number of concurrently connected clients via IP:

tux > sudo yast ftp-server max_clients_ip set_max_clients=20

max_rate_anon

Specifies 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

Specifies 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

Specifies 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

Specifies the file umask for authenticated:anonymous users:

tux > sudo yast ftp-server umask set_umask=177:077

welcome_message

Specifies the text to display when someone connects to the FTP server:

tux > sudo yast ftp-server welcome_message set_message="hello everybody"

5.4.3.8 yast http-server #Edit source

Configures the HTTP server (Apache2). yast http-server accepts the following commands:

configure

Configures 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

Configures 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

Specifies 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
[...]
Enabled rewrite
Disabled ssl
Enabled php5
[...]

5.4.3.9 yast kdump #Edit source

Configures kdump settings. For more information on kdump, refer to the Book “System Analysis and Tuning Guide”, Chapter 17 “Kexec and Kdump”, Section 17.7 “Basic Kdump Configuration”. yast kdump accepts the following commands:

copykernel

Copies the kernel into the dump directory.

customkernel

Specifies the kernel_string part of the name of the custom kernel. The naming scheme is /boot/vmlinu[zx]-kernel_string[.gz].

tux > sudo yast kdump customkernel kernel=kdump

For a complete list of options, run yast kdump customkernel help.

dumpformat

Specifies the (compression) format of the dump kernel image. Available formats are 'none', 'ELF', 'compressed', or 'lzo':

tux > sudo yast kdump dumpformat dump_format=ELF

dumplevel

Specifies the dump level number in the range from 0 to 31:

tux > sudo yast kdump dumplevel dump_level=24

dumptarget

Specifies 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

Controls 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

Specifies how many old dump images are kept. Specify zero to keep them all:

tux > sudo yast kdump keepolddumps no=5

kernelcommandline

Specifies the command line that needs to be passed off to the kdump kernel:

tux > sudo yast kdump kernelcommandline command="ro root=LABEL=/"

kernelcommandlineappend

Specifies the command line that you need to append to the default command line string:

tux > sudo yast kdump kernelcommandlineappend command="ro root=LABEL=/"

notificationcc

Specifies an e-mail address for sending copies of notification messages:

tux > sudo yast kdump notificationcc email="user1@example.com user2@example.com"

notificationto

Specifies an e-mail address for sending notification 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

Specifies the file with the plain text SMTP password used for sending notification messages:

tux > sudo yast kdump smtppass pass=/path/to/file

smtpserver

Specifies the SMTP server host name used for sending notification messages:

tux > sudo yast kdump smtpserver server=smtp.server.com

smtpuser

Specifies the SMTP user name used for sending notification 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

5.4.3.10 yast keyboard #Edit source

Configures the system keyboard for virtual consoles. It does not affect the keyboard settings in graphical desktop environments, such as GNOME or KDE. yast keyboard accepts the following commands:

list

Lists all available keyboard layouts.

set

Activates new keyboard layout setting:

tux > sudo yast keyboard set layout=czech

summary

Displays the current keyboard configuration.

5.4.3.11 yast lan #Edit source

Configures network cards. yast lan accepts the following commands:

add

Configures 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 configuration of an existing network card:

tux > sudo yast lan edit id=0 bootproto=dhcp

list

Displays a summary of network card configuration:

tux > sudo yast lan list
id name,           bootproto
0 Ethernet Card 0, NONE
1 Network Bridge,  DHCP

5.4.3.12 yast language #Edit source

Configures system languages. yast language accepts the following commands:

list

Lists all available languages.

set

Specifies the main system languages and secondary languages as well:

tux > sudo yast language set lang=cs_CZ languages=en_US,es_ES no_packages

5.4.3.13 yast mail #Edit source

Displays the configuration of the mail system:

tux > sudo yast mail summary

5.4.3.14 yast nfs #Edit source

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

5.4.3.15 yast nfs-server #Edit source

Configures 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

For 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

Specifies 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 configuration:

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.

5.4.3.16 yast nis #Edit source

Configures the NIS client. yast nis accepts the following commands:

configure

Changes 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 configuration summary of a NIS client.

5.4.3.17 yast nis-server #Edit source

Configures a NIS server. yast nis-server accepts the following commands:

master

Configures 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

Configures 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.

stop

Stops a NIS server:

tux > sudo yast nis-server stop

summary

Displays a configuration summary of a NIS server:

tux > sudo yast nis-server summary

5.4.3.18 yast proxy #Edit source

Configures proxy settings. yast proxy accepts the following commands:

authentication

Specifies 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.

5.4.3.19 yast rdp #Edit source

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

list

Displays the remote desktop configuration summary.

5.4.3.20 yast samba-client #Edit source

Configures 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

Verifies if 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

5.4.3.21 yast samba-server #Edit source

Configures Samba server settings. yast samba-server accepts the following commands:

backend

Specifies 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

Configures 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

Specifies 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.

5.4.3.22 yast security #Edit source

Controls the security level of the host. yast security accepts the following commands:

level

Specifies 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 specific options:

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 configuration:

sudoyast security summary

5.4.3.23 yast sound #Edit source

Configures sound card settings. yast sound accepts the following commands:

add

Configures a new sound card. Without any parameters, the command adds the first one detected.

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
snd-atiixp ATI IXP AC97 controller (snd-atiixp)
snd-atiixp-modem ATI IXP MC97 controller (snd-atiixp-modem)
snd-virtuoso Asus Virtuoso driver (snd-virtuoso)
[...]

playtest

Plays a test sound on a sound card:

tux > sudo yast sound playtest card=0

remove

Removes a configured sound card:

tux > sudo yast sound remove card=0
tux > sudo yast sound remove all

set

Specifies 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 configuration summary for all sound cards on the system:

tux > sudo yast sound summary

volume

Specifies the volume level of a sound card:

sudoyast sound volume card=0 play

5.4.3.24 yast sysconfig #Edit source

Controls the variables in files 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 files, 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 modified 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"
AOU_INCLUDE_RECOMMENDS="false"
[...]

set

Sets a value to a variable:

tux > sudo yast sysconfig set DISPLAYMANAGER=gdm

Tip: Variable in Multiple Files

If the variable is available in several files, use the VARIABLE_NAME$FILE_NAME syntax:

tux > sudo yast sysconfig set CONFIG_TYPE$/etc/sysconfig/mail=advanced

5.4.3.25 yast tftp-server #Edit source

Configures a TFTP server. yast tftp-server accepts the following commands:

directory

Specifies 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

5.4.3.26 yast timezone #Edit source

Configures the time zone. yast timezone accepts the following commands:

list

Lists 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

Specifies new values for the time zone configuration:

tux > sudo yast timezone set timezone=Europe/Prague hwclock=local

summary

Displays the time zone configuration 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

5.4.3.27 yast users #Edit source

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

For a complete list of options, run yast users edit help.

list

Lists existing users filtered 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.

6 Managing Software with Command Line Tools #Edit source

6.1 Using Zypper
6.2 RPM—the Package Manager

6.1 Using Zypper #Edit source

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 #Edit source

The general syntax of Zypper is:

zypper [--global-options] COMMAND  [--command-options] [arguments]

The components enclosed in brackets are not required. See zypper help for a list of general options and all commands. To get help for a specific command, type zypper help COMMAND.

Zypper Commands

The simplest way to execute Zypper is to type its name, followed by a command. For example, to apply all needed patches to the system, use:

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).

Command-Specific Options

To use options that are specific 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 confirm 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 specified repository. --repo is an alias for --from, and you may use either one.

Most Zypper commands have a dry-run option that does a simulation of the given command. It can be used for test purposes.

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 files and plug-ins (such as the Btrfs plug-in). It can be used to mark and identify transactions in log files.

tux > sudo zypper --userdata STRING patch

6.1.2 Using Zypper Subcommands #Edit source

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

  <none>

View the help screen for a subcommand:

tux > zypper help appstream-cache

6.1.3 Installing and Removing Software with Zypper #Edit source

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.

6.1.3.1 Selecting Which Packages to Install or Remove #Edit source

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 finishes 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

By 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>=52.2'
```
You can also combine a hardware architecture and version requirement:
```
tux > sudo zypper install 'firefox.x86_64>=52.2'
```

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 #Edit source

To install and remove packages simultaneously, use the +/- modifiers. 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
tux > sudo zypper install -- -emacs +vim    # Correct
tux > sudo zypper remove emacs +vim         # Correct

6.1.3.3 Cleaning Up Dependencies of Removed Packages #Edit source

If (together with a certain package), you automatically want to remove any packages that become unneeded after removing the specified package, use the --clean-deps option:

tux > sudo zypper rm --clean-deps PACKAGE_NAME

6.1.3.4 Using Zypper in Scripts #Edit source

By default, Zypper asks for a confirmation before installing or removing a selected package, or when a problem occurs. You can override this behavior using the --non-interactive option. This option must be given before the actual command (install, remove, and patch), as can be seen in the following:

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 #Edit source

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 configuration.

This command will also install the build dependencies of the specified 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

Of course, this will only work if you have the repository with the source packages enabled in your repository list (it is added by default, but not enabled). See Section 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 #Edit source

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 specific -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 configured but disabled after successful installation. You can use the --plus-content option to install packages from the installation media instead of the online repositories. Before calling zypper, ensure the media is available, for example by inserting the DVD into the computer's drive.

6.1.3.7 Utilities #Edit source

To verify whether all dependencies are still fulfilled and to repair missing dependencies, use:

tux > zypper verify

In addition to dependencies that must be fulfilled, some packages “recommend” other packages. These recommended packages are only installed if actually available and installable. In case recommended packages were made available after the recommending package has been installed (by adding additional packages or hardware), use the following command:

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 fulfilled.

6.1.4 Updating Software with Zypper #Edit source

There are three different 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 #Edit source

To install all officially released patches that apply to your system, run:

tux > sudo zypper patch

All patches available from repositories configured on your computer are checked for their relevance to your installation. If they are relevant (and not classified as optional or feature), they are installed immediately. Note that the official update repository is only available after registering your SUSE Linux Enterprise Server installation.

If a patch that is about to be installed includes changes that require a system reboot, you will be warned before.

The plain zypper patch command does not apply patches from third party repositories. To update also the third party repositories, use the with-update command option as follows:

tux > sudo zypper patch --with-update

To install also optional patches, use:

tux > sudo zypper patch --with-optional

To install all patches relating to a specific Bugzilla issue, use:

tux > sudo zypper patch --bugzilla=NUMBER

To install all patches relating to a specific 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 affect 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 #Edit source

To find 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 affect Zypper and the package management itself.

List of Needed Patches

To list all needed patches (patches that apply to your system but are not yet installed), use list-patches:

tux > zypper list-patches
Loading repository data...
Reading installed packages...

Repository     | Name        | Version | Category | Status  | Summary
---------------+-------------+---------+----------+---------+---------
SLES12-Updates | SUSE-2014-8 | 1       | security | needed  | openssl: Update for OpenSSL

List of All Patches

To list all patches available for SUSE Linux Enterprise Server, regardless of whether they are already installed or apply to your installation, use zypper patches.

It is also possible to list and install patches relevant to specific issues. To list specific patches, use the zypper list-patches command with the following options:

By Bugzilla Issues

To list all needed patches that relate to Bugzilla issues, use the option --bugzilla.

To list patches for a specific bug, you can also specify a bug number: --bugzilla=NUMBER. To search for patches relating to multiple Bugzilla issues, add commas between the bug numbers, for example:

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 specific CVE database entry, you can also specify a CVE number: --cve=NUMBER. To search for patches relating to multiple CVE database entries, add commas between the CVE numbers, for example:

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-2015-0287 | SUSE-SLE-Module.. | recommended | moderate  | needed
cve   | CVE-2014-3566 | SUSE-SLE-SERVER.. | recommended | moderate  | not needed
[...]

6.1.4.3 Installing New Package Versions #Edit source

If a repository contains only new packages, but does not provide patches, zypper patch does not show any effect. To update all installed packages with newer available versions (while maintaining system integrity), use:

tux > sudo zypper update

To 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 satisfied).

A list of all new available packages (regardless whether installable or not) can be obtained with:

tux > sudo zypper list-updates --all

To find 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 #Edit source

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 #Edit source

When patching, updating or removing packages, there may be running processes on the system which continue to use files having been deleted by the update or removal. Use zypper ps to list processes using deleted files. 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
PID   | 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 files

The output format of zypper ps can be controlled as follows:

zypper ps-s

Create a short table not showing the deleted files.

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 files.

avahi-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 #Edit source

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-12-GEO | SLEHA-12-GEO  | Yes     | No
2 | SLEHA-12     | SLEHA-12      | Yes     | No
3 | SLES12       | SLES12        | 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

6.1.6.1 Adding Repositories #Edit source

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 http://en.opensuse.org/openSUSE:Libzypp_URIs for details). The ALIAS is a shorthand and unique identifier of the repository. You can freely choose it, with the only exception that it needs to be unique. Zypper will issue a warning if you specify an alias that is already in use.

6.1.6.2 Refreshing Repositories #Edit source

zypper enables you to fetch changes in packages from configured 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 #Edit source

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"

6.1.6.4 Modifying Repositories #Edit source

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 #Edit source

Zypper offers 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 #Edit source

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.

Simple 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 #Edit source

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 #Edit source

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)'

The 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 #Edit source

To query single packages, use info with an exact package name as an argument. This displays detailed information about a package. In case the package name does not match any package name from repositories, the command outputs detailed information for non-package matches. If you request a specific type (by using the -t option) and the type does not exist, the command outputs other available matches but without detailed information.

If you specify a source package, the command displays binary packages built from the source package. If you specify a binary package, the command outputs the source packages used to build the binary package.

To also show what is required/recommended by the package, use the options --requires and --recommends:

tux > zypper info --requires MozillaFirefox

6.1.8 Showing Life Cycle Information #Edit source

SUSE products are generally supported for 10 years. Often, you can extend that standard lifecycle by using the extended support offerings of SUSE which add three years of support. Depending on your product, find 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
    SUSE Linux Enterprise Server 15                     n/a*

Module end of support
Basesystem Module                                       n/a*
Server Applications Module                              n/a*

Package end of support if different from product:
SUSEConnect                              Now, installed 0.3.11-1.4, update available 0.3.11-3.3.1
ca-certificates-mozilla                  Now, installed 2.22-2.12, update available 2.24-4.3.1
curl                                     Now, installed 7.60.0-1.1, update available 7.60.0-3.3.1
e2fsprogs                                Now, installed 1.43.8-2.44, update available 1.43.8-4.3.1
glibc                                    Now, installed 2.26-11.8, update available 2.26-13.3.1

6.1.9 Configuring Zypper #Edit source

Zypper now comes with a configuration file, allowing you to permanently change Zypper's behavior (either system-wide or user-specific). For system-wide changes, edit /etc/zypp/zypper.conf. For user-specific changes, edit ~/.zypper.conf. If ~/.zypper.conf does not yet exist, you can use /etc/zypp/zypper.conf as a template: copy it to ~/.zypper.conf and adjust it to your liking. Refer to the comments in the file for help about the available options.

6.1.10 Troubleshooting #Edit source

If you have trouble accessing packages from configured repositories (for example, Zypper cannot find 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 #Edit source

If the Btrfs file system is used on the root partition and snapper is installed, Zypper automatically calls snapper when committing changes to the file system to create appropriate file 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.

6.1.12 For More Information #Edit source

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 http://en.opensuse.org/SDB:Zypper_usage. A list of software changes for the latest SUSE Linux Enterprise Server version can be found at http://en.opensuse.org/openSUSE:Zypper versions.

6.2 RPM—the Package Manager #Edit source

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 five 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 files to install and certain meta information used during the installation by rpm to configure the software package or stored in the RPM database for documentation purposes. RPM archives normally have the extension .rpm.

Tip: Software Development Packages

For several packages, the components needed for software development (libraries, headers, include files, etc.) have been put into separate packages. These development packages are only needed if you want to compile software yourself (for example, the most recent GNOME packages). They can be identified by the name extension -devel, such as the packages alsa-devel and gimp-devel.

6.2.1 Verifying Package Authenticity #Edit source

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 fixing issues in the operating system, you might need to install a Problem Temporary Fix (PTF) into a production system. The packages provided by SUSE are signed against a special PTF key. However, in contrast to SUSE Linux Enterprise 11, this key is not imported by default on SUSE Linux Enterprise 12 systems. To manually import the key, use the following command:

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 #Edit source

Normally, the installation of an RPM archive is quite simple: rpm -i PACKAGE.rpm. With this command the package is installed, but only if its dependencies are fulfilled and if there are no conflicts with other packages. With an error message, rpm requests those packages that need to be installed to meet dependency requirements. In the background, the RPM database ensures that no conflicts arise—a specific file can only belong to one package. By choosing different options, you can force rpm to ignore these defaults, but this is only for experts. Otherwise, you risk compromising the integrity of the system and possibly jeopardize the ability to update the system.

The options -U or --upgrade and -F or --freshen can be used to update a package (for example, rpm -F PACKAGE.rpm). This command removes the files of the old version and immediately installs the new files. The difference between the two versions is that -U installs packages that previously did not exist in the system, while -F merely updates previously installed packages. When updating, rpm updates configuration files carefully using the following strategy:

If a configuration file was not changed by the system administrator, rpm installs the new version of the appropriate file. No action by the system administrator is required.
If a configuration file was changed by the system administrator before the update, rpm saves the changed file with the extension .rpmorig or .rpmsave (backup file) and installs the version from the new package. This is done only if the originally installed file and the newer version are different. If this is the case, compare the backup file (.rpmorig or .rpmsave) with the newly installed file and make your changes again in the new file. Afterward, delete all .rpmorig and .rpmsave files to avoid problems with future updates.
.rpmnew files appear if the configuration file already exists and if the noreplace label was specified in the .spec file.

Following an update, .rpmsave and .rpmnew files should be removed after comparing them, so they do not obstruct future updates. The .rpmorig extension is assigned if the file has not previously been recognized by the RPM database.

Otherwise, .rpmsave is used. In other words, .rpmorig results from updating from a foreign format to RPM. .rpmsave results from updating from an older RPM to a newer RPM. .rpmnew does not disclose any information to whether the system administrator has made any changes to the configuration file. A list of these files is available in /var/adm/rpmconfigcheck. Some configuration files (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.

6.2.3 Delta RPM Packages #Edit source

Delta RPM packages contain the difference between an old and a new version of an RPM package. Applying a delta RPM onto an old RPM results in a completely new RPM. It is not necessary to have a copy of the old RPM because a delta RPM can also work with an installed RPM. The delta RPM packages are even smaller in size than patch RPMs, which is an advantage when transferring update packages over the Internet. The drawback is that update operations with delta RPMs involved consume considerably more CPU cycles than plain or patch RPMs.

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 file 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 file 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 #Edit source

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, “The Most Important RPM Query Options”.

Table 6.1: The Most Important RPM Query Options #

`-i`	Package information
`-l`	File list
`-f FILE`	Query the package that contains the file FILE (the full path must be specified with FILE)
`-s`	File list with status information (implies `-l`)
`-d`	List only documentation files (implies `-l`)
`-c`	List only configuration files (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 <https://www.suse.com/>
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 12

The option -f only works if you specify the complete file name with its full path. Provide as many file names as desired. For example:

tux > rpm -q -f /bin/rpm /usr/bin/wget
rpm-4.11.2-15.1.x86_64
wget-1.14-17.1.x86_64

If only part of the file name is known, use a shell script as shown in Example 6.3, “Script to Search for Packages”. Pass the partial file 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 specific package, sorted by date.

With the installed RPM database, verification checks can be made. Initiate these with -V, or --verify. With this option, rpm shows all files 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`	Modification time
`D`	Major and minor device numbers
`U`	Owner
`G`	Group
`M`	Mode (permissions and file type)

In the case of configuration files, 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 files 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 #Edit source

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 specified custom settings in a file like /etc/rpmrc):

SOURCES: for the original sources (.tar.bz2 or .tar.gz files, etc.) and for distribution-specific adjustments (mostly .diff or .patch files)
SPECS: for the .spec files, similar to a meta Makefile, which control the build process
BUILD: all the sources are unpacked, patched and compiled in this directory
RPMS: where the completed binary packages are stored
SRPMS: here are the source RPMs

When you install a source package with YaST, all the necessary components are installed in /usr/src/packages: the sources and the adjustments in SOURCES and the relevant .spec file 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 files similar to those in the following list:

/usr/src/packages/SOURCES/wget-1.11.4.tar.bz2
/usr/src/packages/SOURCES/wgetrc.patch
/usr/src/packages/SPECS/wget.spec

rpmbuild -bX /usr/src/packages/SPECS/wget.spec starts the compilation. X is a wild card for various stages of the build process (see the output of --help or the RPM documentation for details). The following is merely a brief explanation:

-bp: Prepare sources in /usr/src/packages/BUILD: unpack and patch.
-bc: Do the same as -bp, but with additional compilation.
-bi: Do the same as -bp, but with additional installation of the built software. Caution: if the package does not support the BuildRoot feature, you might overwrite configuration files.
-bb: Do the same as -bi, but with the additional creation of the binary package. If the compile was successful, the binary should be in /usr/src/packages/RPMS.
-ba: Do the same as -bb, but with the additional creation of the source RPM. If the compilation was successful, the binary should be in /usr/src/packages/SRPMS.
--short-circuit: Skip some steps.

The binary RPM created can now be installed with rpm -i or, preferably, with rpm -U. Installation with rpm makes it appear in the RPM database.

Keep in mind, the BuildRoot directive in the spec file is deprecated since SUSE Linux Enterprise Server 12. If you still need this feature, use the --buildroot option as a workaround. For more detailed background information, see the support database at https://www.suse.com/support/kb/doc?id=7017104.

6.2.6 Compiling RPM Packages with build #Edit source

The danger with many packages is that unwanted files are added to the running system during the build process. To prevent this use build, which creates a defined environment in which the package is built. To establish this chroot environment, the build script must be provided with a complete package tree. This tree can be made available on the hard disk, via NFS, or from DVD. Set the position with build --rpms DIRECTORY. Unlike rpm, the build command looks for the .spec file 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 offers several additional options. For example, cause the script to prefer your own RPMs, omit the initialization of the build environment or limit the rpm command to one of the above-mentioned stages. Access additional information with build --help and by reading the build man page.

6.2.7 Tools for RPM Archives and the RPM Database #Edit source

Midnight Commander (mc) can display the contents of RPM archives and copy parts of them. It represents archives as virtual file systems, offering 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.

A full-featured package manager is available as a YaST module. For details, see Book “Deployment Guide”, Chapter 20 “Installing or Removing Software”.

7 System Recovery and Snapshot Management with Snapper #Edit source

7.1 Default Setup
7.2 Using Snapper to Undo Changes
7.3 System Rollback by Booting from Snapshots
7.4 Enabling Snapper in User Home Directories
7.5 Creating and Modifying Snapper Configurations
7.6 Manually Creating and Managing Snapshots
7.7 Automatic Snapshot Clean-Up
7.8 Showing Exclusive Disk Space Used by Snapshots
7.9 Frequently Asked Questions

Snapper has a command-line interface and a YaST interface. Snapper lets you create and manage file system snapshots on the following types of file systems:

Btrfs, a copy-on-write file system for Linux that natively supports file system snapshots of subvolumes. (Subvolumes are separately mountable file 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 files 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.

7.1 Default Setup #Edit source

Snapper on SUSE Linux Enterprise Server is set up as an undo and recovery tool for system changes. By default, the root partition (/) of SUSE Linux Enterprise Server is formatted with Btrfs. Taking snapshots is automatically enabled if the root partition (/) is big enough (more than approximately 16 GB). By default, snapshots are disabled on partitions other than /.

Tip: Enabling Snapper in the Installed System

If you disabled Snapper during the installation, you can enable it at any time later. To do so, create a default Snapper configuration for the root file system by running:

tux > sudo snapper -c root create-config /

Afterward enable the different snapshot types as described in Section 7.1.3.1, “Disabling/Enabling Snapshots”.

Note that on a Btrfs root file system, snapshots require a file 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 file system. So, initially a snapshot does not occupy additional disk space. If data in the original file system is modified, changed data blocks are copied while the old data blocks are kept for the snapshot. Therefore, a snapshot occupies the same amount of space as the data modified. So, over time, the amount of space a snapshot allocates, constantly grows. As a consequence, deleting files from a Btrfs file system containing snapshots may not free disk space!

Note: Snapshot Location

Snapshots always reside on the same partition or subvolume on which the snapshot has been taken. It is not possible to store snapshots on a different partition or subvolume.

As a result, partitions containing snapshots need to be larger than partitions not containing snapshots. The exact amount depends strongly on the number of snapshots you keep and the amount of data modifications. As a rule of thumb, give partitions twice as much space as you normally would. To prevent disks from running out of space, old snapshots are automatically cleaned up. Refer to Section 7.1.3.4, “Controlling Snapshot Archiving” for details.

7.1.1 Types of Snapshots #Edit source

Although snapshots themselves do not differ in a technical sense, we distinguish between three types of snapshots, based on the events that trigger them:

Timeline Snapshots: A single snapshot is created every hour. Old snapshots are automatically deleted. By default, the first 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 finished (“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: Whenever 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.

7.1.2 Directories That Are Excluded from Snapshots #Edit source

Some directories need to be excluded from snapshots for different reasons. The following list shows all directories that are excluded:

/boot/grub2/i386-pc, /boot/grub2/x86_64-efi, /boot/grub2/powerpc-ieee1275, /boot/grub2/s390x-emu: A rollback of the boot loader configuration is not supported. The directories listed above are architecture-specific. The first 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 files 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 files, 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.

7.1.3 Customizing the Setup #Edit source

SUSE Linux Enterprise Server comes with a reasonable default setup, which should be sufficient for most use cases. However, all aspects of taking automatic snapshots and snapshot keeping can be configured according to your needs.

7.1.3.1 Disabling/Enabling Snapshots #Edit source

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.

7.1.3.2 Controlling Installation Snapshots #Edit source

Taking snapshot pairs upon installing packages with YaST or Zypper is handled by the snapper-zypp-plugin. An XML configuration file, /etc/snapper/zypp-plugin.conf defines, when to make snapshots. By default the file looks like the following:

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <snapper-zypp-plugin-conf>
 3  <solvables>
 4   <solvable match="w"1 important="true"2>kernel-*3</solvable>
 5   <solvable match="w" important="true">dracut</solvable>
 6   <solvable match="w" important="true">glibc</solvable>
 7   <solvable match="w" important="true">systemd*</solvable>
 8   <solvable match="w" important="true">udev</solvable>
 9   <solvable match="w">*</solvable>4
10  </solvables>
11 </snapper-zypp-plugin-conf>

1	The match attribute defines whether the pattern is a Unix shell-style wild card (`w`) or a Python regular expression (`re`).
2	If the given pattern matches and the corresponding package is marked as important (for example kernel packages), the snapshot 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 configuration snapshot, pairs are made whenever a package is installed (line 9). When the kernel, dracut, glibc, systemd, or udev packages marked as important are installed, the 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 <?xml version="1.0" encoding="utf-8"?>
 2 <snapper-zypp-plugin-conf>
 3  <solvables>
 4   <solvable match="w" important="true">kernel-*</solvable>
 5   <solvable match="w" important="true">dracut</solvable>
 6   <solvable match="w" important="true">glibc</solvable>
 7   <solvable match="w" important="true">systemd*</solvable>
 8   <solvable match="w" important="true">udev</solvable>
 9   <!-- <solvable match="w">*</solvable> -->
10  </solvables>
11 </snapper-zypp-plugin-conf>

7.1.3.3 Creating and Mounting New Subvolumes #Edit source

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.

SUSE Linux Enterprise Server is configured 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 file 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 files that constantly change, such as virtualized disk images, database files, or log files. 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 files or directories, use the command chattr +C PATH.

7.1.3.4 Controlling Snapshot Archiving #Edit source

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 file 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.

7.1.3.5 Using Snapper on Thinly-Provisioned LVM Volumes #Edit source

Apart from snapshots on Btrfs file 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 configuration for it. On LVM it is required to specify the file 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 configuration according to your needs as described in Section 7.5.1, “Managing Existing Configurations”.

7.2 Using Snapper to Undo Changes #Edit source

Snapper on SUSE Linux Enterprise Server is preconfigured to serve as a tool that lets you undo changes made by zypper and YaST. For this purpose, Snapper is configured to create a pair of snapshots before and after each run of zypper and YaST. Snapper also lets you restore system files that have been accidentally deleted or modified. Timeline snapshots for the root partition need to be enabled for this purpose—see Section 7.1.3.1, “Disabling/Enabling Snapshots” for details.

By default, automatic snapshots as described above are configured for the root partition and its subvolumes. To make snapshots available for other partitions such as /home for example, you can create custom configurations.

Important: Undoing Changes Compared to Rollback

When working with snapshots to restore data, it is important to know that there are two fundamentally different scenarios Snapper can handle:

Undoing Changes: When undoing changes as described in the following, two snapshots are being compared and the changes between these two snapshots are made undone. Using this method also allows to explicitly select the files that should be restored.
Rollback: When 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 files 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 file (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 file. Restoring such a file will cause problems. Furthermore, some system files such as /etc/mtab must never be restored. Therefore it is strongly recommended to always closely review the list of changed files and their diffs. Only restore files that really belong to the action you want to revert.

7.2.1 Undoing YaST and Zypper Changes #Edit source

If you set up the root partition with Btrfs during the installation, Snapper—preconfigured for doing rollbacks of YaST or Zypper changes—will automatically be installed. Every time you start a YaST module or a Zypper transaction, two snapshots are created: a “pre-snapshot” capturing the state of the file system before the start of the module and a “post-snapshot” after the module has been finished.

Using the YaST Snapper module or the snapper command line tool, you can undo the changes made by YaST/Zypper by restoring files from the “pre-snapshot”. Comparing two snapshots the tools also allow you to see which files have been changed. You can also display the differences between two versions of a file (diff).

Procedure 7.1: Undoing Changes Using the YaST Snapper Module #

Start the Snapper module from the Miscellaneous section in YaST or by entering yast2 snapper.
Make sure Current Configuration is set to root. This is always the case unless you have manually added own Snapper configurations.
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).
Click Show Changes to open the list of files that differ between the two snapshots.
Review the list of files. To display a “diff” between the pre- and post-version of a file, select it from the list.
To restore one or more files, select the relevant files or directories by activating the respective check box. Click Restore Selected and confirm the action by clicking Yes.
To restore a single file, activate its diff view by clicking its name. Click Restore From First and confirm your choice with Yes.

Procedure 7.2: Undoing Changes Using the `snapper` Command #

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)

Get a list of changed files for a snapshot pair with snapper status PRE..POST. Files with content changes are marked with c, files that have been added are marked with + and deleted files 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/みかちゃん-p.ttf
+..... /usr/share/fonts/truetype/みかちゃん-pb.ttf
+..... /usr/share/fonts/truetype/みかちゃん-ps.ttf
+..... /usr/share/fonts/truetype/みかちゃん.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

To display the diff for a certain file, run snapper diff PRE..POST FILENAME. If you do not specify FILENAME, a diff for all files will be displayed.

tux > sudo snapper diff 350..351 /usr/share/fonts/truetype/fonts.scale
--- /.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
[...]

To restore one or more files run snapper -v undochange PRE..POST FILENAMES. If you do not specify a FILENAMES, all changed files 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/みかちゃん-p.ttf
     deleting /usr/share/fonts/truetype/みかちゃん-pb.ttf
     deleting /usr/share/fonts/truetype/みかちゃん-ps.ttf
     deleting /usr/share/fonts/truetype/みかちゃん.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

Warning: Reverting User Additions

Reverting user additions via undoing changes with Snapper is not recommended. Since certain directories are excluded from snapshots, files belonging to these users will remain in the file system. If a user with the same user ID as a deleted user is created, this user will inherit the files. 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 #Edit source

Apart from the installation and administration snapshots, Snapper creates timeline snapshots. You can use these backup snapshots to restore files that have accidentally been deleted or to restore a previous version of a file. By using Snapper's diff feature you can also find out which modifications have been made at a certain point of time.

Being able to restore files 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 files from home directories, for example, create a separate Snapper configuration 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 file system (defined by Snapper's root configuration), can be used to do a system rollback. The recommended way to do such a rollback is to boot from the snapshot and then perform the rollback. See Section 7.3, “System Rollback by Booting from Snapshots” for details.

Performing a rollback would also be possible by restoring all files from a root file system snapshot as described below. However, this is not recommended. You may restore single files, for example a configuration file from the /etc directory, but not the complete list of files from the snapshot.

This restriction only affects snapshots taken from the root file system!

Procedure 7.3: Restoring Files Using the YaST Snapper Module #

Start the Snapper module from the Miscellaneous section in YaST or by entering yast2 snapper.
Choose the Current Configuration from which to choose a snapshot.
Select a timeline snapshot from which to restore a file and choose Show Changes. Timeline snapshots are of the type Single with a description value of timeline.
Select a file from the text box by clicking the file name. The difference between the snapshot version and the current system is shown. Activate the check box to select the file for restore. Do so for all files you want to restore.
Click Restore Selected and confirm the action by clicking Yes.

Procedure 7.4: Restoring Files Using the `snapper` Command #

Get a list of timeline snapshots for a specific configuration by running the following command:
```
tux > sudo snapper -c CONFIG list -t single | grep timeline
```
CONFIG needs to be replaced by an existing Snapper configuration. Use snapper list-configs to display a list.
Get a list of changed files 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 file(s).
Optionally list the differences between the current file 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 <FILE NAME>, the difference for all files are shown.
To restore one or more files, run
```
tux > sudo snapper -c CONFIG -v undochange SNAPSHOT_ID..0 FILENAME1 FILENAME2
```
If you do not specify file names, all changed files will be restored.

7.3 System Rollback by Booting from Snapshots #Edit source

The GRUB 2 version included on SUSE Linux Enterprise Server can boot from Btrfs snapshots. Together with Snapper's rollback feature, this allows to recover a misconfigured system. Only snapshots created for the default Snapper configuration (root) are bootable.

Important: Supported Configuration

As of SUSE Linux Enterprise Server 15 SP1 system rollbacks are only supported if the default subvolume configuration of the root partition has not been changed.

When booting a snapshot, the parts of the file system included in the snapshot are mounted read-only; all other file systems and parts that are excluded from snapshots are mounted read-write and can be modified.

Important: Undoing Changes Compared to Rollback

When working with snapshots to restore data, it is important to know that there are two fundamentally different scenarios Snapper can handle:

Undoing Changes: When undoing changes as described in Section 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 files 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 file system needs to be Btrfs. Booting from LVM volume snapshots is not supported.
The root file 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 7.1.2, “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:

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 first.
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.
Depending on whether you want to perform the rollback or not, choose your next step:
1. If the system is in a state where you do not want to do a rollback, reboot to boot into the current system state. You can then choose a different snapshot, or start the rescue system.
2. 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 file 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 identified 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).

7.3.1 Snapshots after Rollback #Edit source

Before a rollback is performed, a snapshot of the running file 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 #Edit source

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 #Edit source

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 first, the oldest last. Use the keys ↓ and ↑ to navigate and press Enter to activate the selected snapshot. Activating a snapshot from the boot menu does not reboot the machine immediately, but rather opens the boot loader of the selected snapshot.

Figure 7.1: Boot Loader: Snapshots #

Each snapshot entry in the boot loader follows a naming scheme which makes it possible to identify it easily:

[*]1OS2 (KERNEL3,DATE4TTIME5,DESCRIPTION6)

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 field contains a description of the snapshot. In case of a manually created snapshot this is the string created with the option `--description` or a custom string (see Tip: Setting a Custom Description for Boot Loader Snapshot Entries). In case of an automatically created snapshot, it is the tool that was called, for example `zypp(zypper)` or `yast_sw_single`. Long descriptions may be truncated, depending on the size of the boot screen.

Tip: Setting a Custom Description for Boot Loader Snapshot Entries

It is possible to replace the default string in the description field of a snapshot with a custom string. This is for example useful if an automatically created description is not sufficient, or a user-provided description is too long. To set a custom string STRING for snapshot NUMBER, use the following command:

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 #Edit source

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 #Edit source

Root file system snapshots do not contain all directories. See Section 7.1.2, “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 file permissions and/or ownership in between snapshot and current system, the application may not be able to access these files. Reset permissions and/or ownership for the affected files after the rollback.
Incompatible Data Formats: If a service or an application has established a new data format in between snapshot and current system, the application may not be able to read the affected data files 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 files. Use a tool like find to locate and remove orphaned files.

7.3.3.2 No Rollback of Boot Loader Data #Edit source

A rollback of the boot loader is not possible, since all “stages” of the boot loader must fit together. This cannot be guaranteed when doing rollbacks of /boot.

7.4 Enabling Snapper in User Home Directories #Edit source

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 configuration files, documentation, and so on.
Samba shares with home directories and Btrfs backend.

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 configuration.

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 configuration files.

7.4.1 Installing pam_snapper and Creating Users #Edit source

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 files from /etc/skel will be copied into the user's home directory at their first login. Verify that the user's configuration was created by listing your Snapper configurations:

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 #Edit source

Remove users with the /usr/lib/pam_snapper/pam_snapper_userdel.sh script. By default it performs a dry run, so edit it to change DRYRUN=1 to DRYRUN=0. This removes the user, the user's home subvolume, Snapper configuration, and deletes all snapshots.

root # /usr/lib/pam_snapper/pam_snapper_userdel.sh username

7.4.3 Manually Enabling Snapshots in Home Directories #Edit source

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 #Edit source

The way Snapper behaves is defined in a configuration file that is specific for each partition or Btrfs subvolume. These configuration files reside under /etc/snapper/configs/.

In case the root file system is big enough (approximately 12 GB), snapshots are automatically enabled for the root file system / upon installation. The corresponding default configuration 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 file 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 file 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 file /control.xml from the installation media:

<root_base_size>
<btrfs_increase_percentage>

It is calculated with the following formula: ROOT_BASE_SIZE * (1 + BTRFS_INCREASE_PERCENTAGE/100)

Keep in mind that this value is a minimum size. Consider using more space for the root file system. As a rule of thumb, double the size you would use when not having enabled snapshots.

You may create your own configurations for other partitions formatted with Btrfs or existing subvolumes on a Btrfs partition. In the following example we will set up a Snapper configuration for backing up the Web server data residing on a separate, Btrfs-formatted partition mounted at /srv/www.

After a configuration has been created, you can either use snapper itself or the YaST Snapper module to restore files from these snapshots. In YaST you need to select your Current Configuration, while you need to specify your configuration for snapper with the global switch -c (for example, snapper -c myconfig list).

To create a new Snapper configuration, run snapper create-config:

tux > sudo snapper -c www-data1 create-config /srv/www2

1	Name of configuration file.
2	Mount point of the partition or `Btrfs` subvolume on which to take snapshots.

This command will create a new configuration file /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 configuration are taken from /etc/snapper/config-templates/default. To use your own set of defaults, create a copy of this file in the same directory and adjust it to your needs. To use it, specify the -t option with the create-config command:

tux > sudo snapper -c www-data create-config -t MY_DEFAULTS /srv/www

7.5.1 Managing Existing Configurations #Edit source

The snapper command offers several subcommands for managing existing configurations. You can list, show, delete and modify them:

Listing Configurations

Use the subcommand snapper list-configs to get all existing configurations:

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 specified configuration. Replace CONFIG with one of the configuration names shown by snapper list-configs. For more information about the configuration options, see Section 7.5.1.1, “Configuration Data”.

To display the default configuration, 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 specified configuration. Replace CONFIG with one of the configuration names shown by snapper list-configs. Possible values for OPTION and VALUE are listed in Section 7.5.1.1, “Configuration Data”.

Deleting a Configuration

Use the subcommand snapper -c CONFIG delete-config to delete a configuration. Replace CONFIG with one of the configuration names shown by snapper list-configs.

7.5.1.1 Configuration Data #Edit source

Each configuration contains a list of options that can be modified from the command line. The following list provides details for each option. To change a value, run snapper -c CONFIG set-config "KEY=VALUE".

ALLOW_GROUPS, ALLOW_USERS

Granting permissions to use snapshots to regular users. See Section 7.5.1.2, “Using Snapper as Regular User” for more information.

The default value is "".

BACKGROUND_COMPARISON

Defines whether pre and post snapshots should be compared in the background after creation.

The default value is "yes".

EMPTY_*

Defines 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_*

Defines 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 files within them. If SYNC_ACL is set to yes, Snapper automatically makes them accessible using ACLs for users and groups from the ALLOW_USERS or ALLOW_GROUPS entries.

The default value is "no".

TIMELINE_CREATE

If set to yes, hourly snapshots are created. Valid values: yes, no.

The default value is "no".

TIMELINE_CLEANUP / TIMELINE_LIMIT_*

Defines the clean-up algorithm for timeline snapshots. See Section 7.7.2, “Cleaning Up Timeline Snapshots” for details.

7.5.1.2 Using Snapper as Regular User #Edit source

By default Snapper can only be used by root. However, there are cases in which certain groups or users need to be able to create snapshots or undo changes by reverting to a snapshot:

Web site administrators who want to take snapshots of /srv/www
Users who want to take a snapshot of their home directory

For these purposes, you can create Snapper configurations that grant permissions to users or/and groups. The corresponding .snapshots directory needs to be readable and accessible by the specified users. The easiest way to achieve this is to set the SYNC_ACL option to yes.

Procedure 7.5: Enabling Regular Users to Use Snapper #

Note that all steps in this procedure need to be run by root.

If a Snapper configuration does not exist yet, create one for the partition or subvolume on which the user should be able to use Snapper. Refer to Section 7.5, “Creating and Modifying Snapper Configurations” for instructions. Example:
```
tux > sudo snapper --config web_data create /srv/www
```
The configuration file is created under /etc/snapper/configs/CONFIG, where CONFIG is the value you specified with -c/--config in the previous step (for example /etc/snapper/configs/web_data). Adjust it according to your needs. For more information, see Section 7.5.1, “Managing Existing Configurations”.
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"
```
The given Snapper configuration can now be used by the specified user(s) and/or group(s). You can test it with the list command, for example:
```
www_admin:~ > snapper -c web_data list
```

7.6 Manually Creating and Managing Snapshots #Edit source

Snapper is not restricted to creating and managing snapshots automatically by configuration; you can also create snapshot pairs (“before and after”) or single snapshots manually using either the command-line tool or the YaST module.

All Snapper operations are carried out for an existing configuration (see Section 7.5, “Creating and Modifying Snapper Configurations” for details). You can only take snapshots of partitions or volumes for which a configuration exists. By default the system configuration (root) is used. To create or manage snapshots for your own configuration you need to explicitly choose it. Use the Current Configuration drop-down box in YaST or specify the -c on the command line (snapper -c MYCONFIG COMMAND).

7.6.1 Snapshot Metadata #Edit source

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 configuration home. To list snapshots for the default configuration (root), use snapper -c root list or snapper list.
snapper list -a: Lists snapshots for all existing configurations.
snapper list -t pre-post: Lists all pre and post snapshot pairs for the default (root) configuration.
snapper list -t single: Lists all snapshots of the type single for the default (root) configuration.

The following metadata is available for each snapshot:

Type: Snapshot type, see Section 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: Specifies the number of the corresponding pre snapshot. For snapshots of type post only. This data cannot be changed.
Description: A description of the snapshot.
Userdata: An extended description where you can specify custom data in the form of a comma-separated key=value list: reason=testing, project=foo. This field 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 #Edit source

Snapper knows three different types of snapshots: pre, post, and single. Physically they do not differ, but Snapper handles them differently.

pre: Snapshot of a file system before a modification. Each pre snapshot corresponds to a post snapshot. For example, this is used for the automatic YaST/Zypper snapshots.
post: Snapshot of a file system after a modification. Each post snapshot corresponds to a pre snapshot. For example, this is used for the automatic YaST/Zypper snapshots.
single: Stand-alone snapshot. For example, this is used for the automatic hourly snapshots. This is the default type when creating snapshots.

7.6.1.2 Cleanup Algorithms #Edit source

Snapper provides three algorithms to clean up old snapshots. The algorithms are executed in a daily cron job. It is possible to define the number of different types of snapshots to keep in the Snapper configuration (see Section 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.
empty-pre-post: Deletes pre/post snapshot pairs with empty diffs.

7.6.2 Creating Snapshots #Edit source

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 --description "Snapshot for week 2 2014": Creates a stand-alone snapshot (type single) for the default (root) configuration with a description. Because no cleanup-algorithm is specified, the snapshot will never be deleted automatically.
snapper --config home create --description "Cleanup in ~tux": Creates a stand-alone snapshot (type single) for a custom configuration named home with a description. Because no cleanup-algorithm is specified, the snapshot will never be deleted automatically.
snapper --config home create --description "Daily data backup" --cleanup-algorithm timeline>: Creates a stand-alone snapshot (type single) for a custom configuration named home with a description. The snapshot will automatically be deleted when it meets the criteria specified for the timeline cleanup-algorithm in the configuration.
snapper create --type pre --print-number --description "Before the Apache config cleanup" --userdata "important=yes": Creates a snapshot of the type pre and prints the snapshot number. First command needed to create a pair of snapshots used to save a “before” and “after” state. The snapshot is marked as important.
snapper create --type post --pre-number 30 --description "After the Apache config cleanup" --userdata "important=yes": Creates a snapshot of the type post paired with the pre snapshot number 30. Second command needed to create a pair of snapshots used to save a “before” and “after” state. The snapshot is marked as important.
snapper create --command COMMAND --description "Before and after COMMAND": Automatically creates a snapshot pair before and after running COMMAND. This option is only available when using snapper on the command line.

7.6.3 Modifying Snapshot Metadata #Edit source

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: Modifies the metadata of snapshot 10 for the default (root) configuration. The cleanup algorithm is set to timeline.
snapper --config home modify --description "daily backup" -cleanup-algorithm "timeline" 120: Modifies the metadata of snapshot 120 for a custom configuration named home. A new description is set and the cleanup algorithm is unset.

7.6.4 Deleting Snapshots #Edit source

To delete a snapshot with the YaST Snapper module, choose a snapshot from the list and click Delete.

To delete a snapshot with the command-line tool, you need to know its number. Get it by running snapper list. To delete a snapshot, run snapper delete NUMBER.

Deleting the current default subvolume snapshot is not allowed.

When deleting snapshots with Snapper, the freed space will be claimed by a Btrfs process running in the background. Thus the visibility and the availability of free space is delayed. In case you need space freed by deleting a snapshot to be available immediately, use the option --sync with the delete command.

Tip: Deleting Snapshot Pairs

When deleting a pre snapshot, you should always delete its corresponding post snapshot (and vice versa).

snapper delete 65: Deletes snapshot 65 for the default (root) configuration.
snapper -c home delete 89 90: Deletes snapshots 89 and 90 for a custom configuration named home.
snapper delete --sync 23: Deletes snapshot 23 for the default (root) configuration and makes the freed space available immediately.

Tip: Delete Unreferenced Snapshots

Sometimes the Btrfs snapshot is present but the XML file 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 first. The older a snapshot is, the more disk space it occupies.

Snapshots 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 #Edit source

Snapshots occupy disk space and over time the amount of disk space occupied by the snapshots may become large. To prevent disks from running out of space, Snapper offers algorithms to automatically delete old snapshots. These algorithms differentiate between timeline snapshots and numbered snapshots (administration plus installation snapshot pairs). You can specify the number of snapshots to keep for each type.

In addition to that, you can optionally specify a disk space quota, defining the maximum amount of disk space the snapshots may occupy. It is also possible to automatically delete pre and post snapshots pairs that do not differ.

A clean-up algorithm is always bound to a single Snapper configuration, so you need to configure algorithms for each configuration. To prevent certain snapshots from being automatically deleted, refer to Can a snapshot be protected from deletion? .

The default setup (root) is configured to do clean-up for numbered snapshots and empty pre and post snapshot pairs. Quota support is enabled—snapshots may not occupy more than 50% of the available disk space of the root partition. Timeline snapshots are disabled by default, therefore the timeline clean-up algorithm is also disabled.

7.7.1 Cleaning Up Numbered Snapshots #Edit source

Cleaning up numbered snapshots—administration plus installation snapshot pairs—is controlled by the following parameters of a Snapper configuration.

NUMBER_CLEANUP

Enables or disables clean-up of installation and admin snapshot pairs. If enabled, snapshot pairs are deleted when the total snapshot count exceeds a number specified with NUMBER_LIMIT and/or NUMBER_LIMIT_IMPORTANT and an age specified with 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"

NUMBER_LIMIT / NUMBER_LIMIT_IMPORTANT

Defines how many regular and/or important installation and administration snapshot pairs to keep. Only the youngest snapshots will be kept. Ignored if NUMBER_CLEANUP is set to "no".

The default value is "2-10" for NUMBER_LIMIT and "4-10" for NUMBER_LIMIT_IMPORTANT.

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 specified as a minimum-maximum range, for example 2-10. If quota support is disabled, a constant value, for example 10, needs to be provided, otherwise cleaning-up will fail with an error.

NUMBER_MIN_AGE

Defines the minimum age in seconds a snapshot must have before it can automatically be deleted. Snapshots younger than the value specified here will not be deleted, regardless of how many exist.

The default value is "1800".

Example command to change or set:

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 defined with NUMBER_LIMIT* regardless of their age, set NUMBER_MIN_AGE to 0.

The following example shows a configuration to keep the last 10 important and regular snapshots regardless of age:

NUMBER_CLEANUP=yes
NUMBER_LIMIT_IMPORTANT=10
NUMBER_LIMIT=10
NUMBER_MIN_AGE=0

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 configuration 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 #Edit source

Cleaning up timeline snapshots is controlled by the following parameters of a Snapper configuration.

TIMELINE_CLEANUP

Enables or disables clean-up of timeline snapshots. If enabled, snapshots are deleted when the total snapshot count exceeds a number specified with TIMELINE_LIMIT_* and an age specified with TIMELINE_MIN_AGE. Valid values: yes, no.

The default value is "yes".

Example command to change or set:

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

Defines the minimum age in seconds a snapshot must have before it can automatically be deleted.

The default value is "1800".

Example 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 configuration enables hourly snapshots which are automatically cleaned up. TIMELINE_MIN_AGE and TIMELINE_LIMIT_* are always both evaluated. In this example, the minimum age of a snapshot before it can be deleted is set to 30 minutes (1800 seconds). 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 first snapshot of the day is kept, too.

Snapshots to be Kept #

Hourly: The last 24 snapshots that have been made.
Daily: The first daily snapshot that has been made is kept from the last seven days.
Monthly: The first snapshot made on the last day of the month is kept for the last twelve months.
Weekly: The first snapshot made on the last day of the week is kept from the last four weeks.
Yearly: The first 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 #Edit source

As explained in Section 7.1.1, “Types of Snapshots”, whenever you run a YaST module or execute Zypper, a pre snapshot is created on start-up and a post snapshot is created when exiting. In case you have not made any changes there will be no difference between the pre and post snapshots. Such “empty” snapshot pairs can be automatically be deleted by setting the following parameters in a Snapper configuration:

EMPTY_PRE_POST_CLEANUP

If set to yes, pre and post snapshot pairs that do not differ will be deleted.

The default value is "yes".

EMPTY_PRE_POST_MIN_AGE

Defines the minimum age in seconds a pre and post snapshot pair that does not differ must have before it can automatically be deleted.

The default value is "1800".

7.7.4 Cleaning Up Manually Created Snapshots #Edit source

Snapper does not offer custom clean-up algorithms for manually created snapshots. However, you can assign the number or timeline clean-up algorithm to a manually created snapshot. If you do so, the snapshot will join the “clean-up queue” for the algorithm you specified. You can specify a clean-up algorithm when creating a snapshot, or by modifying an existing snapshot:

snapper create --description "Test" --cleanup-algorithm number: Creates a stand-alone snapshot (type single) for the default (root) configuration and assigns the number clean-up algorithm.
snapper modify --cleanup-algorithm "timeline" 25: Modifies the snapshot with the number 25 and assigns the clean-up algorithm timeline.

7.7.5 Adding Disk Quota Support #Edit source

In addition to the number and/or timeline clean-up algorithms described above, Snapper supports quotas. You can define what percentage of the available space snapshots are allowed to occupy. This percentage value always applies to the Btrfs subvolume defined in the respective Snapper configuration.

Btrfs quotas are applied to subvolumes, not to users. You may apply disk space quotas to users and groups (for example, with the quota command) in addition to using Btrfs quotas.

If Snapper was enabled during the installation, quota support is automatically enabled. In case you manually enable Snapper at a later point in time, you can enable quota support by running snapper setup-quota. This requires a valid configuration (see Section 7.5, “Creating and Modifying Snapper Configurations” for more information).

Quota support is controlled by the following parameters of a Snapper configuration.

QGROUP: The Btrfs quota group used by Snapper. If not set, run snapper setup-quota. If already set, only change if you are familiar with man 8 btrfs-qgroup. This value is set with snapper setup-quota and should not be changed.
SPACE_LIMIT: Limit of space snapshots are allowed to use in fractions of 1 (100%). Valid values range from 0 to 1 (0.1 = 10%, 0.2 = 20%, ...).

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 first run will apply the rules specified for number and timeline snapshots. Only if the quota is exceeded after this run, the quota-specific rules will be applied in a second run.
Even if quota support is enabled, Snapper will always keep the number of snapshots specified with the NUMBER_LIMIT* and TIMELINE_LIMIT* values, even if the quota will be exceeded. It is therefore recommended to specify ranged values (MIN-MAX) for 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 first 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 five snapshots will always be kept, regardless of the amount of space they occupy.

7.8 Showing Exclusive Disk Space Used by Snapshots #Edit source

Snapshots share data, for efficient 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     
----+--------+-------+---------------------+------+------------+---------+-----------------------+--------------
 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 identification number for each subvolume, assigning a qgroup level/ID combination.

The rfer column displays the total amount of data referred to in the subvolume.

The excl column displays the exclusive data in each subvolume.

The parent column shows the parent qgroup of the subvolumes.

The final item, 1/0, shows the totals for the parent qgroup. In the above example, 222.95 MiB will be freed if all subvolumes are removed. Run the following command to see which snapshots are associated with each subvolume:

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 #Edit source

Q: Why does Snapper never show changes in /var/log, /tmp and other directories?: For some directories we decided to exclude them from snapshots. See Section 7.1.2, “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?: Yes—refer to Section 7.3, “System Rollback by Booting from Snapshots” for details.

Q: Can a snapshot be protected from deletion?

Currently Snapper does not offer 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”) have 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:

List all available snapshots:
```
tux > sudo snapper list -a
```
Memorize the number of the snapshot(s) you want to prevent from being deleted.
Run the following command and replace the number placeholders with the number(s) you memorized:
```
tux > sudo snapper modify --cleanup-algorithm "" #1 #2 #n
```
Check the result by running snapper list -a again. The entry in the column Cleanup should now be empty for the snapshots you modified.

Q: Where can I get more information on Snapper?: See the Snapper home page at http://snapper.io/.

8 Live Kernel Patching with KLP #Edit source

This document describes the basic principles of the Kernel Live Patching (KLP) technology, and provides usage guidelines for the SLE Live Patching service.

8.1 Advantages of Kernel Live Patching
8.2 Low-level Function of Kernel Live Patching
8.3 Activation of SLE Live Patching
8.4 Installing and Removing Patches
8.5 The klp Tool
8.6 Stuck Kernel Execution Threads
8.7 Patch Lifecycle
8.8 Scope of Kernel Live Patching Technology
8.9 Scope of SLE Live Patching
8.10 Interaction with the Support Processes

KLP is a live patching technology for runtime patching of the Linux kernel, without stopping the kernel. This maximizes system uptime, and thus system availability, which is important for mission-critical systems. By enabling dynamic patching of the kernel, the technology also encourages users to install critical security updates without deferring them to a scheduled downtime.

Enabling KLP requires no special steps other than enabling the Live Patching service, and then applying the patches as they become available. The service is part of the normal software management system, and patches are installed (or removed) with the usual package management tools. There is no need to install or manually select special kernels.

A KLP patch is a kernel module, intended for replacing whole functions in the kernel. Kernel Live Patching primarily offers in-kernel infrastructure for integration of the patched code with the base kernel code at runtime.

The information provided in this document relates to the AMD64/Intel 64 and POWER architectures. KLP is supported on the Xen hypervisor.

8.1 Advantages of Kernel Live Patching #Edit source

Kernel Live Patching using KLP is for quick emergency response, when serious vulnerabilities or system stability issues are known and should be fixed as quickly as possible. It is not used for scheduled updates where time is not critical.

Typical use cases for Kernel Live Patching include systems like memory databases with huge amounts of RAM, where boot-up times of 15 minutes or more are not uncommon, large simulations that need weeks or months without a restart, or infrastructure building blocks providing continuous service to many customers.

The main advantage of Kernel Live Patching is that it never requires stopping the kernel, not even for a short time period.

A KLP patch is a .ko kernel module in an RPM package. It is inserted into the kernel using the insmod command when the package is installed or updated. Kernel Live Patching replaces whole functions in the kernel, even if they are being executed. An updated KLP module can replace an existing patch if necessary.

Kernel Live Patching is also lean—it contains only a small amount of code, because it leverages other standard Linux technologies.

8.2 Low-level Function of Kernel Live Patching #Edit source

Kernel Live Patching uses the ftrace infrastructure to perform patching. The following describes the implementation on the AMD64/Intel 64 architecture.

To patch a kernel function, Kernel Live Patching needs some space at the start of the function to insert a jump to a new function. This space is allocated during kernel compilation by GCC with function profiling turned on. In particular, a 5-byte call instruction is injected to the start of kernel functions. When such instrumented kernel is booting, profiling calls are replaced by 5-byte NOP (no operation) instructions.

After patching starts, the first byte is replaced by the INT3 (breakpoint) instruction. This ensures atomicity of the 5-byte instruction replacement. The other four bytes are replaced by the address to the new function. Finally, the first byte is replaced by the JMP (long jump) opcode.

Inter-processor non-maskable interrupts (IPI NMI) are used throughout the process to flush speculative decoding queues of other CPUs in the system. This allows switching to the new function without ever stopping the kernel, not even for a very short moment. The interruptions by IPI NMIs can be measured in microseconds and are not considered service interruptions as they happen while the kernel is running in any case.

Callers are never patched. Instead, the callee's NOPs are replaced by a JMP to the new function. JMP instructions remain forever. This takes care of function pointers, including in structures, and does not require saving any old data for the possibility of un-patching.

However, these steps alone would not be good enough: since the functions would be replaced non-atomically, a new fixed function in one part of the kernel could still be calling an old function elsewhere or vice versa. If the semantics of the function interfaces changed in the patch, chaos would ensue.

Thus, until all functions are replaced, Kernel Live Patching uses an approach based on trampolines and similar to RCU (read-copy-update), to ensure a consistent view of the world to each user space thread, kernel thread and kernel interrupt. A per-thread flag is set on each kernel entry and exit. This way, an old function would always call another old function and a new function always a new one. Once all processes have the "new universe" flag set, patching is complete, trampolines can be removed and the code can operate at full speed without performance impact other than an extra-long jump for each patched function.

8.3 Activation of SLE Live Patching #Edit source

To activate SLE Live Patching on your system, follow these steps:

Your SLES system must be registered. Register your system either during system installation, or after installation with the YaST Product Registration module (yast2 registration). If your SLES system is already registered, but SLE Live Patching is not yet activated, run the yast2 registration command and click Select Extensions.
Select SUSE Linux Enterprise Live Patching 15 in the list of available extensions and click Next.
Confirm the license terms and click Next.
Enter your SLE Live Patching registration code and click Next.
Check the Installation Summary and selected Patterns. The patterns Live Patching and SLE Live Patching Lifecycle Data should be automatically selected for installation, and there may be additional packages to satisfy dependencies.
Click Accept to complete the installation. This will install the base Kernel Live Patching components on your system, the initial live patch, and any dependencies.

8.4 Installing and Removing Patches #Edit source

This section describes how to find, install, and remove KLP patches.

8.4.1 Installing a KLP Patch #Edit source

Before installing new patches, run the klp status command to query current status, which must be ready and not in_progress. You cannot apply new patches until previous patch installations are completed. Invocations of the old kernel functions are not completely eliminated until all sleeping processes wake up and get out of the way. This can take a considerable amount of time. Sleeping processes that use the old kernel functions are not considered a security issue. (See Section 8.6, “Stuck Kernel Execution Threads” for information on managing prolonged in_progress states.)

Use the normal package management system, zypper or YaST, to view and install available patches. The following example searches for available patches, and then installs the most recent patch. It is not necessary to install all patches in order; when there are multiple patches available install the most recent.

tux > sudo zypper se kernel-livepatch 
| kernel-livepatch-4_12_14-25_16-default  | Kernel live patch module  | package   
| kernel-livepatch-4_12_14-25_19-default  | Kernel live patch module  | package   
| kernel-livepatch-4_12_14-25_22-default  | Kernel live patch module  | package

tux > sudo zypper in kernel-livepatch-4_12_14-25_22-default

8.4.2 Removing a KLP Patch #Edit source

If you need to remove a KLP patch, use zypper just as you would for any other package. List your installed live patch packages by using zypper to search for kernel-livepatch:

tux > sudo zypper se kernel-livepatch 
  | kernel-livepatch-4_12_14-25_16-default  | Kernel live patch module  | package   
  | kernel-livepatch-4_12_14-25_19-default  | Kernel live patch module  | package   
i | kernel-livepatch-4_12_14-25_22-default  | Kernel live patch module  | package

Remove the patch using zypper:

tux > sudo zypper rm kernel-livepatch-4_12_14-25_22-default

Wait for initrd to automatically rebuild, then reboot the machine.

8.5 The `klp` Tool #Edit source

Several Kernel Live Patching management tasks can be simplified with the klp tool. The available commands are:

klp status: Displays the overall status of Kernel Live Patching (ready or in_progress).
klp patches: Displays the list of loaded KLP patches.
klp blocking: Lists processes that are preventing Kernel Live Patching from finishing. By default only the PIDs are listed. Specifying -v prints command lines if available. -vv displays stack traces.

For detailed information, see man klp.

8.6 Stuck Kernel Execution Threads #Edit source

Kernel threads must be prepared to handle Kernel Live Patching. Third-party software may not support Kernel Live Patching, and may spawn kernel execution threads. These threads will block the patching process indefinitely. As an emergency measure, you may force the completion of the patching process without waiting for all execution threads to cross the safety checkpoint by writing 0 into /sys/kernel/livepatch/*/transition/ (replacing the asterisk wildcard with your file name). Consult SUSE support before performing this procedure.

8.7 Patch Lifecycle #Edit source

Expiration dates of live patches can be accessed with zypper lifecycle. (Make sure that the package lifecycle-data-sle-module-live-patching is installed.)

When the expiration date of a patch is reached, no further live patches for this kernel version will be supplied. Plan an update of your kernel before the end of the live patch lifecycle period.

For details about zypper lifecycle, see the Showing Life Cycle Information in the Admin Guide.

8.8 Scope of Kernel Live Patching Technology #Edit source

Kernel Live Patching is based on replacing functions. Data structure alteration can be accomplished only indirectly with Kernel Live Patching. As a result, changes to kernel data structure require special care and, if the change is too large, rebooting might be required. Kernel Live Patching also might not be able to handle situations where one compiler is used to compile the old kernel and another compiler is used for compiling the patch.

Because of the way Kernel Live Patching works, support for third-party modules that are spawning kernel threads is limited.

8.9 Scope of SLE Live Patching #Edit source

Fixes for SUSE Common Vulnerability Scoring System (CVSS; SUSE CVSS is based on the CVSS v3.0 system) level 7+ vulnerabilities and bug fixes related to system stability or data corruption will be shipped in the scope of SLE Live Patching. It might not be possible to produce a live patch for all kinds of fixes fulfilling the above criteria. SUSE reserves the right to skip fixes where production of a kernel live patch is unviable because of technical reasons. For more information on CVSS, which is the base for the SUSE CVSS rating, see https://www.first.org/cvss/.

8.10 Interaction with the Support Processes #Edit source

While resolving a technical difficulty with SUSE support, you may receive a Program Temporary Fix (PTF). PTFs may be issued for various packages including those forming the base of SLE Live Patching.

Kernel Live Patching PTFs complying with the conditions described in the previous section can be installed as usual and SUSE will ensure that the system in question does not need to be rebooted and that future live updates are applied cleanly.

PTFs issued for the base kernel disrupt the live patching process. First, installing the PTF kernel means a reboot as the kernel cannot be replaced as a whole at runtime. Second, another reboot is needed to replace the PTF with any regular maintenance updates for which the live patches are issued.

PTFs for other packages in SLE Live Patching can be treated like regular PTFs with the usual guarantees.

9 Transactional Updates #Edit source

Only packages that are part of the snapshot of the root file system can be updated. If packages contain files 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 Technical Preview
9.2 Enabling transactional-update
9.3 Managing Automatic Updates
9.4 The transactional-update Command
9.5 Troubleshooting

9.1 Limitations of Technical Preview #Edit source

As a technical 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-*
mpi-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 filesystem 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 configuration files in /etc will work.
For php7-fastcgi, you must manually create a symlink, /srv/www/cgi-bin/php, that points to /usr/bin/php-cgi.
ntpis 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 filesystem.
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 #Edit source

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 #Edit source

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

9.4 The `transactional-update` Command #Edit source

The transactional-update command enables you to install or remove updates of your system in an atomic way. 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.

cleanup

If the current root filesystem is identical to the active root filesystem (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 will 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 files.

root # transactional-update pkg install package_name

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 files.

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 file 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 file system after reboot.

root # transactional-update dup

patch

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 file system snapper rollback is called. On a read-only file system and without any argument, the current system is set to a new default root file system. If you specify a number, that snapshot is used as the default root file system. On a read-only file system, it does not create any additional snapshots.

root # transactional-update rollback snapshot_number

grub.cfg

This creates a new GRUB2 configuration. Sometimes it is necessary to adjust the boot configuration, for example adding additional kernel parameters. Edit /etc/default/grub, run transactional-update grub.cfg, and then reboot to activate the change. You must immediately reboot, or the new GRUB2 configuration 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 #Edit source

If the upgrade fails, run supportconfig to collect log data. Provide the resulting files, including /var/log/transactional-update.log to SUSE Support.

10 Remote Graphical Sessions with VNC #Edit source

A VNC server can offer both kinds of sessions simultaneously on different ports, but an open session cannot be converted from one type to the other.

10.1 The vncviewer Client
10.2 Remmina: the Remote Desktop Client
10.3 Configuring One-time Sessions on the VNC Server
10.4 Configuring Persistent VNC Server Sessions
10.5 Configuring Encryption on the VNC Server

10.1 The `vncviewer` Client #Edit source

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 #Edit source

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.

10.1.2 Connecting Using the vncviewer GUI #Edit source

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 field 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 #Edit source

The VNC protocol supports different kinds of encrypted connections, not to be confused with password authentication. If a connection does not use TLS, the text “(Connection not encrypted!)” can be seen in the window title of the VNC viewer.

10.2 Remmina: the Remote Desktop Client #Edit source

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 #Edit source

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

10.2.2 Main Window #Edit source

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 #Edit source

To add and save a new remote session, click Add new session in the top left of the main window. The Remote Desktop Preference window opens.

Figure 10.3: Remote Desktop Preference #

Complete the fields that specify your newly added remote session profile. The most important are:

Name: Name of the profile. It will be listed in the main window.
Protocol: The protocol to use when connecting to the remote session, for example VNC.
Server: The IP or DNS address and display number of the remote server.
User name, Password: Credentials to use for remote authentication. Leave empty for no authentication.
Color depth, Quality: Select the best options according to your connection speed and quality.

Select the Advanced tab to enter more specific settings.

Tip: Disable Encryption

If the communication between the client and the remote server is not encrypted, activate Disable encryption, otherwise the connection fails.

Select the SSH tab for advanced SSH tunneling and authentication options.

Confirm with Save. Your new profile will be listed in the main window.

10.2.4 Starting Remote Sessions #Edit source

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 #Edit source

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 confirm with Enter.

10.2.4.2 Opening Saved Remote Sessions #Edit source

To open a specific remote session, double-click it from the list of sessions.

10.2.4.3 Remote Sessions Window #Edit source

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 specific keystrokes to the session, take screenshots of the session, or set the image quality.

Figure 10.5: Remmina Viewing Remote Session #

10.2.5 Editing, Copying, and Deleting Saved Sessions #Edit source

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 fields.

To copy a saved remote session, right-click its name in Remmina's main window and select Copy. In the Remote Desktop Preference window, change the name of the profile, optionally adjust relevant options, and confirm with Save.

To Delete a saved remote session, right-click its name in Remmina's main window and select Delete. Confirm with Yes in the next dialog.

10.2.6 Running Remote Sessions from the Command Line #Edit source

If you need to open a remote session from the command line or from a batch file without first opening the main application window, use the following syntax:

 tux > remmina -c profile_name.remmina

Remmina's profile files are stored in the .local/share/remmina/ directory in your home directory. To determine which profile file belongs to the session you want to open, run Remmina, click the session name in the main window, and read the path to the profile file 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 profile file to a more reasonable file name, such as sle15.remmina. You can even copy the profile file to your custom directory and run it using the remmina -c command from there.

10.3 Configuring One-time Sessions on the VNC Server #Edit source

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 #

Start YaST › Network Services › Remote Administration (VNC).
Check Allow Remote Administration Without Session Management.
Activate Enable access using a web browser if you plan to access the VNC session in a Web browser window.
If necessary, also check Open Port in Firewall (for example, when your network interface is configured to be in the External Zone). If you have more than one network interface, restrict opening the firewall ports to a specific interface via Firewall Details.
Confirm your settings with Next.
In case not all needed packages are available yet, you need to approve the installation of missing packages.
Tip: Restart the Display Manager
YaST makes changes to the display manager settings. You need to log out of your current graphical session and restart the display manager for the changes to take effect.

Figure 10.7: Remote Administration #

10.3.1 Available Configurations #Edit source

The default configuration on SUSE Linux Enterprise Server serves sessions with a resolution of 1024x768 pixels at a color depth of 16-bit. The sessions are available on ports 5901 for “regular” VNC viewers (equivalent to VNC display 1) and on port 5801 for Web browsers.

Other configurations can be made available on different 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 configuration that the server supports (:1 in the example above). Whenever a VNC session is initiated with one of the configurations, 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 certificate, which is generated after installation. You can either use the default one, or replace it with your own. When using the self-signed certificate, you need to confirm its signature before the first connection—both in the VNC viewer and the Web browser.

10.3.2 Initiating a One-time VNC Session #Edit source

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 #Edit source

You can skip this section, if you do not need or want to modify the default configuration.

One-time VNC sessions are started via the systemd socket xvnc.socket. By default it offers six configuration blocks: three for VNC viewers (vnc1 to vnc3), and three serving a JavaScript client (vnchttpd1 to vnchttpd3). By default only vnc1 and vnchttpd1 are active.

To activate the VNC server socket at boot time, run the following command:

tux > sudo  systemctl enable xvnc.socket

To start the socket immediately, run:

tux > sudo  systemctl start xvnc.socket

The Xvnc server can be configured via the server_args option. For a list of options, see Xvnc --help.

When adding custom configurations, make sure they are not using ports that are already in use by other configurations, other services, or existing persistent VNC sessions on the same host.

Activate configuration changes by entering the following command:

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 firewall. If the network interface serving the VNC sessions is protected by a firewall, you need to manually open the respective ports when activating additional ports for VNC sessions. See Book “Security and Hardening Guide”, Chapter 24 “Masquerading and Firewalls” for instructions.

10.4 Configuring Persistent VNC Server Sessions #Edit source

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 trainings 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

10.4.1 VNC Session Initiated Using `vncserver` #Edit source

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` #

Open a shell and make sure you are logged in as the user that should own the VNC session.
If the network interface serving the VNC sessions is protected by a firewall, you need to manually open the port used by your session in the firewall. If starting multiple sessions you may alternatively open a range of ports. See Book “Security and Hardening Guide”, Chapter 24 “Masquerading and Firewalls” for details on how to configure the firewall.
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.
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 first 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 significant length (eight or more characters). Do not share these passwords.

To 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 #Edit source

Persistent VNC sessions can be configured 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 configured in a single per-user configuration. Multiple sessions started by the same user will all use the same start-up and password files.

10.4.2 VNC Session Initiated Using `vncmanager` #Edit source

Procedure 10.3: Enabling Persistent VNC Sessions #

Start YaST › Network Services › Remote Administration (VNC).
Activate Allow Remote Administration With Session Management.
Activate Enable access using a web browser if you plan to access the VNC session in a Web browser window.
If necessary, also check Open Port in Firewall (for example, when your network interface is configured to be in the External Zone). If you have more than one network interface, restrict opening the firewall ports to a specific interface via Firewall Details.
Confirm your settings with Next.
In case not all needed packages are available yet, you need to approve the installation of missing packages.
Tip: Restart the Display Manager
YaST makes changes to the display manager settings. You need to log out of your current graphical session and restart the display manager for the changes to take effect.

10.4.2.1 Configuring Persistent VNC Sessions #Edit source

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 #

There are several settings that influence the VNC session's behavior:

Non-persistent, private: This is equivalent to a one-time session. It is not visible to others and 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 identified 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 trainings.

Confirm with OK.

10.4.2.2 Joining Persistent VNC Sessions #Edit source

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 #Edit source

If the VNC server is set up properly, all communication between the VNC server and the client is encrypted. The authentication happens at the beginning of the session; the actual data transfer only begins afterward.

Whether for a one-time or a persistent VNC session, security options are configured via the -securitytypes parameter of the /usr/bin/Xvnc command located on the server_args line. The -securitytypes parameter selects both authentication method and encryption. It has the following options:

Authentications #

None, TLSNone, X509None: No authentication.
VncAuth, TLSVnc, X509Vnc: Authentication using custom password.
Plain, TLSPlain, X509Plain: Authentication using PAM to verify user's password.

Encryptions #

None, VncAuth, Plain: No encryption.
TLSNone, TLSVnc, TLSPlain: Anonymous TLS encryption. Everything is encrypted, but there is no verification of the remote host. So you are protected against passive attackers, but not against man-in-the-middle attackers.
X509None, X509Vnc, X509Plain: TLS encryption with certificate. If you use a self-signed certificate, you will be asked to verify it on the first connection. On subsequent connections you will be warned only if the certificate changed. So you are protected against everything except man-in-the-middle on the first connection (similar to typical SSH usage). If you use a certificate signed by a certificate authority matching the machine name, then you get full security (similar to typical HTTPS usage).
Tip: Path to Certificate and Key
With X509 based encryption, you need to specify the path to the X509 certificate and the key with -X509Cert and -X509Key options.

If you select multiple security types separated by comma, the first one supported and allowed by both client and server will be used. That way you can configure opportunistic encryption on the server. This is useful if you need to support VNC clients that do not support encryption.

On the client, you can also specify the allowed security types to prevent a downgrade attack if you are connecting to a server which you know has encryption enabled (although our vncviewer will warn you with the "Connection not encrypted!" message in that case).

11 File Copying with RSync #Edit source

11.1 Conceptual Overview
11.2 Basic Syntax
11.3 Copying Files and Directories Locally
11.4 Copying Files and Directories Remotely
11.5 Configuring and Using an Rsync Server
11.6 For More Information

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 files.

11.1 Conceptual Overview #Edit source

For synchronizing a large amount of data over a slow network connection, Rsync offers a reliable method of transmitting only changes within files. This applies not only to text files but also binary files. To detect the differences between files, Rsync subdivides the files 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 #Edit source

Rsync is a command-line tool that has the following basic syntax:

rsync [OPTION] SOURCE [SOURCE]... DEST

You 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 files recursively and preserves time stamps, user/group ownership, file 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 #Edit source

The following description assumes that the current user has write permissions to the directory /var/backup. To copy a single file from one directory on your machine to another path, use the following command:

tux > rsync -avz backup.tar.xz /var/backup/

The file 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 file backup.tar.xz is copied to /var/backup (file) not inside the directory /var/backup/!

Copying a directory is similar to copying a single file. The following example copies the directory tux/ and its content into the directory /var/backup/:

tux > rsync -avz tux /var/backup/

Find the copy in the absolute path /var/backup/tux/.

11.4 Copying Files and Directories Remotely #Edit source

The Rsync tool is required on both machines. To copy files 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 file 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 configuration, 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 find the copy in the absolute path /var/backup/tux.

11.5 Configuring and Using an Rsync Server #Edit source

Rsync can run as a daemon (rsyncd) listing on default port 873 for incoming connections. This daemon can receive “copying targets”.

The 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 #

On jupiter, create a directory to store all your backup files. In this example, we use /var/backup:
```
root # mkdir /var/backup
```
Specify ownership. In this case, the directory is owned by user tux in group users:
```
root # chown tux.users /var/backup
```

Configure the rsyncd daemon.

We will separate the configuration file into a main file 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 files, whereas your modules are placed in /etc/rsyncd.d/*.conf files:

Create a directory /etc/rsyncd.d/:
```
root # mkdir /etc/rsyncd.d/
```

In the main configuration file /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` files into the main configuration file.
2	Loads any modules (or targets) from `/etc/rsyncd.d/*.conf` files. These files should not contain any references to global values.

Create your module (your backup target) in the file /etc/rsyncd.d/backup.conf with the following lines:

# backup.conf: backup module
[backup] 1
   uid = tux 2
   gid = users 2
   path = /var/backup 3
   auth users = tux  4
   secrets file = /etc/rsyncd.secrets 5
   comment = Our backup target

1	The backup target. You can use any name you like. However, it is a good idea to name a target according to its purpose and use the same name in your `*.conf` file.
2	Specifies the user name or group name that is used when the file transfer takes place.
3	Defines the path to store your backups (from Step 1).
4	Specifies a comma-separated list of allowed users. In its simplest form, it contains the user names that are allowed to connect to this module. In our case, only user `tux` is allowed.
5	Specifies the path of a file that contains lines with user names and plain passwords.

Create the /etc/rsyncd.secrets file with the following content and replace PASSPHRASE:
```
# user:passwd
tux:PASSPHRASE
```
Make sure the file is only readable by root:
```
root # chmod 0600 /etc/rsyncd.secrets
```

Start and enable the rsyncd daemon with:

root # systemctl enable rsyncd
root # systemctl start rsyncd

Test the access to your Rsync server:
```
tux > rsync jupiter::
```
You should see a response that looks like this:
```
backup          Our backup target
```
Otherwise, check your configuration file, firewall and network settings.

The above steps create an Rsync server that can now be used to store backups. The example also creates a log file listing all connections. This file 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 files present in the directory /var/backup on the server. This request is also logged in the log file /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 files and directories when it runs. To enable deletion, the additional option --delete must be stated. To ensure that no newer files are deleted, the option --update can be used instead. Any conflicts that arise must be resolved manually.

11.6 For More Information #Edit source

Csync: Bidirectional file synchronizer, see https://www.csync.org/.
RSnapshot: Creates incremental backups, see http://rsnapshot.org.
Unison: A file synchronizer similar to CSync but with a graphical interface, see http://www.seas.upenn.edu/~bcpierce/unison/.
Rear: A disaster recovery framework, see the Administration Guide of the SUSE Linux Enterprise High Availability Extension https://documentation.suse.com/sle-ha/.

Part II Booting a Linux System #Edit source

12 Introduction to the Boot Process: Booting a Linux system involves different components and tasks. After a firmware 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 configurations for everyday usage, maintenance or emergencies.
13 UEFI (Unified Extensible Firmware Interface): UEFI (Unified Extensible Firmware Interface) is the interface between the firmware that comes with the system hardware, all the hardware components of the system, and the operating system.
14 The Boot Loader GRUB 2: This chapter describes how to configure GRUB 2, the boot loader used in SUSE® Linux Enterprise Server. It is the successor to the traditional GRUB boot loader—now called “GRUB Legacy”. GRUB 2 has been the default boot loader in SUSE® Linux Enterprise Server since version 12. A YaST module is available for configuring 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).
15 The systemd Daemon: The program systemd is the process with process ID 1. It is responsible for initializing the system in the required way. 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 chi…

12 Introduction to the Boot Process #Edit source

Booting a Linux system involves different components and tasks. After a firmware 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 configurations for everyday usage, maintenance or emergencies.

12.1 Terminology
12.2 The Linux Boot Process

12.1 Terminology #Edit source

This chapter uses terms that can be interpreted ambiguously. To understand how they are used here, read the definitions below:

init

Two different processes are commonly named “init”:

The initramfs process mounting the root file system
The operating system process that starts all other processes that is executed from the real root file system

In both cases, the systemd program is taking care of this task. It is first executed from the initramfs to mount the root file system. Once that has succeeded, it is re-executed from the root file system as the initial process. To avoid confusing these two systemd processes, we refer to the first process as init on initramfs and to the second one as systemd.

initrd/initramfs

An initrd (initial RAM disk) is an image file containing a root file system image which is loaded by the kernel and mounted from /dev/ram as the temporary root file system. Mounting this file system requires a file system driver.

Beginning with kernel 2.6.13, the initrd has been replaced by the initramfs (initial RAM file system), which does not require a file 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.

12.2 The Linux Boot Process #Edit source

The Linux boot process consists of several stages, each represented by a different component:

Section 12.2.1, “The Initialization and Boot Loader Phase”
Section 12.2.2, “The Kernel Phase”
Section 12.2.3, “The init on initramfs Phase”
Section 12.2.4, “The systemd Phase”

12.2.1 The Initialization and Boot Loader Phase #Edit source

During the initialization phase the machine's hardware is set up and the devices are prepared. This process differs significantly between hardware architectures.

SUSE Linux Enterprise Server uses the boot loader GRUB 2 on all architectures. Depending on the architecture and firmware, 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 file 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 #Edit source

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 first physical 512-byte data sector (the Master Boot Record, MBR) of the boot disk can be loaded. Only a minimal GRUB 2 fits into the MBR. Its sole purpose is to load a GRUB 2 core image containing file system drivers from the gap between the MBR and the first partition (MBR partition table) or from the BIOS boot partition (GPT partition table). This image contains file system drivers and therefore is able to access /boot located on the root file 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.

When booting a BIOS system from an encrypted file system that includes an encrypted /boot partition, you need to enter the password for decryption twice. It is first 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 firmware 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-fledged GRUB 2 which is directly loaded and executed by the firmware.

If the BIOS/UEFI supports network booting, it is also possible to configure a boot server that provides the boot loader. The system can then be booted via PXE. The BIOS/UEFI acts as the boot loader. It gets the boot image from the boot server and starts the system. This is completely independent of local hard disks.

12.2.1.2 Initialization and Boot Loader Phase on IBM IBM Z #Edit source

On IBM IBM Z the boot process must be initialized by a boot loader called zipl (z initial program load). Although zipl supports reading from various file systems, it does not support the SLE default file 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:

zipl boots from the ext2-formatted partition /boot/zipl. 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.
The kernel mounts the root file system, so /boot becomes accessible. Now GRUB 2 is started from the initramfs. It reads its configuration from /boot/grub2/grub.cfg and loads the final kernel and initramfs from /boot. The new kernel now gets loaded via Kexec.

12.2.2 The Kernel Phase #Edit source

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 file system (initramfs) into memory and the kernel takes over.

After 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 file system from the memory that was loaded with the initramfs.

12.2.2.1 The `initramfs` file #Edit source

initramfs (initial RAM file 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 file system is mounted. This minimal Linux environment is loaded into memory by BIOS or UEFI routines and does not have specific hardware requirements other than sufficient memory. The initramfs archive must always provide an executable named init that executes the systemd daemon on the root file system for the boot process to proceed.

Before the root file 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 file system is located. These drivers may include special drivers for certain kinds of hard disks or even network drivers to access a network file system. The needed modules for the root file 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 file 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 #Edit source

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

Adding Drivers Because of Hardware Changes

If you need to change hardware (for example, hard disks), and this hardware requires different drivers to be in the kernel at boot time, you must update the initramfs file.

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 files, 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 file 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 files (/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 file. 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.

Generate a new initramfs file by running
```
dracut MY_INITRAMFS
```
Replace MY_INITRAMFS with a file 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 file.
(Skip this step if you ran dracut -f in the previous step.) Create a link to the initramfs file you created in the previous step:
```
(cd /boot && ln -sf MY_INITRAMFS initrd)
```
On the IBM IBM Z architecture, additionally run grub2-install.

12.2.3 The init on initramfs Phase #Edit source

The temporary root file 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 file system. It provides kernel functionality for the needed file 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 file system. Depending on your system configuration, init on initramfs is responsible for the following tasks.

Loading Kernel Modules

Depending on your hardware configuration, special drivers may be needed to access the hardware components of your computer (the most important component being your hard disk). To access the final root file system, the kernel needs to load the proper file 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 files on a RAM file system in /dev. Without those special files, the file system and other devices would not be accessible.

Managing RAID and LVM Setups

If you configured your system to hold the root file system under RAID or LVM, init on initramfs sets up LVM or RAID to enable access to the root file system later.

Managing the Network Configuration

If you configured your system to use a network-mounted root file 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 file system.

If the file system resides on a network block device like iSCSI or SAN, the connection to the storage server is also set up by init on initramfs. SUSE Linux Enterprise Server supports booting from a secondary iSCSI target if the primary target is not available. For more details regarding configuration of the booting iSCSI target refer to Book “Storage Administration Guide”, Chapter 14 “Mass Storage over IP Networks: iSCSI”, Section 14.3.1 “Using YaST for the iSCSI Initiator Configuration”.

Note: Handling of Mount Failures

If the root file system fails to mount from within the boot environment, it must be checked and repaired before the boot can continue. The file system checker will be automatically started for Ext3 and Ext4 file systems. The repair process is not automated for XFS and Btrfs file systems, and the user is presented with information describing the options available to repair the file system. When the file system has been successfully repaired, exiting the boot environment will cause the system to retry mounting the root file system. If successful, the boot will continue normally.

12.2.3.1 The init on initramfs Phase in the Installation Process #Edit source

When init on initramfs is called during the initial boot as part of the installation process, its tasks differ 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 file 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 configurations. On AArch64, POWER, and AMD64/Intel 64 machines, linuxrc starts an initial hardware scanning process that determines the set of drivers suitable for your hardware configuration. On IBM IBM Z, a list of drivers and their parameters needs to be provided, for example via linuxrc or a parmfile.

These drivers are used to generate a custom initramfs that is needed to boot the system. If the modules are not needed for boot but for coldplug, the modules can be loaded with systemd; for more information, see Section 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 files and linuxrc starts the installation system with the YaST installer.

Starting YaST

Finally, linuxrc starts YaST, which starts the package installation and the system configuration.

12.2.4 The systemd Phase #Edit source

After the “real” root file 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 file 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.

13 UEFI (Unified Extensible Firmware Interface) #Edit source

13.1 Secure Boot
13.2 For More Information

UEFI (Unified Extensible Firmware Interface) is the interface between the firmware that comes with the system hardware, all the hardware components of the system, and the operating system.

UEFI is becoming more and more available on PC systems and thus is replacing the traditional PC-BIOS. UEFI, for example, properly supports 64-bit systems and offers secure booting (“Secure Boot”, firmware version 2.3.1c or better required), which is one of its most important features. Lastly, with UEFI a standard firmware will become available on all x86 platforms.

UEFI additionally offers the following advantages:

Booting from large disks (over 2 TiB) with a GUID Partition Table (GPT).
CPU-independent architecture and drivers.
Flexible pre-OS environment with network capabilities.
CSM (Compatibility Support Module) to support booting legacy operating systems via a PC-BIOS-like emulation.

For more information, see 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 #Edit source

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 firmware could be considered the “platform”. In other words, it is the hardware vendor, and the chain of trust flows 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 firmware, 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 firmware unless it has been signed by one of these “trusted” keys—be it an OS boot loader, some driver located in the flash memory of some PCI Express card or on disk, or be it an update of the firmware itself.

To use Secure Boot, you need to have your OS loader signed with a key trusted by the firmware, and you need the OS loader to verify that the kernel it loads can be trusted.

Key Exchange Keys (KEK) can be added to the UEFI key database. This way, you can use other certificates, as long as they are signed with the private part of the PK.

13.1.1 Implementation on SUSE Linux Enterprise Server #Edit source

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 find 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 firmware, 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 find the EFI programs on a FAT-formatted EFI System Partition (ESP).

Supporting UEFI Secure Boot requires having a boot loader with a digital signature that the firmware recognizes as a trusted key. That key is trusted by the firmware 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 Certification program to have the boot loader certified 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 simplifies the certification 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 configure UEFI.

UEFI offers two types of variables to fulfill the needs of those users:

The first 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 first type, as this allows online updating, adding, and blacklisting of keys, drivers, and firmware fingerprints. It is the second type of variable, the “Boot Services Only Variable”, that helps to implement Secure Boot in a secure and open source-friendly manner, and thus compatible with GPLv3.

SUSE starts with shim—a small and simple EFI boot loader signed by SUSE and Microsoft.

This allows shim to load and execute.

shim then goes on to verify that the boot loader it wants to load is trusted. In a default situation shim will use an independent SUSE certificate embedded in its body. In addition, shim will allow to “enroll” additional keys, overriding the default SUSE key. In the following, we call them “Machine Owner Keys” or MOKs for short.

Next the boot loader will verify and then boot the kernel, and the kernel will do the same on the modules.

13.1.2 MOK (Machine Owner Key) #Edit source

If the user (“machine owner”) wants to replace any components of the boot process, Machine Owner Keys (MOKs) are to be used. The mokutils tool will help with signing components and managing MOKs.

The enrollment process begins with rebooting the machine and interrupting the boot process (for example, pressing a key) when shim loads. shim will then go into enrollment mode, allowing the user to replace the default SUSE key with keys from a file on the boot partition. If the user chooses to do so, shim will then calculate a hash of that file and put the result in a “Boot Services Only” variable. This allows shim to detect any change of the file made outside of Boot Services and thus avoid tampering with the list of user-approved MOKs.

All of this happens during boot time—only verified code is executing now. Therefore, only a user present at the console can use the machine owner's set of keys. It cannot be malware or a hacker with remote access to the OS because hackers or malware can only change the file, but not the hash stored in the “Boot Services Only” variable.

The boot loader, after having been loaded and verified by shim, will call back to shim when it wants to verify the kernel—to avoid duplication of the verification code. Shim will use the same list of MOKs for this and tell the boot loader whether it can load the kernel.

This way, you can install your own kernel or boot loader. It is only necessary to install a new set of keys and authorize them by being physically present during the first reboot. Because MOKs are a list rather than a single MOK, you can make shim trust keys from several vendors, allowing dual- and multi-boot from the boot loader.

13.1.3 Booting a Custom Kernel #Edit source

The following is based on http://en.opensuse.org/openSUSE:UEFI#Booting_a_custom_kernel.

Secure Boot does not prevent you from using a self-compiled kernel. You must sign it with your own certificate and make that certificate known to the firmware or MOK.

Create a custom X.509 key and certificate used for signing:
```
openssl req -new -x509 -newkey rsa:2048 -keyout key.asc \
  -out cert.pem -nodes -days 666 -subj "/CN=$USER/"
```
For more information about creating certificates, see http://en.opensuse.org/openSUSE:UEFI_Image_File_Sign_Tools#Create_Your_Own_Certificate.

Package the key and the certificate as a PKCS#12 structure:

tux > openssl pkcs12 -export -inkey key.asc -in cert.pem \
  -name kernel_cert -out cert.p12

Generate an NSS database for use with pesign:
```
tux > certutil -d . -N
```
Import the key and the certificate contained in PKCS#12 into the NSS database:
```
tux > pk12util -d . -i cert.p12
```

“Bless” the kernel with the new signature using pesign:

tux > pesign -n . -c kernel_cert -i arch/x86/boot/bzImage \
  -o vmlinuz.signed -s

List the signatures on the kernel image:
```
tux > pesign -n . -S -i vmlinuz.signed
```
At that point, you can install the kernel in /boot as usual. Because the kernel now has a custom signature the certificate used for signing needs to be imported into the UEFI firmware or MOK.
Convert the certificate to the DER format for import into the firmware or MOK:
```
tux > openssl x509 -in cert.pem -outform der -out cert.der
```
Copy the certificate to the ESP for easier access:
```
tux > sudo cp cert.der /boot/efi/
```
Use mokutil to launch the MOK list automatically.
- 1. Import the certificate to MOK:
```
tux > mokutil --root-pw --import cert.der
```
    The --root-pw option enables usage of the root user directly.
  2. Check the list of certificates that are prepared to be enrolled:
```
tux > mokutil --list-new
```
  3. Reboot the system; shim should launch MokManager. You need to enter the root password to confirm the import of the certificate to the MOK list.
  4. Check if the newly imported key was enrolled:
```
tux > mokutil --list-enrolled
```
- 1. Alternatively, this is the procedure if you want to launch MOK manually:
    Reboot
  2. In the GRUB 2 menu press the 'c' key.
  3. Type:
```
chainloader $efibootdir/MokManager.efi
boot
```
  4. Select Enroll key from disk.
  5. Navigate to the cert.der file and press Enter.
  6. Follow the instructions to enroll the key. Normally this should be pressing '0' and then 'y' to confirm.
    Alternatively, the firmware menu may provide ways to add a new key to the Signature Database.

13.1.4 Using Non-Inbox Drivers #Edit source

There is no support for adding non-inbox drivers (that is, drivers that do not come with SUSE Linux Enterprise Server) during installation with Secure Boot enabled. The signing key used for SolidDriver/PLDP is not trusted by default.

It is possible to install third party drivers during installation with Secure Boot enabled in two different ways. In both cases:

Add the needed keys to the firmware database via firmware/system management tools before the installation. This option depends on the specific hardware you are using. Consult your hardware vendor for more information.
Use a bootable driver ISO from https://drivers.suse.com/ or your hardware vendor to enroll the needed keys in the MOK list at first boot.

To use the bootable driver ISO to enroll the driver keys to the MOK list, follow these steps:

Burn the ISO image above to an empty CD/DVD medium.
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 first boot from the driver kit and then ask to insert the first installation disk of the product.
An initrd containing updated drivers will be used for installation.

For more information, see https://drivers.suse.com/doc/Usage/Secure_Boot_Certificate.html.

13.1.5 Features and Limitations #Edit source

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 configure 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 effect on the kernel.

13.2 For More Information #Edit source

https://www.uefi.org —UEFI home page where you can find the current UEFI specifications.
Blog posts by Olaf Kirch and Vojtěch Pavlík (the chapter above is heavily based on these posts):
https://en.opensuse.org/openSUSE:UEFI —UEFI with openSUSE.

14 The Boot Loader GRUB 2 #Edit source

This chapter describes how to configure GRUB 2, the boot loader used in SUSE® Linux Enterprise Server. It is the successor to the traditional GRUB boot loader—now called “GRUB Legacy”. GRUB 2 has been the default boot loader in SUSE® Linux Enterprise Server since version 12. A YaST module is available for configuring 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
14.2 Configuration File Structure
14.3 Configuring the Boot Loader with YaST
14.4 Differences in Terminal Usage on IBM Z
14.5 Helpful GRUB 2 Commands
14.6 More Information

14.1 Main Differences between GRUB Legacy and GRUB 2 #Edit source

The configuration is stored in different files.
More file systems are supported (for example, Btrfs).
Can directly read files 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 file 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 #Edit source

The configuration of GRUB 2 is based on the following files:

/boot/grub2/grub.cfg: This file contains the configuration of the GRUB 2 menu items. It replaces menu.lst used in GRUB Legacy. grub.cfg should not be edited—it is automatically generated by the command grub2-mkconfig -o /boot/grub2/grub.cfg.
/boot/grub2/custom.cfg: This optional file 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 these entries will also be parsed when using grub-once.
/etc/default/grub: This file 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 configuration file /boot/grub/grub.cfg.
/etc/sysconfig/bootloader: This configuration file 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 configuration files contain architecture-specific options.

GRUB 2 can be controlled in various ways. Boot entries from an existing configuration can be selected from the graphical menu (splash screen). The configuration is loaded from the file /boot/grub2/grub.cfg which is compiled from other configuration files (see below). All GRUB 2 configuration files are considered system files, and you need root privileges to edit them.

Note: Activating Configuration Changes

After having manually edited GRUB 2 configuration files, you need to run grub2-mkconfig -o /boot/grub2/grub.cfg to activate the changes. However, this is not necessary when changing the configuration with YaST, because YaST will automatically run this command.

14.2.1 The File `/boot/grub2/grub.cfg` #Edit source

The graphical splash screen with the boot menu is based on the GRUB 2 configuration file /boot/grub2/grub.cfg, which contains information about all partitions or operating systems that can be booted by the menu.

Every time the system is booted, GRUB 2 loads the menu file directly from the file system. For this reason, GRUB 2 does not need to be re-installed after changes to the configuration file. grub.cfg is automatically rebuilt with kernel installations or removals.

grub.cfg is compiled from the file /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 file manually. Instead, edit the related source files or use the YaST Boot Loader module to modify the configuration as described in Section 14.3, “Configuring the Boot Loader with YaST”.

14.2.2 The File `/etc/default/grub` #Edit source

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 defined 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 configuration file with grub2-mkconfig -o /boot/grub2/grub.cfg.

Note: Scope

All options set in this file are general options that affect all boot entries. Specific options for Xen kernels or the Xen hypervisor can be set via the GRUB_*_XEN_* configuration 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 first 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”.

GRUB_DEFAULT=saved boots the entry specified 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 specified number of seconds for the user to press a key. During the period no menu is shown unless the user presses a key. If no key is pressed during the time specified, the control is passed to GRUB_TIMEOUT. GRUB_HIDDEN_TIMEOUT=0 first checks whether Shift is pressed and shows the boot menu if yes, otherwise immediately boots the default menu entry. This is the default when only one bootable OS is identified by GRUB 2.

GRUB_HIDDEN_TIMEOUT_QUIET

If false is specified, a countdown timer is displayed on a blank screen when the GRUB_HIDDEN_TIMEOUT feature is active.

GRUB_TIMEOUT

Time period in seconds the boot menu is displayed before automatically booting the default boot entry. If you press a key, the timeout is cancelled and GRUB 2 waits for you to make the selection manually. GRUB_TIMEOUT=-1 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 ofGRUB_CMDLINE_LINUX_DEFAULT.

GRUB_CMDLINE_XEN

This entry specifies 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 specifies an input/output terminal device. Can be console (PC BIOS and EFI consoles), serial (serial terminal), ofconsole (Open Firmware console), or the default gfxterm (graphics-mode output). It is also possible to enable more than one device by quoting the required options, for example GRUB_TERMINAL="console serial".

GRUB_GFXMODE

The resolution used for the gfxterm graphical terminal. 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 file readable by GRUB 2 at boot time, and it must end with the .png, .tga, .jpg, or .jpeg suffix. If necessary, the image will be scaled to fit 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.

14.2.3 Scripts in `/etc/grub.d` #Edit source

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 files in this directory are run. Files with a leading numeral are executed first, beginning with the lowest number. 00_header is run before 10_linux, which would run before 40_custom. If files with alphabetic names are present, they are executed after the numerically-named files. Only executable files generate output to grub.cfg during execution of grub2-mkconfig. By default all files 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 file 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 file.
10_linux: Identifies Linux kernels on the root device and creates relevant menu entries. This includes the associated recovery mode option if enabled. Only the latest kernel is displayed on the main menu page, with additional kernels included in a submenu.
30_os-prober: This script uses os-prober to search for Linux and other operating systems and places the results in the GRUB 2 menu. There are sections to identify specific other operating systems, such as Windows or macOS.
40_custom: This file 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 first. 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 fill 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 #Edit source

In GRUB Legacy, the device.map configuration file was used to derive Linux device names from BIOS drive numbers. The mapping between BIOS drives and Linux devices cannot always be guessed correctly. For example, GRUB Legacy would get a wrong order if the boot sequence of IDE and SCSI drives is exchanged in the BIOS configuration.

GRUB 2 avoids this problem by using device ID strings (UUIDs) or file system labels when generating grub.cfg. GRUB 2 utilities create a temporary device map on the fly, which is usually sufficient, 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 file /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

14.2.5 Editing Menu Entries during the Boot Procedure #Edit source

Being able to directly edit menu entries is useful when the system does not boot anymore because of a faulty configuration. It can also be used to test new settings without altering the system configuration.

In the graphical boot menu, select the entry you want to edit with the arrow keys.
Press E to open the text-based editor.
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:
1. 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 http://en.opensuse.org/Linuxrc.
2. Or edit the general options to change for example the kernel version. The →| key suggests all possible completions.
Press F10 to boot the system with the changes you made or press Esc to discard your edits and return to the GRUB 2 menu.

Changes made this way only apply to the current boot process and are not saved permanently.

Important: Keyboard Layout During the Boot Procedure

The US keyboard layout is the only one available when booting. See Book “Deployment Guide”, Chapter 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 differ—see Section 14.4, “Differences in Terminal Usage on IBM Z” for details.

14.2.6 Setting a Boot Password #Edit source

Even before the operating system is booted, GRUB 2 enables access to file systems. Users without root permissions can access files 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 ).

Encrypt the password using grub2-mkpasswd-pbkdf2:

tux > sudo grub2-mkpasswd-pbkdf2
Password: ****
Reenter password: ****
PBKDF2 hash of your password is grub.pbkdf2.sha512.10000.9CA4611006FE96BC77A...

Paste the resulting string into the file /etc/grub.d/40_custom together with the set superusers command.
```
set superusers="root"
password_pbkdf2 root grub.pbkdf2.sha512.10000.9CA4611006FE96BC77A...
```
To import the changes into the main configuration file, 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 #Edit source

The easiest way to configure general options of the boot loader in your SUSE Linux Enterprise Server system is to use the YaST module. In the YaST Control Center, select System › Boot Loader. The module shows the current boot loader configuration of your system and allows you to make changes.

Use the Boot Code Options tab to view and change settings related to type, location and advanced loader settings. You can choose whether to use GRUB 2 in standard or EFI mode.

Figure 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 first 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.

14.3.1 Boot Loader Location and Boot Code Options #Edit source

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 #

Select the Boot Code Options tab and then choose one of the following options for Boot Loader Location:
Boot from Master Boot Record
This installs the boot loader in the MBR of the disk containing the directory /boot. Usually this will be the disk mounted to /, but if /boot is mounted to a separate partition on a different disk, the MBR of that disk will be used.
Boot from Root Partition
This installs the boot loader in the boot sector of the / partition.
Custom Boot Partition
Use this option to specify the location of the boot loader manually.
Click OK to apply your changes.

Figure 14.3: Code Options #

The 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 flag 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 #Edit source

If your computer has more than one hard disk, you can specify the boot sequence of the disks. The first 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”).

Warning: 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 first 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 #

Open the Boot Code Options tab.
Click Edit Disk Boot Order.
If more than one disk is listed, select a disk and click Up or Down to reorder the displayed disks.
Click OK two times to save the changes.

14.3.3 Configuring Advanced Options #Edit source

Advanced boot parameters can be configured via the Boot Loader Options tab.

14.3.3.1 Boot Loader Options Tab #Edit source

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 configuration, 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 Entry Modification Only. With this setting, anybody is allowed to select a boot entry and boot the system, whereas the password for the GRUB 2 root user is only required for modifying boot entries.

14.3.3.2 Kernel Parameters Tab #Edit source

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 Multithreading (SMT) to avoid side-channel attacks across multiple CPU threads. This setting may further impact performance, depending on the workload.

Off. Disables all mitigations. Side-channel attacks against your CPU are possible, 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 definition file can be specified with the Console theme file-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 #Edit source

On 3215 and 3270 terminals there are some differences and limitations on how to move the cursor and how to issue editing commands within GRUB 2.

14.4.1 Limitations #Edit source

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.
Cursor Movement: “Traditional” cursor movement is not possible. Alt, Meta, Ctrl and the cursor keys do not work. To move the cursor, use the key combinations listed in Section 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 #Edit source

Common Substitutes:	^–J	engage (“Enter”)
	^–L	abort, return to previous “state”
	^–I	tab completion (in edit and shell mode)
Keys Available in Menu Mode:	^–A	first entry
	^–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
	C	enter GRUB-Shell
Keys Available in Edit Mode:	^–P	previous line
	^–N	next line
	^–B	backward char
	^–F	forward char
	^–A	beginning of line
	^–E	end of line
	^–H	backspace
	^–D	delete
	^–K	kill line
	^–Y	yank
	^–O	open line
	^–L	refresh screen
	^–X	boot entry
	^–C	enter GRUB-Shell
Keys Available in Command Line Mode:	^–P	previous command
	^–N	next command from history
	^–A	beginning of line
	^–E	end of line
	^–B	backward char
	^–F	forward char
	^–H	backspace
	^–D	delete
	^–K	kill line
	^–U	discard line
	^–Y	yank

14.5 Helpful GRUB 2 Commands #Edit source

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 configuration 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 Shim and regenerate the UEFI boot table. To do so, use:

root # shim-install --config-file=/boot/grub2/grub.cfg

grub2-mkrescue

Creates a bootable rescue image of your installed GRUB 2 configuration.

Example 14.2: Usage of grub2-mkrescue #

grub2-mkrescue -o save_path/name.iso iso

grub2-script-check

Checks the given file 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 #Edit source

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.

15 The `systemd` Daemon #Edit source

15.1 The systemd Concept
15.2 Basic Usage
15.3 System Start and Target Management
15.4 Managing Services with YaST
15.5 Customization of systemd
15.6 Advanced Usage
15.7 More Information

The program systemd is the process with process ID 1. It is responsible for initializing the system in the required way. 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. systemd is fully compatible with System V init (by supporting init scripts). One of the main advantages of systemd is that it considerably speeds up boot time by aggressively paralleling service starts. Furthermore, systemd only starts a service when it is really needed. Daemons are not started unconditionally at boot time, but rather when being required for the first time. systemd also supports Kernel Control Groups (cgroups), snapshotting and restoring the system state and more. See http://www.freedesktop.org/wiki/Software/systemd/ for details.

15.1 The systemd Concept #Edit source

This section will go into detail about the concept behind systemd.

15.1.1 What Is systemd #Edit source

systemd is a system and session manager for Linux, compatible with System V and LSB init scripts. The main features are:

provides aggressive parallelization capabilities
uses socket and D-Bus activation for starting services
offers on-demand starting of daemons
keeps track of processes using Linux cgroups
supports snapshotting and restoring of the system state
maintains mount and automount points
implements an elaborate transactional dependency-based service control logic

15.1.2 Unit File #Edit source

A unit configuration file contains information about a service, a socket, a device, a mount point, an automount point, a swap file or partition, a start-up target, a watched file system path, a timer controlled and supervised by systemd, a temporary system state snapshot, a resource management slice or a group of externally created processes. “Unit file” is a generic term used by systemd for the following:

Service. Information about a process (for example running a daemon); file ends with .service
Targets. Used for grouping units and as synchronization points during start-up; file ends with .target
Sockets. Information about an IPC or network socket or a file system FIFO, for socket-based activation (like inetd); file ends with .socket
Path. Used to trigger other units (for example running a service when files change); file ends with .path
Timer. Information about a timer controlled, for timer-based activation; file ends with .timer
Mount point. Usually auto-generated by the fstab generator; file ends with .mount
Automount point. Information about a file system automount point; file ends with .automount
Swap. Information about a swap device or file for memory paging; file ends with .swap
Device. Information about a device unit as exposed in the sysfs/udev(7) device tree; file ends with .device
Scope / Slice. A concept for hierarchically managing resources of a group of processes; file ends with .scope/.slice

For more information about systemd.unit see http://www.freedesktop.org/software/systemd/man/systemd.unit.html

15.2 Basic Usage #Edit source

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.

Tip: Terminal Output and Bash Completion

If the output goes to a terminal (and not to a pipe or a file, for example) systemd commands send long output to a pager by default. Use the --no-pager option to turn off paging mode.

systemd also supports bash-completion, allowing you to enter the first letters of a subcommand and then press →| to automatically complete it. 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 #Edit source

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
Restarting. Shuts down services and starts them afterward. If a service is not yet running it will be started.	restart	restart
Restarting conditionally. Restarts services if they are currently running. Does nothing for services that are not running.	try-restart	try-restart
Reloading. Tells services to reload their configuration files without interrupting operation. Use case: Tell Apache to reload a modified `httpd.conf` configuration file. Note that not all services support reloading.	reload	reload
Reloading or restarting. Reloads services if reloading is supported, otherwise restarts them. If a service is not yet running it will be started.	reload-or-restart	n/a
Reloading or restarting conditionally. Reloads services if reloading is supported, otherwise restarts them if currently running. Does nothing for services that are not running.	reload-or-try-restart	n/a
Getting detailed status information. Lists 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 differs from service to service.	status	status
Getting short status information. Shows whether services are active or not.	is-active	status

15.2.2 Permanently Enabling/Disabling Services #Edit source

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 #Edit source

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 MY_SERVICE(S)`	`insserv MY_SERVICE(S)`, `chkconfig -a MY_SERVICE(S)`
Disabling.	`systemctl disable MY_SERVICE(S).service`	`insserv -r MY_SERVICE(S)`, `chkconfig -d MY_SERVICE(S)`
Checking. Shows whether a service is enabled or not.	`systemctl is-enabled MY_SERVICE`	`chkconfig MY_SERVICE`
Re-enabling. Similar to restarting a service, this command first disables and then enables a service. Useful to re-enable a service with its defaults.	`systemctl reenable MY_SERVICE`	n/a
Masking. After “disabling” a service, it can still be started manually. To completely disable a service, you need to mask it. Use with care.	`systemctl mask MY_SERVICE`	n/a
Unmasking. A service that has been masked can only be used again after it has been unmasked.	`systemctl unmask MY_SERVICE`	n/a

15.3 System Start and Target Management #Edit source

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 #Edit source

With System V init the system was booted into a so-called “Runlevel”. A runlevel defines how the system is started and what services are available in the running system. Runlevels are numbered; the most commonly known ones are 0 (shutting down the system), 3 (multiuser with network) and 5 (multiuser with network and display manager).

systemd introduces a new concept by using so-called “target units”. However, it remains fully compatible with the runlevel concept. Target units are named rather than numbered and serve specific purposes. For example, the targets local-fs.target and swap.target mount local file systems and swap spaces.

The target graphical.target provides a multiuser system with network and display manager capabilities and is equivalent to runlevel 5. Complex targets, such as graphical.target act as “meta” targets by combining a subset of other targets. Since systemd makes it easy to create custom targets by combining existing targets, it offers great flexibility.

The following list shows the most important systemd target units. For a full list refer to man 7 systemd.special.

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

Table 15.3: System V Runlevels and `systemd` Target Units #

System V runlevel	`systemd` target	Purpose
0	`runlevel0.target`, `halt.target`, `poweroff.target`	System shutdown
1, S	`runlevel1.target`, `rescue.target`,	Single-user mode
2	`runlevel2.target`, `multi-user.target`,	Local multiuser without remote network
3	`runlevel3.target`, `multi-user.target`,	Full multiuser with network
4	`runlevel4.target`	Unused/User-defined
5	`runlevel5.target`, `graphical.target`,	Full multiuser with network and display manager
6	`runlevel6.target`, `reboot.target`,	System reboot

Important: systemd Ignores `/etc/inittab`

The runlevels in a System V init system are configured in /etc/inittab. systemd does not use this configuration. Refer to Section 15.5.3, “Creating Custom Targets” for instructions on how to create your own bootable target.

15.3.1.1 Commands to Change Targets #Edit source

Use the following commands to operate with target units:

Task	systemd Command	System V init Command
Change the current target/runlevel	`systemctl isolate` MY_TARGET.target	`telinit` X
Change to the default target/runlevel	`systemctl default`	n/a
Get the current target/runlevel	`systemctl list-units --type=target` With systemd there is usually more than one active target. The command lists all currently active targets.	`who -r` or `runlevel`
persistently change the default runlevel	Use the Services Manager or run the following command: `ln -sf /usr/lib/systemd/system/` MY_TARGET.target /etc/systemd/system/default.target	Use the Services Manager or change the line `id:` X:initdefault: in `/etc/inittab`
Change the default runlevel for the current boot process	Enter the following option at the boot prompt `systemd.unit=` MY_TARGET.target	Enter the desired runlevel number at the boot prompt.
Show a target's/runlevel's dependencies	`systemctl show -p "Requires"` MY_TARGET.target `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).	n/a

15.3.2 Debugging System Start-Up #Edit source

systemd offers the means to analyze the system start-up process. You can review the list of all services and their status (rather than having to parse /var/log/). systemd also allows you to scan the start-up procedure to find out how much time each service start-up consumes.

15.3.2.1 Review Start-Up of Services #Edit source

To review the complete list of services that have been started since booting the system, enter the command systemctl. It lists all active services like shown below (shortened). To get more information on a specific service, use systemctl status MY_SERVICE.

Example 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
plymouth-start.service loaded failed failed     Show Plymouth Boot Screen

[...]

15.3.2.2 Debug Start-Up Time #Edit source

To debug system start-up time, systemd offers the systemd-analyze command. It shows the total start-up time, a list of services ordered by start-up time and can also generate an SVG graphic showing the time services took to start in relation to the other services.

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

15.3.2.3 Review the Complete Start-Up Process #Edit source

The above-mentioned commands let you review the services that started and the time it took to start them. If you need to know more details, you can tell systemd to verbosely log the complete start-up procedure by entering the following parameters at the boot prompt:

systemd.log_level=debug systemd.log_target=kmsg

Now systemd writes its log messages into the kernel ring buffer. View that buffer with dmesg:

tux > dmesg -T | less

15.3.3 System V Compatibility #Edit source

systemd is compatible with System V, allowing you to still use existing System V init scripts. However, there is at least one known issue where a System V init script does not work with systemd out of the box: starting a service as a different user via su or sudo in init scripts 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 finished. 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:

Create a service file wrapper with the same name as the init script plus the file name extension .service:

[Unit]
Description=DESCRIPTION
After=network.target

[Service]
User=USER
Type=forking1
PIDFile=PATH TO PID FILE1
ExecStart=PATH TO INIT SCRIPT start
ExecStop=PATH TO INIT SCRIPT stop
ExecStopPost=/usr/bin/rm -f PATH TO PID FILE1

[Install]
WantedBy=multi-user.target2

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.

Start the daemon with systemctl start APPLICATION.

15.4 Managing Services with YaST #Edit source

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 Active column shows whether it is currently running (Active) or not (Inactive). Toggle its status by choosing Start/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.

Enabling or Disabling a Service

Select a service from the table. The Enabled column shows whether it is currently Enabled or Disabled. Toggle its status by choosing Enable/Disable.

By enabling or disabling a service you configure whether it is started during booting (Enabled) or not (Disabled). This setting will not affect the current session. To change its status in the current session, you need to start or stop it.

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.

Warning: Faulty Runlevel Settings May Damage Your System

Faulty runlevel settings may make your system unusable. Before applying your changes, make absolutely sure that you know their consequences.

15.5 Customization of `systemd` #Edit source

The following sections contain some examples for systemd customization.

Warning: Avoiding Overwritten Customization

Always do systemd customization in /etc/systemd/, never in /usr/lib/systemd/. Otherwise your changes will be overwritten by the next update of systemd.

15.5.1 Customizing Unit Files #Edit source

The systemd unit files are located in /usr/lib/systemd/system. If you want to customize them, proceed as follows:

Copy the files you want to modify from /usr/lib/systemd/system to /etc/systemd/system. Keep the file names identical to the original ones.
Modify the copies in /etc/systemd/system according to your needs.
For an overview of your configuration changes, use the systemd-delta command. It can compare and identify configuration files that override other configuration files. For details, refer to the systemd-delta man page.

The modified files in /etc/systemd will take precedence over the original files in /usr/lib/systemd/system, provided that their file name is the same.

15.5.1.1 Converting `xinetd` Services to `systemd` #Edit source

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 files to systemd sockets.

For each xinetd service file, you need at least two systemd unit files: the socket file (*.socket) and an associated service file (*.service). The socket file tells systemd which socket to create, and the service file tells systemd which executable to start.

Consider the following example xinetd service file:

root # cat /etc/xinetd.d/example
service example
{
  socket_type = stream
  protocol = tcp
  port = 10085
  wait = no
  user = user
  group = users
  groups = yes
  server = /usr/libexec/example/exampled
  server_args = -auth=bsdtcp exampledump
  disable = no
}

To convert it to systemd, you need the following two matching files:

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' file options, refer to the systemd.socket and systemd.service manual pages (man 5 systemd.socket, man 5 systemd.service).

15.5.2 Creating “Drop-in” Files #Edit source

If you only want to add a few lines to a configuration file or modify a small part of it, you can use so-called “drop-in” files. Drop-in files let you extend the configuration of unit files without having to edit or override the unit files themselves.

For example, to change one value for the FOOBAR service located in /usr/lib/systemd/system/FOOBAR.SERVICE, proceed as follows:

Create a directory called /etc/systemd/system/FOOBAR.service.d/.
Note the .d suffix. The directory must otherwise be named like the service that you want to patch with the drop-in file.
In that directory, create a file WHATEVERMODIFICATION.conf.
Make sure it only contains the line with the value that you want to modify.
Save your changes to the file. It will be used as an extension of the original file.

15.5.3 Creating Custom Targets #Edit source

On System V init SUSE systems, runlevel 4 is unused to allow administrators to create their own runlevel configuration. systemd allows you to create any number of custom targets. It is suggested to start by adapting an existing target such as graphical.target.

Copy the configuration file /usr/lib/systemd/system/graphical.target to /etc/systemd/system/MY_TARGET.target and adjust it according to your needs.
The configuration file 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.
For each wanted service, create a symbolic link from /usr/lib/systemd/system into /etc/systemd/system/MY_TARGET.target.wants.
When you have finished setting up the target, reload the systemd configuration to make the new target available:
```
tux > sudo systemctl daemon-reload
```

15.6 Advanced Usage #Edit source

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 #Edit source

systemd supports cleaning temporary directories regularly. The configuration from the previous system version is automatically migrated and active. tmpfiles.d—which is responsible for managing temporary files—reads its configuration from /etc/tmpfiles.d/*.conf , /run/tmpfiles.d/*.conf, and /usr/lib/tmpfiles.d/*.conf files. Configuration placed in /etc/tmpfiles.d/*.conf overrides related configurations from the other two directories (/usr/lib/tmpfiles.d/*.conf is where packages store their configuration files).

The configuration format is one line per path containing action and path, and optionally mode, ownership, age and argument fields, depending on the action. The following example unlinks the X11 lock files:

Type Path               Mode UID  GID  Age Argument
r    /tmp/.X[0-9]*-lock

To get the status the tmpfile 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 files handling, see man 5 tmpfiles.d.

15.6.2 System Log #Edit source

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 filters or changing the output format.

15.6.3 Snapshots #Edit source

You can save the current state of systemd to a named snapshot and later revert to it with the isolate subcommand. This is useful when testing services or custom targets, because it allows you to return to a defined state at any time. A snapshot is only available in the current session and will automatically be deleted on reboot. A snapshot name must end in .snapshot.

Create a Snapshot

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 #Edit source

With systemd, kernel modules can automatically be loaded at boot time via a configuration file in /etc/modules-load.d. The file should be named MODULE.conf and have the following content:

# load module MODULE at boot time
MODULE

In case a package installs a configuration file for loading a kernel module, the file gets installed to /usr/lib/modules-load.d. If two configuration files 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 #Edit source

With System V init actions that need to be performed before loading a service, needed to be specified in /etc/init.d/before.local. This procedure is no longer supported with systemd. If you need to do actions before starting services, do the following:

Loading Kernel Modules

Create a drop-in file 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 file in /etc/tmpfiles.d (see man tmpfiles.d for the syntax)

Other Tasks

Create a system service file, 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 file 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 file, you need to run:

tux > sudo systemctl daemon-reload

15.6.6 Kernel Control Groups (cgroups) #Edit source

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 difficult 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 effective way to label all processes spawned by a service with the name of the service.

To list all processes belonging to a service, use the command systemd-cgls. 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

[...]

See Book “System Analysis and Tuning Guide”, Chapter 9 “Kernel Control Groups” for more information about cgroups.

15.6.7 Terminating Services (Sending Signals) #Edit source

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 difficult 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 confining 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 specified cgroup. You can restrict it to the control or the main process. The latter is for example useful to force a service to reload its configuration by sending SIGHUP:

tux > sudo systemctl kill -s SIGHUP --kill-who=main MY_SERVICE

15.6.8 Important Notes on the D-Bus Service #Edit source

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.

Terminating 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 configured to skip the packages that require reboot.

15.6.9 Debugging Services #Edit source

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 different formats, making it a powerful debugging tool.

Show Service Start-Up Failure

Whenever a service fails to start, use systemctl status MY_SERVICE to get a detailed error message:

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

The default behavior of the status subcommand is to display the last ten messages a service issued. To change the number of messages to show, use the --lines=N parameter:

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 fields.
cat: Terse output without time stamps.

15.7 More Information #Edit source

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.

Part III System #Edit source

16 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. But SUSE Linux Enterprise Server supports 32-bit application use in 64-bit system environments. This chapter offers a brief overview of 32-bit support im…
17 journalctl: Query the systemd Journal: When systemd replaced traditional init scripts in SUSE Linux Enterprise 12 (see Chapter 15, The systemd Daemon), it introduced its own logging system called journal. There is no need to run a syslog based service anymore, as all system events are written in the journal.
18 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 different versions side by side, the alternatives system allows managing such versions consistently.
19 Basic Networking: Linux offers the necessary networking tools and features for integration into all types of network structures. Network access using a network card can be configured with YaST. Manual configuration is also possible. In this chapter only the fundamental mechanisms and the relevant network configuration files are covered.
20 Printer Operation: SUSE® Linux Enterprise Server supports printing with many types of printers, including remote network printers. Printers can be configured manually or with YaST. For configuration instructions, refer to Book “Deployment Guide”, Chapter 19 “Setting Up Hardware Components with YaST”, Section 19.3 “Set…
21 Graphical User Interface: SUSE Linux Enterprise Server includes the X.org server and the GNOME desktop. This chapter describes the configuration of the graphical user interface for all users.
22 Accessing File Systems with FUSE: FUSE is the acronym for file system in user space. This means you can configure and mount a file 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 file systems like remote SSH connections, ISO images, and more.
23 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 itsel…
24 Dynamic Kernel Device Management with udev: The kernel can add or remove almost any device in a running system. Changes in the device state (whether a device is plugged in or removed) need to be propagated to user space. Devices need to be configured when they are plugged in and recognized. Users of a certain device need to be informed about …
25 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-specific settings (I18N and L10N).
26 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 Net…
27 Power Management: The features and hardware described in this chapter do not exist on IBM Z, making this chapter irrelevant for these platforms.
28 VM Guest: This chapter contains additional information on when SUSE Linux Enterprise Server is used in a virtual machine.
29 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.

16 32-Bit and 64-Bit Applications in a 64-Bit System Environment #Edit source

16.1 Runtime Support
16.2 Kernel Specifications

SUSE® Linux Enterprise Server is available for several 64-bit platforms. The developers have not ported all 32-bit applications to 64-bit systems. But SUSE Linux Enterprise Server supports 32-bit application use in 64-bit system environments. This chapter offers a brief overview of 32-bit support implementation on 64-bit SUSE Linux Enterprise Server platforms.

SUSE Linux Enterprise Server for the 64-bit platforms POWER, IBM Z and AMD64/Intel 64 is designed so that existing 32-bit applications run in the 64-bit environment “out-of-the-box.” The corresponding 32-bit platforms are ppc for POWER, and x86 for AMD64/Intel 64. This support means that you can continue to use your preferred 32-bit applications without waiting for a corresponding 64-bit port to become available. The current POWER system runs most applications in 32-bit mode, but you can run 64-bit applications.

Note: No Support for Building 32-bit Applications

SUSE Linux Enterprise Server does not support compilation of 32-bit applications. It only offers runtime support for 32-bit binaries.

16.1 Runtime Support #Edit source

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 differentiated from each other in another way.

To 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 files are located in directories called lib64. The 64-bit object files 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 file 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 #Edit source

The 64-bit kernels for AMD64/Intel 64, POWER and IBM Z offer both a 64-bit and a 32-bit kernel ABI (application binary interface). The latter is identical to the ABI for the corresponding 32-bit kernel. This means that communication between both 32-bit and 64-bit applications with 64-bit kernels are identical.

The 32-bit system call emulation for 64-bit kernels does not support all the APIs used by system programs. This depends on the platform. For this reason, few applications, like lspci, must be compiled on non-POWER platforms as 64-bit programs to function properly. On IBM Z, not all ioctls are available in the 32-bit kernel ABI.

A 64-bit kernel can only load 64-bit kernel modules. You must compile 64-bit modules specifically 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.

17 `journalctl`: Query the `systemd` Journal #Edit source

17.1 Making the Journal Persistent
17.2 journalctl Useful Switches
17.3 Filtering the Journal Output
17.4 Investigating systemd Errors
17.5 Journald Configuration
17.6 Using YaST to Filter the systemd Journal
17.7 Viewing Logs in GNOME

When systemd replaced traditional init scripts in SUSE Linux Enterprise 12 (see Chapter 15, The systemd Daemon), it introduced its own logging system called journal. There is no need to run a syslog based service anymore, as all system events are written in 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 #Edit source

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:

As root, open /etc/systemd/journald.conf for editing.
```
root # vi /etc/systemd/journald.conf
```

Uncomment the line containing Storage= and change it to

[...]
[Journal]
Storage=persistent
#Compress=yes
[...]

Save the file and restart systemd-journald:
```
root # systemctl restart systemd-journald
```

17.2 `journalctl` Useful Switches #Edit source

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 specific 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.

-e

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 first.

-k

Shows only kernel messages. This is equivalent to the field match _TRANSPORT=kernel (see Section 17.3.3, “Filtering Based on Fields”).

-u

Shows only messages for the specified systemd unit. This is equivalent to the field 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.

17.3 Filtering the Journal Output #Edit source

When called without switches, journalctl shows the full content of the journal, the oldest entries listed first. The output can be filtered by specific switches and fields.

17.3.1 Filtering Based on a Boot Number #Edit source

journalctl can filter messages based on a specific 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 first column lists the boot offset: 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 specific 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 offset 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 field:

tux > sudo journalctl _BOOT_ID=156019a44a774a0bb0148a92df4af81b

17.3.2 Filtering Based on Time Interval #Edit source

You can filter the output of journalctl by specifying the starting and/or ending date. The date specification should be of the format "2014-06-30 9:17:16". If the time part is omitted, midnight is assumed. If seconds are omitted, ":00" is assumed. If the date part is omitted, the current day is assumed. Instead of numeric expression, you can specify the keywords "yesterday", "today", or "tomorrow". They refer to midnight of the day before the current day, of the current day, or of the day after the current day. If you specify "now", it refers to the current time. You can also specify relative times prefixed with - or +, referring to times before or after the current time.

Show only new messages since now, and update the output continuously:

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 #Edit source

You can filter the output of the journal by specific fields. The syntax of a field to be matched is FIELD_NAME=MATCHED_VALUE, such as _SYSTEMD_UNIT=httpd.service. You can specify multiple matches in a single query to filter the output messages even more. See man 7 systemd.journal-fields for a list of default fields.

Show messages produced by a specific process ID:

tux > sudo journalctl _PID=1039

Show messages belonging to a specific user ID:

# journalctl _UID=1000

Show messages from the kernel ring buffer (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 specified service only:

tux > sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service

If two different fields are specified, 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 field, all entries matching either expression are shown:

tux > sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service _SYSTEMD_UNIT=dbus.service

You can use the '+' separator to combine two expressions in a logical 'OR'. The following example shows all messages from the Avahi service process with the process ID 1480 together with all messages from the D-Bus service:

tux > sudo journalctl _SYSTEMD_UNIT=avahi-daemon.service _PID=1480 + _SYSTEMD_UNIT=dbus.service

17.4 Investigating `systemd` Errors #Edit source

This section introduces a simple example to illustrate how to find and fix the error reported by systemd during apache2 start-up.

Try to start the apache2 service:

# systemctl start apache2
Job for apache2.service failed. See 'systemctl status apache2' and 'journalctl -xn' for details.

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.

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
[...]

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
   Loaded: loaded (/usr/lib/systemd/system/apache2.service; disabled)
   Active: active (running) since Tue 2014-06-03 11:26:24 CEST; 4ms ago
  Process: 11026 ExecStop=/usr/sbin/start_apache2 -D SYSTEMD -DFOREGROUND
           -k graceful-stop (code=exited, status=1/FAILURE)
 Main PID: 11263 (httpd2-prefork)
   Status: "Processing requests..."
   CGroup: /system.slice/apache2.service
           ├─11263 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
           ├─11280 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
           ├─11281 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
           ├─11282 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
           ├─11283 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]
           └─11285 /usr/sbin/httpd2-prefork -f /etc/apache2/httpd.conf -D [...]

17.5 Journald Configuration #Edit source

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 file description, see man 5 journald.conf. Note that you need to restart the journal for the changes to take effect with

tux > sudo systemctl restart systemd-journald

17.5.1 Changing the Journal Size Limit #Edit source

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 file 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` #Edit source

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

17.5.3 Forwarding the Journal to Syslog Facility #Edit source

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 #Edit source

For an easy way of filtering the systemd journal (without dealing with the journalctl syntax), you can use the YaST journal module. After installing it with sudo zypper in yast2-journal, start it from YaST by selecting System › Systemd Journal. Alternatively, start it from command line by entering sudo yast2 journal.

Figure 17.1: YaST systemd Journal #

The module displays the log entries in a table. The search box on top allows you to search for entries that contain certain characters, similar to using grep. To filter the entries by date and time, unit, file, or priority, click Change filters and set the respective options.

17.7 Viewing Logs in GNOME #Edit source

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.

18 `update-alternatives`: Managing Multiple Versions of Commands and Files #Edit source

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 different versions side by side, the alternatives system allows managing such versions consistently.

18.1 Overview
18.2 Use Cases
18.3 Getting an Overview of Alternatives
18.4 Viewing Details on Specific Alternatives
18.5 Setting the Default Version of Alternatives
18.6 Installing Custom Alternatives
18.7 Defining Dependent Alternatives

18.1 Overview #Edit source

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 specific file in the file 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 file out of several available using the alternatives system.

Link group

A set of related symbolic links that can be updated as a group.

Master link

The link in a link group that determines how the other links in the group are configured.

Slave link

A link in a link group controlled by the master link.

Symbolic link (Symlink)

A file that is a reference to another file in the same file system. The alternatives system uses symbolic links in the alternatives directory to switch between versions of a file.

Symbolic links in the alternatives directory can be modified by the administrator through the update-alternatives command.

The alternatives system provides the update-alternatives command to create, remove, 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 files. Examples in this chapter use commands and man pages, but they are also applicable to other file 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.

18.2 Use Cases #Edit source

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 files for an alternative.

18.3 Getting an Overview of Alternatives #Edit source

To retrieve the names of all configured alternatives, use:

tux > ls /var/lib/alternatives

To get an overview of all configured 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 #Edit source

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
java - 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 #Edit source

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 <enter> to keep the current choice[*], or type selection number:

Depending on your system and installed versions, the exact Java version number will be different. 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)

Also, keep in mind the following points:

When working in manual mode and installing another Java version, the alternatives system neither touches the links nor changes the generic name.
When working in automatic mode and installing another Java version, the alternatives system changes the Java master link and all slave links (as you can see in Section 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 #Edit source

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 conflicts with the system tools in /usr/bin.
There is a master link foo that points to either foo-2 or foo-3.

To provide alternatives on your system, follow these steps:

Copy your scripts into the /usr/local/bin directory.

Make the scripts executable:

tux > sudo chmod +x /usr/local/bin/foo-{2,3}

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

The 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 significant number increase to separate priorities. For example, a priority of 200 for `foo-2` and 300 for `foo-3`.

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 #Edit source

If you have alternatives, the script itself is not enough. Most commands are not completely stand-alone: They usually ship with additional files, such as extensions, configurations, or man pages. To create alternatives which are dependent on a master link, use slave alternatives.

Let us assume we want to extend our example in Section 18.6, “Installing Custom Alternatives” and provide man pages and configuration files:

Two man pages, foo-2.1.gz and foo-3.1.gz stored in the /usr/local/man/man1 directory.
Two configuration files, foo-2.conf and foo-3.conf, stored in /etc.

Follow these steps to add the additional files to your alternatives:

Copy the configuration files into /etc:
```
tux > sudo cp foo-{2,3}.conf /etc
```
Copy the man pages into the /usr/local/man/man1 directory:
```
tux > sudo cp foo-{2,3}.1.gz /usr/local/man/man1/
```

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

Check the master link:

foo - auto mode
  link best version is /usr/local/bin/foo-3
  link currently points to /usr/local/bin/foo-3
  link foo is /usr/local/bin/foo
  slave foo.1.gz is /usr/local/man/man1/foo.1.gz
  slave foo.conf is /etc/foo.conf
/usr/local/bin/foo-2 - priority 200
  slave foo.1.gz: /usr/local/man/man1/foo-2.1.gz
  slave foo.conf: /etc/foo-2.conf
/usr/local/bin/foo-3 - priority 300
  slave foo.1.gz: /usr/local/man/man1/foo-3.1.gz
  slave foo.conf: /etc/foo-3.conf

If you change the links with update-alternatives --config foo to foo-2, then all slave links will change as well.

19 Basic Networking #Edit source

Linux offers the necessary networking tools and features for integration into all types of network structures. Network access using a network card can be configured with YaST. Manual configuration is also possible. In this chapter only the fundamental mechanisms and the relevant network configuration files are covered.

19.1 IP Addresses and Routing
19.2 IPv6—The Next Generation Internet
19.3 Name Resolution
19.4 Configuring a Network Connection with YaST
19.5 Configuring a Network Connection Manually
19.6 Basic Router Setup
19.7 Setting Up Bonding Devices
19.8 Setting Up Team Devices for Network Teaming
19.9 Software-Defined Networking with Open vSwitch

Linux and other Unix operating systems use the TCP/IP protocol. It is not a single network protocol, but a family of network protocols that offer 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 first sent by the application as a stream of data and converted into the appropriate format by the operating system. The data arrives at the respective application on the destination host in the original data stream format it was initially sent. TCP determines whether any data has been lost or jumbled during the transmission. TCP is implemented wherever the data sequence matters.
UDP: User Datagram Protocol: a connectionless, insecure protocol. The data to transmit is sent in the form of packets generated by the application. The order in which the data arrives at the recipient is not guaranteed and data loss is possible. UDP is suitable for record-oriented applications. It features a smaller latency period than TCP.
ICMP: Internet Control Message Protocol: This is not a protocol for the end user, but a special control protocol that issues error reports and can control the behavior of machines 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 different layers. The actual network layer is the insecure data transfer via IP (Internet protocol). On top of IP, TCP (transmission control protocol) guarantees, to a certain extent, security of the data transfer. The IP layer is supported by the underlying hardware-dependent protocol, such as Ethernet.

Figure 19.1: Simplified Layer Model for TCP/IP #

The 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 fifteen 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 simplifies 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 100 Mbit/s FDDI network or via a 56-Kbit/s modem line. Likewise, it is irrelevant for the data line which kind of data is transmitted, as long as packets are in the correct format.

19.1 IP Addresses and Routing #Edit source

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 #Edit source

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 inflexible and was discontinued. Now, classless routing (CIDR, classless interdomain routing) is used.

19.1.2 Netmasks and Routing #Edit source

Netmasks are used to define the address range of a subnet. If two hosts are in the same subnet, they can reach each other directly. If they are not in the same subnet, they need the address of a gateway that handles all the traffic for the subnet. To check if two IP addresses are in the same subnet, simply “AND” both addresses with the netmask. If the result is identical, both IP addresses are in the same local network. If there are differences, the remote IP address, and thus the remote interface, can only be reached over a gateway.

To understand how the netmask works, look at Example 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 first net with 24 bits could also be written as 192.168.0.0/24.

Example 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 configured for the target network. In the most common case, there is only one gateway that handles all traffic that is external. However, it is also possible to configure several gateways for different subnets.

If a gateway has been configured, all external IP packets are sent to the appropriate gateway. This gateway then attempts to forward the packets in the same manner—from host to host—until it reaches the destination host or the packet's TTL (time to live) expires.

Specific Addresses #

Base Network Address: This is the netmask AND any address in the network, as shown in Example 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 defined with IPv4. With IPv6 there is only one loopback address (::1).

Because 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 specified 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 #Edit source

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 fifteen 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 shortage. The problem with them lies in their configuration, 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 configuration should be a thing of the past. The following sections tell more about the improvements and benefits brought by IPv6 and about the transition from the old protocol to the new one.

19.2.1 Advantages #Edit source

The most important and most visible improvement brought by the new protocol is the enormous expansion of the available address space. An IPv6 address is made up of 128 bit values instead of the traditional 32 bits. This provides for as many as several quadrillion IP addresses.

However, IPv6 addresses are not only different from their predecessors with regard to their length. They also have a different internal structure that may contain more specific information about the systems and the networks to which they belong. More details about this are found in Section 19.2.2, “Address Types and Structure”.

The following is a list of other advantages of the new 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 configuration. The new host uses its automatic configuration mechanism to derive its own address from the information made available by the neighboring routers, relying on a protocol called the neighbor 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 flags telling the hosts of a network how they should interact with each other. For more information, see RFC 2462 and the radvd.conf(5) man page, and RFC 3315.

Mobility

IPv6 makes it possible to assign several addresses to one network interface at the same time. This allows users to access several networks easily, something that could be compared with the international roaming services offered by mobile phone companies. When you take your 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 fine-grained approach by enabling servers to address hosts through multicasting, that is by addressing several hosts as parts of a group. This is different from addressing all hosts through broadcasting or each host individually through unicasting. Which hosts are addressed as a group may depend on the concrete application. There are some predefined 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 #Edit source

As mentioned, the current IP protocol has two major limitations: there is an increasing shortage of IP addresses, and configuring the network and maintaining the routing tables is becoming a more complex and burdensome task. IPv6 solves the first 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 different types of addresses:

Unicast: Addresses of this type are associated with exactly one network interface. Packets with such an address are delivered to only one destination. Accordingly, unicast addresses are used to transfer packets to individual hosts on the local network or the Internet.
Multicast: Addresses of this type relate to a group of network interfaces. Packets with such an address are delivered to all destinations that belong to the group. Multicast addresses are mainly used by certain network services to communicate with certain groups of hosts in a well-directed manner.
Anycast: Addresses of this type are related to a group of interfaces. Packets with such an address are delivered to the member of the group that is closest to the sender, according to the principles of the underlying routing protocol. Anycast addresses are used to make it easier for hosts to find out about servers offering certain services in the given network area. All servers of the same type have the same anycast address. Whenever a host requests a service, it receives a reply from the server with the closest location, as determined by the routing protocol. If this server should fail 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 fields, each representing 16 bits, written in hexadecimal notation. They are separated by colons (:). Any leading zero bytes within a given field may be dropped, but zeros within the field 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 defined function. The first bytes form the prefix and specify the type of address. The center part is the network portion of the address, but it may be unused. The end of the address forms the host part. With IPv6, the netmask is defined by indicating the length of the prefix after a slash at the end of the address. An address, as shown in Example 19.4, “IPv6 Address Specifying the Prefix Length”, contains the information that the first 64 bits form the network part of the address and the last 64 form its host part. In other words, the 64 means that the netmask is filled 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 predefined types of prefixes. 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 prefix 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 prefix should not be routed and should therefore only be reachable from within the same subnet.
fec0::/10: Site-local addresses. These may be routed, but only within the network of the organization to which they belong. In effect, they are the IPv6 equivalent of the current private network address space, such as 10.x.x.x.
ff: These are multicast addresses.

A unicast address consists of three basic components:

Public Topology: The first part (which also contains one of the prefixes mentioned above) is used to route packets through the public Internet. It includes information about the company or institution that provides the Internet access.
Site Topology: The second part contains routing information about the subnet to which to deliver the packet.
Interface ID: The third part identifies the interface to which to deliver the packet. This also allows for the MAC to form part of the address. Given that the MAC is a globally unique, fixed identifier coded into the device by the hardware maker, the configuration procedure is substantially simplified. In fact, the first 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 five different types of unicast addresses:

:: (unspecified)

This address is used by the host as its source address when the interface is initialized for the first time (at which point, the address cannot yet be determined by other means).

::1 (loopback)

The address of the loopback device.

IPv4 Compatible Addresses

The IPv6 address is formed by the IPv4 address and a prefix consisting of 96 zero bits. This type of compatibility address is used for tunneling (see Section 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 specifies a pure IPv4 address in IPv6 notation.

Local Addresses

There are two address types for local use:

link-local: This type of address can only be used in the local subnet. Packets with a source or target address of this type should not be routed to the Internet or other subnets. These addresses contain a special prefix (fe80::/10) and the interface ID of the network card, with the middle part consisting of zero bytes. Addresses of this type are used during automatic configuration to communicate with other hosts belonging to the same subnet.
site-local: Packets with this type of address may be routed to other subnets, but not to the wider Internet—they must remain inside the organization's own network. Such addresses are used for intranets and are an equivalent of the private address space defined by IPv4. They contain a special prefix (fec0::/10), the interface ID, and a 16 bit field specifying the subnet ID. Again, the rest is filled 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 configured completely automatically using the MAC and a known prefix with the result that all hosts on the local network can be reached when IPv6 is enabled (using the link-local address). With the MAC forming part of it, any IP address used in the world is unique. The only variable parts of the address are those specifying the site topology and the public topology, depending on the actual network in which the host is currently operating.

For a host to go back and forth between different networks, it needs at least two addresses. One of them, the home address, not only contains the interface ID but also an identifier of the home network to which it normally belongs (and the corresponding prefix). The home address is a static address and, as such, it does not normally change. Still, all packets destined to the mobile host can be delivered to it, regardless of whether it operates in the home network or somewhere outside. This is made possible by the completely new features introduced with IPv6, such as stateless autoconfiguration and neighbor discovery. In addition to its home address, a mobile host gets one or more additional addresses that belong to the foreign networks where it is roaming. These are called care-of addresses. The home network has a facility that forwards any packets destined to the host when it is roaming outside. In an IPv6 environment, this task is performed by the home agent, which takes all packets destined to the home address and relays them through a tunnel. 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 #Edit source

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 offer tunneling and compatibility addresses (see Section 19.2.2, “Address Types and Structure”).

IPv6 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 prefix) and the IPv4 address of the remote host at the receiving end of the tunnel. A basic tunnel can be configured manually according to an agreement between the hosts' administrators. This is also called static tunneling.

However, the configuration and maintenance of static tunnels is often too labor-intensive to use them for daily communication needs. Therefore, IPv6 provides for three different methods of dynamic tunneling:

6over4: IPv6 packets are automatically encapsulated as IPv4 packets and sent over an IPv4 network capable of multicasting. IPv6 is tricked into seeing the whole network (Internet) as a 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 specifications 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 #Edit source

To configure 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.

Because of the autoconfiguration concept of IPv6, the network card is assigned an address in the link-local network. Normally, no routing table management takes place on a workstation. The network routers can be queried by the workstation, using the router advertisement protocol, for what prefix and gateways should be implemented. The radvd program can be used to set up an IPv6 router. This program informs the workstations which prefix to use for the IPv6 addresses and which routers. Alternatively, use zebra/quagga for automatic configuration of both addresses and routing.

For information about how to set up various types of tunnels using the /etc/sysconfig/network files, see the man page of ifcfg-tunnel (man ifcfg-tunnel).

19.2.5 For More Information #Edit source

The above overview does not cover the topic of IPv6 comprehensively. For a more in-depth look at the new 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, find 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).

19.3 Name Resolution #Edit source

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 qualified domain name (FQDN), consists of a host name and a domain name (example.com). The latter also includes the top level domain or TLD (com).

TLD assignment has become 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 file /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 configuration 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 find out who is responsible for a given domain.

Note: MDNS and .local Domain Names

The .local top level domain is treated as link-local domain by the resolver. DNS requests are send as multicast DNS requests instead of normal DNS requests. If you already use the .local domain in your name server configuration, you must switch this option off in /etc/host.conf. For more information, see the host.conf manual page.

To switch off 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 #Edit source

There are many supported networking types on Linux. Most of them use different device names and the configuration files are spread over several locations in the file system. For a detailed overview of the aspects of manual network configuration, see Section 19.5, “Configuring a Network Connection Manually”.

All network interfaces with link up (with a network cable connected) are automatically configured. Additional hardware can be configured any time on the installed system. The following sections describe the network configuration for all types of network connections supported by SUSE Linux Enterprise Server.

Tip: IBM Z: Hotpluggable Network Cards

On IBM Z platforms, hotpluggable network cards are supported, but not their automatic network integration via DHCP (as is the case on the PC). After they have been detected, you need to manually configure the interface.

19.4.1 Configuring the Network Card with YaST #Edit source

To configure your Ethernet or Wi-Fi/Bluetooth card in YaST, select System › Network Settings. After starting the module, YaST displays the Network Settings dialog with four tabs: Global 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”.

The Overview tab contains information about installed network interfaces and configurations. Any properly detected network card is listed with its name. You can manually configure new cards, remove or change their configuration in this dialog. To manually configure a card that was not automatically detected, see Section 19.4.1.3, “Configuring an Undetected Network Card”. To change the configuration of an already configured 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 configuration 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 #Edit source

The Global Options tab of the YaST Network Settings module allows you to set important global networking options, such as the use of NetworkManager, IPv6 and DHCP client options. These settings are applicable for all network interfaces.

Note: NetworkManager Provided by Workstation Extension

NetworkManager is now provided by the SUSE Linux Enterprise Workstation Extension. To install NetworkManager, activate the Workstation Extension repository, and select the NetworkManager packages.

In the Network Setup Method choose the way network connections are managed. If you want a NetworkManager desktop applet to manage connections for all interfaces, choose 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 configure network options and the Overview, Hostname/DNS and Routing tabs of the Network Settings module are disabled. For more information on NetworkManager, see the SUSE Linux Enterprise Desktop documentation.

In the IPv6 Protocol Settings choose whether to use the IPv6 protocol. It is possible to use IPv6 together with IPv4. By default, IPv6 is enabled. However, in networks not using IPv6 protocol, response times can be faster with IPv6 protocol disabled. To disable IPv6, deactivate Enable IPv6. If IPv6 is disabled, the kernel no longer loads the IPv6 module automatically. This setting will be applied after reboot.

In the DHCP Client Options configure options for the DHCP client. The DHCP Client Identifier must be different for each DHCP client on a single network. If left empty, it defaults to the hardware address of the network interface. However, if you are running several virtual machines using the same network interface and, therefore, the same hardware address, specify a unique free-form identifier here.

The Hostname to Send specifies a string used for the host name option field 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 field to contain a specific string in the DHCP messages from clients. Leave AUTO to send the current host name (that is the one defined in /etc/HOSTNAME). Make the option field 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.

19.4.1.2 Changing the Configuration of a Network Card #Edit source

To change the configuration of a network card, select a card from the list of the detected cards in Network Settings › Overview in YaST and click Edit. The Network Card Setup dialog appears in which to adjust the card configuration using the General, Address and Hardware tabs.

19.4.1.2.1 Configuring IP Addresses #Edit source

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 first network card with link that is available during the installation is automatically configured to use automatic address setup via DHCP.

Note: IBM Z and DHCP

On IBM Z platforms, DHCP-based address configuration is only supported with network cards that have a MAC address. This is only the case with OSA and OSA Express cards.

DHCP should also be used if you are using a DSL line but with no static IP assigned by the ISP (Internet Service Provider). If you decide to use DHCP, configure the details in DHCP Client Options in the Global Options tab of the Network Settings dialog of the YaST network card configuration module. If you have a virtual host setup where different hosts communicate through the same interface, an DHCP Client Identifier is necessary to distinguish them.

DHCP is a good choice for client configuration but it is not ideal for server configuration. To set a static IP address, proceed as follows:

Select a card from the list of detected cards in the Overview tab of the YaST network card configuration module and click Edit.
In the Address tab, choose Statically Assigned IP Address.
Enter the IP Address. Both IPv4 and IPv6 addresses can be used. Enter the network mask in Subnet Mask. If the IPv6 address is used, use Subnet Mask for prefix length in format /64.
Optionally, you can enter a fully qualified Hostname for this address, which will be written to the /etc/hosts configuration file.
Click Next.
To activate the configuration, click OK.

Note: Interface Activation and Link Detection

During activation of a network interface, wicked checks for a carrier and only applies the IP configuration when a link has been detected. If you need to apply the configuration regardless of the link status (for example, when you want to test a service listening to a certain address), you can skip link detection by adding the variable LINK_R

SUSE Linux Enterprise Server 15 SP1

Administration Guide

About This Guide #Edit source

1 Available Documentation #Edit source

Note: Online Documentation and Latest Updates

2 Giving Feedback #Edit source

3 Documentation Conventions #Edit source

Warning: Warning Notice

Important: Important Notice

Note: Note Notice

Tip: Tip Notice

4 Product Life Cycle and Support #Edit source

4.1 Support Statement for SUSE Linux Enterprise Server #Edit source

4.2 Technology Previews #Edit source

Part I Common Tasks #Edit source

1 Bash and Bash Scripts #Edit source

1.1 What is “The Shell”? #Edit source

1.1.1 Bash Configuration Files #Edit source

Table 1.1: Bash Configuration Files for Login Shells #

Table 1.2: Bash Configuration Files for Non-Login Shells #

Table 1.3: Special Files for Bash #

No-Login Shells#Edit source

1.1.2 The Directory Structure #Edit source

Table 1.4: Overview of a Standard Directory Tree #

Note: Home Directory in a Network Environment

Important: Cleaning up /tmp at Boot Time

1.2 Writing Shell Scripts #Edit source

Example 1.1: A Shell Script Printing a Text #

1.3 Redirecting Command Events #Edit source

1.4 Using Aliases #Edit source

1.5 Using Variables in Bash #Edit source

Table 1.5: Useful Environment Variables #

1.5.1 Using Argument Variables #Edit source

1.5.2 Using Variable Substitution #Edit source

1.6 Grouping and Combining Commands #Edit source

1.7 Working with Common Flow Constructs #Edit source

1.7.1 The if Control Command #Edit source

1.7.2 Creating Loops with the for Command #Edit source

1.8 For More Information #Edit source

2 sudo #Edit source

2.1 Basic sudo Usage #Edit source

2.1.1 Running a Single Command #Edit source

Tip: I/O Redirection

2.1.2 Starting a Shell #Edit source

2.1.3 Environment Variables #Edit source

2.2 Configuring sudo #Edit source

Note: Locked yourself out of sudo

2.2.1 Editing the Configuration Files #Edit source

Note: Ignored Files in /etc/sudoers.d

2.2.2 Basic sudoers Configuration Syntax #Edit source

Table 2.1: Useful Flags and Options #

2.2.3 Rules in sudoers #Edit source

Syntax for sudoers Rules #

Warning: Dangerous constructs

2.3 Common Use Cases #Edit source

2.3.1 Using sudo without root Password #Edit source

Warning: Dangerous rule in sudoers

2.3.2 Using sudo with X.Org Applications #Edit source

2.4 More Information #Edit source

3 YaST Online Update #Edit source

Note: Error on Accessing the Update Catalog

3.1 The Online Update Dialog #Edit source

Figure 3.1: YaST Online Update #

3.2 Installing Patches #Edit source

Procedure 3.1: Applying Patches with YaST Online Update #

Important: Always Apply Security Updates

3.3 Automatic Online Update #Edit source

Procedure 3.2: Configuring the Automatic Online Update #

Figure 3.2: YaST Online Update Configuration #

4 YaST #Edit source

4.1 Advanced Key Combinations #Edit source

5 YaST in Text Mode #Edit source

Figure 5.1: Main Window of YaST in Text Mode #

Tip: Refreshing YaST Dialogs

5.1 Navigation in Modules #Edit source

Figure 5.2: The Software Installation Module #

5.2 Advanced Key Combinations #Edit source

5.3 Restriction of Key Combinations #Edit source

5.4 YaST Command Line Options #Edit source

5.4.1 Installing Packages from the Command Line #Edit source

Important: Cleaning up `/tmp` at Boot Time

1.7.2 Creating Loops with the `for` Command #Edit source

2.1 Basic `sudo` Usage #Edit source

2.2 Configuring `sudo` #Edit source

Note: Ignored Files in `/etc/sudoers.d`

2.3.1 Using `sudo` without `root` Password #Edit source

2.3.2 Using `sudo` with X.Org Applications #Edit source

Tip: Removing all `-debuginfo` Packages

Note: Default Behavior of `zypper`