Enhance system stability

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zh-CN:Enhancing Arch Linux Stability

The purpose of this wiki article is to provide tips on how to make an Arch Linux system as stable as possible. While Arch Developers and Trusted Users work hard to produce high quality packages, given Arch's rolling release system and rapid package turnover, an Arch system may not be suitable for a mission critical, commercial production environment.

However, Arch is inherently stable due to its commitment to simplicity in configuration, coupled with a rapid bug-report/bug-fix cycle, and the use of unpatched upstream source code. Thus, by following the advice below on setting up and maintaining Arch, the user should be able enjoy a very stable system. Furthermore, advice is included that will ease system repair in the event of a major malfunction.

How stable can Arch Linux really be? There are numerous reports in the Arch forums of skilled system administrators successfully using Arch for production servers. Archlinux.org is one such example. On the desktop, a properly configured and maintained Arch installation can offer excellent stability.

Setting Up Arch

When first installing and configuring Arch Linux, the user has a variety of choices to make about configuration, software, and drivers. These choices will impact overall system stability.

Arch Specific Tips

Keeping old packages in a large /var partition

Pacman archives all of the previously installed packages in /var/cache/pacman/pkg, which over time may grow to a few GB in size. If you are setting up separate partitions during installation, always be sure to allocate plenty of space for a large /var partition. 4 to 8 GB should do, although more may be required for some server uses. Retaining these packages is helpful in case a recent package upgrade causes instability, requiring a downgrade to an older, archived package. See the section below entitled, #Revert package upgrades that cause instability.

Use recommended configurations

In the detailed Arch Linux installation and configuration documentation, there is often more than one way to configure a specific aspect of the system. Always choose the recommended, default configuration when setting up the system. The recommended, default configurations reflect best practices, chosen for optimum system stability and ease of system repair.

Be careful with unofficial and less tested packages

Avoid any use of the testing repository, or individual packages from testing. These experimental packages are for development and testing, and are not suitable for a stable system.

Use precaution when using packages from AUR. Most of the packages in AUR are supplied by user and thus might not have the same packaging standard as those in official repositories. Always check AUR package's PKGBUILD for any signs of mistake or malicious code before you build and install them.

Be careful with AUR helpers which highly simplify installation of AUR packages and could lead to user build and install package that have malformed or malicious PKGBUILD. You should always sanity check PKGBUILDs before building and/or installing the package.

Finally, it is extremely unwise to ever run any AUR helpers, or the makepkg command as root user.

Only use 3rd party repository if absolutely necessary or if you know what you're doing. Always use 3rd party repository from a trusted source.

Use up-to-date mirrors

Use mirrors that are frequently updated with the latest packages from the main Arch FTP server. Review the Mirror Status webpage to verify that your chosen mirror is up to date. By using recently rsync'd mirrors, this ensures that your system will always have the freshest packages and package databases available during the course of routine maintenance.

Also, if it is used, edit the mirror list in /etc/pacman.d by placing local mirrors, those within your country or region, at the top of the list. Refer to the Enabling your favorite mirror Arch wikipage section for additional details, including the installation of the rankmirrors script to enable the fastest mirrors. These steps will ensure that the system uses the fastest, most reliable mirrors.

After changing the server mirror used for updates, ensure that your system is up-to-date by doing pacman -Syu.

Avoid development packages

To prevent serious breakage of the system, do not install any development packages, which are usually found in AUR and occasionally in community. These are packages taken directly from upstream development branches, and usually feature one of the following words appended to the package name: dev, devel, svn, cvs, git, hg, bzr, or darcs.

Most especially, avoid installing any development version of crucial system packages such as the kernel or glibc.

If building a custom package using makepkg, be sure that the PKGBUILD follows the Arch packaging standards, including a provides array. Use namcap to check the final .tar.gz or PKGBUILD file.

Install the linux-lts package

The linux-lts package is an alternative Arch kernel package based upon Linux kernel 3.10 and is available in the [core] repository. This particular kernel version enjoys long-term support (LTS) from upstream, including security fixes and some feature backports, especially useful for users seeking to use Arch Linux on a server, or who want a fallback kernel in case a new kernel version causes problems.

To make it available as a boot option, you will need to update the bootloader's configuration file. For Syslinux, you have to edit /boot/syslinux/syslinux.cfg and duplicate the current entries, except using vmlinuz-linux-lts and initramfs-linux-lts.img. For GRUB, the recommended method is to automatically re-generate the configuration file.

Generic Best Practices

Use the package manager to install software

Pacman does a much better job than you at keeping track of files. If you install things manually you will, sooner or later forget what you did, where you installed to, install conflicting software, install to the wrong locations, etc.

From a stability standpoint you should try to avoid unsupported package and custom software, but if you really need such things making a package is better than manually compiling and installing.

Use proven software packages

Install mature and proven software; while avoiding cutting edge software that is still buggy. Do not deploy newly developed software until it is proven to be reliable. For example, PulseAudio's early versions could be unreliable. Users interested in maximum stability would use the ALSA sound system instead. Finally, use software that has a strong and active development community, as well as a high number of competent users.

Choose open-source drivers

Wherever possible, choose open source drivers. Try to avoid proprietary drivers. Most of the time, open source drivers are more stable and reliable than proprietary drivers. Open source driver bugs are fixed more easily and quickly. While proprietary drivers can offer more features and capabilities, this can come at the cost of stability. To avoid this dilemma, choose hardware components known to have mature open source driver support with full features. Information about hardware with open source Linux drivers is available at linux-drivers.org.

Maintaining Arch

In addition to configuring Arch for stability, there are steps one can take during maintenance which will enhance stability. Paying attention to a few SysAdmin details will help to ensure continued system reliability.

Arch Specific Tips

Upgrade entire system with reasonable frequency

Many Arch users update frequently, even upgrading their systems daily using pacman -Syu. While updating so frequently is not necessary, one should upgrade fairly often to enjoy the latest bugfix and security updates. Weekly or biweekly upgrades are thus a good idea.

If the system has packages from the AUR, carefully upgrade all AUR packages.

Read before upgrading the system

Before upgrading Arch, always read the latest Arch News to find out if there are any major software or configuration changes with the latest packages. Before upgrading fundamental software, such as the kernel, xorg, or glibc to a new version, look over the appropriate forum to see if there have been any reported problems.

Act on alerts during an upgrade

When upgrading the system, be sure to pay attention to the alert notices provided by pacman. If any additional actions are required by the user, be sure to take care of them right away. If a pacman alert is confusing, search the forums and the recent news posts for more detailed instructions.

Deal promptly with new configuration files

When pacman is invoked .pacnew, .pacsave, and .pacorig files can be created. When pacman removes a package that has a configuration file, it normally creates a backup copy of that config file and appends .pacsave to the name of the file. Likewise, when pacman upgrades a package which includes a new config file created by the maintainer differing from the currently installed file, it writes a .pacnew config file. Occasionally, under special circumstances, a .pacorig file is created. Pacman provides notice when these files are written.

Users must deal with these files promptly when pacman creates them, in order to ensure optimum system stability. The pacdiff tool, provided by pacman, can assist with this. Users are referred to the Pacnew and Pacsave Files wiki page for detailed instructions.

Also, think about other configuration files you you may have copied or created. If a package had an example configuration that you copied to your home directory, check to see if a new one has been created.

Consider using pacmatic

Pacmatic is a pacman wrapper which automates the process of checking Arch News prior to upgrading. Pacmatic also ensures that the local pacman database is correctly synchronized with online mirrors, thus avoiding potential problems with botched pacman -Sy database updates. Finally, it provides more stringent warnings about updated or obsolete config files. pacman can be aliased to pacmatic, and various AUR helpers can be configured to use it instead of pacman.

Avoid certain pacman commands

Arch being a rolling release distribution, it can be dangerous to install new packages without doing a full system upgrade immediately before. Avoid using pacman -S package to install a package, but always use pacman -Syu package instead. Also never run pacman -Sy, instead use pacman -Syu.

Avoid using the -f option with pacman, especially in commands such as pacman -Syuf involving more than one package. The --force option ignores file conflicts and can even cause file loss when files are relocated between different packages! In a properly maintained system, it should never need to be used.

Do not use pacman -Rdd package. Using the -d flag skips dependency checks during package removal. As a result, a package providing a critical dependency could be removed, resulting in a broken system.

Never run pacman -Scc unless there is a desperate need for the disk space, and little or no need for archived package files. It is safer to keep older packages available in the cache archives in the event a package upgrade causes problems, requiring a package reversion. Instead, just use pacman -Sc to clean out the archived packages in the pacman cache, of packages previously removed from the pacman database.

Tip: As an alternative to both the -Sc and -Scc switches, consider using paccache from pacman. This offers more control over what and how many packages are deleted. Run paccache -h for instructions.

Revert package upgrades that cause instability

In the event that a particular package upgrade results in system instability, install the last known stable version of the package from the local pacman cache using the following command:

pacman -U /var/cache/pacman/pkg/Package-Name.pkg.tar.gz

For more detailed information on reverting to older packages, consult the Arch wikipage, Downgrading packages.

Once the package is reverted, temporarily add it to the IgnorePkg section of pacman.conf, until the difficulty with the updated package is resolved. Consult the Arch wiki and/or webforums for advice, and file a bug report if necessary.

Regularly back up a list of installed packages

Merge-arrows-2.pngThis article or section is a candidate for merging with Pacman_Tips#Backing_up_and_retrieving_a_list_of_installed_packages.Merge-arrows-2.png

Notes: The pacman tips page explains this topic in much more detail. (Discuss in Talk:Enhance system stability#)

At regular intervals, create a list of installed packages and make a backup of the list. Use the following command to create the list:

pacman -Qqne > pkglist.txt

If a complete re-installation is inevitable, the packages from the list can be quickly reinstalled using the command:

pacman -S --needed $(< pkglist.txt )

Regularly back up the pacman database

The following command can be used to back up the local pacman database, and can be run as a cronjob:

tar -cjf /path/to/chosen/directory/pacman-database.tar.bz2 /var/lib/pacman/local

Store the backup pacman database file on one or more offline media, such as a USB stick, external hard drive, or CD-R.

Restore the backup pacman database file by moving the pacman-database.tar.bz2 file into the / directory and executing the following command:

tar -xjvf pacman-database.tar.bz2

If the pacman database files are corrupted, and there is no backup file available, there exists some hope of rebuilding the pacman database. Consult the Arch wikipage, How To Restore Pacman's Local Database.

Systemd Automation

You can configure systemd to back up the pacman database everytime a new package is installed or updated. For details see the article Pacman Tips#Backing up Local database with systemd.

Generic Best Practices

Subscribe to NVD/CVE alerts and only upgrade on a security alert

Subscribe to the Common Vulnerabilities and Exposure Security Alert updates, made available by National Vulnerability Database, and found on the NVD Download webpage. Only update the Arch system when a security alert is issued for a package installed on that particular system.

This is the alternative to upgrading the entire system frequently. It ensures that security problems in various packages are resolved promptly, while keeping all the rest of the packages frozen in a known, stable configuration. However, reviewing the frequent CVE Alerts to see if any apply to installed Arch packages can be tedious and time consuming.

Warning: Partial updates are not supported by Arch Linux, the whole system should be upgraded when upgrading a component. Infrequent system updates could potentially complicate the update process.

Test updates on a non-critical system

If possible, test changes to configuration files, as well as updates to software packages, on a non-critical duplicate system first. Then, if no problems arise, roll out the changes to the production system.

Always back up config files before editing

Before editing any configuration file, always back up a known working version of that config file. In the event that changes in the config file cause problems, one can revert to the previous stable config file. Do this from a text editor by first saving the file to a backup copy before making any alterations; or execute the following command:

cp config config~

Using ~ will ensure there is a readily distinguishable human-made backup conf file if pacman creates a .pacnew, .pacsave, or .pacorig file using the active config file.

etckeeperAUR can help dealing with config files. It keeps the whole /etc directory in a version control.

Regularly back up the /etc, /home, /srv, and /var directories

Merge-arrows-2.pngThis article or section is a candidate for merging with Backup programs.Merge-arrows-2.png

Notes: Any backup program besides tar could be used. (Discuss in Talk:Enhance system stability#)

Since /etc, /home, /srv and /var directories contain important system files and configs, it is advisable to make backups of these folders at regular intervals. The following is a simple guide on how to go about it.

  • /etc: Back up the /etc directory by executing the following command as root or as a cronjob:
tar -cjf /path/to/chosen/directory/etc-backup.tar.bz2 /etc

Store the /etc backup file on one or more offline media, such as a USB stick, external hard drive, or CD-R. Occasionally verify the integrity of the backup process by comparing original files and directories with their backups.

Restore corrupted /etc files by extracting the etc-backup.tar.bz2 file in a temporary working directory, and copying over individual files and directories as needed. To restore the entire /etc directory with all its contents, move the etc-backup.tar.bz2 files into the / directory. As root, execute the following command:

tar -xvjf etc-backup.tar.bz2
  • /home: At regular intervals, back up the /home directory to an external hard drive, Network Attached Server, or online backup service. Occasionally verify the integrity of the backup process by comparing original files and directories with their backups.
  • /srv: Server installations should have the /srv directory regularly backed up.
  • /var: Additional directories in /var, such a /var/spool/mail or /var/lib, which also require backup and occasional verification.

If you want to back up much faster (using parallel compression, SMP), you should use pbzip2 (Parallel bzip2). The steps are slightly different, but not by much.

First we will back up the files to a plain tarball with no compression:

tar -cvf /path/to/chosen/directory/etc-backup.tar /etc

Then we will use pbzip2 to compress it in parallel (Make sure you install it with pacman -S pbzip2)

pbzip2 /path/to/chosen/directory/etc-backup.tar.bz2

and that's it. Your files should be backing up using all of your cores.