Difference between revisions of "Enhance system stability"

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(Regularly backup the pacman database)
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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, [[Pacman_Tips#Restore_pacman.27s_local_database|How To Restore Pacman's Local Database]].
 
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, [[Pacman_Tips#Restore_pacman.27s_local_database|How To Restore Pacman's Local Database]].
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 +
===== Systemd Automation =====
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 +
To have [https://wiki.archlinux.org/index.php/Systemd systemd] backup the pacman database everytime a new package is installed or updated, save and run the following scripts:
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 +
{{Tip| Save the following script as {{ic|/usr/lib/systemd/scripts/pakbak_script}}.}}
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{{Note| Change the directory where the compressed pacman database is stored by changing {{ic|$pacbak}} string.}}
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{{bc|<nowiki>
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#!/bin/bash
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declare -r pacbak="/pakbak.bz2";  ## set backup directory
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tar -cjf "$pacbak" "/var/lib/pacman/local";  ## compress local packages and store them in backup directory
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</nowiki>}}
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{{Tip| Save the following script as {{ic|/usr/lib/systemd/system/pakbak.service}}.}}
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{{bc|<nowiki>
 +
[Unit]
 +
Description=Back up pacman database
 +
 +
[Service]
 +
Type=oneshot
 +
ExecStart=/usr/lib/systemd/scripts/pakbak_script
 +
RemainAfterExit=no
 +
 +
[Install]
 +
WantedBy=multi-user.target
 +
</nowiki>}}
 +
 +
{{Tip| Save the following script as {{ic|/usr/lib/systemd/scripts/pakbak.path}}.}}
 +
{{bc|<nowiki>
 +
[Unit]
 +
Description=Back up pacman database
 +
 +
[Path]
 +
PathChanged=/var/lib/pacman/local
 +
Unit=pakbak.service
 +
 +
[Install]
 +
WantedBy=multi-user.target
 +
</nowiki>}}
 +
 +
{{Tip| Enable the systemd service with
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{{bc|<nowiki>
 +
# systemctl enable pakbak.path
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</nowiki>}}}}
  
 
=== Generic Best Practices ===
 
=== Generic Best Practices ===

Revision as of 02:53, 2 February 2013

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

Set up a large /var partition and keep old packages

When setting up partitions during installation, always be sure to allocate plenty of space for a large, separate /var partition. A /var partition should have a generous 6 to 8 GB of space - more for some server uses. Pacman archives all of the previously installed packages in /var/cache/pacman/pkg, which requires significant amounts of storage space. Retaining these packages is helpful if 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. For example, there are several ways to configure a login manager to run during startup. Always choose the recommended, default configuration when setting up the system. (In the case of login manager configuration, this is the inittab method). 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 3.0 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 Arch users seeking to use such a kernel 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 example, if you use 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 .cfg.

Some prefer to install the linux-lts package in addition to the regular linux package and edit the Fallback entry to use the LTS kernel.

Generic Best Practices

Use the package manager to install software

The package manager (in Arch: 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 stuff, install to 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.

You should also disable make install command (which is typical for beginning of all problems) in /root/.bashrc

 make() {
   [ "$1" == 'install' ] &&
     echo -e "WARNING:\nDON'T INSTALL SOFTWARE MANUALLY\nDON'T USE unset make TO OVERRIDE" &&
     echo "Tip: It's easy to make own custom package see: man PKGBUILD makepkg" &&
     return 1;
   /usr/bin/make $@;
 }

Use proven, mainstream software packages

Install mature, proven, mainstream software; while avoiding cutting edge software that is still buggy. Try to avoid installing "point-oh", aka x.y.0, software releases. For example, instead of installing Foobar 2.5.0, wait until Foobar 2.5.1 is available. 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.

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 webforum 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 .pacnew, .pacsave, and .pacorig files

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. Users are referred to the Pacnew and Pacsave Files wiki page for detailed instructions.

There are various tools to help resolve .pacnew and .pacsave file issues. The standard diff utility (alternatively, colordiff) provides an easy way to compare the files. The pacman-contrib package includes a tool, pacdiff, which helps to sort through such files. Finally, the pacnews bash script provides similar functionality. Both pacdiff and pacnews use vimdiff to compare and edit .pacnew and .pacsave files.

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 refresh pacman databases without doing a full system upgrade immediately after. Avoid using pacman -Sy package to install a package, but always use pacman -S package instead. And upgrade your system regularly with 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.

Make sure to only use this command if there is no intention of re-installing recently removed packages. If such packages are re-installed after this command has been executed, there will be no older, archived versions of the packages in the pacman cache.

In the event that /var disk space becomes scarce, move all archived packages to the home directory using the fduparch.sh script. Use the fduppkg script to move all but the last previously installed package versions in the pacman cache archives, to the home directory.

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 backup a list of installed packages

At regular intervals, create a list of installed packages and store a copy on one or more offline media, such as a USB stick, external hard drive, or CD-R. Use the following command to create a pkglist:

pacman -Qqe | grep -vx "$(pacman -Qqm)" > /path/to/chosen/directory/pkg.list

In the event of a catastrophic system failure requiring a complete re-installation, these packages can be quickly reinstalled using the command:

xargs -a /path/to/chosen/directory/pkg.list pacman -S --needed

Regularly backup the pacman database

The following command can be used to backup 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

To have systemd backup the pacman database everytime a new package is installed or updated, save and run the following scripts:

Tip: Save the following script as /usr/lib/systemd/scripts/pakbak_script.
Note: Change the directory where the compressed pacman database is stored by changing $pacbak string.
#!/bin/bash

declare -r pacbak="/pakbak.bz2";  ## set backup directory
tar -cjf "$pacbak" "/var/lib/pacman/local";  ## compress local packages and store them in backup directory
Tip: Save the following script as /usr/lib/systemd/system/pakbak.service.
[Unit]
Description=Back up pacman database

[Service]
Type=oneshot
ExecStart=/usr/lib/systemd/scripts/pakbak_script
RemainAfterExit=no

[Install]
WantedBy=multi-user.target
Tip: Save the following script as /usr/lib/systemd/scripts/pakbak.path.
[Unit]
Description=Back up pacman database

[Path]
PathChanged=/var/lib/pacman/local
Unit=pakbak.service

[Install]
WantedBy=multi-user.target
Tip: Enable the systemd service with
# systemctl enable pakbak.path

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.

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 backup 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.bak

Using .bak 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.

Regularly backup the /etc, /home, /srv, and /var directories

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

  • /etc: Backup 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, backup 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 backup much faster (using parallel compression, SMP), you should use pbzip2 (Parallel bzip2). The steps are slightly different, but not by much.

First we will backup 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.