pacman/Tips and tricks

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zh-cn:Pacman/Tips and tricks

See pacman for the main article.

For general methods to improve the flexibility of the provided tips or pacman itself, see Core utilities and Bash.

Contents

Cosmetic and convenience

Operations and Bash syntax

Merge-arrows-2.pngThis article or section is a candidate for merging with pacman#Installing specific packages.Merge-arrows-2.png

Notes: Although this is definitely a tip/trick, it fits to the main pacman page much better than here. It shows generic examples of how to do things, not specific commands needed to achieve something non-trivial/unrelated. (Discuss in Talk:Pacman/Tips and tricks#)

In addition to pacman's standard set of features, there are ways to extend its usability through rudimentary Bash commands/syntax.

To install a number of packages sharing similar patterns in their names -- not the entire group nor all matching packages; eg. plasma:

# pacman -S plasma-{desktop,mediacenter,nm}

Of course, that is not limited and can be expanded to however many levels needed:

# pacman -S plasma-{workspace{,-wallpapers},pa}

Sometimes, -s's builtin ERE can cause a lot of unwanted results, so it has to be limited to match the package name only; not the description nor any other field:

# pacman -Ss '^vim-'

pacman has the -q operand to hide the version column, so it is possible to query and reinstall packages with "compiz" as part of their name:

# pacman -S $(pacman -Qq | grep compiz)

Graphical front-ends

  • Discover — A collection of package management tools for KDE, using PackageKit.
https://projects.kde.org/projects/kde/workspace/discover || discover
  • GNOME packagekit — GTK based package management tool
http://www.freedesktop.org/software/PackageKit/ || gnome-packagekit
  • GNOME Software — Gnome Software App. (Curated selection for GNOME)
https://wiki.gnome.org/Apps/Software || gnome-software
  • pcurses — Package management in a curses frontend
https://github.com/schuay/pcurses || pcurses
  • tkPacman — GUI front-end for pacman. Depends on Tcl/Tk and X11 but neither on GTK+, nor on QT. It only interacts with the package database via the CLI of 'pacman'. So, installing and removing packages with tkPacman or with pacman leads to exactly the same result.
http://sourceforge.net/projects/tkpacman || tkpacmanAUR

Utilities

  • Lostfiles — Script for detecting orphaned files.
https://github.com/graysky2/lostfiles || lostfilesAUR
  • Pacmatic — Pacman wrapper to check Arch News before upgrading, avoid partial upgrades, and warn about configuration file changes.
http://kmkeen.com/pacmatic || pacmatic
  • pkgfile — Tool that finds what package owns a file.
http://github.com/falconindy/pkgfile || pkgfile
  • pkgtools — Collection of scripts for Arch Linux packages.
https://github.com/Daenyth/pkgtools || pkgtoolsAUR
  • srcpac — Simple tool that automates rebuilding packages from source.
https://projects.archlinux.org/srcpac.git || srcpac
  • snap-pac — Make pacman automatically use snapper to create pre/post snapshots like openSUSE's YaST.
https://github.com/wesbarnett/snap-pac || snap-pacAUR

Maintenance

See also System maintenance.

Listing packages

You may want to get the list of installed packages with their version, which is useful when reporting bugs or discussing installed packages.

  • List all explicitly installed packages: pacman -Qe .
  • List all foreign packages (typically manually downloaded and installed): pacman -Qm .
  • List all native packages (installed from the sync database(s)): pacman -Qn .
  • List packages by regex: pacman -Qs regex.
  • List packages by regex with custom output format: expac -s "%-30n %v" regex (needs expac).

With size

To get a list of installed packages sorted by size, which may be useful when freeing space on your hard drive:

  • Install expac and run expac -H M '%m\t%n' | sort -h.
  • Run pacgraph with the -c option.
  • Run apacmanAUR with the -L option.

To list the download size of several packages (leave packages blank to list all packages):

$ expac -S -H M '%k\t%n' packages

To list explicitly installed packages not in base nor base-devel with size and description:

$ expac -H M "%011m\t%-20n\t%10d" $( comm -23 <(pacman -Qqen|sort) <(pacman -Qqg base base-devel|sort) ) | sort -n

Latest installed packages

Install expac and run expac --timefmt='%Y-%m-%d %T' '%l\t%n' | sort | tail -20 or expac --timefmt=%s '%l\t%n' | sort -n | tail -20

All packages that nothing else depends on

If you want to generate a list of all installed packages that nothing else depends on, you can use the following script. This is very helpful if you are trying to free hard drive space and have installed a lot of packages that you may not remember. You can browse through the output to find packages which you no longer need.

Note: This script will show all packages that nothing else depends on, including those explicitly installed. To get a list of packages installed as dependencies but no longer required by any installed package, see #Orphans.
ignoregrp="base base-devel"
ignorepkg=""

comm -23 <(pacman -Qqt | sort) <(echo $ignorepkg | tr ' ' '\n' | cat <(pacman -Sqg $ignoregrp) - | sort -u)

For list with descriptions for packages:

expac -HM "%-20n\t%10d" $( comm -23 <(pacman -Qqt|sort) <(pacman -Qqg base base-devel|sort) )

Installed packages that are not in a specified group or repository

The following command will list any installed packages that are not in either base or base-devel, and as such were likely installed manually by the user:

$ comm -23 <(pacman -Qeq | sort) <(pacman -Qgq base base-devel | sort)

List all installed packages that are not in specified repository (repo_name in example):

$ comm -23 <(pacman -Qtq | sort) <(pacman -Slq repo_name | sort)

List all installed packages that are in the repo_name repository:

$ comm -12 <(pacman -Qtq | sort) <(pacman -Slq repo_name | sort)

Listing files owned by a package with size

This one might come in handy if you have found that a specific package uses a huge amount of space and you want to find out which files make up the most of that.

$ pacman -Qlq package | grep -v '/$' | xargs du -h | sort -h

Identify files not owned by any package

If your system has stray files not owned by any package (a common case if you do not use the package manager to install software), you may want to find such files in order to clean them up. The general process for doing so is:

  1. Create a sorted list of the files you want to check ownership of:
    $ find /etc /opt /usr | sort > all_files.txt
  2. Create a sorted list of the files tracked by pacman (and remove the trailing slashes from directories):
    $ pacman -Qlq | sed 's|/$||' | sort > owned_files.txt
  3. Find lines in the first list that are not in the second:
    $ comm -23 all_files.txt owned_files.txt

This process is tricky in practice because many important files are not part of any package (e.g. files generated at runtime, custom configs) and so will be included in the final output, making it difficult to pick out the files that can be safely deleted.

The lostfilesAUR script performs similar steps, but also includes an extensive blacklist to remove common false positives from the output.

Removing unused packages

Orphans

For recursively removing orphans and their configuration files:

# pacman -Rns $(pacman -Qtdq)

If no orphans were found, pacman errors with error: no targets specified. This is expected as no arguments were passed to pacman -Rns.

Note: Since pacman version 4.2.0 only true orphans are listed. To make pacman also list packages which are only optionally required by another package, pass the -t/--unrequired flag twice:
$ pacman -Qdttq
Use this carefully, as it is not taken into account whether the package is an optional dependency and therefore bears the risk to remove packages which actually are not real orphans.

Explicitly installed

Because a lighter system is easier to maintain, occasionally looking through explicitly installed packages and manually selecting unused packages to be removed can be helpful.

To list explicitly installed packages available in the official repositories:

$ pacman -Qen

To list explicitly installed packages not available in official repositories:

$ pacman -Qem

Removing everything but base group

If it is ever necessary to remove all packages except the base group, try this one liner:

# pacman -R $(comm -23 <(pacman -Qq|sort) <((for i in $(pacman -Qqg base); do pactree -ul $i; done)|sort -u|cut -d ' ' -f 1))

The one-liner was originally devised in this discussion, and later improved in this article.

Notes:

  1. comm requires sorted input otherwise you get e.g. comm: file 1 is not in sorted order.
  2. pactree prints the package name followed by what it provides. For example:
$ pactree -lu logrotate
logrotate
popt
glibc
linux-api-headers
tzdata
dcron cron
bash
readline
ncurses
gzip

The dcron cron line seems to cause problems, that is why cut -d ' ' -f 1 is needed - to keep just the package name.

Getting the dependencies list of several packages

Dependencies are alphabetically sorted and doubles are removed. Note that you can use pacman -Qi to improve response time a little. But you will not be able to query as many packages. Unfound packages are simply skipped (hence the 2>/dev/null).

$ pacman -Si $@ 2>/dev/null | awk -F ": " -v filter="^Depends" \ '$0 ~ filter {gsub(/[>=<][^ ]*/,"",$2) ; gsub(/ +/,"\n",$2) ; print $2}' | sort -u

Alternatively, you can use expac: expac -l '\n' %E -S $@ | sort -u.

Listing changed backup files

If you want to backup your system configuration files you could copy all files in /etc/, but usually you are only interested in the files that you have changed. Modified backup files can be viewed with the following command:

# pacman -Qii | awk '/^MODIFIED/ {print $2}'

Running this command with root permissions will ensure that files readable only by root (such as /etc/sudoers) are included in the output.

Tip: See #Listing all changed files from packages to list all changed files pacman knows, not only backup files.

Back-up the pacman database

The following command can be used to back up the local pacman database:

$ tar -cjf 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.

The database can be restored by moving the pacman_database.tar.bz2 file into the / directory and executing the following command:

# tar -xjvf pacman_database.tar.bz2
Note: If the pacman database files are corrupted, and there is no backup file available, there exists some hope of rebuilding the pacman database. Consult Pacman tips#Restore pacman's local database.
Tip: The pakbak-gitAUR package provides a script and a systemd service to automate the task. Configuration is possible in /etc/pakbak.conf.

Check changelogs easily

When maintainers update packages, commits are often commented in a useful fashion. Users can quickly check these from the command line by installing paclogAUR. This utility lists recent commit messages for packages from the official repositories or the AUR, by using paclog package.

Installation and recovery

Alternative ways of getting and restoring packages.

Installing packages from a CD/DVD or USB stick

To download packages, or groups of packages:

# cd ~/Packages
# pacman -Syw base base-devel grub-bios xorg gimp --cachedir .
# repo-add ./custom.db.tar.gz ./*

Then you can burn the "Packages" folder to a CD/DVD or transfer it to a USB stick, external HDD, etc.

To install:

1. Mount the media:

# mkdir /mnt/repo
# mount /dev/sr0 /mnt/repo    #For a CD/DVD.
# mount /dev/sdxY /mnt/repo   #For a USB stick.

2. Edit pacman.conf and add this repository before the other ones (e.g. extra, core, etc.). This is important. Do not just uncomment the one on the bottom. This way it ensures that the files from the CD/DVD/USB take precedence over those in the standard repositories:

/etc/pacman.conf
[custom]
SigLevel = PackageRequired
Server = file:///mnt/repo/Packages

3. Finally, synchronize the pacman database to be able to use the new repository:

# pacman -Syu

Custom local repository

Use the repo-add script included with Pacman to generate a database for a personal repository. Use repo-add --help for more details on its usage. Simply store all of the built packages to be included in the repository in one directory, and execute the following command (where repo is the name of the custom repository):

$ repo-add /path/to/repo.db.tar.gz /path/to/*.pkg.tar.xz
Note: A package database is a tar file, optionally compressed. Valid extensions are “.db” or “.files” followed by an archive extension of “.tar”, “.tar.gz”, “.tar.bz2”, “.tar.xz”, or “.tar.Z”. The file does not need to exist, but all parent directories must exist. Furthermore when using repo-add keep in mind that the database and the packages do not need to be in the same directory. But when using pacman with that database, they should be together.

To add a new package to the database, or to replace the old version of an existing package in the database, run:

$ repo-add /path/to/repo.db.tar.gz /path/to/packagetoadd-1.0-1-i686.pkg.tar.xz

repo-remove is used in the exact same manner as repo-add, except that the packages listed on the command line are removed from the repository database.

Once the local repository database has been created, add the repository to pacman.conf for each system that is to use the repository. An example of a custom repository is in pacman.conf. The repository's name is the database filename with the file extension omitted. In the case of the example above the repository's name would simply be repo. Reference the repository's location using a file:// url, or via FTP using ftp://localhost/path/to/directory.

If willing, add the custom repository to the list of unofficial user repositories, so that the community can benefit from it.

Network shared pacman cache

If you happen to run several Arch boxes on your LAN, you can share packages so that you can greatly decrease your download times. Keep in mind you should not share between different architectures (i.e. i686 and x86_64) or you'll run into problems.

Read-only cache

If you are looking for a quick and dirty solution, you can simply run a standalone webserver which other computers can use as a first mirror: darkhttpd /var/cache/pacman/pkg. Just add this server at the top of your mirror list. Be aware that you might get a lot of 404 errors, due to cache misses, depending on what you do, but pacman will try the next (real) mirrors when that happens.

Read-write cache

Tip: See pacserve for an alternative (and probably simpler) solution than what follows.

In order to share packages between multiple computers, simply share /var/cache/pacman/ using any network-based mount protocol. This section shows how to use shfs or sshfs to share a package cache plus the related library-directories between multiple computers on the same local network. Keep in mind that a network shared cache can be slow depending on the file-system choice, among other factors.

First, install any network-supporting filesystem; for example sshfs, shfs, ftpfs, smbfs or nfs.

Tip: To use sshfs or shfs, consider reading Using SSH Keys.

Then, to share the actual packages, mount /var/cache/pacman/pkg from the server to /var/cache/pacman/pkg on every client machine.

Dynamic reverse proxy cache using nginx

nginx can be used to proxy requests to official upstream mirrors and cache the results to local disk. All subsequent requests for that file will be served directly from the local cache, minimizing the amount of internet traffic needed to update a large number of servers with minimal effort.

Warning: This method has a limitation. You must use mirrors that use the same relative path to package files and you must configure your cache to use that same path. In this example, we are using mirrors that use the relative path /archlinux/$repo/os/$arch and our cache's Server setting in mirrorlist is configured similarly.

In this example, we will run the cache server on http://cache.domain.local:8080/ and storing the packages in /srv/http/pacman-cache/.

Create the directory for the cache and adjust the permissions so nginx can write files to it:

 # mkdir /srv/http/pacman-cache
 # chown http:http /srv/http/pacman-cache

Next, configure nginx as our dynamic cache (read the comments for an explanation of the commands):

/etc/nginx/nginx.conf
http
{
    ...

    # nginx may need to resolve domain names at run time
    resolver 8.8.8.8 8.8.4.4;

    # Pacman Cache
    server
    {
        listen      8080;
        server_name cache.domain.local;
        root        /srv/http/pacman-cache;
        autoindex   on;

        # Requests for package db and signature files should redirect upstream without caching
        location ~ \.(db|sig)$ {
            proxy_pass http://mirrors$request_uri;
        }

        # Requests for actual packages should be served directly from cache if available.
        #   If not available, retrieve and save the package from an upstream mirror.
        location ~ \.tar\.xz$ {
            try_files $uri @pkg_mirror;
        }

        # Retrieve package from upstream mirrors and cache for future requests
        location @pkg_mirror {
            proxy_store    on;
            proxy_redirect off;
            proxy_store_access  user:rw group:rw all:r;
            proxy_next_upstream error timeout http_404;
            proxy_pass          http://mirrors$request_uri;
        }
    }

    # Upstream Arch Linux Mirrors
    # - Configure as many backend mirrors as you want in the blocks below
    # - Servers are used in a round-robin fashion by nginx
    # - Add "backup" if you want to only use the mirror upon failure of the other mirrors
    # - Separate "server" configurations are required for each upstream mirror so we can set the "Host" header appropriately
    upstream mirrors {
        server localhost:8001;
        server localhost:8002 backup;
        server localhost:8003 backup;
    }

    # Arch Mirror 1 Proxy Configuration
    server
    {
        listen      8001;
        server_name localhost;

        location / {
            proxy_pass       http://mirror.rit.edu$request_uri;
            proxy_set_header Host mirror.rit.edu;
        }
    }

    # Arch Mirror 2 Proxy Configuration
    server
    {
        listen      8002;
        server_name localhost;

        location / {
            proxy_pass       http://mirrors.acm.wpi.edu$request_uri;
            proxy_set_header Host mirrors.acm.wpi.edu;
        }
    }

    # Arch Mirror 3 Proxy Configuration
    server
    {
        listen      8003;
        server_name localhost;

        location / {
            proxy_pass       http://lug.mtu.edu$request_uri;
            proxy_set_header Host lug.mtu.edu;
        }
    }
}

Finally, update your other Arch Linux servers to use this new cache by adding the following line to the mirrorlist file:

/etc/pacman.d/mirrorlist
Server = http://cache.domain.local:8080/archlinux/$repo/os/$arch
...
Note: You will need to create a method to clear old packages, as this directory will continue to grow over time. paccache (which is included with pacman) can be used to automate this using retention criteria of your choosing. For example, find /srv/http/pacman-cache/ -type d -exec paccache -v -r -k 2 -c {} \; will keep the last 2 versions of packages in your cache directory.

Synchronize pacman package cache using BitTorrent Sync

BitTorrent Sync is a new way of synchronizing folder via network (it works in LAN and over the internet). It is peer-to-peer so you do not need to set up a server: follow the link for more information. How to share a pacman cache using BitTorrent Sync:

  • First install the btsyncAUR package from the AUR on the machines you want to sync
  • Follow the installation instructions of the AUR package or on the BitTorrent Sync wiki page
    • set up BitTorrent Sync to work for the root account. This process requires read/write to the pacman package cache.
    • make sure to set a good password on btsync's web UI
    • start the systemd daemon for btsync.
    • in the btsync Web GUI add a new synchronized folder on the first machine and generate a new Secret. Point the folder to /var/cache/pacman/pkg
    • Add the folder on all the other machines using the same Secret to share the cached packages between all systems. Or, to set the first system as a master and the others as slaves, use the Read Only Secret. Be sure to point it to /var/cache/pacman/pkg

Now the machines should connect and start synchronizing their cache. Pacman works as expected even during synchronization. The process of syncing is entirely automatic.

Preventing unwanted cache purges

By default, pacman -Sc removes package tarballs from the cache that correspond to packages that are not installed on the machine the command was issued on. Because pacman cannot predict what packages are installed on all machines that share the cache, it will end up deleting files that should not be.

To clean up the cache so that only outdated tarballs are deleted, add this entry in the [options] section of /etc/pacman.conf:

CleanMethod = KeepCurrent

Recreate a package from the file system

To recreate a package from the file system, use bacman (included with pacman). Files from the system are taken as they are, hence any modifications will be present in the assembled package. Distributing the recreated package is therefore discouraged; see ABS and Arch Rollback Machine for alternatives.

Tip: bacman honours the PACKAGER, PKGDEST and PKGEXT options from makepkg.conf. Custom options for the compression tools can be configured by exporting the relevant environment variable, for example XZ_OPT="-T 0" will enable parallel compression for xz.

An alternative tool would be fakepkgAUR. It supports parallelization and can handle multiple input packages in one command, which bacman both does not support.

Backing up and retrieving a list of installed packages

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: Optional dependencies that are not required by any other package (comm -13 <(pacman -Qdtq) <(pacman -Qdttq)) are ignored by this procedure. (Discuss in Talk:Pacman/Tips and tricks#)
Tip: You may want to use plist-gistAUR or bacpac to automatise the below tasks.

It is good practice to keep periodic backups of all pacman-installed packages. In the event of a system crash which is unrecoverable by other means, pacman can then easily reinstall the very same packages onto a new installation.

  • First, backup the current list of non-local packages: $ pacman -Qqen > pkglist.txt
  • Store the pkglist.txt on a USB key or other convenient medium or gist.github.com or Evernote, Dropbox, etc.
  • Copy the pkglist.txt file to the new installation, and navigate to the directory containing it.
  • Issue the following command to install from the backup list: # pacman -S $(< pkglist.txt)

In the case you have a list which was not generated like mentioned above, there may be foreign packages in it (i.e. packages not belonging to any repos you have configured, or packages from the AUR).

In such a case, you may still want to install all available packages from that list:

# pacman -S --needed $(comm -12 <(pacman -Slq|sort) <(sort badpkdlist) )

Explanation:

  • pacman -Slq lists all available softwares, but the list is sorted by repository first, hence the sort command.
  • Sorted files are required in order to make the comm command work.
  • The -12 parameter display lines common to both entries.
  • The --needed switch is used to skip already installed packages.

Finally, you may want to remove all the packages on your system that are not mentioned in the list.

Warning: Use this command wisely, and always check the result prompted by pacman.
# pacman -Rsu $(comm -23 <(pacman -Qq|sort) <(sort pkglist))

Listing all changed files from packages

If you are suspecting file corruption (e.g. by software / hardware failure), but don't know for sure whether / which files really got corrupted, you might want to compare with the hash sums in the packages. This can be done with the following script.

The script depends on the accuracy of pacman's database in /var/lib/pacman/local/ and the used programs such as bash, grep and so on. For recovery of the database see #Restore pacman's local database. The mtree files can also be extracted as .MTREE from the respective package files.

Note:
  • This should not be used as is when suspecting malicious changes! In this case security precautions such as using a live medium and an independent source for the hash sums are advised.
  • This could take a long time, depending on the hardware and installed packages.
#!/bin/bash -e

# Select the hash algorithm. Currently available (see mtree files and mtree(5)):
# md5, sha256
algo="md5"

for package in /var/lib/pacman/local/*; do
    [ "$package" = "/var/lib/pacman/local/ALPM_DB_VERSION" ] && continue

    # get files and hash sums
    zgrep " ${algo}digest=" "$package/mtree" | grep -Ev '^\./\.[A-Z]+' | \
        sed 's/^\([^ ]*\).*'"${algo}"'digest=\([a-f0-9]*\).*/\1 \2/' | \
        while read -r file hash
    do
        # expand "\nnn" (in mtree) / "\0nnn" (for echo) escapes of ASCII
        # characters (octal representation)
        for ascii in $(grep -Eo '\\[0-9]{1,3}' <<< "$file"); do
            file="$(sed "s/\\$ascii/$(echo -e "\0${ascii:1}")/" <<< "$file")"
        done

        # check file hash
        if [ "$("${algo}sum" /"$file" | awk '{ print $1; }')" != "$hash" ]; then
            echo "$(basename "$package")" /"$file"
        fi
    done
done

Reinstalling all packages

To reinstall all native packages, use:

# pacman -Qenq | pacman -S -

Foreign (AUR) packages must be reinstalled separately; you can list them with pacman -Qemq.

Pacman preserves the installation reason by default.

Restore pacman's local database

Tango-view-refresh-red.pngThis article or section is out of date.Tango-view-refresh-red.png

Reason: testdb has been removed in pacman 5.0 [1]. (Discuss in Talk:Pacman/Tips and tricks#)

Signs that pacman needs a local database restoration:

  • pacman -Q gives absolutely no output, and pacman -Syu erroneously reports that the system is up to date.
  • When trying to install a package using pacman -S package, and it outputs a list of already satisfied dependencies.
  • When testdb (part of pacman) reports database inconsistency.

Most likely, pacman's database of installed software, /var/lib/pacman/local, has been corrupted or deleted. While this is a serious problem, it can be restored by following the instructions below.

Firstly, make sure pacman's log file is present:

$ ls /var/log/pacman.log

If it does not exist, it is not possible to continue with this method. You may be able to use Xyne's package detection script to recreate the database. If not, then the likely solution is to re-install the entire system.

Generating the package recovery list

Warning: If for some reason your pacman cache or makepkg package destination contain packages for other architectures, remove them before continuation.

Run the script (optionally passing additional directories with packages as parameters):

$ paclog-pkglist /var/log/pacman.log | ./pacrecover >files.list 2>pkglist.orig

This way two files will be created: files.list with package files, still present on machine and pkglist.orig, packages from which should be downloaded. Later operation may result in mismatch between files of older versions of package, still present on machine, and files, found in new version. Such mismatches will have to be fixed manually.

Here is a way to automatically restrict second list to packages available in a repository:

$ { cat pkglist.orig; pacman -Slq; } | sort | uniq -d > pkglist

Check if some important base package are missing, and add them to the list:

$ comm -23 <(pacman -Sgq base) pkglist.orig >> pkglist

Proceed once the contents of both lists are satisfactory, since they will be used to restore pacman's installed package database; /var/lib/pacman/local/.

Performing the recovery

Define bash alias for recovery purposes:

# recovery-pacman() {
    pacman "$@"       \
    --log /dev/null   \
    --noscriptlet     \
    --dbonly          \
    --force           \
    --nodeps          \
    --needed          \
    #
}

--log /dev/null allows to avoid needless pollution of pacman log, --needed will save some time by skipping packages, already present in database, --nodeps will allow installation of cached packages, even if packages being installed depend on newer versions. Rest of options will allow pacman to operate without reading/writing filesystem.

Populate the sync database:

# pacman -Sy

Start database generation by installing locally available package files from files.list:

# recovery-pacman -U $(< files.list)

Install the rest from pkglist:

# recovery-pacman -S $(< pkglist)

Update the local database so that packages that are not required by any other package are marked as explicitly installed and the other as dependences. You will need be extra careful in the future when removing packages, but with the original database lost is the best we can do.

# pacman -D --asdeps $(pacman -Qq)
# pacman -D --asexplicit $(pacman -Qtq)

Optionally check all installed packages for corruption:

# pacman -Qk

Optionally #Identify files not owned by any package.

Update all packages:

# pacman -Su

Recovering a USB key from existing install

If you have Arch installed on a USB key and manage to mess it up (e.g. removing it while it is still being written to), then it is possible to re-install all the packages and hopefully get it back up and working again (assuming USB key is mounted in /newarch)

# pacman -S $(pacman -Qq --dbpath /newarch/var/lib/pacman) --root /newarch --dbpath /newarch/var/lib/pacman

Extracting contents of a .pkg file

The .pkg files ending in .xz are simply tar'ed archives that can be decompressed with:

$ tar xvf package.tar.xz

If you want to extract a couple of files out of a .pkg file, this would be a way to do it.

Viewing a single file inside a .pkg file

For example, if you want to see the contents of /etc/systemd/logind.conf supplied within the systemd package:

$ tar -xOf /var/cache/pacman/pkg/systemd-204-3-x86_64.pkg.tar.xz etc/systemd/logind.conf

Or you can use vim, then browse the archive:

$ vim /var/cache/pacman/pkg/systemd-204-3-x86_64.pkg.tar.xz

Find applications that use libraries from older packages

Even if you installed a package the existing long-running programs (like daemons and servers) still keep using code from old package libraries. And it is a bad idea to let these programs running if the old library contains a security bug.

Here is a way how to find all the programs that use old packages code:

# lsof +c 0 | grep -w DEL | awk '1 { print $1 ": " $NF }' | sort -u

It will print running program name and old library that was removed or replaced with newer content.

Performance

Database access speeds

Pacman stores all package information in a collection of small files, one for each package. Improving database access speeds reduces the time taken in database-related tasks, e.g. searching packages and resolving package dependencies. The safest and easiest method is to run as root:

# pacman-optimize

This will attempt to put all the small files together in one (physical) location on the hard disk so that the hard disk head does not have to move so much when accessing all the data. This method is safe, but is not foolproof: it depends on your filesystem, disk usage and empty space fragmentation. Another, more aggressive, option would be to first remove uninstalled packages from cache and to remove unused repositories before database optimization:

# pacman -Sc && pacman-optimize

Download speeds

Note: If your download speeds have been reduced to a crawl, ensure you are using one of the many mirrors and not ftp.archlinux.org, which is throttled since March 2007.

When downloading packages pacman uses the mirrors in the order they are in /etc/pacman.d/mirrorlist. The mirror which is at the top of the list by default however may not be the fastest for you. To select a faster mirror, see Mirrors.

Pacman's speed in downloading packages can also be improved by using a different application to download packages, instead of Pacman's built-in file downloader.

In all cases, make sure you have the latest Pacman before doing any modifications.

# pacman -Syu

Powerpill

Powerpill is a full wrapper for Pacman that uses parallel and segmented downloads to speed up the download process. Normally Pacman will download one package at a time, waiting for it to complete before beginning the next download. Powerpill takes a different approach: it tries to download as many packages as possible at once.

The Powerpill wiki page provides basic configuration and usage examples along with package and upstream links.

wget

This is also very handy if you need more powerful proxy settings than pacman's built-in capabilities.

To use wget, first install the wget package then modify /etc/pacman.conf by uncommenting the following line in the [options] section:

XferCommand = /usr/bin/wget -c -q --show-progress --passive-ftp -O %o %u

Instead of uncommenting the wget parameters in /etc/pacman.conf, you can also modify the wget configuration file directly (the system-wide file is /etc/wgetrc, per user files are $HOME/.wgetrc.

aria2

aria2 is a lightweight download utility with support for resumable and segmented HTTP/HTTPS and FTP downloads. aria2 allows for multiple and simultaneous HTTP/HTTPS and FTP connections to an Arch mirror, which should result in an increase in download speeds for both file and package retrieval.

Note: Using aria2c in Pacman's XferCommand will not result in parallel downloads of multiple packages. Pacman invokes the XferCommand with a single package at a time and waits for it to complete before invoking the next. To download multiple packages in parallel, see the powerpill section above.

Install aria2, then edit /etc/pacman.conf by adding the following line to the [options] section:

XferCommand = /usr/bin/aria2c --allow-overwrite=true --continue=true --file-allocation=none --log-level=error --max-tries=2 --max-connection-per-server=2 --max-file-not-found=5 --min-split-size=5M --no-conf --remote-time=true --summary-interval=60 --timeout=5 --dir=/ --out %o %u
Tip: This alternative configuration for using pacman with aria2 tries to simplify configuration and adds more configuration options.

See OPTIONS in man aria2c for used aria2c options.

-d, --dir

The directory to store the downloaded file(s) as specified by pacman.

-o, --out

The output file name(s) of the downloaded file(s).

%o

Variable which represents the local filename(s) as specified by pacman.

%u

Variable which represents the download URL as specified by pacman.

Other applications

There are other downloading applications that you can use with Pacman. Here they are, and their associated XferCommand settings:

  • snarf: XferCommand = /usr/bin/snarf -N %u
  • lftp: XferCommand = /usr/bin/lftp -c pget %u
  • axel: XferCommand = /usr/bin/axel -n 2 -v -a -o %o %u