pacman can update all packages on the system with just one command. This could take quite a while depending on how up-to-date the system is. This command can synchronize the repository databases and update the system's packages (excluding "local" packages that are not in the configured repositories):
# pacman -Syu
Querying package databases
pacman queries the local package database with the -Q flag; see:
$ pacman -Q --help
and queries the sync databases with the -S flag; see:
$ pacman -S --help
pacman can search for packages in the database, searching both in packages' names and descriptions:
$ pacman -Ss string1 string2 ...
To search for already installed packages:
$ pacman -Qs string1 string2 ...
To display extensive information about a given package:
$ pacman -Si package_name
For locally installed packages:
$ pacman -Qi package_name
Passing two -i flags will also display the list of backup files and their modification states:
$ pacman -Qii package_name
To retrieve a list of the files installed by a package:
$ pacman -Ql package_name
For packages not installed, use pkgfile.
To verify the presence of the files installed by a package:
$ pacman -Qk package_name
Passing the k flag twice will perform a more thorough check.
One can also query the database to know which package a file in the file system belongs to:
$ pacman -Qo /path/to/file_name
To list all packages no longer required as dependencies (orphans):
$ pacman -Qdt
To list all packages explicitly installed and not required as dependencies:
$ pacman -Qet
To list a dependency tree of a package:
$ pactree package_name
To list all the packages recursively depending on an installed package, use whoneeds from pkgtoolsAUR:
$ whoneeds package_name
or the reverse flag to pactree:
$ pactree -r package_name
See pacman tips for more examples. Database structure
The pacman databases are normally located at /var/lib/pacman/sync. For each repository specified in /etc/pacman.conf there will be a corresponding database file located there. Database files are tar-gzipped archives containing one directory for each package, for example for the which package:
% tree which-2.20-6
which-2.20-6
|-- depends
`-- desc
The depends file lists the packages this package depends on, while desc has a description of the package such as the file size and the MD5 hash. Cleaning the package cache
pacman stores its downloaded packages in /var/cache/pacman/pkg/ and does not remove the old or uninstalled versions automatically, therefore it is necessary to deliberately clean up that folder periodically to prevent such folder to grow indefinitely in size.
The built-in option to remove all the cached packages that are not currently installed is:
# pacman -Sc
Warning:
Only do this when certain that previous package versions are not required, for example for a later downgrade. pacman -Sc only leaves the versions of packages which are currently installed available, older versions would have to be retrieved through other means, such as the Archive.
It is possible to empty the cache folder fully with pacman -Scc. In addition to the above, this also prevents from reinstalling a package directly from the cache folder in case of need, thus requiring a new download. It should be avoided unless there is an immediate need for disk space.
Because of the above limitations, consider an alternative for more control over which packages, and how many, are deleted from the cache:
The paccache script, provided by the pacman package itself, deletes all cached versions of each package, except for the most recent 3, by default:
# paccache -r
Used this way, it will not check whether a package is still installed or not, and uninstalled packages will remain in the cache. To remove all cached versions of uninstalled packages, re-run paccache with:
# paccache -ruk0
See paccache -h for more options.
pkgcachecleanAUR and pacleanerAUR are two further alternatives. Additional commands
Download a package without installing it:
# pacman -Sw package_name
Install a 'local' package that is not from a remote repository (e.g. the package is from the AUR):
# pacman -U /path/to/package/package_name-version.pkg.tar.xz
To keep a copy of the local package in pacman's cache, use:
# pacman -U file:///path/to/package/package_name-version.pkg.tar.xz
Install a 'remote' package (not from a repository stated in pacman's configuration files):
# pacman -U http://www.example.com/repo/example.pkg.tar.xz
To inhibit the -S, -U and -R actions, -p can be used.
pacman always lists packages to be installed or removed and asks for permission before it takes action.