User:Doru001/Pacman - An Introduction
Packages in arch repositories are constantly upgraded. When a package is upgraded, its old version is removed from the repository. There are no major arch releases. Each package is upgraded as new versions become available from upstream sources. The repository is always coherent. (The packages in the repository always have compatible versions.) This type of repository is called a rolling archive. Before packages are upgraded in the core, extra and community repositories, they are tested in the testing repository, to ensure that the distribution is stable.
Pacman saves to disk a list of packages available in the repository. This list is not automatically updated (refreshed). (The list is a.k.a. repository databases and the update of the list is a.k.a. synchronizing those databases.) The list can be refreshed using
pacman -Syy refreshes the list even if it appears to be up to date. (Running
pacman -Syy is a good idea after the repository mirror used by
pacman is changed by the user. Mirrors can be out of sync and the package list from the old mirror may not correspond to the package list of the new mirror, even though the dates of the lists may suggest that they do. See Installing packages for an unlikely but possible problem which could arise from the use of this command.)
pacman -S mypackage installs
mypackage and all its dependencies. If
mypackage has been upgraded by the user since the last refresh of the package list, then the required version of
mypackage will not be found in the repository and
pacman -S mypackage fails with a message.
mypackage's dependencies are listed in the Depends On entry of
mypackage's metainformation. (
mypackage's metainformation can be listed with
pacman -Si mypackage for packages in the package list and with
pacman -Qi mypackage for installed packages). If
mypackage or its dependencies are already installed, they are upgraded to the version in the package list. If
pacman -S mypackage finds any conflicts (installed packages which are listed in the Conflicts With entry of the
mypackage's metainformation) then it fails with a message.
pacman -S mypackagedoes not check for broken dependencies which may appear from the possible upgrade of
mypackageor one of its dependencies. It is possible that an already installed package which depends on an upgraded package is unable to function with the new version of the upgraded package. This can happen if the package list has been refreshed by the user but all installed packges have not been upgraded and it could result in a non functional system after reboot.
The solution is to never run
pacman -Sy, which could be followed by
pacman -S mypackage, but to always run
pacman -Syu, which upgrades all packages after the refresh of the package list. This ensures that when
pacman -S mypackage is run all packages installed on the system have compatible versions.
pacman -Syu is run there is a small chance that corrections on the system will be needed in order to have it running as desired. Important corrections are advertised here: Arch Home. They are very rare (six in 2012). However, it is advisable to run
pacman -Syu only when time to perform corrections is available to the user and not when the system is relied upon. It is advisable to run
pacman -Syu often in order to minimize the difficulty of adjustment, whenever it arises.
See also Installing packages.
pacman -R mypackage removes
mypackage. If other packages depend on
mypackage, then it fails with a message. To remove them too,
pacman -Rc mypackage should be run.
pacman -R mypackage does not remove
mypackage's dependencies which have been installed as dependencies (not explicitly, Install Reason in
mypackage's metainformation) and are not required by other packages. For that to happen,
pacman -Rs mypackage must be run. The complete command would be
pacman -Rcs mypackage.
See also Removing Packages.
pacman always lists packages to be installed or removed and asks for permission before it takes action. To inhibit any action,
-p should be used.
pacman operates at a lower level compared to
apt. This requires more attention from the user, but it also empowers him or her with better control over his or her system.
For those who have used other Linux distributions before, there is a helpful Pacman Rosetta.