Provided by: apt_0.8.3ubuntu7_i386 bug

NAME

       apt_preferences - Preference control file for APT

DESCRIPTION

       The APT preferences file /etc/apt/preferences and the fragment files in
       the /etc/apt/preferences.d/ folder can be used to control which
       versions of packages will be selected for installation.

       Several versions of a package may be available for installation when
       the sources.list(5) file contains references to more than one
       distribution (for example, stable and testing). APT assigns a priority
       to each version that is available. Subject to dependency constraints,
       apt-get selects the version with the highest priority for installation.
       The APT preferences file overrides the priorities that APT assigns to
       package versions by default, thus giving the user control over which
       one is selected for installation.

       Several instances of the same version of a package may be available
       when the sources.list(5) file contains references to more than one
       source. In this case apt-get downloads the instance listed earliest in
       the sources.list(5) file. The APT preferences file does not affect the
       choice of instance, only the choice of version.

       Preferences are a strong power in the hands of a system administrator
       but they can become also their biggest nightmare if used without care!
       APT will not questioning the preferences so wrong settings will
       therefore lead to uninstallable packages or wrong decisions while
       upgrading packages. Even more problems will arise if multiply
       distribution releases are mixed without a good understanding of the
       following paragraphs. Packages included in a specific release aren't
       tested in and therefore doesn't always work as expected in older or
       newer releases or together with other packages from different releases.
       You have been warned.

       Note that the files in the /etc/apt/preferences.d directory are parsed
       in alphanumeric ascending order and need to obey the following naming
       convention: The files have no or "pref" as filename extension and which
       only contain alphanumeric, hyphen (-), underscore (_) and period (.)
       characters - otherwise they will be silently ignored.

   APT's Default Priority Assignments
       If there is no preferences file or if there is no entry in the file
       that applies to a particular version then the priority assigned to that
       version is the priority of the distribution to which that version
       belongs. It is possible to single out a distribution, "the target
       release", which receives a higher priority than other distributions do
       by default. The target release can be set on the apt-get command line
       or in the APT configuration file /etc/apt/apt.conf. Note that this has
       precedence over any general priority you set in the
       /etc/apt/preferences file described later, but not over specifically
       pinned packages. For example,

           apt-get install -t testing some-package

           APT::Default-Release "stable";

       If the target release has been specified then APT uses the following
       algorithm to set the priorities of the versions of a package. Assign:

       priority 1
           to the versions coming from archives which in their Release files
           are marked as "NotAutomatic: yes" like the debian experimental
           archive.

       priority 100
           to the version that is already installed (if any).

       priority 500
           to the versions that are not installed and do not belong to the
           target release.

       priority 990
           to the versions that are not installed and belong to the target
           release.

       If the target release has not been specified then APT simply assigns
       priority 100 to all installed package versions and priority 500 to all
       uninstalled package versions, expect versions coming from archives
       which in their Release files are marked as "NotAutomatic: yes" - these
       versions get the priority 1.

       APT then applies the following rules, listed in order of precedence, to
       determine which version of a package to install.

       o   Never downgrade unless the priority of an available version exceeds
           1000. ("Downgrading" is installing a less recent version of a
           package in place of a more recent version. Note that none of APT's
           default priorities exceeds 1000; such high priorities can only be
           set in the preferences file. Note also that downgrading a package
           can be risky.)

       o   Install the highest priority version.

       o   If two or more versions have the same priority, install the most
           recent one (that is, the one with the higher version number).

       o   If two or more versions have the same priority and version number
           but either the packages differ in some of their metadata or the
           --reinstall option is given, install the uninstalled one.

       In a typical situation, the installed version of a package (priority
       100) is not as recent as one of the versions available from the sources
       listed in the sources.list(5) file (priority 500 or 990). Then the
       package will be upgraded when apt-get install some-package or apt-get
       upgrade is executed.

       More rarely, the installed version of a package is more recent than any
       of the other available versions. The package will not be downgraded
       when apt-get install some-package or apt-get upgrade is executed.

       Sometimes the installed version of a package is more recent than the
       version belonging to the target release, but not as recent as a version
       belonging to some other distribution. Such a package will indeed be
       upgraded when apt-get install some-package or apt-get upgrade is
       executed, because at least one of the available versions has a higher
       priority than the installed version.

   The Effect of APT Preferences
       The APT preferences file allows the system administrator to control the
       assignment of priorities. The file consists of one or more multi-line
       records separated by blank lines. Records can have one of two forms, a
       specific form and a general form.

       o   The specific form assigns a priority (a "Pin-Priority") to one or
           more specified packages and specified version or version range. For
           example, the following record assigns a high priority to all
           versions of the perl package whose version number begins with
           "5.8". Multiple packages can be separated by spaces.

               Package: perl
               Pin: version 5.8*
               Pin-Priority: 1001

       o   The general form assigns a priority to all of the package versions
           in a given distribution (that is, to all the versions of packages
           that are listed in a certain Release file) or to all of the package
           versions coming from a particular Internet site, as identified by
           the site's fully qualified domain name.

           This general-form entry in the APT preferences file applies only to
           groups of packages. For example, the following record assigns a
           high priority to all package versions available from the local
           site.

               Package: *
               Pin: origin ""
               Pin-Priority: 999

           A note of caution: the keyword used here is "origin" which can be
           used to match a hostname. The following record will assign a high
           priority to all versions available from the server identified by
           the hostname "ftp.de.debian.org"

               Package: *
               Pin: origin "ftp.de.debian.org"
               Pin-Priority: 999

           This should not be confused with the Origin of a distribution as
           specified in a Release file. What follows the "Origin:" tag in a
           Release file is not an Internet address but an author or vendor
           name, such as "Debian" or "Ximian".

           The following record assigns a low priority to all package versions
           belonging to any distribution whose Archive name is "unstable".

               Package: *
               Pin: release a=unstable
               Pin-Priority: 50

           The following record assigns a high priority to all package
           versions belonging to any distribution whose Codename is "squeeze".

               Package: *
               Pin: release n=squeeze
               Pin-Priority: 900

           The following record assigns a high priority to all package
           versions belonging to any release whose Archive name is "stable"
           and whose release Version number is "3.0".

               Package: *
               Pin: release a=stable, v=3.0
               Pin-Priority: 500

   How APT Interprets Priorities
       Priorities (P) assigned in the APT preferences file must be positive or
       negative integers. They are interpreted as follows (roughly speaking):

       P > 1000
           causes a version to be installed even if this constitutes a
           downgrade of the package

       990 < P <=1000
           causes a version to be installed even if it does not come from the
           target release, unless the installed version is more recent

       500 < P <=990
           causes a version to be installed unless there is a version
           available belonging to the target release or the installed version
           is more recent

       100 < P <=500
           causes a version to be installed unless there is a version
           available belonging to some other distribution or the installed
           version is more recent

       0 < P <=100
           causes a version to be installed only if there is no installed
           version of the package

       P < 0
           prevents the version from being installed

       If any specific-form records match an available package version then
       the first such record determines the priority of the package version.
       Failing that, if any general-form records match an available package
       version then the first such record determines the priority of the
       package version.

       For example, suppose the APT preferences file contains the three
       records presented earlier:

           Package: perl
           Pin: version 5.8*
           Pin-Priority: 1001

           Package: *
           Pin: origin ""
           Pin-Priority: 999

           Package: *
           Pin: release unstable
           Pin-Priority: 50

       Then:

       o   The most recent available version of the perl package will be
           installed, so long as that version's version number begins with
           "5.8". If any 5.8* version of perl is available and the installed
           version is 5.9*, then perl will be downgraded.

       o   A version of any package other than perl that is available from the
           local system has priority over other versions, even versions
           belonging to the target release.

       o   A version of a package whose origin is not the local system but
           some other site listed in sources.list(5) and which belongs to an
           unstable distribution is only installed if it is selected for
           installation and no version of the package is already installed.

   Determination of Package Version and Distribution Properties
       The locations listed in the sources.list(5) file should provide
       Packages and Release files to describe the packages available at that
       location.

       The Packages file is normally found in the directory
       .../dists/dist-name/component/arch: for example,
       .../dists/stable/main/binary-i386/Packages. It consists of a series of
       multi-line records, one for each package available in that directory.
       Only two lines in each record are relevant for setting APT priorities:

       the Package: line
           gives the package name

       the Version: line
           gives the version number for the named package

       The Release file is normally found in the directory
       .../dists/dist-name: for example, .../dists/stable/Release, or
       .../dists/lenny/Release. It consists of a single multi-line record
       which applies to all of the packages in the directory tree below its
       parent. Unlike the Packages file, nearly all of the lines in a Release
       file are relevant for setting APT priorities:

       the Archive: or Suite: line
           names the archive to which all the packages in the directory tree
           belong. For example, the line "Archive: stable" or "Suite: stable"
           specifies that all of the packages in the directory tree below the
           parent of the Release file are in a stable archive. Specifying this
           value in the APT preferences file would require the line:

               Pin: release a=stable

       the Codename: line
           names the codename to which all the packages in the directory tree
           belong. For example, the line "Codename: squeeze" specifies that
           all of the packages in the directory tree below the parent of the
           Release file belong to a version named squeeze. Specifying this
           value in the APT preferences file would require the line:

               Pin: release n=squeeze

       the Version: line
           names the release version. For example, the packages in the tree
           might belong to Debian GNU/Linux release version 3.0. Note that
           there is normally no version number for the testing and unstable
           distributions because they have not been released yet. Specifying
           this in the APT preferences file would require one of the following
           lines.

               Pin: release v=3.0
               Pin: release a=stable, v=3.0
               Pin: release 3.0

       the Component: line
           names the licensing component associated with the packages in the
           directory tree of the Release file. For example, the line
           "Component: main" specifies that all the packages in the directory
           tree are from the main component, which entails that they are
           licensed under terms listed in the Debian Free Software Guidelines.
           Specifying this component in the APT preferences file would require
           the line:

               Pin: release c=main

       the Origin: line
           names the originator of the packages in the directory tree of the
           Release file. Most commonly, this is Debian. Specifying this origin
           in the APT preferences file would require the line:

               Pin: release o=Debian

       the Label: line
           names the label of the packages in the directory tree of the
           Release file. Most commonly, this is Debian. Specifying this label
           in the APT preferences file would require the line:

               Pin: release l=Debian

       All of the Packages and Release files retrieved from locations listed
       in the sources.list(5) file are stored in the directory
       /var/lib/apt/lists, or in the file named by the variable
       Dir::State::Lists in the apt.conf file. For example, the file
       debian.lcs.mit.edu_debian_dists_unstable_contrib_binary-i386_Release
       contains the Release file retrieved from the site debian.lcs.mit.edu
       for binary-i386 architecture files from the contrib component of the
       unstable distribution.

   Optional Lines in an APT Preferences Record
       Each record in the APT preferences file can optionally begin with one
       or more lines beginning with the word Explanation:. This provides a
       place for comments.

EXAMPLES

   Tracking Stable
       The following APT preferences file will cause APT to assign a priority
       higher than the default (500) to all package versions belonging to a
       stable distribution and a prohibitively low priority to package
       versions belonging to other Debian distributions.

           Explanation: Uninstall or do not install any Debian-originated
           Explanation: package versions other than those in the stable distro
           Package: *
           Pin: release a=stable
           Pin-Priority: 900

           Package: *
           Pin: release o=Debian
           Pin-Priority: -10

       With a suitable sources.list(5) file and the above preferences file,
       any of the following commands will cause APT to upgrade to the latest
       stable version(s).

           apt-get install package-name
           apt-get upgrade
           apt-get dist-upgrade

       The following command will cause APT to upgrade the specified package
       to the latest version from the testing distribution; the package will
       not be upgraded again unless this command is given again.

           apt-get install package/testing

   Tracking Testing or Unstable
       The following APT preferences file will cause APT to assign a high
       priority to package versions from the testing distribution, a lower
       priority to package versions from the unstable distribution, and a
       prohibitively low priority to package versions from other Debian
       distributions.

           Package: *
           Pin: release a=testing
           Pin-Priority: 900

           Package: *
           Pin: release a=unstable
           Pin-Priority: 800

           Package: *
           Pin: release o=Debian
           Pin-Priority: -10

       With a suitable sources.list(5) file and the above preferences file,
       any of the following commands will cause APT to upgrade to the latest
       testing version(s).

           apt-get install package-name
           apt-get upgrade
           apt-get dist-upgrade

       The following command will cause APT to upgrade the specified package
       to the latest version from the unstable distribution. Thereafter,
       apt-get upgrade will upgrade the package to the most recent testing
       version if that is more recent than the installed version, otherwise,
       to the most recent unstable version if that is more recent than the
       installed version.

           apt-get install package/unstable

   Tracking the evolution of a codename release
       The following APT preferences file will cause APT to assign a priority
       higher than the default (500) to all package versions belonging to a
       specified codename of a distribution and a prohibitively low priority
       to package versions belonging to other Debian distributions, codenames
       and archives. Note that with this APT preference APT will follow the
       migration of a release from the archive testing to stable and later
       oldstable. If you want to follow for example the progress in testing
       notwithstanding the codename changes you should use the example
       configurations above.

           Explanation: Uninstall or do not install any Debian-originated package versions
           Explanation: other than those in the distribution codenamed with squeeze or sid
           Package: *
           Pin: release n=squeeze
           Pin-Priority: 900

           Explanation: Debian unstable is always codenamed with sid
           Package: *
           Pin: release n=sid
           Pin-Priority: 800

           Package: *
           Pin: release o=Debian
           Pin-Priority: -10

       With a suitable sources.list(5) file and the above preferences file,
       any of the following commands will cause APT to upgrade to the latest
       version(s) in the release codenamed with squeeze.

           apt-get install package-name
           apt-get upgrade
           apt-get dist-upgrade

       The following command will cause APT to upgrade the specified package
       to the latest version from the sid distribution. Thereafter, apt-get
       upgrade will upgrade the package to the most recent squeeze version if
       that is more recent than the installed version, otherwise, to the most
       recent sid version if that is more recent than the installed version.

           apt-get install package/sid

FILES

       /etc/apt/preferences
           Version preferences file. This is where you would specify
           "pinning", i.e. a preference to get certain packages from a
           separate source or from a different version of a distribution.
           Configuration Item: Dir::Etc::Preferences.

       /etc/apt/preferences.d/
           File fragments for the version preferences. Configuration Item:
           Dir::Etc::PreferencesParts.

SEE ALSO

       apt-get(8) apt-cache(8) apt.conf(5) sources.list(5)

BUGS

       APT bug page[1]. If you wish to report a bug in APT, please see
       /usr/share/doc/debian/bug-reporting.txt or the reportbug(1) command.

AUTHOR

       APT team

NOTES

        1. APT bug page
           http://bugs.debian.org/src:apt