apt_preferences

APT_PREFERENCES(5)                                          APT_PREFERENCES(5)



NAME
       apt_preferences - Preference control file for APT

DESCRIPTION
       The APT preferences file /etc/apt/preferences 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.

   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.  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 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.

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

       · 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.)

       · Install the highest priority version.

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

       · 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.

       · The specific form assigns a priority (a "Pin-Priority") to a
         specified package 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".

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

       · 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".  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 release whose Archive name is "stable" and whose
         release Version number is "3.0".

         Package: *
         Pin: release a=unstable, v=3.0
         Pin-Priority: 50

   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:

       · 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.

       · 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.

       · 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/woody/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: line
              names the archive to which all the packages in the directory
              tree belong.  For example, the line "Archive: 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 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.

       The Pin-Priority: line in each APT preferences record is optional.  If
       omitted, APT assigs a priority of 1 less than the last value specified
       on a line beginning with Pin-Priority: release ....

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

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

BUGS
       See the APT bug page <URL:http://bugs.debian.org/src:apt>.  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 was written by the APT team <apt@packages.debian.org>.



                                16 October 2007             APT_PREFERENCES(5)