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    Command:

    apt_preferences

    
    
    

    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 either no or "pref" as filename extension
           and only contain alphanumeric, hyphen (-), underscore (_) and period
           (.) characters. Otherwise APT will print a notice that it has ignored a
           file if the file doesn't match a pattern in the
           Dir::Ignore-Files-Silently configuration list - in this case it 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,
    
           priority 100
               to the version that is already installed (if any) and to the
               versions coming from archives which in their Release files are
               marked as "NotAutomatic: yes" and "ButAutomaticUpgrades: yes" like
               the debian backports archive since squeeze-backports.
    
           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, except versions coming from archives
           which in their Release files are marked as "NotAutomatic: yes" - these
           versions get the priority 1 or priority 100 if it is additionally
           marked as "ButAutomaticUpgrades: yes".
    
           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
               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
    
           ?   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 "wheezy".
    
                   Package: *
                   Pin: release n=wheezy
                   Pin-Priority: 900
    
               The following record assigns a high priority to all package
               versions belonging to any release whose Archive name is "stable"
               Package: gnome* /kde/
               Pin: release n=experimental
               Pin-Priority: 500
    
           The rule for those expressions is that they can occur anywhere where a
           string can occur. Thus, the following pin assigns the priority 990 to
           all packages from a release starting with karmic.
    
               Package: *
               Pin: release n=karmic*
               Pin-Priority: 990
    
           If a regular expression occurs in a Package field, the behavior is the
           same as if this regular expression were replaced with a list of all
           package names it matches. It is undecided whether this will change in
           the future, thus you should always list wild-card pins first, so later
           specific pins override it.
    
           The pattern "*" in a Package field is not considered a glob()
           expression in itself.
    
       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
    
               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/squeeze/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
    
           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

               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
               Explanation: other than those in the distribution codenamed with wheezy or sid
               Package: *
               Pin: release n=wheezy
               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 wheezy.
    
               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 wheezy 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
    
    
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