Description</> <para> The APT preferences file <filename>/etc/apt/preferences</> can be used to control which version of a package will be selected for installation. </para> <para>Several versions of a package may be available for installation when the &sources-list; file contains references to more than one distribution (for example, <literal>stable</literal> and <literal>testing</literal>); furthermore, several instances of the same version of a package may be available when the file contains references to more than one download site for a particular distribution. APT assigns a "priority" to each instance that is available. (In what follows, an "instance" will be an instance of a package that is available according to &sources-list;.) Subject to dependency constraints, <command>apt-get</command> installs the instance with the highest priority. If two instances have the same priority then it installs the more recent one, that is, the one with the higher version number. </para> <para>The APT preferences file overrides the priorities that APT assigns to package instances by default, thus giving the user control over which one is selected for installation. </para> <RefSect2><Title>APT's Default Priority Assignments</> <para>If there is no preferences file, or if there is no entry in the file that applies to a particular instance, then the priority assigned to that instance is the priority of the distribution to which that instance belongs. It is possible to single out a distribution, called the "target release", which receives a higher priority than other distributions. The target release can be set on the <command>apt-get</command> command line or in the APT configuration file <filename>/etc/apt/apt.conf</filename>. For example, <programlisting> # Command to install the <literal/testing/ version of <replaceable>some-package</replaceable> <command>apt-get install -t testing <replaceable>some-package</replaceable></command> </programlisting> <programlisting> # Configuration setting to make <literal/stable/ the target release APT::Default-Release "stable"; </programlisting> </para> <para>If a target release has been specified then APT uses the following algorithm to set the priorities of the instances of a package. Assign: <variablelist> <varlistentry> <term>priority 100</term> <listitem><simpara>to the instance that is already installed (if any). </simpara></listitem> </varlistentry> <varlistentry> <term>priority 500</term> <listitem><simpara>to the instances that are not installed and do not belong to the target release. </simpara></listitem> </varlistentry> <varlistentry> <term>priority 990</term> <listitem><simpara>to the instances that are not installed and belong to the target release. </simpara></listitem> </varlistentry> </variablelist> </para> <para>If no target release has been specified then APT simply assigns priority 100 to all installed package instances and priority 500 to all uninstalled package instances. </para> <para>APT then applies the following rules, listed in order of precedence, to determine which instance of a package to install. <itemizedlist> <listitem><simpara>Never downgrade unless the priority of an available instance 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.) </simpara></listitem> <listitem><simpara>Install the highest priority instance. </simpara></listitem> <listitem><simpara>If two or more instances have the same priority, install the most recent one. </simpara></listitem> <listitem><simpara>If two or more instances have the same version number, install the one whose source is listed earliest in &sources-list;. (The installed instance, if there is one, is always preferred in such a comparison unless <command>apt-get --reinstall</command> is used.) </simpara></listitem> </itemizedlist> </para> <para>In a typical situation, the installed instance of a package (priority 100) is not as recent as one of the instances available from the sources listed in the &sources-list; file (priority 500 or 990). Then the package will be upgraded with the command: <command>apt-get install</command> or <command>apt-get dist-upgrade</command>. </para> <para>Rarely, the installed instance of a package is <emphasis/more/ recent than any of the other available instances. The package will not be downgraded. </para> <para>Sometimes the installed instance 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, because at least <emphasis/one/ of the available instances has a higher priority than the installed instance. </para> </RefSect2> <RefSect2><Title>The Effect of APT Preferences</> <para>The APT preferences file allows the system administrator to customize 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. <itemizedlist> <listitem> <simpara>The "specific" form pins a priority (a "Pin-Priority") to a specified package and specified version or version range. For example, the following record pins a high priority to all versions of the <filename/perl/ package whose version number begins with "<literal/5.8/". </simpara> <programlisting> Package: perl Pin: version 5.8* Pin-Priority: 1001 </programlisting> </listitem> <listitem><simpara> The "general" form pins 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 <filename/Release/ file), or to all of the package instances coming from a particular Internet site, as identified by its fully qualified domain name. </simpara> <simpara>This general-form entry in the APT preferences file applies only to groups of packages. For example, the following record causes APT to assign a high priority to all package instances available from the local site. </simpara> <programlisting> Package: * Pin: origin "" Pin-Priority: 999 </programlisting> <simpara>A note of caution: the keyword used here is "<literal/origin/". This should not be confused with the "Origin:" of a distribution as specified in a <filename/Release/ file. What follows the "Origin:" tag in a <filename/Release/ file is usually not an Internet site address but an author or vendor name, such as "Debian" or "Ximian". </simpara> <simpara>The following record causes APT to assign a low priority to all package versions belonging to any distribution whose "Archive" (<literal/a/) name is "<literal/unstable/". </simpara> <programlisting> Package: * Pin: release a=unstable Pin-Priority: 50 </programlisting> <simpara>The following record causes APT to assign a high priority to all package versions belonging to any release whose "Archive" (<literal/a/) name is "<literal/stable/" and whose release "Version" (<literal/v/) number is "<literal/3.0/". </simpara> <programlisting> Package: * Pin: release a=unstable, v=3.0 Pin-Priority: 50 </programlisting> </listitem> </itemizedlist> </para> </RefSect2> <RefSect2><Title>How APT Interprets Priorities

%aptent; ]> &apt-docinfo; apt_preferences 5 apt_preferences Preference control file for APT Description</> <para> The APT preferences file <filename>/etc/apt/preferences</> can be used to control which version of a package will be selected for installation. </para> <para>Several versions of a package may be available for installation when the &sources-list; file contains references to more than one distribution (for example, <literal>stable</literal> and <literal>testing</literal>); furthermore, several instances of the same version of a package may be available when the file contains references to more than one download site for a particular distribution. APT assigns a "priority" to each instance that is available. (In what follows, an "instance" will be an instance of a package that is available according to &sources-list;.) Subject to dependency constraints, <command>apt-get</command> installs the instance with the highest priority. If two instances have the same priority then it installs the more recent one, that is, the one with the higher version number. </para> <para>The APT preferences file overrides the priorities that APT assigns to package instances by default, thus giving the user control over which one is selected for installation. </para> <RefSect2><Title>APT's Default Priority Assignments</> <para>If there is no preferences file, or if there is no entry in the file that applies to a particular instance, then the priority assigned to that instance is the priority of the distribution to which that instance belongs. It is possible to single out a distribution, called the "target release", which receives a higher priority than other distributions. The target release can be set on the <command>apt-get</command> command line or in the APT configuration file <filename>/etc/apt/apt.conf</filename>. For example, <programlisting> # Command to install the <literal/testing/ version of <replaceable>some-package</replaceable> <command>apt-get install -t testing <replaceable>some-package</replaceable></command> </programlisting> <programlisting> # Configuration setting to make <literal/stable/ the target release APT::Default-Release "stable"; </programlisting> </para> <para>If a target release has been specified then APT uses the following algorithm to set the priorities of the instances of a package. Assign: <variablelist> <varlistentry> <term>priority 100</term> <listitem><simpara>to the instance that is already installed (if any). </simpara></listitem> </varlistentry> <varlistentry> <term>priority 500</term> <listitem><simpara>to the instances that are not installed and do not belong to the target release. </simpara></listitem> </varlistentry> <varlistentry> <term>priority 990</term> <listitem><simpara>to the instances that are not installed and belong to the target release. </simpara></listitem> </varlistentry> </variablelist> </para> <para>If no target release has been specified then APT simply assigns priority 100 to all installed package instances and priority 500 to all uninstalled package instances. </para> <para>APT then applies the following rules, listed in order of precedence, to determine which instance of a package to install. <itemizedlist> <listitem><simpara>Never downgrade unless the priority of an available instance 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.) </simpara></listitem> <listitem><simpara>Install the highest priority instance. </simpara></listitem> <listitem><simpara>If two or more instances have the same priority, install the most recent one. </simpara></listitem> <listitem><simpara>If two or more instances have the same version number, install the one whose source is listed earliest in &sources-list;. (The installed instance, if there is one, is always preferred in such a comparison unless <command>apt-get --reinstall</command> is used.) </simpara></listitem> </itemizedlist> </para> <para>In a typical situation, the installed instance of a package (priority 100) is not as recent as one of the instances available from the sources listed in the &sources-list; file (priority 500 or 990). Then the package will be upgraded with the command: <command>apt-get install</command> or <command>apt-get dist-upgrade</command>. </para> <para>Rarely, the installed instance of a package is <emphasis/more/ recent than any of the other available instances. The package will not be downgraded. </para> <para>Sometimes the installed instance 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, because at least <emphasis/one/ of the available instances has a higher priority than the installed instance. </para> </RefSect2> <RefSect2><Title>The Effect of APT Preferences</> <para>The APT preferences file allows the system administrator to customize 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. <itemizedlist> <listitem> <simpara>The "specific" form pins a priority (a "Pin-Priority") to a specified package and specified version or version range. For example, the following record pins a high priority to all versions of the <filename/perl/ package whose version number begins with "<literal/5.8/". </simpara> <programlisting> Package: perl Pin: version 5.8* Pin-Priority: 1001 </programlisting> </listitem> <listitem><simpara> The "general" form pins 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 <filename/Release/ file), or to all of the package instances coming from a particular Internet site, as identified by its fully qualified domain name. </simpara> <simpara>This general-form entry in the APT preferences file applies only to groups of packages. For example, the following record causes APT to assign a high priority to all package instances available from the local site. </simpara> <programlisting> Package: * Pin: origin "" Pin-Priority: 999 </programlisting> <simpara>A note of caution: the keyword used here is "<literal/origin/". This should not be confused with the "Origin:" of a distribution as specified in a <filename/Release/ file. What follows the "Origin:" tag in a <filename/Release/ file is usually not an Internet site address but an author or vendor name, such as "Debian" or "Ximian". </simpara> <simpara>The following record causes APT to assign a low priority to all package versions belonging to any distribution whose "Archive" (<literal/a/) name is "<literal/unstable/". </simpara> <programlisting> Package: * Pin: release a=unstable Pin-Priority: 50 </programlisting> <simpara>The following record causes APT to assign a high priority to all package versions belonging to any release whose "Archive" (<literal/a/) name is "<literal/stable/" and whose release "Version" (<literal/v/) number is "<literal/3.0/". </simpara> <programlisting> Package: * Pin: release a=unstable, v=3.0 Pin-Priority: 50 </programlisting> </listitem> </itemizedlist> </para> </RefSect2> <RefSect2><Title>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 an instance to be installed even if this constitutes a downgrade of the package 990 < P <=1000 causes an instance to be installed even if it does not come from the target release, unless the installed instance is more recent 500 < P <=990 causes an instance to be installed unless there is an instance available belonging to the target release or the installed version is more recent 100 < P <=500 causes an instance to be installed unless there is an instance available belonging to some other distribution or the installed version is more recent 0 <= P <=100 causes an instance to be installed only if there is no installed instance of the package P < 0 prevents the instance from being installed If one of the specific-form records described above matches an available package instance, then that record determines the priority of the instance. If two specific-form records match an available instance, then the first record encountered determines the priority. If two general-form records match an available instance, then the first record encountered determines the priority. 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 An instance of any package other than An instance of a package whose origin is not the local system but some other site listed in &sources-list;, and which belongs to an " Determination of Package Version and Distribution Properties The locations listed in a system's &sources-list; file should provide Packages and Release files to describe the package instances 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 gives the package name the 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 the names the archive to which all the package instances in the directory tree belong. For example, the line Pin: release a=stable the names the release version. For example, the package instances in the tree might belong to Debian GNU/Linux release version 3.0. There is normally no version number for the "testing" and "unstable" distributions because they have not yet been released. 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 names the licensing component associated with the package instances in the directory tree of the Pin: release c=main the names the producer of the package instances in the directory tree of the Pin: release o=Debian the seems redundant. Most commonly, this is Pin: release l=Debian All of the Packages and Release files retrieved from locations listed in the &sources-list; file are kept in the directory /var/lib/apt/lists, or in the file named by the variable debian.lcs.mit.edu_debian_dists_unstable_contrib_binary-i386_Release contains the Release file retrieved from the site 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 The Examples</> <RefSect2><Title>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 Package: * Pin: release a=stable Pin-Priority: 900 Explanation: Uninstall or do not install any Debian-originated Explanation: instances other than those in the stable distro Package: * Pin: release o=Debian Pin-Priority: -10 With a suitable &sources-list; file and the above preferences file, any of the following commands will cause APT to upgrade to the latest 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 apt-get install package/testing Tracking Testing The following APT preferences file will cause APT to assign a high priority to package versions from the 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 the above APT preferences file, any of the following commands will cause APT to upgrade to the latest 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 apt-get dist-upgrade and the others apt-get install package/unstable See Also</> <para> &apt-get; &apt-cache; &apt-conf; &sources-list; </RefSect1> &manbugs; &manauthor; </refentry>