<?xml version="1.0" encoding="utf-8" standalone="no"?> <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [ <!ENTITY % aptent SYSTEM "apt.ent"> %aptent; ]> <refentry> <refentryinfo> &apt-author.team; &apt-email; &apt-product; <!-- The last update date --> <date>16 February 2010</date> </refentryinfo> <refmeta> <refentrytitle>apt_preferences</refentrytitle> <manvolnum>5</manvolnum> <refmiscinfo class="manual">APT</refmiscinfo> </refmeta> <!-- Man page title --> <refnamediv> <refname>apt_preferences</refname> <refpurpose>Preference control file for APT</refpurpose> </refnamediv> <refsect1> <title>Description</title> <para>The APT preferences file <filename>/etc/apt/preferences</filename> and the fragment files in the <filename>/etc/apt/preferences.d/</filename> folder can be used to control which versions of packages 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>). APT assigns a priority to each version that is available. Subject to dependency constraints, <command>apt-get</command> 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.</para> <para>Several instances of the same version of a package may be available when the &sources-list; file contains references to more than one source. In this case <command>apt-get</command> downloads the instance listed earliest in the &sources-list; file. The APT preferences file does not affect the choice of instance, only the choice of version.</para> <para>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.</para> <para>Note that the files in the <filename>/etc/apt/preferences.d</filename> directory are parsed in alphanumeric ascending order and need to obey the following naming convention: The files have no or "<literal>pref</literal>" as filename extension and which only contain alphanumeric, hyphen (-), underscore (_) and period (.) characters - otherwise they will be silently ignored.</para> <refsect2><title>APT's Default Priority Assignments</title> <para>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 <command>apt-get</command> command line or in the APT configuration file <filename>/etc/apt/apt.conf</filename>. Note that this has precedence over any general priority you set in the <filename>/etc/apt/preferences</filename> file described later, but not over specifically pinned packages. For example, <programlisting> <command>apt-get install -t testing <replaceable>some-package</replaceable></command> </programlisting> <programlisting> APT::Default-Release "stable"; </programlisting> </para> <para>If the target release has been specified then APT uses the following algorithm to set the priorities of the versions of a package. Assign: <variablelist> <varlistentry> <term>priority 100</term> <listitem><simpara>to the version that is already installed (if any).</simpara></listitem> </varlistentry> <varlistentry> <term>priority 500</term> <listitem><simpara>to the versions that are not installed and do not belong to the target release.</simpara></listitem> </varlistentry> <varlistentry> <term>priority 990</term> <listitem><simpara>to the versions that are not installed and belong to the target release.</simpara></listitem> </varlistentry> </variablelist> </para> <para>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.</para> <para>APT then applies the following rules, listed in order of precedence, to determine which version of a package to install. <itemizedlist> <listitem><simpara>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.)</simpara></listitem> <listitem><simpara>Install the highest priority version.</simpara></listitem> <listitem><simpara>If two or more versions have the same priority, install the most recent one (that is, the one with the higher version number).</simpara></listitem> <listitem><simpara>If two or more versions have the same priority and version number but either the packages differ in some of their metadata or the <literal>--reinstall</literal> option is given, install the uninstalled one.</simpara></listitem> </itemizedlist> </para> <para>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; file (priority 500 or 990). Then the package will be upgraded when <command>apt-get install <replaceable>some-package</replaceable></command> or <command>apt-get upgrade</command> is executed. </para> <para>More rarely, the installed version of a package is <emphasis>more</emphasis> recent than any of the other available versions. The package will not be downgraded when <command>apt-get install <replaceable>some-package</replaceable></command> or <command>apt-get upgrade</command> is executed.</para> <para>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 <command>apt-get install <replaceable>some-package</replaceable></command> or <command>apt-get upgrade</command> is executed, because at least <emphasis>one</emphasis> of the available versions has a higher priority than the installed version.</para> </refsect2> <refsect2><title>The Effect of APT Preferences</title> <para>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. <itemizedlist> <listitem> <simpara>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 <filename>perl</filename> package whose version number begins with "<literal>5.8</literal>". Multiple packages can be separated by spaces.</simpara> <programlisting> Package: perl Pin: version 5.8* Pin-Priority: 1001 </programlisting> </listitem> <listitem><simpara>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 <filename>Release</filename> file) or to all of the package versions coming from a particular Internet site, as identified by the site's 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 assigns a high priority to all package versions 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</literal>". This should not be confused with the Origin of a distribution as specified in a <filename>Release</filename> file. What follows the "Origin:" tag in a <filename>Release</filename> file is not an Internet address but an author or vendor name, such as "Debian" or "Ximian".</simpara> <simpara>The following record assigns a low priority to all package versions belonging to any distribution whose Archive name is "<literal>unstable</literal>".</simpara> <programlisting> Package: * Pin: release a=unstable Pin-Priority: 50 </programlisting> <simpara>The following record assigns a high priority to all package versions belonging to any distribution whose Codename is "<literal>squeeze</literal>".</simpara> <programlisting> Package: * Pin: release n=squeeze Pin-Priority: 900 </programlisting> <simpara>The following record assigns a high priority to all package versions belonging to any release whose Archive name is "<literal>stable</literal>" and whose release Version number is "<literal>3.0</literal>".</simpara> <programlisting> Package: * Pin: release a=stable, v=3.0 Pin-Priority: 500 </programlisting> </listitem> </itemizedlist> </para> </refsect2> <refsect2> <title>How APT Interprets Priorities</title> <para> Priorities (P) assigned in the APT preferences file must be positive or negative integers. They are interpreted as follows (roughly speaking): <variablelist> <varlistentry> <term>P > 1000</term> <listitem><simpara>causes a version to be installed even if this constitutes a downgrade of the package</simpara></listitem> </varlistentry> <varlistentry> <term>990 < P <=1000</term> <listitem><simpara>causes a version to be installed even if it does not come from the target release, unless the installed version is more recent</simpara></listitem> </varlistentry> <varlistentry> <term>500 < P <=990</term> <listitem><simpara>causes a version to be installed unless there is a version available belonging to the target release or the installed version is more recent</simpara></listitem> </varlistentry> <varlistentry> <term>100 < P <=500</term> <listitem><simpara>causes a version to be installed unless there is a version available belonging to some other distribution or the installed version is more recent</simpara></listitem> </varlistentry> <varlistentry> <term>0 < P <=100</term> <listitem><simpara>causes a version to be installed only if there is no installed version of the package</simpara></listitem> </varlistentry> <varlistentry> <term>P < 0</term> <listitem><simpara>prevents the version from being installed</simpara></listitem> </varlistentry> </variablelist> </para> <para>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.</para> <para>For example, suppose the APT preferences file contains the three records presented earlier:</para> <programlisting> Package: perl Pin: version 5.8* Pin-Priority: 1001 Package: * Pin: origin "" Pin-Priority: 999 Package: * Pin: release unstable Pin-Priority: 50 </programlisting> <para>Then: <itemizedlist> <listitem><simpara>The most recent available version of the <literal>perl</literal> package will be installed, so long as that version's version number begins with "<literal>5.8</literal>". If <emphasis>any</emphasis> 5.8* version of <literal>perl</literal> is available and the installed version is 5.9*, then <literal>perl</literal> will be downgraded.</simpara></listitem> <listitem><simpara>A version of any package other than <literal>perl</literal> that is available from the local system has priority over other versions, even versions belonging to the target release. </simpara></listitem> <listitem><simpara>A version of a package whose origin is not the local system but some other site listed in &sources-list; and which belongs to an <literal>unstable</literal> distribution is only installed if it is selected for installation and no version of the package is already installed. </simpara></listitem> </itemizedlist> </para> </refsect2> <refsect2> <title>Determination of Package Version and Distribution Properties</title> <para>The locations listed in the &sources-list; file should provide <filename>Packages</filename> and <filename>Release</filename> files to describe the packages available at that location. </para> <para>The <filename>Packages</filename> file is normally found in the directory <filename>.../dists/<replaceable>dist-name</replaceable>/<replaceable>component</replaceable>/<replaceable>arch</replaceable></filename>: for example, <filename>.../dists/stable/main/binary-i386/Packages</filename>. 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: <variablelist> <varlistentry> <term>the <literal>Package:</literal> line</term> <listitem><simpara>gives the package name</simpara></listitem> </varlistentry> <varlistentry> <term>the <literal>Version:</literal> line</term> <listitem><simpara>gives the version number for the named package</simpara></listitem> </varlistentry> </variablelist> </para> <para>The <filename>Release</filename> file is normally found in the directory <filename>.../dists/<replaceable>dist-name</replaceable></filename>: for example, <filename>.../dists/stable/Release</filename>, or <filename>.../dists/woody/Release</filename>. It consists of a single multi-line record which applies to <emphasis>all</emphasis> of the packages in the directory tree below its parent. Unlike the <filename>Packages</filename> file, nearly all of the lines in a <filename>Release</filename> file are relevant for setting APT priorities: <variablelist> <varlistentry> <term>the <literal>Archive:</literal> or <literal>Suite:</literal> line</term> <listitem><simpara>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 <filename>Release</filename> file are in a <literal>stable</literal> archive. Specifying this value in the APT preferences file would require the line: </simpara> <programlisting> Pin: release a=stable </programlisting> </listitem> </varlistentry> <varlistentry> <term>the <literal>Codename:</literal> line</term> <listitem><simpara>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 <filename>Release</filename> file belong to a version named <literal>squeeze</literal>. Specifying this value in the APT preferences file would require the line: </simpara> <programlisting> Pin: release n=squeeze </programlisting> </listitem> </varlistentry> <varlistentry> <term>the <literal>Version:</literal> line</term> <listitem><simpara>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 <literal>testing</literal> and <literal>unstable</literal> distributions because they have not been released yet. Specifying this in the APT preferences file would require one of the following lines. </simpara> <programlisting> Pin: release v=3.0 Pin: release a=stable, v=3.0 Pin: release 3.0 </programlisting> </listitem> </varlistentry> <varlistentry> <term>the <literal>Component:</literal> line</term> <listitem><simpara>names the licensing component associated with the packages in the directory tree of the <filename>Release</filename> file. For example, the line "Component: main" specifies that all the packages in the directory tree are from the <literal>main</literal> 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: </simpara> <programlisting> Pin: release c=main </programlisting> </listitem> </varlistentry> <varlistentry> <term>the <literal>Origin:</literal> line</term> <listitem><simpara>names the originator of the packages in the directory tree of the <filename>Release</filename> file. Most commonly, this is <literal>Debian</literal>. Specifying this origin in the APT preferences file would require the line: </simpara> <programlisting> Pin: release o=Debian </programlisting> </listitem> </varlistentry> <varlistentry> <term>the <literal>Label:</literal> line</term> <listitem><simpara>names the label of the packages in the directory tree of the <filename>Release</filename> file. Most commonly, this is <literal>Debian</literal>. Specifying this label in the APT preferences file would require the line: </simpara> <programlisting> Pin: release l=Debian </programlisting> </listitem> </varlistentry> </variablelist> </para> <para>All of the <filename>Packages</filename> and <filename>Release</filename> files retrieved from locations listed in the &sources-list; file are stored in the directory <filename>/var/lib/apt/lists</filename>, or in the file named by the variable <literal>Dir::State::Lists</literal> in the <filename>apt.conf</filename> file. For example, the file <filename>debian.lcs.mit.edu_debian_dists_unstable_contrib_binary-i386_Release</filename> contains the <filename>Release</filename> file retrieved from the site <literal>debian.lcs.mit.edu</literal> for <literal>binary-i386</literal> architecture files from the <literal>contrib</literal> component of the <literal>unstable</literal> distribution.</para> </refsect2> <refsect2> <title>Optional Lines in an APT Preferences Record</title> <para>Each record in the APT preferences file can optionally begin with one or more lines beginning with the word <literal>Explanation:</literal>. This provides a place for comments.</para> <para>The <literal>Pin-Priority:</literal> line in each APT preferences record is optional. If omitted, APT assigns a priority of 1 less than the last value specified on a line beginning with <literal>Pin-Priority: release ...</literal>.</para> </refsect2> </refsect1> <refsect1> <title>Examples</title> <refsect2> <title>Tracking Stable</title> <para>The following APT preferences file will cause APT to assign a priority higher than the default (500) to all package versions belonging to a <literal>stable</literal> distribution and a prohibitively low priority to package versions belonging to other <literal>Debian</literal> distributions. <programlisting> 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 </programlisting> </para> <para>With a suitable &sources-list; file and the above preferences file, any of the following commands will cause APT to upgrade to the latest <literal>stable</literal> version(s). <programlisting> apt-get install <replaceable>package-name</replaceable> apt-get upgrade apt-get dist-upgrade </programlisting> </para> <para>The following command will cause APT to upgrade the specified package to the latest version from the <literal>testing</literal> distribution; the package will not be upgraded again unless this command is given again. <programlisting> apt-get install <replaceable>package</replaceable>/testing </programlisting> </para> </refsect2> <refsect2> <title>Tracking Testing or Unstable</title> <para>The following APT preferences file will cause APT to assign a high priority to package versions from the <literal>testing</literal> distribution, a lower priority to package versions from the <literal>unstable</literal> distribution, and a prohibitively low priority to package versions from other <literal>Debian</literal> distributions. <programlisting> Package: * Pin: release a=testing Pin-Priority: 900 Package: * Pin: release a=unstable Pin-Priority: 800 Package: * Pin: release o=Debian Pin-Priority: -10 </programlisting> </para> <para>With a suitable &sources-list; file and the above preferences file, any of the following commands will cause APT to upgrade to the latest <literal>testing</literal> version(s). <programlisting> apt-get install <replaceable>package-name</replaceable> apt-get upgrade apt-get dist-upgrade </programlisting> </para> <para>The following command will cause APT to upgrade the specified package to the latest version from the <literal>unstable</literal> distribution. Thereafter, <command>apt-get upgrade</command> will upgrade the package to the most recent <literal>testing</literal> version if that is more recent than the installed version, otherwise, to the most recent <literal>unstable</literal> version if that is more recent than the installed version. <programlisting> apt-get install <replaceable>package</replaceable>/unstable </programlisting> </para> </refsect2> <refsect2> <title>Tracking the evolution of a codename release</title> <para>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 <literal>Debian</literal> distributions, codenames and archives. Note that with this APT preference APT will follow the migration of a release from the archive <literal>testing</literal> to <literal>stable</literal> and later <literal>oldstable</literal>. If you want to follow for example the progress in <literal>testing</literal> notwithstanding the codename changes you should use the example configurations above. <programlisting> 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 a=sid Pin-Priority: 800 Package: * Pin: release o=Debian Pin-Priority: -10 </programlisting> </para> <para>With a suitable &sources-list; 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 <literal>squeeze</literal>. <programlisting> apt-get install <replaceable>package-name</replaceable> apt-get upgrade apt-get dist-upgrade </programlisting> </para> <para>The following command will cause APT to upgrade the specified package to the latest version from the <literal>sid</literal> distribution. Thereafter, <command>apt-get upgrade</command> will upgrade the package to the most recent <literal>squeeze</literal> version if that is more recent than the installed version, otherwise, to the most recent <literal>sid</literal> version if that is more recent than the installed version. <programlisting> apt-get install <replaceable>package</replaceable>/sid </programlisting> </para> </refsect2> </refsect1> <refsect1> <title>Files</title> <variablelist> &file-preferences; </variablelist> </refsect1> <refsect1> <title>See Also</title> <para>&apt-get; &apt-cache; &apt-conf; &sources-list; </para> </refsect1> &manbugs; </refentry>