&apt-email;
&apt-product;
<!-- The last update date -->
- <date>04 May 2009</date>
+ <date>16 February 2010</date>
</refentryinfo>
<refmeta>
<refsect1>
<title>Description</title>
<para>The APT preferences file <filename>/etc/apt/preferences</filename>
-can be used to control which versions of packages will be selected
+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 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
algorithm to set the priorities of the versions of a package. Assign:
<variablelist>
+<varlistentry>
+<term>priority 1</term>
+<listitem><simpara>to the versions coming from archives which in their <filename>Release</filename>
+files are marked as "NotAutomatic: yes" like the debian experimental archive.</simpara></listitem>
+</varlistentry>
+
<varlistentry>
<term>priority 100</term>
<listitem><simpara>to the version that is already installed (if any).</simpara></listitem>
<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>
+uninstalled package versions, expect versions coming from archives which
+in their <filename>Release</filename> files are marked as "NotAutomatic: yes" -
+these versions get the priority 1.</para>
<para>APT then applies the following rules, listed in order of precedence,
to determine which version of a package to install.
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
+<simpara>A note of caution: the keyword used here is "<literal>origin</literal>"
+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"</simpara>
+<programlisting>
+Package: *
+Pin: origin "ftp.de.debian.org"
+Pin-Priority: 999
+</programlisting>
+<simpara>This should <emphasis>not</emphasis> 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>
</programlisting>
<simpara>The following record assigns a high priority to all package versions
-belonging to any distribution whose Codename is "<literal>squeeze</literal>".</simpara>
+belonging to any distribution whose Codename is "<literal>&testing-codename;</literal>".</simpara>
<programlisting>
Package: *
-Pin: release n=squeeze
+Pin: release n=&testing-codename;
Pin-Priority: 900
</programlisting>
<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>.
+or <filename>.../dists/&stable-codename;/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>
<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"
+"Codename: &testing-codename;"
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
+<literal>&testing-codename;</literal>. Specifying this value in the APT preferences file
would require the line:
</simpara>
<programlisting>
-Pin: release n=squeeze
+Pin: release n=&testing-codename;
</programlisting>
</listitem>
</varlistentry>
<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>
<programlisting>
Explanation: Uninstall or do not install any Debian-originated package versions
-Explanation: other than those in the distribution codenamed with squeeze or sid
+Explanation: other than those in the distribution codenamed with &testing-codename; or sid
Package: *
-Pin: release n=squeeze
+Pin: release n=&testing-codename;
Pin-Priority: 900
Explanation: Debian unstable is always codenamed with sid
Package: *
-Pin: release a=sid
+Pin: release n=sid
Pin-Priority: 800
Package: *
<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>.
+latest version(s) in the release codenamed with <literal>&testing-codename;</literal>.
<programlisting>
apt-get install <replaceable>package-name</replaceable>
<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
+the package to the most recent <literal>&testing-codename;</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.
</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;
projects / apt.git / blobdiff