1 <?xml version=
"1.0" encoding=
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"no"?>
2 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.5//EN"
3 "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
4 <!ENTITY % aptent SYSTEM
"apt.ent"> %aptent;
5 <!ENTITY % aptverbatiment SYSTEM
"apt-verbatim.ent"> %aptverbatiment;
6 <!ENTITY % aptvendor SYSTEM
"apt-vendor.ent"> %aptvendor;
15 <!-- The last update date -->
16 <date>2015-
08-
15T00:
00:
00Z
</date>
20 <refentrytitle>apt_preferences
</refentrytitle>
21 <manvolnum>5</manvolnum>
22 <refmiscinfo class=
"manual">APT
</refmiscinfo>
25 <!-- Man page title -->
27 <refname>apt_preferences
</refname>
28 <refpurpose>Preference control file for APT
</refpurpose>
32 <title>Description
</title>
33 <para>The APT preferences file
<filename>/etc/apt/preferences
</filename>
34 and the fragment files in the
<filename>/etc/apt/preferences.d/
</filename>
35 folder can be used to control which versions of packages will be selected
36 for installation.
</para>
38 <para>Several versions of a package may be available for installation when
39 the &sources-list; file contains references to more than one distribution
40 (for example,
<literal>stable
</literal> and
<literal>testing
</literal>).
41 APT assigns a priority to each version that is available.
42 Subject to dependency constraints,
<command>apt-get
</command> selects the
43 version with the highest priority for installation.
44 The APT preferences override the priorities that APT assigns to
45 package versions by default, thus giving the user control over which
46 one is selected for installation.
</para>
48 <para>Several instances of the same version of a package may be available when
49 the &sources-list; file contains references to more than one source.
50 In this case
<command>apt-get
</command> downloads the instance listed
51 earliest in the &sources-list; file.
52 The APT preferences do not affect the choice of instance, only
53 the choice of version.
</para>
55 <para>Preferences are a strong power in the hands of a system administrator
56 but they can become also their biggest nightmare if used without care!
57 APT will not question the preferences, so wrong settings can
58 lead to uninstallable packages or wrong decisions while upgrading packages.
59 Even more problems will arise if multiple distribution releases are mixed
60 without a good understanding of the following paragraphs.
61 Packages included in a specific release aren't tested in (and
62 therefore don't always work as expected in) older or newer releases, or
63 together with other packages from different releases.
64 You have been warned.
</para>
66 <para>Note that the files in the
<filename>/etc/apt/preferences.d
</filename>
67 directory are parsed in alphanumeric ascending order and need to obey the
68 following naming convention: The files have either no or "
<literal>pref
</literal>"
69 as filename extension and only contain alphanumeric, hyphen (-),
70 underscore (_) and period (.) characters.
71 Otherwise APT will print a notice that it has ignored a file, unless that
72 file matches a pattern in the <literal>Dir::Ignore-Files-Silently</literal>
73 configuration list - in which case it will be silently ignored.</para>
75 <refsect2><title>APT's Default Priority Assignments</title>
77 <para>If there is no preferences file or if there is no entry in the file
78 that applies to a particular version then the priority assigned to that
79 version is the priority of the distribution to which that version
80 belongs. It is possible to single out a distribution, "the target release",
81 which receives a higher priority than other distributions do by default.
82 The target release can be set on the
<command>apt-get
</command> command
83 line or in the APT configuration file
<filename>/etc/apt/apt.conf
</filename>.
84 Note that this has precedence over any general priority you set in the
85 <filename>/etc/apt/preferences
</filename> file described later, but not
86 over specifically pinned packages.
90 <command>apt-get install -t testing
<replaceable>some-package
</replaceable></command>
93 APT::Default-Release "stable";
97 <para>If the target release has been specified then APT uses the following
98 algorithm to set the priorities of the versions of a package. Assign:
102 <term>priority
1</term>
103 <listitem><simpara>to the versions coming from archives which in their
<filename>Release
</filename>
104 files are marked as "NotAutomatic: yes" but
<emphasis>not
</emphasis> as "ButAutomaticUpgrades: yes"
105 like the Debian
<literal>experimental
</literal> archive.
</simpara></listitem>
109 <term>priority
100</term>
110 <listitem><simpara>to the version that is already installed (if any) and to the versions coming
111 from archives which in their
<filename>Release
</filename> files are marked as "NotAutomatic: yes" and
112 "ButAutomaticUpgrades: yes" like the Debian backports archive since
<literal>squeeze-backports
</literal>.
113 </simpara></listitem>
117 <term>priority
500</term>
118 <listitem><simpara>to the versions that do not belong to the target release.
</simpara></listitem>
122 <term>priority
990</term>
123 <listitem><simpara>to the versions that belong to the target release.
</simpara></listitem>
127 The highest of those priorities whose description matches the version is assigned to the
131 <para>If the target release has not been specified then APT simply assigns
132 priority
100 to all installed package versions and priority
500 to all
133 uninstalled package versions, except versions coming from archives which
134 in their
<filename>Release
</filename> files are marked as "NotAutomatic: yes" -
135 these versions get the priority
1 or priority
100 if it is additionally marked
136 as "ButAutomaticUpgrades: yes".
</para>
138 <para>APT then applies the following rules, listed in order of precedence,
139 to determine which version of a package to install.
141 <listitem><simpara>Never downgrade unless the priority of an available
142 version exceeds
1000. ("Downgrading" is installing a less recent version
143 of a package in place of a more recent version. Note that none of APT's
144 default priorities exceeds
1000; such high priorities can only be set in
145 the preferences file. Note also that downgrading a package
146 can be risky.)
</simpara></listitem>
147 <listitem><simpara>Install the highest priority version.
</simpara></listitem>
148 <listitem><simpara>If two or more versions have the same priority,
149 install the most recent one (that is, the one with the higher version
150 number).
</simpara></listitem>
151 <listitem><simpara>If two or more versions have the same priority and
152 version number but either the packages differ in some of their metadata or the
153 <literal>--reinstall
</literal> option is given, install the uninstalled one.
</simpara></listitem>
157 <para>In a typical situation, the installed version of a package (priority
100)
158 is not as recent as one of the versions available from the sources listed in
159 the &sources-list; file (priority
500 or
990). Then the package will be upgraded
160 when
<command>apt-get install
<replaceable>some-package
</replaceable></command>
161 or
<command>apt-get upgrade
</command> is executed.
164 <para>More rarely, the installed version of a package is
<emphasis>more
</emphasis> recent
165 than any of the other available versions. The package will not be downgraded
166 when
<command>apt-get install
<replaceable>some-package
</replaceable></command>
167 or
<command>apt-get upgrade
</command> is executed.
</para>
169 <para>Sometimes the installed version of a package is more recent than the
170 version belonging to the target release, but not as recent as a version
171 belonging to some other distribution. Such a package will indeed be upgraded
172 when
<command>apt-get install
<replaceable>some-package
</replaceable></command>
173 or
<command>apt-get upgrade
</command> is executed,
174 because at least
<emphasis>one
</emphasis> of the available versions has a higher
175 priority than the installed version.
</para>
178 <refsect2><title>The Effect of APT Preferences
</title>
180 <para>The APT preferences file allows the system administrator to control the
181 assignment of priorities. The file consists of one or more multi-line records
182 separated by blank lines. Records can have one of two forms, a specific form
186 <simpara>The specific form assigns a priority (a "Pin-Priority") to one or more
187 specified packages with a specified version or version range. For example,
188 the following record assigns a high priority to all versions of
189 the
<filename>perl
</filename> package whose version number begins with "
<literal>&good-perl;
</literal>".
190 Multiple packages can be separated by spaces.</simpara>
194 Pin: version &good-perl;*
199 <listitem><simpara>The general form assigns a priority to all of the package versions in a
200 given distribution (that is, to all the versions of packages that are
201 listed in a certain <filename>Release</filename> file) or to all of the package
202 versions coming from a particular Internet site, as identified by the
203 site's fully qualified domain name.</simpara>
205 <simpara>This general-form entry in the APT preferences file applies only
206 to groups of packages. For example, the following record assigns a high
207 priority to all package versions available from the local site.</simpara>
215 <simpara>A note of caution: the keyword used here is "
<literal>origin
</literal>"
216 which can be used to match a hostname. The following record will assign a high priority
217 to all versions available from the server identified by the hostname "ftp.de.debian.org
"</simpara>
220 Pin: origin "ftp.de.debian.org"
223 <simpara>This should
<emphasis>not
</emphasis> be confused with the Origin of a distribution as
224 specified in a
<filename>Release
</filename> file. What follows the "Origin:" tag
225 in a
<filename>Release
</filename> file is not an Internet address
226 but an author or vendor name, such as "Debian" or "Ximian".
</simpara>
228 <simpara>The following record assigns a low priority to all package versions
229 belonging to any distribution whose Archive name is "
<literal>unstable
</literal>".</simpara>
233 Pin: release a=unstable
237 <simpara>The following record assigns a high priority to all package versions
238 belonging to any distribution whose Codename is "<literal>&testing-codename;
</literal>".</simpara>
242 Pin: release n=&testing-codename;
246 <simpara>The following record assigns a high priority to all package versions
247 belonging to any release whose Archive name is "<literal>stable
</literal>"
248 and whose release Version number is "<literal>&stable-version;
</literal>".</simpara>
252 Pin: release a=stable, v=&stable-version;
258 The effect of the comma operator is similar to an "and" in logic: All
259 conditions must be satisfied for the pin to match. There is one exception:
260 For any type of condition (such as two "a" conditions), only the last such
261 condition is checked.
266 <refsect2><title>Regular expressions and
&glob; syntax
</title>
268 APT also supports pinning by
&glob; expressions, and regular
269 expressions surrounded by slashes. For example, the following
270 example assigns the priority
500 to all packages from
271 experimental where the name starts with gnome (as a
&glob;-like
272 expression) or contains the word kde (as a POSIX extended regular
273 expression surrounded by slashes).
277 Package: gnome* /kde/
278 Pin: release a=experimental
283 The rule for those expressions is that they can occur anywhere
284 where a string can occur. Thus, the following pin assigns the
285 priority
990 to all packages from a release starting with &ubuntu-codename;.
290 Pin: release n=&ubuntu-codename;*
295 If a regular expression occurs in a
<literal>Package
</literal> field,
296 the behavior is the same as if this regular expression were replaced
297 with a list of all package names it matches. It is undecided whether
298 this will change in the future; thus you should always list wild-card
299 pins first, so later specific pins override it.
301 The pattern "
<literal>*
</literal>" in a Package field is not considered
302 a &glob; expression in itself.
311 <title>How APT Interprets Priorities</title>
314 Priorities (P) assigned in the APT preferences file must be positive
315 or negative integers. They are interpreted as follows (roughly speaking):
319 <term>P >= 1000</term>
320 <listitem><simpara>causes a version to be installed even if this
321 constitutes a downgrade of the package</simpara></listitem>
324 <term>990 <= P < 1000</term>
325 <listitem><simpara>causes a version to be installed
326 even if it does not come from the target release,
327 unless the installed version is more recent</simpara></listitem>
330 <term>500 <= P < 990</term>
331 <listitem><simpara>causes a version to be installed
332 unless there is a version available belonging to the target release
333 or the installed version is more recent</simpara></listitem>
336 <term>100 <= P < 500</term>
337 <listitem><simpara>causes a version to be installed
338 unless there is a version available belonging to some other
339 distribution or the installed version is more recent</simpara></listitem>
342 <term>0 < P < 100</term>
343 <listitem><simpara>causes a version to be installed
344 only if there is no installed version of the package</simpara></listitem>
347 <term>P < 0</term>
348 <listitem><simpara>prevents the version from being installed</simpara></listitem>
352 <listitem><simpara>has undefined behaviour, do not use it.</simpara></listitem>
358 The first specific-form record matching an available package version determines
359 the priority of the package version.
360 Failing that, the priority of the package is defined as the maximum of all
361 priorities defined by generic-form records matching the version.
362 Records defined using patterns in the Pin field other than "*" are treated like
363 specific-form records.
366 <para>For example, suppose the APT preferences file contains the three
367 records presented earlier:
</para>
371 Pin: version &good-perl;*
379 Pin: release unstable
385 <listitem><simpara>The most recent available version of the
<literal>perl
</literal>
386 package will be installed, so long as that version's version number begins
387 with "
<literal>&good-perl;
</literal>". If <emphasis>any</emphasis> &good-perl;* version of <literal>perl</literal> is
388 available and the installed version is &bad-perl;*, then <literal>perl</literal> will be
389 downgraded.</simpara></listitem>
390 <listitem><simpara>A version of any package other than <literal>perl</literal>
391 that is available from the local system has priority over other versions,
392 even versions belonging to the target release.
393 </simpara></listitem>
394 <listitem><simpara>A version of a package whose origin is not the local
395 system but some other site listed in &sources-list; and which belongs to
396 an <literal>unstable</literal> distribution is only installed if it is selected
397 for installation and no version of the package is already installed.
398 </simpara></listitem>
404 <title>Determination of Package Version and Distribution Properties</title>
406 <para>The locations listed in the &sources-list; file should provide
407 <filename>Packages</filename> and <filename>Release</filename> files
408 to describe the packages available at that location. </para>
410 <para>The <filename>Packages</filename> file is normally found in the directory
411 <filename>.../dists/<replaceable>dist-name</replaceable>/<replaceable>component</replaceable>/<replaceable>arch</replaceable></filename>:
412 for example, <filename>.../dists/stable/main/binary-i386/Packages</filename>.
413 It consists of a series of multi-line records, one for each package available
414 in that directory. Only two lines in each record are relevant for setting
418 <term>the <literal>Package:</literal> line</term>
419 <listitem><simpara>gives the package name</simpara></listitem>
422 <term>the <literal>Version:</literal> line</term>
423 <listitem><simpara>gives the version number for the named package</simpara></listitem>
428 <para>The <filename>Release</filename> file is normally found in the directory
429 <filename>.../dists/<replaceable>dist-name</replaceable></filename>:
430 for example, <filename>.../dists/stable/Release</filename>,
431 or <filename>.../dists/&stable-codename;/Release</filename>.
432 It consists of a single multi-line record which applies to <emphasis>all</emphasis> of
433 the packages in the directory tree below its parent. Unlike the
434 <filename>Packages</filename> file, nearly all of the lines in a <filename>Release</filename>
435 file are relevant for setting APT priorities:
439 <term>the <literal>Archive:</literal> or <literal>Suite:</literal> line</term>
440 <listitem><simpara>names the archive to which all the packages
441 in the directory tree belong. For example, the line
444 specifies that all of the packages in the directory
445 tree below the parent of the
<filename>Release
</filename> file are in a
446 <literal>stable
</literal> archive. Specifying this value in the APT preferences file
447 would require the line:
450 Pin: release a=stable
456 <term>the
<literal>Codename:
</literal> line
</term>
457 <listitem><simpara>names the codename to which all the packages
458 in the directory tree belong. For example, the line
459 "Codename: &testing-codename;"
460 specifies that all of the packages in the directory
461 tree below the parent of the
<filename>Release
</filename> file belong to a version named
462 <literal>&testing-codename;
</literal>. Specifying this value in the APT preferences file
463 would require the line:
466 Pin: release n=&testing-codename;
472 <term>the
<literal>Version:
</literal> line
</term>
473 <listitem><simpara>names the release version. For example, the
474 packages in the tree might belong to Debian release
475 version &stable-version;. Note that there is normally no version number for the
476 <literal>testing
</literal> and
<literal>unstable
</literal> distributions because they
477 have not been released yet. Specifying this in the APT preferences
478 file would require one of the following lines.
482 Pin: release v=&stable-version;
483 Pin: release a=stable, v=&stable-version;
484 Pin: release &stable-version;
491 <term>the
<literal>Component:
</literal> line
</term>
492 <listitem><simpara>names the licensing component associated with the
493 packages in the directory tree of the
<filename>Release
</filename> file.
494 For example, the line "Component: main" specifies that
495 all the packages in the directory tree are from the
<literal>main
</literal>
496 component, which entails that they are licensed under terms listed
497 in the Debian Free Software Guidelines. Specifying this component
498 in the APT preferences file would require the line:
507 <term>the
<literal>Origin:
</literal> line
</term>
508 <listitem><simpara>names the originator of the packages in the
509 directory tree of the
<filename>Release
</filename> file. Most commonly, this is
510 <literal>Debian
</literal>. Specifying this origin in the APT preferences file
511 would require the line:
514 Pin: release o=Debian
520 <term>the
<literal>Label:
</literal> line
</term>
521 <listitem><simpara>names the label of the packages in the directory tree
522 of the
<filename>Release
</filename> file. Most commonly, this is
523 <literal>Debian
</literal>. Specifying this label in the APT preferences file
524 would require the line:
527 Pin: release l=Debian
534 <para>All of the
<filename>Packages
</filename> and
<filename>Release
</filename>
535 files retrieved from locations listed in the &sources-list; file are stored
536 in the directory
<filename>/var/lib/apt/lists
</filename>, or in the file named
537 by the variable
<literal>Dir::State::Lists
</literal> in the
<filename>apt.conf
</filename> file.
538 For example, the file
539 <filename>debian.lcs.mit.edu_debian_dists_unstable_contrib_binary-i386_Release
</filename>
540 contains the
<filename>Release
</filename> file retrieved from the site
541 <literal>debian.lcs.mit.edu
</literal> for
<literal>binary-i386
</literal> architecture
542 files from the
<literal>contrib
</literal> component of the
<literal>unstable
</literal>
547 <title>Optional Lines in an APT Preferences Record
</title>
549 <para>Each record in the APT preferences file can optionally begin with
550 one or more lines beginning with the word
<literal>Explanation:
</literal>.
551 This provides a place for comments.
</para>
556 <title>Examples
</title>
558 <title>Tracking Stable
</title>
560 <para>The following APT preferences file will cause APT to assign a
561 priority higher than the default (
500) to all package versions belonging
562 to a
<literal>stable
</literal> distribution and a prohibitively low priority to
563 package versions belonging to other
<literal>Debian
</literal> distributions.
566 Explanation: Uninstall or do not install any Debian-originated
567 Explanation: package versions other than those in the stable distro
569 Pin: release a=stable
573 Pin: release o=Debian
578 <para>With a suitable &sources-list; file and the above preferences file,
579 any of the following commands will cause APT to upgrade to the
580 latest
<literal>stable
</literal> version(s).
583 apt-get install
<replaceable>package-name
</replaceable>
589 <para>The following command will cause APT to upgrade the specified
590 package to the latest version from the
<literal>testing
</literal> distribution;
591 the package will not be upgraded again unless this command is given
595 apt-get install
<replaceable>package
</replaceable>/testing
601 <title>Tracking Testing or Unstable
</title>
603 <para>The following APT preferences file will cause APT to assign
604 a high priority to package versions from the
<literal>testing
</literal>
605 distribution, a lower priority to package versions from the
606 <literal>unstable
</literal> distribution, and a prohibitively low priority
607 to package versions from other
<literal>Debian
</literal> distributions.
611 Pin: release a=testing
615 Pin: release a=unstable
619 Pin: release o=Debian
624 <para>With a suitable &sources-list; file and the above preferences file,
625 any of the following commands will cause APT to upgrade to the latest
626 <literal>testing
</literal> version(s).
629 apt-get install
<replaceable>package-name
</replaceable>
635 <para>The following command will cause APT to upgrade the specified
636 package to the latest version from the
<literal>unstable
</literal> distribution.
637 Thereafter,
<command>apt-get upgrade
</command> will upgrade
638 the package to the most recent
<literal>testing
</literal> version if that is
639 more recent than the installed version, otherwise, to the most recent
640 <literal>unstable
</literal> version if that is more recent than the installed
644 apt-get install
<replaceable>package
</replaceable>/unstable
651 <title>Tracking the evolution of a codename release
</title>
653 <para>The following APT preferences file will cause APT to assign a
654 priority higher than the default (
500) to all package versions belonging
655 to a specified codename of a distribution and a prohibitively low priority to
656 package versions belonging to other
<literal>Debian
</literal> distributions,
657 codenames and archives.
658 Note that with this APT preference APT will follow the migration of a release
659 from the archive
<literal>testing
</literal> to
<literal>stable
</literal> and
660 later
<literal>oldstable
</literal>. If you want to follow for example the progress
661 in
<literal>testing
</literal> notwithstanding the codename changes you should use
662 the example configurations above.
665 Explanation: Uninstall or do not install any Debian-originated package versions
666 Explanation: other than those in the distribution codenamed with &testing-codename; or sid
668 Pin: release n=&testing-codename;
671 Explanation: Debian unstable is always codenamed with sid
677 Pin: release o=Debian
682 <para>With a suitable &sources-list; file and the above preferences file,
683 any of the following commands will cause APT to upgrade to the
684 latest version(s) in the release codenamed with
<literal>&testing-codename;
</literal>.
687 apt-get install
<replaceable>package-name
</replaceable>
693 <para>The following command will cause APT to upgrade the specified
694 package to the latest version from the
<literal>sid
</literal> distribution.
695 Thereafter,
<command>apt-get upgrade
</command> will upgrade
696 the package to the most recent
<literal>&testing-codename;
</literal> version if that is
697 more recent than the installed version, otherwise, to the most recent
698 <literal>sid
</literal> version if that is more recent than the installed
702 apt-get install
<replaceable>package
</replaceable>/sid
716 <title>See Also
</title>
717 <para>&apt-get; &apt-cache; &apt-conf; &sources-list;