APT_PREFERENCES(5)apt_preferencesAPT_PREFERENCES(5)NAMEapt_preferences - Preference control file for APT
DESCRIPTION
The APT preferences file /etc/apt/preferences 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 distribu‐
tion (for example, stable and testing). APT assigns a priority to each
version that is available. Subject to dependency constraints, apt-
get(8) 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(8) 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.
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(8) command
line or in the APT configuration file /etc/apt/apt.conf(5). For exam‐
ple,
apt-get install -t testing some-package
To configure the default release in the configuration file, use:
APT::Default-Release "stable";
If the target release has been specified then APT uses the following
algorithm to set the priorities of the versions of a package. Assign:
priority 100
to the version that is already installed (if any).
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.
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 pack‐
age 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 --rein‐
stall 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
belonging to some other distribution. Such a package will indeed be
upgraded when apt-get install some-package or apt-get upgrade is exe‐
cuted, because at least one of the available versions has a higher pri‐
ority than the installed version.
THE EFFECT OF APT PREFERENCES
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.
· The specific form assigns a priority (a "Pin-Priority") to a speci‐
fied package and specified version or version range. For example,
the following record assigns a high priority to all versions of the
perl package whose version number begins with "5.8".
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 ver‐
sions 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". 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 release whose Archive name is "stable" and whose
release Version number is "3.0".
Package: *
Pin: release a=unstable, v=3.0
Pin-Priority: 50
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 ver‐
sion 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.
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 pack‐
age version.
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 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 belong‐
ing 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 Pack‐
ages and Release files to describe the packages available at that loca‐
tion.
The Packages File
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:
Package:
this line gives the package name.
Version:
this line gives the version number for the named package.
The Release File
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 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:
Archive:
this line names the archive to which all the packages in the
directory tree belong. For example, the line "Archive: stable"
specifies that all of the packages in the directory tree below
the parent of the Release file are in a stable archive. Speci‐
fying this value in the APT preferences file would require the
line:
Pin: release a=stable
Version:
this 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
Component:
this 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 pref‐
erences file would require the line:
Pin: release c=main
Origin:
this line names the originator of the packages in the directory
tree of the Release file. Most commonly, this is Debian. Spec‐
ifying this origin in the APT preferences file would require the
line:
Pin: release o=Debian
Label: this 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(5) 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.
The Pin-Priority: line in each APT preferences record is optional. If
omitted, APT assigs a priority of 1 less than the last value specified
on a previous line beginning with Pin-Priority: release ....
EXAMPLES
The following examples make use of the component names "stable", "test‐
ing", and "unstable", but these are obviously defined by the vendor and
are determined by the repository layout.
Tracking a "STABLE" distribution
The following APT preferences file will cause APT to assign a priority
higher than the default (500) to all package versions belonging to a
"stable" distribution and a prohibitively low priority to package ver‐
sions belonging to other distributions.
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
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
("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 a "TESTING" or "UNSTABLE" distribution
The following APT preferences file will cause APT to assign a high pri‐
ority to package versions from the testing distribution, a lower prior‐
ity to package versions from the unstable distribution, and a prohibi‐
tively low priority to package versions from other Debian distribu‐
tions.
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
SEE ALSOapt-get(8)apt-cache(8)apt.conf(5)sources.list(5)BUGS
Reporting bugs in APT-RPM is best done in the APT-RPM mailinglist at
http://apt-rpm.org/mailinglist.shtml.
AUTHOR
Maintainer and contributor information can be found in the credits page
http://apt-rpm.org/about.shtml of APT-RPM.
APT-RPM 14 Jun 2006 APT_PREFERENCES(5)
