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[apt-legacy.git] / doc / apt_preferences.5

.\"     Title: apt_preferences
.\"    Author: APT team
.\" Generator: DocBook XSL Stylesheets v1.71.0 <http://docbook.sf.net/>
.\"      Date: 29 February 2004
.\"    Manual: 
.\"    Source: Linux
.\"
.TH "APT_PREFERENCES" "5" "29 February 2004" "Linux" ""
.\" disable hyphenation
.nh
.\" disable justification (adjust text to left margin only)
.ad l
.SH "NAME"
apt_preferences \- Preference control file for APT
.SH "DESCRIPTION"
.PP
The APT preferences file
\fI/etc/apt/preferences\fR
can be used to control which versions of packages will be selected for installation.
.PP
Several versions of a package may be available for installation when the
\fBsources.list\fR(5)
file contains references to more than one distribution (for example,
stable
and
testing). APT assigns a priority to each version that is available. Subject to dependency constraints,
\fBapt\-get\fR
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.
.PP
Several instances of the same version of a package may be available when the
\fBsources.list\fR(5)
file contains references to more than one source. In this case
\fBapt\-get\fR
downloads the instance listed earliest in the
\fBsources.list\fR(5)
file. The APT preferences file does not affect the choice of instance, only the choice of version.
.SS "APT's Default Priority Assignments"
.PP
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
\fBapt\-get\fR
command line or in the APT configuration file
\fI/etc/apt/apt.conf\fR. For example,
.sp
.RS 3n
.nf
\fBapt\-get install \-t testing \fR\fB\fIsome\-package\fR\fR
.fi
.RE
.sp

.sp
.RS 3n
.nf
APT::Default\-Release "stable";
.fi
.RE
.sp
.PP
If the target release has been specified then APT uses the following algorithm to set the priorities of the versions of a package. Assign:
.PP
priority 100
.RS 3n
to the version that is already installed (if any).
.RE
.PP
priority 500
.RS 3n
to the versions that are not installed and do not belong to the target release.
.RE
.PP
priority 990
.RS 3n
to the versions that are not installed and belong to the target release.
.RE
.PP
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.
.PP
APT then applies the following rules, listed in order of precedence, to determine which version of a package to install.
.TP 3n
\(bu
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.)
.TP 3n
\(bu
Install the highest priority version.
.TP 3n
\(bu
If two or more versions have the same priority, install the most recent one (that is, the one with the higher version number).
.TP 3n
\(bu
If two or more versions have the same priority and version number but either the packages differ in some of their metadata or the
\-\-reinstall
option is given, install the uninstalled one.
.sp
.RE
.PP
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
\fBsources.list\fR(5)
file (priority 500 or 990). Then the package will be upgraded when
\fBapt\-get install \fR\fB\fIsome\-package\fR\fR
or
\fBapt\-get upgrade\fR
is executed.
.PP
More rarely, the installed version of a package is
\fImore\fR
recent than any of the other available versions. The package will not be downgraded when
\fBapt\-get install \fR\fB\fIsome\-package\fR\fR
or
\fBapt\-get upgrade\fR
is executed.
.PP
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
\fBapt\-get install \fR\fB\fIsome\-package\fR\fR
or
\fBapt\-get upgrade\fR
is executed, because at least
\fIone\fR
of the available versions has a higher priority than the installed version.
.SS "The Effect of APT Preferences"
.PP
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.
.TP 3n
\(bu
The specific form assigns a priority (a "Pin\-Priority") to a specified package and specified version or version range. For example, the following record assigns a high priority to all versions of the
\fIperl\fR
package whose version number begins with "5.8".
.sp
.RS 3n
.nf
Package: perl
Pin: version 5.8*
Pin\-Priority: 1001
.fi
.RE
.TP 3n
\(bu
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
\fIRelease\fR
file) or to all of the package versions coming from a particular Internet site, as identified by the site's fully qualified domain name.
.sp
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.
.sp
.RS 3n
.nf
Package: *
Pin: origin ""
Pin\-Priority: 999
.fi
.RE
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
\fIRelease\fR
file. What follows the "Origin:" tag in a
\fIRelease\fR
file is not an Internet address but an author or vendor name, such as "Debian" or "Ximian".
.sp
The following record assigns a low priority to all package versions belonging to any distribution whose Archive name is "unstable".
.sp
.RS 3n
.nf
Package: *
Pin: release a=unstable
Pin\-Priority: 50
.fi
.RE
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".
.sp
.RS 3n
.nf
Package: *
Pin: release a=stable, v=3.0
Pin\-Priority: 500
.fi
.RE
.sp
.RE
.SS "How APT Interprets Priorities"
.PP
Priorities (P) assigned in the APT preferences file must be positive or negative integers. They are interpreted as follows (roughly speaking):
.PP
P > 1000
.RS 3n
causes a version to be installed even if this constitutes a downgrade of the package
.RE
.PP
990 < P <=1000
.RS 3n
causes a version to be installed even if it does not come from the target release, unless the installed version is more recent
.RE
.PP
500 < P <=990
.RS 3n
causes a version to be installed unless there is a version available belonging to the target release or the installed version is more recent
.RE
.PP
100 < P <=500
.RS 3n
causes a version to be installed unless there is a version available belonging to some other distribution or the installed version is more recent
.RE
.PP
0 < P <=100
.RS 3n
causes a version to be installed only if there is no installed version of the package
.RE
.PP
P < 0
.RS 3n
prevents the version from being installed
.RE
.PP
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.
.PP
For example, suppose the APT preferences file contains the three records presented earlier:
.sp
.RS 3n
.nf
Package: perl
Pin: version 5.8*
Pin\-Priority: 1001

Package: *
Pin: origin ""
Pin\-Priority: 999

Package: *
Pin: release unstable
Pin\-Priority: 50
.fi
.RE
.PP
Then:
.TP 3n
\(bu
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
\fIany\fR
5.8* version of
perl
is available and the installed version is 5.9*, then
perl
will be downgraded.
.TP 3n
\(bu
A version of any package other than
perl
that is available from the local system has priority over other versions, even versions belonging to the target release.
.TP 3n
\(bu
A version of a package whose origin is not the local system but some other site listed in
\fBsources.list\fR(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.
.sp
.RE
.SS "Determination of Package Version and Distribution Properties"
.PP
The locations listed in the
\fBsources.list\fR(5)
file should provide
\fIPackages\fR
and
\fIRelease\fR
files to describe the packages available at that location.
.PP
The
\fIPackages\fR
file is normally found in the directory
\fI.../dists/\fR\fI\fIdist\-name\fR\fR\fI/\fR\fI\fIcomponent\fR\fR\fI/\fR\fI\fIarch\fR\fR: for example,
\fI.../dists/stable/main/binary\-i386/Packages\fR. 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:
.PP
the Package: line
.RS 3n
gives the package name
.RE
.PP
the Version: line
.RS 3n
gives the version number for the named package
.RE
.PP
The
\fIRelease\fR
file is normally found in the directory
\fI.../dists/\fR\fI\fIdist\-name\fR\fR: for example,
\fI.../dists/stable/Release\fR, or
\fI.../dists/woody/Release\fR. It consists of a single multi\-line record which applies to
\fIall\fR
of the packages in the directory tree below its parent. Unlike the
\fIPackages\fR
file, nearly all of the lines in a
\fIRelease\fR
file are relevant for setting APT priorities:
.PP
the Archive: line
.RS 3n
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
\fIRelease\fR
file are in a
stable
archive. Specifying this value in the APT preferences file would require the line:
.sp
.RS 3n
.nf
Pin: release a=stable
.fi
.RE
.RE
.PP
the Version: line
.RS 3n
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.
.sp
.RS 3n
.nf
Pin: release v=3.0
Pin: release a=stable, v=3.0
Pin: release 3.0
.fi
.RE
.RE
.PP
the Component: line
.RS 3n
names the licensing component associated with the packages in the directory tree of the
\fIRelease\fR
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 preferences file would require the line:
.sp
.RS 3n
.nf
Pin: release c=main
.fi
.RE
.RE
.PP
the Origin: line
.RS 3n
names the originator of the packages in the directory tree of the
\fIRelease\fR
file. Most commonly, this is
Debian. Specifying this origin in the APT preferences file would require the line:
.sp
.RS 3n
.nf
Pin: release o=Debian
.fi
.RE
.RE
.PP
the Label: line
.RS 3n
names the label of the packages in the directory tree of the
\fIRelease\fR
file. Most commonly, this is
Debian. Specifying this label in the APT preferences file would require the line:
.sp
.RS 3n
.nf
Pin: release l=Debian
.fi
.RE
.RE
.PP
All of the
\fIPackages\fR
and
\fIRelease\fR
files retrieved from locations listed in the
\fBsources.list\fR(5)
file are stored in the directory
\fI/var/lib/apt/lists\fR, or in the file named by the variable
Dir::State::Lists
in the
\fIapt.conf\fR
file. For example, the file
\fIdebian.lcs.mit.edu_debian_dists_unstable_contrib_binary\-i386_Release\fR
contains the
\fIRelease\fR
file retrieved from the site
debian.lcs.mit.edu
for
binary\-i386
architecture files from the
contrib
component of the
unstable
distribution.
.SS "Optional Lines in an APT Preferences Record"
.PP
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.
.PP
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 line beginning with
Pin\-Priority: release ....
.SH "EXAMPLES"
.SS "Tracking Stable"
.PP
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 versions belonging to other
Debian
distributions.
.sp
.RS 3n
.nf
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
.fi
.RE
.sp
.PP
With a suitable
\fBsources.list\fR(5)
file and the above preferences file, any of the following commands will cause APT to upgrade to the latest
stable
version(s).
.sp
.RS 3n
.nf
apt\-get install \fIpackage\-name\fR
apt\-get upgrade
apt\-get dist\-upgrade
.fi
.RE
.sp
.PP
The following command will cause APT to upgrade the specified package to the latest version from the
testing
distribution; the package will not be upgraded again unless this command is given again.
.sp
.RS 3n
.nf
apt\-get install \fIpackage\fR/testing
.fi
.RE
.sp
.SS "Tracking Testing or Unstable"
.PP
The following APT preferences file will cause APT to assign a high priority to package versions from the
testing
distribution, a lower priority to package versions from the
unstable
distribution, and a prohibitively low priority to package versions from other
Debian
distributions.
.sp
.RS 3n
.nf
Package: *
Pin: release a=testing
Pin\-Priority: 900

Package: *
Pin: release a=unstable
Pin\-Priority: 800

Package: *
Pin: release o=Debian
Pin\-Priority: \-10
.fi
.RE
.sp
.PP
With a suitable
\fBsources.list\fR(5)
file and the above preferences file, any of the following commands will cause APT to upgrade to the latest
testing
version(s).
.sp
.RS 3n
.nf
apt\-get install \fIpackage\-name\fR
apt\-get upgrade
apt\-get dist\-upgrade
.fi
.RE
.sp
.PP
The following command will cause APT to upgrade the specified package to the latest version from the
unstable
distribution. Thereafter,
\fBapt\-get upgrade\fR
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.
.sp
.RS 3n
.nf
apt\-get install \fIpackage\fR/unstable
.fi
.RE
.sp
.SH "SEE ALSO"
.PP
\fBapt\-get\fR(8)
\fBapt\-cache\fR(8)
\fBapt.conf\fR(5)
\fBsources.list\fR(5)
.SH "BUGS"
.PP
[1]\&\fIAPT bug page\fR. If you wish to report a bug in APT, please see
\fI/usr/share/doc/debian/bug\-reporting.txt\fR
or the
\fBreportbug\fR(1)
command.
.SH "AUTHOR"
.PP
\fBAPT team\fR
.sp -1n
.IP "" 3n
Author.
.SH "REFERENCES"
.TP 3
1.\ APT bug page
\%http://bugs.debian.org/src:apt