New apt_preferences from Thomas Hood, Susan Kleinmann

Author: jgg
Date: 2003-01-11 07:20:32 GMT
New apt_preferences from Thomas Hood, Susan Kleinmann

diff --git a/doc/apt_preferences.5.sgml b/doc/apt_preferences.5.sgml
index cb4d0c5a9d6e83a08d38e75a5b313374d8515af5..2d9c9a0526a509cfb977436bb99e5e5c63040771 100644 (file)
--- a/doc/apt_preferences.5.sgml
+++ b/doc/apt_preferences.5.sgml
@@ -8,221 +8,541 @@
 
 <refentry>
  &apt-docinfo;
 
 <refentry>
  &apt-docinfo;

- 
+

  <refmeta>
    <refentrytitle>apt_preferences</>
    <manvolnum>5</>
  </refmeta>
  <refmeta>
    <refentrytitle>apt_preferences</>
    <manvolnum>5</>
  </refmeta>

- 
+

  <!-- Man page title -->
  <refnamediv>
     <refname>apt_preferences</>
     <refpurpose>Preference control file for APT</>
  </refnamediv>
  <!-- Man page title -->
  <refnamediv>
     <refname>apt_preferences</>
     <refpurpose>Preference control file for APT</>
  </refnamediv>

- 
- <RefSect1><Title>Description</>
-   <para>
-   The APT preferences file controls various aspects of the APT system. 
-   It is meant to be user editable and manipulatable from software. The file
-   consists of a number of records formed like the dpkg status file, space
-   seperated sections of text with at the start of each line tags seperated 
-   by a colon. It is stored in <filename>/etc/apt/preferences</>.
- </RefSect1>

 
 

- <RefSect1><Title>Versioning</>
-   <para>
-   One purpose of the preferences file is to let the user select which version
-   of a package will be installed. This selection can be made in a number of
-   ways that fall into three categories, version, release and origin.   
-   <para>
-   Selection by version can be done by exact match or prefix match. The format
-   is <literal/2.1.2/ or <literal/2.2*/ for a prefix match. Matching by prefix 
-   can be used to ignore the <literal/r/ in the Debian release versioning, like
-   <literal/2.1r*/ or to ignore Debian specific revisions, <literal/1.1-*/.
-   When matching versions with a prefix the highest matching version will
-   always be picked.
-   <para>
-   Selection by release is more complicated and has three forms. The primary
-   purpose of release selections is to identify a set of packages that match
-   a specific vendor, or release (ie Debian 2.1). The first two forms are 
-   shortcuts intended for quick command line use. If the first character of the
-   specification is a digit then it is considered to be a release version match, 
-   otherwise a release label match. Specifications which contain equals are
-   full release data matches and are a comma seperated list of one letter keys
-   followed by an equals then by the string. Examples:
-<informalexample><programlisting>
-v=2.1*,o=Debian,c=main
-l=Debian
-a=stable
-</programlisting></informalexample>   
-   <para>
-   The data for these matches are taken from the <filename/Release/ files
-   that APT downloads during an <literal/update/. The available keys are:
-   <VariableList>
-     <VarListEntry><term>a= Archive</term>
-     <ListItem><Para>
-     This is the common name we give our archives, such as <literal/stable/ or
-     <literal/unstable/. The special name <literal/now/ is used to designate
-     the set of packages that are currently installed.
-     </VarListEntry>
-     
-     <VarListEntry><term>c= Component</term>
-     <ListItem><Para>
-     Referes to the sub-component of the archive, <literal/main/, 
-     <literal/contrib/ etc. Component may be omitted if there are no 
-     components for this archive.
-     </VarListEntry>
-     
-     <VarListEntry><term>v= Version</term>
-     <ListItem><Para>
-     This is a version string with the same properties as in the Packages file.
-     It represents the release level of the archive. Typical Debian release
-     numbers look like <literal/2.1r2/ with the r designating the release of 
-     2.1. New releases are limited to security updates and other important
-     changes.
-     </VarListEntry>
-
-     <VarListEntry><term>o= Origin</term>
-     <ListItem><Para>
-     This specifies who is providing this archive. In the case of Debian the
-     string will read <literal/Debian/. Other providers may use their own 
-     string.
-     </VarListEntry>
-
-     <VarListEntry><term><term>l= Label</term>
-     <ListItem><Para>
-     This carries the encompassing name of the distribution. For Debian proper
-     this field reads <literal/Debian/. For derived distributions it should 
-     contain their proper name.
-     </VarListEntry>
-   </VariableList>   
-   <para>
-   The final selection method is by origin. This is simply the site name
-   of the originating package files. The empty string is used for file URIs.
-   <para>
-   Version selection, particularly the latter two methods, are used in many
-   different parts of APT, not just the preferences file.
- </RefSect1>
- 
- <RefSect1><Title>Candidate Version Policy</>
-   <para>
-   Internally APT maintains a list of all available versions for all packages.
-   If you place multiple releases or vendors in your &sources-list; file then
-   these features are available. By default APT selects the highest version
-   from all automatic sources. Some sources, such as 
-   <filename>project/experimental</> are marked Not Automatic - these fall 
-   to the bottom of the selection pile.
-   <para>
-   When deciding what version to use APT assigns a priority to each available
-   version of the package. It then does two things, first it selects
-   the highest priorty version that is newer than the installed version of the 
-   package, then it selects the highest priority version that is older than
-   the installed version. Next, if the older versions have a priority greater
-   than 1000 they are compared with the priority of the upgrade set, the larger
-   becomes the selected result. Otherwise the downgrade versions are ignored
-   and the highest priority of the ugprade set is selected.
-   <para>
-   It is possible to think of the priorities in strata:
-   <VariableList>
-     <VarListEntry><term>above 1000</term>
-     <ListItem><Para>
-     Downgradable priorities
-     </VarListEntry>
-     
-     <VarListEntry><term>1000</term>
-     <ListItem><Para>
-     The downgrade prevention barrier
-     </VarListEntry>
-     
-     <VarListEntry><term>101 to 999</term>
-     <ListItem><Para>
-     Standard priorities. 990 is the priority set by the 
-     <option/--target-release / &apt-get; option. 989 is the start for auto
-     priorities and 500 are all the default package files.
-     </VarListEntry>
-     
-     <VarListEntry><term>100</term>
-     <ListItem><Para>
-     The currently installed version
-     </VarListEntry>
-
-     <VarListEntry><term>0 to 99</term>
-     <ListItem><Para>
-     Non automatic priorities. These are only used if the package
-     is not installed and there is no other version available.
-     </VarListEntry>
-
-     <VarListEntry><term>less than 0</term>
-     <ListItem><Para>
-     The version is never selected.
-     </VarListEntry>
-   </VariableList>   
-   <para>
-   Giving a pin a priority greater than 1000 will allow APT to downgrade
-   in order to get to that version.   
-   <para>
-   Each package may be pinned to a specific version and each Packages file
-   has a priority for every package inside. The highest priority assigned
-   to a package is the one that is used.
-   <para>
-   A package pin looks like this:
-<informalexample><programlisting>
-Package: apt
-Pin: version 0.4.0
+<RefSect1><Title>Description</>
+<para>
+The APT preferences file <filename>/etc/apt/preferences</>
+can be used to control which version of a package 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>);
+furthermore, several instances of the same version of a package may be
+available when the file contains references to more than one download site
+for a particular distribution.  APT assigns a "priority" to each instance
+that is available.  (In what follows, an "instance" will be an instance of
+a package that is available according to &sources-list;.)
+Subject to dependency constraints, <command>apt-get</command> installs the
+instance with the highest priority.  If two instances have the same
+priority then it installs the more recent one, that is, the one with the
+higher version number.
+</para>
+
+<para>The APT preferences file overrides the priorities that APT assigns
+to package instances by default, thus giving the user control over which
+one is selected for installation.
+</para>
+
+<RefSect2><Title>APT's Default Priority Assignments</>
+
+<para>If there is no preferences file, or if there is no entry in the file
+that applies to a particular instance, then the priority assigned to that
+instance is the priority of the distribution to which that instance
+belongs.  It is possible to single out a distribution, called the
+"target release", which receives a higher priority than other distributions.
+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>.
+For example,
+
+<programlisting>
+# Command to install the <literal/testing/ version of <replaceable>some-package</replaceable>
+<command>apt-get install -t testing <replaceable>some-package</replaceable></command>
+</programlisting>
+
+<programlisting>
+# Configuration setting to make <literal/stable/ the target release
+APT::Default-Release "stable";
+</programlisting>
+</para>
+
+<para>If a target release has been specified then APT uses the following
+algorithm to set the priorities of the instances of a package.  Assign:
+
+<variablelist>
+<varlistentry>
+<term>priority 100</term>
+<listitem><simpara>to the instance that is already installed (if any).
+</simpara></listitem>
+</varlistentry>
+<varlistentry>
+<term>priority 500</term>
+<listitem><simpara>to the instances that are not installed
+and do not belong to the target release.
+</simpara></listitem>
+</varlistentry>
+<varlistentry>
+<term>priority 990</term>
+<listitem><simpara>to the instances that are not installed
+and belong to the target release.
+</simpara></listitem>
+</varlistentry>
+</variablelist>
+</para>
+
+<para>If no target release has been specified then APT simply assigns
+priority 100 to all installed package instances and priority 500 to all
+uninstalled package instances.
+</para>
+
+<para>APT then applies the following rules, listed in order of precedence,
+to determine which instance of a package to install.
+
+<itemizedlist>
+<listitem><simpara>Never downgrade unless the priority of an available instance
+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.)
+</simpara></listitem>
+<listitem><simpara>Install the highest priority instance.
+</simpara></listitem>
+<listitem><simpara>If two or more instances have the same priority,
+install the most recent one.
+</simpara></listitem>
+<listitem><simpara>If two or more instances have the same version number,
+install the one whose source is listed earliest in &sources-list;.
+(The installed instance, if there is one, is always preferred in such a
+comparison unless <command>apt-get --reinstall</command> is used.)
+</simpara></listitem>
+</itemizedlist>
+</para>
+
+<para>In a typical situation, the installed instance of a package (priority 100)
+is not as recent as one of the instances available from the sources listed in
+the &sources-list; file (priority 500 or 990).  Then the package will be
+upgraded with the command:
+<command>apt-get install</command> or <command>apt-get dist-upgrade</command>.
+</para>
+
+<para>Rarely, the installed instance of a package is <emphasis/more/ recent
+than any of the other available instances.  The package will not be downgraded.
+</para>
+
+<para>Sometimes the installed instance 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,
+because at least <emphasis/one/ of the available instances has a higher
+priority than the installed instance.
+</para>
+
+</RefSect2>
+
+<RefSect2><Title>The Effect of APT Preferences</>
+
+<para>The APT preferences file allows the system administrator to customize
+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 pins a priority (a "Pin-Priority") to a
+specified package and specified version or version range.  For
+example, the following record pins a high priority to all versions of
+the <filename/perl/ package whose version number begins with
+"<literal/5.8/".
+</simpara>
+
+<programlisting>
+Package: perl
+Pin: version 5.8*
+Pin-Priority: 1001
+</programlisting>
+</listitem>
+
+<listitem><simpara>
+The "general" form pins 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/ file), or to all of the package
+instances coming from a particular Internet site, as identified by its
+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 causes APT to
+assign a high priority to all package instances 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/".
+This should not be confused with the "Origin:" of a distribution as
+specified in a <filename/Release/ file.  What follows the "Origin:" tag
+in a <filename/Release/ file is usually not an Internet site address
+but an author or vendor name, such as "Debian" or "Ximian".
+</simpara>
+
+<simpara>The following record causes APT to assign a low priority to all
+package versions belonging to any distribution whose "Archive"
+(<literal/a/) name is "<literal/unstable/".
+</simpara>
+
+<programlisting>
+Package: *
+Pin: release a=unstable
+Pin-Priority: 50
+</programlisting>
+
+<simpara>The following record causes APT to assign a high priority to all
+package versions belonging to any release whose "Archive" (<literal/a/)
+name is "<literal/stable/" and whose release "Version" (<literal/v/)
+number is "<literal/3.0/".
+</simpara>
+
+<programlisting>
+Package: *
+Pin: release a=unstable, v=3.0
+Pin-Priority: 50
+</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 &gt; 1000</term>
+<listitem><simpara>causes an instance to be installed
+even if this constitutes a downgrade of the package
+</simpara></listitem>
+</varlistentry>
+<varlistentry><term>990 &lt; P &lt;=1000</term>
+<listitem><simpara>causes an instance to be installed
+even if it does not come from the target release,
+unless the installed instance is more recent
+</simpara></listitem>
+</varlistentry>
+<varlistentry><term>500 &lt; P &lt;=990</term>
+<listitem><simpara>causes an instance to be installed
+unless there is an instance available belonging to the target release
+or the installed version is more recent
+</simpara></listitem>
+</varlistentry>
+<varlistentry><term>100 &lt; P &lt;=500</term>
+<listitem><simpara>causes an instance to be installed
+unless there is an instance available belonging to some other
+distribution or the installed version is more recent
+</simpara></listitem>
+<varlistentry><term>0 &lt;= P &lt;=100</term>
+<listitem><simpara>causes an instance to be installed
+only if there is no installed instance of the package
+</simpara></listitem>
+</varlistentry>
+<varlistentry><term>P &lt; 0</term>
+<listitem><simpara>prevents the instance from being installed
+</simpara></listitem>
+</varlistentry>
+</variablelist>
+</para>
+
+<para>If one of the specific-form records described above matches an
+available package instance, then that record determines the priority of
+the instance.  If two specific-form records match an available instance,
+then the first record encountered determines the priority.  If two
+general-form records match an available instance, then the first record
+encountered determines the priority.
+</para>
+
+<para>For example, suppose the APT preferences file contains the three
+records presented earlier:
+
+<programlisting>
+Package: perl
+Pin: version 5.8*

 Pin-Priority: 1001
 Pin-Priority: 1001

-</programlisting></informalexample>   
-   The first line specifies the package, the second gives the Pin specification
-   and the last gives the priority of this pin. The first word of the pin
-   specification may be version, release or origin, the remainder of the field
-   is described in the Versioning section above.
-   <para>
-   A default pin is how the priorities of package files are set. Any number
-   of default pins may be specified, the first matching default will select
-   the priority of the package file. Only release or origin may be used in 
-   the Pin specification since they match Packages files.
-<informalexample><programlisting>
+

 Package: *
 Package: *

-Pin: release v=2.1*
-Pin-Priority: 998
-</programlisting></informalexample>
-   <para>
-   If the Pin-Priority field is omitted then the priority defaults to 989 for
-   both cases.
-   
-   <RefSect2><title>Interesting Effects</>
-   <para>
-   Due to the downgrade prevention barrier at priority 1000 it is possible
-   that a lower priority version  will be selected if the higher priority 
-   would cause a downgrade. For instance, if package foo has versions
-   <literal/1.2/, <literal/1.1/ and <literal/1.0/ installed, with 
-   <literal/1.1/ being the currently installed version and the priorities of 
-   each version being 900, 100 and 950 repectively the winning version will be 
-   <literal/1.2/.
-   <para>
-   In practice this is often desired. A user may use a default pin to
-   make the stable distribution the default and then use the 
-   <option/--target-dist/ option with &apt-get; to select newer versions
-   from unstable. The packages that have been upgraded to unstable will
-   continue to follow the versions that are available in unstable since
-   the stable versions now fall below the downgrade prevention barrier.
-   <para>
-   If this is not desired then a default pin should be used to make unstable
-   have a priority less than 100.
-   <para>
-   Users of 3rd party add ons such as Helix GNOME can use this mechanism to
-   force the usage of Helix packages, or force the usage of Debian packages
-   by setting the priority of that source sufficiently high. It is even
-   possible to mass downgrade from one set of packages to another by
-   using a priority larger than 1000.
-   </RefSect2>
- </RefSect1>
-  
+Pin: origin ""
+Pin-Priority: 999
+
+Package: *
+Pin: release unstable
+Pin-Priority: 50
+</programlisting>
+
+Then:
+
+<itemizedlist>
+<listitem><simpara>The most recent available version of the <literal/perl/
+package will be installed, so long as that version's version number begins
+with "<literal/5.8/".  If <emphasis/any/ 5.8* version of <literal/perl/ is
+available and the installed version is 5.9*, then <literal/perl/ will be
+downgraded.</simpara></listitem>
+<listitem><simpara>An instance of any package other than <literal/perl/
+that is available from the local system has priority over other instances,
+even instances belonging to the target release.
+</simpara></listitem>
+<listitem><simpara>An instance 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/" distribution, is only installed if it is selected
+for installation and no instance 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 a system's &sources-list; file should provide
+<filename>Packages</filename> and <filename>Release</filename> files
+to describe the package instances 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:/ line</term>
+<listitem><simpara>gives the package name</simpara></listitem>
+</varlistentry>
+<varlistentry>
+<term>the <literal/Version:/ 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/ of
+the package instances in the directory tree below its parent.  Unlike the
+<filename/Packages/ file, nearly all of the lines in a <filename/Release/
+file are relevant for setting APT priorities:
+
+<variablelist>
+<varlistentry>
+<term>the <literal/Archive:/ line</term>
+<listitem><simpara>names the archive to which all the package instances
+in the directory tree belong.  For example, the line
+<literal/Archive: stable/ specifies that all of the packages in the directory
+tree below the parent of the <filename/Release/ file are in the
+<literal/stable/ 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/Version:/ line</term>
+<listitem><simpara>names the release version.  For example, the
+package instances in the tree might belong to Debian GNU/Linux release
+version 3.0.  There is normally no version number for the "testing" and
+"unstable" distributions because they have not yet been released.
+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:/ line</term>
+<listitem><simpara>names the licensing component associated with the
+package instances in the directory tree of the <filename/Release/
+file.  For example, the line <literal/Component: main/ specifies that
+all the instances in the directory tree are from the <literal/main/
+component, meaning 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:/ line</term>
+<listitem><simpara>names the producer of the package instances in the
+directory tree of the <filename/Release/ file.  Most commonly, this is
+<literal/Debian/.  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:/ line</term>
+<listitem><simpara>seems redundant.  Most commonly, this is
+<literal/Debian/.  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 kept
+in the directory <filename>/var/lib/apt/lists</filename>, or in the file named
+by the variable <literal/Dir::State::Lists/ in the <filename/apt.conf/ 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/ for <literal/binary-i386/ architecture
+files from the <literal/contrib/ component of the <literal/unstable/
+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:/.
+This provides an opportunity to comment on the record.
+</para>
+
+<para>The <literal/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 <literal/Pin-Priority: release .../.
+</para>
+</RefSect2>
+</RefSect1>
+
+<RefSect1><Title>Examples</>
+<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/ distribution and a prohibitively low priority to
+package versions belonging to other <literal/Debian/ distributions.
+
+<programlisting>
+Package: *
+Pin: release a=stable
+Pin-Priority: 900
+
+Explanation: Uninstall or do not install any Debian-originated
+Explanation: instances other than those in the stable distro
+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/ 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/ distribution;
+further upgrades will not occur automatically, however.
+
+<programlisting>
+apt-get install <replaceable>package</replaceable>/testing
+</programlisting>
+</RefSect2>
+
+ <RefSect2><Title>Tracking Testing</Title>
+
+<para>The following APT preferences file will cause APT to assign
+a high priority to package versions from the <literal/testing/
+distribution, a lesser priority to package versions from the
+<literal/unstable/ distribution, and a prohibitively low priority
+to package versions from other <literal/Debian/ 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 the above APT preferences file, any of the
+following commands will cause APT to upgrade to the latest
+<literal/testing/ 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/ distribution.
+Thereafter, <command>apt-get dist-upgrade</command> and the others
+<emphasis/will/ cause upgrade of the package to the latest
+<literal/unstable/ version.
+
+<programlisting>
+apt-get install <replaceable>package</replaceable>/unstable
+</programlisting>
+</para>
+
+</RefSect2>
+</RefSect1>
+

  <RefSect1><Title>See Also</>
  <RefSect1><Title>See Also</>

-   <para>
-   &apt-cache; &apt-conf;
+<para>
+&apt-get; &apt-cache; &apt-conf; &sources-list;

  </RefSect1>
 
  &manbugs;
  &manauthor;
  </RefSect1>
 
  &manbugs;
  &manauthor;

- 
+

 </refentry>
 </refentry>