Translation(s): English - Italiano

Apt is configured by several resources, including:

apt_preferences (APT pinning)

Debian Reference - Debian package management - 2.7.3. Tweaking candidate version
man 5 apt_preferences
man 5 apt.conf
man apt-config

When multiple Apt repositories are enabled, a package can exist in several of them. To know which one should be installed, Apt assigns priorities to packages. The default is


Pinning allows changing priorities for only some packages/repositories, so that you can:

<!> With a few exceptions (DebianBackports) it is not recommended to mix repositories/releases unless they were specially prepared . See DontBreakDebian.. Don't enable DebianUnstable repositories on DebianStable. When pinning, you must ensure compatibility of packages by yourself since Debian does not guarantee it.

To view the priority of a specific package, use apt-cache policy mypackage:

$ apt-cache policy claws-mail
  Installed : (none)
  Candidate : 3.14.1-3+b1
 Version table :
     3.17.1-1~bpo9+1 100
        100 stretch-backports/main amd64 Packages
     3.14.1-3+b1 500
        500 stretch/main amd64 Package

In the example above, the package that would be installed (Candidate) would be the older, 3.14 version from stretch/main. stretch-backports/main has a newer version 3.17, but a lower priority (100 vs 500 for stretch)

To view the global priority for each Apt source (repository):

$ apt-cache policy 
Package files: 
 # The default repository with a priority of 500
 500 stable/main amd64 Packages

 # The repository for Debian (security and grave bug fixes ~every 2 months)
 500 stable-updates/main amd64 Packages
     release o=Debian,a=oldstable-updates,n=stable-updates,l=Debian,c=main,b=amd64

 # The repository with short response time for security fixes
 500 stable/updates/main amd64 Packages
     release v=9,o=Debian,a=oldstable,n=stable,l=Debian-Security,c=main,b=amd64

 # The repository, comes with a default priority of 100
 100 stable-backports/main amd64 Packages
     release o=Debian Backports,a=stable-backports,n=stable-backports,l=Debian Backports,c=main,b=amd64

 # The priority of locally installed packages
 100 /var/lib/dpkg/status 
     release a=now

Force installation of a package from a repository

To tell Apt to install a package from stretch-backports, even if the package has a low priority:

apt install -t stretch-backports claws-mail

Note that the package will not be automatically upgraded when running an Apt Upgrade.

Always prefer packages from a repository

To always prefer packages from stretch-backports (and hence allow Apt Upgrades), set a higher priority for this package coming from the stretch-backports release. Edit the file /etc/apt/preferences.d/99debian-backports (create it):

Package: claws-mail
Pin: release a=stretch-backports
Pin-Priority: 900

Now installing the claws-mail package will install the version from  stretch-backports. Running an Apt Upgrade will automatically pick up newer versions from stable-backports. Running apt-cache policy again you would see:

Pinned packages:
     claws-mail -> 3.17.1-1~bpo9+1 with priority 900

Prevent/selective installation from third-party a repository

To prevent installation of newer packages from a third-party repository (DontBreakDebian), even if it has equal priority, edit the file /etc/apt/preferences.d/99my-custom-repository:

# Never prefer packages from the my-custom-repo repository
Package: *
Pin: origin o=my-custom-repo
Pin-Priority: 1

# Allow upgrading only my-specific-software from my-custom-repo
Package: my-specific-software
Pin: origin o=my-custom-repo
Pin-Priority: 500

File naming in /etc/apt/preferences.d/ is free but the last in alphabetical order takes precedence.

The * after Package: is not a wildcard, but a special case that means "everything". Wildcards are NOT supported. However, traling wildcards are accepted in versions (2.6* will match both 2.6 and 2.6.18).

Other pinning notes

In addition origin, you can pin packages based on other variables. apt-cache policy shows other variables that can be used as the Pin: key:

   1 stretch-backports/non-free i386 Packages
     release o=Debian Backports,a=stretch-backports,n=stretch-backports,l=Debian Backports,c=non-free,b=i386

These variables are provided by Release files in Debian repositories.

See also:


Apt accepts configuration files (without extension) in /etc/apt/apt.conf.d/. These are processed by Apt in numeric/alphabetical order. /etc/apt/apt.conf is also valid but deprecated.

These files can contain various directives:

If you really have to use FTP, this sets the FTP proxy:

   Proxy "ftp://proxy:2121/";
      "USER $(SITE_USER)@$(SITE)";
      "PASS $(SITE_PASS)";

CategoryPackageManagement | CategorySoftware | CategorySystemAdministration