6.2.5 Tracking a distribution using APT

To track the testing distribution as it changes, make your /etc/apt/preferences file look like this:

     Package: *
     Pin: release a=testing
     Pin-Priority: 800
     
     Package: *
     Pin: release a=stable
     Pin-Priority: 600

Note that tracking the testing distribution can have the side effect of delaying the installation of packages containing security fixes. Such packages are uploaded to unstable and migrate to testing only after a delay.

See apt_preferences(5) for more complicated examples which will allow you, for example, to track testing while installing selected packages from unstable.

Examples which lock particular packages at particular versions while tracking other packages as they are released are available in the examples subdirectory as preferences.testing and preferences.unstable.

If you mix distributions, e.g., testing with stable or unstable with stable, you will eventually pull in core packages such as libc6 from testing or unstable and there is no guarantee that these will not contain bugs. You have been warned.

Another example, preferences.stable, forces all packages to be downgraded to stable.

Downgrading from a later release of a package to an earlier one is not officially supported in Debian. However, you may find that you have to downgrade a specific package in order to re-install a version of a package that works when a new version malfunctions. You may find these previous package files locally in /var/cache/apt/archives/ or remotely at https://snapshot.debian.net/. See also Rescue using dpkg, Section 6.3.3.

Downgrading from a later release of a distribution to an earlier one is not officially supported either and is very likely to cause problems. However, this may be worth trying as a last resort if you are desperate.