Upgrade-system offers a convenient way to keep a Debian system up-to-date, yet free from accumulated cruft such as obsolete libraries.

It is particularly useful on systems that mix packages from different releases (stable/testing/unstable) and on desktop systems where packages are frequently installed or removed according to evolving user tastes.

By default, it is configured to purge all packages that are not listed as another package's dependency. Less drastic settings are possible by editing /etc/upgrade-system.conf(5).