command for upgrading and sanitizing a Debian system

 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).