6.8 What is a Virtual Package?

A virtual package is a generic name that applies to any one of a group of packages, all of which provide similar basic functionality. For example, both the tin and trn programs are news readers, and should therefore satisfy any dependency of a program that required a news reader on a system, in order to work or to be useful. They are therefore both said to provide the "virtual package" called news-reader.

Similarly, smail and sendmail both provide the functionality of a mail transport agent. They are therefore said to provide the virtual package, "mail transport agent". If either one is installed, then any program depending on the installation of a mail-transport-agent will be satisfied by the existence of this virtual package.

Debian provides a mechanism so that, if more than one package which provide the same virtual package is installed on a system, then system administrators can set one as the preferred package. The relevant command is update-alternatives, and is described further in Some users like mawk, others like gawk; some like vim, others like elvis; some like trn, others like tin; how does Debian support diversity?, Section 10.10.