Two special package types, meta and virtual, also exist. Meta packages are standard binary packages
that do not contain any files, but depend on a number of other packages. Installation of a
meta package results in the automatic installation of all packages that they depend on. These can
be used as a convenient method for installing a set of related packages.
Virtual packages do not actually exist as files but can be referenced in the package interrelationship
fields. They are most commonly used in cases where more than one package fulfills a specific requirement.
Packages with this requirement can reference the virtual package in their Depends field, and
packages that satisfy this dependency reference it in their Provides field.
Because most programs providing a virtual package are mutually exclusive, they also include the
virtual package in their Conflicts field to prevent the installation of conflicting packages. An
example of this is the mail-transport-agent virtual package, which is required by most system programs
in order to send mail.
An easy way to browse the list of available packages is through the Debian Web site at
www.debian.org/distrib/packages. The current release comes with more than
18,200 packages.
Debian Package Management Tools
Perhaps the most interesting and well-known part of the Debian package management system is
APT, the Advanced Package Tool.
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