The Debian GNU/Linux FAQ
Chapter 6 - Basics of the Debian package management system

6.1 What is a Debian package?

Packages generally contain all of the files necessary to implement a set of related commands or features. There are two types of Debian packages:

• Binary packages, which contain executables, configuration files, man/info pages, copyright information, and other documentation. These packages are distributed in a Debian-specific archive format (see What is the format of a Debian binary package?, Section 6.2); they are usually distinguished by having a '.deb' file extension. Binary packages can be unpacked using the Debian utility dpkg; details are given in its manual page.

• Source packages, which consist of a .dsc file describing the source package (including the names of the following files), a .orig.tar.gz file that contains the original unmodified source in gzip-compressed tar format and usually a .diff.gz file that contains the Debian-specific changes to the original source. The utility dpkg-source packs and unpacks Debian source archives; details are provided in its manual page.

Installation of software by the package system uses "dependencies" which are carefully designed by the package maintainers. These dependencies are documented in the control file associated with each package. For example, the package containing the GNU C compiler (gcc) "depends" on the package binutils which includes the linker and assembler. If a user attempts to install gcc without having first installed binutils, the package management system (dpkg) will send an error message that it also needs binutils, and stop installing gcc. (However, this facility can be overridden by the insistent user, see dpkg(8).) See more in What is meant by saying that a package Depends, Recommends, Suggests, Conflicts, Replaces or Provides another package?, Section 6.9 below.

Debian's packaging tools can be used to:

• manipulate and manage packages or parts of packages,

• aid the user in the break-up of packages that must be transmitted through a limited-size medium such as floppy disks,

• aid developers in the construction of package archives, and

• aid users in the installation of packages which reside on a remote FTP site.