The Advanced Packaging Tool, or APT, is a Free software user interface that works with core libraries to handle the installation and removal of software on the Debian GNU/Linux computer operating system and its variants.

APT was originally designed as a front-end for dpkg to work with Debian's .deb packages, but it has since been modified to also work with the RPM Package Manager system via apt-rpm. The Fink project has ported APT to Mac OS X for some of its own package management tasks, and APT is also available in OpenSolaris (included in Nexenta OS distribution). The Telesphoreo is a project dedicated to porting APT to smartphone devices - currently the iPhone.

Usage

There is no single "apt" program; apt is itself the package name containing the set of tools (and requiring the libraries) that support its functionality. A significant part of apt is a C++ library of functions (another package known as libapt) which are used by these related front-end programs for dealing with packages, such as apt-get and apt-cache. They are commonly used in examples due to their simplicity and ubiquity; apt-get and apt-cache are of "important" priority in all current Debian releases, and are therefore installed in a default Debian installation. Apt can be functionally considered to be a front-end to dpkg, and a friendlier front end to this than dselect. While dpkg performs actions on individual packages, apt tools manage relations (especially dependencies) between them, as well as sourcing and management of higher-level versioning decisions (release tracking and version pinning).

APT is often hailed as one of Debian's best features.

A major feature in APT is the way it calls dpkg - it does topological sorting of the list of packages to be installed or removed and calls dpkg in the best possible sequence. In some cases it utilizes the --force options in dpkg. However, it only does this when it is unable to calculate how to avoid the reason dpkg requires the action to be forced.

The most used apt-get commands are apt-get install package name (frequently the package name is simply the name of the desired executable application), apt-get update, upgrade and apt-get dist-upgrade.

Installation of software

An install directive is followed by the name of one or more packages desired for installation. Each package name is phrased as just the name portion of the package, not a fully qualified filename (for instance, in a Debian GNU/Linux system, libc6 would be the argument provided, not libc6_1.9.6-2.deb). Notably, all packages containing dependencies required by the package(s) specified for installation will also be automatically retrieved and installed. This was an original distinguishing characteristic of apt-based package management systems whereby software installation failure due to missing dependencies, a type of DLL-hell, was specifically avoided.