Editing APT (software) (section)

===Installing software===
The user indicates one or more packages to be installed. Each package name is phrased as just the name portion of the package, not a fully qualified filename (for instance, in a Debian system, <code>libc6</code> would be the argument provided, not <code>libc6_1.9.6-2.deb</code>). Notably, APT automatically gets and installs packages upon which the indicated package depends (if necessary). This was an original distinguishing characteristic of APT-based package management systems, as it avoided installation failure due to missing dependencies, a type of [[dependency hell]].

Another distinction is the retrieval of packages from remote repositories. APT uses a location configuration file (<code>/etc/apt/sources.list</code>) to locate the desired packages, which might be available on the network or a removable storage medium, for example, and retrieve them, and also obtain information about available (but not installed) packages.

APT provides other command options to override decisions made by apt-get's conflict resolution system. One option is to force a particular version of a package. This can downgrade a package and render dependent software inoperable, so the user must be careful.

Finally, the <code>apt_preferences</code> mechanism allows the user to create an alternative installation policy for individual packages.

The user can specify packages using a POSIX [[regular expression]].

APT searches its cached list of packages and lists the dependencies that must be installed or updated.

APT retrieves, configures and installs the dependencies automatically.

[[dpkg|Triggers]] are the treatment of deferred actions.