Editing APT (software) (section)

===Update, upgrade and dist-upgrade===
Usage modes of <code>apt</code> and <code>apt-get</code> that facilitate updating installed packages include:
* <code>update</code> is used to resynchronize the '''package index''' files from their sources. The lists of available packages are fetched from the location(s) specified in <code>/etc/apt/sources.list</code>. For example, when using a Debian archive, this command retrieves and scans the <code>Packages.gz</code> files, so that information about new and updated packages is available.
* <code>upgrade</code> is used to install the newest versions of all packages currently installed on the system from the sources enumerated in <code>/etc/apt/sources.list</code>. Packages currently installed with new versions available are retrieved and upgraded; under no circumstances are currently installed packages removed, or packages not already installed retrieved and installed. New versions of currently installed packages that cannot be upgraded without changing the install status of another package will be left at their current version.
* <code>full-upgrade</code> (<code>apt</code>) and <code>dist-upgrade</code> (<code>apt-get</code>), in addition to performing the function of <code>upgrade</code>, also intelligently handles changing dependencies with new versions of packages; <code>apt</code> and <code>apt-get</code> have a "smart" conflict resolution system, and will attempt to upgrade the most important packages at the expense of less important ones if necessary. The <code>/etc/apt/sources.list</code> file contains a list of locations from which to retrieve desired package files.<ref name="manpage"/> [[aptitude (software)|aptitude]] has a smarter <code>dist-upgrade</code> feature called <code>full-upgrade</code>.<ref>{{cite web|url=http://forums.debian.net/viewtopic.php?f=10&t=39379|title=Discussion on dist-upgrade vs. full-upgrade|access-date=18 December 2021}}</ref>