apt-get – APT package handling utility
# apt-get update
Update is used to resynchronize the package index files from their sources. The indexes of available packages are fetched from the location(s) specified in /etc/apt/sources.list. For example, when using a Debian archive, this command retrieves and scans the Packages.gz files, so that information about new and updated packages is available. An update should always be performed before an upgrade or dist-upgrade. Please be aware that the overall progress meter will be incorrect as the size of the package files cannot be known in advance.
# apt-get upgrade
Upgrade is used to install the newest versions of all packages currently installed on the system from the sources enumerated in /etc/apt/sources.list. 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. An update must be performed first so that apt-get knows that new versions of packages are available.
# apt list –installed
List all packages installed.
# apt-get install Package_Name
Install is followed by one or more packages desired for installation or upgrading. Each package is a package name, not a fully qualified filename (for instance, in a Debian system, apt-utils would be the argument provided, not apt-utils_1.2.24_amd64.deb). All packages required by the package(s) specified for installation will also be retrieved and installed. The /etc/apt/sources.list file is used to locate the desired packages. If a hyphen is appended to the package name (with no intervening space), the identified package will be removed if it is installed. Similarly a plus sign can be used to designate a package to install. These latter features may be used to override decisions made by apt-get’s conflict
A specific version of a package can be selected for installation by following the package name with an equals and the version of the package to select. This will cause that version to be located and selected for install. Alternatively a specific distribution can be selected by following the package name with a slash and the version of the distribution or the Archive name (stable, testing, unstable).
Both of the version selection mechanisms can downgrade packages and must be used with care.
This is also the target to use if you want to upgrade one or more already-installed packages without upgrading every package you have on your system. Unlike the “upgrade” target, which installs the newest version of all currently installed packages, “install” will install the newest version of only the package(s) specified. Simply provide the name of the package(s) you wish to upgrade, and if a newer version is available, it (and its dependencies, as described above) will be downloaded and installed.
Finally, the apt_preferences(5) mechanism allows you to create an alternative installation policy for individual packages.
If no package matches the given expression and the expression contains one of ‘.’, ‘?’ or ‘*’ then it is assumed to be a POSIX regular expression, and it is applied to all package names in the database. Any matches are then installed (or removed). Note that matching is done by substring so ‘lo.*’ matches ‘how-lo’ and ‘lowest’. If this is undesired, anchor the regular expression with a ‘^’ or ‘$’ character, or create a more specific regular expression.
# apt-get remove Package_Name
Remove is identical to install except that packages are removed instead of installed. Note that removing a package leaves its configuration files on the system. If a plus sign is appended to the package name (with no intervening space), the identified package will be installed instead of removed.
# apt-get purge Package_Name
Purge is identical to remove except that packages are removed and purged (any configuration files are deleted too).
Removes packages and all their global (systemwide) configuration files:
Example, remove rhythmbox
$ sudo apt-get purge rhythmbox*
# apt-get clean
Clean clears out the local repository of retrieved package files. It removes everything but the lock file from /var/cache/apt/archives/ and /var/cache/apt/archives/partial/.