Search for and install software packages (Debian/Ubuntu).

      apt-get [-sqdyfmubV] [-o= config_string ] [-c= config_file ]
         [-t= target] update 

      apt-get [-sqdyfmubV] [-o= config_string ] [-c= config_file ]
         [-t= target] upgrade

      apt-get [-sqdyfmubV] [-o= config_string ] [-c= config_file ]
         [-t= target] dselect-upgrade

      apt-get [-sqdyfmubV] [-o= config_string ] [-c= config_file ]
         [-t= target] dist-upgrade 

      apt-get [-sqdyfmubV] [-o= config_string ] [-c= config_file ]
         [-t= target] install pkg [ { =pkg_version_number | /target_release_name | /target_release_codename } ] ...

      apt-get [-sqdyfmubV] [-o= config_string ] [-c= config_file ]
         [-t= target] remove pkg...  

      apt-get [-sqdyfmubV] [-o= config_string ] [-c= config_file ]
         [-t= target] purge pkg...  

      apt-get [-sqdyfmubV] [-o= config_string ] [-c= config_file ]
         [-t= target] source pkg [ { =pkg_version_number | /target_release_name | /target_release_codename } ] ...

      apt-get [-sqdyfmubV] [-o= config_string ] [-c= config_file ]
         [-t= target] build-dep pkg...  

      apt-get [-sqdyfmubV] [-o= config_string ] [-c= config_file ]
         [-t= target] check

      apt-get [-sqdyfmubV] [-o= config_string ] [-c= config_file ]
         [-t= target] clean

      apt-get [-sqdyfmubV] [-o= config_string ] [-c= config_file ]
         [-t= target] autoclean

      apt-get [-sqdyfmubV] [-o= config_string ] [-c= config_file ]
         [-t= target] autoremove

      apt-get {-v | --version} 
      apt-get {-h | --help}}

 Where Target = {target_release_name | target_release_number_expression | target_release_codename}


apt-get and aptitude now share the same list of installed packages and so can be used interchangeably.

All command line options can be set using the configuration file, the descriptions indicate the configuration option to set.
For boolean options you can override the config file by using something like -f-,--no-f, -f=no or several other variations.

        Ignore if packages can't be authenticated and don't prompt about it.
        This is useful for tools like pbuilder.
        Configuration Item: APT::Get::AllowUnauthenticated.

        Only process architecture-dependent build-dependencies.
        Configuration Item: APT::Get::Arch-Only.

   -b, --compile, --build
        Compile source packages after downloading them.
        Configuration Item: APT::Get::Compile.

   -c, --config-file
        Configuration File; Specify a configuration file to use.
        The program will read the default configuration file and then this configuration file.
        See apt.conf(5) for syntax information.

   --diff-only, --dsc-only, --tar-only
        Download only the diff, dsc, or tar file of a source archive.
        Configuration Item: APT::Get::Diff-Only, APT::Get::Dsc-Only, and APT::Get::Tar-Only.

   -d, --download-only
        Download only; package files are only retrieved, not unpacked or installed.
        Configuration Item: APT::Get::Download-Only.

   -f, --fix-broken
        Fix; attempt to correct a system with broken dependencies in place.
        This option, when used with install/remove, can omit any packages to permit APT to
        deduce a likely solution. If packages are specified, these have to completely correct
        the problem. The option is sometimes necessary when running APT for the first time;
        APT itself does not allow broken package dependencies to exist on a system.
        It is possible that a system's dependency structure can be so corrupt as to require
        manual intervention (which usually means using dselect(1) or dpkg --remove
        to eliminate some of the offending packages).
        Use of this option together with -m may produce an error in some situations.
        Configuration Item: APT::Get::Fix-Broken.

        Force yes; This is a dangerous option that will cause apt to continue without prompting if
        it is doing something potentially harmful. It should not be used except in very special
        situations. Using force-yes can potentially destroy your system!
        Configuration Item: APT::Get::force-yes.

   -h, --help
        Show a short usage summary.

        Also install recommended packages.

   -m, --ignore-missing, --fix-missing
        Ignore missing packages; If packages cannot be retrieved or fail the integrity check after retrieval
        (corrupted package files), hold back those packages and handle the result.
        Use of this option together with -f might produce an error in some situations.

        If a package is selected for installation (particularly if it is mentioned on the command line)
        and it could not be downloaded then it will be silently held back.
        Configuration Item: APT::Get::Fix-Missing.

        Disables downloading of packages. This is best used with --ignore-missing to force APT to use 
        only the .debs it has already downloaded. Configuration Item: APT::Get::Download.

        Do not consider recommended packages as a dependency for installing.
        Configuration Item: APT::Install-Recommends.

        Ignore package Holds; This causes apt-get to ignore a hold placed on a package.
        This can be useful in conjunction with dist-upgrade to override a large number of undesired holds.
        Configuration Item: APT::Ignore-Hold.

        This option defaults to on, use --no-list-cleanup to turn it off.
        When on apt-get will automatically manage the contents of  /var/lib/apt/lists to ensure that
        obsolete files are erased. The only reason to turn it off is if you frequently change your source
        list. Configuration Item: APT::Get::List-Cleanup.

        Do not upgrade packages; When used in conjunction with install, no-upgrade will prevent packages on the
        command line from being upgraded if they are already installed.
        Configuration Item: APT::Get::Upgrade.

        Only has meaning for the source and build-dep commands. Indicates that the given source
        names are not to be mapped through the binary table.
        This means that if this option is specified, these commands will only accept source package names
        as arguments, rather than accepting binary package names and looking up the corresponding
        source package. Configuration Item: APT::Get::Only-Source.

   -o, --option
        Set a Configuration Option; This will set an arbitrary configuration option.
        The syntax is -o Foo::Bar=bar.  -o and --option can be used multiple times
        to set different options.

        Instead of fetching the files to install their URIs are printed.Each URI will have the path,
        the destination file name, the size and the expected md5 hash.
        Note that the file name to write to will  not always match the file name on the remote site!
        This also works with the source and update commands.

        When used with the update command the MD5 and size are not included, and it is up to the user
        to decompress any compressed files.
        Configuration Item: APT::Get::Print-URIs.

        Use purge instead of remove for anything that would be removed.
        An asterisk ("*") will be displayed  next to packages which are scheduled to be purged.
        'apt-get remove --purge' is equivalent to the 'apt-get purge' command.
        Configuration Item: APT::Get::Purge.

   -q, --quiet
        Quiet; produces output suitable for logging, omitting progress indicators.
        More q's will produce more quiet up to a maximum of 2.
        You can also use -q=# to set the quiet level, overriding the  configuration file.

        Note that quiet level 2 implies -y, you should never use -qq without a no-action modifier
        such as -d, --print-uris or -s as APT decided to do something you did not expect.
        Configuration Item: quiet.

        Re-Install packages that are already installed and at the newest version.
        Configuration Item: APT::Get::ReInstall.

        If any packages are to be removed apt-get immediately exits without prompting.
        Configuration Item: APT::Get::Remove.

        If the command is either install or remove, then this option acts like running autoremove command,
        removing the unused dependency packages.
        Configuration Item: APT::Get::AutomaticRemove.

   -s, --simulate, --just-print, --dry-run, --recon, --no-act
        No action; perform a simulation of events that would occur but do not actually change the system.
        Configuration Item: APT::Get::Simulate.

        Simulation run as user will deactivate locking (Debug::NoLocking)  automatic.
        Also a notice will be displayed indicating that this is only a simulation, if the option
        APT::Get::Show-User-Simulation-Note is set (Default: true). Neither  NoLocking nor the
        notice will be triggered if run as root (root should know what she is doing without
        further warnings by apt-get).

        Simulate prints out a series of lines each one representing a dpkg operation, Configure (Conf),
        Remove (Remv), Unpack (Inst). Square brackets indicate broken packages and empty set of square
        brackets meaning breaks that are of no consequence (rare).

   -t, --target-release, --default-release
        This option controls the default input to the policy engine, it creates a default pin at priority
        990 using the specified releases tring.
        This overrides the general settings in /etc/apt/preferences.
        Specifically pinned packages are not affected by the value of this option.
        In short, this option lets you have simple control over which distribution packages will be retrieved from.
        Some common examples might be -t '2.1*', -t unstable or -t sid. 
        Configuration Item: APT::Default-Release; see also the apt_preferences(5) man page.

        Only perform operations that are 'trivial'. Logically this can be considered related to --assume-yes,
        where --assume-yes will answer yes to any prompt, --trivial-only will answer no.
        Configuration Item: APT::Get::Trivial-Only.

   -u, --show-upgraded
        Show upgraded packages; Print out a list of all packages that are to be upgraded.
        Configuration Item: APT::Get::Show-Upgraded.

   -v, --version
        Show the program version.

   -V, --verbose-versions
        Show full versions for upgraded and installed packages.
        Configuration Item: APT::Get::Show-Versions.

   -y, --yes, --assume-yes
        Automatic yes to prompts; assume "yes" as answer to all prompts and run non-interactively.
        If an undesirable situation, such as changing a held package, trying to install a unauthenticated
        package or removing an essential package occurs then apt-get will exit.
        Configuration Item: APT::Get::Assume-Yes.
apt-get option Description apt equivalent
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 update
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 upgrade
dselect‑upgrade dselect-upgrade is used in conjunction with the traditional Debian packaging front-end, dselect(1). dselect-upgrade follows the changes made by dselect(1) to the Status field of available packages, and performs the actions necessary to realize that state (for instance, the removal of old and the installation of new packages).  
dist‑upgrade dist-upgrade in addition to performing the function of upgrade, also intelligently handles changing dependencies with new versions of packages; apt-get has a "smart" conflict resolution system, and it will attempt to upgrade the most important packages at the expense of less important ones if necessary. So, dist-upgrade command might remove some packages. The /etc/apt/sources.list file contains a list of locations from which to retrieve desired package files. See also apt_preferences(5) for a mechanism for overriding the general settings for individual packages. apt full‑upgrade

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 GNU/Linux system, libc6 would be the argument provided, not libc6_1.9.6-2.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 can be used to override decisions made by apt-get's conflict resolution system.

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 install
remove remove is identical to install except that packages are removed instead of installed. Note the removing a package leaves its configuration files in 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 remove
purge purge is identical to remove except that packages are removed and purged (any configuration files are deleted too).  

source causes apt-get to fetch source packages. APT will examine the available packages to decide which source package to fetch. It will then find and download into the current directory the newest available version of that source package while respect the default release, set with the option APT::Default-Release, the -t option or per package with the pkg/release syntax, if possible.

Source packages are tracked separately from binary packages via deb-src type lines in the sources.list(5) file. This means that you will need to add such a line for each repository you want to get sources from. If you don't do this you will properly get another (newer, older or none) source version than the one you have installed or could install.

If the --compile option is specified then the package will be compiled to a binary .deb using dpkg-buildpackage, if --download-only is specified then the source package will not be unpacked.

A specific source version can be retrieved by postfixing the source name with an equals and then the version to fetch, similar to the mechanism used for the package files. This enables exact matching of the source package name and version, implicitly enabling the APT::Get::Only-Source option.
Note that source packages are not tracked like binary packages, they exist only in the current directory and are similar to downloading source tar balls.

build‑dep build-dep causes apt-get to install/remove packages in an attempt to satisfy the build dependencies for a source package.  
check check is a diagnostic tool; it updates the package cache and checks for broken dependencies.  
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/. When APT is used as a dselect(1) method, clean is run automatically. Those who do not use dselect will likely want to run apt-get clean from time to time to free up disk space.  
autoclean Like clean, autoclean clears out the local repository of retrieved package files. The difference is that it only removes package files that can no longer be downloaded, and are largely useless. This allows a cache to be maintained over a long period without it growing out of control. The configuration option APT::Clean-Installed will prevent installed packages from being erased if it is set to off.  
autoremove autoremove is used to remove packages that were automatically installed to satisfy dependencies for some package and that are no more needed.  


Locations to fetch packages from. It takes the following format:
deb [web address] [distribution name][maincontribnon-free]
For example, in Ubuntu, it could be something like:
deb http://in.archive.ubuntu.com/ubuntu lucid main restrcted
or for debian
deb http://ftp.de.debian.org/debian lenny main
Configuration Item:

File fragments for locations to fetch packages from. Configuration
Item: Dir::Etc::SourceParts.

APT configuration file. Configuration Item: Dir::Etc::Main.

APT configuration file fragments. Configuration Item:

Version preferences file. This is where you would specify
"pinning", i.e. a preference to get certain packages from a
separate source or from a different version of a distribution.
Configuration Item: Dir::Etc::Preferences.

File fragments for the version preferences. Configuration Item:

Storage area for retrieved package files. Configuration Item:

Storage area for package files in transit. Configuration Item:
Dir::Cache::Archives (implicit partial).

Storage area for state information for each package resource
specified in sources.list(5) Configuration Item: Dir::State::Lists.

Storage area for state information in transit. Configuration Item:
Dir::State::Lists (implicit partial).


These examples assume that /etc/apt/sources.list already includes the web address of at least one software repository.

Sync the local software database with the repository database (build cache):
$ sudo apt-get update

Search for a particular program (search the cache) in this case the gimp program:
$ apt-cache search gimp

If the above succeeds then the software is available and can be installed:
$ sudo apt-get install gimp

To remove the software if you no longer need it:
$ sudo apt-get remove gimp

Upgrade all the software on your system to the latest versions:
$ sudo apt-get upgrade

Upgrading the whole linux distribution to a new version:
$ sudo apt-get dist-upgrade

“Be not the first by whom the new are tried,
Nor yet the last to lay the old aside” ~ Alexander Pope

Related linux commands

apt-cache(8), apt-cdrom(8), dselect(1), sources.list(5), apt.conf(5), apt-config(8), apt-secure(8), apt_preferences(5)
dpkg - Low level Package management.
The APT User's guide in /usr/share/doc/apt-doc/
wiki.debian.org/Apt - APT Wiki (Debian).
Synaptic Package Manager - GUI for APT (In Ubuntu this is under System ➞ Administration).
Tasksel - Debian/Ubuntu tool to install multiple related packages, typically on servers.
aptitude - Package manager.
dpkg - Package manager (Debian/Ubuntu).
Equivalent Windows command: Package managers

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