apt-get

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

Syntax
      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}

Options

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.

   --allow-unauthenticated
        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.

   --arch-only
        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
        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.

   --install-recommends
        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.

   --no-download
        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.

   --no-install-recommends
        Do not consider recommended packages as a dependency for installing.
        Configuration Item: APT::Install-Recommends.

   --ignore-hold
        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.

   --list-cleanup
        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.

   --no-upgrade
        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-source
        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.

   --print-uris
        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.

   --purge
        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.

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

   --no-remove
        If any packages are to be removed apt-get immediately exits without prompting.
        Configuration Item: APT::Get::Remove.

   --auto-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.

   --trivial-only
        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.

FILES

/etc/apt/sources.list
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:
Dir::Etc::SourceList.

/etc/apt/sources.list.d/
File fragments for locations to fetch packages from. Configuration
Item: Dir::Etc::SourceParts.

/etc/apt/apt.conf
APT configuration file. Configuration Item: Dir::Etc::Main.

/etc/apt/apt.conf.d/
APT configuration file fragments. Configuration Item:
Dir::Etc::Parts.

/etc/apt/preferences
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.

/etc/apt/preferences.d/
File fragments for the version preferences. Configuration Item:
Dir::Etc::PreferencesParts.

/var/cache/apt/archives/
Storage area for retrieved package files. Configuration Item:
Dir::Cache::Archives.

/var/cache/apt/archives/partial/
Storage area for package files in transit. Configuration Item:
Dir::Cache::Archives (implicit partial).

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

/var/lib/apt/lists/partial/
Storage area for state information in transit. Configuration Item:
Dir::State::Lists (implicit partial).

Examples

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