The apt-get command is a powerful command-line tool used to work with Ubuntu's Advanced Packaging Tool (APT) performing such functions as installation of new software packages, upgrade of existing software packages, updating of the package list index, and even upgrading the entire Ubuntu system.
Being a simple command-line tool, apt-get has numerous advantages over other package management tools available in Ubuntu for server administrators. Some of these advantages include ease of use over simple terminal connections (SSH) and the ability to be used in system administration scripts, which can in turn be automated by the cron scheduling utility.
Some examples of popular uses for the apt-get utility:
Install a Package: Installation of packages using the apt-get tool is quite simple. For example, to install the network scanner nmap, type the following:
sudo apt-get install nmap
Remove a Package: Removal of a package or packages is also a straightforward and simple process. To remove the nmap package installed in the previous example, type the following:
sudo apt-get remove nmap
Tip: Multiple Packages: You may specify multiple packages to be installed or removed, separated by spaces.
Update the Package Index: The APT package index is essentially a database of available packages from the repositories defined in the /etc/apt/sources.list file. To update the local package index with the latest changes made in repositories, type the following:
sudo apt-get update
Upgrade Packages: Over time, updated versions of packages currently installed on your computer may become available from the package repositories (for example security updated). To upgrade your system, first update your package index as outlined above, and then type:
sudo apt-get upgrade
If a package needs to install or remove new dependencies when being upgraded, it will not be upgraded by the upgrade command. For such an upgrade, it is necessary to use the dist-upgrade command.
Also, you may upgrade your entire Ubuntu system from one revision to another with dist-upgrade. For example, to upgrade from Ubuntu version 5.10 to version 6.06 LTS, you would first ensure the version 6.06 LTS repositories replace the existing 5.10 repositories in your computer's /etc/apt/sources.list, then simply issue the apt-get update command as detailed above, and finally, perform the actual upgrade by typing:
sudo apt-get dist-upgrade
After a fairly considerable amount of time, your computer will be upgraded to the new revision. Typically, some post-upgrade steps would be required as detailed in the upgrade notes for the revision you are upgrading to.
Actions of the apt-get command, such as installation and removal of packages, are logged in the /var/log/dpkg.log log file.
For further information about the use of APT, read the comprehensive Debian APT User Manual or type: