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3. Apt
The apt command is a powerful command-line tool, which works 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 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 utility:
• Install a Package: Installation of packages using the apt tool is quite simple. For example, to install the network scanner nmap, type the following:
sudo apt install nmap
• Remove a Package: Removal of a package (or packages) is also straightforward. To remove the package installed in the previous example, type the following:
sudo apt remove nmap
Multiple Packages: You may specify multiple packages to be installed or removed, separated by spaces.
Also, adding the --purge option to apt remove will remove the package configuration files as well. This may or may not be the desired effect, so use with caution.
• 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 and in the /etc/apt/sources.list.d directory. To update the local package index with the latest changes made in the repositories, type the following:
sudo apt update
• Upgrade Packages: Over time, updated versions of packages currently installed on your computer may become available from the package repositories (for example security updates). To upgrade your system, first update your package index as outlined above, and then type:
sudo apt upgrade
For information on upgrading to a new Ubuntu release see Section 4, “Upgrading” [p. 11].
Actions of the apt 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 Manual1 or type:
apt help
1 http://www.debian.org/doc/user-manuals#apt-howto