Software management in Ubuntu 13.04

Complementing Package Sources

In Software Center, you can download from external repositories using Edit | Software Sources. To use the Medibuntu project's external sources, for example, click Other Software and Add, then enter:

deb http://packages.medibuntu.org/ raring free non-free

This address wasn't invented: Usually, the address is the website for the external repository. Click the Add Source button to accept the repository (Figure 6).

Figure 6: Obtain additional packages from external repositories.

External repositories often protect themselves from abuse with keys, and this applies to Medibuntu sources as well. Every package has a signature verified with a key, so that manipulated packages with mismatched signatures fall by the wayside. Often you can't access a package offering without a key, but how do you find the key?

To import the key for the Medibuntu repository, invoke a terminal with Ctrl+Alt+T and use the command:

$ sudo apt-get update

The command updates the list of available software for Software Center and returns an error message. Then, enter:

$ sudo apt-key adv --recv-keys --keyserverhkp://keyserver.ubuntu.com:802EBC26B60C5A2783

This downloads the appropriate key and integrates it with package management. If you can't get to the keyserver, it might be temporarily overloaded. Replace keyserver.ubuntu.com in the command with another keyserver, such as subkeys.pgp.net, pgp.mit.edu, or keys.gnupg.net. After the sudo apt-get update command, you should be able to install the software from the source. The new repository might not show up in the Software Center right away.

Key Over Terminal

Importing the key can be handled another way. Most websites show a simple line you can copy with Ctrl+C and paste to the terminal with Ctrl+V. The line might appear as in the following VirtualBox example:

$ wget -q http://download.virtualbox.org/virtualbox/debian/oracle_vbox.asc-O - | sudo apt-key add -

The command downloads the key from the website (with wget -q {HTTP-LINK}), sends it to the console (with -O -), and passes it to the sudo apt-key add command. To update the package list and load up the VirtualBox package, use sudo apt-get update.