Software management in Ubuntu 16.04

Complementing Package Sources

As explained above, in the Software app, you can download from external repositories using Ubuntu Software | Software and Updates . To use the Opera project's external sources, for example, click Other Software and Add , then enter deb http://deb.opera.com/opera/stable 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. 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 Opera repository, invoke a terminal through Ctrl+Alt+T and use the following command:

$ sudo apt update

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

$ sudo wget -O - http://deb.opera.com/archive.key | sudo apt-key add -

For other repositories more tied in with Ubuntu, you may have to query the Ubuntu keyserver:

$ sudo apt-key adv --recv-keys --keyserver hkp://keyserver.ubuntu.com:80 B9A06DE3

In this case, the preceding command downloads the appropriate key (B9A06DE3) for the developer's Launchpad PPA for the Inkscape vector design software and integrates it with package management. If you can't get to the keyserver, it may 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 update command, you should be able to install the software from the source. The new repository might not show up in the Software app right away.

Key Over Terminal

As seen above, most websites show a simple line that you can copy with Ctrl+C and Ctrl+V to the terminal. 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 (using wget -q {HTTP-LINK} ), sends it to the console (with -O - ), and passes it to the sudo apt-key add command. Then, use sudo apt-get update to update the package list and load up the VirtualBox package.