Other sources of software available for Ubuntu are out there that you might need or like to set up. You can access them using the Other Software tab in the Software Sources tool, shown in Figure.
Figure . The Other Software tab at the Software Sources tool
By default you will see the Canonical partner repositories, of which the main component is selected and the source code component is not. This is the software source listed under Canonical Partners in the Ubuntu Software Center. You can also add PPAs and other software sources.
The PPAs or Personal Package Archives are repositories hosted by Canonical in its Launchpad service, on behalf of third-party developers. A developer can activate a PPA, and Launchpad will generate a unique key to sign any package contained in that PPA. The developer can then submit the source code for its applications, and the people at Canonical build the binaries and packages needed to install the application. Ubuntu users benefits from this collaboration because they can add those PPAs to their software sources and install the applications with Ubuntu Software Center. Note that the software contained in a PPA is considered untrusted by Canonical, so extra care should be taken.
Follow these steps to add a PPA to your software sources:
1. First you need to find the right PPA. You can search for PPAs at the PPAs main page, https://launchpad.net/ubuntu/+ppas, or browse to a PPA directly if you know its URL (it will always be contained in the same site). For example, the Chromium web browser’s daily build is hosted in https://launchpad.net/~chromium-daily/+archive/ppa.
2. Locate the Adding this PPA to your System section. You will see the address of the PPA in the format ppa:<software_name>/ppa. For example, for Chromium daily build it is ppa:chromium-daily/ppa. Copy that text to the clipboard.
3. Open the Software Sources tool and access the Other Software tab. Press the Add button and paste the PPA’s address in the APT line text box. Press Add Source. You will see a URL for the added PPA.
4. The key generated by Launchpad for that PPA will also be imported, as you can see in the Authentication tab in Software Sources (you will see an entry called Launchpad PPA for <software_name>)
5. Click Close. The catalog in your hard disk will be updated to take into account the new software source.
Now that the catalog is updated, the software available at that PPA can be installed by using the Ubuntu Software Center. You will see an entry for the PPA under Get Software.
You can also add software sources hosted at other services. You need to know the server name and the component name. Go to the Other Software tab, click the Add… button, and fill the APT line field with the information of the repository, using the following format:
deb http://<server>/<repository> natty <component>
Click Add Source and then Close to add the source to the catalog.