You can manage what components of the official repositories to make available to download in your catalog by using the Software Sources tool, which you can select from the Edit menu in Ubuntu Software Center.
The Ubuntu Software tab is shown in Figure. Here you can:
• Select the repository components downloadable from the Internet. You can choose to make available the main, universe, restricted, and multiverse repository components, as well as the source code of the applications (which you will rarely need). We have already talked about those components.
• Select the server from which you will download applications. If you select Other… from the drop-down list, you will see a series of servers from all around the world. If you are unsure which server best suits your needs, click the Select Best Server button and the system will start checking how long it takes for each listed server to respond to its requests, to determine which one is the best selection.
• Select the Installable from CD-ROM/DVD option if you want to install software available directly in the Ubuntu CD or DVD, without an Internet connection. This source will be listed in the Ubuntu Software Center under the Get Software element.
Click Close when finished.
Figure . The Ubuntu Software tab at the Software Sources tool