Ubuntu Software Repositories

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Four main components, or sections, make up the Ubuntu repository: main, restricted, universe, and multiverse. These components are described in detail at http://ubuntu.com/ubuntu/components. To see a listing of all packages in the Ubuntu repository, check http://packages.ubuntu.com. To see available repositories and their sections, open the Synaptic Package Manager and choose Settings Repositories.


Repository Components
The following repository components are included in the main Ubuntu repository:

• Main Officially supported Ubuntu software (canonical), includes GStreamer Good plugins.

• Restricted Commonly used and required for many applications, but not open source or freely licensed, such as proprietary graphics card drivers from Nvidia and ATI needed for hardware support. Because they are not open source, they are not guaranteed to work.

• Universe All open source Linux software not directly supported by Ubuntu; includes GStreamer Bad plug-ins.

• Multiverse Linux software that does not meet licensing requirements and is not considered essential. It may not necessarily work. For example, the GStreamer Ugly package is in this repository. Check http://ubuntu.com/community/ubuntustory/licensing.


Repositories
In addition to the main repository, Ubuntu maintains several other repositories used primarily for maintenance and support for existing packages, as shown in the following list:

• Main repository Collection of Ubuntu-compliant software packages for releases.

• Updates Corresponding updates for packages in the main repository, both main and restricted sections. Universe and multiverse sections are not updated.

• Backports Software under development for the next Ubuntu release, but packaged for use in the current one. Not guaranteed or fully tested.

• Security updates Critical security fixes for main software. In addition, the backports repository provides unfinalized or development versions for new or current software. They are not guaranteed to work but may provide needed features.


Software Sources
With the Software Sources tool, you can enable or disable repository sections as well as add new entries. This tool edits the /etc/apt/sources.list file directly. Choose System Administration Software Sources. This opens the Software Sources window with five tabs: Ubuntu Software, Third-Party Software, Updates, Authentication, and Statistics. The Ubuntu Software tab lists all your current repository section entries. These include the main repository, universe, restricted, and multiverse, as well as source code.

Those that are enabled will be checked. You can enable or disable a repository section by checking or unchecking its entry. You can select the server to use from the Download From drop-down list. To install software from a CD/DVD, just insert it and begin. On the Third-Party Software tab, you can add repositories for third-party software. The repository for Ubuntu Software Partners will already be listed, but not checked. Check that entry if you want access software from the partners. To add a third-party repository click the Add button. This opens a dialog where you enter the complete APT entry, starting with the DEB format, followed by the URL, distribution, and components or packages. This line will appear in the /etc/apt/sources.list file. Once entered, click the Add Channel button. The Updates tab lets you configure how updates are handled. The tab specifies both your update sources and how automatic updates are handled. You can install Important Security Updates (hardy-security), Recommended Updates (hardy-updates), Pre-released Updates (hardy-proposed), and Unsupported Updates (hardy backports). The Important Security and Recommended updates will already be selected; these cover updates for the entire Ubuntu repository. Pre-released and Unsupported updates are useful if you have installed any packages from the backports or development repositories. Your system is already configured to check for updates automatically on a daily basis. You can opt not to check for updates at all by removing the check mark from the Check For Updates option. You also have options for how updates are handled. You can install any security updates automatically, without confirmation; download updates in the background; or be notified of available updates and then manually choose to install them when you want. The options are exclusive.

The Authentication tab shows the repository software signature keys that are installed on your system. Signature keys will already be installed for Ubuntu repositories, including your CD/DVD-ROM. If you are adding a third-party repository, you will need to add its signature key. Click the Import Key File button to browse for and locate a downloaded signature key file.

Ubuntu requires a signature key for any package that it installs. Signature keys for all the Ubuntu repositories are already installed and are listed on this panel. For third-party repositories, you will have to locate their signature key on their Web site, download it to a file, and then import that file. Most repositories will provide a signature key file for you to download and import. Click the Import Key File to open a file browser, where you can select the downloaded key file. This procedure is the same as the apt-key add operation. Both add keys that APT then uses to verify DEB software packages downloaded from repositories before it installs them.

The Statistics tab lets you provide Ubuntu with software usage information to let it know what software is being used. After you have made changes and clicked the Close button, the Software Sources tool will notify you that your software package information is out of date, displaying a Reload button. Click the Reload button to make the new repositories or components available on package managers such as the Synaptic Package Manager. If you do not click Reload, you can run apt-get update or perform the check operation on the Synaptic Package Manager to reload the repository configuration.

Source of Information : McGraw Hill Ubuntu The Complete Reference

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