What's the difference between the various repository branches for a given version and flavor of Ubuntu?

Question

What's the difference between the different branches of the repositories for a specific version and flavor of Ubuntu? Such as main/universe/restricted and so on?

Answer 1

From the Ubuntu Wiki:

The Ubuntu software repositories are organized into four separate areas or "components", according to the level of support offered by Ubuntu and whether or not the program in question complies with Ubuntu's Free Software Philosophy.

The repository components are:

• Main - Officially supported software.

• Restricted - Supported software that is not available under a completely free license.

• Universe - Community maintained software, i.e. not officially supported software.

• Multiverse - Software that is not free.

For example:

• The Ubuntu Desktop team manages the gnome-terminal package, it is officially supported and in the main repository.

• bcmwl-kernel-source (the Broadcom wireless driver) is in restricted, since it is a supported, but proprietary, driver.

• Community written software that is not officially supported (for example, the game supertuxkart) is in the universe repository.

• Packages like ubuntu-restricted-extras (which contains proprietary codecs that allow you to play media files, including flash player) are in the multiverse repository because they are not free and their restrictive licenses prevent inclusion in the default package set.

Related to these are the Ubuntu Update "repos". These manage what types of updates you would like to receive (you can see them in action if you peek inside your /etc/apt/sources.list):

Ubuntu Updates

• "Important Security Updates (raring-security)". Patches for security vulnerabilities in Ubuntu packages. They are managed by the Ubuntu Security Team and are designed to change the behavior of the package as little as possible -- in fact, the minimum required to resolve the security problem. As a result, they tend to be very low-risk to apply and all users are urged to apply security updates.
• "Recommended Updates (raring-updates)". Updates for serious bugs in Ubuntu packaging that do not affect the security of the system.
• "Pre-released Updates (raring-proposed)". The testing area for updates. This repository is recommended only to those interested in helping to test updates and provide feedback.

• "Unsupported Updates (raring-backports)". As the name states, these are unsupported new versions of packages which have been backported to an older release. Packages may contain new features, may introduce new interfaces, and bugs.

  For more information on backports, visit UbuntuBackports

It is also possible to add your own custom repositories. These are called "PPAs", which stands for "Personal Package Archives". See the Ubuntu Wiki for more information.