Package Classification and Support
Ubuntu divides all software into four domains to reflect differences in licensing and the degree of support available. Some unsupported applications receive updates from community members, but not from Canonical Ltd.
| Free software | Non-free software | |
|---|---|---|
| Supported | Main | Restricted |
| Unsupported | Universe | Multiverse |
Free software includes only software that has met the Ubuntu licensing requirements, which roughly correspond to the Debian Free Software Guidelines. Exceptions, however, include firmware and fonts, in the Main category, because although they are not allowed to be modified, their distribution is otherwise unencumbered.
Non-free software is usually unsupported (Multiverse), but some exceptions (Restricted) are made for important non-free software. Supported non-free software includes device drivers that can be used to run Ubuntu on some current hardware, such as binary-only graphics card drivers. The level of support in the Restricted category is more limited than that of Main, because the developers may not have access to the source code. It is intended that Main and Restricted should contain all software needed for a complete desktop environment. Alternative programs for the same tasks and programs for specialized applications are placed in the Universe and Multiverse categories.
In addition to the above, in which the software does not receive new features after an initial release, Ubuntu Backports is an officially recognized repository for backporting newer software from later versions of Ubuntu. The repository is not comprehensive; it consists primarily of user-requested packages, which are approved if they meet quality guidelines. Backports receives no support at all from Canonical, and is entirely community-maintained.
The -updates repository provides stable release updates (SRU) of Ubuntu and are generally installed through update-manager. Each release is given its own -updates repository (e.g. intrepid-updates). The repository is supported by Canonical Ltd. for packages in main and restricted, and by the community for packages in universe and multiverse. All updates to the repository must meet certain requirements and go through the -proposed repository before being made available to the public. Updates are scheduled to be available until the end of life for the release.
In addition to the -updates repository, the unstable -proposed repository contains uploads which must be confirmed before being copied into -updates. All updates must go through this process to ensure that the patch does truly fix the bug and there is no risk of regression. Updates in -proposed are confirmed by either Canonical or members of the community.
Canonical's partner repository lets vendors of proprietary software deliver their products to Ubuntu users at no cost through the same familiar tools for installing and upgrading software. The software in the partner repository is officially supported with security and other important updates by its respective vendors. Canonical supports the packaging of the software for Ubuntu and provides guidance to vendors. The partner repository is disabled by default and can be enabled by the user. Some popular products distributed via the partner repository as of November 2011 are Adobe Flash Player, Adobe Reader, Braid and Oil Rush.
Read more about this topic: Ubuntu (operating System)
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