A Linux repository is a group of packages with some common theme. Ubuntu software packages are organized in a number of different repositories. Ubuntu repositories are available for all Ubuntu releases. In other words, I'm able to install the KDE Desktop environment on my Ubuntu Linux system. When developers talk about Ubuntu Linux as being based on Debian Linux, what they're really saying is that each Ubuntu Linux release uses the latest available packages from the Debian Unstable Repository, but that's just the start of the development process and a subset of the packages used on Ubuntu Linux. There are 4 major repositories associated with each Ubuntu Linux release, 2 are standard repositories. The Ubuntu Main Repository includes packages required for the standard distribution and they are all available through some sort of open source license, the Ubuntu Restricted Repository is a matter of some controversy, as Restricted Repositories have closed source licenses. However, these packages are key to the Ubuntu approach to Linux, specifically to an operating system that just works. For example, the Ubuntu Restricted Repository includes packages associated with closed source hardware, common examples include video cards and wireless network cards. Packages in the Ubuntu Main and Restricted Repositories are supported by Canonical. In other words, if there's a problem with packages in these repositories, developers employed by Canonical will address them. The other major repositories are known as Universe and Multiverse and they parallel the main and restricted repositories. The Ubuntu Universe Repository includes other open-source packages. The Ubuntu Multiverse Repository includes other packages where the source code is not available. Packages in the Universe and Multiverse Repositories are not supported by Canonical. There are additional repositories available for Ubuntu Linux. They're associated with updates which includes updates that incorporate major bug fixes available after the final release. Backports, these include packages which incorporate features that are introduced in later releases. Security, the Security Repository includes packages that address security issues. Finally, there's one more repository associated with Ubuntu partners. For example, Opera, which is not open source but is commonly used in Linux releases, is included in the Partner Repository. The Opera web browser is an excellent alternative to the Firefox web browser. Each of these repositories are associated with different Ubuntu releases. For example, there are Unique, Main, Restricted, Universe, and Multiverse repositories associated with the Hardy Heron release. Later in this course, I'll describe how these repositories are configured on a per client basis. For a preview, look at the etc/App/sources.listfile on your own system.