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Ubuntu is a computer operating system based on the Debian GNU/Linux distribution and is distributed as free and open source software with additional proprietary software available.
It is named after the Southern African ethical ideology Ubuntu ("humanity towards others"). Ubuntu provides an up-to-date, stable operating system for the average user, with a strong focus on usability and ease of installation. Web statistics suggest that Ubuntu's share of Linux desktop usage is about 50%, and upward trending usage as a web server.
Ubuntu is composed of many software packages, of which the vast majority are distributed under a free software license (also known as open source). The main license used is the GNU General Public License (GNU GPL) which, along with the GNU Lesser General Public License (GNU LGPL), explicitly declares that users are free to run, copy, distribute, study, change, develop and improve the software. Ubuntu is sponsored by the UK-based company Canonical Ltd., owned by South African entrepreneur Mark Shuttleworth. By keeping Ubuntu free and open source, Canonical is able to utilize the talents of community developers in Ubuntu's constituent components. Instead of selling Ubuntu for profit, Canonical creates revenue by selling technical support and from creating several services tied to Ubuntu.
Canonical endorses and provides support for three additional Ubuntu-derived operating systems: Kubuntu, Edubuntu and Ubuntu Server Edition. There are several other derivative operating systems including local language and hardware-specific versions.
Canonical releases new versions of Ubuntu every six months and supports Ubuntu for eighteen months by providing security fixes, patches to critical bugs and minor updates to programs. LTS (Long Term Support) versions, which are released every two years, are supported for three years on the desktop and five years for servers. The latest version of Ubuntu, 10.04 (Lucid Lynx), is such an LTS version, and was released on April 29, 2010. (source : wikipedia.org)