The Linux kernel and most GNU software are licensed under the GNU General Public License (GPL), version 2. The GPL requires that all distributed source code modifications and derived works also be licensed under the GPL, and is sometimes referred to as a "share and share-alike", "copyleft", or, pejoratively, a viral license. In 1997, Linus Torvalds stated, "Making Linux GPL'd was definitely the best thing I ever did."[20] Other software may use other licenses; many libraries use the GNU Lesser General Public License (LGPL), a more permissive variant of the GPL, and the X Window System uses the MIT License.

After more than ten years, the Free Software Foundation announced that they would be upgrading the GPL to version 3, citing increasing concerns with software patents and digital rights management (DRM).[21] In particular, DRM is appearing in systems running copyleft software, a phenomenon dubbed "tivoization" after digital video recorder maker Tivo's use of DRM in their Linux-based appliances.[22] Linus Torvalds has publicly stated on the Linux Kernel Mailing List that, based on the drafts of the license, he would not move the Linux kernel to GPL v.3, specifically citing the DRM provisions.[23][24]

In March 2003, the SCO Group filed a lawsuit against IBM, claiming that IBM had contributed parts of SCO's copyrighted code to the Linux kernel, violating IBM's license to use Unix. Also, SCO sent letters to several companies warning that their use of Linux without a license from SCO may be actionable, and claimed in the press that they would be suing individual Linux users. Per the Utah District Court ruling on July 3, 2006; 182 out of 294 items of evidence provided by SCO against IBM in discovery were dismissed.[25]

See also: SCO-Linux controversies
In 2004, Ken Brown, president of the Alexis de Tocqueville Institution, published Samizdat, a highly controversial book which, among other criticism of open source software, denied Torvalds' authorship of the Linux kernel (attributing it to Tanenbaum, instead). This was rebutted by Tanenbaum himself.[26][27]

In the United States, the name Linux is a trademark registered to Linus Torvalds.[28] Initially, nobody registered it, but on August 15, 1994, William R. Della Croce, Jr. filed for the trademark Linux, and then demanded royalties from Linux distributors. In 1996, Torvalds and some affected organizations sued to have the trademark assigned to Torvalds, and in 1997 the case was settled.[29] The licensing of the trademark has since been handled by the Linux Mark Institute. Torvalds has stated that he only trademarked the name to prevent someone else from using it, but was bound in 2005 by United States trademark law to take active measures to enforce the trademark. As a result, the LMI sent out a number of letters to distribution vendors requesting that a fee be paid for the use of the name, and a number of companies have complied

Source : wikipedia.org

The Unix operating system was conceived and implemented in the 1960s and first released in 1970. Its wide availability and portability meant that it was widely adopted, copied and modified by academic institutions and businesses, with its design being influential on authors of other systems.

The GNU Project, with the goal of creating a Unix-like, POSIX-compatible operating system composed entirely of free software,[9] began development in 1984, and a year later Richard Stallman had created the Free Software Foundation and wrote the first draft of the GNU General Public License (GPLv1). By the early 1990s, the project had produced or collected many necessary operating system components, including libraries, compilers, text editors, and a Unix shell, and the upper level could be supplied by the X Window System, but development of the lower level, which consisted of a kernel, device drivers and daemons had stalled and was incomplete.[10]

MINIX, a Unix-like system intended for academic use, was released by Andrew S. Tanenbaum in 1987. While source code for the system was available, modification and redistribution were restricted. In addition, MINIX's 16-bit design was not well adapted to the increasingly cheap and popular Intel 386 architecture for personal computers.

In 1991, Linus Torvalds began to work on a non-commercial replacement for MINIX while he was attending the University of Helsinki.[11] This eventually became the Linux kernel. Torvalds intended Linux to be specifically tailored to the capabilities of the 32-bit Intel 386 platform.[12]

Linux was dependent on the Minix userspace at first. With code from the GNU system freely available, it was advantageous if this could be used with the fledgeling OS. Code licensed under the GNU GPL can be used in other projects, so long as they too are released under the GPL. In order to make the Linux kernel compatible with the components from the GNU project, Torvalds changed his original license (which prohibited commercial redistribution) to the GPLv2.[13] Linux and GNU developers worked to integrate GNU components with Linux. Thus Linux became a complete, fully functional free operating system

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