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The GNU General Public License (English: GNU General Public License, abbreviated GNU GPL or GPL), is a widely used free software license that gives end users the freedom to run, learn, share, and modify software. [6] The license was originally written by Richard Stallman of the Free Software Foundation for the GNU Project and grants users of computer programs the right to The Free Software Definition. [7] The GPL is a Copyleft license, which means that derivative works can only be distributed under the same license terms. The GPL was the first commonly used copyleft license, as distinguished from loose free software licenses such as the BSD license and the MIT license.

Historically, the GPL license family has been one of the most popular software licenses in the free and open source software space. [6][8][9][10][10][10][11][12] Examples of exceptional free software programs licensed under the GPL are the Linux kernel and the GNU Compiler Collection (GCC). David A. Wheeler argues that the Copyleft provided by the GPL is critical to the success of Linux-based systems, giving programmers who contribute to the kernel the assurance that their work will benefit the world at large and remain free from exploitation by unscrupulous software companies that do not provide feedback to the community. 13]

In 2007, a third version of the license (GNU GPLv3) was released to address some of the nuisances that had occurred with the second version (GNU GPLv2) found during its long use. To keep the license up-to-date, the GPL license includes an optional “and extends to future versions” clause that allows users to choose between the original terms of the FSF update or the new version. Some developers choose to omit it when licensing software; for example, the Linux kernel is already licensed under the GPLv2 and does not need to include the “and extends to future versions” statement. [14][15]

The GPL grants the recipient of a program the right, or “freedom”, or “copyleft”, to

The freedom to run the software as you wish, for any purpose (the zero of freedom).

The freedom to learn how the software works, and the freedom to modify the software to fit your calculations as you wish (one of the freedoms). Access to the source code is a prerequisite for this freedom. The freedom to distribute copies of the software so you can help your friends (freedom number two). The freedom to redistribute your modified version of the software to others (freedom three). This gives the whole community the opportunity to share your changes to the software. Access to the source code is a prerequisite for this freedom. [16] In contrast, the end-user licenses that accompany all copyrighted software almost never grant the user any rights (other than the right to use it), and may even restrict some legally permissible actions, such as reverse engineering.

The main difference between the GPL and some other more “permissive” free software licenses (such as the BSD license) is that the GPL seeks to ensure that these freedoms are guaranteed in the reproduction of software and derivative works. This is achieved through a legal mechanism invented by Stallman called Copyleft, which requires that derivative works of GPL programs also be under the GPL. In contrast, a BSD-style license does not prohibit a deductive work from becoming proprietary software.

The GPL is the most popular license for free and open source software [17]. By April 2004, the GPL had accounted for about 75% of the free software listed on Freshmeat and about 68% of SourceForge. Similarly, a 2001 survey on Red Hat Linux 7.1 showed that the average code was distributed under the GPL. Notable GPL free software includes EMACS, the Linux kernel (not all Linux distributions have open source kernels), and GCC.

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