|Source model||Free software|
|Latest unstable release||) [+/−](June 16, 1997|
|Kernel type||Microkernel (Monolithic in Linux)|
|Default user interface||GNOME|
|License||GNU General Public License and other free software licenses|
GNU (pronounced /ˈɡnuː/ ( listen), or in some countries /ˈnjuː/) is a computer operating system composed entirely of free software. Its name is a recursive acronym for “GNU's Not Unix!” This name was chosen because GNU's design is Unix-like, but differs from Unix by being free software and containing no Unix code. Development of GNU was initiated by Richard Stallman and was the original focus of the Free Software Foundation (FSF).
GNU is developed by the GNU Project, and programs released under the auspices of the project are called GNU packages or GNU programs. The system's basic components include the GNU Compiler Collection (GCC), the GNU Binary Utilities (binutils), the bash shell, the GNU C library (glibc), and GNU Core Utilities (coreutils).
GNU is in active development. Although nearly all components were completed long ago and have been in production use for a decade or more, its official kernel, GNU Hurd, is incomplete. Thus, the third-party Linux kernel is most commonly used instead. While the Linux kernel was not originally developed for the sake of the GNU project, GNU developers have contributed Linux ports of GNU applications and utilities, which are now also widely used on other operating systems such as BSD variants, Solaris and Mac OS X.
The plan for the GNU operating system was publicly announced on September 27, 1983, on the net.unix-wizards and net.usoft newsgroups by Richard Stallman. Software development began on January 5, 1984, when Stallman quit his job at the Massachusetts Institute of Technology (MIT) Artificial Intelligence Laboratory so that they could not claim ownership or interfere with distributing GNU as free software. Richard Stallman chose the name by using various plays on words, including the song The Gnu.
The goal was to bring a wholly free software operating system into existence. Stallman wanted computer users to be "free", as most were in the 1960s and 1970s — free to study the source code of the software they use, free to share the software with other people, free to modify the behaviour of the software, and free to publish their modified versions of the software. This philosophy was later published as the GNU Manifesto in March 1985.
Richard Stallman's experience with the Incompatible Timesharing System (ITS), an early operating system written in assembly language that became obsolete due to discontinuation of PDP-10, the computer architecture for which ITS was written, led to a decision that a portable system was necessary. It was thus decided that GNU would be mostly compatible with Unix. At the time, Unix was already a popular proprietary operating system. The design of Unix had proven to be solid, and it was modular, so it could be reimplemented piece by piece.
Much of the needed software had to be written from scratch, but existing compatible free software components were also used such as the TeX typesetting system, and the X Window System. Most of GNU has been written by volunteers; some in their spare time, some paid by companies, educational institutions, and other non-profit organizations. In October 1985, Stallman set up the Free Software Foundation (FSF). In the late 1980s and 1990s, the FSF hired software developers to write the software needed for GNU.
As GNU gained prominence, interested businesses began contributing to development or selling GNU software and technical support. The most prominent and successful of these was Cygnus Solutions, now part of Red Hat.
The initial plan for GNU was to be mostly Unix-compatible, while adding enhancements where they were useful. By 1990, the GNU system had an extensible text editor (Emacs), a very successful optimizing compiler (GCC), and most of the core libraries and utilities of a standard Unix distribution. As the goal was to make a whole free operating system exist — rather than necessarily to write a whole free operating system — Stallman tried to use existing free software when possible. In the 1980s there was not much free software, but there was the X Window System for graphical display, the TeX typesetting system, and the Mach microkernel. These components were integrated into GNU .
In the GNU Manifesto, Stallman had mentioned that "an initial kernel exists but many more features are needed to emulate Unix." He was referring to TRIX, a remote procedure call kernel developed at MIT Technology, whose authors had decided to distribute it as free software, and which was compatible with Version 7 Unix. In December 1986, work had started on modifying this kernel. However, the developers eventually decided it was unusable as a starting point, primarily because it only ran on "an obscure, expensive 68000 box" and would therefore have to be ported to other architectures before it could be used.
The GNU Project's early plan was to adapt the BSD 4.4-Lite kernel for GNU. However, due to a lack of cooperation from the Berkeley programmers, by 1988 Stallman decided instead to use the Mach kernel being developed at Carnegie Mellon University, although its release as free software was delayed until 1990 while its developers worked to remove code copyrighted to AT&T. Thomas Bushnell, the initial Hurd architect, said in hindsight that the decision to start a new kernel rather than adapt the BSD work set the project back considerably, and that the project should have used the BSD kernel for this reason.
The design of the kernel was to be GNU's largest departure from "traditional" Unix. GNU's kernel was to be a set of programs called servers, forming a multi-server microkernel that would provide the same functionality as the traditional Unix kernel. Since the Mach microkernel, by design, provided just the low-level kernel functionality, the GNU Project had to develop the higher-level parts of the kernel, as a collection of user programs. Initially, this collection was to be called Alix, but developer Thomas Bushnell later preferred the name Hurd, so the Alix name was moved to a subsystem and eventually dropped completely. Eventually, development progress of the Hurd became very slow due to ongoing technical issues.
Despite an optimistic announcement by Stallman in 2002 predicting a release of GNU/Hurd, further development and design are still required. The latest release of the Hurd is version 0.2. It is fairly stable, suitable for use in non-critical applications. As of 2005, Hurd is in slow development, and is now the official kernel of the GNU system. There are also projects working on porting the GNU system to the kernels of FreeBSD, NetBSD, and OpenSolaris.
After the Linux kernel became usable and was switched to a free software license, it became the most common host for GNU software. The GNU project coined the term GNU/Linux for such systems.
Copyright law grants the copyright-holder significant control over the copying and distributing of a work, but FSF wrote a license for the GNU software which grant recipients permission to copy and redistribute the software under highly permissive terms. For most of the 80s, each GNU package had its own license - the Emacs General Public License, the GCC General Public License, etc. In 1989, FSF published a single license they could use for all their software, and which could be used by non-GNU projects: the GNU General Public License (GPL).
This license is now used by most GNU programs, as well as a large number of free software programs that are not part of the GNU project; it is the most commonly used free software license. It gives all recipients of a program the right to run, copy, modify and distribute it, while forbidding them from imposing further restrictions on any copies they distribute. This idea is often referred to as copyleft.
In 1991, the GNU Lesser General Public License (LGPL), then known as the Library General Public License, was written for certain libraries. 1991 also saw the release of version 2 of the GNU GPL. The GNU Free Documentation License (FDL), for documentation, followed in 2000. The GPL and LGPL were revised to version 3 in 2007, improving their international applicability, and adding protection for users whose hardware restricts software changes.
Many GNU programs have been ported to a multitude of other operating systems, including various proprietary platforms such as Microsoft Windows and Mac OS X. They are often installed on proprietary Unix systems as replacements for the proprietary utilities originally included. However, this practice is controversial: these GNU component programs were developed with the goal of replacing entire proprietary UNIX systems with free software, not enhancing these systems.
Many GNU programs have been tested against their proprietary Unix counterparts and shown as being more reliable.
As of 2007, there are a total of 319 GNU packages hosted on the official GNU development site.
Other GNU variants which do not use the Hurd as a kernel include Nexenta OS (GNU plus the kernel of OpenSolaris) and GNU-Darwin. Debian GNU/kFreeBSD and Debian GNU/NetBSD from Debian bring the early plan of GNU on a BSD kernel full circle. GNU itself is distributed as Debian GNU/Hurd by the Debian project, and a Live CD is also available from superunprivileged.org.
The logo for GNU is a gnu head. The well-known drawing was originally done by Etienne Suvasa. It appears in GNU software and in printed and electronic documentation for the GNU project, and is also used in Free Software Foundation materials.