|Written in||Various (notably C and assembly language)|
|Source model||Free software|
|Marketing target||Personal computers, mobile devices, embedded devices, servers, mainframes, supercomputers|
|Platforms||IA-32 (with Hurd kernel only) and Alpha, ARC, ARM, AVR32, Blackfin, C6x, ETRAX CRIS, FR-V, H8/300, Hexagon, Itanium, M32R, m68k, META, MicroBlaze, MIPS, MN103, OpenRISC, PA-RISC, PowerPC, s390, S+core, SuperH, SPARC, TILE64, Unicore32, x86, Xtensa (with Linux-libre kernel only)|
|Kernel type||Microkernel (GNU Hurd) or Monolithic kernel (GNU Linux-libre, fork of Linux)|
|License||GNU GPL, GNU LGPL, GNU AGPL, GNU FDL, GNU FSDG|
GNU  is an operating system and an extensive collection of computer software. GNU is composed wholly of free software, most of which is licensed under the GNU Project's own General Public License (GPL).
GNU is a recursive acronym for "GNU's Not Unix!", chosen because GNU's design is Unix-like, but differs from Unix by being free software and containing no Unix code. The GNU project includes an operating system kernel, GNU Hurd, which was the original focus of the Free Software Foundation (FSF). However, given the Hurd kernel's status as not yet production-ready, non-GNU kernels, most popularly the Linux kernel, can also be used with GNU software. The combination of GNU and Linux has become ubiquitous to the point that the duo is often referred to as just "Linux" in short, or, less frequently, GNU/Linux. (see the GNU/Linux naming controversy)
Richard Stallman, the founder of the project, views GNU as a "technical means to a social end". Relatedly Lawrence Lessig states in his introduction to the second edition of Stallman's book Free Software, Free Society that in it Stallman has written about "the social aspects of software and how Free Software can create community and social justice".
Development of the GNU operating system was initiated by Richard Stallman while he worked at MIT Artificial Intelligence Laboratory. It was called the GNU Project, and was publicly announced on September 27, 1983, on the net.unix-wizards and net.usoft newsgroups by Stallman. Software development began on January 5, 1984, when Stallman quit his job at the Lab so that they could not claim ownership or interfere with distributing GNU components as free software. Richard Stallman chose the name by using various plays on words, including the song The Gnu.(00:45:30)
The goal was to bring a wholly free software operating system into existence. Stallman wanted computer users to be free to study the source code of the software they use, share software with other people, modify the behavior of software, and publish their own 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.(00:40:52) It was thus decided that the development would be started using C and Lisp as system programming languages, and that GNU would be compatible with Unix. At the time, Unix was already a popular proprietary operating system. The design of Unix was modular, so it could be reimplemented piece by piece.
Much of the needed software had to be written from scratch, but existing compatible third-party free software components were also used such as the TeX typesetting system, the X Window System, and the Mach microkernel that forms the basis of the GNU Mach core of GNU Hurd (the official kernel of GNU). With the exception of the aforementioned third-party components, 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 system's basic components include the GNU Compiler Collection (GCC), the GNU C library (glibc), and GNU Core Utilities (coreutils), but also the GNU Debugger (GDB), GNU Binary Utilities (binutils), the GNU Bash shell. GNU developers have contributed to Linux ports of GNU applications and utilities, which are now also widely used on other operating systems such as BSD variants, Solaris and macOS.[better source needed]
Many GNU programs have been ported to other operating systems, including proprietary platforms such as Microsoft Windows and macOS. GNU programs have been shown to be more reliable than their proprietary Unix counterparts.
As of November 2015, there are a total of 466 GNU packages (including decommissioned, 383 excluding) hosted on the official GNU development site.
The official kernel of GNU Project was the GNU Hurd microkernel; however, as of 2012, the Linux kernel became officially part of the GNU Project in the form of Linux-libre, a variant of Linux with all proprietary components removed.
With the April 30, 2015 release of the Debian GNU/Hurd 2015 distro, GNU OS now provides the components to assemble an operating system that users can install and use on a computer. This includes the GNU Hurd kernel, that is currently in a pre-production state. The Hurd status page states that "it may not be ready for production use, as there are still some bugs and missing features. However, it should be a good base for further development and non-critical application usage."
Due to Hurd not being ready for production use, in practice these operating systems are Linux distributions. They contain the Linux kernel, GNU components and software from many other free software projects. Looking at all program code contained in the Ubuntu Linux distribution in 2011, GNU encompassed 8% (13% including GNOME) and the Linux kernel 6% (increased to 9% when including its direct dependencies).
Other kernels like the FreeBSD kernel also work together with GNU software to form a working operating system. The FSF maintains that an operating system built using the Linux kernel and GNU tools and utilities, should be considered a variant of GNU, and promotes the term GNU/Linux for such systems (leading to the GNU/Linux naming controversy). The GNU Project has endorsed Linux distributions, such as gNewSense, Trisquel and Parabola GNU/Linux-libre. Other GNU variants which do not use the Hurd as a kernel include Debian GNU/kFreeBSD and Debian GNU/NetBSD, bringing to fruition the early plan of GNU on a BSD kernel.
The GNU Project recommends that contributors assign the copyright for GNU packages to the Free Software Foundation, though the Free Software Foundation considers it acceptable to release small changes to an existing project to the public domain. However, this is not required; package maintainers may retain copyright to the GNU packages they maintain, though since only the copyright holder may enforce the license used (such as the GNU GPL), the copyright holder in this case enforces it rather than the Free Software Foundation.
For the development of needed software, Stallman wrote a license called the GNU General Public License (first called Emacs General Public License), with the goal to guarantee users freedom to share and change free software. Stallman wrote this license after his experience with James Gosling and a program called UniPress, over a controversy around software code use in the GNU Emacs program. 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 of GNU software, as well as a large number of free software programs that are not part of the GNU Project; it is also 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 the GNU C Library to allow it to be linked with proprietary software. 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, adding clauses to protect users against hardware restrictions that prevent user to run modified software on their own devices.
Besides GNU's own packages, the GNU Project's licenses are used by many unrelated projects, such as the Linux kernel, often used with GNU software. A minority of the software used by most of Linux distributions, such as the X Window System, is licensed under permissive free software licenses.
The logo for GNU is a gnu head. Originally drawn by Etienne Suvasa, a bolder and simpler version designed by Aurelio Heckert is now preferred. It appears in GNU software and in printed and electronic documentation for the GNU Project, and is also used in Free Software Foundation materials.
The name 'GNU' is a recursive acronym for 'GNU's Not Unix'; it is pronounced g-noo, as one syllable with no vowel sound between the g and the n.
...we have selected a set of fifteen operating systems: Unix, Solaris/Sun OS, BSD, Windows, MS-DOS, MAC OS, Linux, Net Ware, HP UX, GNU Hurd, IBM Aix, Compaq/ DEC VMS, OS/2.
Variants of the GNU operating system, which use the kernel Linux, are now widely used; though these systems are often referred to as "Linux", they are more accurately called "GNU/Linux systems".
Debian port to Hurd...: The GNU Hurd is a totally new operating system being put together by the GNU group.
GNU is an operating system that offers a set of free open source programs.
Nearly twenty years later the HURD has still to reach maturity, and has never achieved production quality. ... Some of us are still wishing and hoping for the real deal, a GNU operating system with a GNU kernel.
Both C and Lisp will be available as system programming languages.
RMS's idea (which I have heard first-hand) is that Linux systems should be considered GNU systems with Linux as the kernel.