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Screenshot of a GNU-based OS
Screenshot from a GNU-based OS
GNU Project
OS family: Unix-like
Source model: Free software
Kernel type: Microkernel
License: Mostly GPL, some LGPL
Working state: Functional, but unfinished

GNU ( pronounced /gnu/ ) is a free operating system consisting of a kernel, libraries, system utilities, compilers, and end-user applications. Its name is a recursive acronym for "GNU's Not Unix", which was chosen because its design is Unix-like, but differs from Unix by being free software and by not containing any UNIX code. The plan for the GNU operating system was announced in September 1983 by Richard Stallman and software development work began in January 1984. As of 2006, GNU is being actively developed. The project to develop GNU is known as the GNU Project, and programs released under the auspices of the GNU Project are called GNU packages or GNU programs.

As of 2006, a complete GNU system has not been released. The official kernel is the GNU Hurd. However, Hurd is not yet finished so most GNU users use the third-party Linux kernel. While Linux has not been officially adopted as the kernel of GNU, GNU does officially include other third party software such as the Xorg windowing system and the TeX typesetting system.

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 coreutils. GNU uses the third-party packages X.Org and TeX for the foundation of its graphical user interface and its typesetting system, respectively. Not all GNU software works yet with the GNU Hurd kernel.

Versions of GNU using the Linux kernel are often called Linux, after the kernel. The GNU project asks people to call these systems "GNU/Linux." See GNU/Linux naming controversy.

Many GNU programs have also been ported to numerous other operating systems such as Windows, BSD, Solaris and Mac OS.

The GNU General Public License (GPL), the GNU Lesser General Public License (LGPL), and the GNU Free Documentation License (GFDL) were written for GNU, but are also used by many unrelated projects.


The GNU Project was announced publicly on September 27, 1983, on the net.unix-wizards and net.usoft newsgroups. Software development began on January 5, 1984, when Stallman quit his job at Massachusetts Institute of Technology so that they could not claim ownership or interfere with distributing GNU as free software. According to Stallman, the name was inspired by 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 modify the behaviour of the software, and free to publish their modified versions of the software. This philosophy was published in March 1985 as the GNU Manifesto.

Much of the needed software had to be written from scratch, but existing compatible free software components were used. Two examples were 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, FSF hired software developers to write the software needed for GNU. At its peak it had 15 people on its staff. FSF also holds the copyrights for some GNU software packages. Most GNU packages are licensed under the GNU General Public License (GNU GPL), while a few use the GNU Lesser General Public License (GNU LGPL), and a still smaller amount use other free software licenses.

So that it would be convenient for people to switch to GNU, it was decided that GNU would be mostly compatible with Unix. At the time, Unix was 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.

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.


In order to ensure that GNU software remains free, the project released the first version of the GNU General Public License (GNU GPL) in 1989. 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 referred to as copyleft.

In 1991, the GNU Lesser General Public License was written for certain libraries.

In 2000, the GNU Free Documentation License was written for technical manuals.

Design and implementation

The initial plan for GNU was to be mostly Unix-compatible, while adding enhancements where they were useful. The design of the kernel was GNU's largest departure from "traditional" Unix. GNU's kernel was to be a multi-server micro-kernel.

The GNU Hurd runs on a microkernel (currently Mach) and consists of a set of programs called servers that offers the same functionality as the traditional Unix kernel (or Linux).

GNU (using Hurd) can be tried using a live CD. (See Distributions of GNU).

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. The main component still missing was the kernel. 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 Massachusetts Institute of Technology, whose authors had decided to distribute for free, and 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. By 1988, the Mach message-passing kernel being developed at Carnegie Mellon University was being considered instead, although its release as free software was delayed until 1990 while its developers worked to remove code owned by AT&T.

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 Michael (now Thomas) Bushnell later preferred the name Hurd, so the Alix name was moved to a subsystem and eventually dropped completely. Eventually, development of the Hurd stalled due to technical reasons and personality conflicts.

In 1991, Linus Torvalds wrote the Unix-compatible Linux kernel. Although the original license for Linux had restrictions on commercial distribution and hence was not software that was free as in speech, Torvalds quickly changed the license to the GNU GPL in 1992 in what he later termed the best decision he ever made. Linux was further developed by various programmers over the Internet. In 1992, it was combined with the GNU system, resulting in a functional free operating system. The GNU system is most commonly encountered in this form, usually referred to as a " Linux distribution" (but see naming controversy section below). As of 2005, Hurd is in slow development, and is now the official kernel of the GNU system. There is also a project working on porting the GNU system to the kernels of FreeBSD and NetBSD.


GNU, GNU Hurd and GNU/Hurd

GNU/Hurd refers to a GNU OS distribution that uses GNU Hurd as its core. GNU Hurd is a set of programs or servers running on top of a microkernel, that provides the same services as a traditional monolithic Unix kernel. (GNU currently uses the GNU Mach microkernel, but efforts to port Hurd to the L4 microkernel are currently ongoing.) The "GNU" in GNU Hurd indicates that it is a part of the GNU Project, while "GNU/Hurd" distinguishes it as one of the two currently available GNU systems -- Hurd-based GNU systems ( "GNU/Hurd"), or Linux-based GNU systems ( "GNU/Linux"). Just "GNU" refers to GNU/Hurd.

GNU/Linux naming controversy

A system with a Linux kernel and a mostly GNU userland is usually referred to as a "Linux system". However the FSF insists that the GNU project made the biggest contribution and "ought to get at least equal mention".

"GNU/Linux" is pronounced "GNU-slash-Linux", or more often, just "GNU Linux". However, the FSF contests that "GNU Linux", by the rules of the English language, refers to a distribution of the kernel Linux by the GNU project or GNU project's version of it ; "GNU/Linux", they say, makes it clear that a person is referring to the combination of the Linux kernel and the GNU userland binaries, forming a complete GNU OS. Linus Torvalds, original author of Linux, does not approve of the term "GNU/Linux"; he prefers "GNU Linux" if the GNU project "wants its own distribution."

GNU software

Prominent components of the GNU system include the GNU Compiler Collection (GCC), the GNU C Library (glibc), the GNU Emacs text editor, and the GNOME desktop environment.

Many GNU programs have been ported to other operating systems and are often installed on proprietary UNIX systems to replace the proprietary utilities. These GNU programs have in contested cases been tested to show as more reliable than their proprietary Unix counterparts . The reputation of GNU software is especially good among Linux users, for its software development tools - which are sometimes collectively called the GNU toolset. Making up but a small fraction of the GNU system as a whole, these GNU versions are not POSIX compliant. With the popularity of GNU/Linux systems, many developers install the GNU toolset on other systems for compatibility or to capture uniform behaviour across platforms. Many GNU programs have also been ported to Microsoft Windows, Mac OS X, and various other proprietary platforms, however, this is often a hot topic among enthusiasts, as the motive for developing these programs was to replace those systems with free software, not to enhance them.

A list of packages that are well known in the free software community includes:

  • System software
    • Bison – parser generator intended to replace yacc
    • Bash – Unix shell
    • BFD – object file library
    • Classpath – libraries for Java
    • Coreutils – basic Unix utilities such as cat, ls, and rm
    • Emacs – extensible, self-documenting text editor
    • GNU C Library – Standard POSIX C library, plus additional functionality
    • gzip – a library and program for data compression
    • The GNU toolchain for software development:
      • GNU Binary Utilities – assembler, linker, and related tools
      • GNU build system – Autoconf, Automake, Libtool
      • GCC – optimizing compiler for many programming languages, including C, C++, Fortran, Ada, and Java
      • GDB – debugger
    • Screen – a terminal multiplexer
    • Texinfo – documentation system for producing online and printed manuals
    • Wget – advanced file retrieval from networks and the Internet
    • GNUnet – decentralized, peer-to-peer communication network designed to be resistant to censorship
    • GNU Hurd – a microkernel-based set of servers that perform the same function as a Unix kernel
  • Application software
    • GIMP – GNU Image Manipulation Program
    • Gnash – player for movies in Adobe Flash format.
    • GMP – arbitrary precision numerical calculation programming library
    • GNOME – graphical desktop environment
    • GNU LilyPond – sheet music engraving program
    • GNU Octave – program for numerical computations similar to MATLAB
    • GNU Privacy Guard (GnuPG) – free encryption tool which can replace PGP
    • GNU Robots – small but addictive game for computer programmers
    • GNU Scientific Library
    • GNUstep – implementation of the OpenStep standard for a set of libraries and development tools for graphical applications
    • GNU Guile – embeddable Scheme interpreter

As of January 2005, there are a total of 288 GNU packages hosted on the GNU hosting site . Others are hosted elsewhere.

Distributions of GNU

  • Bee GNU/Hurd
  • Debian GNU/Hurd
  •'s Hurd LiveCD
  • Unofficial Gentoo/Hurd Project

Operating systems based on GNU but not using Hurd

  • GNU/kFreeBSD
  • GNU/Linux, by far the most popular variant of GNU.
  • GNU/NetBSD
  • GNU/Solaris
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