INTRODUCTION TO THE WORLD OF LINUX

LINUX

Linux is a generic term referring to Unix-like computer operating systems based on the Linux kernel. Their development is one of the most prominent examples of free and open source software collaboration; typically all the underlying source code can be used, freely modified, and redistributed by anyone under the terms of the GNU GPL and other free licenses.

Linux is predominantly known for its use in servers, although it is installed on a wide variety of computer hardware, ranging from embedded devices and mobile phones to supercomputers. Linux distributions, installed on both desktop and laptop computers, have become increasingly commonplace in recent years, owing largely to the popular Ubuntu distribution and to the emergence of netbooks.

The name "Linux" comes from the Linux kernel, originally written in 1991 by Linus Torvalds[Left Image]. The rest of the system, including utilities and libraries, usually comes from the GNU operating system announced in 1983 by Richard Stallman. The GNU contribution is the basis for the alternative name GNU/Linux.

As well as those designed for general purpose use on desktops and servers, distributions may be specialized for different purposes including: computer architecture support, embedded systems, stability, security, localization to a specific region or language, targeting of specific user groups, support for real-time applications, or commitment to a given desktop environment. Furthermore, some distributions deliberately include only free software. Currently, over three hundred distributions are actively developed, with about a dozen distributions being most popular for general-purpose use.[37]

Linux is a widely ported operating system kernel. The Linux kernel runs on the most diverse range of computer architectures: in the hand-held ARM-based iPAQ and the mainframe IBM System z9, in devices ranging from mobile phones to supercomputers.[38] Specialized distributions exist for less mainstream architectures. The ELKS kernel fork can run on Intel 8086 or Intel 80286 16-bit microprocessors, while the µClinux kernel fork may run on systems without a memory management unit. The kernel also runs on architectures that were only ever intended to use a manufacturer-created operating system, such as Macintosh computers (with both PowerPC and Intel processors), PDAs, video game consoles, portable music players, and mobile phones.

GNU

GNU is a computer operating system composed entirely of free software. Its name is a recursive acronym for GNU's Not Unix; it was chosen because its 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[Right Image] 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 have been completed long ago and have been in production use for a decade or more, its official kernel, GNU Hurd, is incomplete and not all GNU components work with it. Thus, the third-party Linux kernel is most commonly used instead. While this kernel has not been officially adopted by the GNU project, some third-party software is included, such as the X.Org release of the X Window System and the TeX typesetting system. Many GNU programs have also been ported to numerous other operating systems such as Microsoft Windows, BSD variants, 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 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's 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.[5] 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.

GPL

The GNU General Public License (GNU GPL or simply GPL) is a widely used free software license, originally written by Richard Stallman for the GNU project. The GPL is the most popular and well-known example of the type of strong copyleft license that requires derived works to be available under the same copyleft. Under this philosophy, the GPL grants the recipients of a computer program the rights of the free software definition and uses copyleft to ensure the freedoms are preserved, even when the work is changed or added to. This is in distinction to permissive free software licences, of which the BSD licences are the standard examples.

The GNU Lesser General Public License (LGPL) is a modified, more permissive, version of the GPL, originally intended for some software libraries. There is also a GNU Free Documentation License, which was originally intended for use with documentation for GNU software, but has also been adopted for other uses, such as the Wikipedia project.

The Affero General Public License (GNU AGPL) is a similar licence with a focus on networking server software. The GNU AGPL is similar to the GNU General Public License, except that it additionally covers the use of the software over a computer network, requiring that the complete source code be made available to any network user of the AGPLed work, for example a web application. The Free Software Foundation recommends that this license is considered for any software that will commonly be run over the network.

The GPL was written by Richard Stallman in 1989 for use with programs released as part of the GNU project. The original GPL was based on a unification of similar licenses used for early versions of GNU Emacs, the GNU Debugger and the GNU Compiler Collection. These licenses contained similar provisions to the modern GPL, but were specific to each program, rendering them incompatible, despite being the same license. Stallman's goal was to produce one license that could be used for any project, thus making it possible for many projects to share code.

As of August 2007, the GPL accounted for nearly 65% of the 43,442 free software projects listed on Freshmeat,and as of January 2006[update], about 68% of the projects listed on SourceForge.net. Similarly, a 2001 survey of Red Hat Linux 7.1 found that 50% of the source code was licensed under the GPL and a 1997 survey of MetaLab, then the largest free software archive, showed that the GPL accounted for about half of the licenses used. One survey of a large repository of open-source software reported that in July 1997, about half the software packages with explicit license terms used the GPL. Prominent free software programs licensed under the GPL include the Linux kernel and the GNU Compiler Collection (GCC). Some other free software programs are dual-licensed under multiple licenses, often with one of the licenses being the GPL.

Some observers believe that the strong copyleft provided by the GPL was crucial to the success of Linux, giving the programmers who contributed to it the confidence that their work would benefit the whole world and remain free, rather than being exploited by software companies that would not have to give anything back to the community.

The second version of the license, version 2, was released in 1991. Over the following 15 years, some members of the FOSS (Free and Open Source Software) community came to believe that some software and hardware vendors were finding loopholes in the GPL, allowing GPL-licensed software to be exploited in ways that were contrary to the intentions of the programmers. These concerns included tivoization (the inclusion of GPL-licensed software in hardware that will refuse to run modified versions of its software); the use of unpublished, modified versions of GPL software behind web interfaces; and patent deals between Microsoft and Linux and Unix distributors that may represent an attempt to use patents as a weapon against competition from Linux.

Version 3 was developed to attempt to address these concerns. It was officially released on June 29, 2007.