The Unix operating system was conceived and implemented in 1969 at AT&T's Bell Laboratories in the United States by Ken Thompson, Dennis Ritchie, Douglas McIlroy, and Joe Ossanna. It was first released in 1971, and initially, was written entirely in assembly language, a common practice at the time. Later, in a key pioneering approach in 1973, Unix was re-written in the programming language C by Dennis Ritchie (with exceptions to the kernel and I/O). The availability of an operating system written in a high-level language allowed easier portability to different computer platforms.
With AT&T being required to license the operating system's source code to anyone who asked (due to an earlier antitrust case forbidding them from entering the computer business), Unix grew quickly and became widely adopted by academic institutions and businesses. In 1984, AT&T divested itself of Bell Labs. Free of the legal obligation requiring free licensing, Bell Labs began selling Unix as a proprietary product.
In 1991, while attending the University of Helsinki, Torvalds became curious about operating systems and frustrated by the licensing of MINIX, which limited it to educational use only. He began to work on his own operating system which eventually became the Linux kernel.
Torvalds began the development of the Linux kernel on MINIX, and applications written for MINIX were also used on Linux. Later, Linux matured and further Linux kernel development took place on Linux systems. GNU applications also replaced all MINIX components, because it was advantageous to use the freely available code from the GNU Project with the fledgling operating system; code licensed under the GNU GPL can be reused in other projects as long as they also are released under the same or a compatible license. Torvalds initiated a switch from his original license, which prohibited commercial redistribution, to the GNU GPL. Developers worked to integrate GNU components with the Linux kernel, making a fully functional and free operating system.
Linux distributions have also gained popularity with various local and national governments. The federal government of Brazil is well known for its support for Linux. News of the Russian military creating its own Linux distribution has also surfaced, and has come to fruition as the G.H.ost Project. The Indian state of Kerala has gone to the extent of mandating that all state high schools run Linux on their computers.China uses Linux exclusively as the operating system for its Loongson processor family to achieve technology independence. In Spain some regions have developed their own Linux distributions, which are widely used in education and official institutions, like gnuLinEx in Extremadura and Guadalinex in Andalusia. Portugal is also using its own Linux distribution Caixa M√°gica, used in the Magalh√£es netbook and the e-escola government program. France and Germany have also taken steps toward the adoption of Linux.
Linux distributions have also become popular in the netbook market, with many devices such as the ASUS Eee PC and Acer Aspire One shipping with customized Linux distributions installed.
Torvalds continues to direct the development of the kernel. Stallman heads the Free Software Foundation, which in turn supports the GNU components. Finally, individuals and corporations develop third-party non-GNU components. These third-party components comprise a vast body of work and may include both kernel modules and user applications and libraries.
A Linux-based system is a modular Unix-like operating system. It derives much of its basic design from principles established in Unix during the 1970s and 1980s. Such a system uses a monolithic kernel, the Linux kernel, which handles process control, networking, and peripheral and file system access. Device drivers are either integrated directly with the kernel or added as modules loaded while the system is running.
Separate projects that interface with the kernel provide much of the system's higher-level functionality. The GNU userland is an important part of most Linux-based systems, providing the most common implementation of the C library, a popular shell, and many of the common Unix tools which carry out many basic operating system tasks. The graphical user interface (or GUI) used by most Linux systems is built on top of an implementation of the X Window System.
Some components of an installed Linux system are:
A bootloader, for example GNU GRUB or LILO. This is a program which is executed by the computer when it is first turned on, and loads the Linux kernel into memory.
An init program. This is the first process launched by the Linux kernel, and is at the root of the process tree: in other terms, all processes are launched through init. It starts processes such as system services and login prompts (whether graphical or in terminal mode).
Software libraries which contain code which can be used by running processes. On Linux systems using ELF-format executable files, the dynamic linker which manages use of dynamic libraries is "ld-linux.so". The most commonly used software library on Linux systems is the GNU C Library. If the system is set up for the user to compile software themselves, header files will also be included to describe the interface of installed libraries.
User interface programs such as command shells or windowing environments.
Other GUIs may be classified as simple X window managers, such as FVWM, Enlightenment, and Window Maker, which provide a minimalist functionality with respect to the desktop environments. A window manager provides a means to control the placement and appearance of individual application windows, and interacts with the X Window System. The desktop environments include window managers as part of their standard installations (Mutter for GNOME,KWin for KDE,Xfwm for Xfce as of January 2012) although users may choose to use a different window manager if preferred.
Linux currently has two modern kernel-userspace APIs for handing video input devices: V4L2 API for video streams and radio, and DVB API for digital TV reception.
Due to the complexity and diversity of different devices, and due to the large amount of formats and standards handled by those APIs, this infrastructure needs to evolve to better fit other devices. Also, a good userspace device library is the key of the success for having userspace applications to be able to work with all formats supported by those devices.
Simplified history of Unix-like operating systems. Linux shares similar architecture and concepts (as part of the POSIX standard) but does not share non-free source code with the original Unix or MINIX.
The primary difference between Linux and many other popular contemporary operating systems is that the Linux kernel and other components are free and open source software. Linux is not the only such operating system, although it is by far the most widely used. Some free and open source software licenses are based on the principle of copyleft, a kind of reciprocity: any work derived from a copyleft piece of software must also be copyleft itself. The most common free software license, the GNU General Public License (GPL), is a form of copyleft, and is used for the Linux kernel and many of the components from the GNU Project.
Linux based distributions are intended by developers for interoperability with other operating systems and established computing standards. Linux systems adhere to POSIX,SUS,LSB, ISO, and ANSI standards where possible, although to date only one Linux distribution has been POSIX.1 certified, Linux-FT.
Free software projects, although developed in a collaborative fashion, are often produced independently of each other. The fact that the software licenses explicitly permit redistribution, however, provides a basis for larger scale projects that collect the software produced by stand-alone projects and make it available all at once in the form of a Linux distribution.
Many Linux distributions, or "distros", manage a remote collection of system software and application software packages available for download and installation through a network connection. This allows users to adapt the operating system to their specific needs. Distributions are maintained by individuals, loose-knit teams, volunteer organizations, and commercial entities. A distribution is responsible for the default configuration of the installed Linux kernel, general system security, and more generally integration of the different software packages into a coherent whole. Distributions typically use a package manager such as dpkg, Synaptic, YAST, yum, or Portage to install, remove and update all of a system's software from one central location.
A distribution is largely driven by its developer and user communities. Some vendors develop and fund their distributions on a volunteer basis, Debian being a well-known example. Others maintain a community version of their commercial distributions, as Red Hat does with Fedora and SUSE does with openSUSE.
In many cities and regions, local associations known as Linux User Groups (LUGs) seek to promote their preferred distribution and by extension free software. They hold meetings and provide free demonstrations, training, technical support, and operating system installation to new users. Many Internet communities also provide support to Linux users and developers. Most distributions and free software / open source projects have IRC chatrooms or newsgroups. Online forums are another means for support, with notable examples being LinuxQuestions.org and the various distribution specific support and community forums, such as ones for Ubuntu, Fedora, and Gentoo. Linux distributions host mailing lists; commonly there will be a specific topic such as usage or development for a given list.
There are several technology websites with a Linux focus. Print magazines on Linux often include cover disks including software or even complete Linux distributions.
Although Linux distributions are generally available without charge, several large corporations sell, support, and contribute to the development of the components of the system and of free software. An analysis of the Linux kernel showed 75 percent of the code from December 2008 to January 2010 was developed by programmers working for corporations, leaving about 18 percent to volunteers and 7% unclassified. Some of the major corporations that contribute include Dell, IBM, HP, Oracle, Sun Microsystems (now part of Oracle), SUSE, and Nokia. A number of corporations, notably Red Hat, Canonical, and SUSE, have built a significant business around Linux distributions.
The free software licenses, on which the various software packages of a distribution built on the Linux kernel are based, explicitly accommodate and encourage commercialization; the relationship between a Linux distribution as a whole and individual vendors may be seen as symbiotic. One common business model of commercial suppliers is charging for support, especially for business users. A number of companies also offer a specialized business version of their distribution, which adds proprietary support packages and tools to administer higher numbers of installations or to simplify administrative tasks.
Another business model is to give away the software in order to sell hardware. This used to be the norm in the computer industry, with operating systems such as CP/M, Apple DOS and versions of Mac OS prior to 7.6 freely copyable (but not modifiable). As computer hardware standardized throughout the 1980s, it became more difficult for hardware manufacturers to profit from this tactic, as the OS would run on any manufacturer's computer that shared the same architecture.
A common feature of Unix-like systems, Linux includes traditional specific-purpose programming languages targeted at scripting, text processing and system configuration and management in general. Linux distributions support shell scripts, awk, sed and make. Many programs also have an embedded programming language to support configuring or programming themselves. For example, regular expressions are supported in programs like grep, or locate, while advanced text editors, like GNU Emacs have a complete Lisp interpreter built-in.
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.
The popularity of Linux on standard desktop computers and laptops has been increasing over the years. Currently most distributions include a graphical user environment, with the two most popular environments being GNOME (which can utilize additional shells such as the default GNOME Shell and UbuntuUnity), and the KDE Plasma Desktop.
There is no "one" Linux desktop, but rather there is a pool of free and open-source software from which desktop environments and Linux distributions select components with which they construct a GUI implementing some more or less strict design guide. GNOME, for example, has its Human interface guidelines as a design guide, which gives the Human-Machine Interface an important role, not just when doing the graphical design, but also when looking at people with disabilities, and even when looking at security.
The collaborative nature of free software development allows distributed teams to perform language localization of some Linux distributions for use in locales where localizing proprietary systems would not be cost-effective. For example the Sinhalese language version of the Knoppix distribution was available significantly before Microsoft Windows XP was translated to Sinhalese. In this case the Lanka Linux User Group played a major part in developing the localized system by combining the knowledge of university professors, linguists, and local developers.
The performance of Linux on the desktop has been a controversial topic; for example in 2007 Con Kolivas accused the Linux community of favoring performance on servers. He quit Linux kernel development because he was frustrated with this lack of focus on the desktop, and then gave a "tell all" interview on the topic. Since then a significant amount of development has been undertaken in an effort to improve the desktop experience. Projects such as Upstart and systemd aim for a faster boot time.
Many popular applications are available for a wide variety of operating systems. For example Mozilla Firefox, OpenOffice.org/LibreOffice and Blender have downloadable versions for all major operating systems. Furthermore, some applications were initially developed for Linux, such as Pidgin, and GIMP, and were ported to other operating systems including Windows and Mac OS X due to their popularity. In addition, a growing number of proprietary desktop applications are also supported on Linux, such as Autodesk Maya, Softimage XSI and Apple Shake in the high-end field of animation and visual effects; see the List of proprietary software for Linux for more details. There are also several companies that have ported their own or other companies' games to Linux, with Linux also being a supported platform on both the popular Steam and Desura digital distribution services.
Besides externally visible components, such as X window managers, a non-obvious but quite central role have the programs hosted by freedesktop.org, such as D-Bus or PulseAudio; both big desktop enironments (GNOME and KDE) include them, each offering graphical front-ends written using the corresponding toolkit (GTK+ or Qt). A display server is another component, which for the longest time has been communicating in the X11 display server protocol with its clients; prominent software talking X11 includes the X.Org Server and Xlib. Frustration over the cumbersome X11 core protocol, and especially over its numerous extensions, has led to the creation of a new display server protocol, Wayland.
Installing, updating and removing software in Linux is typically done through the use of package managers such as the Synaptic Package Manager, PackageKit, and Yum Extender. While most major Linux distributions have extensive repositories, often containing tens of thousands of packages, not all the software that can run on Linux is available from the official repositories. Alternatively, users can install packages from unofficial repositories, download pre-compiled packages directly from websites, or compile the source code by themselves. All these methods come with different degrees of difficulty; compiling the source code is in general considered a challenging process for new Linux users, but it is hardly needed in modern distributions and is not a method specific to Linux.
Broad overview of the LAMP software bundle, displayed here together with Squid. A high-performance and high-availability web server solution providing security in a hostile environment.
Linux distributions have long been used as server operating systems, and have risen to prominence in that area; Netcraft reported in September 2006 that eight of the ten most reliable internet hosting companies ran Linux distributions on their web servers. Since June 2008, Linux distributions represented five of the top ten, FreeBSD three of ten, and Microsoft two of ten; since February 2010, Linux distributions represented six of the top ten, FreeBSD two of ten, and Microsoft one of ten.
Linux distributions are the cornerstone of the LAMP server-software combination (Linux, Apache, MariaDB/MySQL, Perl/PHP/Python) which has achieved popularity among developers, and which is one of the more common platforms for website hosting.
Linux distributions have become increasingly popular on mainframes in the last decade partly due to pricing and the open-source model. In December 2009, computer giant IBM reported that it would predominantly market and sell mainframe-based Enterprise Linux Server.
In the mobile sub-sector of the Telecommunications equipment sector there are three major platforms based on a more or less modified version of the Linux kernel: mer, Tizen and Android. Android has become the dominant mobile operating system for smartphones, during the second quarter of 2013, 79.3% of smartphones sold worldwide used Android. Cell phones and PDAs running Linux on open-source platforms became more common from 2007; examples include the Nokia N810, Openmoko's Neo1973, and the Motorola ROKR E8. Continuing the trend, Palm (later acquired by HP) produced a new Linux-derived operating system, webOS, which is built into its new line of Palm Pre smartphones.
In the non-mobile telecommunications equipment sector, the majority of Customer-premises equipment-hardware runs some Linux-based operating system. OpenWrt is a community driven example upon which many of the OEM firmwares are based.
Many quantitative studies of free / open source software focus on topics including market share and reliability, with numerous studies specifically examining Linux. The Linux market is growing rapidly, and the revenue of servers, desktops, and packaged software running Linux was expected to exceed $35.7 billion by 2008.
IDC's Q1 2007 report indicated that Linux held 12.7% of the overall server market at that time. This estimate was based on the number of Linux servers sold by various companies, and did not include server hardware purchased separately which had Linux installed on it later. In September 2008 Microsoft CEO Steve Ballmer admitted that 60% of web-servers run Linux versus 40% that run Windows Server.
Analysts and proponents attribute the relative success of Linux to its security, reliability, low cost, and freedom from vendor lock-in.
The Wine compatibility layer allows users to run many programs designed for Windows under Linux. About half of Wine's code has been contributed by volunteers and half sponsored by commercial interests including CodeWeavers, which produces a commercial version of the software. Since 2009, Google has also provided funding to the Wine project.
The XO laptop project of One Laptop Per Child is creating a new and potentially much larger Linux community which is planned to reach millions of schoolchildren and their families in the developing world. Major supporters of the project include Google, Red Hat, and eBay. Although the XO will have a Windows option, it will be primarily deployed with Fedora Linux while using Sugar as the desktop environment.
Linux kernel is licensed under the GNU General Public License (GPL), version 2. The GPL requires that anyone who distributes a software product based on GPL-licensed source code, must make the originating source code (and any modifications) available to the recipient under the same terms. Other key components of a typical Linux distribution are also mainly licensed under the GPL, but they may use other licenses; many libraries use the GNU Lesser General Public License (LGPL), a more permissive variant of the GPL, and the X.org implementation of the X Window System uses the MIT License.
Torvalds states that the Linux kernel will not move from version 2 of the GPL to version 3. He specifically dislikes some provisions in the new license which prohibit the use of the software in digital rights management. It would also be impractical to obtain permission from all the copyright holders, who number in the thousands.
A 2001 study of Red Hat Linux 7.1 found that this distribution contained 30 million source lines of code. Using the Constructive Cost Model, the study estimated that this distribution required about eight thousand man-years of development time. According to the study, if all this software had been developed by conventional proprietary means, it would have cost about $1.46¬†billion (2013 US dollars) to develop in the United States. Most of the source code (71%) was written in the Cprogramminglanguage, but many other languages were used, including C++, Lisp, assembly language, Perl, Python, Fortran, and various shell scripting languages. Slightly over half of all lines of code were licensed under the GPL. The Linux kernel itself was 2.4 million lines of code, or 8% of the total.
In a later study, the same analysis was performed for Debian GNU/Linux version 4.0 (etch, which was released in 2007). This distribution contained close to 283 million source lines of code, and the study estimated that it would have required about seventy three thousand man-years and cost US$8.07¬†billion (in 2013 dollars) to develop by conventional means.
In the United States, the name Linux is a trademark registered to Linus Torvalds. Initially, nobody registered it, but on 15 August 1994, William R. Della Croce, Jr. filed for the trademark Linux, and then demanded royalties from Linux distributors. In 1996, Torvalds and some affected organizations sued him to have the trademark assigned to Torvalds, and in 1997 the case was settled. The licensing of the trademark has since been handled by the Linux Mark Institute. Torvalds has stated that he trademarked the name only to prevent someone else from using it. LMI originally charged a nominal sublicensing fee for use of the Linux name as part of trademarks, but later changed this in favor of offering a free, perpetual worldwide sublicense.
The Free Software Foundation views Linux distributions that use GNU software as GNU variants and they ask that such operating systems be referred to as GNU/Linux or a Linux-based GNU system. The media and common usage, however, refers to this family of operating systems simply as Linux, as do many large Linux distributions (e.g. SUSE Linux and Mandriva Linux). Some distributions, notably Debian, use GNU/Linux. The naming issue remains controversial.
^Torvalds, Linus (5 January 1992). "Release notes for Linux v0.12". Linux Kernel Archives. Retrieved 23 July 2007. "The Linux copyright will change: I've had a couple of requests to make it compatible with the GNU copyleft, removing the ‚Äúyou may not distribute it for money‚ÄĚ condition. I agree. I propose that the copyright be changed so that it confirms to GNU ‚ĒÄ pending approval of the persons who have helped write code. I assume this is going to be no problem for anybody: If you have grievances ("I wrote that code assuming the copyright would stay the same") mail me. Otherwise The GNU copyleft takes effect since the first of February. If you do not know the gist of the GNU copyright ‚ĒÄ read it."¬†
^"Linux Mark Institute". Retrieved 24 February 2008. "LMI has restructured its sublicensing program. Our new sublicense agreement is: Free ‚Äď approved sublicense holders pay no fees; Perpetual ‚Äď sublicense terminates only in breach of the agreement or when your organization ceases to use its mark; Worldwide ‚Äď one sublicense covers your use of the mark anywhere in the world"¬†