Linux ( ) is a family of free and open-source software Operating system built around the Linux kernel. Typically, Linux is packaged in a form known as a Linux distribution (or distro for short) for both desktop and server use. The defining component of a Linux distribution is the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds.
Linux was originally developed for personal computers based on the Intel x86 architecture, but has since been porting to more platforms than any other operating system. Because of the dominance of the Linux kernel-based Android OS on , Linux has the largest installed base of all general-purpose operating systems. Linux is also the leading operating system on servers and other big iron systems such as mainframe computers, and the only OS used on TOP500 (since November 2017, having before gradually eliminated all competitors). It is used by around 2.3% of . The Chromebook, which runs the Linux kernel-based Chrome OS, dominates the US K–12 education market and represents nearly 20% of the sub-$300 Laptop sales in the US. Linux also runs on —devices whose operating system is typically built into the firmware and is highly tailored to the system. This includes TiVo and similar DVR devices, network routers, facility automation controls, televisions, video game consoles and . Many smartphones and run Android and other Linux derivatives.
The development of Linux is one of the most prominent examples of free and open-source software collaboration. The underlying source code may be used, modified and distributed—commercially or non-commercially—by anyone under the terms of its respective licenses, such as the GNU General Public License.
Some of the most popular and mainstream Linux distributions are Arch Linux, CentOS, Debian, Fedora, Gentoo Linux, Linux Mint, Mageia, openSUSE and Ubuntu, together with commercial distributions such as Red Hat Enterprise Linux and SUSE Linux Enterprise Server. Distributions include the Linux kernel, supporting System software and libraries, many of which are provided by the GNU Project, and usually a large amount of application software to fulfil the distribution's intended use. Desktop Linux distributions include a windowing system, such as X11, Mir or a Wayland implementation, and an accompanying desktop environment such as GNOME or KDE Plasma; some distributions may also include a less resource-intensive desktop, such as LXDE or Xfce. Distributions intended to run on servers may omit all graphical environments from the standard install, and instead include other software to set up and operate a solution stack such as LAMP. Because Linux is freely redistributable, anyone may create a distribution for any intended use. Many Linux distributions use the word "Linux" in their name. The Free Software Foundation uses the name "GNU/Linux" to refer to the operating system family, as well as specific distributions, to emphasize that most Linux distributions are not just the Linux kernel, and that they have in common not only the kernel, but also numerous utilities and libraries, a large proportion of which are from the GNU project. This has led to some controversy.
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. First released in 1971, Unix was written entirely in assembly language, as was common practice at the time. Later, in a key pioneering approach in 1973, it was rewritten in the C programming language by Dennis Ritchie (with the exception of some hardware and I/O routines). The availability of a high-level language implementation of Unix made its porting to different computer platforms easier.
Due to an earlier antitrust case forbidding it from entering the computer business, AT&T was required to license the operating system's source code to anyone who asked. As a result, Unix grew quickly and became widely adopted by academic institutions and businesses. In 1984, AT&T divested itself of Bell Labs; freed of the legal obligation requiring free licensing, Bell Labs began selling Unix as a proprietary product, where users weren't legally allowed to modify Unix. The GNU Project, started in 1983 by Richard Stallman, had the goal of creating a "complete Unix-compatible software system" composed entirely of free software. Work began in 1984. Later, in 1985, Stallman started the Free Software Foundation and wrote the GNU General Public License (GNU GPL) in 1989. By the early 1990s, many of the programs required in an operating system (such as libraries, , , a Unix shell, and a windowing system) were completed, although low-level elements such as , daemons, and the kernel, called GNU/Hurd, were stalled and incomplete.
Linus Torvalds has stated that if the GNU kernel had been available at the time (1991), he would not have decided to write his own.
Although not released until 1992, due to legal complications, development of 386BSD, from which NetBSD, OpenBSD and FreeBSD descended, predated that of Linux. Torvalds has also stated that if 386BSD had been available at the time, he probably would not have created Linux.
MINIX was created by Andrew S. Tanenbaum, a computer science professor, and released in 1987 as a minimal Unix-like operating system targeted at students and others who wanted to learn the operating system principles. Although the complete source code of MINIX was freely available, the licensing terms prevented it from being free software until the licensing changed in April 2000. "MINIX is now available under the BSD license" , April 9, 2000, minix1.woodhull.com
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 computer programs 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.
Linus Torvalds had wanted to call his invention " Freax", a portmanteau of "free", "freak", and "x" (as an allusion to Unix). During the start of his work on the system, some of the project's included the name "Freax" for about half a year. Torvalds had already considered the name "Linux", but initially dismissed it as too egotistical.Torvalds, Linus and Diamond, David, Just for Fun: The Story of an Accidental Revolutionary, 2001,
In order to facilitate development, the files were uploaded to the FTP server (ftp.funet.fi) of FUNET in September 1991. Ari Lemmke, Torvalds' coworker at the Helsinki University of Technology (HUT), who was one of the volunteer administrators for the FTP server at the time, did not think that "Freax" was a good name. So, he named the project "Linux" on the server without consulting Torvalds. Later, however, Torvalds consented to "Linux".
Adoption of Linux in production environments, rather than being used only by hobbyists, started to take off first in the mid-1990s in the supercomputing community, where organizations such as NASA started to replace their increasingly expensive machines with clusters of inexpensive commodity computers running Linux. Commercial use followed when Dell and IBM, followed by Hewlett-Packard, started offering Linux support to escape Microsoft's monopoly in the desktop operating system market.
Today, Linux systems are used throughout computing, from to virtually all , and have secured a place in server installations such as the popular LAMP application stack. Use of Linux distributions in home and enterprise desktops has been growing. Linux distributions have also become popular in the netbook market, with many devices shipping with customized Linux distributions installed, and Google releasing their own Chrome OS designed for netbooks.
Linux's greatest success in the consumer market is perhaps the mobile device market, with Android being one of the most dominant operating systems on and very popular on Tablet computer and, more recently, on wearables. Linux gaming is also on the rise with Valve showing its support for Linux and rolling out its own gaming oriented Linux distribution. Linux distributions have also gained popularity with various local and national governments, such as the federal government of Brazil.
Linux vendors and communities combine and distribute the kernel, GNU components, and non-GNU components, with additional package management software in the form of Linux distributions.
The GNU userland is a key part of most systems based on the Linux kernel, with Android being the notable exception. The Project's implementation of the C library functions as a wrapper for the system calls of the Linux kernel necessary to the kernel-userspace interface, the GNU toolchain is a broad collection of programming tools vital to Linux development (including the compilers used to build the Linux kernel itself), and the coreutils implement many basic Unix commands. The project also develops a popular CLI shell. The graphical user interface (or GUI) used by most Linux systems is built on top of an implementation of the X Window System. More recently, the Linux community seeks to advance to Wayland as the new display server protocol in place of X11. Many other open-source software projects contribute to Linux systems.
CLI shells are text-based user interfaces, which use text for both input and output. The dominant shell used in Linux is the Bourne-Again Shell (bash), originally developed for the GNU project. Most low-level Linux components, including various parts of the userland, use the CLI exclusively. The CLI is particularly suited for automation of repetitive or delayed tasks, and provides very simple inter-process communication.
On desktop systems, the most popular user interfaces are the , packaged together with extensive desktop environments, such as the KDE, GNOME desktop, MATE, Cinnamon, Unity, LXDE, Elementary OS and Xfce, though a variety of additional user interfaces exist. Most popular user interfaces are based on the X Window System, often simply called "X". It provides network transparency and permits a graphical application running on one system to be displayed on another where a user may interact with the application; however, certain extensions of the X Window System are not capable of working over the network. Several X display servers exist, with the reference implementation, X.Org Server, being the most popular.
Several types of exist for X11, including tiling, dynamic, stacking and compositing. Window managers provide means to control the placement and appearance of individual application windows, and interact with the X Window System. Simpler X window managers such as dwm or ratpoison provide a minimalist functionality, while more elaborate window managers such as FVWM, Enlightenment or Window Maker provide more features such as a built-in taskbar and themes, but are still lightweight when compared to desktop environments. Desktop environments include window managers as part of their standard installations, such as Mutter (GNOME), KWin (KDE) or Xfwm (xfce), although users may choose to use a different window manager if preferred.
Wayland is a display server protocol intended as a replacement for the X11 protocol; , it has not received wider adoption. Unlike X11, Wayland does not need an external window manager and compositing manager. Therefore, a Wayland compositor takes the role of the display server, window manager and compositing manager. Weston is the reference implementation of Wayland, while GNOME's Mutter and KDE's KWin are being ported to Wayland as standalone display servers. Enlightenment has already been successfully ported since version 19.
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.
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 through collaboration, 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 apt, yum, zypper, pacman or portage to install, remove, and update all of a system's software from one central location.
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 . 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. Linux distributions host ; commonly there will be a specific topic such as usage or development for a given list.
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. Major corporations that provide contributions include Dell, IBM, Hewlett-Packard, Oracle, Sun Microsystems (now part of Oracle) 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 symbiosis. 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 and locate, the traditional Unix MTA Sendmail contains its own Turing complete scripting system, and the advanced text editor GNU Emacs is built around a general purpose Emacs Lisp interpreter.
Most distributions also include support for PHP, Perl, Ruby, Python and other dynamic languages. While not as common, Linux also supports C# (via Mono), Vala, and Scheme. Guile Scheme acts as an extension language targeting the GNU system utilities, seeking to make the conventionally small, static typing, compiler C programs of Unix philosophy rapidly and dynamically extensible via an elegant, functional high-level scripting system; many GNU programs can be compiled with optional Guile language binding to this end. A number of Java Virtual Machines and development kits run on Linux, including the original Sun Microsystems JVM (HotSpot), and IBM's J2SE RE, as well as many open-source projects like Kaffe and JikesRVM.
GNOME and KDE are popular desktop environments and provide a framework for developing applications. These projects are based on the GTK+ and Qt , respectively, which can also be used independently of the larger framework. Both support a wide variety of languages. There are a number of Integrated development environments available including Anjuta, , CodeLite, Eclipse, Geany, ActiveState Komodo, KDevelop, Lazarus, MonoDevelop, NetBeans, and Qt Creator, while the long-established editors Vim, GNU nano and Emacs remain popular.
There are several industry associations and hardware conferences devoted to maintaining and improving support for diverse hardware under Linux, such as FreedomHEC. Over time, support for different hardware has improved in Linux, resulting in any off-the-shelf purchase having a "good chance" of being compatible.
No single official Linux desktop exists: rather desktop environments and Linux distributions select components from a pool of free and open-source software 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 considering people with disability, and even when focusing on 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 became available significantly before Microsoft translated Windows XP into 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, , and local developers.
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 initially developed for Linux, such as Pidgin, and GIMP, 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.
Many other types of applications available for Microsoft Windows and Mac OS X also run on Linux. Commonly, either a free software application will exist which does the functions of an application found on another operating system, or that application will have a version that works on Linux, such as with Skype and some video games like Dota 2 and Team Fortress 2. Furthermore, the Wine project provides a Windows compatibility layer to run unmodified Windows applications on Linux. It is 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. CrossOver, a proprietary solution based on the open-source Wine project, supports running Windows versions of Microsoft Office, Intuit applications such as Quicken and QuickBooks, Adobe Photoshop versions through CS2, and many popular games such as World of Warcraft. In other cases, where there is no Linux port of some software in areas such as desktop publishing and professional audio, there is equivalent software available on Linux. It is also possible to run applications written for Android OS on other versions of Linux using Anbox.
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.
In 2009, Google announced its Chrome OS as a minimal Linux-based operating system, using the Chrome browser as the main user interface. Chrome OS does not run any non-web applications, except for the bundled file manager and media player (a certain level of support for Android applications was added in later versions). Netbooks that shipped with the operating system, termed Chromebooks, started appearing on the market in June 2011.
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, 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. At LinuxCon, IBM announced LinuxONE, a series of mainframes specifically designed to run Linux and open-source software.
Android has become the dominant mobile operating system for , running on 79.3% of units sold worldwide during the second quarter of 2013. Android is also a popular operating system for tablets, and Android smart TVs and in-vehicle infotainment systems have also appeared in the market.
Cellphones 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 Hewlett-Packard) produced a new Linux-derived operating system, webOS, which is built into its line of Palm Pre smartphones.
Nokia's Maemo, one of the earliest mobile operating systems, was based on Debian. It was later merged with Intel's Moblin, another Linux-based operating system, to form MeeGo. The project was later terminated in favor of Tizen, an operating system targeted at mobile devices as well as IVI. Tizen is a project within The Linux Foundation. Several Samsung products are already running Tizen, Samsung Gear 2 being the most significant example. Samsung Z smartphones will use Tizen instead of Android.
As a result of MeeGo's termination, the Mer project forked the MeeGo codebase to create a basis for mobile-oriented operating systems. In July 2012, Jolla announced Sailfish OS, their own mobile operating system built upon Mer technology.
Canonical has released Ubuntu Touch, aiming to bring convergence to the user experience on this mobile operating system and its desktop counterpart, Ubuntu. The operating system also provides a full Ubuntu desktop when connected to an external monitor.
Due to its low cost and ease of customization, embedded Linux is often used in . In the non-mobile telecommunications equipment sector, the majority of customer-premises equipment (CPE) hardware runs some Linux-based operating system. OpenWrt is a community driven example upon which many of the OEM firmware releases are based.
For example, the popular TiVo digital video recorder also uses a customized Linux, as do several network firewalls and routers from such makers as Cisco/Linksys. The Korg OASYS, the Korg KRONOS, the Yamaha Motif XS/Motif XF music workstations, Yamaha S90XS/S70XS, Yamaha MOX6/MOX8 synthesizers, Yamaha Motif-Rack XS synthesizer, and Roland RD-700GX digital piano also run Linux. Linux is also used in stage lighting control systems, such as the WholeHogIII console.
On February 14, 2013, Valve released a Linux version of Steam, a popular game distribution platform on PC. Many Steam games were ported to Linux. On December 13, 2013, Valve released SteamOS, a gaming oriented OS based on Debian, for beta testing, and has plans to ship Steam Machines as a gaming and entertainment platform. Valve has also developed VOGL, an OpenGL debugger intended to aid video game development, as well as porting its Source game engine to desktop Linux. As a result of Valve's effort, several prominent games such as DotA 2, Team Fortress 2, Portal, Portal 2 and Left 4 Dead 2 are now natively available on desktop Linux.
Some Linux users play Windows games through Wine or CrossOver Linux.
OpenELEC, a Linux distribution that incorporates the media center software Kodi, is an OS tuned specifically for an HTPC. Having been built from the ground up adhering to the JeOS principle, the OS is very lightweight and very suitable for the confined usage range of an HTPC.
There are many Linux distributions created with privacy, secrecy, network anonymity and information security in mind, including Tails, Tin Hat Linux and Tinfoil Hat Linux. Lightweight Portable Security is a distribution based on Arch Linux and developed by the United States Department of Defense. Tor-ramdisk is a minimal distribution created solely to host the network anonymity software Tor.
In addition, Windows was used as an operating system on non-mission critical systemslaptops used on board the space station, for examplebut it has been replaced with Linux; the first Linux-powered humanoid robot is also undergoing in-flight testing.
The Jet Propulsion Laboratory has used Linux for a number of years "to help with projects relating to the construction of unmanned space flight and deep space exploration"; NASA uses Linux in robotics in the Mars rover, and Ubuntu Linux to "save data from satellites".
The Ubuntu derivatives Edubuntu and The Linux Schools Project, as well as the Debian derivative Skolelinux, provide education-oriented software packages. They also include tools for administering and building school computer labs and computer-based classrooms, such as the Linux Terminal Server Project (LTSP).
There are general-purpose Linux distributions that target a specific audience, such as users of a specific language or geographical area. Such examples include Ubuntu Kylin for Chinese language users and BlankOn targeted at Indonesians. Profession-specific distributions include Ubuntu Studio for media creation and DNALinux for bioinformatics. There is also a Muslim-oriented distribution of the name Sabily, as well as an Arabic-focused distribution called Ojuba Linux that consequently also provides some Islamic tools. Certain organizations use slightly specialized Linux distributions internally, including GendBuntu used by the French National Gendarmerie, Goobuntu used internally by Google, and Astra Linux developed specifically for the Russian army.
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 COCOMO, the study estimated that this distribution required about eight thousand person-years of development time. According to the study, if all this software had been developed by conventional proprietary means, it would have cost about $ ( US dollars) to develop in the United States. Most of the source code (71%) was written in the C programming language, but many other languages were used, including C++, Lisp, assembly language, Perl, Python, Fortran, and various 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 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$ (in 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 August 15, 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 (LMI). 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 (FSF) prefers GNU/Linux as the name when referring to the operating system as a whole, because it considers Linux distributions to be GNU variants of the GNU operating system initiated in 1983 by Richard Stallman, president of the FSF. They explicitly take no issue over the name Android for the Android OS, which is also an operating system based on the Linux kernel, as GNU is not a part of it.
A minority of public figures and software projects other than Stallman and the FSF, notably Debian (which had been sponsored by the FSF up to 1996), also use GNU/Linux when referring to the operating system as a whole. Most media and common usage, however, refers to this family of operating systems simply as Linux, as do many large Linux distributions (for example, SUSE Linux and Red Hat Enterprise Linux). By contrast, Linux distributions containing only free software use "GNU/Linux" or simply "GNU", such as Trisquel GNU/Linux, Parabola GNU/Linux-libre, BLAG Linux and GNU, and gNewSense.
, about 8% to 13% of a modern Linux distribution is made of GNU components (the range depending on whether GNOME is considered part of GNU), as determined by counting lines of source code making up Ubuntu's "Natty" release; meanwhile, 6% is taken by the Linux kernel, increased to 9% when including its direct dependencies. (self-published data)