Linux ( LIN-uuks) is a family of free and open-source software Unix-like operating systems based on the Linux kernel, which was first released on 17 September 1991 by Linus Torvalds. Some members of the family are typically packaged as a distribution (a.k.a. distro), which includes the kernel alongside supporting system software and libraries developed by third parties—such as GNU, Red Hat, and X.Org—to create a complete operating system; however, not all Linux-based operating systems are considered distros, with Android being an example. Linux was originally designed as a clone of Unix and is distributed under the copyleft GPL license.
There are many thousands of Linux distributions, many based directly or indirectly on other distributions; popular Linux distros include Debian, Fedora Linux, Linux Mint, Arch Linux, and Ubuntu, while commercial distributions include Red Hat Enterprise Linux, SUSE Linux Enterprise, and ChromeOS. Linux distributions are frequently used in server platforms. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses and recommends the name "GNU/Linux", to emphasize the use and importance of GNU software in many distributions. There is controversy surrounding this. Other than the Linux kernel, key components that make up a distribution may include a display server (windowing system), a package manager, a bootloader, and a Unix shell.
Linux is one of the most prominent examples of free and open-source software collaboration. The Linux kernel is considered by many to be the largest free and open source project. While originally developed for x86-based personal computers, it has since been ported to more platforms than any other operating system. When combined with Android, which uses a Linux-based kernel and is designed for smartphones, they have the largest installed base of all general-purpose operating systems.
The Linux kernel was created by Linus Torvalds, following the lack of a working kernel for GNU, a Unix-compatible operating system made entirely of free software that had been in development since 1983 by the GNU Project, led by Richard Stallman. A working Unix system called Minix was later released but its license was not entirely free at the time and it was made for education purposes. The first entirely free Unix for personal computers, 386BSD, did not appear until 1992, by which time Torvalds had already built and publicly released the first version of the Linux kernel on the Internet. Like GNU and 386BSD, Linux did not have any Unix code, being a fresh re-implementation, and therefore avoided legal issues from AT&T. Linux distributions became popular in the 1990s and made Unix technologies accessible to home users on personal computers whereas previously it had been confined to sophisticated workstations.
Desktop Linux distributions include a windowing system such as X11 or Wayland and a desktop environment such as KDE Plasma, GNOME, or Xfce. Distributions intended for servers may not have a graphical user interface at all or include a solution stack such as LAMP.
The source code of Linux 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 (GPL). The license means creating novel distributions is permitted by anyone and is easier than it would be for an operating system such as macOS or Microsoft Windows. The Linux kernel, for example, is licensed under the GPLv2, with an exception for system calls that allows code that calls the kernel via system calls not to be licensed under the GPL.
Because of the dominance of Linux-based Android on smartphones, Linux, including Android, has the largest installed base of all general-purpose operating systems as of May 2022.
Linux is, as of March 2024, used by around 4 percent of desktop computers. The Chromebook, which runs the Linux kernel-based ChromeOS, dominates the US K–12 education market and represents nearly 20 percent of sub-$300 laptop sales in the US. Linux is the leading operating system on servers (over 96.4% of the top one million web servers' operating systems are Linux), leads other big iron systems such as mainframe computers, and is used on all of the world's 500 fastest supercomputers (as of November 2017, having gradually displaced all competitors).
Linux also runs on embedded systems, i.e., devices whose operating system is typically built into the firmware and is highly tailored to the system. This includes routers, automation controls, smart home devices, video game consoles, televisions (Samsung and LG smart TVs), automobiles (Tesla, Audi, Mercedes-Benz, Hyundai, and Toyota), and spacecraft (Falcon 9 rocket, Dragon crew capsule, and the Ingenuity Mars helicopter).
The Unix operating system was conceived of and implemented in 1969, at AT&T's Bell Labs 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. In 1973, in a key pioneering approach, it was rewritten in the C programming language by Dennis Ritchie (except for some hardware and I/O routines). The availability of a high-level language implementation of Unix made its porting to different computer platforms easier.
As a 1956 antitrust case forbade AT&T from entering the computer business, AT&T provided the operating system's source code to anyone who asked. As a result, Unix use grew quickly and it became widely adopted by academic institutions and businesses. In 1984, AT&T divested itself of its regional operating companies, and was released from its obligation not to enter the computer business; freed of that obligation, Bell Labs began selling Unix as a proprietary product, where users were not legally allowed to modify it.
Onyx Systems began selling early microcomputer-based Unix workstations in 1980. Later, Sun Microsystems, founded as a spin-off of a student project at Stanford University, also began selling Unix-based desktop workstations in 1982. While Sun workstations did not use commodity PC hardware, for which Linux was later originally developed, it represented the first successful commercial attempt at distributing a primarily single-user microcomputer that ran a Unix operating system.
With Unix increasingly "locked in" as a proprietary product, 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, compilers, text editors, a command-line shell, and a windowing system) were completed, although low-level elements such as device drivers, daemons, and the kernel, called GNU Hurd, were stalled and incomplete.
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 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.
While attending the University of Helsinki in 1990, Torvalds enrolled in a Unix course. The course used a MicroVAX minicomputer running Ultrix, and one of the required texts was Operating Systems: Design and Implementation by Andrew S. Tanenbaum. This textbook included a copy of Tanenbaum's Minix operating system. It was with this course that Torvalds first became exposed to Unix. In 1991, he became curious about operating systems. Frustrated by the licensing of Minix, which at the time limited it to educational use only, he began to work on his operating system kernel, which eventually became the Linux kernel.