Linux


Linux is a family of open source Unix-like operating systems based on the Linux kernel, a kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which includes the kernel and supporting system software and libraries—most of which are provided by third parties—to create a complete operating system, designed as a clone of Unix and released under the copyleft GPL license.
Thousands of Linux distributions exist, many based directly or indirectly on other distributions; popular Linux distributions 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, causing some controversy. Other than the Linux kernel, key components that make up a distribution may include a display server, a package manager, a bootloader and a Unix shell.
Linux is one of the most prominent examples of free and open-source software collaboration. While originally developed for x86-based personal computers, it has since been ported to more platforms than any other operating system, and is used on a wide variety of devices including PCs, workstations, mainframes and embedded systems. Linux is the predominant operating system for servers and is also used on all of the world's 500 fastest supercomputers. When combined with Android, which is Linux-based and designed for smartphones, they have the largest installed base of all general-purpose operating systems.

Overview

The Linux kernel was designed 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 undergoing development since 1983 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 an educative purpose. 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 reimplementation, and therefore avoided the legal issues. Linux distributions became popular in the 1990s and effectively 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 GNOME, KDE Plasma 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. 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 2022. Linux is, as of 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 notebook sales in the US. Linux is the leading operating system on servers, leads other big iron systems such as mainframe computers, and is used on all of the world's 500 fastest supercomputers.
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, automobiles, and spacecraft.

History

Precursors

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. 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 in 1989. By the early 1990s, many of the programs required in an operating 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.

Creation

While attending the University of Helsinki in the fall of 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.
On July 3, 1991, to implement Unix system calls, Linus Torvalds attempted unsuccessfully to obtain a digital copy of the POSIX standards documentation with a request to the comp.os.minix newsgroup. After not finding the POSIX documentation, Torvalds initially resorted to determining system calls from SunOS documentation owned by the university for use in operating its Sun Microsystems server. He also learned some system calls from Tanenbaum's Minix text.
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, creating a fully functional and free operating system.
Although not released until 1992, due to legal complications, the development of 386BSD, from which NetBSD, OpenBSD and FreeBSD descended, predated that of Linux. Linus Torvalds has stated that if the GNU kernel or 386BSD had been available in 1991, he probably would not have created Linux.

Naming

Linus Torvalds had wanted to call his invention "Freax", a portmanteau of "free", "freak", and "x". During the start of his work on the system, some of the project's makefiles included the name "Freax" for about half a year. Torvalds considered the name "Linux" but dismissed it as too egotistical.
To facilitate development, the files were uploaded to the FTP server of FUNET in September 1991. Ari Lemmke, Torvalds' coworker at the Helsinki University of Technology 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".
According to a newsgroup post by Torvalds, the word "Linux" should be pronounced with a short 'i' as in 'print' and 'u' as in 'put'. To further demonstrate how the word "Linux" should be pronounced, he included an audio guide with the kernel source code. However, in this recording, he pronounces Linux as with a short but close front unrounded vowel, instead of a near-close near-front unrounded vowel as in his newsgroup post.