Linux

• 1. Introduction

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  Linux is an operating system family whose kernel Linus Torvalds first released on the 17th of September 1991. It now runs all 500 of the world's fastest supercomputers. That is a strange destination for a project that began with one student's frustration over a software license. Its descendants also sit inside Android phones and aboard the Falcon 9 rocket. Yet no company designed it, and its creator wanted to give it a different name. How did a hobby kernel inherit the work of earlier projects? Why did its author keep it free? And who pays for the code that now powers so much of the digital world?

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• 2. The Unix Lineage

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  In 1969, at AT&T's Bell Labs, Ken Thompson, Dennis Ritchie, Douglas McIlroy and Joe Ossanna conceived and built Unix. It was first released in 1971, written entirely in assembly language, as was normal practice then. In 1973 Ritchie rewrote nearly all of it in the C programming language. That choice made moving Unix to new computers far easier.

  A 1956 antitrust case barred AT&T from the computer business, so the company gave its Unix source code to anyone who asked. Universities and businesses adopted it quickly. Commercial machines followed. Onyx Systems sold early microcomputer Unix workstations in 1980, and Sun Microsystems, a spin-off of a Stanford student project, began selling its own in 1982.

  Then came 1984. AT&T divested its regional operating companies and the restriction on computers ended, so Bell Labs began selling Unix as a proprietary product. Users were no longer legally allowed to modify it.

  Richard Stallman had already reacted. In 1983 he started the GNU Project, aiming for a complete Unix-compatible system made only of free software, and work began in 1984. He founded the Free Software Foundation in 1985 and wrote the GNU General Public License in 1989. By the early 1990s the project had finished libraries, compilers, text editors, a command-line shell and a windowing system. The kernel, called GNU Hurd, stalled along with device drivers and daemons.

  Other options were thin. In 1987 Andrew S. Tanenbaum, a computer science professor, released Minix, a minimal Unix-like system for students learning how operating systems work. Its source code was freely available, but its license kept it from counting as free software until April 2000. The first fully free Unix for personal computers, 386BSD, only appeared in 1992. Tanenbaum's textbook would soon reach a student at the University of Helsinki.

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• 3. A Helsinki Student

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  In the fall of 1990, Torvalds enrolled in a Unix course at the University of Helsinki. The course ran on a MicroVAX minicomputer under Ultrix. One required text was Tanenbaum's Operating Systems: Design and Implementation, which came bundled with a copy of Minix. This was Torvalds' first real contact with Unix. By 1991 he was curious about operating systems and annoyed that Minix was licensed for education only, so he began writing his own kernel.

  On the 3rd of July 1991, he asked the comp.os.minix newsgroup for digital copies of the POSIX standards. He needed them to implement Unix system calls. He did not get them. Instead he worked out the calls from SunOS documentation the university owned for its Sun server. He learned a few more from Tanenbaum's book.

  At first Torvalds built the kernel on Minix itself, and Minix programs ran on it. As Linux matured, development moved onto Linux machines. GNU applications replaced every Minix component, because free GNU code was ready to use. Code under the GPL can be reused in other programs, provided they carry the same or a compatible license.

  Torvalds abandoned his first license, which banned commercial redistribution, and switched to the GNU GPL. Developers then fitted GNU components around his kernel, producing a fully functional and free operating system. Linux, like GNU and 386BSD, contained no Unix code. As a fresh re-implementation, it avoided legal trouble with AT&T.

  Legal complications held 386BSD back until 1992, although its development predated Linux. NetBSD, OpenBSD and FreeBSD all descend from it. Torvalds has said that if the GNU kernel or 386BSD had existed in 1991, he probably would not have created Linux. The kernel still needed a name, and the one on his makefiles was not Linux.

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• 4. Freax and Other Names

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  Torvalds wanted to call his creation Freax, a blend of free, freak and an x borrowed from Unix. For about half a year, some of the project's makefiles carried that name. He had considered Linux and dismissed it as too egotistical. In September 1991 the files went onto the FUNET FTP server. Ari Lemmke, Torvalds' coworker at the Helsinki University of Technology and a volunteer administrator of that server, disliked Freax. He labeled the project Linux without asking, and Torvalds later accepted it.

  Pronunciation has its own wrinkle. In a newsgroup post, Torvalds said the word has a short i as in print and a short u as in put. He included an audio guide with the kernel source to demonstrate. In that recording, however, he says LEEN-uuks, with a closer vowel than his written description implies.

  Ownership of the name was just as messy. Nobody registered it at first. On the 15th of August 1994, William R. Della Croce Jr. filed for the trademark and demanded royalties from distributors. In 1996 Torvalds and some affected organizations sued to have it assigned to Torvalds, and the case settled in 1997. The Linux Mark Institute then took over licensing. Torvalds says he registered the name only to stop anyone else from using it. The institute first charged a nominal sublicensing fee, but later switched to a free, perpetual worldwide sublicense.

  A different dispute concerns the whole system. The Free Software Foundation, whose president is Stallman, prefers GNU/Linux. It considers distributions to be variants of the GNU system begun in 1983. It raises no objection to the name Android, since GNU is not part of that system. Debian, which the foundation sponsored until 1996, also uses GNU/Linux. Most media and large distributions such as SUSE Linux and Red Hat Enterprise Linux say simply Linux.

  In 2011, Ubuntu's Natty release was measured at about 8 to 13 percent GNU components, depending on whether GNOME counts as GNU. The Linux kernel made up 6 percent, rising to 9 percent with its direct dependencies.

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• 5. Evolution Not Design

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  Torvalds himself describes his kernel as something that evolved. Unix, he says, served as scaffolding, but "Linux grew with a lot of mutations" that were less random than chance would suggest. Many open-source developers agree that the kernel was never designed in the usual sense.

  Eric S. Raymond locates the revolution in people rather than code. Before Linux, he argued, complex software came from carefully organized small groups. Linux was instead hacked on casually by huge numbers of volunteers who coordinated only through the Internet. Weekly releases brought feedback from hundreds of users within days. The result, in his words, was "rapid Darwinian selection on the mutations introduced by developers."

  Bryan Cantrill, an engineer working on a competing operating system, accepts that Linux evolved. He treats this as a weakness. Some features, especially security, he argues, cannot be reached by evolution alone. In his words, "this is not a biological system at the end of the day, it's a software system."

  The structure underneath is conventional. A Linux-based system draws much of its basic design from Unix principles set down in the 1970s and 1980s. The Linux kernel is monolithic, handling process control, networking, access to peripherals and file systems. Device drivers either live inside the kernel or load as modules while the machine is running.

  The license shapes the project as much as the architecture. The kernel is released under version 2 of the GPL. Anyone distributing it must pass along the source and any changes on the same terms. An exception for system calls lets programs that call the kernel avoid the GPL. Torvalds says the kernel will not move to version 3. He dislikes provisions in the newer license that prohibit use in digital rights management, and obtaining permission from thousands of copyright holders would be impractical. Everything a user touches, from the login prompt to the shell, comes from software beyond the kernel.

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• 6. Inside a Distribution

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  When a computer powers on and its firmware finishes initializing, a bootloader such as GNU GRUB, LILO, SYSLINUX or systemd-boot loads the kernel into memory. The first process the kernel launches is an init program, either the traditional sysvinit or newer ones such as systemd, OpenRC and Upstart. Init sits at the root of the process tree and starts system services and login prompts.

  The GNU C Library, known as glibc, is the standard C library and acts as a wrapper for the kernel's system calls. Embedded systems use alternatives such as musl, EGLIBC and uClibc. Android uses its own library, Bionic, while Void Linux runs musl even on desktops. Basic Unix commands usually come from GNU coreutils, with BusyBox and Toybox serving embedded devices. Bash, developed for the GNU Project, is the dominant shell, though Zsh is also used.

  Most graphical interfaces rest on the X Window System, whose reference implementation, X.Org Server, is the most popular. X permits an application running on one machine to be displayed on another. Wayland is designed to replace it, and by 2022 it had gained relatively wide adoption. A Wayland compositor combines the roles of display server, window manager and compositing manager. Sway and Hyprland are window managers built for it.

  On top sit desktop environments such as KDE Plasma, GNOME, MATE, Cinnamon, LXDE, Pantheon and Xfce, built on toolkits like GTK and Qt. Servers may skip the graphical layer entirely or ship a solution stack such as LAMP.

  Package managers such as apt, yum, zypper, pacman and portage install, remove and update all of a system's software from one central place. The distribution is responsible for default kernel configuration, general security and fitting the pieces together. Many thousands of distributions exist, from Debian, Fedora Linux, Linux Mint, Arch Linux and Ubuntu to commercial ones such as SUSE Linux Enterprise and ChromeOS. They come with very different sponsors behind them.

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• 7. Who Writes It

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  A 2017 analysis of the Linux kernel found that well over 85 percent of its code came from paid programmers. Unpaid developers wrote about 8.2 percent, and 4.1 percent could not be classified. Intel, Samsung, Google, AMD, Oracle and Facebook are among the corporate contributors. Red Hat, Canonical and SUSE have built significant businesses around distributions.

  The scale of the effort has been measured. A 2001 study of Red Hat Linux 7.1 counted 30 million lines of source code. Using the Constructive Cost Model, it estimated about eight thousand person-years of development. The kernel itself was 2.4 million lines, or 8 percent of the total. C accounted for 71 percent of the code, alongside C++, Lisp, assembly, Perl, Python, Fortran and shell scripting languages. Slightly over half of the lines were under the GPL.

  The same analysis of Debian 4.0, called etch and released in 2007, found close to 283 million lines. Its estimated effort was about seventy three thousand man-years.

  Companies earn money in several ways. Some charge for support, especially to business users, or sell a business edition with proprietary administration tools. Another model gives software away to sell hardware. CP/M, Apple DOS and versions of the classic Mac OS before 7.6 once worked that way. As hardware standardized through the 1980s, that approach became harder, since one operating system could run on any maker's compatible machine.

  Volunteers and communities carry much of the rest. Debian is a well-known volunteer effort. Red Hat maintains Fedora as a community version of its commercial product, and SUSE does the same with openSUSE. Torvalds guides kernel development as lead maintainer, and Greg Kroah-Hartman leads the stable branch. Local Linux User Groups hold meetings, give demonstrations and install the system for newcomers. Support also flows through IRC chatrooms, newsgroups, Unix & Linux Stack Exchange and LinuxQuestions.org. Print Linux magazines often bundle cover disks carrying complete distributions.

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• 8. Everywhere It Runs

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  Production use began in the mid-1990s in supercomputing, where organizations such as NASA replaced increasingly expensive machines with clusters of cheap commodity computers running Linux. Dell and IBM, followed by Hewlett-Packard, then started offering Linux support to escape Microsoft's monopoly in desktop operating systems.

  Web servers became its strongest territory. ZDNet reports that 96.3 percent of the top one million web servers run Linux. Counting a wider set of domains, W3Techs estimates 39 percent, against 21.9 percent for Windows and 40.1 percent for other Unix systems. In Q1 2007, IDC put Linux at 12.7 percent of the overall server market. As of 2024, estimates suggest Linux handles at least 80 percent of public cloud workloads on Amazon Web Services, Microsoft Azure and Google Cloud Platform.

  Desktops tell a different story. In October 2024, Linux held an estimated 4.3 percent of desktop computers, while Windows had around 73.4 percent and macOS around 15.5 percent. Chromebooks running ChromeOS dominate the US K-12 education market and account for nearly 20 percent of sub-$300 notebook sales in the US.

  On phones, Android is overwhelming. In April 2023-68.61 percent of mobile devices reaching websites measured by StatCounter ran Android. Android was responsible for more than 60 percent of tablet sales as of 2013. Combined with Android, Linux had the largest installed base of any general-purpose operating system as of May 2022.

  Embedded devices round out the picture. Linux runs routers, automation controls, smart home gadgets, video game consoles and Samsung and LG smart TVs. It also drives cars from Tesla, Audi, Mercedes-Benz, Hyundai and Toyota, and the Dragon crew capsule and Ingenuity Mars helicopter. Its hardware reach spans ARM smartphones and IBM Z mainframes. The ELKS fork targets 16-bit Intel 8086 and 80286 chips, while the uClinux fork handles machines with no memory management unit. Valve built SteamOS on it, later used in the Steam Deck.

  Film studios adopted it early. The first major film produced on Linux servers was Titanic in 1997. DreamWorks Animation, Pixar, Weta Digital and Industrial Light & Magic have since migrated. According to the Linux Movies Group, over 95 percent of servers and desktops at large animation and effects companies run Linux.

  Governments have followed. The Indian state of Kerala mandated Linux in all state high schools. China uses it exclusively for its Loongson processor family to achieve technology independence. Extremadura and Andalusia in Spain built gnuLinEx and Guadalinex for education and official institutions. North Korea's Red Star OS, developed as of 2002, is based on Fedora Linux. Russia's military has reportedly created the G.H.ost Project, and the federal government of Brazil is another adopter. In April 2026 France ordered its ministries to begin replacing 2.5 million Windows desktops with Linux. That order lands on a desktop share of only around 4 percent as of March 2024.

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