Follow TV Tropes


Useful Notes / UNIX

Go To

"It's a UNIX system! I know this!"

Quirky, seemingly counter-intuitive, but incredibly flexible, UNIX has gone from a little-known research operating system in the 1970s to an entire design philosophy. In its experimental days, UNIX stood in the background, influencing OSes but not making much noise on its own; that changed starting in the early 1980s, when the first commercial UNIX products appeared, and exploded in the mid-1990s, as OSes either based directly on UNIX or following its principles came to the forefront via the World Wide Web. Even though you might think Microsoft Windows dominates the computer market, since 2014, UNIX-based operating systems outrank Microsoft's in terms of usage share, spanning pretty much all the scales and sizes of computing — from uCLinux for micro-controllers and embedded devices, to Apple iOS and Android for smartphones, to Linux and macOS for desktop computers, Oracle Solaris, HP-UX and IBM AIX for servers and mainframes. Even when it's not in use, however, it can be said that UNIX is, in TV Tropes parlance, the Trope Codifier and sometimes even Trope Maker for many of the features we take for granted in modern computer systems.

UNIX was once considered unfriendly, requiring expensive licensing and large minicomputers to run; now, almost all of UNIX's source code is freely licensed.much longer explanation 

Sun's (now Oracle's) Solaris, a UNIX System V OS (since version 2), had much of its code freed with OpenSolaris; while this was discontinued by Oracle in favor of the original proprietary Solaris OS, the irrevocable nature of free and open-source licenses such as OpenSolaris's Common Development and Distribution License (derived from the Mozilla Public License) allowed it's kernel to be forked into illumos, while the OS itself was given a Spiritual Successor in the form of OpenIndiana, by the late Ian Murdock of Debian fame, who grew up and went to school in Indiana.

Last but not least, the Linux kernel has been free and open-source software for quite some time, having been released under the GNU General Public License (GPL) since early on in its life, ever since Linus Torvalds switched from a license prohibiting non-commercial use, and GNU (the UNIX-style environment typically used with Linux) is free and open source as its principal aim.

    open/close all folders 

Multics was a research OS; it was highly ambitious, highly secure, required expensive GE and Honeywell mainframes to run, and was also stuck in Development Hell. One of the research partners was Bell Labs, then the experimental division of the Bell System, and in 1969, they decided to leave the project. This left one programmer there, Ken Thompson, with not much else to do.

Thompson had a pet project going on Bell's Multics machine, a game called Space Travel, but at several dollars (in 1969 money) per run, using it was not economically sound. Looking for a cheaper alternative (as well as a new project to work on), he spotted a spare DEC PDP-7 in his lab, and began porting Space Travel to it. As he did, he found himself recreating various parts of Multics around it; eventually, he had a file system, kernel and utilities ready to go. Since it was kind of like Multics, but "neutered", he decided to call the new system "Unics". Eventually, after getting a more powerful system (a DEC PDP-11) to improve Unics and work on the first real application for it (a typesetting package that eventually became nroff), Ken and his development partner Dennis Ritchie started setting the name in small caps, at which point it mutated into "UNIX," which would have been displayed as "Uɴɪx" with Ritchie's formatting.

    Portability, C and the Berkeley connection 

Not long after the first edition of UNIX was published inside Bell Labs, Ken Thompson and Dennis Ritchie started work on making the system portable. In the early 1970s, this was a big deal, since almost all OSes up to that point had been written specifically for the machine they were going to run on. The idea was to write most of the kernel in a higher-level language that could be "compiled" into code for different machines, then add small bits of machine-dependent code where needed to handle things like interrupts and memory.note  The language Dennis invented for the project was called C, and became extremely influential after he and Brian Kernighan published a book on it.

Once UNIX was ported to C, Bell Labs started allowing researchers at universities to study its insides. Since the Bell System was still a regulated monopoly at the time, and thus couldn't sell computers or OSes, Bell Labs would give university computer science departments access to the UNIX source code for the cost of duplication once they signed a non-disclosure agreement. UNIX became very popular in operating systems classes after this. The lecture notes of one Australian computer science professor, John Lions of the University of New South Wales, were compiled into a book (Lions' Commentary on UNIX 6th Edition, with Source Code, aka the Lions Book) and became a widely bootlegged underground publication and circulated for years this way due to both the Bell System's licensing strictures and the later UNIX Wars (see below);note  it was, finally, legally published in book form 20 years later, in 1996.

The college with the most influence by far, though, was the University of California at Berkeley. Berkeley's Computer Science Research Group added many new features to UNIX, eventually creating their own version of UNIX called the Berkeley Software Distribution, or BSD. Among the many things they did were porting UNIX from the PDP-11 to the VAX, adding networking support, improving the user input/output functions significantly, and generally cleaning things up. The icing on the cake was the licensing — Berkeley put their changes under a license that allowed free distribution and modification. This meant that anyone with a Bell UNIX license could use BSD.

In the meantime, Bell Labs released what would be the last important version of "classic" UNIX, the 7th Edition (otherwise known as "Version 7" or "V7" to fans). V7 was considered by many the last true version of UNIX ever, and through ports like Xenix found its way onto many machines not powerful enough to run BSD UNIX. There was also a full rewrite called "MINIX", aimed at teaching UNIX concepts (and, later, advanced concepts such as microkernels) to students and curious enthusiasts who couldn't get a V7 license from Bell, and as a legal substitute for the Lions Book. This was many people's first introduction to UNIX concepts, and like BSD, it would have a huge influence later on. (MINIX 3, whose first version was released in 2005, dropped the license fees in favor of being licensed similarly to BSD. This was eventually followed by the OS borrowing code from NetBSD.)

    UNIX goes commercial; GNU is born (with the Free Software Movement) 

In the early 80s, it looked like things would keep going as they had, with UNIX being primarily an academic research OS, for the foreseeable future. But as usually happens in history, a major change was triggered by something that at first seemed completely unrelated. In the case of UNIX, the seemingly unrelated trigger was American antitrust law.

In 1982, AT&T (the Bell System's parent company) lost a long-running lawsuit with the US Department of Justice, and was forced to divest itself of its local telephone service companies. In return, they were finally allowed to enter the computer industry, and commercializing UNIX was at the top of their priorities. They changed the licensing such that various parts of the system were "unbundled" or a la carte, making a usable UNIX system much more expensive. In the meantime, the UNIX group at Bell continued working on the original UNIX tree, which eventually became UNIX System V, the basis of all of AT&T and its partners' commercial UNIX offerings. Most vendors ended up merging it with their own code bases and creating their own UNIX variants such as HP-UX (Hewlett-Packard) and AIX (IBM). Direct ports of System V were available from outside porting houses like Interactive Systems.

At around the same time, a researcher at MIT's AI Lab named Richard Stallman decided he was fed up with companies founded by ex-AI-lab-members which often built upon AI lab software and were expected to be used by the AI lab, "hoarding" their innovations and preventing sharing of code.note  His main concerns were that, once the source to various parts of an OS were "non-free" or made unavailable, fixing or improving on them was impossible (or, at least, extremely difficult), and that this could lead to monopoly behavior and rip communities apart. note  This was hastened by the death of the AI lab's own operating system, ITS. He envisioned a complete operating system where all of the parts were "free software" (in analogy with "free speech")note  and could be modified and/or shared with others at will, but with the caveat that the programming code for the changes had to be shared as well. note  He called his vision "GNU", a Recursive Acronym for "GNU's Not UNIX!", posted a manifesto describing his intentions to Usenet in 1983, and created the Free Software Foundation to oversee the effort. By 1990, the FSF would have most of the parts of GNU ready, including a compiler, utilities, libraries and such, but no kernel to run the system under.

On the other side of the US, in Silicon Valley, some of the Berkeley researchers, along with hardware designers from Stanford, got together to make the first computers designed specifically to run UNIX, called workstations, which shrunk the power of minicomputers down to the desktop form factor. The most famous of these was Sun Microsystems, named after the Stanford University Network, a part of the ARPANET, the ancestor of the Internet. Other companies, like Silicon Graphics, soon followed, and even companies that historically had ignored UNIX before (HP and IBM) got into the fold with the HP 9000 (running HP/UX) and the IBM RT-PC (running either AIX or AOS, a BSD derivative). Bolstered by the existing popularity of UNIX in academia, particularly in STEM (Science, Technology, Engineering, and Mathematics) fields, these workstations made it the computing platform of choice for scientists and engineers around the world. UNIX workstations, especially those from Silicon Graphics, also helped make CGI ubiquitous in TV and film through the '80s and '90s.

    The UNIX Wars; Linux and the unencumbered BSDs appear 

Starting around 1988, Sun and AT&T entered into an agreement to develop UNIX-based software together, and called the joint venture "UNIX International". As part of the agreement, Sun (who had been using a custom BSD variant called SunOS up to this point) and AT&T agreed to make a "merged" UNIX that would combine the best parts of BSD and System V; this was released as System V Release 4 in 1990, with Sun's version being released under the name Solaris 2note . Other vendors, specifically DEC, IBM, and HP, felt snubbed and formed the Open Software Foundation in protest, and began work on a UNIX derivative called OSF/1, which (like NeXTStep and, much later, Mac OS X), was based on the Mach microkernel and parts from 4.3 BSD.

In the meantime, the IBM Personal Computer and its clones were taking the commercial market by storm, and the Mac was introducing people to a new way of working that many felt no one could touch. UNIX was in a state of disarray; most vendors had proprietary changes to their UNIX builds, none of which were compatible with the others, and porting software was becoming more difficult. This inspired some of the first standards for UNIX, promulgated by the POSIX working groups and by X/Open. Getting everyone to agree would be difficult, but as the PC became more and more powerful and Microsoft began talking about making a version of Windows to compete with UNIX, the impetus to cooperate grew. By the mid-1990s, UNIX International had been disbanded, and OSF stopped development on OSF/1 (leaving DEC to maintain their own branch, renamed "Tru64", for their Alpha machines); OSF merged with X/Open to form the aforementioned Open Group.

At Berkeley, a programmer by the name of Keith Bostic, inspired by Stallman's GNU Project (and Berkeley's own separation of their TCP/IP code in "Networking Release 1"), came up with a large project of his own: purge the BSD codebase of proprietary AT&T code to allow Berkeley-based startups to market it without licenses from AT&T. Involving almost all of the UCB Computer Science Research Group, the project was almost completely successful, with the results being released as "Networking Release 2" or "Net/2", and two "forks" soon emerged; "BSD/OS" from startup BSDi, and "386/BSD", a free software product from Bill Jolitz, nicknamed "Jolix."

Eventually, AT&T decided to wash their hands of the whole thing, and spun off the UNIX group as UNIX System Laboratories (USL). In one final salvo before concluding the war, USL sued Berkeley and BSDi, claiming copyright infringement and restraint of trade. The possibility of a free UNIX appearing in the near future appeared dim.

In 1990, the GNU Project would launch the GNU Hurd kernel, hoping to create a kernel that would be free of any copyrighted code, as that was at the time the only part of the puzzle missing from the GNU Project. However, development was slow as the contributors were mostly hobbyists who worked on their own free time. Additionally, the choice of making the kernel a microkernel (as opposed to the monolithic kernel design Linux went with) meant it was exponentially harder to build and debug, as microkernels presented several additional obstacles not faced by monolithic kernel developers.

In 1991, a programmer in Helsinki, Finland, named Linus Torvalds, who was inspired by MINIXnote  posted his intent to build a "little" UNIX clone (which he intended to be "just a hobby" and "nothing big like GNU") to Usenet, with some of the work already done. Others agreed to help, and by 1992 Linux, as it was dubbed by one of Linus's helpers,note  was maturing quickly.

As the complete system itself incorporated GNU software, with Linus's kernel being the main original contribution, Linus made the important decision to put the Linux kernel under the same license as GNU's tools and utilities, making it attractive to developers who appreciated GNU's stance. With commercial UNIX still expensive, and BSD's future unclear, Linux grew quickly, and by 1995 had reached version 1.0; already, there were several vendors offering "distributions" ("distros" for short), or fully usable OSes incorporating the Linux kernel and GNU software at that time.note  Some of them, like Linspire, SLS and AV Linux, came and went; others such as Slackware, Red Hat (later splitting into the free Fedora and the commercial Red Hat Enterprise Linux), SuSE, and Debian lived on, and new distros appear on the scene periodically; more on this later.

While all this was going on, Jolitz suddenly dropped support for 386BSD, resulting in a set of unofficial patches to the last version appearing. Eventually, these patches were cleaned up, improved, and became the subject of two forks: NetBSD, which focused on porting the Net/2 tapes to as many platforms as possible, and FreeBSD, which sought to continue where 386BSD left off, and make a quality BSD release intended specifically for PC compatibles. The USL lawsuit still loomed large, though, and progress was slow compared to Linux (which wasn't party to the lawsuit and could move at full speed).

Finally, USL was bought by Novell, and Novell decided to call a truce. It was decided that, with the exception of small parts of code inside the kernel, BSD was solely under Berkeley's license, and the UNIX trademark would be given over to X/Open. The decision meant that NetBSD and FreeBSD could return to full development, and by the late 1990s, development speed was on par with Linux. NetBSD itself would later be forked into OpenBSD, which has an emphasis on security, and FreeBSD 4.0 was forked into DragonFlyBSD, due to a disagreement over an architectural change in FreeBSD 5.0.

Linux and the BSDs were so successful that they relegated proprietary UNIX systems to specialized uses through the '90s and the '00s.

    The Open Source Movement 

Not long after this, another development in the software world had a huge impact on UNIX and the Internet. The World Wide Web was finally gaining in popularity after years of development, and the vehicle most people used to access web content was a program called "Netscape Navigator". The company behind it, also called Netscape, had placed the software under a license that allowed free usage for individuals and non-commercial organizations, but required payment for use in corporations; it was hoped that corporations would also invest in their server software, which was top-of-the-line for the time and quite expensive. The problems started when it turned out few people were registering their copies of Netscape; despite what the license said, registration was never mandatory and the program was effectively free to anyone interested. To add to this, Netscape's server software was being severely threatened by the Apache HTTP Server, which was not only free but gaining steadily in market share (and to this day is still the most popular Web server on the Internet by a wide margin, even beating Microsoft's own Internet Information Services). Finally, Microsoft introduced Windows 98 with an "Active Desktop" feature that integrated Web-browser functionality with the Windows desktop.

Strangely, Netscape was actually more upset over what Microsoft did (and the loss of affiliate revenue it would have cost them) than the fact that their server business was dying, and decided to sue Microsoft in a landmark antitrust suit. But that wasn't the only strange thing Netscape did in 1998.

Inspired by the success of Linux and the BSDs, and no doubt knowing that the company itself was in bad shape, Netscape decided to release the sources to the latest version of Communicator (amounting to Navigator plus an email client and an HTML editor) under a free license. Out of the meetings for this came a term called "open source", which attempted to provide the gist of the free software movement's goals without having to go into licensing details, making it easier for people not up on their legalese to understand what was going on.

This was a controversial move. GNU partisans have said that it draws attention away from the ideological purpose, "missing the point" as it were, whereas others have argued that the English word "free" is too often used to mean "free-of-charge" to be understood correctly, and that said misunderstanding would give the impression that the software is worthless from a business perspective.note 

Either way, the term stuck, and "open source" now indicates any software license that conforms to the Open Source Definition, a set of rules based on the Debian Free Software Guidelines (Debian being a highly influential and somewhat conservative distribution of Linux).

As for Netscape, most of the company migrated to Mozilla Foundation (originally known as the Mozilla Organization),note  a non-profit founded to handle the development of a new browser based on the Communicator code. After a few false starts (including a decision to rewrite most of the client from scratch, a move that rankled some of the Netscape veterans), the new browser was in usable shape by 2003. A slimmed-down version corresponding to Navigator only (without the built-in mail/news reader or the Web page editor) was developed alongside it, and eventually became Mozilla Firefox.note  A slimmed-down version consisting of only the email/news reader eventually became Mozilla Thunderbird. note  The full-blown internet suite was originally planned to be left for dead, but said group of Netscape veterans saved it by bringing it under their wing, rechristened it Seamonkey, and brought it back in shape.

UNIX today

Now, in The New Twenties, UNIX and its clones and derivatives have become more popular than ever. ChromeOS and various other PC-centric distributions of Linux are giving Microsoft a run for its money for the first time in years, especially on low-end PCs that can't run the latest versions of Microsoft Windows well. The adoption of Linux on older PCs was also helped by supply chain issues in the wake of the COVID-19 Pandemic making new PCs harder to come by. A resurgent Mac (running UNIX itself) is also competing with Microsoft on the high end. Still, desktop use of Linux is more popular with developers, engineers and anti-Microsoft technophiles rather than the general public, though pre-installed Linux computers are more common outside of the U.S. The BSDs are popular in server, networking and security-related applications; NetBSD in particular also supports a bevy of older machines (including vintage minicomputers like the DEC VAX) that would otherwise be forgotten.

Amusingly, Windows itself eventually added official support for Linux distributions and applications through the Windows Subsystem for Linux; the first version is Middleware like the existing open-source MSYS and Cygwin packages, but WSL 2 uses a real Linux kernel virtualized through Hyper-V, which increases performance and compatibility, especially with networking tools. WSLg allows both X11 and Wayland graphical apps to run in Windows.

Apple decided to open-source the kernel and user tools for Darwin (the basis of macOS (formerly OS X) and iOS), and even Solaris (one of the last bastions of old-school commercial UNIX) has since been opened up—just to close again after Sun was bought up by Oracle, which caused much of the community to fork the last open release into the illumos project, and OpenIndiana, formerly a community respin of OpenSolaris, was subsequently refactored to use the illumos kernel.

There are also several forks of the official Linux kernel, and other UNIX-style systems, being used on high-end electronic devices and smartphones, as well as in networking gear like Ethernet switches and routers, and in many embedded devices. For example: Apple's iOS, used on the iPhone, iPod Touch, and iPad, contains code from the Darwin base of MacOS (formerly OS X), which contains code forked from FreeBSD and NeXTSTEP, the latter of which is based on 4.3BSD. Google's Android operating system, iOS's main competitor, contains a fork of the Linux kernel at its core. Also, Sony has confirmed that the PlayStation 4's OS is in fact a customized version of FreeBSD while its predecessor, PlayStation 3, used a customized FreeBSD kernel alongside various proprietary libraries. This continues into the release of the PlayStation 5, which also used the FreeBSD kernel. Several home routers also run Linux: either by default, or modded by way of DD-WRT, OpenWRT or Tomato. Linux even powers a number of Midway Games' slot and gambling machines, and some arcade game manufacturers (ie Bandai Namco Entertainment with their Wangan Midnight series starting from WMMT4) prefer Linux to Windows Embedded due to the practically nonexistent licensing costs.

The development of "netbooks"—small, simple, low-cost, low-power laptop computers geared towards Internet functionality at the expense of gaming and multimedia—also worked in UNIX's favor. Many discarded the traditional x86 architecture, due to power consumption and cost concerns, in favor of the ARM (Advanced RISC Machinenote ) architecture used by the vast majority of embedded devices such as cell phones. The only current version of Microsoft Windows for ARM processors is a variant of Windows 10 for tablets and netbooks, which replaced both the largely incompatible "Windows RT" (a modified version of Windows 8) and Windows 10 Mobile, and the vast majority of ARM netbooks run UNIX-style OSs, usually Linux OSs. For example, Chromebooks run Chrome OS, a specialized Gentoo Linux variant.

Gaming on Linux has long been a sore spot, with many bigger studios declining to port their games over to the platform. This began to improve in 2013 when Valve Software created a derivative of Debian called SteamOS More info , which powers its line of Steam Machine consoles but also is free to download for anyone interested in using their own custom hardware. However, the OS and its complementary Steam Machine hardware failed to take off, with fewer than a million units sold and most vendors discontinuing the product by 2016. It has been speculated that this was due to poor initial builds and delays in updates and hardware, with Microsoft rolling out the free Windows 10 upgrade promotion at the same time to steal its thunder. Though development was put in hiatus on July 2019, in July 2021 the Steam Deck was announced: a handheld designed for PC games, running an overhauled version of SteamOS, now based on Arch Linux. In 2018 Valve released Proton, a compatibility layer that essentially makes it possible to run Windows software on Linux.More info  A site, ProtonDB, keeps track of how well each game performs on Linux, and as of December 2021 about 75% of all Steam games can be played with little issue, of which around 20% have native Linux ports. With over a million Decks sold, this led to Linux finally beginning to gain a much stronger foothold in the gaming market.

Furthermore, a lot of game engines and anti-cheat systems that were previously either hard to port over to Linux, or just outright incompatible - such as Unity, Unreal Engine, Source / Source 2, EasyAntiCheat and BattlEye - are being properly supported now. This is largely due to the common practice of indie developers making Linux ports for crowdfunding backers and a (very) slow, but noteworthy, increase in Linux market share renewing interest in the platform by larger companies. The move is seen as encouraging, and many fans of Linux believe this to be finally signalling the rise of Linux as a serious competitor to Windows in the gaming arena. Several game console and computer emulators also have native Linux support, so that's a bonus.

Whatever happens, Unix's flexibility and portability mean that it will continue to be a platform of choice for technical computer users for a long time.

Linux and its distributions

A distribution, or distro, is simply a packaged up Linux kernel with various apps to support it in order to create a fully functioning operating system. If you think of an operating system as a vehicle, the Linux kernel is the engine. A single engine design can can support multiple types of vehicles, with each vehicle catering to certain customers' specific needs.

While there are dozens upon dozens of distributions, most of them have branched off from one of these main roots:

  • Slackware: One of the first distributions to be widely circulated. Its goals are to be the most "Unix-like" distribution with as few software packages and modifications as possible. As such, it requires more work to get it set up and is recommended for advanced Linux users.
  • SUSE: One of the earliest distributions, mostly aimed at business and enterprise use. Very similar to Red Hat, both in use of the RPM package format and having spawned openSUSE (which also spawned a user-friendly distro in GeckoLinux, as well).
  • Debian: Debian's aim is to be as stable as possible, boasting smooth upgrades between major and minor versions. With stability also comes security, two things the Debian maintainers boast. Because of this, Debian has many distributions based on it, with Ubuntu and its children being one of the most successful line of derivatives. Other notable distributions based on Debian include MX Linux, antiX (both MX and antiX are based off of the former MEPIS OS), elementary OS (for newcomers from Apple Mac OS), Zorin OS (for newcomers from Windows), deepin, Linux Mint, Pop!_OS and early versions of both Solus and steamOS.
  • Red Hat: A distribution aimed at the commercial and enterprise market, Red Hat takes advantage of a note in GNU's philosophy that even though software down to its source should be made freely available, that doesn't mean one can't find a way to make money off of it. The company that originally maintained it was even bought out by IBM. As such, Red Hat doesn't sell a product (the software), it sells a service (support). However, due to the package management services requiring a subscription fee, Red Hat has spawned free (as in beer) community supported offshoots in Fedora, with some like AlmaLinux, EuroLinux and Rocky Linux used by smaller businesses in place of Red Hat. A few notable Fedora forks include Nobara (mainly for gamers), Ultramarine (meant to be the spiritual successor to the now-dead Korora which was an all-purpose respin that started out as a Gentoo fork) and risiOS.
  • Gentoo (previously Enoch): Gentoo is all about performance and customizability. To this end, virtually everything on a Gentoo system is built from source code. The Portage package manager lets the user specify the features they want and don't want in each app through USE flags, so apps can be built specifically for their intended use case without unnecessary functionality. Such customization is not possible with conventional Linux distributions that provide ready-made executables. This build process also allows the use of machine-specific compiler optimizations to maximize performance for the specific hardware in use. But these advantages come at a cost. Gentoo is notorious for being one of the most difficult Linux distributions to properly install and configure, and the compilation process can be extremely taxing on hardware. Some apps, such as Chromium,note  can require hours to compile, even on the fastest consumer multi-core processors. For these reasons, compiled binary packages are also available. Its most popular offshoot is Chrome OS. Other distributions from it include Calculate Linux, Funtoo, Mocaccino OS (formerly Sabayon Linux), Pentoo and Redcore Linux.
  • Arch: Arch's primary philosophy is to be on the cutting edge. As such, it uses a rolling release model for updates (going so far as to release monthly snapshots as installation media) and applications are distributed as compiled binaries. Arch is officially only optimized for x86-64 architectures, although there is also limited community-backed support for ARM and the legacy x86 architecture. In addition, Arch also holds onto the design philosophy that thing are kept as simple as possible, such as having no official graphical front-end for its package distribution system (although a third party GUI front-end, tkpacman, does exist). This leads it to being one of the harder distributions to work with. Seven notable distributions based on Arch include Endeavour OS, which is based upon a former easy-installer distribution in Antergos (also found with Reborn OS); Manjaro, Garuda (mainly centered around gamers), ArcoLinux, Artix Linux (an Arch-based system that uses different init systems such as OpenRC, runit and s6), Obarun (another Arch-based system that uses only the s6 init system) and recent versions of steamOS.

Other notable Linux kernel based distributions/operating systems include:

  • Softlanding Linux System (or SLS): SLS was one of the very first distributions to hit the scene. The name "softlanding" comes from the idea that it has a "gentler" learning curve for DOS users to transition to. However, a lot of its users found SLS to be buggy, to the point where some of them decided to do one better. This spawned Slackware, which started off as a clean-up project of SLS, and Debian.
  • Linux From Scratch: More of an e-book than a Linux distro, the e-book contains instructions to build a working Linux distribution from scratch. It is very time-consuming and somewhat difficult as it assumes that the user has a basic understanding of how Linux works, and new users are advised to steer clear of it; as even straying from the formula a bit would result in failure. Likewise, it is often recommended to newbies by trolls to create frustration.
  • DD-WRT: A Linux distribution that aims to be the replacement firmware for a number of routers, most notably Cisco's and Linksys' kits. You're likely to have heard of it while browsing for router suggestions online. This distribution has three spinoffs: OpenWRT, AdvancedTomato (formerly TomatoWRT) which is a fork of DD-WRT that specializes on Broadcom System-on-Chips, and AsusWRT-Merlin (formerly MerlinWRT) which primarily targets Asus routers.
  • Android: A Linux-based OS designed for mobile devices, although it was later co-opted by set-top boxes and Smart TVs. Although it had a slow start in the late 2000s, its open nature allowed many manufacturers to build a smartphone based around it. It eventually displaced other smartphone based OSes like Blackberry OS, webOS (from Palm), Symbian OS (latterly from Nokia), and Windows Mobile. It's now the most popular smartphone OS, outpacing its immediate competitor of Apple's iOSnote  nearly 3 to 1. As for offshoots, mobile manufacturers often distribute Android with their own customisations (such as TouchWiz and OneUI from Samsung) but these are usually still authorized to call themselves Android and use the Google Play app store; exceptions include Amazon's Fire OS and certain versions of Huawei's EMUI which use their own app stores. Android has also been spun off several times, the most active spinoff at the moment is LineageOS. Android was primarily made with ARM processors in mind, but there is a fork named Android-x86 that is Exactly What It Says on the Tin, an Android system geared for x86_64 processors made by Intel and AMD with its own slew of spinoffs such as Bliss OS, Remix OS and Phoenix OS. And yes Windows recently added support for Android apps with Windows 11.
    • Many modern Linux users got their start with Android, so in a way, Android is considered a Gateway Series.
  • kaiOS: What Android is to smartphones, kaiOS is to keypad based, lower end feature phones. It had its roots from the defunct smartphone OS alternative Firefox OS, reworked to be light on resource usage, updated for the latest web technologies with help from Mozilla, and apps are primarily web-based despite having an app store.
  • Red Star OS: Red Star OS note  is a North Korean Linux distribution, with development first starting in 1998 at the Korea Computer Center (KCC). While earlier versions have designs modelled after Windows XP or 7, version 3 onwards are made to look like Mac OS.
  • Raspberry Pi OS, previously known as Raspbiannote , is a customised distribution intended for use with the Raspberry Pi family of compact single-board computers, and optimised to run on their hardware. As a seriously popular choice for hobbyists (it's the best selling British computer in history, surpassing the unit sales of the previous record holder, the ZX Spectrum, as of 2015) the Pi and Pi OS have become a pretty popular way to begin using Linux.
Wikipedia has an image showing a timeline of many Linux distributions and their lineage if they were branched off one from another distribution. There's also a comparison of selected distributions.

The first question most people ask when getting into Linux for the first time is which distribution should they go with? Typically one designed for user-friendliness such as Ubuntu or Linux Mint are highly recommended as they hide much of the more nuanced things you have to learn with the other types of Linux distros. Some even aim to emulate Windows or macOS to ease the learning curve in using another OS. Overall though, unless you're doing something really esoteric or novel, there's likely a Linux distribution that suits your needs.

Alternative Title(s): Linux