View source for Unix

{{Short description|Family of computer operating systems}}
{{pp-move|small=yes}}
{{Use mdy dates|date=October 2018}}
{{Use American English|date=August 2018}}
{{Infobox OS
| name = Unix
| logo = UNIX logo.svg
| logo_size = 220px
| screenshot = Simh-pdp11-unix-sysiii.png
| screenshot_size = 250px
| caption = [[Unix System III]] running on a [[PDP-11]] simulator
| developer = [[Ken Thompson]], [[Dennis Ritchie]], [[Brian Kernighan]], [[Douglas McIlroy]], and [[Joe Ossanna]] at [[Bell Labs]]
| programmed_in = [[C (programming language)|C]] and [[assembly language]]
| family = Unix
| source_model = Historically [[proprietary software]], while some Unix projects (including [[Berkeley Software Distribution|BSD]] family and [[illumos]]) are [[open-source software|open-source]] and historical Unix source code is archived.
| released = Development started in 1969<br />First manual published [[Research Unix|internally]] in {{start date|1971|11}}<ref name="reader"/><br />Announced outside Bell Labs in {{start date|1973|10}}<ref>{{cite journal |first1=D. M. |last1=Ritchie |author1-link=Dennis Ritchie |first2=K. |last2=Thompson |author2-link=Ken Thompson |year=1974 |url=https://www.bell-labs.com/usr/dmr/www/cacm.pdf |title=The UNIX Time-Sharing System |journal=Communications of the ACM |volume=17 |issue=7 |pages=365–375 |url-status=live |archive-url=https://web.archive.org/web/20150611114359/https://www.bell-labs.com/usr/dmr/www/cacm.pdf |archive-date=June 11, 2015 |df=dmy-all |doi=10.1145/361011.361061 |citeseerx=10.1.1.118.1214 |s2cid=53235982 }}</ref>
| language = English
| kernel_type = Varies; [[Monolithic kernel|monolithic]], [[microkernel]], [[hybrid kernel|hybrid]]
| influenced_by = [[Compatible Time-Sharing System|CTSS]],<ref>{{cite conference
 |last=Ritchie
 |first=Dennis M.
 |author-link=Dennis Ritchie
 |year=1977
 |title=The Unix Time-sharing System: A retrospective
 |conference=Tenth Hawaii International Conference on the System Sciences
 |url=https://www.bell-labs.com/usr/dmr/www/retro.pdf
 |url-status=live
 |access-date=2024-09-26
 |archive-url=https://web.archive.org/web/20150611114405/https://www.bell-labs.com/usr/dmr/www/retro.pdf
 |archive-date=2015-06-11
 |quote=a good case can be made that [UNIX] is in essence a modern implementation of MIT’s CTSS system
}}</ref> [[Multics]]
| ui = [[Command-line interface]] and [[Graphical user interface|Graphical]] ([[Wayland (protocol)|Wayland]] and [[X Window System]]; [[Android (operating system)|Android]] [[SurfaceFlinger]]; [[macOS]] [[Quartz (graphics layer)|Quartz]])
| license = Varies; some versions are [[Proprietary software|proprietary]], others are [[free software|free/libre]] or [[open-source software]]
| website = {{URL|www.opengroup.org/unix}}
}}
{{Internet history timeline}}

'''Unix''' ({{IPAc-en|ˈ|j|uː|n|ᵻ|k|s|audio=en-us-Unix.oga}}, {{Respell|YOO|niks}}; trademarked as '''UNIX''') is a family of [[Computer multitasking|multitasking]], [[multi-user software|multi-user]] computer [[operating system]]s that derive from the original [[AT&T Corporation|AT&T]] Unix, whose development started in 1969<ref name="reader">{{cite tech report |first1=M. D. |last1=McIlroy |author-link1=Doug McIlroy |year=1987 |url=http://www.cs.dartmouth.edu/~doug/reader.pdf |title=A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 |series=CSTR |number=139 |institution=Bell Labs |url-status=live |archive-url=https://web.archive.org/web/20171111151817/http://www.cs.dartmouth.edu/~doug/reader.pdf |archive-date=November 11, 2017 |df=dmy-all }}</ref> at the [[Bell Labs]] research center by [[Ken Thompson]], [[Dennis Ritchie]], and others.<ref name="Ritchie">{{cite journal | last = Ritchie | first = D.M. | author-link = Dennis Ritchie | author2 = Thompson, K. | author2-link=Ken Thompson | title = The UNIX Time-Sharing System | journal = Bell System Tech. J. | volume = 57 | issue = 6 | pages = 1905–1929 | date = July 1978 | url = https://archive.org/details/bstj57-6-1905 | access-date = December 9, 2012 | doi = 10.1002/j.1538-7305.1978.tb02136.x| citeseerx = 10.1.1.112.595 }}</ref> Initially intended for use inside the [[Bell System]], AT&T [[license]]d Unix to outside parties in the late 1970s, leading to a variety of both academic and commercial Unix variants from vendors including [[University of California, Berkeley]] ([[Berkeley Software Distribution|BSD]]), [[Microsoft]] ([[Xenix]]), [[Sun Microsystems]] ([[SunOS]]/[[Solaris (operating system)|Solaris]]), [[Hewlett-Packard|HP]]/[[Hewlett Packard Enterprise|HPE]] ([[HP-UX]]), and [[IBM]] ([[IBM AIX|AIX]]).<!--END Brief intro-->

<!--Capabilities and use:-->The early versions of Unix—which are retrospectively referred to as "[[Research Unix]]"—ran on computers such as the [[PDP-11]] and [[VAX]]; Unix was commonly used on [[minicomputers]] and [[Mainframe computer|mainframes]] from the 1970s onwards.<ref>{{cite news |last1=Schwartz |first1=John |title=Microsoft's Next Trials |url=https://www.washingtonpost.com/archive/business/2000/06/11/microsofts-next-trials/4087113f-05e9-4ce2-bb3d-3ea0ee2faf9b/ |access-date=17 December 2024 |newspaper=[[The Washington Post]] |date=11 June 2000 |archive-url=https://web.archive.org/web/20241213184850/https://www.washingtonpost.com/archive/business/2000/06/11/microsofts-next-trials/4087113f-05e9-4ce2-bb3d-3ea0ee2faf9b/ |archive-date=13 December 2024}}</ref> It distinguished itself from its predecessors as the first [[Software portability|portable]] operating system: almost the entire operating system is written in the [[C (programming language)|C programming language]] (in 1973), which allows Unix to operate on numerous platforms.<ref name="dottcl">{{cite web |last=Ritchie |first=Dennis M. |author-link=Dennis Ritchie |date=January 1993 |title=The Development of the C Language |url=https://www.bell-labs.com/usr/dmr/www/chist.pdf |url-status=live |archive-url=https://web.archive.org/web/20150611114354/https://www.bell-labs.com/usr/dmr/www/chist.pdf |archive-date=June 11, 2015 |access-date=July 30, 2022 |df=dmy-all}}</ref> Unix systems are characterized by a [[modular design]] that is sometimes called the "[[Unix philosophy]]". According to this philosophy, the operating system should provide a set of simple tools, each of which performs a limited, well-defined function.<ref>{{cite book |title=The Art of Unix Programming |first=Eric |last=Raymond |author-link=Eric S. Raymond |date=September 19, 2003 |isbn=978-0-13-142901-7 |publisher=Addison-Wesley |url=http://www.catb.org/~esr/writings/taoup/html/ |access-date=February 9, 2009 |url-status=live |archive-url=https://web.archive.org/web/20090212183726/http://www.catb.org/~esr/writings/taoup/html/ |archive-date=February 12, 2009 |df=dmy-all }}</ref> A unified and [[inode]]-based [[Unix filesystem|filesystem]] and an [[inter-process communication]] mechanism known as "[[pipeline (Unix)|pipes]]" serve as the main means of communication,<ref name="Ritchie" /> and a [[shell (computing)|shell]] scripting and command language (the [[Unix shell]]) is used to combine the tools to perform complex workflows.<!--END Capabilities and use-->

<!--Brief history of releases:-->[[Version 7 Unix|Version 7]] in 1979 was the final widely released Research Unix, after which AT&T sold [[UNIX System III]], based on Version 7, commercially in 1982; to avoid confusion between the Unix variants, AT&T combined various versions developed by others and released it as [[UNIX System V]] in 1983. However as these were closed-source, the University of California, Berkeley continued developing BSD as an alternative. Other vendors that were beginning to create commercialized versions of Unix would base their version on either System V (like [[Silicon Graphics]]'s [[IRIX]]) or BSD (like SunOS). Amid the "[[Unix wars]]" of standardization, AT&T alongside Sun merged System V, BSD, SunOS and Xenix, soldifying their features into one package as UNIX System V Release 4 (SVR4) in 1989, and it was commercialized by [[Unix System Laboratories]], an AT&T spinoff.<ref name="timeline-40-years">{{Cite web |first=Gary |last=Anthes |date=June 4, 2009 |title=Timeline: 40 Years Of Unix |url=https://www.computerworld.com/article/1554222/timeline-40-years-of-unix-3.html |access-date=2024-12-04 |website=[[Computerworld]]}}</ref><ref>{{cite news |last1=Lewis |first1=Peter H. |title=Is Unix's Time Finally at hand? |url=https://www.nytimes.com/1988/06/12/business/the-executive-computer-is-unix-s-time-finally-at-hand.html |url-access=subscription |access-date=17 December 2024 |work=[[The New York Times]] |date=12 June 1988 |archive-url=https://web.archive.org/web/20110205124224/https://www.nytimes.com/1988/06/12/business/the-executive-computer-is-unix-s-time-finally-at-hand.html |archive-date=5 February 2011}}</ref> A rival Unix by other vendors was released as [[OSF/1]], however most commercial Unix vendors eventually changed their distributions to be based on SVR4 with BSD features added on top.<!--END Brief history of releases--><!--Legacy & current:-->

AT&T sold Unix to [[Novell]] in 1992, who later sold the UNIX trademark to a new industry consortium called [[The Open Group]] which allow the use of the mark for certified operating systems that comply with the [[Single UNIX Specification]] (SUS).<ref name="timeline-40-years" /> Since the 1990s, Unix systems have appeared on [[Home computers|home-class computers]]: [[BSD/OS]] was the first to be commercialized for [[i386]] computers and since then free [[Unix-like]] clones of existing systems have been developed, such as [[FreeBSD]] and the combination of [[Linux]] and [[GNU]], the latter of which have since eclipsed Unix in popularity. Unix was, until 2005, the most widely used [[Server (computing)|server]] operating system.<ref>{{Cite web |last=Bangeman |first=Eric |date=2006-02-22 |title=Windows passes Unix in server sales |url=https://arstechnica.com/uncategorized/2006/02/6236/ |access-date=2024-12-05 |website=Ars Technica |language=en-US}}</ref> However in the present day, Unix distributions like IBM AIX, Oracle Solaris and [[OpenServer]] continue to be widely used in certain fields.<ref>{{Cite web |last=Garvin |first=Skip |date=2019-09-19 |title=Top IBM Power Systems myths: "IBM AIX is dead and Unix isn't relevant in today's market" (part 2) |url=https://www.ibm.com/blog/top-ibm-power-systems-myths-ibm-aix-is-dead-and-unix-isnt-relevant-in-todays-market-part-2/ |access-date=2024-12-05 |website=IBM Blog |language=en-US}}</ref><ref>{{cite news | url=https://www.theregister.com/2023/01/17/unix_is_dead/ | title=Unix is dead. Long live Unix! }}</ref><!--END Legacy & current--><!--Do not add more than 4 paragraphs; keep the intro simple and concise.-->

== Overview ==
[[File:Version 7 Unix SIMH PDP11 Emulation DMR.png|thumb|[[Version 7 Unix]], the [[Research Unix]] ancestor of all modern Unix systems]]

Unix was originally meant to be a convenient platform for programmers developing software to be run on it and on other systems, rather than for non-programmers.<ref>{{cite book|url=http://www.catb.org/~esr/writings/taoup/html/|title=The Art of Unix Programming|chapter-url=http://www.faqs.org/docs/artu/ch03s01.html|chapter=The Elements of Operating-System Style|first=Eric Steven|last=Raymond|author-link=Eric S. Raymond|date=2003|access-date=August 16, 2020}}</ref><ref>{{cite book |quote=UNIX was created by software developers for software developers, to give themselves an environment they could completely manipulate.|url=https://archive.org/stream/Whole_Earth_Software_Catalog_1984_Point/Whole_Earth_Software_Catalog_1984_Point_djvu.txt |title=Tandy/Radio Shack Book: Whole Earth Software Catalog |year=1984|isbn=9780385191661 |last1=Brand |first1=Stewart |publisher=Quantum Press/Doubleday |author1-link=Stewart Brand }}</ref><ref>{{cite web |last1=Spolsky |first1=Joel |author1-link=Joel Spolsky |title=Biculturalism |url=https://www.joelonsoftware.com/2003/12/14/biculturalism/ |website=Joel on Software |access-date=21 March 2021 |date=14 December 2003 |quote=When Unix was created and when it formed its cultural values, ''there were no end users''.}}</ref> The system grew larger as the operating system started spreading in academic circles, and as users added their own tools to the system and shared them with colleagues.<ref>{{cite book | last1 = Powers | first1 = Shelley | author1-link = Shelley Powers | last2 = Peek | first2 = Jerry | last3 = O'Reilly | first3 = Tim | author3-link = Tim O'Reilly | last4 = Loukides | first4 = Mike | title = Unix Power Tools | year = 2002 | publisher = "O'Reilly Media, Inc." | isbn = 978-0-596-00330-2}}</ref>

At first, Unix was not designed to support [[computer multitasking|multi-tasking]]<ref name="DMR"/> or to be [[porting|portable]].<ref name="dottcl" /> Later, Unix gradually gained multi-tasking and [[multi-user]] capabilities in a [[time-sharing]] configuration, as well as portability. Unix systems are characterized by various concepts: the use of [[plain text]] for storing data; a [[hierarchical file system]]; treating devices and certain types of [[inter-process communication]] (IPC) as files; and the use of a large number of [[programming tool|software tools]], small programs that can be strung together through a [[command-line interpreter]] using [[pipeline (Unix)|pipes]], as opposed to using a single monolithic program that includes all of the same functionality. These concepts are collectively known as the "[[Unix philosophy]]". [[Brian Kernighan]] and [[Rob Pike]] summarize this in ''[[The Unix Programming Environment]]'' as "the idea that the power of a system comes more from the relationships among programs than from the programs themselves".<ref>Kernighan, Brian W. Pike, Rob. ''The UNIX Programming Environment.'' 1984. viii</ref>

By the early 1980s, users began seeing Unix as a potential universal operating system, suitable for computers of all sizes.<ref>{{cite news | url=https://archive.org/stream/byte-magazine-1983-10/1983_10_BYTE_08-10_UNIX#page/n133/mode/2up | title=The Unix Tutorial / Part 3: Unix in the Microcomputer Marketplace | work=BYTE | date=October 1983 | access-date=January 30, 2015 | author=Fiedler, Ryan | page=132}}</ref><ref>{{cite book |quote=The best thing about UNIX is its portability. UNIX ports across a full range of hardware—from the single-user $5000 IBM PC to the $5 million Cray. For the first time, the point of stability becomes the software environment, not the hardware architecture; UNIX transcends changes in hardware technology, so programs written for the UNIX environment can move into the next generation of hardware. |title=Tandy/Radio Shack Book: Whole Earth Software Catalog |url=https://archive.org/stream/Whole_Earth_Software_Catalog_1984_Point/Whole_Earth_Software_Catalog_1984_Point_djvu.txt |year=1984|isbn=9780385191661 |last1=Brand |first1=Stewart |publisher=Quantum Press/Doubleday |author1-link=Stewart Brand }}</ref> The Unix environment and the [[client–server]] program model were essential elements in the development of the [[Internet]] and the reshaping of computing as centered in [[Computer network|networks]] rather than in individual computers.

Both Unix and the [[C (programming language)|C programming language]] were developed by [[AT&T]] and distributed to government and academic institutions, which led to both being ported to a wider variety of machine families than any other operating system.

The Unix operating system consists of many libraries and utilities along with the master control program, the [[Kernel (operating system)|kernel]]. The kernel provides services to start and stop programs, handles the [[file system]] and other common "low-level" tasks that most programs share, and schedules access to avoid conflicts when programs try to access the same resource or device simultaneously. To mediate such access, the kernel has special rights, reflected in the distinction of ''kernel space'' from [[user space and kernel space|user space]], the latter being a lower priority realm where most application programs operate.

== History ==
{{main|History of Unix}}

The origins of Unix date back to the mid-1960s when the [[Massachusetts Institute of Technology]], [[Bell Labs]], and [[General Electric]] were developing [[Multics]], a [[time-sharing]] operating system for the [[GE 645]] mainframe computer.<ref>{{cite book
|title=Principles of operating systems: design & applications
|last=Stuart |first=Brian L.
|year=2009
|publisher=Thompson Learning
|location=Boston, Massachusetts
|isbn=978-1-4188-3769-3
|page=23
}}</ref>
Multics featured [[Multics#Novel ideas|several innovations]], but also presented severe problems. Frustrated by the size and complexity of Multics, but not by its goals, individual researchers at Bell Labs started withdrawing from the project. The last to leave were [[Ken Thompson]], [[Dennis Ritchie]], [[Douglas McIlroy]], and [[Joe Ossanna]],<ref name="DMR">{{cite web |first=Dennis M. |last=Ritchie |author-link=Dennis Ritchie |title=The Evolution of the Unix Time-sharing System |url=https://www.bell-labs.com/usr/dmr/www/hist.pdf |access-date=January 9, 2017 |url-status=live |archive-url=https://web.archive.org/web/20170403063715/https://www.bell-labs.com/usr/dmr/www/hist.pdf |archive-date=April 3, 2017 |df=dmy-all }}</ref> who decided to reimplement their experiences in a new project of smaller scale. This new operating system was initially without organizational backing, and also without a name.

The new operating system was a single-tasking system.<ref name="DMR" /> In 1970, the group coined the name ''Unics'' for ''Uniplexed Information and Computing Service'' as a [[word play|pun]] on ''[[Multics]]'', which stood for ''Multiplexed Information and Computer Services''. [[Brian Kernighan]] takes credit for the idea, but adds that "no one can remember" the origin of the final spelling ''Unix''.<ref>{{cite web |website=[[Linux Journal]] |first=Aleksey |last=Dolya |date=July 29, 2003 |url=http://www.linuxjournal.com/article/7035 |title=Interview with Brian Kernighan |url-status=live |archive-url=https://web.archive.org/web/20171018090033/https://www.linuxjournal.com/article/7035 |archive-date=October 18, 2017 |df=dmy-all }}</ref> Dennis Ritchie,<ref name="DMR" /> Doug McIlroy,{{r|reader}} and [[Peter G. Neumann]]<ref>{{cite journal|url=https://www.usenix.org/system/files/login/issues/login_winter17_issue.pdf|title=An Interview with Peter G. Neumann|author=Rik Farrow|journal=[[;login:]]|volume=42|issue=4|page=38|quote=That then led to Unics (the castrated one-user Multics, so- called due to Brian Kernighan) later becoming UNIX (probably as a result of AT&T lawyers).}}</ref> also credit Kernighan.

The operating system was originally written in [[assembly language]], but in 1973, Version 4 Unix was rewritten in [[C (programming language)|C]]. [[Ken Thompson]] faced multiple challenges attempting the kernel port due to the evolving state of C, which lacked key features like structures at the time.<ref name="DMR" /><ref>{{cite journal |last=Georgiadis |first=Evangelos |title=Dismantling Scaffolding |department=Letters to the Editor |journal=Communications of the ACM |date=2024 |volume=67 |doi=10.1145/3654698 |issn=0001-0782 |url=http://dx.doi.org/10.1145/3654698#sec-4}}</ref> Version 4 Unix, however, still had much [[PDP-11]] specific code, and was not suitable for porting. The first port to another platform was a port of Version 6, made four years later (1977) at the [[University of Wollongong]] for the [[Interdata 7/32 and 8/32|Interdata 7/32]],<ref>{{cite web|last1=Reinfelds|first1=Juris|title=The First Port of UNIX|url=https://www.uow.edu.au/content/groups/public/@web/@inf/@scsse/documents/doc/uow103747.pdf|access-date=30 June 2015}}</ref> followed by a Bell Labs port of Version 7 to the [[Interdata 7/32 and 8/32|Interdata 8/32]] during 1977 and 1978.<ref>{{cite web|url=https://www.bell-labs.com/usr/dmr/www/portpap.html |title=Portability of C Programs and the UNIX System |publisher=Bell-labs.com | access-date=August 24, 2018}}</ref>

Bell Labs produced several versions of Unix that are collectively referred to as ''[[Research Unix]]''. In 1975, the first source license for ''UNIX'' was sold to [[Donald B. Gillies]] at the [[University of Illinois Urbana–Champaign]] (UIUC) Department of Computer Science.<ref>{{cite web |website=UBC ECE website |first=Ken |last=Thompson |author-link=Ken Thompson |date=September 16, 2014 |url=http://www.ece.ubc.ca/~gillies/mail/dbgillies_ken_thompson.txt |title=personal communication, Ken Thompson to Donald W. Gillies |url-status=dead |archive-url=https://web.archive.org/web/20160322042314/http://www.ece.ubc.ca/~gillies/mail/dbgillies_ken_thompson.txt |archive-date=March 22, 2016 |df=dmy-all }}</ref>

During the late 1970s and early 1980s, the influence of Unix in academic circles led to large-scale adoption of Unix ([[Berkeley Software Distribution|BSD]] and [[UNIX System V|System V]]) by commercial startups, which in turn led to Unix fragmenting into multiple, similar — but often slightly and mutually incompatible — systems including [[DYNIX]], [[HP-UX]], [[SunOS]]/[[Solaris (operating system)|Solaris]], [[IBM AIX|AIX]], and [[Xenix]]. In the late 1980s, [[AT&T]] [[Unix System Laboratories]] and [[Sun Microsystems]] developed System&nbsp;V Release&nbsp;4 ([[SVR4]]), which was subsequently adopted by many commercial Unix vendors.

In the 1990s, Unix and [[Unix-like]] systems grew in popularity and became the operating system of choice for [[Usage share of operating systems#Supercomputers|over 90% of the world's top 500 fastest supercomputers]],<ref name="top500osfam201706">{{cite web | url = http://www.top500.org/statistics/overtime | title = Operating system Family - Systems share | publisher = Top 500 project}}</ref> as [[Berkeley Software Distribution|BSD]] and [[Linux]] distributions were developed through collaboration by a worldwide network of programmers. In 2000, Apple released [[Darwin (operating system)|Darwin]], also a Unix system, which became the core of the Mac OS X operating system, later renamed [[macOS]].<ref>{{cite web
 |url         = https://developer.apple.com/library/mac/#documentation/MacOSX/Conceptual/OSX_Technology_Overview/SystemTechnology/SystemTechnology.html#//apple_ref/doc/uid/TP40001067-CH207-BCICAIFJ
 |title       = Loading
 |publisher   = Apple Developer
 |access-date  = August 22, 2012
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20120609170929/http://developer.apple.com/library/mac/#documentation/MacOSX/Conceptual/OSX_Technology_Overview/SystemTechnology/SystemTechnology.html
 |archive-date = June 9, 2012
 |df          = dmy-all
}}</ref>

Unix-like operating systems are widely used in modern [[Server (computing)|servers]], [[workstation]]s, and [[mobile device]]s.<ref>{{cite web |url=http://www.asymco.com/2010/09/29/unixs-revenge/ |title=Unix's Revenge |publisher=asymco |date=September 29, 2010 |access-date=November 9, 2010 |url-status=live |archive-url=https://web.archive.org/web/20101109010117/http://www.asymco.com/2010/09/29/unixs-revenge/ |archive-date=November 9, 2010 |df=dmy-all }}</ref>

== Standards ==
[[File:CDE 2012 on Linux.png|thumb|The [[Common Desktop Environment]] (CDE), part of the [[Common Open Software Environment|COSE initiative]]]]

In the late 1980s, an open operating system standardization effort now known as [[POSIX]] provided a common baseline for all operating systems; [[IEEE]] based POSIX around the common structure of the major competing variants of the Unix system, publishing the first POSIX standard in 1988. In the early 1990s, a separate but very similar effort was started by an industry consortium, the [[Common Open Software Environment]] (COSE) initiative, which eventually became the [[Single UNIX Specification]] (SUS) administered by [[The Open Group]]. Starting in 1998, the Open Group and IEEE started the [[Austin Group]], to provide a common definition of POSIX and the Single UNIX Specification, which, by 2008, had become the Open Group Base Specification.

In 1999, in an effort towards compatibility, several Unix system vendors agreed on SVR4's [[Executable and Linkable Format]] (ELF) as the standard for binary and object code files. The common format allows substantial binary compatibility among different Unix systems operating on the same CPU architecture.

The [[Filesystem Hierarchy Standard]] was created to provide a reference directory layout for Unix-like operating systems; it has mainly been used in Linux.

== Components ==
{{see also|List of Unix commands}}
{{More citations needed|section|date=October 2023}}

The Unix system is composed of several components that were originally packaged together. By including the development environment, libraries, documents and the portable, modifiable source code for all of these components, in addition to the [[Kernel (operating system)|kernel]] of an operating system, Unix was a self-contained software system. This was one of the key reasons it emerged as an important teaching and learning tool and has had a broad influence. See {{section link||Impact}}, below.

The inclusion of these components did not make the system large{{snd}} the original V7 UNIX distribution, consisting of copies of all of the compiled binaries plus all of the source code and documentation occupied less than 10&nbsp;MB and arrived on a single nine-track [[Magnetic-tape data storage|magnetic tape]], earning its reputation as a portable system.<ref>{{Cite web |title=Unix: the operating system setting new standards |url=https://www.ionos.com/digitalguide/server/know-how/unix-a-history/ |access-date=2022-05-10 |website=IONOS Digitalguide |date=May 29, 2020 |language=en}}</ref> The printed documentation, typeset from the online sources, was contained in two volumes.

The names and filesystem locations of the Unix components have changed substantially across the history of the system. Nonetheless, the V7 implementation has the canonical early structure:
* ''Kernel''{{snd}} source code in /usr/sys, composed of several sub-components:
** ''conf''{{snd}} configuration and machine-dependent parts, including boot code
** ''dev''{{snd}} device drivers for control of hardware (and some pseudo-hardware)
** ''sys''{{snd}} operating system "kernel", handling memory management, process scheduling, system calls, etc.
** ''h''{{snd}} header files, defining key structures within the system and important system-specific invariables
* ''Development environment''{{snd}} early versions of Unix contained a development environment sufficient to recreate the entire system from source code:
** ''[[ed (software)|ed]]''{{snd}} text editor, for creating source code files
** ''cc''{{snd}} [[C (programming language)|C language]] compiler (first appeared in V3 Unix)
** ''as''{{snd}} machine-language assembler for the machine
** ''ld''{{snd}} [[linker (computing)|linker]], for combining object files
** ''lib''{{snd}} object-code libraries (installed in /lib or /usr/lib). ''[[C standard library|libc]]'', the system library with C run-time support, was the primary library, but there have always been additional libraries for things such as mathematical functions (''[[libm]]'') or database access. V7 Unix introduced the first version of the modern "Standard I/O" library ''stdio'' as part of the system library. Later implementations increased the number of libraries significantly.
** ''[[make (software)|make]]''{{snd}} build manager (introduced in [[PWB/UNIX]]), for effectively automating the build process
** ''include''{{snd}} header files for software development, defining standard interfaces and system invariants
** ''Other languages''{{snd}} V7 Unix contained a Fortran-77 compiler, a programmable arbitrary-precision calculator (''bc'', ''dc''), and the [[AWK|awk]] scripting language; later versions and implementations contain many other language compilers and toolsets. Early BSD releases included [[Pascal (programming language)|Pascal]] tools, and many modern Unix systems also include the [[GNU Compiler Collection]] as well as or instead of a proprietary compiler system.
** ''Other tools''{{snd}} including an object-code archive manager (''[[ar (Unix)|ar]]''), symbol-table lister (''nm''), compiler-development tools (e.g. ''[[Lex (software)|lex]]'' & ''[[yacc]]''), and debugging tools.
* ''Commands''{{snd}} Unix makes little distinction between commands (user-level programs) for system operation and maintenance (e.g. ''[[cron]]''), commands of general utility (e.g. ''[[grep]]''), and more general-purpose applications such as the text formatting and typesetting package. Nonetheless, some major categories are:
** ''[[Bourne shell|sh]]''{{snd}} the "shell" programmable [[command-line interpreter]], the primary user interface on Unix before window systems appeared, and even afterward (within a "command window").
** ''Utilities''{{snd}} the core toolkit of the Unix command set, including ''[[cp (Unix)|cp]]'', ''[[ls]]'', ''[[grep]]'', ''[[find (Unix)|find]]'' and many others. Subcategories include:
*** ''System utilities''{{snd}} administrative tools such as ''[[mkfs]]'', ''[[fsck]]'', and many others.
*** ''User utilities''{{snd}} environment management tools such as ''passwd'', ''kill'', and others.
** ''Document formatting''{{snd}} Unix systems were used from the outset for document preparation and typesetting systems, and included many related programs such as ''[[nroff]]'', ''[[troff]]'', ''[[tbl]]'', ''[[eqn (software)|eqn]]'', ''[[refer (software)|refer]]'', and ''[[PIC (markup language)|pic]]''. Some modern Unix systems also include packages such as [[TeX]] and [[Ghostscript]].
** ''Graphics''{{snd}} the ''plot'' subsystem provided facilities for producing simple vector plots in a device-independent format, with device-specific interpreters to display such files. Modern Unix systems also generally include [[X Window System|X11]] as a standard windowing system and [[Graphical user interface|GUI]], and many support [[OpenGL]].
** ''Communications''{{snd}} early Unix systems contained no inter-system communication, but did include the inter-user communication programs ''mail'' and ''write''. V7 introduced the early inter-system communication system [[UUCP]], and systems beginning with BSD release 4.1c included [[Internet protocol suite|TCP/IP]] utilities.
* ''Documentation''{{snd}} Unix was one of the first operating systems to include all of its documentation online in machine-readable form.<ref name="PowersPeekO'Reilly2003">{{cite book | author1 = Shelley Powers | author1-link = Shelley Powers | author2 = Jerry Peek | author3 = Tim O'Reilly | author3-link = Tim O'Reilly | author4 = Michael Kosta Loukides | author5 = Mike Loukides | date = 2003 | title = Unix Power Tools | publisher = "O'Reilly Media, Inc." | page =32 | isbn = 978-0-596-00330-2 | url = {{GBurl|id=Xk6THylQxRUC}}|access-date=8 August 2022}}</ref> The documentation included:
** ''[[man page|man]]''{{snd}} manual pages for each command, library component, [[system call]], header file, etc.
** ''doc''{{snd}} longer documents detailing major subsystems, such as the C language and troff

== Impact ==
{{See also|Unix-like}}

[[File:Ken Thompson and Dennis Ritchie.jpg|thumb|[[Ken Thompson]] and [[Dennis Ritchie]], principal developers of [[Research Unix]]]]
[[File:Usenix84 1.jpg|thumb|Photo from [[USENIX]] 1984, including [[Dennis Ritchie]] (center)]]

The Unix system had a significant impact on other operating systems. It achieved its reputation by its interactivity, by providing the software at a nominal fee for educational use, by running on inexpensive hardware, and by being easy to adapt and move to different machines. Unix was originally written in [[assembly language]], but was soon rewritten in [[C (programming language)|C]], a [[high-level programming language]].<ref>{{cite web |author=Ritchie, Dennis |author-link=Dennis Ritchie |url=https://www.bell-labs.com/usr/dmr/www/hist.html |title=The Evolution of the Unix Time-sharing System |year=1979 |access-date=April 30, 2016 |publisher=Bell Labs |quote=Perhaps the most important watershed occurred during 1973, when the operating system kernel was rewritten in C. |url-status=live |archive-url=https://web.archive.org/web/20150611114353/https://www.bell-labs.com/usr/dmr/www/hist.html |archive-date=June 11, 2015 |df=dmy-all }}</ref> Although this followed the lead of [[Compatible Time-Sharing System|CTSS]], [[Multics]] and [[Burroughs MCP]], it was Unix that popularized the idea.

Unix had a drastically simplified file model compared to many contemporary operating systems: treating all kinds of files as simple byte arrays. The file system hierarchy contained machine services and devices (such as [[Printer (computing)|printers]], [[computer terminal|terminals]], or [[disk storage|disk drives]]), providing a uniform interface, but at the expense of occasionally requiring additional mechanisms such as [[ioctl]] and mode flags to access features of the hardware that did not fit the simple "stream of bytes" model. The [[Plan 9 from Bell Labs|Plan 9]] operating system pushed this model even further and eliminated the need for additional mechanisms.

Unix also popularized the hierarchical file system with arbitrarily nested subdirectories, originally introduced by Multics. Other common operating systems of the era had ways to divide a storage device into multiple directories or sections, but they had a fixed number of levels, often only one level. Several major proprietary operating systems eventually added recursive subdirectory capabilities also patterned after Multics. DEC's [[RSX-11M]]'s "group, user" hierarchy evolved into [[OpenVMS]] directories, [[CP/M]]'s volumes evolved into [[MS-DOS]] 2.0+ subdirectories, and HP's [[HP Multi-Programming Executive|MPE]] group.account hierarchy and IBM's [[System Support Program|SSP]] and [[OS/400]] library systems were folded into broader POSIX file systems.

Making the command interpreter an ordinary user-level program, with additional commands provided as separate programs, was another Multics innovation popularized by Unix. The [[Unix shell]] used the same language for interactive commands as for scripting ([[shell script]]s&nbsp;– there was no separate job control language like IBM's [[Job Control Language|JCL]]). Since the shell and OS commands were "just another program", the user could choose (or even write) their own shell. New commands could be added without changing the shell itself. Unix's innovative command-line syntax for creating modular chains of producer-consumer processes ([[pipeline (Unix)|pipelines]]) made a powerful programming paradigm ([[coroutine]]s) widely available. Many later command-line interpreters have been inspired by the Unix shell.

A fundamental simplifying assumption of Unix was its focus on [[newline]]-[[Delimiter|delimited]] text for nearly all file formats. There were no "binary" editors in the original version of Unix&nbsp;– the entire system was configured using textual shell command scripts. The common denominator in the I/O system was the byte&nbsp;– unlike [[Record-oriented filesystem|"record-based" file systems]]. The focus on text for representing nearly everything made Unix pipes especially useful and encouraged the development of simple, general tools that could easily be combined to perform more complicated ''ad hoc'' tasks. The focus on text and bytes made the system far more scalable and portable than other systems. Over time, text-based applications have also proven popular in application areas, such as printing languages ([[PostScript]], [[OpenDocument|ODF]]), and at the application layer of the [[Internet protocol suite|Internet protocols]], e.g., [[File Transfer Protocol|FTP]], [[Simple Mail Transfer Protocol|SMTP]], [[HTTP]], [[SOAP]], and [[Session Initiation Protocol|SIP]].

Unix popularized a syntax for [[regular expression]]s that found widespread use. The Unix programming interface became the basis for a widely implemented operating system interface standard (POSIX, see above). The [[C (programming language)|C programming language]] soon spread beyond Unix, and is now ubiquitous in systems and applications programming.

Early Unix developers were important in bringing the concepts of [[Modular programming|modularity]] and [[reusability]] into [[software engineering]] practice, spawning a "software tools" movement. Over time, the leading developers of Unix (and programs that ran on it) established a set of cultural norms for developing software, norms which became as important and influential as the technology of Unix itself; this has been termed the [[Unix philosophy]].

The [[Internet protocol suite|TCP/IP networking protocols]] were quickly implemented on the Unix versions widely used on relatively inexpensive computers, which contributed to the [[Internet]] explosion of worldwide, real-time connectivity and formed the basis for implementations on many other platforms.

The Unix policy of extensive on-line documentation and (for many years) ready access to all system source code raised programmer expectations, and contributed to the launch of the [[free software movement]] in 1983.

=== Free Unix and Unix-like variants ===
{{See also|Operating system#Unix and Unix-like operating systems}}
{{Multiple image
 | width = 220
 | direction = vertical
 | image1 = Debian 6.0 Console Login.png
 | image2 = FreeBSD 9.1 Console Login.png
 | footer = Console screenshots of [[Debian]] (top, a popular [[Linux distribution]]) and [[FreeBSD]] (bottom, a popular [[Unix-like]] operating system)
}}

In 1983, [[Richard Stallman]] announced the [[GNU]] (short for "GNU's Not Unix") project, an ambitious effort to create a [[free software]] [[Unix-like]] system—"free" in the sense that everyone who received a copy would be free to use, study, modify, and redistribute it. The GNU project's own kernel development project, [[GNU Hurd]], had not yet produced a working kernel, but in 1991 [[Linus Torvalds]] released the [[Linux kernel]] as free software under the [[GNU General Public License]]. In addition to their use in the [[GNU]] operating system, many GNU packages&nbsp;– such as the [[GNU Compiler Collection]] (and the rest of the [[GNU toolchain]]), the [[glibc|GNU C library]] and the [[GNU Core Utilities]]&nbsp;– have gone on to play central roles in other free Unix systems as well.

[[Linux distribution]]s, consisting of the Linux kernel and large collections of compatible software have become popular both with individual users and in business. Popular distributions include [[Red Hat Enterprise Linux]], [[Fedora Linux|Fedora]], [[SUSE Linux|SUSE Linux Enterprise]], [[openSUSE]], [[Debian]], [[Ubuntu]], [[Linux Mint]], [[Slackware|Slackware Linux]], [[Arch Linux]] and [[Gentoo Linux|Gentoo]].<ref>{{cite web |url=https://distrowatch.com/dwres.php?resource=major| title=Major Distributions|website=distrowatch.com}}</ref>

A free derivative of [[Berkeley Software Distribution|BSD]] Unix, [[386BSD]], was released in 1992 and led to the [[NetBSD]] and [[FreeBSD]] projects. With the 1994 settlement of a lawsuit brought against the University of California and Berkeley Software Design Inc. (''[[USL v. BSDi]]'') by [[Unix System Laboratories]], it was clarified that Berkeley had the right to distribute BSD Unix for free if it so desired. Since then, BSD Unix has been developed in several different product branches, including [[OpenBSD]] and [[DragonFly BSD]].

Because of the modular design of the Unix model, sharing components is relatively common: most or all Unix and Unix-like systems include at least some BSD code, while some include GNU utilities in their distributions. Linux and BSD Unix are increasingly filling market needs traditionally served by proprietary Unix operating systems, expanding into new markets such as the [[Desktop computer|consumer desktop]], [[mobile device]]s and [[Embedded system|embedded devices]].

In a 1999 interview, Dennis Ritchie voiced his opinion that Linux and BSD Unix operating systems are a continuation of the basis of the Unix design and are derivatives of Unix:<ref name="Interview_1999">{{cite web|author=Benet, Manuel|url=http://www.linuxfocus.org/English/July1999/article79.html|title=Interview With Dennis M. Ritchie|year=1999|publisher=LinuxFocus.org|url-status=live|archive-url=https://web.archive.org/web/20180104061618/http://www.linuxfocus.org/English/July1999/article79.html|archive-date=January 4, 2018|df=dmy-all|access-date=August 16, 2020}}</ref>

{{blockquote|I think the Linux phenomenon is quite delightful, because it draws so strongly on the basis that Unix provided. Linux seems to be among the healthiest of the direct Unix derivatives, though there are also the various BSD systems as well as the more official offerings from the workstation and mainframe manufacturers.}}

In the same interview, he states that he views both Unix and Linux as "the continuation of ideas that were started by Ken and me and many others, many years ago".<ref name="Interview_1999" />

[[OpenSolaris]] was the [[free software]] counterpart to [[Solaris (operating system)|Solaris]] developed by [[Sun Microsystems]], which included a [[Common Development and Distribution License|CDDL]]-licensed kernel and a primarily [[GNU]] userland. However, [[Oracle Corporation|Oracle]] discontinued the project upon their acquisition of Sun, which prompted a group of former Sun employees and members of the OpenSolaris community to fork OpenSolaris into the [[illumos]] kernel. As of 2014, illumos remains the only active, open-source System V derivative.

=== ARPANET ===
In May 1975, RFC 681 described the development of ''Network Unix'' by the Center for Advanced Computation at the [[University of Illinois Urbana-Champaign]].<ref name="rfc681">{{cite IETF
| title       = Network Unix
| rfc         = 681
| last1       = Holmgren
| first1      = Steve
| date        = May 1975
| publisher   = [[Internet Engineering Task Force|IETF]]
| access-date = April 22, 2021
}}</ref> The Unix system was said to "present several interesting capabilities as an [[ARPANET]] mini-host". At the time, Unix required a license from [[Bell Labs|Bell Telephone Laboratories]] that cost US$20,000 for non-university institutions, while universities could obtain a license for a nominal fee of $150. It was noted that Bell was "open to suggestions" for an ARPANET-wide license.

The RFC specifically mentions that Unix "offers powerful local processing facilities in terms of user programs, several [[compiler]]s, an [[Text editor|editor]] based on [[QED (text editor)|QED]], a versatile document preparation system, and an efficient [[file system]] featuring sophisticated access control, [[Mount (computing)|mountable]] and de-mountable volumes, and a unified treatment of peripherals as [[Device file|special files]]." The latter permitted the [[Network Control Program (ARPANET)|Network Control Program]] (NCP) to be integrated within the Unix file system, treating [[Transport layer|network connections]] as special files that could be accessed through standard Unix [[System call|I/O calls]], which included the added benefit of closing all connections on program exit, should the user neglect to do so. In order "to minimize the amount of code added to the basic Unix [[Kernel (operating system)|kernel]]", much of the NCP code ran in a [[Memory paging|swappable]] user process, running only when needed.<ref name="rfc681" />

== Branding ==
{{See also|List of Unix systems}}
[[File:UNIX-Licence-Plate.JPG|thumb|Promotional [[license plate]] by [[Digital Equipment Corporation]]. Actual license plate is used by [[Jon Hall (programmer)|Jon Hall]].]]
[[File:HP-HP9000-C110-Workstation 10.jpg|thumb|[[HP 9000]] [[workstation]] running [[HP-UX]], a certified Unix operating system]]

AT&T originally did not allow licensees to use the Unix name; thus Microsoft called its variant Xenix, for example.<ref name="bytelines198211">{{Cite magazine |last=Libes |first=Sol |date=November 1982 |title=Bytelines |url=https://archive.org/details/byte-magazine-1982-11/page/n565/mode/1up?view=theater |magazine=BYTE |pages=540–547}}</ref> In October 1988, they allowed licensees to use the UNIX trademark for systems based on System V Release 3.2, if certain conditions were met.<ref>{{cite press release |url=https://www.tech-insider.org/unix/research/1988/1031.html |title=AT&T Expands Unix Trademark Licensing Program |date=October 31, 1988}}</ref> In October 1993, [[Novell]], the company that owned the rights to the Unix System V source at the time, transferred the [[trademark]]s of Unix to the X/Open Company (now [[The Open Group]]),<ref name="autogenerated2" >{{cite newsgroup |title=The name UNIX is now the property of X/Open |author=Chuck Karish |date=October 12, 1993 |newsgroup=comp.std.unix |message-id=29hug3INN4qt@rodan.UU.NET |url=http://groups.google.com/group/comp.std.unix/msg/c9974cf0022884f8 |access-date=February 21, 2020}}</ref> and in 1995 sold the related business operations to [[Santa Cruz Operation]] (SCO).<ref>{{Cite web |title=Novell Completes Sale of UnixWare Business to The Santa Cruz Operation {{!}} Micro Focus |url=http://www.novell.com/news/press/archive/1995/12/pr95274.html |url-status=live |archive-url=https://web.archive.org/web/20151220013149/http://www.novell.com/news/press/archive/1995/12/pr95274.html |archive-date=December 20, 2015 |access-date=December 20, 2015 |website=www.novell.com |df=dmy-all}}</ref><ref name="autogenerated1">{{cite web |url=http://www.novell.com/news/press/archive/1995/09/pr95220.html |title=HP, Novell and SCO To Deliver High-Volume UNIX OS With Advanced Network And Enterprise Services |publisher=Novell.com |date=September 20, 1995 |access-date=November 9, 2010 |url-status=live |archive-url=https://web.archive.org/web/20070123203442/http://www.novell.com/news/press/archive/1995/09/pr95220.html |archive-date=January 23, 2007 |df=mdy-all }}</ref> Whether Novell also sold the [[copyright]]s to the actual software was the subject of a federal lawsuit in 2006, ''[[SCO v. Novell]]'', which Novell won. The case was appealed, but on August 30, 2011, the United States Court of Appeals for the Tenth Circuit affirmed the trial decisions, closing the case.<ref>{{cite web |last=Jones |first=Pamela |author-link=Pamela Jones |title=SCO Files Docketing Statement and We Find Out What Its Appeal Will Be About |url=http://groklaw.net/article.php?story=20100723230825165 |work=Groklaw |publisher=Groklaw.net |access-date=April 12, 2011 |archive-url=https://web.archive.org/web/20240621043005/http://groklaw.net/article.php?story=20100723230825165 |archive-date=June 21, 2024 |url-status=dead}}</ref> Unix vendor [[SCO Group|SCO Group Inc.]] accused Novell of [[slander of title]].

The present owner of the trademark ''UNIX'' is The Open Group, an industry standards consortium. Only systems fully compliant with and certified to the [[Single UNIX Specification]] qualify as "UNIX" (others are called "[[Unix-like]]").

By decree of The Open Group, the term "UNIX" refers more to a class of operating systems than to a specific implementation of an operating system; those operating systems which meet The Open Group's Single UNIX Specification should be able to bear the [[UNIX 98]] or [[UNIX 03]] trademarks today, after the operating system's vendor pays a substantial certification fee and annual trademark royalties to The Open Group.<ref>{{cite web|author=The Open Group|title=The Open Brand Fee Schedule|url=http://www.opengroup.org/openbrand/Brandfees.htm|access-date=December 26, 2011|quote=The right to use the UNIX Trademark requires the Licensee to pay to The Open Group an additional annual fee, calculated in accordance with the fee table set out below.|url-status=live|archive-url=https://web.archive.org/web/20111231234203/http://www.opengroup.org/openbrand/Brandfees.htm|archive-date=December 31, 2011|df=mdy-all}}</ref> Systems that have been licensed to use the UNIX trademark include [[IBM AIX|AIX]],<ref>{{cite web|author=The Open Group|title=AIX 6 Operating System V6.1.2 with SP1 or later certification|url=http://www.opengroup.org/openbrand/register/brand3576.htm|url-status=live|archive-url=https://web.archive.org/web/20160408231050/http://www.opengroup.org/openbrand/register/brand3576.htm|archive-date=April 8, 2016|df=mdy-all}}</ref> [[EulerOS]],<ref>{{cite web|author=The Open Group|title=Huawei EulerOS 2.0 certification|url=https://www.opengroup.org/openbrand/register/brand3622.htm|date=September 8, 2016|df=mdy-all}}</ref> [[HP-UX]],<ref>{{cite web|author=The Open Group|title=HP-UX 11i V3 Release B.11.31 or later certification|url=http://www.opengroup.org/openbrand/register/brand3543.htm|url-status=live|archive-url=https://web.archive.org/web/20160408224320/http://www.opengroup.org/openbrand/register/brand3543.htm|archive-date=April 8, 2016|df=mdy-all}}</ref> [[Inspur K-UX]],<ref>{{cite web|author=The Open Group|title=Inspur K-UX 2.0 certification|url=http://www.opengroup.org/openbrand/register/brand3596.htm|url-status=live|archive-url=https://web.archive.org/web/20140709002355/http://www.opengroup.org/openbrand/register/brand3596.htm|archive-date=July 9, 2014|df=mdy-all}}</ref> [[IRIX]],<ref>{{cite web|author=The Open Group|title=IRIX 6.5.28 with patches (4605 and 7029) certification|url=http://www.opengroup.org/openbrand/register/brand2686.htm|url-status=live|archive-url=https://web.archive.org/web/20160304043134/http://www.opengroup.org/openbrand/register/brand2686.htm|archive-date=March 4, 2016|df=mdy-all}}</ref> [[macOS]],<ref>{{cite web|publisher=The Open Group|url=http://www.opengroup.org/openbrand/register/brand3627.htm|title=macOS version 10.12 Sierra on Intel-based Mac computers|url-status=live|archive-url=https://web.archive.org/web/20161002105135/http://www.opengroup.org/openbrand/register/brand3627.htm|archive-date=October 2, 2016|df=mdy-all}}</ref> [[Solaris (operating system)|Solaris]],<ref>{{cite web|author=The Open Group|title=Oracle Solaris 11 FCS and later certification|url=http://www.opengroup.org/openbrand/register/brand3585.htm|url-status=live|archive-url=https://web.archive.org/web/20150924073536/http://www.opengroup.org/openbrand/register/brand3585.htm|archive-date=September 24, 2015|df=mdy-all}}</ref> [[Tru64 UNIX]] (formerly "Digital UNIX", or [[OSF/1]]),<ref>{{cite web| url=http://www.opengroup.org/csq/repository/RID=dec%252FXU2%252F1.html| title=Hewlett-Packard Company Conformance Statement| author=Bonnie Talerico| publisher=The Open Group| access-date=December 8, 2015| url-status=live| archive-url=https://web.archive.org/web/20151210212245/http://www.opengroup.org/csq/repository/RID=dec%252FXU2%252F1.html| archive-date=December 10, 2015| df=mdy-all}}</ref> and [[z/OS]].<ref>{{cite web| url=http://www.opengroup.org/csq/repository/norationale=1&noreferences=1&RID=ibm%252FXU1%252F6.html| title=IBM Corporation Conformance Statement| author=Vivian W. Morabito| publisher=The Open Group| access-date=January 21, 2018}}</ref> Notably, EulerOS and Inspur K-UX are Linux distributions certified as UNIX&nbsp;03 compliant.<ref>{{cite web| url=http://www.opengroup.org/csq/repository/norationale=1&noreferences=1&RID=huawei%252FXY1%252F1.html| title=Huawei Conformance Statement| author=Peng Shen| publisher=The Open Group| access-date=January 22, 2020}}</ref><ref>{{cite web| url=http://www.opengroup.org/csq/repository/norationale=1&noreferences=1&RID=huawei%252FCX1%252F1.html| title=Huawei Conformance Statement: Commands and Utilities V4| author=Peng Shen| publisher=The Open Group| access-date=January 22, 2020}}</ref>

Sometimes a representation like ''Un*x'', ''*NIX'', or ''*N?X'' is used to indicate all operating systems similar to Unix. This comes from the use of the asterisk (''*'') and the question mark characters as wildcard indicators in many utilities. This notation is also used to describe other Unix-like systems that have not met the requirements for UNIX branding from the Open Group.

The Open Group requests that ''UNIX'' always be used as an adjective followed by a generic term such as ''system'' to help avoid the creation of a [[genericized trademark]].

''Unix'' was the original formatting,{{disputed inline|Original formatting of the name - "Unix" or "UNIX"?|date=September 2019}} but the usage of ''UNIX'' remains widespread because it was once typeset in [[small caps]] (''<span style="font-variant: small-caps;">Unix</span>''). According to [[Dennis Ritchie]], when presenting the original Unix paper to the third Operating Systems Symposium of the American [[Association for Computing Machinery]] (ACM), "we had a new typesetter and ''[[troff]]'' had just been invented and we were intoxicated by being able to produce small caps".<ref>{{cite web |url=http://catb.org/jargon/html/U/Unix.html |title=Unix |work=[[The Jargon File]] |editor-first=Eric S. |editor-last=Raymond |access-date=November 9, 2010 |url-status=live |archive-url=https://web.archive.org/web/20110604153220/http://catb.org/jargon/html/U/Unix.html |archive-date=June 4, 2011 |df=mdy-all }}</ref> Many of the operating system's predecessors and contemporaries used all-uppercase lettering, so many people wrote the name in upper case due to force of habit. It is not an acronym.<ref name="USDT">{{cite book
 | last = Troy
 | first = Douglas
 | title = UNIX Systems
 | publisher = Benjamin/Cumming Publishing Company
 | series = Computing Fundamentals
 | year = 1990
 | pages = 4
 | isbn = 978-0-201-19827-0
}}</ref>

Trademark names can be registered by different entities in different countries and trademark laws in some countries allow the same trademark name to be controlled by two different entities if each entity uses the trademark in easily distinguishable categories. The result is that Unix has been used as a brand name for various products including bookshelves, ink pens, bottled glue, diapers, hair driers and food containers.<ref>{{cite web |url=https://www.bell-labs.com/usr/dmr/www/otherunix.html |title=Autres Unix, autres moeurs (OtherUnix) |website=[[Bell Laboratories]] |date=April 1, 2000 |access-date=January 3, 2018 |url-status=live |archive-url=https://web.archive.org/web/20170403063714/https://www.bell-labs.com/usr/dmr/www/otherunix.html |archive-date=April 3, 2017 |df=mdy-all }}</ref>

Several plural forms of Unix are used casually to refer to multiple brands of Unix and Unix-like systems. Most common is the conventional ''Unixes'', but ''Unices'', treating Unix as a [[Latin]] noun of the [[Latin declension#Third declension (i)|third declension]], is also popular. The pseudo-[[Anglo-Saxon language|Anglo-Saxon]] plural form ''Unixen'' is not common, although occasionally seen. [[Sun Microsystems]], developer of the Solaris variant, has asserted that the term ''Unix'' is itself plural, referencing its many implementations.<ref>{{cite web|url=https://cse.unl.edu/~witty/class/csce351/howto/history_of_solaris.pdf|title=History of Solaris|quote=UNIX is plural. It is not one operating system but, many implementations of an idea that originated in 1965.|url-status=live|archive-url=https://web.archive.org/web/20170318195534/http://cse.unl.edu/~witty/class/csce351/howto/history_of_solaris.pdf|archive-date=March 18, 2017|df=mdy-all}}</ref>

== See also ==
* [[Comparison of operating systems]] and [[Comparison of open-source and closed-source software|free and proprietary software]]
* [[List of operating systems]], [[List of Unix systems|Unix systems]], and [[List of Unix commands|Unix commands]]
* [[Plan 9 from Bell Labs]]
* [[Timeline of operating systems]]
* [[Unix time]]
* [[Usage share of operating systems|Market share of operating systems]]
* [[Year 2038 problem]]

== References ==
{{Reflist|30em}}

== Further reading ==
;General
* {{cite journal|last1=Ritchie|first1=D.M.|author1-link=Dennis Ritchie|last2=Thompson|first2=K.|author-link2=Ken Thompson|title=The UNIX Time-Sharing System|journal=[[Bell System Technical Journal]]|url=http://bstj.bell-labs.com/oldfiles/year.1978/BSTJ.1978.5706-2.html|archive-url=https://web.archive.org/web/20101103053325/http://bstj.bell-labs.com/oldfiles/year.1978/BSTJ.1978.5706-2.html|date=July–August 1978|volume=57|issue=6|archive-date=November 3, 2010}}
* {{cite web | url=http://www.levenez.com/unix/ | title=UNIX History | work=www.levenez.com | access-date= March 17, 2005 }}
* {{cite web | url=http://www.unixguide.net/ | title=AIX, FreeBSD, HP-UX, Linux, Solaris, Tru64 | work=UNIXguide.net | access-date= March 17, 2005 }}
* {{cite web | url=https://lwn.net/2002/0221/bigpage.php3 | title=Linux Weekly News, February 21, 2002 | work=lwn.net | access-date = April 7, 2006 }}
* [[John Lions|Lions, John]]: ''Lions' {{cite web | url=http://www.lemis.com/grog/Documentation/Lions/ | title=Commentary on the Sixth Edition UNIX Operating System}} with Source Code'', Peer-to-Peer Communications, 1996; {{ISBN|1-57398-013-7}}
;Books
* [[Peter H. Salus|Salus, Peter H.]]: ''A Quarter Century of UNIX'', Addison Wesley, June 1, 1994; {{ISBN|0-201-54777-5}}
;Television
* [[Computer Chronicles]] (1985). "[https://archive.org/details/UNIX1985 UNIX]".
* [[Computer Chronicles]] (1989). "[https://archive.org/details/unix_2 Unix]".
;Talks
* {{cite interview | author = Ken Thompson | title = VCF East 2019 -- Brian Kernighan interviews Ken Thompson | date = 2019 | url = https://www.youtube.com/watch?v=EY6q5dv_B-o}}
* {{cite AV media | author = Marshall Kirk McKusick | title = History of the Berkeley Software Distributions (three one-hour lectures) | date = 2006 | url = http://www.mckusick.com/history/index.html}}

== External links ==
{{sister project links|auto=1|wikt=Unix|d=y|b=Guide to Unix}}
* [https://opengroup.org/unix The UNIX Standard], at [[The Open Group]].
* {{webarchive |url=https://web.archive.org/web/20150408054606/http://cm.bell-labs.com/cm/cs/who/dmr/hist.html |date=April 8, 2015 |title=The Evolution of the Unix Time-sharing System }}
* {{webarchive |url=https://web.archive.org/web/20140402192351/http://www.bell-labs.com/history/unix/ |date=April 2, 2014 |title=The Creation of the UNIX Operating System }}
* [https://www.tuhs.org/cgi-bin/utree.pl The Unix Tree: source code and manuals from historic releases]
* {{GitHub |dspinellis/unix-history-repo |Unix History Repository — a git repository representing a reconstructed version of the Unix history}}
* [https://www.bell-labs.com/usr/dmr/www/1stEdman.html The Unix 1st Edition Manual]
** [http://man.cat-v.org/unix-1st/ 1st Edition manual rendered to HTML]
* {{YouTube|tc4ROCJYbm0|AT&T Tech Channel Archive: The UNIX Operating System: Making Computers More Productive (1982)}} <!-- former url: http://techchannel.att.com/play-video.cfm/2012/2/22/AT&T-Archives-The-UNIX-System --> (film about Unix featuring Dennis Ritchie, Ken Thompson, Brian Kernighan, Alfred Aho, and more)
* {{YouTube|XvDZLjaCJuw|AT&T Tech Channel Archive: The UNIX System: Making Computers Easier to Use (1982)}} <!-- former url: https://techchannel.att.com/playvideo/2014/01/27/ATT-Archives-The-UNIX-System-Making-Computers-Easier-to-Use --> (complementary film to the preceding "Making Computers More Productive")
* [https://archive.org/details/bsdtalk170 audio bsdtalk170 - Marshall Kirk McKusick at DCBSDCon -- on history of tcp/ip (in BSD) -- abridgement of the three lectures on the history of BSD.]
* [http://www.darwinsys.com/history/hist.html A History of UNIX before Berkeley: UNIX Evolution: 1975-1984]
* [https://archive.org/stream/byte-magazine-1986-09/1986_09_BYTE_11-09_The_68000_Family#page/n171/mode/2up BYTE Magazine, September 1986: UNIX and the MC68000]{{snd}} a software perspective on the MC68000 CPU architecture and UNIX compatibility

{{Unix-like|state=expanded}}
{{Unix commands}}
{{Ken Thompson}}
{{Rob Pike}}
{{Time-sharing operating systems}}
{{Operating system}}

{{Authority control}}

[[Category:Unix| ]]
[[Category:1969 software]]
[[Category:Products introduced in 1969]]
[[Category:Operating system families]]
[[Category:Time-sharing operating systems]]