Unix-like
Encyclopedia
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
is one that behaves in a manner similar to a Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification
Single UNIX Specification
The Single UNIX Specification is the collective name of a family of standards for computer operating systems to qualify for the name "Unix"...
.
There is no standard for defining the term, and some difference of opinion is possible as to the degree to which a given OS is "Unix-like".
The term can include free and open source
Free and open source software
Free and open-source software or free/libre/open-source software is software that is liberally licensed to grant users the right to use, study, change, and improve its design through the availability of its source code...
operating systems inspired by Bell Labs
Bell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...
’ Unix or designed to emulate its features, commercial and proprietary work-alikes, and even versions based on the licensed UNIX source code (which may be sufficiently "Unix-like" to pass certification and bear the "UNIX" trademark).
Definition
The Open GroupThe Open Group
The Open Group is a vendor and technology-neutral industry consortium, currently with over three hundred member organizations. It was formed in 1996 when X/Open merged with the Open Software Foundation...
owns the UNIX
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
trademark
Trademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...
and administers the Single UNIX Specification, with the "UNIX" name being used as a certification mark
Certification mark
A certification mark on a commercial product indicates five things:* The existence of a legal follow-up or product certification agreement between the manufacturer of a product and an organization with national accreditation for both testing and certification,* Legal evidence that the product was...
. They do not approve of the construction "Unix-like", and consider it a misuse of their trademark. Their guidelines require "UNIX" to be presented in uppercase or otherwise distinguished from the surrounding text, strongly encourage using it as a branding adjective for a generic word such as "system", and discourage its use in hyphenated phrases.
Other parties frequently treat "Unix" as a genericized trademark
Genericized trademark
A genericized trademark is a trademark or brand name that has become the colloquial or generic description for, or synonymous with, a general class of product or service, rather than as an indicator of source or affiliation as intended by the trademark's holder...
. Some add a wildcard character
Wildcard character
-Telecommunication:In telecommunications, a wildcard character is a character that may be substituted for any of a defined subset of all possible characters....
to the name to make a euphemistic
Euphemism
A euphemism is the substitution of a mild, inoffensive, relatively uncontroversial phrase for another more frank expression that might offend or otherwise suggest something unpleasant to the audience...
abbreviation like "Un*x" or "*nix", since Unix-like systems often have Unix-like names such as AIX
AIX operating system
AIX AIX AIX (Advanced Interactive eXecutive, pronounced "a i ex" is a series of proprietary Unix operating systems developed and sold by IBM for several of its computer platforms...
, HP-UX
HP-UX
HP-UX is Hewlett-Packard's proprietary implementation of the Unix operating system, based on UNIX System V and first released in 1984...
, IRIX
IRIX
IRIX is a computer operating system developed by Silicon Graphics, Inc. to run natively on their 32- and 64-bit MIPS architecture workstations and servers. It was based on UNIX System V with BSD extensions. IRIX was the first operating system to include the XFS file system.The last major version...
, Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
, Minix
Minix
MINIX is a Unix-like computer operating system based on a microkernel architecture created by Andrew S. Tanenbaum for educational purposes; MINIX also inspired the creation of the Linux kernel....
, Ultrix
Ultrix
Ultrix was the brand name of Digital Equipment Corporation's native Unix systems. While ultrix is the Latin word for avenger, the name was chosen solely for its sound.-History:...
, and Xenix
Xenix
Xenix is a version of the Unix operating system, licensed to Microsoft from AT&T in the late 1970s. The Santa Cruz Operation later acquired exclusive rights to the software, and eventually superseded it with SCO UNIX ....
. These patterns do not literally match many system names, but are still generally recognized to refer to any UNIX descendant or work-alike system, even those with completely dissimilar names such as Solaris
Solaris Operating System
Solaris is a Unix operating system originally developed by Sun Microsystems. It superseded their earlier SunOS in 1993. Oracle Solaris, as it is now known, has been owned by Oracle Corporation since Oracle's acquisition of Sun in January 2010....
or FreeBSD
FreeBSD
FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
.
In 2007, Wayne R. Gray sued to dispute the status of UNIX as a trademark, but lost his case, and lost again on appeal.
Also in 2007, the Open Group reached a binding legal agreement to prevent the German University of Kassel
University of Kassel
The University of Kassel, founded in 1970, is one of the newer universities in the state of Hesse. The university is in Kassel, and as of September 2010 has about 18,113 students...
from using "UNIK" as its short form name.
History
"Unix-like" systems started to appear in the late 1970s and early 1980s. Many proprietaryProprietary software
Proprietary software is computer software licensed under exclusive legal right of the copyright holder. The licensee is given the right to use the software under certain conditions, while restricted from other uses, such as modification, further distribution, or reverse engineering.Complementary...
versions, such as Idris
Idris (operating system)
Idris is a multi-tasking, Unix-like, multi-user, real-time operating system released by Whitesmiths, of Westford, Massachusetts. The product was commercially available from 1979 through 1988.-Background:...
(1978), Coherent
Coherent (operating system)
The Coherent operating system was a Version 7 Unix clone by the now-defunct Mark Williams Company, originally produced for the PDP-11 in 1980. A port was introduced in 1983 as the first Unix-like system for IBM PC compatible computers....
(1983), UNOS (1983), and UniFlex
UniFlex
UniFLEX is a Unix-like operating system developed by Technical Systems Consultants for the Motorola 6809 family which allowed multitasking and multiprocessing. It was released for DMA-capable 8" floppy, extended memory addressing hardware , Motorola 6809 based computers. Examples included machines...
(1985), aimed to provide businesses with the functionality available to academic users of UNIX.
When AT&T later allowed commercial licensing of UNIX in the 1980s, a variety of proprietary systems were developed based on it, including AIX
AIX operating system
AIX AIX AIX (Advanced Interactive eXecutive, pronounced "a i ex" is a series of proprietary Unix operating systems developed and sold by IBM for several of its computer platforms...
, HP-UX
HP-UX
HP-UX is Hewlett-Packard's proprietary implementation of the Unix operating system, based on UNIX System V and first released in 1984...
, IRIX
IRIX
IRIX is a computer operating system developed by Silicon Graphics, Inc. to run natively on their 32- and 64-bit MIPS architecture workstations and servers. It was based on UNIX System V with BSD extensions. IRIX was the first operating system to include the XFS file system.The last major version...
, SunOS
SunOS
SunOS is a version of the Unix operating system developed by Sun Microsystems for their workstation and server computer systems. The SunOS name is usually only used to refer to versions 1.0 to 4.1.4 of SunOS...
, Tru64, Ultrix
Ultrix
Ultrix was the brand name of Digital Equipment Corporation's native Unix systems. While ultrix is the Latin word for avenger, the name was chosen solely for its sound.-History:...
, and Xenix
Xenix
Xenix is a version of the Unix operating system, licensed to Microsoft from AT&T in the late 1970s. The Santa Cruz Operation later acquired exclusive rights to the software, and eventually superseded it with SCO UNIX ....
. These largely displaced the proprietary clones. Growing incompatibility between these systems led to the creation of interoperability standards, including POSIX
POSIX
POSIX , an acronym for "Portable Operating System Interface", is a family of standards specified by the IEEE for maintaining compatibility between operating systems...
and the Single UNIX Specification
Single UNIX Specification
The Single UNIX Specification is the collective name of a family of standards for computer operating systems to qualify for the name "Unix"...
.
Meanwhile, the GNU Project
GNU Project
The GNU Project is a free software, mass collaboration project, announced on September 27, 1983, by Richard Stallman at MIT. It initiated GNU operating system development in January, 1984...
was launched in 1983 with the goal of making GNU
GNU
GNU is a Unix-like computer operating system developed by the GNU project, ultimately aiming to be a "complete Unix-compatible software system"...
, an operating system which all computer users could freely use, study, modify, and redistribute. Various "Unix-like" operating systems developed alongside GNU, frequently sharing substantial components with it (leading to some disagreement about whether they should be called "GNU" or not). These primarily served as low-cost and unrestricted substitutes for UNIX, and include 4.4BSD
Berkeley Software Distribution
Berkeley Software Distribution is a Unix operating system derivative developed and distributed by the Computer Systems Research Group of the University of California, Berkeley, from 1977 to 1995...
, Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
, and Minix
Minix
MINIX is a Unix-like computer operating system based on a microkernel architecture created by Andrew S. Tanenbaum for educational purposes; MINIX also inspired the creation of the Linux kernel....
. Some of these have in turn been the basis for commercial "Unix-like" systems, such as BSD/OS
BSD/OS
BSD/OS was a proprietary version of the BSD operating system developed by Berkeley Software Design, Inc. ....
and Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
. Notably, Mac OS X 10.5 and Mac OS X 10.6 running on Intel Macs are certified under the Single UNIX Specification.
The various BSD variants are notable in that they are in fact descendants of UNIX, developed by the University of California at Berkeley with UNIX source code from Bell Labs. However, the BSD code base has evolved since then, replacing all of the AT&T code. Since the BSD
Berkeley Software Distribution
Berkeley Software Distribution is a Unix operating system derivative developed and distributed by the Computer Systems Research Group of the University of California, Berkeley, from 1977 to 1995...
variants are not certified as compliant with the Single UNIX Specification (except for Mac OS X 10.5 Leopard and Mac OS X 10.6 Snow Leopard), they are referred to as "UNIX-like".
Categories
Dennis RitchieDennis Ritchie
Dennis MacAlistair Ritchie , was an American computer scientist who "helped shape the digital era." He created the C programming language and, with long-time colleague Ken Thompson, the UNIX operating system...
, one of the original creators of Unix, has expressed his opinion that Unix-like systems such as Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
are de facto
De facto
De facto is a Latin expression that means "concerning fact." In law, it often means "in practice but not necessarily ordained by law" or "in practice or actuality, but not officially established." It is commonly used in contrast to de jure when referring to matters of law, governance, or...
Unix systems. Eric S. Raymond
Eric S. Raymond
Eric Steven Raymond , often referred to as ESR, is an American computer programmer, author and open source software advocate. After the 1997 publication of The Cathedral and the Bazaar, Raymond was for a number of years frequently quoted as an unofficial spokesman for the open source movement...
and Rob Langley have suggested that there are three kinds of Unix-like systems:
Genetic UNIX: Those systems with a historical connection to the AT&T
AT&T
AT&T Inc. is an American multinational telecommunications corporation headquartered in Whitacre Tower, Dallas, Texas, United States. It is the largest provider of mobile telephony and fixed telephony in the United States, and is also a provider of broadband and subscription television services...
codebase. Most (but not all) commercial UNIX systems fall into this category. So do the BSD
Berkeley Software Distribution
Berkeley Software Distribution is a Unix operating system derivative developed and distributed by the Computer Systems Research Group of the University of California, Berkeley, from 1977 to 1995...
systems, which are descendants of work done at the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
in the late 1970s and early 1980s. Some of these systems have no original AT&T code but can still trace their ancestry to AT&T designs.
Trademark or Branded UNIX: These systems—largely commercial in nature—have been determined by the Open Group to meet the Single UNIX Specification
Single UNIX Specification
The Single UNIX Specification is the collective name of a family of standards for computer operating systems to qualify for the name "Unix"...
and are allowed to carry the UNIX name. Most such systems are commercial derivatives of the System V code base in one form or another, although Apple Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
10.5 and later is a BSD
Berkeley Software Distribution
Berkeley Software Distribution is a Unix operating system derivative developed and distributed by the Computer Systems Research Group of the University of California, Berkeley, from 1977 to 1995...
variant, and has been certified, and a few certified systems (such as IBM z/OS
Z/OS
z/OS is a 64-bit operating system for mainframe computers, produced by IBM. It derives from and is the successor to OS/390, which in turn followed a string of MVS versions.Starting with earliest:*OS/VS2 Release 2 through Release 3.8...
) earned the trademark through a POSIX
POSIX
POSIX , an acronym for "Portable Operating System Interface", is a family of standards specified by the IEEE for maintaining compatibility between operating systems...
compatibility layer
Compatibility layer
A compatibility layer is a term that refers to components that allow for non-native support of components.In software engineering, a compatibility layer allows binaries for a legacy or foreign system to run on a host system. This translates system calls for the foreign system into native system...
and are not otherwise inherently Unix systems. Many ancient UNIX systems no longer meet this definition.
Functional UNIX: Broadly, any Unix-like system that behaves in a manner roughly consistent with the UNIX specification; more specifically, this can refer to systems such as Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
or Minix
Minix
MINIX is a Unix-like computer operating system based on a microkernel architecture created by Andrew S. Tanenbaum for educational purposes; MINIX also inspired the creation of the Linux kernel....
that behave similarly to a UNIX system but have no genetic or trademark connection to the AT&T code base. Most free/open-source implementations of the UNIX design, whether genetic UNIX or not, fall into the restricted definition of this third category due to the expense of obtaining Open Group certification, which costs thousands of dollars, not being commercially necessary.
Compatibility layers
Some non-Unix-like operating systems provide a Unix-like compatibility layerCompatibility layer
A compatibility layer is a term that refers to components that allow for non-native support of components.In software engineering, a compatibility layer allows binaries for a legacy or foreign system to run on a host system. This translates system calls for the foreign system into native system...
, with variable degrees of Unix-like functionality.
- IBM z/OSZ/OSz/OS is a 64-bit operating system for mainframe computers, produced by IBM. It derives from and is the successor to OS/390, which in turn followed a string of MVS versions.Starting with earliest:*OS/VS2 Release 2 through Release 3.8...
's POSIX compatibility layer is sufficiently complete to be certified as trademark UNIX. - CygwinCygwinCygwin is a Unix-like environment and command-line interface for Microsoft Windows. Cygwin provides native integration of Windows-based applications, data, and other system resources with applications, software tools, and data of the Unix-like environment...
and MSYS both provide a reasonably complete GNUGNUGNU is a Unix-like computer operating system developed by the GNU project, ultimately aiming to be a "complete Unix-compatible software system"...
environment, sufficient for most common open sourceOpen sourceThe term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
software to be compiled and run, with some emulation of LinuxLinuxLinux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
, on top of the Microsoft WindowsMicrosoft WindowsMicrosoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
user APIWindows APIThe Windows API, informally WinAPI, is Microsoft's core set of application programming interfaces available in the Microsoft Windows operating systems. It was formerly called the Win32 API; however, the name "Windows API" more accurately reflects its roots in 16-bit Windows and its support on...
. - InterixInterixInterix is the name of an optional, full-featured POSIX and Unix environment subsystem for Microsoft's Windows NT-based operating systems.Interix is a component of the Services for Unix release 3.0 and 3.5...
provides Unix-like functionality as a Windows NTWindows NTWindows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
subsystem.
See also
- Berkeley Software DistributionBerkeley Software DistributionBerkeley Software Distribution is a Unix operating system derivative developed and distributed by the Computer Systems Research Group of the University of California, Berkeley, from 1977 to 1995...
- Linux distributionLinux distributionA Linux distribution is a member of the family of Unix-like operating systems built on top of the Linux kernel. Such distributions are operating systems including a large collection of software applications such as word processors, spreadsheets, media players, and database applications...
- List of Linux distributions
- List of Unix utilities
- List of operating systems
External links
- Unix-like Definition by The Linux Information Project (LINFO)
- UNIX history a history time line graph of most UNIX and Unix-like systems by Éric Lévénez
- Grokline's UNIX Ownership History Project a project to map out the technical history of UNIX and Unix-like systems