A "Unix-like" operating system is one that behaves in a manner similar to a UNIX system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. The term can include open source operating systems inspired by Bell Labs' 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 deemed so "Unix-like" that they are certified to bear the "UNIX" trademark). There is no formal standard for defining the term, and some difference of opinion is possible as to whether a certain OS is "Unix-like" or not.


The term "Unix-like" and the UNIX trademark

The Open Group owns the UNIX® trademark and administers the Single UNIX Specification. They do not approve of the construction "Unix-like", and consider it 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. The closest phrase they consider correct is "UNIX system-like". [1] (http://www.opengroup.org/tm-guidelines.htm)

Other parties frequently disregard these guidelines, willfully treating "Unix" as a generic noun or descriptor for operating systems that are not necessarily covered by the "UNIX" trademark, in much the same way that "Band-Aid" is used in reference to any bandage or "Xerox" to any photocopier. Some abbreviate or "wildcard" the name as "Un*x", "*nix", or some similar construction, which is also contrary to Open Group guidelines. These euphemistic spellings were derived as a way to say "Unix" without formally saying it. They were inspired in part by a tendency for Unix-like systems to be given names resembling "Unix", particularly ending in "x", such as AIX, IRIX, Linux, Minix, Ultrix, and Xenix. Few of these names actually match "*nix". However, wildcards like "*nix" are often meant to match any Unix descendant system, even Solaris or FreeBSD, which do not even have an "x" at the end.

Development of Unix-like systems

The first "Unix-like" operating systems (other than Bell Labs' Unix itself) were developed because of AT&T's licensing of the software, which prevented its sale for commercial purposes. These systems were intended to provide businesses with the functionality available to academic users of Unix. The proprietary "Unix-like" operating systems that were available in the 1980s and early 1990s included Idris, Coherent, and UniFlex.

When AT&T later allowed commercial licensing of Unix in the 1980s, a variety of proprietary systems were developed based on it, including AIX, HP-UX, IRIX, Solaris, Tru64, Ultrix, and Xenix. These largely displaced the clones. Growing incompatibility between these systems led to the creation of interoperability standards, including POSIX and the Single UNIX Specification.

Meanwhile, non-commercial "Unix-like" operating systems were developed to serve as inexpensive or free substitutes for Unix. These include BSD, GNU, Minix, and Linux. Some of these have in turn been the basis for commercial "Unix-like" systems, such as BSD/OS, NEXTSTEP, and Mac OS X.

The various BSD systems are notable in that they are in fact descendents 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, and these operating systems are not compliant with the Single UNIX Specification, so they are merely "Unix-like".

Current examples

Open Source


*UNIX® systems

See also

External links



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