Unix-like |
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 . [http://www.opengroup.org/tm-guidelines.htm]
Other parties frequently disregard these guidelines, wilfully 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 euphemism 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 operating system, 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.
Despite the trademark, the Unix community at large is somewhat more nebulously defined, and Dennis Ritchie, one of the original creators of Unix, has expressed his opinion that Unix-like systems such as Linux are de facto Unix systems. Eric S. Raymond has suggested that the Unix world can be broken down into three categories:
*Genetic Unix -- those systems with a historical connection to the AT&T codebase. Most but not all commercial Unix systems fall into this category, as do the BSD systems, descendants of work done at the University of California at Berkeley in the late 70s and early 80s. 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 and are allowed to carry the UNIX(tm) name. Most such systems are commercial derivatives of the System V code base in one form or another, though a few (such as IBM s z/OS) earned the trademark through a POSIX compatibility layer and are not otherwise inherently Unix systems. (Interestingly, many Ancient UNIX systems might not meet current versions of this definition.) *Functional Unix or Unix-like -- Broadly, any Unix-like system that behaves in a manner roughly consistent with the Unix specification; more specifically, can be used to refer to systems such as Linux, GNU Hurd, or Minix that behave similarly to a Unix system but have no genetic or trademark connection to the AT&T code base. Most 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.
There is considerable overlap between these categories. Not all commercial Unix-like systems are Branded Unix, for example -- MacOS X is a prime example. Despite being one of the most popular commercial Unix implementations available, it does not bear the UNIX(tm) branding.
The UNIX trademark, in practice by X/Open, is actually used as a certification mark. There is an active legal battle in the TTAB of the USPTO between Wayne R. Gray and X/Open that is centered around the use of the UNIX trademark [http://ttabvue.uspto.gov/ttabvue/vqt=adv&pno=&qs=&propno=75680034&propnameop=&propname=&pop=&pn=&pop2=&pn2=&cop=&cn=]. Mr. Gray s legal team has been trying, unsuccessfully, to compel X/Open to provide documentation that proves the legitimacy of their trademark claim. To date, X/Open, via counsel, has refused to provide the requested information, according to TTAB court documents.
=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 (operating system), Coherent (operating system), 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 operating system, HP-UX, IRIX, Solaris Operating Environment, 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 Berkeley Software Distribution, 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 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, and these operating systems are not compliant with the Single UNIX Specification, so they are merely Unix- like .
=Current examples=
== Free Software & Open Source ==
Most free/open-source Unix-like systems do not seek Unix branding for their product even if fully or mostly conformant; the costs for certification (especially given frequent release cycles) are generally considered prohibitive. The term Freenix is occasionally but rarely used to refer to such systems.
==Proprietary==
=See also=
*Berkeley Software Distribution *Linux distributions *List of Unix programs
=External links=
*[http://www.levenez.com/unix/ Unix history] – a history time line graph of most Unix and Unix-like systems by Ã?ric Lévénez *[http://grokline.net/ Grokline s UNIX Ownership History Project] – a project to map out the technical history of Unix and Unix-like systems *[http://www.unix.com/ The UNIX Forums] Commercial-free technical Q&A for Unix and Linux users - actively moderated by experts.|
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