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A Unix-like (sometimes referred to as UN*X or *nix) 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. Unix-like_sentence_0

A Unix-like application is one that behaves like the corresponding Unix command or shell. Unix-like_sentence_1

There is no standard for defining the term, and some difference of opinion is possible as to the degree to which a given operating system or application is "Unix-like". Unix-like_sentence_2

The term can include free and 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 sufficiently "Unix-like" to pass certification and bear the "UNIX" trademark). Unix-like_sentence_3

Definition Unix-like_section_0

The Open Group owns the UNIX trademark and administers the Single UNIX Specification, with the "UNIX" name being used as a certification mark. Unix-like_sentence_4

They do not approve of the construction "Unix-like", and consider it a misuse of their trademark. Unix-like_sentence_5

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. Unix-like_sentence_6

Other parties frequently treat "Unix" as a genericized trademark. Unix-like_sentence_7

Some add a wildcard character to the name to make an abbreviation like "Un*x" or "*nix", since Unix-like systems often have Unix-like names such as AIX, A/UX, HP-UX, IRIX, Linux, Minix, Ultrix, Xenix, and XNU. Unix-like_sentence_8

These patterns do not literally match many system names, but are still generally recognized to refer to any UNIX system, descendant, or work-alike, even those with completely dissimilar names such as Darwin/macOS, illumos/Solaris or FreeBSD. Unix-like_sentence_9

In 2007, Wayne R. Gray sued to dispute the status of UNIX as a trademark, but lost his case, and lost again on appeal, with the court upholding the trademark and its ownership. Unix-like_sentence_10

History Unix-like_section_1

Categories Unix-like_section_2

Dennis Ritchie, one of the original creators of Unix, expressed his opinion that Unix-like systems such as Linux are de facto Unix systems. Unix-like_sentence_11

Eric S. Raymond and Rob Landley have suggested that there are three kinds of Unix-like systems: Unix-like_sentence_12

Genetic UNIX Unix-like_section_3

Those systems with a historical connection to the AT&T codebase. Unix-like_sentence_13

Most commercial UNIX systems fall into this category. Unix-like_sentence_14

So do the BSD systems, which are descendants of work done at the University of California, Berkeley in the late 1970s and early 1980s. Unix-like_sentence_15

Some of these systems have no original AT&T code but can still trace their ancestry to AT&T designs. Unix-like_sentence_16

Trademark or branded UNIX Unix-like_section_4

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 name. Unix-like_sentence_17

Most such systems are commercial derivatives of the System V code base in one form or another, although Apple macOS 10.5 and later is a BSD variant that has been certified, EulerOS and Inspur K-UX are Linux distributions that have been certified, and a few other systems (such as IBM z/OS) earned the trademark through a POSIX compatibility layer and are not otherwise inherently Unix systems. Unix-like_sentence_18

Many ancient UNIX systems no longer meet this definition. Unix-like_sentence_19

Functional UNIX Unix-like_section_5

Broadly, any Unix-like system that behaves in a manner roughly consistent with the UNIX specification, including having a "program which manages your login and command line sessions"; more specifically, this can refer to systems such as Linux or Minix that behave similarly to a UNIX system but have no genetic or trademark connection to the AT&T code base. Unix-like_sentence_20

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 for commercial closed source systems. Unix-like_sentence_21

Around 2001, Linux was given the opportunity to get a certification including free help from the POSIX chair Andrew Josey for the symbolic price of one dollar. Unix-like_sentence_22

There have been some activities to make Linux POSIX-compliant, with Josey having prepared a list of differences between the POSIX standard and the Linux Standard Base specification, but in August 2005, this project was shut down because of missing interest at the LSB work group. Unix-like_sentence_23

Compatibility layers Unix-like_section_6

Some non-Unix-like operating systems provide a Unix-like compatibility layer, with varying degrees of Unix-like functionality. Unix-like_sentence_24


Other means of Windows-Unix interoperability include: Unix-like_sentence_25


  • The above Windows packages can be used with various X servers for WindowsUnix-like_item_1_6
  • Hummingbird Connectivity provides several ways for Windows machines to connect to Unix and Linux machines, from terminal emulators to X clients and servers, and othersUnix-like_item_1_7
  • The Windows Resource Kits for versions of Windows NT include a Bourne Shell, some command-line tools, and a version of PerlUnix-like_item_1_8
  • Hamilton C shell is a version of csh written specifically for Windows.Unix-like_item_1_9

See also Unix-like_section_7


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Unix-like.