Unix-like

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A Unix-like operating system is one that behaves in a manner similar to the UNIX system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification.

With the rise of Linux and its strong competitive showing against certified Unix, Unix certification is becoming less relevant to the marketplace.

The Open Group, which owns the UNIX trademark, considers "UNIX-like" to be a usage problem, and believes that a better alternative term would be the term "POSIX-conforming system". However, the term POSIX-conforming system has its own problems. For example, there are systems which conform to at least the key POSIX standards (e.g., Microsoft Windows) and can claim to be POSIX-conforming, but that are nevertheless not Unix-like and many applications written to compile and run on Unix will not work on them.

Table of contents

1 Early Unix-like systems
2 Unix-like open source operating systems
3 See also

Early Unix-like systems

The first "Unix-like" operating systems were developed because of AT&T's licencing of Unix, which prevented the sale of Unix to commercial organisations. The Unix-like operating systems that were available in the early 1980s included Idris, Coherent, UniFlex and Minix (a computer science teaching system). When AT&T allowed Unix to be sold to commercial organisations, the market for these early Unix-like operating systems dried up.

Unix-like open source operating systems

The term is often used to refer to the Unix-like open source operating systems:

Cygwin
FreeBSD and descendants: PicoBSD, DragonFly BSD, TrustedBSD, etc.
GNU HURD
Linux
MinGW
NetBSD
OpenBSD and descendants: ekkoBSD, MicroBSD, MirBSD, etc.
Darwin

A not complete but very comprehensive history time line graph of most unix-like operating systems can be found at http://www.levenez.com/unix/