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.
The term is now most often used to refer to the Unix-like open source operating systems.
With the rise of Linux and its strong competitive showing against certified Unix, Unix certification is becoming less relevant to the marketplace.
The term "Unix-like" and the UNIX trademark
The Open Group, which owns the UNIX trademark and administers the Single UNIX Specification, 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" 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.
Early Unix-like systems
The first "Unix-like" operating systems were developed because of AT&T's licensing of Unix, which prevented the sale of Unix to commercial organisations. The Unix-like operating systems that were available in the 1980s and early 1990s included Idris, Coherent, UniFlex and Minix (a computer science teaching system).
When AT&T allowed Unix to be sold to commercial organisations in the 1980s, the market for the earliest Unix-like operating systems dried up. The rise of Linux in the 1990s killed the rest.
Unix-like open source operating systems
The term is most often used as a simple way of referring to the Unix-like open source operating systems:
- Darwin
- FreeBSD and descendants: PicoBSD, DragonFly BSD, TrustedBSD, etc.
- GNU Hurd
- Linux
- Minix
- NetBSD
- OpenBSD and descendants: ekkoBSD, MicroBSD, MirBSD, etc.
External links
- Unix history (Éric Lévénez) — an incomplete but comprehensive history time line graph of most Unix and Unix-like systems
- Grokline's UNIX Ownership History Project — a project to map out the technical history of Unix and Unix-like systems