Possible Duplicate:
What exactly is POSIX?
What is Unix now?

Are they only the Unix’s developed by Bell Labs or do the SCO ones count too? Are there others?

marked as duplicate by Chris Down, Renan, jasonwryan, manatwork, Gilles Nov 18 '12 at 20:51

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.


UNIX (POSIX) is a set of "guidelines" which must be followed by an operating system (and it's parts) for it to be considered a "UNIX".

So asking which is the UNIX OS that the others are based on or which was the first doesn't really mean anything. Sure there was an operating system which was the first to be coined a UNIX -- but really, what you're talking about it the guidelines it follows.

  • 1
    So there is no current vanilla Unix OS at all? – 5ives Nov 18 '12 at 1:10
  • 2
    @5ives, no because something like that doesn't exist. All operating systems which have the "UNIX" label follow the same standards and rules that have been defined by the organization which owns the UNIX label. – n0pe Nov 18 '12 at 1:32
  • 1
    Ok; is there a Unix that has a direct line to the original Unix rather than being some kind of branch? Which is the most current Unix by the original developers? Which Unix (not Unix-like) is the most popular? Sorry if I'm being stubborn. – 5ives Nov 18 '12 at 1:46
  • 1
    @5ives FreeBSD is not Unix but is a direct descendant of the original ATT Unix and once contained original ATT Unix code. en.wikipedia.org/wiki/Freebsd – Rob Nov 18 '12 at 2:20
  • 1
    @Abdul I don't know and I don't think anyone cares. I would lean toward Unix based if I had to cause it had Unix in its code. Linux was Unix like because it copied Unix though it has strayed from that. – Rob Jul 14 '16 at 11:54

Unix is a trademarked name and there is only one specification for Unix. To be called a Unix system, you must apply for and be certified to use that name.


If your question is about code base lineage and not standards, current OSes directly descending from the original Bell Labs / AT&T Unix releases are AIX, HP-UX, Oracle Solaris & OpenSolaris derivatives all coming from System V release 4 and (Open/Free/Net)BSD and derivatives from the much earlier Unix version 6.

While Mac OS X has some BSD code, its core is not a descendant of the Unix kernel code.

  • I'm wondering, if OS X is BSD based, and BSD had code from one of the original AT&T releases, how can you tell OS X's core isn't descendant from the Unix kernel code, when it isn't fully open source? – Abdul Jul 14 '16 at 10:59

The history and timeline of UNIX is nicely presented here and shown pictorially here.

As noted, there is a single UNIX specification that defines "Unix" to which all products must conform to be officially compliant and branded. The various vendor brands can be found here.

Not the answer you're looking for? Browse other questions tagged or ask your own question.