I’m on a mailing list for UNIX enthusiasts here in St. Louis, & a member posted this the other day:
I DO count MacOS X as UNIX. However, I know there are some of our users who object claiming that the fact that it is NOT completely Open Source disqualifies it from our respect.
I responded thusly:
Speaking as both a Linux and Mac user, Mac OS X is more UNIX than any Linux is. This is a fact.
“The Single UNIX Specification (SUS) is the collective name of a family of standards for computer operating systems to qualify for the name “Unix”. The SUS is developed and maintained by the Austin Group, based on earlier work by the IEEE and The Open Group. … Beginning in 1998, a joint working group known as the Austin Group began to develop the combined standard that would be known as the Single UNIX Specification Version 3 and as POSIX:2001 (formally: IEEE Std 1003.1-2001). It was released on January 30, 2002. …
Darwin is an open source operating system: it is essentially the open source subset of Mac OS X. Darwin is compliant with the SUS 03. …
Linux aims to be compliant, but as certification is expensive, no Linux distribution has been registered as SUS compliant.”
(Of course, I consider Linux to be a variant of UNIX, as anyone with a brain does.)
Anyone who says that Mac OS X is not a UNIX is putting their biases before fact.
Open Source != UNIX. The two have absolutely nothing, strictly speaking, to do with each other.