What is UNIX and what's UNIX-like?

Question

Derived from this question:

If opensolaris, freebsd, openbsd, netbsd are not UNIX, what is then?

What confuses me more, is the fact OSX1.5+ is UNIX, while prior version of OSX weren't

What is the difference between UNIX and UNIX-like?

And what is the diff between UNIX-Like and Linux?

Solution 1

UNIX is Unix and Unix is unix. But unix may not be Unix and Unix is not always UNIX.

• UNIX in all caps refers to the Trademark of The Open Group
• Unix is the genericized trademark of UNIX-Like systems.
• unix is the common term for UNIX like system.

Solution 2

Unix is a trademark owned by The Open Group. "Only systems fully compliant with and certified according to the Single UNIX Specification are qualified to use the trademark." (1) (2)

That explains why version of OSX before 1.5 is not UNIX, because it wasn't fully compliant.

Solution 3

OS X, Solaris, HP-UX, and AIX are the remaining UNIX distributions doing well in the market. UNIX-Like refers to an operating system that behaves like traditional UNIX (forking methods, same method of interprocess communication, Kernel features, etc) but does not conform to the Single UNIX specification. Examples of these are BSD variants, GNU/Linux distributions, and Minix. In the end it's more tied to It's Trademark and system behaviors.

Comments

[John T]

"UNIX-Like OS's like BSD and Linux" - Linux is only a kernel. I normally wouldn't nitpick about it but this is a question completely about these operating systems.

[heavyd]

And GNU is definitely not Unix!

[KFro]

Lets throw POSIX into the mix!

[OscarRyz]

Yeah, what about POSIX?

[sal]

@heavyd, I wish I could double or triple up-vote that comment.

[Richard Hoskins]

The name that can be named is not the eternal name. Free from desire, you realize the mystery. Caught in desire, you see only the manifestations. --Lao-tzu