According to Wikipedia the current OS's which are licensed to use the UNIX trademark are AIX, HP-UX, IRIX, Solaris, Tru64, A/UX, Mac OS X Leopard (on Intel only), and part of z/OS.
Now, I don't know about IRIX, Tru64, A/UX and z/OS, but as I understand it AIX, HP-UX and Solaris are derived from AT&T's original UNIX source code, as IBM, Hewlett-Packard and Sun respectively licensed this from AT&T, so they include code from the original UNIX.
Now BSD was created at University of California, Berkeley, using AT&T's original UNIX source code. Later, in the early 90's, all the code that was licensed from AT&T was reimplemented. Therefore, as I understand it, BSD contains none of the original UNIX source code, and operating systems like FreeBSD and NetBSD can't call themselves UNIX for that reason.
OK, so that explains to my satisfaction why AIX, HP-UX and Solaris are real UNIX, and I assume the same applies for IRIX, Tru64, A/UX and z/OS. But OS X?
Unless I've got my wires crossed somewhere, OS X contains none of the original AT&T UNIX source code:
- The XNU kernel consists of the Mach microkernel, which was developed as a replacement for the BSD kernel, together with userland tools taken from FreeBSD4.4. So, as I see it, no AT&T source code here.
- The shell used in Leopard is bash. Many of the other tools used are also the GNU versions as used in GNU/Linux and GNU/Open Solaris.
- I believe the X Window Server used is a fork of Xfree86.
So far as I can see, UNIX certification means that it's been certified as being POSIX-compliant by the owner of the UNIX trademark. Well, that really doesn't mean that much, does it? To the best of my knowledge, this would just mean you'd pay The Open Group to certify it as being real UNIX. Is there any reason why any Linux vendor couldn't pay this fee and have their distro certified as being real UNIX? I really don't think this would be a good use of their money, but I see no good reason why this couldn't be done.
So, dear lazyweb, here are my questions:
1) What actual benefits are there to an OS being certified as real UNIX?
2) Does OS X Leopard contain any of the original UNIX source code?
3) If not, what right does it actually have to call itself real UNIX?
Seriously, I'm not trolling here, I just cannot see that Leopard has any more right to call itself real UNIX than Linux does on the basis of the source code. And if it's based on certification, then what's to stop a Linux distro vendor from having their OS certified as being real UNIX?