Quote Originally Posted by mips View Post
http://en.wikipedia.org/wiki/POSIX#M...OSIX-compliant

OS X is fully posix compliant. Linux & BSD not so much and I suspect linux to be less than BSD but at the same time I also suspect it's a certification thing where those with the money to certify trumps all.

Thing with compliance is you have to pay money for a compliance certificate and you have to do it for every single release you put out there so for open source stuff where money is tight it does not make a whole lot of sense to go down the compliance/certification road.
Linux goes by the Linux Standard Base instead. LSB is based mostly on POSIX standards, along with some other open standards, but it extends it.