I have been a Linux user for the last decade or so, but cranked up a FBSD (6) machine about 4 months ago to give it a try. I can move around in it pretty good by now, but I am a long way from FBSD gurudom. Since this machine is learning only, I have always had plenty of time to figure out how it works, either from the books or googling.
But a question has come up that I can't answer - or more accurately, am not qualified to answer.
Our school district has switched over to Macs after a disasterous trial of Vista and they like them very well. I knew that Apple's OSX was some kind of 'nix based OS but never thought on it before. After a little googling, it appears that Apple used FBSD as the basis for their OSX platform.
Some of the techier/nerdier/smarter kids have found the terminal application and have (with permission) descended into the insides of the platform. I have also looked and it appears to be fairly FBSD'ish. Their question is , does Apple use fairly standard FBSD, or have they redone it to their needs? In other words, if these kids learn the platform OS on their new Macs, are they learning FBSD or some hybrid OS that only applies to Macs?
Obviously the best place to ask this question would seem to be on a Mac forum, but I have found that while there are many Mac experts who can detail every corner of OSX, very few know anything once they drop out of the GUI. Some even argue that I am in the wrong forum, that OSX has nothing to do with "Unix".
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Short answer - no.
Long answer - Mac OS X is based upon the Mach kernel. Certain parts from FreeBSD's and NetBSD's implementation of Unix were incorporated in Nextstep, the core of Mac OS X. See
History of Mac OS X - Wikipedia, the free encyclopedia
However, OS X Leopard is UNIX-compliant with some sort of certification. OS X does have FreeBSD's virtual file system, network stack, components of its userspace and few other stuff. See apples on webpage about UNIX technology that is included with OS X -
http://www.apple.com/macosx/technology/unix.html
Personally, I own a mac book and I find it command line quite like UNIX with perl, python, shell and friends. YMMV.