If Mac OS X is a Unix, as answered in this question, why is it that it is not open sourced and the license is proprietary, as stated in this Wikipedia article?

According the the genealogy from this Wikipedia article OS X came from BSD, so again, why is it closed source and licensed as proprietary? But, the Darwin OS, also from Apple is open sourced?

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    You seem to think that being UNIX implies an opened source base, but you can't use modus ponens here, as there's no implication. Some UNIX-like systems, such as GNU/Linux may have opened their sources, being free software, but correlation does not imply causation. – njsg Mar 14 '12 at 13:56
  • thanks for your answers, I'm a bit enlightened with licensing. Thank you! – radztech Mar 15 '12 at 7:46
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    There's a subtle irony here that people would equate UNIX with "open". – tylerl Mar 15 '12 at 9:56
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    UNIX doesn't imply "open source" but does certainly imply "open". Long before "Open Source" was coined, "Open Systems" was a common way to refer about all UNIX implementations. en.wikipedia.org/wiki/Open_system_%28computing%29 – jlliagre Apr 7 '12 at 13:25

Three reasons:

First, being certified as a Unix says nothing about your licensing, just your compliance to the established standards for being Unix.

Second, because being Unix has nothing to do with your licensing, and everything to do with your being like Unix, an originally proprietary system, and one with a long legacy.

Finally, don't mistake licensing: BSD code can subsequently be closed, and there is no duty of disclosure or source availability. The BSD license is more free on one axis, and less free on another, because of that.

  • Doesn't it being certified as Unix makes it Unix-like and not Unix? – radztech Mar 14 '12 at 10:09
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    The other way around, not being certified as UNIX means you can't call it UNIX. (Trademark legalese, they own the trademark and decide only certified systems can carry that "name".) – njsg Mar 14 '12 at 13:47
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    If you modify BSD-licensed code and distribute it without the source code, that's legal, but the resulting code can no longer be called BSD-licensed. – Flimm Mar 15 '12 at 17:57
  • @Flimm - absolutely. I didn't think the finer detail was necessary to answer the question, but that is a good clarification. – Daniel Pittman Mar 15 '12 at 18:00

If a system is certified as Unix, that system's vendor is allowed to call it Unix. That is precisely what the certification is for.

Systems such as GNU/Linux and *BSD, which look and behave like Unix, but are not actually certified as Unix, are called Unix-like. Since the various open source projects have limited finances, they generally want to spend their money on development and not certification, so don't expect the status quo to change greatly any time soon.

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    Not only that, some systems are really like UNIX, but do not conform to IEEE 1003.1, the Portable Operating System Interface (POSIX). GNU/Linux, like Windows (but to a way lesser extent, and not including Interix, which may or may not be POSIX-compliant, I don't know), does not follow all of POSIX, so it's not even a matter of getting a certification, it's really a matter of not following the standard. Even then, these are probably systems we would all call UNIX, weren't it for the Open Group saying we can't. – njsg Mar 14 '12 at 13:53

Apple did Open Source a good portion of the underlying, BSD based, pieces of OSX. See Wikipedia's Darwin Entry for full details as well as a release history. Apple keeps the upper level stuff proprietary, like their UX components and does not release those as OSS. If you want a full list of all the Apple OSS projects/inclusions, check out Apple's Open Source page.


OS X has components which are based on FreeBSD, OpenBSD and Mach.

OpenBSD and FreeBSD is licensed under the BSD License which says:




This explicitly allows one to distribute a modified binary without delivering source.

Apple did release Darwin under a free license but that was their decision which is not legally enforceable (unlike had the kernel been released under the GPL).


Apple has released the source code for Darwin and some parts of OS X.

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