As I understand it most Linux distros adhere to the UNIX specifications while only a few actually get UNIX certified. If plenty of Linux distros can happily adhere to the standard without being certified in it, what then motivated Apple to get MacOS UNIX certified?

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    You are referring to OSX, right?
    – RonJohn
    Commented Jun 4, 2023 at 21:18
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    What does this have to do with retrocomputing? MacOS is a currently-supported operating system!
    – user24811
    Commented Jun 5, 2023 at 1:04
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    @user24811 just because a subject is not defunct does not mean questions about is roots are not retro. The decision to become unix certified happened 20 yeard ago. How much more retro do you need?
    – Neil Meyer
    Commented Jun 5, 2023 at 6:59
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    How old does something have to be for it to graduate from "out-of-date" to "retro"? If you look at the question of how old does a building need to be in order to be historical, that age varies from nation to nation. Commented Jun 5, 2023 at 11:57
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    @slebetman Strictly, I think it's ‘macOS, the operating system formerly known as ”OS X, the operating system formerly known as ‘Mac OS X’”‘.
    – gidds
    Commented Jun 5, 2023 at 23:02

3 Answers 3


According to Terry Lambert, the engineer who led the project to make MacOS comply with the Single UNIX Specification,

[...] it was done to get Apple out of a $200M lawsuit filed by The Open Group, for use of the UNIX™ trademark in advertising.

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    This post can be improved by adding more detials about the lawsuit. Im not willing to go to quora to read what should be in the answer.
    – Neil Meyer
    Commented Jun 5, 2023 at 6:57
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    While I appreciate the need for pro forma answers, it seems to me that additional material would not add value wrt. answering the question. If the answer is that it's a due to a lawsuit, what other details would make the answer better? Commented Jun 5, 2023 at 12:12
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    If I understand correctly, this answer is basically saying that Apple had to get OS X Unix certified because they were marketing OS X as a Unix operating system. But that feels like only a partial answer, because we're left wondering what motivated Apple to market OS X as a Unix operating system. Commented Jun 5, 2023 at 14:27
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    The legal case appears to hold up to fact checking, so the part about the Terry Lambert impostor is remote google.com/search?q=%22The+Open+Group%22+%22apple%22+law Commented Jun 6, 2023 at 1:32
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    @ToddWilcox Kind of true. The entire operating system (at least initially) was a reskinned version of the Next operating system with a new device driver subsystem and the MacOS 9 compatibility layers (Classic and Carbon).
    – JeremyP
    Commented Jun 7, 2023 at 10:59

So the systems could be sold into organizations that happened to have a "must be Unix certified" on their checklist of requirements.

Who would have such a requirement? Who knows. Certainly much less germane today, but back when it was introduced, the workstation wars were still going strong.

The assorted Linux systems don't have the certification because they never went through the process and cost of doing it. Apple could do that, so, check that box and move on.

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    Used to be military contractors required such certification, by military mandate. It's also the reason by Windows NT came out of the door with a POSIX subsystem. (USA)
    – davidbak
    Commented Jun 4, 2023 at 16:38
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    In addition to Linux not being certified as UNIX, none of the Bell Labs UNIX versions were ever certified. Does this mean they are not UNIX? See Master Foo Discourses on the Unix-Nature. catb.org/~esr/writings/unix-koans/unix-nature.html Commented Jun 5, 2023 at 12:04
  • @AcceptableName Bell Labs were the original owners of the trademark, before there was an Open Group? So, yes, they were an official UNIX.
    – Davislor
    Commented Jun 6, 2023 at 2:33
  • @Davislor it's a joke about a funny OS that nobody would have heard of if it wasn't turned into such a seemingly-endless variety of commercial products that it took committees and and specifications to reign in, leading to a set of tests that define it. Meanwhile its creators went on developing their version which the world only got to see in retrospect. Then the creators abandoned it and made something else, while the world built a work-alike of what had become of the creator's first OS. Commented Jun 6, 2023 at 11:16

I do not know the exact answer (so if this is too much speculation, feel free to close as subjective), but I do remember the situation Apple was back in at the time, and my theory is "Because they desperately needed the marketing boost".

Mac OS X started as a push into the Server market as well - the very first version you could buy was Mac OS X Server 1.0 which even lacked the Aqua user interface and still looked like Mac OS Classic.

Also, they actually had a line of bona-fide servers with their Xserve line, including a Fibre-Channel SAN with a specialized SAN File System.

Combined with the fact that Mac OS X's XNU kernel is based on a "real" unix (4.3BSD), it seems like a logical choice (and low hanging fruit) to get the "UNIX Certified" badge to show that they are serious about things - in the corporate world, you couldn't get much more serious in the late 90's than "UNIX".

I don't know if there were markets where the certification mattered for compliance or if they just wanted to impress decision-makers (e.g., Apple's a huge player in the American education market ever since the Apple II), but I almost see more reasons for than against getting UNIX certified at this point for them.

That said, this is my speculation. I do know that Apple had a pretty rough reputation in the late 90s (Michael Dell's "Sell the company and return value to the shareholders" quote is legendary for how it aged like milk, but wasn't all that uncommon of a thought at the time) and if you listen to the Boston 1997 Keynote you can clearly see a just-returned Steve Jobs trying to find ways to rebuild the brand - and what better way to tell companies you're serious by making a serious UNIX? The 2002 Xserve event shows a very humble Steve Jobs really needing to convince people to trust Apple.

Also, Mac OS Classic had a reputation for bad system stability - it was possible for an application to crash in a way that destabilizes the entire system, which was acceptable in the 80's and early 90's, but for people used to Windows NT and UNIX, it was becoming less and less acceptable. That said, the Mac OS-Classic based iMac was an absolutely massive success, so I don't think that the consumer market mattered, even with the NT-based Windows XP now moving consumer-Windows into the modern age.

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