[KerrAvon]

Has everyone forgotten that Unix is the common ancestor of Linux and every other Unixlike? I’m seeing an uptick of people writing nonsensical comments like “this was written for Linux (or Mac OS X, which implements POSIX and is therefore really Linux in drag)”.

[jchw]

No... That's why they had the parenthetical. The problem is, your computer probably doesn't boot the common ancestor. If you're writing UNIX-like stuff, most likely it boots macOS or Linux. If you're cool maybe it's one of the other modern BSD variants aside macOS. In practice there's a pretty low probability that your code also runs on all POSIX-compliant operating systems, and more honest/experienced people often don't kid themselves into thinking that they're seriously targeting that. Even if you believe it, you probably have some dependency somewhere that doesn't care, like Qt for example. Saying something like "Linux (or macOS, which is similar)" is a realization that you're significantly more likely to be targeting both Linux and macOS than you are to even test on BSD. And to solidify that point, note that lots of modern CI platforms don't even have great BSD support to begin with.

Of course, there is a semantic point here. macOS nominally really is UNIX, except for when someone finds out it's not actually POSIX compliant due to a bug somewhere every year or so. Still, it IS UNIX. But what people mostly run with that capability, is stuff that mostly targets Linux. So... yeah.

Of course it is true that some people really think macOS is actually Linux, but that misunderstanding is quite old by this point.

addendum: I feel like I haven't really done a good job putting my point across. What I'm really saying is, I believe most developers targeting macOS or Linux today only care about POSIX or UNIX insofar as they result in similarities between macOS and Linux. That macOS is truly UNIX makes little difference; if it happened to differ in some way, developers would happily adjust to handle it, just like they do for Linux which definitely isn't UNIX.

[copperx]

Apparently yes, because all I ever hear is "macOS is like Linux" and even "macOS is really Linux behind the scenes" from less enlightened people.

[naniwaduni]

Well, a pretty big part of the point of Linux is that it's not a Unix-descendant, just a Unix-clone.

[pcl]

What’s the distinction between those two?

[dwheeler]

"Unix" implies paying annual fees for use of the "Unix" trademark, and/or at least direct descent from the original Unix code.

According to: https://kb.iu.edu/d/agat "To use the Unix trademark, an operating system vendor must pay a licensing fee and annual trademark royalties to The Open Group. Officially licensed Unix operating systems (and their vendors) include macOS (Apple), Solaris (Oracle), AIX (IBM), IRIX (SGI), and HP-UX (Hewlett-Packard). Operating systems that behave like Unix systems and provide similar utilities but do not conform to Unix specification or are not licensed by The Open Group are commonly known as Unix-like systems."

Many will include the *BSDs as a Unix, because their code does directly descend from the original Unix code. But Linux distros generally do not meet either definition of "Unix".

[GabrielTFS]

It should be noted that Linux generally does actually conform to UNIX standards, though, and that two actual Linux distributions (Inspur K-UX and EulerOS) have in the past obtained UNIX certification. While this doesn't make all Linux distributions UNIX certified, it puts a rather large dent in the claim that they cannot be qualified as UNIX because of some claimed divergence from the standards.

(It also seems odd from my perspective to call exactly only those two Linux distributions "UNIX" unless you're essentially using it as a legal qualification and not a practical one)

[dwheeler]

> While this doesn't make all Linux distributions UNIX certified, it puts a rather large dent in the claim that they cannot be qualified as UNIX because of some claimed divergence from the standards.

No one is claiming it can't be a Unix. But as you noted, Linux distributions normally do not meet the legal criteria, nor are they descended from one that did.

Legally Unix is a trademark and has a very specific legal meaning. If you don't mean that legal meaning, then it is clearer if you use another term. The usual term is "Unux-like"; that is the widely-used term and it has been for decades.

A rose by any other name may smell as sweet, but calling it a different word risks confusion.

[pjmlp]

Only if their code for the certification is fully available upstream.

[asgeir]

Part of it is whether the code can be traced back to original AT&T code. Which would be true for e.g. BSD variants (which includes MacOS). https://i.redd.it/kgv4ckmz3zb51.jpg

Another part is the trademark and certification fee. https://www.opengroup.org/openbrand/Brandfees.htm

[sterlind]

Darwin forked BSD, and BSD is a fork of the original Unix source. Linux is a fresh implementation of POSIX, and doesn't directly inherit any code from Unix.

Linux is as much Unix as WSL1 was Linux - i.e. not at all, just clones.

[avgcorrection]

I just call Linx+Mac+Bsds Unix (not “Unix-like” and certainly not that “*nix” nonsense). I don’t respect Unix enough to be perfectly precise with it.