[tialaramex]

We typically distinguish UNIX® which is everybody who has money and wanted to say they're Unix, from just Unix, meaning the things that in practice behave like Unix.

Money talks, so I'm confident that Apple will get to call their mac OS UNIX® until they don't care regardless of whether in any useful sense it's still Unix. On the other hand, regardless of whether some organisation pays money to effect this, Linux is still Unix and so is FreeBSD.

You've probably seen other situations in the real world where the thing you actually care about is distinct from legal status - because our social cues aren't tied to legal status. That doesn't make the legal status worthless, but it is distinct - Obergefell for example is a case where doubtless normal people just accepted that these guys are married - there was a ceremony and everything, but in Ohio at the time the asserted legal status was that they aren't married, therefore the death certificate claims otherwise and hence the case in front of the Supreme Court.

[krylon]

Apparently Oracle has stopped caring, new Solaris releases haven't been certified in a few years, says Wikipedia.

I don't really know what the certification gets you these days other than bragging rights. I imagine in the past, government and corporate customers had check lists that included a box for "certified Posix", but I'm not sure if that is still the case.

[mtillman]

It is/was a useful credential to have when responding to government RFPs as governments had purchased UNIX systems and wanted new systems to be interoperable. This might no longer be an advantage in most requests but my guess is there are still some that require it.

[graemep]

There is another meaning. Derived from originally Unix code: so MacOS and FreeBSD are Unix, while Linux is not.

[znpy]

> We typically distinguish UNIX® which is everybody who has money and wanted to say they're Unix, from just Unix, meaning the things that in practice behave like Unix.

From what i've seen Apple gets every Mac Os release UNIX-certified, which is somewhat cool.

But frankly, is it of any actual relevance ? Nowadays it's gnu/linux in (probably) 95-98% of the industry and the rest is likely to be shared across FreeBSD and a few other players.

But in general, I'd say any "POSIX implementation" that's not been certified should not be taken any seriously: as an example, i had a friend that was working with the Zephyr RTOS which claimed to have some kind of posix compliance... Except it wasn't full and it broke in subtle ways. Still a good RTOS (it seems, not my area of expertise) but the "posix compliat" claim should be taken with many grains of salt probably.

[sillywalk]

Certified Unix. The source link has more details:

    Apple Inc.: macOS version 14.0 Sonoma on Apple silicon-based Mac computers

    Apple Inc.: macOS version 14.0 Sonoma on Intel-based Mac computers

    IBM Corporation: z/OS 3.1 or later with: z/OS 3.1 or later Security Server and z/OS 3.1 or later C/C++ Compiler on IBM Series Processors that support z/OS Version 3.1 or later

    IBM Corporation: AIX version 7, at 7.2 TL5 (or later) on systems using CHRP system architecture with POWER™ processors

    IBM Corporation: AIX version 7, at either 7.1 TL5 (or later) or 7.2 TL2 (or later) on systems using CHRP system architecture with POWER™ processors

    Hewlett Packard Enterprise: HP-UX 11i V3 Release B.11.31 or later on HP Integrity Servers

    IBM Corporation: AIX 6 Operating System V6.1.2 with SP1 or later on Systems using CHRP system architecture with POWER™ processors and 2, 8 or 128 port async cards

    IBM Corporation: AIX 5L for POWER V5.3 dated 7-2006 or later on Systems using CHRP system architecture with POWER™processors

    IBM Corporation: z/OS V2R1 or later with: z/OS V2R1 or later Security Server and z/OS V2R1 or later C/C++ Compiler on IBM zSeries Processors that support z/OS Version 2 Release 1 or later

    The SCO Group, Inc.: UnixWare ® 7.1.3 and later for single and multiprocessor systems based on IA-32 and compatible processors and conforming to PC architecture

    The SCO Group, Inc.: SCO OpenServer Release 5 and OpenServer Release 6 on Single and Multi-processor Industry Standard Intel architecture platforms

Source: https://www.opengroup.org/openbrand/register

[jasomill]

Compliance with various POSIX standards remains useful and relevant, though the only list of actually certified products I can find[1] includes only RTOSes.

Even without certification, POSIX remains a useful baseline for implementing and consuming cross-platform system services, taken with your suggested grains of salt on the consumer side for any details not specifically documented as POSIX-compliant.

UNIX certification seems mostly only relevant in terms of OS marketing, in the sense that it signifies a vendor's intention to provide a usable POSIX-ish programming environment.

As a target for cross-platform application developers, the list of certified UNIX platforms is at best weirdly specific:

macOS: supported

AIX: supported, though even IBM seems to prefer Linux for new development; IBM-supported Linux runs natively alongside AIX on the same hardware, further limiting appeal

z/OS: supported, but only a "UNIX system" in that it offers a POSIX compatibility layer on top of a system that's fundamentally non-POSIX in design (EBCDIC, expensive process creation, etc.); IBM-supported Linux runs natively alongside z/OS on the same hardware, further limiting appeal

HP-UX: supported until 2025-12-31; Itanium-only

SCO UnixWare and OpenServer: supported (?), but no substantial updates since 2018 (?)

[1] https://posix.opengroup.org/register.html

[vorakl]

> the Zephyr RTOS which claimed to have some kind of posix compliance...

The work is still in progress. It's also important to note, that Zephyr is intended to run on resource-constrained systems. There is not much logic in implementing fork() for example, since technically, there is only one process. So it implements a subset of the interface. Here is the link to the talk from the EOSS 2024 where Chris Friedt shares the current state of POSIX support in Zephyr: https://www.youtube.com/watch?v=nLnmXxXuS6w

[znpy]

Hey, I meant no dissing at Zephyr, i hope it was clear.

What i wanted to get across is that claims about "Posix compliance" might have wide variance in meaningfulness unless backed by a certification.

[iforgotmysocks]

> From what i've seen Apple gets every Mac Os release UNIX-certified, which is somewhat cool.

I reckon it is because of the lawsuit they got because they used unix in marketing without actually paying for the certificate. see - https://www.quora.com/What-goes-into-making-an-OS-to-be-Unix...

[musicale]

> Linux is still Unix and so is FreeBSD

I thought the *BSD kernels derive (at least in part) from (BSD) Unix kernel code, while the Linux kernel is a different, independently created workalike.

Moreover, typical Linux distro userlands are GNU, and "GNU's Not Unix."[1]

[1] https://www.gnu.org/doc/doc.html

[iforgotmysocks]

Ironically the macOS kernel is named XNU - X is Not Unix