COMMENT It's the end of an era. As The Reg covered last week, IBM has transferred development of AIX to India. Why should IBM pay for an expensive US-based team to maintain its own proprietary flavor of official Unix when it paid 34 billion bucks for its own FOSS flavor in Red Hat?

Here at The Reg FOSS desk, we've felt this was coming ever since we reported that Big Blue was launching new POWER servers which didn't support AIX – already nearly eight years ago. Even if it was visibly coming over the horizon, this is a significant event: AIX is the last proprietary Unix which was in active development, and constitutes four of the 10 entries in the official Open Group list.

Within Oracle, Solaris is in maintenance mode. Almost exactly six years ago, we reported that the next major release, Solaris 12, had disappeared from Oracle's roadmap. HPE's HP-UX is also in maintenance mode because there's no new hardware to run it on. Itanium really is dead now and at the end that's all HP-UX could run on. It's over a decade since we reported that HP investigated but canceled an effort to port it to x86-64.

The last incarnation of the SCO Group, Xinuos, is still around and offers not one but two proprietary UNIX variants: SCO OpenServer, descended from SCO Xenix, and UnixWare, descended from Novell's Unix. We note that OpenServer 10, a more modern OS based on FreeBSD 10, has disappeared from Xinuos's homepage. It's worth pointing out that the SCO Group was the company formerly known as Caldera, and isn't the same SCO as the Santa Cruz Operation which co-created Xenix with Microsoft in the 1980s.

There used to be two Chinese Linux distros which had passed the Open Group's testing and could use the Unix trademark: Inspur K/UX and Huawei EulerOS. Both companies have let the rather expensive trademark lapse, though. But the important detail here is that Linux passed and was certified as a UNIX™. And it wasn't just one distro, although both were CentOS Linux derivatives. We suspect that any Linux would breeze through because many un-Unix-like OSes have passed before.

Other OSes have passed or probably easily would, though. IBM's z/OS is alive and well: version 2.5 came out in 2021 and in 2022 Big Blue started offering cloud instances. z/OS has a Unix-compatible environment which has passed the compatibility tests so officially, it's a UNIX™, even if that wasn't its original native API.

The "open" in the name "OpenVMS" originally referred to the POSIX compatibility it gained with version 5, way back in 1991, and was first applied to the new version for DEC's Alpha CPUs. Last year VMS Software released version 9.2 for x86-64 hypervisors (and a single supported box, HPE's DL380).

Ever since Windows NT in 1993, Windows has had a POSIX environment. Now, with WSL, it arguably has two of them, and we suspect that if Microsoft were so inclined, it could have Windows certified as an official Unix-compatible OS.

• IBM shifts remaining US-based AIX dev jobs to India – source
• Haiku beta 4: BeOS rebuild / almost ready for release / A thing of beauty
• What did Unix fans learn from the end of Unix workstations?
• NixOS 22.11 'Raccoon': Like a proof of concept you can do things with

In our recent story on Beta 4 of Haiku, we said it wasn't really a Unix. As you can see, there's an editor's note attached to the end of the story explaining why.

We had heard from Haiku's primary full-time developer, who vigorously disagreed with our point of view. To his mind, the fact that Haiku now has strong Unix compatibility, with some of the main Unix directories present in its filesystem, a quite complete set of Unix API calls, a Unix shell, and so on, means that Haiku is quite definitely a Unix. We feel that inasmuch as it's a reimplementation of BeOS, with its own native filesystem, API, GUI and so on, it's something different, which offers Unix compatibility as well.

But this illustrates the difficulty of defining precisely what the word "Unix" means in the 21st century. It hasn't meant "based on AT&T code" since Novell bought Unix System Labs from AT&T in 1993, kept the code, and donated the trademark to the Open Group. Since that time, if it passes the Open Group's testing (and you pay a fee to use the trademark), it's UNIX™. Haiku hasn't so it isn't. Linux has so it is. But then so is z/OS, which is a direct descendant of OS/390, or IBM MVS as it was called when it was launched in 1974. In other words, an OS which isn't actually based on, similar to, or even related to Unix.

Which means that the last officially trademarked commercial UNIX™ is Apple's macOS 13, which underneath the proprietary GUI layer is mostly an open source OS called Darwin anyway. The kernel, XNU, is based on Mach with an in-kernel "Unix server" derived from FreeBSD.

So, as of 2023, open source really has won. There are more Unix-like OSes than ever, and some very un-Unix-like OSes which are highly compatible with it, but the official line is, to all intents and purposes, dead and gone. All the proprietary, commercial Unixes are now on life support: they will get essential bug fixes and security updates, but we won't be seeing any major new releases.

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