I think this is less technical and more 'political' / contractual, as it used to be:
> This is to certify that Oracle Corporation has entered into a Trademark License Agreement with X/Open Company Limited in accordance with which the following are registered under the X/Open Brand Program.
> We are pleased to announce that Oracle Corporation has achieved certification to the UNIX V7 Product Standard for: Oracle Solaris 11.4 Operating System and later on SPARC-based and X86 based platforms. For more information: http://ow.ly/8fT830lBjfu #UNIX
> Solaris supports SPARC and x86-64 workstations and servers from Oracle and other vendors. Solaris was registered as compliant with UNIX 03 until 29 April 2019.[6][7][8]
They did, but (IIRC, and this is an old memory) to make GNU/Linux pass certification you have to hack it up quite a bit; lots of GNU tools have POSIX modes that significantly change how they behave - things like du defaulting to 1024-byte units by default but using 512-byte units if you set POSIXLY_CORRECT because parts of the standard are, um, "interesting". But yes, neat to know that it can be done.
AFAIR, Red Hat once had a version of their system certified, too. But it's not as useful as one might think - the certification applies to a specific distro and release only, so it needs to be renewed with every new release.
It's honestly a little weird that Oracle doesn't see the value in continuing to have Solaris certified, same with Redhat and RHEL, but Apple continue to get macOS certified.
At this point Solaris is a zombie product that's only still on sale to bring in revenue from people who're so committed to the platform they'll buy it no matter what.
The development team was basically disbanded a while back, and the hardware team even further back than that, and any customer who's not going to be put off by that seems fairly unlikely to be put off by the lack of certification.
Depends on the version of OpenServer.
Up to 6 (released in 2005) it was a descendant of Xenix, so plenty of AT&T (well Bell Labs I guess) code still in there probably.
Later on SCO finally died and Xinuos got the trademark, which was reused for a FreeBSD-derived product as well
> This is to certify that Oracle Corporation has entered into a Trademark License Agreement with X/Open Company Limited in accordance with which the following are registered under the X/Open Brand Program.
* https://web.archive.org/web/20191022053203/https://www.openg...
* https://www.opengroup.org/openbrand/register/brand3642.htm
An August 2018 tweet:
> We are pleased to announce that Oracle Corporation has achieved certification to the UNIX V7 Product Standard for: Oracle Solaris 11.4 Operating System and later on SPARC-based and X86 based platforms. For more information: http://ow.ly/8fT830lBjfu #UNIX
* https://twitter.com/theopengroup/status/1034785507610447872
There's a renewal process:
* https://www.opengroup.org/openbrand/docs/UNIXV7_Certificatio...
Oracle did not bother renewing in April 2019:
> Solaris supports SPARC and x86-64 workstations and servers from Oracle and other vendors. Solaris was registered as compliant with UNIX 03 until 29 April 2019.[6][7][8]
* https://en.wikipedia.org/wiki/Oracle_Solaris