Certification isn't required to be compliant, and I'd argue that very few people actually care or refer to it in the real world. It meets the same bar that all

Certification isn't required to be compliant, and I'd argue that very few people actually care or refer to it in the real world. It meets the same bar that all of the other "mostly compliant" OSes listed on the POSIX wiki page meet: you can write code against a POSIX stdlib and it'll work without involving a VM as long as you stick to some subset of interfaces and behaviors. WSL1's compliance was actually larger than most of the OSes on that list. The last time I asked Mentor Graphics which parts of POSIX they supported on Nucleus they said "tell us what APIs your application needs and we'll implement them" (anything beyond PSE51 was largely unimplemented). Zephyr is nice enough to actually document their limitations, but the support is far from comprehensive either: https://docs.zephyrproject.org/latest/services/portability/posix.html https://docs.zephyrproject.org/latest/services/portability/p...