Originally Posted by Didier Spaier

Of course. POSIX is a standard, UNIX an OS thus UNIX is not POSIX if that's what you mean. Similarly the drawing of a cat is not a cat (sorry for the loose comparison, I tried hard but failed to find a cat's specifications).

But nowadays when people refer to "UNIX compliance" I assume they actually mean "POSIX compliance".

Incidentally this reminds us that one should always write the specification after having built the system. That's by far the safest and costless way to make sure that the system complies with the specification

If the part I quoted of his interview at the FOSDEM 2011 isn't clear enough here are two more quotes from LP.

In The Biggest Myths he acknowledges that systemd is not portable, and states the reason of this design choice:He made a similar statement in an interview he gave to linuxfr.org:

To make your own opinion I encourage you to follow the links I provided to read the whole article and interviews quoted.