As i found out, utmpx.h is in POSIX, but it (of course) has no
notion of a runlevel (RUN_LVL is not defined, it's only in utmp.h).

This somehow makes my questions less applicable to the actual
problem I'm trying to solve.

It still is generally interesting, but for a "POSIX-portable"
solution to my specific (nodm) problem, i had to find a different
approach anyway.

Kind regards,
T.

On 08/29/2015 07:53 AM, i wrote myself:
> [...]
> (1) if utmp is there (it's in POSIX), but the utmp support (being
> optional) is not there, will utmp simply remain not updated?
>
> (2) If the answer to (1) was "yes" then, how to determine if I am
> dealing with an utmp that is not actually being maintained but just
> remains there as sort of a compatibility placeholder (again, it's in
> POSIX)? Check for installed systemd and its version being >= 217?
>
> (3) In the light of questions (1) and (2), does systemd care about
> POSIX at all?
> [...]