Comment # 4 on bug 1224148 from Thorsten Kukuk

(In reply to Fabian Vogt from comment #3)
> What should sddm do? Just ignore ENOENT?

glibc (and several other implementations I saw) do a "return 0" if the utmp
file cannot be open'd, for all reasons.
So they do nothing if they cannot open the utmp file RDONLY.