Comment # 6 on bug 1229813 from Thorsten Kukuk

(In reply to Dominique Leuenberger from comment #5)
> (In reply to Thorsten Kukuk from comment #0)
> 
> > dbus-broker has no dbus.service file, thus this dependencies are broken and
> > a boot only succeeds by pure luck.
> 
> That part is only partially true: when dbus-broker is enabled, systemd
> creates
> /etc/systemd/system/dbus.service (and also /etc/systemd/user/dbus.service)
> due to the alias present in dbus-broker.service)

Could it be that this get's only created when systemd starts the service, but
it is needed already upfront?

wtmpdb got started on one failing machine before dbus got started and
systemd-logind reported dbus errors.