Summary says mostly all.
When starting prosody via init-script:
Apr 15 00:46:46 localhost:posix error Danger, Will Robinson! Prosody doesn't need to be run as root, so don't do it!
Apr 15 00:46:46 localhost:posix error For more information on running Prosody as root, see http://prosody.im/doc/root
Apr 15 00:46:46 localhost:posix error Failed to daemonize: already-daemonized
While module posix disabled, there is no error message but Prosody doesn't start, too.
When starting prosody via prosodyctl start, it works like a charm.
Maybe the initscript has to be reworked to use prosodyctl instead of prosody directly?
I think the issue is dependant of the version of baselayout used. With baselayout-1.x the -u option of start-stop-daemon does not change the user, you have to use the -c option too. With baselaout-2.x it works fine.
However with baselayout-1.x and the option -c and -b, I have a weird issue, the prosody process is killed but it works without the -b option.
I switched to =baselayout-2, now it works. Thanks for the hint.
As bl-2 is stable, closing as obsolete. hope this is ok