Comment 2 for bug 435484

If you run su as $USER the su process will either a) prompt you for a password (if one is set) or b) return "su: Permission denied" if the password field is a *. Either way this blocks the startup of the process or the machine.

Example a:
herb@ramble:~$ id
uid=1000(herb) gid=1000(herb) groups=1000(herb)
herb@ramble:~$ su herb
Password:

Example b:
couchdb@ramble:~$ id
uid=111(couchdb) gid=120(couchdb) groups=120(couchdb)
couchdb@ramble:~$ su couchdb
su: Permission denied