Comment # 4 on bug 900095 from Andreas Schneider

Oct 07 16:55:00 magrathea.cryptomilk.site unix_chkpwd[9435]: check pass; user
unknown
Oct 07 16:55:00 magrathea.cryptomilk.site unix_chkpwd[9436]: check pass; user
unknown
Oct 07 16:55:00 magrathea.cryptomilk.site unix_chkpwd[9436]: password check
failed for user (root)
Oct 07 16:55:00 magrathea.cryptomilk.site su[9434]: pam_unix(su:auth):
authentication failure; logname= uid=1000 euid=1000 tty=pts/17 ruser=asn rhost=
 user=root
Oct 07 16:55:02 magrathea.cryptomilk.site su[9434]: FAILED SU (to root) asn on
pts/17

Hmm, could be a PAM issue.