I can only login with root user. I think there is a new format of the sudo -l -S output.
xyz@mediaserver2:~$ sudo -l -S
[sudo] password for xyz:
Matching Defaults entries for eko on this host:
env_reset, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin
User xyz may run the following commands on this host:
(ALL : ALL) ALL
That format actually looks fine. However, I have a couple of questions :
1. Does the line sudo=1 appear in /etc/webmin/miniserv.conf
2. Is the user you are trying to login as stored in LDAP ?
Also, Webmin doesn't even properly support Ubuntu 12.04 yet. Wait until the 1.506 release is available at http://www.webmin.com/devel.html , then un-install your current Webmin, delete the /etc/webmin directory (to clear all settings), and then re-install from the .deb file.
I today tried Version 1.587. Sign on is possible now, even with non root user. You may close this issue.
Thank you.