Regular user can't change his own password
 

What should I look for if a regular user is unable to change his own password? I'm able to change it for him via root but as soon as he logs in and tries passwd "regular user" he get's denied.

Whats Linux distribution are you using (please put it in your profile) and whats the exact error message you get when the user tries to change their password?

If you tried
it might well be rejected (only root should be able to change others' passwords). Just log in and try
and see if it helps. I see no logical reason in those two methods, if username is the username of the logged-in user, except just the one I mentioned above..but it's no big deal to try :)

Also: is there some special group that is able to use passwd, that the user should belong to (like group passwd or something similar)?