I need to create a user manually (need a specific uid and default group), but I would also like to be able to log in via the standard 12.04 login (lightdm). I cannot figure out a way to do both of these. If I created the user with the user accounts GUI, I cannot get the uid I want. If I create the user manually, it does not show up as an option on the log in screen.
Easiest workaround to me would be to change the UID of that user after you created that user. This is the command for it:
(side note: if you need to do this with the current user and do not want to create another account you can do this from the live cd too.)
Userid's by design do not show up when under 1000. You can change this though!
and change UID_MIN to 500 (or anything under 504 (but I would not go a lot lower))