The root user is not allowed to login on several linux distributions by default (Especially the ones have GNOME).
![root-linux-enable Enabling root login](http://1ve0.files.wordpress.com/2012/04/root-linux-enable.png)
To enable root login, apply these commands (It has been tried under Fedora 16. Probably It has similar procedure for other linux systems):
- Open configuration file:
su -gedit /etc/pam.d/gdm
- Find that line and add “#” to beginning of the line. Then save it.
# auth required pam_succeed_if.so user != root quiet
- Do the same thing for
/etc/pam.d/gdm-password
file.