login root

$ su -
Password:
su: Authentication failure

Enable super user account password on Ubuntu

First, set a password for root user as shown below.

$ sudo passwd root
[sudo] password for user:
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully 

sudo gedit /etc/lightdm/lightdm.conf

Tambahkan baris berikut:

greeter-show-manual-login=true


Selanjutnya jika anda ingin menonaktifkan Login Guest, tambahkan baris berikut :

allow-guest=false