Answer: Let us address these two question one by one.
Warning: Enabling root is not recommended. If possible, you should always try to perform all administrative tasks using sudo.
Question 1: I’m unable to login using su command. How to fix this?
By default, root account password is locked in Ubuntu. So, when you do su -, you’ll get Authentication failure error message as shown below.
$ 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 ramesh: Enter new UNIX password: Retype new UNIX password: passwd: password updated successfully
Now with the new password you can login as super user with su command
$ su - Password: #
Disable super user account password on Ubuntu
Later if you don’t want to use su anymore, you can lock the root user password using one of the methods shown below
$ sudo passwd -l root
( or )
$ sudo usermod -p '!' root
Question 2: How do I login to Ubuntu directly using root account?
First, you should allow the root user to be logged in from the X as explained below.
Step 1: Go to System -> Administration -> Login window.
Step 2: In the Security tab, click on the check box “Allow local system administrator” as shown below. After this change, reboot the system and login directly using root account.