Authentication Failure while accessing super-user privilege

Question

I get the root privilege when I type sudo.

But when su asks for the Password, which I type in, the terminal says

su: Authentication Failure

Solution 1

Open Terminal By CTRL+ALT+T and Type :-

sudo passwd

And Re-Enter your password. This command will have you change your current password.

Solution 2

You could just use sudo su

$ sudo su

or sudo -i / sudo -s

$ sudo -i 
$ sudo -s 

Both work fine and will do everything .

Solution 3

Try to change the password of the sudo and login

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

After changing the sudo passwd you will be able to switch user via su

$ su
Password:
root@askmetutorials:/etc#