Root password for sudo (UNIX password)

Open terminal and type

sudo passwd

You will be asked for user password, type it and press enter, then type new root password and confirm it.

Here is the example:

linux@linux:~$ sudo passwd 
[sudo] password for linux: {here type your user password} 
Enter new UNIX password: {type new password} 
Retype new UNIX password: {comfirm new password} 
passwd: password updated successfully