I am getting below massge when I am trying to access root mode on Ubuntu Server.
UbuntuServer:~$ su root
Password: ******
su: Authentication failure
Sorry.
Actullay, you didn’t set root password while we were installing Ubuntu server. You can type "sudo passwd root" and create a new password for root account.
UbuntuServer:~$ sudo passwd root
Enter new UNIX password: ******
Retype new UNIX password: ******
passwd: password updated successfully
Now, you have new root’s password.