For security reason root login is disabled in Ubuntu servers by default. If you want to enable root login for your Ubuntu server follow the steps below.
then under ‘Serial Console (KVM)’ or IPMI Access click on ‘Generate login’ , then click on ‘Open Console’ now login with the username and password you just generated, after login copy paste the below commands.
apt-get install nano
Now find “PermitRootLogin without-password” and change that to “PermitRootLogin yes” without quote and press ctrl+x to save that file, then pres ‘y’ then press enter. Now restart SSHD with the below command.
service ssh restart
Now you can able to login as root in your Ubuntu server.