Please refer to the below steps to enable root user in ubuntu.
- Login to your ubuntu server using the default user from the console.
- Go to the sshd_config file at the path /etc/ssh/.
- Comment out #PermitRootLogin without password, add PermitRootLogin yes into the line.
- Restart the SSH service to make the changes effect by using the below command.
service sshd restart
That's it, you have enabled Root user in Ubuntu.