To add another layer of security on your Ubuntu server, we have to disable root access to avoid your server exposed to a brute force attack.
Before doing this, first you should have a sudo user account.
Disabling the root access:
sudo nano /etc/ssh/sshd_config
Change PermitRootLogin from yes to no:
Now save the changes by pressing ctrl+o and exit with ctrl+x
Finally, restart the ssh service
sudo service ssh restart
That’s it. You have now disable the root access. As a result, you cannot login directly using root, but still you can switch to root once you have logged in using another username.
Below it the command for switching to root: