If you've lost the root password but are still able to log in as admin in the UI, you may be able to reset the root password.

After logging into the Security Analytics appliance as admin, append this to the IP address or servername in your browser's address line: /settings/initial_config 

On the initial configuration page you can scroll down to the area Root Password.

Be sure to enter a password that matches the Password Strength settings at the bottom of the page.  Save your settings.