How to Disable Password Authentication in Ubuntuby Mike Heldar
Ubuntu Linux makes use of passwords to authenticate user log-on requests in its default configuration. If your system is of a lower security priority and you believe that password information is unnecessary, you can disable password authentication to enable blank login requests from all users who access the proper username on the system.
Log into Ubuntu and open your Terminal program.
Type "sudo nano /etc/sshd_config" (without quotation marks here and throughout) and enter your administrative login password when prompted.
Press "Ctrl+W" to open a search window; type in "PasswordAuthentication" and press "Enter."
Remove the "#" sign at the start of the PasswordAuthentication label, then replace "Yes" with "No" so that the line reads: PasswordAuthentication no
Save the file and restart the server.