How to Disable Password Authentication in Ubuntu

1. Log into Ubuntu and open your Terminal program.
2. Type 'sudo nano /etc/sshd_config' (without quotation marks here and throughout) and enter your administrative login password when prompted.
3. Press 'Ctrl+W' to open a search window; type in 'PasswordAuthentication' and press 'Enter.'
4. Remove the '#' sign at the start of the PasswordAuthentication label, then replace 'Yes' with 'No' so that the line reads:PasswordAuthentication no
5. Save the file and restart the server.