The purpose of this configuration is to disable ssh login using password and force user to use
ssh-key pair instead.
/etc/ssh/sshd_config file using text editor and change following option.
PermitRootLogin no # prevent root login via ssh
PasswordAuthentication no # deny ssh login using password
PubkeyAuthentication yes # enable public key authentication
# Explicitly define which user can login via ssh (optional)
# AllowUsers root otheruser
Note: if the option is commented, delete ‘#’ at the start of line to enable the option.
After we done editing config file, we need to restart
sshd service. On ubuntu/debian based distro, we can use command
sudo service sshd restart