How can I force SSH to only allow users with a public key to log in to my server and disable all password login? Is this possible?
Edit the sshd_config on your server.
sudo nano /etc/ssh/sshd_config
Set up following directives to only allow ssh keys based login and disable passwords
ChallengeResponseAuthentication no
PasswordAuthentication no
PermitRootLogin no
PermitRootLogin prohibit-password
Add ssh keys from all clients
At least make sure admin users can ssh in with your public ssh key and can use the sudo / su - to become the root user. Otherwise you will get locked down. Say from my client:
ssh admin@server
# can I use sudo or su ?
sudo -i
su -
If not, copy ssh-keys and and configure sudo for admin.
Restart or reload sshd
On your server run
sudo systemct reload sshd.service
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Take a look at my guide which explains everything.
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