• OpenSSH server notes
• See OpenSSH Client notes for clients

sudo -e '/etc/ssh/sshd_config'

• Check sshd_config to make sure sshd_config.d is included

/etc/ssh/sshd_config.d

• ArchWiki
• Be sure to generate/restore keys and to copy to server before disabling passwords
• See SSH Client notes
• Tested on Ubuntu Server 20.04

echo 'PasswordAuthentication no' | sudo tee '/etc/ssh/sshd_config.d/custom-pubkey-only.conf' > '/dev/null' && cat '/etc/ssh/sshd_config.d/custom-pubkey-only.conf'

sudo -e '/etc/ssh/sshd_config.d/custom-pubkey-only.conf'

• ArchWiki

chmod '400' ~/'.ssh/authorized_keys'

• ArchWiki

echo 'PermitRootLogin no' | sudo tee '/etc/ssh/sshd_config.d/custom-root-login-disable.conf' > '/dev/null' && cat '/etc/ssh/sshd_config.d/custom-root-login-disable.conf'

sudo -e '/etc/ssh/sshd_config.d/custom-root-login-disable.conf'