SSH
create SSH key
ssh-keygen -q -b 4096 -f ~/.ssh/id_rsa -N '' -C "${USER}@$(hostname -f)"
Copy public key to server (/home/foo/.ssh/authorized_keys)
ssh-copy-id foo@example.com
show log
tail -f /var/log/auth.log
journalctl _COMM=sshd -f
# configuration
~/.ssh/config: user configuration
/etc/ssh/ssh_config: system-wide client configuration
/etc/ssh/sshd_config: system-wide server configurtion
http://www.panticz.de/SSH-server-enable-disable-password-authentication
http://www.panticz.de/ssh_pre-shared-key_authentication