Passphraseless login using ssh-agent and ssh-add with SSH is a bit annoying, so it feels good to use
sudo apt-get install keychain
Add the following settings to ~ / .bashrc and ~ / .zshrc.
You cannot register without a public key, so if you only have a private key, refer to How to generate a public key from an SSH private key and enter the public key. Generate.
Replace key names such as ʻid_rsa` as appropriate.