By executing the following command in the terminal, the private key will be registered on the Mac.
Example: Private key exists in /home/user/Desktop/id_rsa
$ ssh-add /home/user/Desktop/id_rsa
By using ssh-add (transfer agent), you can omit the passphrase of the private key when you log in to the login node.
To delete the registered private key, execute the following command.
$ ssh-add -D