ssh-add

ssh-add adds, removes, or lists agent keys.
Attempts to add default keys (identity, id_rsa, id_dsa) unless files specified.
Asks for passphrase for any passphrase-protected keys.

  reegen$ ssh-add
  Enter passphrase for /home/reegen/.ssh/id_rsa: (passphrase)
  Identity added: /home/reegen/.ssh/id_rsa (My new Key)
  Identity added: /home/reegen/.ssh/identity (My home key)

  reegen$ ssh-add /path/to/passwordless/key
  Identity added: /path/to/passwordless/key