title: ssh-add error with ECDSA and ED25519 identities
body: <p>Linux environment: Debian 9.1, with Gnome desktop</p>
  
  <p>I have both ECDSA and ED25519 identities, but from command line, ssh-add command gives error: </p>
  
  <blockquote>
    <p>Could not add identity</p>
  </blockquote>
  
  <p>How to solve?</p>