title: su: Cannot make/remove an entry for the specified session
body: <p>After configuring the 2 factor authentication I can't login to another user on Ubuntu 14.04.</p>
  
  <p>The changes which I made for 2 factor authentication is</p>
  
  <ul>
  <li><p>edit <code>/etc/pam.d/sshd</code>; insert at the top this file:</p>
  
  <pre><code>auth required pam_google_authenticator.so
  </code></pre></li>
  <li><p>edit <code>/etc/pam.d/common-auth</code>; insert before the <code>pam_unix</code> line:</p>
  
  <pre><code>auth required pam_google_authenticator.so
  </code></pre></li>
  </ul>
  
  <p>Only if I comment out these lines can I login as another user. </p>