title: Until the browser is closed, session maintain without cookie in CodeIgniter
body: <p>I am using codeigniter php framework now in developing backend web application.
  But session is often expired.
  My config.php(application/config/ folder) is ;</p>
  
  <pre><code>  $config['sess_driver'] = 'files';
      $config['sess_cookie_name'] = 'ci_session';
      $config['sess_expiration'] = 0;
      $config['sess_save_path'] = NULL;
      $config['sess_match_ip'] = FALSE;
      $config['sess_time_to_update'] = 300;
      $config['sess_regenerate_destroy'] = TRUE;
  </code></pre>
  
  <p>In codeigniter guide, $config['sess_expiration'] = 0 -> "maintains session  until the browser is closed .".</p>
  
  <p>By the way, in my web application, when the user does nothing for a little time (about 30 mins), session is expired, so users must login again.</p>
  
  <p>What shall I set in config.php?</p>