title: Python Fabric gives: Fatal error: No existing session
body: <p>I have the following simple fabfile.py from the docs:</p>
  
  <pre><code>from fabric.api import run
  
  def host_type():
      run('uname -s')
  </code></pre>
  
  <p>I try to run it using:</p>
  
  <pre><code>fab -H 192.168.0.201 host_type
  </code></pre>
  
  <p>But get the error:</p>
  
  <pre><code>me@ubuntu:~/me$ fab -H 192.168.0.201 host_type
  [192.168.0.201] run: uname -s
  Password for me@192.168.0.201: 
  
  Fatal error: No existing session
  
  Aborting.
  </code></pre>
  
  <p>I can ssh okay into 192.168.0.201. </p>
  
  <p>Any ideas?</p>