title: Configure MPI hostsfile to use multiple user identities
body: <p>I want to run a program with mpirun on different sets of machines (All linux machines with Open Mpi 1.5).  </p>
  
  <p>Right now I have machines where I can log on with <code>username A</code>, and another set of machines where I use the <code>username B</code>. All machines are accessible via ssh, but I can't figure out how to achieve this.</p>
  
  <p>My hosts file would be like this :</p>
  
  <pre><code>localhost          #username local
  
  machine_set_A_1    #username A
  machine_set_A_2    #username A
  ...
  
  machine_set_B_1    #username B
  machine_set_B_2    #username B
  ...
  </code></pre>
  
  <p>Is it possible to achieve this. Thank you.</p>