title: mpirun - not enough slots available
body: <p>Usually when I use mpirun, I can "overload" it, using more processors than there acctually are on my computer. For example, on my four-core mac, I can run <code>mpirun -np 29 python -c "print 'hey'"</code> no problem. I'm on another machine now, which is throwing the following error:</p>
  
  <pre><code>$ mpirun -np 25 python -c "print 'hey'"
  --------------------------------------------------------------------------
  There are not enough slots available in the system to satisfy the 25 slots 
  that were requested by the application:
    python
  
  Either request fewer slots for your application, or make more slots available
  for use.
  --------------------------------------------------------------------------
  </code></pre>
  
  <p>Why isn't "overclocking" mpirun working here? Is there a way I can overcome this error message and successfully run with more processors than are available?</p>