title: Why Do All My Open MPI Processes Have Rank 0?
body: <p>I'm writing a <em>parallel</em> program using <code>Open MPI</code>. I'm running Snow Leopard 10.6.4, and I installed <code>Open MPI</code> through the <a href="https://brew.sh/" rel="nofollow noreferrer">homebrew</a> package manager.</p>
  <p>When I run my program using <code>mpirun -np 8 ./test</code>, every process reports that it has rank 0, and believes the total number of processes to be 1, and 8 lines of <code>process rank: 0, total processes: 1</code> get spit out to the console.</p>
  <p>I know it's not a code issue, since the exact same code will compile and run as expected on some Ubuntu machines in my college's computer lab. I've checked homebrew's bug tracker, and no-one's reported an issue with the Open MPI package. I'm at a loss.</p>