title: MPI Processes Communication error
body: <p>I've got a raspberry pi cluster that has three nodes. I've installed mpi on it and i tried to excute an example code named cpi. The thing is that I get this error:  </p>
  
  <p>The command executed on master node:</p>
  
  <pre><code>mpiexec -f machinefile -n 2 mpi-build/examples/cpi 
  </code></pre>
  
  <p>The result:</p>
  
  <pre><code>Process 0 of 2 is on Pi01
  Fatal error in PMPI_Reduce: A process has failed, 
  error stack:PMPI_Reduce(1259)...............:MPI_Reduce(sbuf=0xbebc6630,rbuf=0xbebc6638,count=1, MPI_DOUBLE, MPI_SUM, root=0, MPI_COMM_WORLD) failed
  MPIR_Reduce_impl(1071)..........:
  MPIR_Reduce_intra(877)..........:
  MPIR_Reduce_binomial(184).......:
  MPIDI_CH3U_Recvq_FDU_or_AEP(630): Communication error with rank 1
  Process 1 of 2 is on Pi02
  </code></pre>
  
  <p>I've used SSH Keygens between the master and each slave so, there is no need to use the password to login between each node. (But if a slave connects to another it must login to another slave using the password, this means that I didn't share the ssh keygens between the slaves, but only between the master and the slaves.)</p>
  
  <p>Programs that print helloworld with the process rank and the PC that executed it work properly, but when a process needs to communicate with another, I get the error as stated above.
  What should I do?</p>