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I am using OpenMPI, starcluster, and Amazon EC2, while running through the tutorials at http://mpitutorial.com/tutorials/ . I set up a master and 2 nodes; node001 and node002. However, whenever I call MPI_Init and retrieve info from the Comm about the World Size, I keep getting a "World Size" of 1, even though I definitely am using 2 processors. These are using the functions in the MPICH library.

The example output shows the server name, rank, and world size:

Hello world from processor node001, rank 0 out of 1 processors 
Hello world from processor node001, rank 0 out of 1 processors
Hello world from processor node002, rank 0 out of 1 processors 
Hello world from processor node002, rank 0 out of 1 processors

There's obviously 2 processors here, both being used, but I still keep getting these values for Rank and World Size. Is there a way I can look into debugging what is happening here?

HoosierPhysics
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    Actually, a better dup would have been http://stackoverflow.com/questions/20287564/mpi-rank-return-same-process-number-for-all-process . – Jonathan Dursi Nov 10 '16 at 17:36
  • Ok, thanks. I apologize for the duplicate. I had made an attempt to search, but didn't come up with anything. I had seen that the Ranks were all 0, but I did not know that was so tied in to World Size. – HoosierPhysics Nov 10 '16 at 18:51
  • No apology necessary; this will stay as a link to the other so that people who pose the question your way will still get directed to the right answer. – Jonathan Dursi Nov 10 '16 at 22:15

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