Hello Ralph and thanks for your answer!
> Where did you install OMPI? If you check "which mpirun", does it point > to the same installation where you edited the default hostfile? It was installed in the default path which is chosen by OFED. And yes, I've edited the right openmpi-default-hostfile : $ which mpirun /usr/mpi/gcc/openmpi-1.4.3/bin/mpirun $ cat /usr/mpi/gcc/openmpi-1.4.3/etc/openmpi-default-hostfile cluster1 cluster2 cluster3 cluster4 $ mpirun -np 4 B4A1 Hello World! I am rank 003 of 4 on hostname=cluster1. Hello World! I am rank 000 of 4 on hostname=cluster1. Hello World! I am rank 002 of 4 on hostname=cluster1. Hello World! I am rank 001 of 4 on hostname=cluster1. $ mpirun -hostfile /usr/mpi/gcc/openmpi-1.4.3/etc/openmpi-default-hostfile -np 4 B4A1 Hello World! I am rank 000 of 4 on hostname=cluster1. Hello World! I am rank 001 of 4 on hostname=cluster2. Hello World! I am rank 002 of 4 on hostname=cluster3. Hello World! I am rank 003 of 4 on hostname=cluster4. Regards, Lukas
