$ mpirun -n 6 -f hosts.txt ./hello
Hello world: rank 0 of 6 running on keisan11
Hello world: rank 1 of 6 running on keisan11
Hello world: rank 2 of 6 running on keisan12
Hello world: rank 3 of 6 running on keisan12
Hello world: rank 4 of 6 running on keisan12
Hello world: rank 5 of 6 running on keisan12