#include <stdio.h>

#include "mpi.h"

int main (argc, argv)

     int argc;

     char *argv[];

{

  int rank, size;

  MPI_Init (&argc, &argv);/* starts MPI */

  MPI_Comm_rank (MPI_COMM_WORLD, &rank);/* get current process id */

  MPI_Comm_size (MPI_COMM_WORLD, &size);/* get number of processes */

  printf( "Hello world from process %d of %d\n", rank, size );

  MPI_Finalize();

  return 0;

}

compile it ($mpicc -o hello hello.c), all went fine too; and finally run it ($mpiexec -n 2 ./hello). However, that is the problem reported by mpiexec:

$ mpiexec -n 2 ./hello

Fatal error in MPI_Init: Other MPI error, error stack:

MPIR_Init_thread(467)..............: 

MPID_Init(177).....................: channel initialization failed

MPIDI_CH3_Init(70).................: 

MPID_nem_init(319).................: 

MPID_nem_tcp_init(171).............: 

MPID_nem_tcp_get_business_card(418): 

MPID_nem_tcp_init(377).............: gethostbyname failed, mac (errno 1)

Fatal error in MPI_Init: Other MPI error, error stack:

MPIR_Init_thread(467)..............: 

MPID_Init(177).....................: channel initialization failed

MPIDI_CH3_Init(70).................: 

MPID_nem_init(319).................: 

MPID_nem_tcp_init(171).............: 

MPID_nem_tcp_get_business_card(418): 

MPID_nem_tcp_init(377).............: gethostbyname failed, mac (errno 1)

===================================================================================

=   BAD TERMINATION OF ONE OF YOUR APPLICATION PROCESSES

=   PID 653 RUNNING AT mac

=   EXIT CODE: 1

=   CLEANING UP REMAINING PROCESSES

=   YOU CAN IGNORE THE BELOW CLEANUP MESSAGES

===================================================================================

The version installed:

$ mpichversion 

MPICH Version:    	3.1

MPICH Release date:	Thu Feb 20 11:41:13 CST 2014

MPICH Device:    	ch3:nemesis

MPICH configure: 	--disable-dependency-tracking --disable-silent-rules --prefix=/usr/local/Cellar/mpich2/3.1 --mandir=/usr/local/Cellar/mpich2/3.1/share/man

MPICH CC: 	clang    -O2

MPICH CXX: 	clang++  

MPICH F77: 	/usr/local/bin/gfortran   -O2

MPICH FC: 	/usr/local/bin/gfortran  