Hi all, I have installed MPICH2 in a Mac 10.9.2 using homebrew. The installation process went OK, no problems were reported. Then I created a small hello world example just to test the MPI: #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 Does anyone have any idea of why I am getting this error? The hostname command is also working fine, so I do NOT understand this problem. Furthermore, the idea is to run MPICH2 on my mac, not in a cluster so it should be straightforward to pick the hostname. My /etc/hosts shows the following: $ cat /etc/hosts ## # Host Database # # localhost is used to configure the loopback interface # when the system is booting. Do not change this entry. ## 127.0.0.1 localhost 255.255.255.255 broadcasthost ::1 localhost fe80::1%lo0 localhost Any ideas? Any help, suggestions or workarounds would be much appreciated. Best regards, Luis The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.