Greetings all, I use OpenMPI 1.3.3 and I tried to spawn child processes (using MPI_Comm_spawn) and send user-defined-datatypes across processes.The child processes should be ranked from 1-5 while the rank 0 is the manager processes (manager.cpp) . But I get rank 0 for manager process and the child processes also ranked starting from 0 (0-4) . So I cannot send data from manager process to first child processes (which suppose to be rank 1) Please give any suggestion to resolve this. thanks in advance, umanga manager.cpp (manager process which spawns child processes) - rank 0 ------------------------------------------------------------ int main(int argc,char *argv[]) { mpi::environment evn(argc,argv); mpi::communicator world; MPI_Comm everyone; //spawn 5 child processes. MPI_Comm_spawn("./worker", MPI_ARGV_NULL, 5, MPI_INFO_NULL, 0, MPI_COMM_SELF, &everyone, MPI_ERRCODES_IGNORE); intercommunicator intcomm(everyone,comm_duplicate); if(rank==0){ GPSPosition *obj=new GPSPosition(100,200,300); shared_ptr<Position> pos(new Position); pos->setVals(); obj->addP(pos); intcomm.send(0,100,obj); } return 0; } worker.cpp (child process)- should be ranked 1-5 ,but get 0-4 ----------------------------------------------------------------------------------- int main(int argc,char *argv[]) { mpi::environment evn(argc,argv); MPI_Comm parent; MPI_Comm_get_parent(&parent); intercommunicator incomm(parent,comm_duplicate); if(parent==MPI_COMM_NULL){ cout << "Intercommunicator is Null !"<<endl; }else{ int r=incomm.rank(); cout <<"Rank !"<<r<< endl; //get 0-4 if(r==1){ //try receiving data send from manager process } } return 0; }