Hi Jinang_Shah, Could you list your configure line ( try `head config.log`)? If you try a simple example where process 0 sends a short message to process 1, would you result in similar error? Can csews1 and csews2 connect to each other freely, i.e. is there firewall, router, etc. between these two hosts? — Hui Zhou On Jun 17, 2019, at 10:11 AM, Jinang_Shah via discuss <[email protected]<mailto:[email protected]>> wrote: $ mpiexec -n 2 -f hostfile ./mpi/mpich-3.3.1/examples/cpi Process 1 of 2 is on csews2 Process 0 of 2 is on csews1 Fatal error in PMPI_Reduce: Unknown error class, error stack: PMPI_Reduce(523)................: MPI_Reduce(sbuf=0x7ffeab580c10, rbuf=0x7ffeab580c18, count=1, datatype=MPI_DOUBLE, op=MPI_SUM, root=0, comm=MPI_COMM_WORLD) failed PMPI_Reduce(509)................: MPIR_Reduce_impl(316)...........: MPIR_Reduce_intra_auto(231).....: MPIR_Reduce_intra_binomial(125).: MPIDI_CH3U_Recvq_FDU_or_AEP(629): Communication error with rank 1 Can anyone explain this error and how to overcome it.I have installed just MPICH and not HYDRA package. By the way this same command works fine with hello program the one where each node says their identity. _______________________________________________ discuss mailing list [email protected]<mailto:[email protected]> To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss