Hi After I installed mpich and used it in a FORTRAN code. There is an error while running this FORTRAN code called real.exe by using the following command $./real.exe or $mpirun ./real.exe real.exe: error: _get_addr: No such file or directory real.exe: error: _get_addr: No such file or directory real.exe: error: _get_addr: No such file or directory Fatal error in MPI_Init: Other MPI error, error stack: MPIR_Init_thread(784).....: MPID_Init(1323)...........: channel initialization failed MPIDI_CH3_Init(120).......: MPID_nem_init_ckpt(852)...: MPIDI_CH3I_Seg_commit(364): PMI_Barrier returned -1 But while using mpirun with specifying number of processors. as follows $mpirun -np 1 ./real.exe There is no error any more. I am not sure why? do you have any explanation? Thank you very much Best regards Zhifeng