Are you using mpiexec or srun when initially launching your job? Hydra (mpiexec) should support the "host" info key, but I'm not sure if srun will. Ken On 1/28/22, 10:41 AM, "Mccall, Kurt E. (MSFC-EV41) via discuss" <[email protected]> wrote: Hi, Running MPICH under Slurm, MPI_Comm_spawn unexpectedly creates new processes on any and all of the nodes that Slurm allocates to the job. I would like it to only create new processes locally on the node that called MPI_Comm_spawn. I’ve tried passing MPI_Comm_spawn an info struct created like this: MPI_Info info; MPI_Info_create(&info); MPI_Info_set(info, "host", host_name); MPI_Info_set(info, "bind_to", "core"); where hostname = “n001” or even the full name “n001.cluster.pssclabs.com” but that doesn’t prevent the problem. Any suggestions? Thanks, Kurt