host process The value returned for MPI_HOST gets the rank of the MPI_HOST HOST process in the group associated with communicator MPI_COMM_WORLD, if there is such. MPI_PROC_NULL is returned if there is no host. This attribute can be used on systems that have a distinguished host processor, in order to identify the process running on this processor. However, MPI does not specify what it means for a process to be a HOST, nor does it requires that a HOST exists.
The attribute MPI_HOST has the same value on all MPI_HOST processes in the group of MPI_COMM_WORLD.