11.1. Environment variables set for MPI applications
Open MPI provides the following environment variables that will be defined on every MPI process:
OMPI_COMM_WORLD_SIZE: the number of processes in this process’s MPI_COMM_WORLD
OMPI_COMM_WORLD_RANK: the MPI rank of this process in MPI_COMM_WORLD
OMPI_COMM_WORLD_LOCAL_SIZE: the number of ranks from this job that are running on this node.
OMPI_COMM_WORLD_LOCAL_RANK: the relative rank of this process on this node within its job. For example, if four processes in a job share a node, they will each be given a local rank ranging from 0 to 3.
OMPI_UNIVERSE_SIZE: the number of process slots allocated to this job. Note that this may be different than the number of processes in the job.
OMPI_COMM_WORLD_NODE_RANK: the relative rank of this process on this node looking across all jobs.