mpirun

mpirun is a command-line launcher used to start programs that use the Message Passing Interface (MPI) on distributed-memory systems. It is provided by MPI implementations such as Open MPI and MPICH, and in some environments by vendor-specific MPI products. mpirun coordinates the creation of multiple processes across compute nodes and establishes the communication infrastructure required by the MPI program.

Typical usage includes launching a fixed number of processes on the local host, for example: mpirun -np 4 ./a.out. More complex configurations specify where to run the processes, using host lists, host files, or resource managers: mpirun -np 8 --hostfile hosts ./a.out or mpirun -np 8 --map-by ppr:2:node ./a.out. mpirun can also cooperate with batch schedulers (such as Slurm, PBS, or SGE) to acquire resources, or run in a stand-alone mode when resources are already allocated.

Internals and options: mpirun forwards launcher and runtime options to the underlying MPI runtime, including process placement (--map-by), binding (--bind-to), and various -mca or equivalent parameters depending on the implementation. It sets necessary environment variables and may influence library loading or the use of the dynamic linker. In practice, mpirun acts as a wrapper around the MPI runtime’s process-spawning and initialization mechanisms (for example ORTE in Open MPI or PMI in MPICH).

Compatibility and variants: While mpirun is widely available, some MPI implementations also provide mpiexec or use mpirun as a synonym. The exact options and syntax can differ between implementations, so users should consult their MPI documentation for implementation-specific behavior.

See also: Message Passing Interface, Open MPI, MPICH, Intel MPI, batch schedulers.