Open MPI

5.0.10 verified Fri May 01 auth: no python

Open MPI is a high performance implementation of the Message Passing Interface (MPI) standard, used for parallel computing. The Python package 'openmpi' is a wrapper that provides MPI bindings for Python. Current version is 5.0.10. Release cadence is irregular, following upstream Open MPI releases.

pip install openmpi

Common errors

error ImportError: No module named mpi4py ↓

cause mpi4py is not installed; openmpi package alone does not provide Python bindings.

fix

Run 'pip install mpi4py' and ensure the system has an MPI implementation (e.g., Open MPI).

error OSError: libmpi.so: cannot open shared object file: No such file or directory ↓

cause The underlying MPI library (e.g., Open MPI) is not installed on the system or not in the library path.

fix

Install Open MPI using your package manager: 'sudo apt install libopenmpi-dev' (Ubuntu) or 'brew install open-mpi' (macOS).

error MPI_Comm_spawn failed with error code 12 ↓

cause Insufficient resources or misconfigured process manager (ORTE/PRRTE).

fix

Check system limits (ulimit -u), ensure PRTE daemon is running, or use '--oversubscribe' flag with mpirun.

Warnings

gotcha The 'openmpi' PyPI package may not provide Python bindings directly; actual MPI programming in Python typically uses 'mpi4py'. Ensure mpi4py is installed and that the underlying Open MPI library is available on your system. ↓

fix Use mpi4py instead. Install via: pip install mpi4py

breaking Open MPI 5.x is not backward compatible with Open MPI 4.x custom MPI extensions. User-defined functions that rely on internal MPI hooks may break. ↓

fix Review application code for any non-standard MPI usage; consult Open MPI 5 migration guide.

deprecated The 'ompi' command-line tool has been deprecated in favor of 'prrte' for runtime launch. Using 'mpirun' is still supported but may emit warnings. ↓

fix Use 'mpirun' or switch to 'prrte' launcher if needed.

gotcha Open MPI requires a compatible Fortran compiler at build time; if you compile from source, you may need to install gfortran. Pre-built Python wheels may not be available. ↓

fix Install system-level Open MPI via package manager (e.g., apt, brew) before using mpi4py.

Imports

MPI
wrong
```
import openmpi
```
correct
```
from mpi4py import MPI
```
Direct import of 'openmpi' is incorrect; the actual MPI Python API is provided by mpi4py.

Quickstart

Initialize MPI, get rank and size, and perform a simple send/receive.

from mpi4py import MPI

comm = MPI.COMM_WORLD
rank = comm.Get_rank()
size = comm.Get_size()

print(f"Hello from rank {rank} of {size}")

# Example: send and receive
if rank == 0:
    data = {'a': 7, 'b': 3.14}
    comm.send(data, dest=1)
elif rank == 1:
    data = comm.recv(source=0)
    print(f"Rank 1 received: {data}")