subprocess.run() failure under Linux when calling mpirun while MPI communicator open

[heplesser]

Bug report

Bug description:

The following code throws a CalledProcessError under Linux (Ubuntu 24) but passed under macOS (15.4).
Using mpi4py here is not essential, any program calling MPI_Init() will do.

The code works as expected if one either calls MPI.finalize() before calling subprocess.run() or just run echo in the subprocess without wrapping it with mpirun.

I used OpenMPI 4.1.6 under Ubuntu and OpenMPI 5.0.7 under macOS.

import subprocess
from mpi4py import MPI

# Uncomment the next line and it works
# MPI.Finalize()

res = subprocess.run(["mpirun", "-np", "1",    # comment out "mpirun" ... and it works
                      "echo", "This is the subprocess"],
                     check=True, capture_output=True)

CPython versions tested on:

3.13, 3.12

Operating systems tested on:

Linux, macOS

[heplesser]

First test with OpenMPI 5.0.7 under Linux suggest that the problem may be fixed by v5.0.7, so that it was an OpenMPI problem all along, thus closing.