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[Chareyre <question700315@xxxxxxxxxxxxxxxxxxxxx>]

Question #700315 on Yade changed:
https://answers.launchpad.net/yade/+question/700315

    Status: Open => Answered

Chareyre proposed the following answer:
Hi,

This:

"mpi4py.MPI.Exception: MPI_ERR_SPAWN: could not spawn processes"

is a message I've seen so many times. It isn't related to yade in most 
cases, I would first try and run some dummy mpi4py scripts to see what 
happens. There can be:

- some version conflicts between OpenMPI and mpi4py, or some bug in one 
of them

- hardware-specific or infrastructure-specific problems (not all HPC may 
enable spawning processes - see [1])

- also mind that the OpenMPI version on the host must be the same (or 
sufficiently close to) the one in the singularity image, else it won't 
connect communicate properly.

- on a cluster in Grenoble I found that the combination MPI/Singularity 
would run properly with a ubuntu16.04 image but not with a 20.04 image 
(no clue why at this point).


[1] If spawning is disabled on purpose on the cluster it might help to 
run mpi explicitely, as in:

mpiexec -np N singularity run 
/beegfs/common/singularity/yade/yade_debian_bookwarm_1.0.sif yade 
Case2_rotating_drum_mpi.py

Last note: if you run "yade -j5" on 10 mpi processes it actually means 
10x5=50 cores (mpi x openMP).


Bruno

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