Comment (by Roland Haas):

This seems to be an OpenMPI issue, in that it checks for rsh or ssh in its $PATH pretty much before it does anything else even when no remote execution is needed.

For example these:

OMPI_MCA_plm_rsh_agent=sh mpirun -n 2 whoami
mpirun -mca plm_rsh_agent sh -n 2 whoami

both work.

A fix may be to set the plm_rsh_agent option in /etc/openmpi-mca-params.confor in $HOME/.openmpi/mca-params.conf after which the simple

mpirun -n 2 whoami

works.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2234/trouble-in-the-tutorial-server