How to define an alternative MPI launcher

The pam script by default launches MPI runs with mpirun. If you cannot use mpirun because you are on a system which does not support it or which offers alternative MPI launchers (SGI, Cray), you can define your own DIRAC_MPI_COMMAND like this:

$ export DIRAC_MPI_COMMAND="mpirun -np 8"
$ export DIRAC_MPI_COMMAND="mpprun"
$ export DIRAC_MPI_COMMAND="aprun -n 24"

This will then launch:

$DIRAC_MPI_COMMAND dirac.x

instead of:

mpirun -np N dirac.x

Note that --mpi overrides DIRAC_MPI_COMMAND.