[mod4 (modulepath)]$ module purge
[mod4 (modulepath)]$ module load pgi/19.4
[mod4 (modulepath)]$ module load openmpi/4.0
[mod4 (modulepath)]$ module list
Currently Loaded Modulefiles:
 1) pgi/19.4   2) openmpi/4.0
[mod4 (modulepath)]$ mpirun
mpirun (openmpi/4.0, pgi/19.4)
[mod4 (modulepath)]$ module unload openmpi
[mod4 (modulepath)]$ module switch --auto pgi intel/2019
[mod4 (modulepath)]$ module load openmpi/4.0
[mod4 (modulepath)]$ module list
Currently Loaded Modulefiles:
 1) intel/2019   2) openmpi/4.0
[mod4 (modulepath)]$ mpirun
mpirun (openmpi/4.0, intel/2019)
[mod4 (modulepath)]$ module unload openmpi
[mod4 (modulepath)]$ module switch --auto intel gcc/9.1.0
[mod4 (modulepath)]$ module load openmpi/4.0
[mod4 (modulepath)]$ mpirun
mpirun (openmpi/4.0, gcc/9.1.0)
[mod4 (modulepath)]$ module unload openmpi
[mod4 (modulepath)]$ module switch --auto gcc gcc/8.2.0
[mod4 (modulepath)]$ module load openmpi/4.0
ERROR: Unable to locate a modulefile for 'openmpi/4.0'
[mod4 (modulepath)]$ module list
Currently Loaded Modulefiles:
 1) gcc/8.2.0
