Introduction

openmpi and mpich2 are the two currently most popular MPI software. They cannot be mixed, only one of them must be used at a time. How to switch from one to another? The info below is copied from http://osdir.com/ml/fedora-list/2009-12/msg00591.html

Check which packages are installed

Check which packages are installed by running:

>> rpm -q openmpi
>> rpm -q openmpi-devel
>> rpm -q mpich2
>> rpm -q mpich2-devel

If any of these 4 packages are missing, install them first, e.g.,

>> yum install openmpi

(need to be root for this)

(re-)start MPI

The management is done on user-level on a session basis. To use the openmpi compiler, just run

>> module load openmpi-x86_64

on x86_64 and

>> module load openmpi-i686

on x86 to get Open MPI working again.

If you have Open MPI support loaded, you can also get rid of it with

>>
module unload openmpi-x86_64

>> module load mpich2-x86_64

For mpich2, after the above, you may also need to start the mpich2 daemon by

>> mpd&

Double-check by running

>> which mpicc
>> which mpiCC

Specify LD_LIBRARY_PATH

Both openmpi and mpich2 are shared libraries, so you need to specify the corresponding LD_LIBRARY_PATH, by running either (for mpich2)

>> LD_LIBRARY_PATH=/usr/lib64/mpich2/lib; export LD_LIBRARY_PATH

or (for openmpi)

>> LD_LIBRARY_PATH=/usr/lib64/openmpi/lib:/opt/acml-4-4-0-gfortran-64bit/gfortran64/lib; export LD_LIBRARY_PATH

If you need to use several shared libraries, use the following format (for openmpi and ACML)

>> LD_LIBRARY_PATH=/usr/lib64/openmpi/lib:/opt/acml-4-4-0-gfortran-64bit/gfortran64/lib; export LD_LIBRARY_PATH

Further notes

Remember that this setup is only active in the given shell window till you close it. Make sure that you name differently the directories where you compile and run the codes. Do not forget to setup the MPI again if you return to the previously compiled code before you run it!

P.S. RHEL 4 and 5 use the mpi-selector command instead.