...
There is also an earlier version of OpenMPI, 1.5.4, available, but OpenMPI 1.8.1 has the advantage of being able to run on hosts at different infiniband speeds. OpenMPI 1.5.4 can have communication problems if it attempts to run across hosts at different speeds. However, If you find a need for that the older version you can set up your environment to use it instead when running on the bullets by making the following changes to the appropriate login script; csh or tcsh users will update .cshrc and bash users will update .bash_profile or .bashrc:
...