3.5. General Run-Time Support Notes
- The Open MPI installation must be in your - PATHon all nodes (and potentially- LD_LIBRARY_PATHor- DYLD_LIBRARY_PATH, if- libmpi/- libshmemis a shared library), unless using the- --prefixor- --enable-mpirun-prefix-by-defaultfunctionality (see below).
- Open MPI’s run-time behavior can be customized via Modular Component Architecture (MCA) parameters (see this section) for more information on how to get/set MCA parameter values). Some MCA parameters can be set in a way that renders Open MPI inoperable. In particular, some parameters have required options that must be included: - If specified, the - btlparameter must include the- selfcomponent, or Open MPI will not be able to deliver messages to the same rank as the sender. For example:- mpirun --mca btl tcp,self ...
- If specified, the - btl_tcp_if_excludeparameter must include the loopback device (- loon many Linux platforms), or Open MPI will not be able to route MPI messages using the TCP BTL. For example:- mpirun --mca btl_tcp_if_exclude lo,eth1 ...
 
- Running on nodes with different endian and/or different datatype sizes within a single parallel job is supported in this release. However, Open MPI does not resize data when datatypes differ in size (for example, sending a 4 byte - MPI_DOUBLEand receiving an 8 byte- MPI_DOUBLEwill fail).