Each MPP is slightly different, and even systems from the same vendor may have different ways for running jobs at different installations. The mpirun program attempts to adapt to this, but you may find that it does not handle your installation. One step that you can take is to use the -t option to mpirun. This shows how mpirun would start your MPI program without actually doing so. Often, you can use this information, along with the instructions for starting programs at your site, to discover how to start the program. Please let us know (email@example.com) about any special needs.
Using mpirun with the IBM SP1 and SP2 computers can be tricky, because there are so many different (and often mutually exclusive) ways of running programs on them. The mpirun distributed with mpich works on systems using the Argonne scheduler (sometimes called EASY) and with systems using the default resource manager values (i.e., those not requiring the user to choose an RMPOOL). If you have trouble running an mpich program, try following the rules at your installation for running an MPL or POE program (if using the ch_eui device) or for running P4 (if using the ch_p4 device).
Using mpirun with an Intel Paragon can be tricky, because there are so many different (and often mutually exclusive) ways of running programs. The mpirun distributed with mpich works with Paragons that provide a default compute partition. There are some options, -paragon..., for selecting other forms. For example, -paragonpn compute1 specifies the pre-existing partition named compute1 to run on.