Q) Why doesn't mpirun work in the cygwin bash shell?
A) The cygwin environment has problems with the Windows API function CreateProcess. A workaround was introduced in mpich.nt.1.2.2 Oct 10, 2001. This and more recent versions of mpirun function in a bash shell running in a command prompt. MPIRun does not work in the XFree86 windowing environment.