MPI_Abort terminates the processes that belong to the communicator passed. When the communicator passed is MPI_COMM_WORLD, it is equivalent to shutting down the entire MPI application. (If the communicator passed is a subset of MPI_COMM_WORLD, it may not be possible for an MPI implementation to terminate only the processes belonging to this communicator. In which case, all processes are terminated instead.) The MPI standard stipulates no directive with regard to how the error code passed should be handled. In a UNIX or POSIX environment however, the error code given "should" become the value returned by the main program.