In a development environment where hangs and crashes can occur, or where processes are killed with the 'kill -9' command, it is possible for the application to not properly clean up its resources (shared memory, semaphores, temp files). This can result in an inconsistent or corrupt startup state.
To be sure that these resources are properly cleaned up you can use the mwcleanup command. This utility will kill all currently running ArcGIS applications owned by the current user and remove their allocated resources and X properties.
To run the 'mwcleanup' command:
% source init_engine.csh
% mwcleanup
% mwcleanup