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If the model stopped in the Fortran executable, most of the time you can find an error message at the end of the listing of process 0. To get there jump to the end of the listing and then search backwards to the end of the listing of the main process. (When using 'vi', 'vim' or 'less' you can jump to the end by pressing 'G' and then search upward with '?00000:'). But even from the end of the main model listing you might still have to look several lines up to find an error. However, once you reached a line saying:
THE TIME STEP n IS COMPLETED
there is probably no error above anymore. In that case you will have to look into the listings of all the other processes.
For a large grid you might have use a lot of MPI processes and it is not easy to find an error message in them. Try looking for the word "Traceback". If you are luck this takes you exactly to the traceback of the error.
If the executable started running but was not able to finish the first timestep, meaning if you do not have at least one line saying:
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