12.5. Application Output Lost with Abnormal Termination

There many be many reasons for application output to be lost when an application abnormally terminates. The Open MPI Team strongly encourages the use of tools (such as debuggers) whenever possible.

One of the reasons, however, may come from inside Open MPI itself. If your application fails due to memory corruption, Open MPI may subsequently fail to output an error message before terminating. Open MPI attempts to aggregate error messages from multiple processes in an attempt to show unique error messages only once (vs. once for each MPI process — which can be unwieldy, especially when running large MPI jobs).

However, this aggregation process requires allocating memory in the MPI process when it displays the error message. If the process’s memory is already corrupted, Open MPI’s attempt to allocate memory may fail and the process will simply terminate, possibly silently. When Open MPI does not attempt to aggregate error messages, most of its setup work is done when the MPI library is initiaized and no memory is allocated during the “print the error” routine. It therefore almost always successfully outputs error messages in real time — but at the expense that you’ll potentially see the same error message for each MPI process that encountered the error.

Hence, the error message aggregation is usually a good thing, but sometimes it can mask a real error. You can disable Open MPI’s error message aggregation with the opal_base_help_aggregate MCA parameter. For example:

shell$ mpirun --mca opal_base_help_aggregate 0 ...