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Displaying MPI Debug Information

The
I_MPI_DEBUG
environment variable provides a convenient way to get detailed information about an MPI application at runtime. You can set the variable value from 0 (the default value) to 1000. The higher the value, the more debug information you get. For example:
$ mpirun -genv I_MPI_DEBUG=2 -n 2 ./testc -genv I_MPI_DEBUG=2 -n 2 testc[1] MPI startup(): Internal info: pinning initialization was done[0] MPI startup(): Internal info: pinning initialization was done...
High values of
I_MPI_DEBUG
can output a lot of information and significantly reduce performance of your application. A value of
I_MPI_DEBUG=5
is generally a good starting point, which provides sufficient information to find common errors.
By default, each printed line contains the MPI rank number and the message. You can also print additional information in front of each message, like process ID, time, host name and other information, or exclude some information printed by default. You can do this in two ways:
  • Add the '
    +
    ' sign in front of the debug level number. In this case, each line is prefixed by the string
    <
    rank
    >#<
    pid
    >@<
    hostname
    >
    . For example:
    $ mpirun -genv I_MPI_DEBUG=+2 -n 2 ./testc [0#3520@clusternode1] MPI startup(): Multi-threaded optimized library ...
    To exclude any information printed in front of the message, add the '
    -
    ' sign in a similar manner.
  • Add the appropriate flag after the debug level number to include or exclude some information. For example, to include time but exclude the rank number:
    $ mpirun -genv I_MPI_DEBUG=2,time,norank -n 2 ./testc 11:59:59 MPI startup(): Multi-threaded optimized library ...
    For the list of all available flags, see the description of
    I_MPI_DEBUG
    in the
    Developer Reference
    .
To redirect the debug information output from
stdout
to
stderr
or a text file, use the
I_MPI_DEBUG_OUTPUT
environment variable:
$ mpirun -genv I_MPI_DEBUG=2 -genv I_MPI_DEBUG_OUTPUT=/tmp/debug_output.txt -n 2 ./testc
Note that the output file name should not be longer than 256 symbols.

See Also

Intel® MPI Library Developer Reference, section
Miscellaneous > Other Environment Variables > I_MPI_DEBUG

Product and Performance Information

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Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.