srun --nodes=16 --constraint=graphics*4 ...
    Based upon work by Kumar Krishna (HP, India).

    job steps to be queued when resources are not available within an existing
    job allocation to dedicate the resources to the job step. Useful for
    executing simultaneous job steps. Provides resource management both at
    the level of jobs and job steps.

    steps rather than cancelling the job. This now matches the behavior of
    all other signals. "scancel <jobid>" still cancels the job and all steps.

    Moab releases until early 2007).

    to task 0 (all other tasks have I/O discarded)

with Munge an alternative.