Running Preexecution Programs

A preexecution program is a program that performs needed setup tasks that an application needs. It may create directories, input files, and so on.

Though LSF-HPC daemons only run on a node with resource manager role, batch jobs can run on any compute node that satisfies the scheduling and allocation requirements.

Where preexecution commands run depends on the type of job:

Before starting a preexecution program, LSF-HPC sets the SLURM_JOBID environment variable. To enable srun to launch preexecution on the first allocated node and other allocated nodes, your preexecution program should pick up the SLURM_JOBID environment variable. The SLURM_JOBID has the information LSF-HPC needs to run the job on the nodes required by your preexecution program.

The following items provide the information you need to run the preexecution program on the resource manager node, on the first allocated node, or on all the allocated nodes:

To run a preexecution program on the resource manager node:	This is the default behavior. Run the preexecution program normally. Your preexecution does not need to make use of the SLURM_JOBID environment variable.
To run a preexecution program on the first allocated node:	Use the SLURM srun -N 1 command. For example: $ /opt/hptc/bin/srun -N 1 my_pre_exec
To run a preexecution program on all allocated nodes:	Use the SLURM srun directly without node options. For example: $ /opt/hptc/bin/srun my_pre_exec

	NOTE: Do not use the srun -b command (for SLURM batch mode) inside preexecution programs. The srun -b command returns immediately after a SLURM batch job is submitted. This can cause the preexecution program to exit with success while the real task is still running in batch mode.

See the SLURM srun(1) manpage for more information about the srun command, its options, and the SLURM_JOBID environment variable.