# Prolog and Epilog Guide

SLURM supports a multitude of prolog and epilog programs. The first table below identifies what prologs and epilogs are available for job allocations, when and where they run.

Parameter | Location | Invoked by | User | When executed
Prolog (from slurm.conf) | Compute or front end node | slurmd daemon | SlurmdUser (normally user root) | First job or job step initiation on that node
PrologSlurmctld (from slurm.conf) | Head node (where slurmctld daemon runs) | slurmctld daemon | SlurmctldUser | At job allocation
Epilog (from slurm.conf) | Compute or front end node | slurmd daemon | SlurmdUser (normally user root) | At job termination
EpilogSlurmctld (from slurm.conf) | Head node (where slurmctld daemon runs) | slurmctld daemon | SlurmctldUser | At job termination

This second table below identifies what prologs and epilogs are available for job step allocations, when and where they run.

Parameter | Location | Invoked by | User | When executed
SrunProlog (from slurm.conf) or srun --prolog | srun invocation node | srun command | User invoking srun command | Prior to launching job step
TaskProlog (from slurm.conf) | Compute node | slurmstepd daemon | User invoking srun command | Prior to launching job step
srun --task-prolog | Compute node | slurmstepd daemon | User invoking srun command | Prior to launching job step
TaskEpilog (from slurm.conf) | Compute node | slurmstepd daemon | User invoking srun command | Completion job step
srun --task-epilog | Compute node | slurmstepd daemon | User invoking srun command | Completion job step
SrunEpilog (from slurm.conf) or srun --epilog | srun invocation node | srun command | User invoking srun command | Completion job step

The task prolog is executed with the same environment as the user tasks to be initiated. The standard output of that program is read and processed as follows:
export name=value sets an environment variable for the user task
unset name clears an environment variable from the user task
print ... writes to the task's standard output.

Plugins functions are may also be useful to execute logic at various well defined points.

SPANK is another mechanism that may be useful to invoke logic in the user commands, slurmd daemon, and slurmstepd daemon.

### Failure Handling

If the Epilog fails (returns a non-zero exit code), this will result in the node being set to a DOWN state. If the EpilogSlurmctld fails (returns a non-zero exit code), this will only be logged. If the Prolog fails (returns a non-zero exit code), this will result in the node being set to a DOWN state and the job requeued to executed on another node. If the PrologSlurmctld fails (returns a non-zero exit code), this will result in the job requeued to executed on another node if possible. Only batch jobs can be requeued. Interactive jobs (salloc and srun) will be cancelled if the PrologSlurmctld fails.

Based upon work by Jason Sollom, Cray Inc. and used by permission.

Last modified 26 February 2013