SGE shepherd

shepherd process exists for each job running on computational nodes (one per job daemon)

• Invoked by sge_execd to handle a single job
• Sets up resources before jobs begin Prolog script, Parallel environment startup, etc.
• Uses setuid behavior to become the user
• Starts the job as a child process
• Controls the job
• Handles suspend/resume/terminate signals. Handles checkpointing
• Performs cleanup after job termination Runs Epilog scripts, Parallel environment shutdown, etc.

sge_shepherd  provides the parent process functionality for a single Sun Grid Engine job. The parent functionality is necessary on UNIX systems to retrieve resource usage information (see getrusage(2)) after a job has finished. In addition, the sge_shepherd  forwards signals to the job, such as the signals for suspension, enabling, termination and the Sun Grid Engine checkpointing signal (see sge_ckpt(1) for details).

The sge_shepherd  receives information about the job to be started from the sge_execd(8). During the execution of the job it actually starts up to 5 child processes. First a prolog script is run if this feature is enabled by the prolog parameter in the cluster configuration. (See sge_conf(5).) Next a parallel environment startup procedure is run if the job is a parallel job. (See sge_pe(5) for more information.) After that, the job itself is run, followed by a parallel environment shutdown procedure for parallel jobs, and finally an epilog script if requested by the epilog parameter in the cluster configuration. The prolog and epilog scripts as well as the parallel environment startup and shutdown procedures are to be provided by the Sun Grid Engine administrator and are intended for site-specific actions to be taken before and after execution of the actual user job.

After the job has finished and the epilog script is processed, sge_shepherd  retrieves resource usage statistics about the job, places them in a job specific subdirectory of the sge_execd(8) spool directory for reporting through sge_execd(8) and finishes.

sge_shepherd  also places an exit status file in the spool directory. This exit status can be viewed with qacct -j JobId (see qacct(1)); it is not the exit status of sge_shepherd  itself but of one of the methods executed by sge_shepherd.  This exit status can have several meanings, depending on in which method an error occurred (if any). The possible methods are: prolog, parallel start, job, parallel stop, epilog, suspend, restart, terminate, clean, migrate, and checkpoint.

The following exit values are returned:

• 0 All methods: Operation was executed successfully.
• 99 Job script, prolog and epilog: When FORBID_RESCHEDULE  is not set in the configuration (see sge_conf(5)), the job gets re-queued. Otherwise see "Other".
• 100 Job script, prolog and epilog: When FORBID_APPERROR  is not set in the configuration (see sge_conf(5)), the job gets re-queued. Otherwise see "Other".

Other

Job script: This is the exit status of the job itself. No action is taken upon this exit status because the meaning of this exit status is not known.

• Prolog, epilog and parallel start: The queue is set to error state and the job is re-queued.
  Parallel stop: The queue is set to error state, but the job is not re-queued. It is assumed that the job itself ran successfully and only the clean up script failed.
  Suspend, restart, terminate, clean, and migrate: Always successful.
  Checkpoint: Success, except for kernel checkpointing: checkpoint was not successful, did not happen (but migration will happen by Sun Grid Engine).

 Step by step job submission process

• Job submitted from submit host or via DRMAA API
• User identity, cwd, environment preserved
• Master host receives job request, places entry in database and notifies the scheduler
• Scheduler attempts to dispatch job to best possible queue. If successful, queue is returned to the qmaster daemon
• Qmaster sends job to the proper sge_execd
• sge_execd spawns a sge_shepherd process; suid() pivot
• Shepherd sets up job, including paths, cwd and environment variables recorded at submission time. The shepherd starts the job, monitors resource usage data and exit status. Shepherd also performs post-job cleanup tasks.
• Exit status & accounting data passed back to sge_execd and sge_qmaster

Files

sgepasswd contains a list of user names and their corresponding encrypted passwords. If available, the password file will be used by sge_shepherd. To change the contents of this file please use the sgepasswd command. It is not advised to change that file manually.

<execd_spool>/job_dir/<job_id>  job specific directory

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sge_intro(1), sge_conf(5), sge_execd(8).

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Last modified: March 12, 2019