====== Jobs at regular intervals ======

If you have small tasks you want to run at regular intervals, Slurm has the [[https://slurm.schedmd.com/scrontab.html|scrontab]] utility available. It gives you a ''cron''-like interface for submitting and running batch jobs at regular intervals, e.g. monitoring tasks or housekeeping scripts.

===== Usage =====
Like ''cron'', Slurm uses a configuration file to define these recurring jobs. Each users has it's own configuartion file. The files are not edited dierctly, but instead you can use ''scrontab -e'' to edit ((''scrontab'' uses the editor saved in the ''$EDITOR'' variable.)) your all your scrontab-jobs.

Inside the scrontab file, you can use ''#SCRON'' to give instructions to the scheduler, similar to the ''#SBATCH'' lines in normal jobscript, though not all options are supported. After the ''#SCRON'' lines, you have one line to define **when** and **what** should be done, just like a normal cron job.

You have two styles of defining when you job should run:
  - common time intervals, e.g. ''@hourly'', ''@daily'', ''@weekly''
  - [[https://wiki.archlinux.org/index.php/cron#Crontab_format|Five fields in the crontab format]]
The latter can get quite complex, but there are [[https://crontab.guru/|online tools]] out there to help you with it.
After defining when something should run, you can give a command or a script that is run at the appropriate time. The command or script has to be on the same line. The command to execute does not need to be a Slurm jobscript (i.e. should not contain ''#SBATCH'' lines).

These ''#SCRON'' lines and the following line comprise a single scrontab entry. All ''#SCRON'' lines following will be counted towards the next command.

You can list your currently defined ''scron'' jobs with ''scrontab -l''.

Slurm cannot guarantee that the jobs will run at the requested times, but tries to schedule it es close as possible. Internally, jobs are submitted to Slurm and set with a specific BeginTime. Once a ''scron'' job ran, it will be requeued with a new BeginTime. These jobs will also show up in ''squeue''.

===== Example =====
<file scrontab>
#SCRON -p fat
#SCRON -t 01:00:00
@daily /usr/users/mboden/update-database.sh

#SCRON -p medium
#SCRON -C scratch
#SCRON -t 05:00
#check scratch every 5 minutes
*/15 * * * * /usr/users/mboden/check-scratch.sh
</file>