Comments for Randomly spacing cron jobs

[sethjensen1]

Comments for https://www.endpointdev.com/blog/2020/06/randomly-spacing-cron-jobs/
By Jon Jensen

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[ghost]

We have a bunch of systems all around the world where we want to perform backups at 12:00, 16:00, and 20:00 local time each day. We had noticed that at the top of most hours the backup server started feeling a bit taxed because of so many systems hitting it all at once, so we implemented a random 999 second start time delay for the backup routine.

We have been using the following to set our randomness:

sleep $(tr -cd 0-9 </dev/urandom | head -c 3)

I must say that using RANDOM sure seems easier:

sleep $(( RANDOM % 999 ))

[JamesUoM]

If you deploy using Ansible or similar you can create the cronjob with a random offset for each host that you are configuring.

[FlorinAndrei]

On Ubuntu 16.04, the only syntax that worked was:

echo 'sleep $(( $RANDOM \% 600 ))' | bash; /path/to/executable

[jonjensen]

I am happy to see that cronie, the default cron daemon on the RHEL family (CentOS Stream/Rocky/Alma/Oracle) versions 8 and 9 now support the OpenBSD syntax ~ for a random value within a range!

The feature was added to cronie in Git on 2021-11-08 and appeared on 2022-05-31 in cronie 1.5.7-7 on CentOS Stream 9 and on 2022-05-02 in cronie 1.5.2-7 on CentOS Stream 8. Strange to see it appears there but not yet in Fedora.