Consider daylight saving time with cron

November 8, 2007

I know it’s over a week after the fact, but a friend said it’s probably worth mentioning our experience with this recent daylight saving time switch. Ignore this if you don’t observe DST or your servers don’t use it (which might not be a bad idea).

If you have cron scripts that are meant to run only once a day and will run on Sundays (such as daily or weekly schedules), do not run them on or between 1am and 2am. Otherwise you risk them running twice or not at all.

Yes, it may seem obvious, but it’s probably overlooked. We certainly didn’t realize it, but since we just happened to be debugging a weekly cron script running at 1am that Sunday, we caught it in the act of doubling a long running, CPU intensive task.

Happy Wednesday!

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