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I have a crontab that looks like this:

* * * * *   /bin/date >> /tmp/every-minute.log
0 8 * * *   /bin/date >> /tmp/eight-am.log

The first line works just fine. The second does not seem to fire at all, no matter what time I set it to run.

The timestamp that is dumped every minute by the first command shows the correct and expected date/time. I have my timezone configured correctly on the raspberry pi.

So why would a cronjob work only if it is set to run every minute and not at a specific time?

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  • 2
    This has really nothing to do with raspberry pi – Ingo Mar 30 '18 at 8:08
  • @Ingo, while this is true, I was completely unaware of that fact when I was dealing with the problem. All I knew is that cron jobs weren't behaving like they do on my other Linux devices that I use from day to day. I find that given the nature of raspberry pis, I wipe and start over from fresh installs frequently. As such, I and perhaps others are therefore more likely to face this problem on a RPi than an everyday-use laptop or desktop running a Linux OS. – b_laoshi Apr 1 '18 at 13:24
  • More importantly, problems which disappear after a reboot and cannot be reproduced are unlikely to be of interest to future readers. – Dmitry Grigoryev Apr 3 '18 at 13:45
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The fix
To answer my own question, cron was unaware of my current timezone. Running sudo /etc/init.d/cron restart fixed everything.

The explanation
Order of events:

  • Booted RPi
  • Used sudo raspi-config to the configure the correct timezone
  • Created cron jobs and tested them; they weren't working

Apparently, cron is unaware of the change in timezone unless you restart the cron service (or restart the whole machine). So when I changed the timezone, cron was still running in the old timezone. Hence, when at 07:59, I configured a job to run at 08:00, it didn't run because cron didn't know it was 08:00. By running sudo /etc/init.d/cron restart, I restarted the cron service at which time it was clued in to the updated timezone.

With cron finally aware of the current timezone, all jobs are now running as scheduled.

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