If your app needs to poll a remote API once an hour, or send out an email report every evening, what tool do you reach for? Probably cron. Triggering events at a given wall clock time is what cron is for, but it works better at the system layer (e.g. rotating logs on a server) than at the app layer (e.g. sending out a daily report to your app’s users). I’ve described all the ways cron could be improved for app clock events in a previous post.

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Cron is a trusty tool in the unix toolbox for scheduling work to run at periodic intervals. In addition to system tasks, it’s common for app developers to use an app-specific crontab to run application tasks. For example, if your app is a feed reader, you might use a cronjob to fetch new feeds every three hours, and another cronjob to clean out old unread articles every night.

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