Cron jobs

Cron jobs allow you to run scheduled tasks at specified times or intervals. The crons section of describes these tasks and the schedule when they are triggered. Each item in the list is a unique name identifying a separate cron job.

It has a few subkeys listed below:

  • spec: The cron specification. For example: */20 * * * * to run every 20 minutes.
  • cmd: The command that is executed, for example cd public ; drush core-cron

The minimum interval between cron runs is 5 minutes, even if specified as less. Additionally, a variable delay is added to each cron job in each project in order to prevent host overloading should every project try to run their nightly tasks at the same time. Your crons will not run exactly at the time that you specify, but will be delayed by 0-300 seconds.

Cron runs are executed using the dash shell, not the bash shell used by normal SSH logins. In most cases that makes no difference but may impact some more involved cron scripts.

If an application defines both a web instance and a worker instance, cron tasks will be run only on the web instance.

How do I setup Cron for a typical Drupal site?

The following example runs Drupal's normal cron hook every 20 minutes, using Drush. It also sets up a second cron task to run Drupal's queue runner on the aggregator_feeds queue every 5 minutes.

    # Run Drupal's cron tasks every 20 minutes.
        spec: '*/20 * * * *'
        cmd: 'cd web ; drush core-cron'
    # But also run pending queue tasks every 5 minutes.
        spec: '*/5 * * * *'
        cmd: 'cd web ; drush queue-run aggregator_feeds'