Cron expressions

Explanation and next runs

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What is Cron expressions?

Cron is the system Linux servers use to schedule automatic tasks, such as backups or sending emails. Its expressions, like “*/15 9-17 * * 1-5”, are hard to read at a glance.

This tool translates any cron expression into a plain-English sentence and shows the next ten dates it will run, so you can check it does what you want.

How to use it

  1. Type a 5-field cron expression or a macro such as @daily.
  2. Read the plain-English explanation and the breakdown of each field.
  3. Check the next 10 run times.
  4. Use one of the templates as a starting point.
  5. Check the syntax reference if you're unsure.

Advantages

Technical details

It parses the standard five-field crontab format: minute (0–59), hour (0–23), day of month (1–31), month (1–12 or JAN–DEC) and day of week (0–7, where 0 and 7 are Sunday, or SUN–SAT). It supports *, comma lists, hyphen ranges, steps with / (*/10, 0-30/5) and ? as a wildcard, plus the macros @yearly, @annually, @monthly, @weekly, @daily, @midnight and @hourly. Following Vixie cron behavior, if both day of month and day of week are restricted, the task runs when either matches. Next runs are calculated in the device's time zone, and expressions that never match, such as February 30, are detected. The seconds field and Quartz's L, W and # extensions are not supported.

Frequently asked questions

What does */5 * * * * mean in cron?

That the task runs every 5 minutes, every hour, every day.

How do I schedule a task Monday to Friday at 9?

With the expression 0 9 * * 1-5: minute 0, hour 9, any day of the month, any month and weekdays 1 (Monday) to 5 (Friday).

What is the order of the fields in cron?

Minute, hour, day of month, month and day of week.

What happens if I set both day of month and day of week?

In standard cron, it's enough for either one to match. For example, 0 0 1 * 1 runs on the 1st of every month and also every Monday.

What is @daily in crontab?

A macro equivalent to 0 0 * * *, that is, once a day at midnight.

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