Cron Expression Syntax: A Complete Guide

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Cron expressions are used to schedule tasks in Unix-like operating systems. They consist of five fields that specify when a command should run.

This guide breaks down every aspect of cron expression syntax so you can write schedules with confidence.

The Five Fields of Cron

A cron expression consists of five time-and-date fields followed by the command to execute.

  • Minute (0-59): which minute of the hour
  • Hour (0-23): which hour of the day
  • Day of Month (1-31): which day of the month
  • Month (1-12): which month of the year
  • Day of Week (0-7): which day of the week (0 and 7 are Sunday)

Special Characters

Cron supports several special characters to create flexible schedules.

  • *: every value (all)
  • ,: list of values (1,3,5)
  • -: range of values (1-5)
  • /: step values (*/5 = every 5)

Common Patterns

Some cron patterns are used so frequently they have become standard.

Frequently Asked Questions

What does * * * * * mean?▼
It means every minute of every hour of every day of every month.
How do I run every 5 minutes?▼
Use */5 * * * * to run a command every 5 minutes.
Can I use day names?▼
Yes, you can use day names (sun, mon, tue...) or numbers (0-7) in the day-of-week field.
Difference between */2 and 0/2?▼
They produce the same result for most fields in practice.

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