Cron Syntax Cheatsheet - Unical Healthchecks

Unical Healthchecks understands most of the traditional cron syntax features. Under the hood, it uses the croniter package to parse and interpret cron expressions. Below is a showcase of supported syntax features.

Pro-tip! On Unix-like operating systems, you can also easily access cron syntax documentation by typing man 5 crontab in shell.

Basics

A cron expression has five fields, separated by spaces. Asterisk is a wild card character and means "any value".

"Run every minute"

*	*	*	*
				Day of week, 0 - 7, 0 or 7 is Sun
			Month, 1 - 12
		Day of month, 1 - 31
	Hour of day, 0 - 23
Minute, 0 - 59

Numeric values

Use numeric values instead of asterisks to match specific minutes, hours, days and months.

"Run at 6PM on Fridays"

18	*	*	5
				Run only on Fridays
			Run every month of the year
		Run every day of the month
	Run at 6PM
Run at the start of the hour

Commas

Use {v1},{v2},...,{vn} to list multiple values.

"Run at 9AM, 12PM and 6PM every day"

9,12,18	*	*	*
				Run on every weekday
			Run every month of the year
		Run every day of the month
	Run at 9AM, 12PM and 6PM
Run at the start of the hour

Ranges of values

Use {start}-{end} to define a range of matching values.

"Run every minute on workdays"

*	*	*	1-5
				Run on Monday to Friday
			Run every month of the year
		Run every day of the month
	Run every hour of the day
Run every minute of the hour

Ranges with a step

Use {start}-{end}/{step} or */{step} to define a range with a step.

"Run every quarter of an hour"

*	*	*	*
				Run on every weekday
			Run every month of the year
		Run every day of the month
	Run every hour of the day
Run every 15 minutes

Combine numeric values and ranges in lists

In the comma-separated lists you can combine not only numeric values but also ranges.

"Run every round hour outside office hours"

18-23,0-8	*	*	*
				Run on every weekday
			Run every month of the year
		Run every day of the month
	Run at 6PM, 7PM, 8PM, ..., 7AM, 8AM
Run at the start of the hour

Abbreviated day and month names

JAN-DEC can be used in the month field and MON-SUN in the weekday field.

"Run every round hour on April 1st"

*	1	APR	*
				Run on every weekday
			Run in April
		Run on the first day of the month
	Run every hour of the day
Run at the start of the hour

Timezones

Cron daemon uses server's local time. If your server's timezone is other than UTC, make sure to set a matching timezone for your check on Unical Healthchecks as well.

On Ubuntu systems you can check the server's timezone with:

cat /etc/timezone