Question 1

What are the five fields in a cron expression?

Accepted Answer

The five fields are, left to right: minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-7, where both 0 and 7 are Sunday). Each field accepts numbers, ranges (1-5), lists (1,3,5), steps (*/5), or a wildcard (*) meaning every value.

Question 2

What is the difference between * and */1 in cron?

Accepted Answer

They are functionally identical. Both mean every value in the field. */1 is just the explicit step form of *, stepping by 1 through the full range. Use * for clarity.

Question 3

Can I use both day of month and day of week in the same expression?

Accepted Answer

Yes, but the behavior is a common source of confusion. In standard (POSIX) cron, if both fields are set to non-wildcard values, the job runs when EITHER condition is true (OR logic), not when both are true. So 0 9 15 * 1 fires at 9 AM on the 15th of every month AND every Monday, not only on Mondays that fall on the 15th.

Question 4

What do the @ shortcuts like @daily and @hourly mean?

Accepted Answer

@daily is equivalent to 0 0 * * * (midnight every day). @hourly is 0 * * * * (top of every hour). Other shortcuts: @weekly = 0 0 * * 0 (Sunday midnight), @monthly = 0 0 1 * * (midnight on the 1st), @yearly = 0 0 1 1 * (midnight on January 1st), @reboot = run once at startup. Not all cron implementations support these.

Question 5

How do I schedule a cron job for the last day of the month?

Accepted Answer

Standard cron has no 'last day of month' syntax. The common workaround is to test the date in the command itself: 0 0 28-31 * * [ $(date -d tomorrow +%d) -eq 01 ] && your_command. This runs daily on the 28th through 31st but only executes the command when tomorrow is the 1st. Some extended cron implementations (like AWS EventBridge) support an L modifier.

Character	Meaning	Example	Result
`*`	Every value	`* * * * *`	Every minute
`,`	List	`1,15 * * * *`	At minute 1 and 15
`-`	Range	`0 9-17 * * *`	Every hour from 9 AM to 5 PM
`/`	Step	`/10 * * *`	Every 10 minutes
`-` + `/`	Range with step	`0 8-18/2 * * *`	Every 2 hours from 8 AM to 6 PM

Expression	Fires	Per hour
`* * * * *`	Every minute	60
`/5 * * *`	Every 5 minutes	12
`/10 * * *`	Every 10 minutes	6
`/15 * * *`	Every 15 minutes	4
`/30 * * *`	Every 30 minutes	2

Expression	Fires
`0 * * * *`	Top of every hour
`0 /2 * *`	Every 2 hours
`0 /6 * *`	Every 6 hours (midnight, 6 AM, noon, 6 PM)
`0 0 * * *`	Daily at midnight
`0 6 * * *`	Daily at 6 AM
`30 4 * * *`	Daily at 4:30 AM (common for maintenance tasks)

Expression	Fires
`0 9 * * 1-5`	Weekdays at 9 AM
`0 0 * * 1-5`	Weekdays at midnight
`0 9 * * 1`	Every Monday at 9 AM
`0 0 * * 0`	Every Sunday at midnight
`0 17 * * 5`	Every Friday at 5 PM

Expression	Fires
`0 0 1 * *`	First day of every month at midnight
`0 0 15 * *`	15th of every month at midnight
`0 0 1 1 *`	January 1st at midnight (yearly)
`0 0 1 /3 `	Every quarter (Jan, Apr, Jul, Oct)

Cron Cheat Sheet: Every Expression You'll

Cron Syntax at a Glance

Special Characters

Common Schedules

Every N Minutes

Hourly and Daily

Weekday Schedules

Monthly and Yearly

Aliases

Field Value Ranges

Common Gotchas

OR logic between day fields

Timezone matters

Step values don’t carry over

No second level precision

Alias	Equivalent	Meaning
`@yearly`	`0 0 1 1 *`	Once a year (January 1st)
`@monthly`	`0 0 1 * *`	Once a month (1st at midnight)
`@weekly`	`0 0 * * 0`	Once a week (Sunday midnight)
`@daily`	`0 0 * * *`	Once a day (midnight)
`@hourly`	`0 * * * *`	Once an hour (top of the hour)
`@reboot`	N/A	Once at system startup

Field	Range	Names allowed
Minute	0-59	No
Hour	0-23	No
Day of month	1-31	No
Month	1-12	JAN, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC
Day of week	0-7	SUN, MON, TUE, WED, THU, FRI, SAT (0 and 7 are both Sunday)