Cron Syntax Reference — Every Field, Every Shortcut, Every Gotcha

The 5 fields

┌─── minute       (0–59)
│ ┌─── hour       (0–23)
│ │ ┌─── day of month (1–31)
│ │ │ ┌─── month    (1–12)
│ │ │ │ ┌─── day of week (0–6, 0=Sunday)
│ │ │ │ │
* * * * *  command_to_run

Field syntax

Syntax	Meaning	Example
*	Every value in this field	* * * * * = every minute
a,b,c	List of specific values	0,15,30,45 * * * * = every 15 min
a-b	Range	0 9-17 * * * = every hour 9am-5pm
*/n	Every n units, starting from 0	*/5 * * * * = every 5 min
a-b/n	Every n units within a range	0 8-18/2 * * * = every 2 hours, 8am-6pm

Shortcuts (most crons, not all)

Shortcut	Equivalent
@yearly / @annually	0 0 1 1 *
@monthly	0 0 1 * *
@weekly	0 0 * * 0
@daily / @midnight	0 0 * * *
@hourly	0 * * * *
@reboot	Runs once when cron starts (systemd cron only)

30 real cron examples

Cron	When it runs
* * * * *	Every minute
*/5 * * * *	Every 5 minutes
*/10 * * * *	Every 10 minutes
*/15 * * * *	Every 15 minutes
*/30 * * * *	Every 30 minutes
0 * * * *	Every hour, on the hour
15 * * * *	15 minutes past every hour
0 */2 * * *	Every 2 hours
0 */6 * * *	Every 6 hours (00:00, 06:00, 12:00, 18:00)
0 9 * * *	Every day at 9:00 AM
30 2 * * *	Every day at 2:30 AM
0 0 * * *	Every day at midnight
0 9 * * 1-5	Weekdays at 9 AM (Mon-Fri)
0 9 * * 1	Every Monday at 9 AM
0 9 * * 6,0	Weekends at 9 AM
0 0 1 * *	First day of every month at midnight
0 0 L * *	Last day of month (Quartz only)
0 0 15 * *	15th of each month at midnight
0 0 * * 0	Every Sunday at midnight
0 22 * * 5	Every Friday at 10 PM
0 0 1 1 *	Once a year, Jan 1st midnight
0 0 1 */3 *	Every quarter (Jan 1, Apr 1, Jul 1, Oct 1)
0 0 1,15 * *	1st and 15th of every month
5 4 * * sun	Sundays at 4:05 AM
0 8-18 * * 1-5	Every hour 8-18, weekdays
45 23 * * *	Daily at 11:45 PM
0 4 8-14 * *	2nd week of the month at 4 AM
0 0 * * 1#2	2nd Monday of the month (Quartz)
H/5 * * * *	Every 5 min, hashed offset (Jenkins)
* * * * * *	Every second (6-field cron only: Quartz, node-cron)

The day-of-month vs day-of-week gotcha

When BOTH day-of-month AND day-of-week are non-star, standard cron uses OR, not AND. So 0 0 15 * 1 means "at midnight on the 15th OR every Monday" — probably not what you want. If you need "the 15th if it's a Monday", handle it in your script with a date check.

Timezone handling

• System cron uses the machine's local time (see TZ env in crontab).
• systemd timers can specify OnCalendar with an explicit timezone.
• Cloudflare Cron Triggers and GitHub Actions use UTC. Always. If your job says "run at 9 AM" in New York time in November, that's 0 14 * * * in UTC — and it becomes 0 13 * * * in daylight saving. If it matters, use two cron entries.
• AWS EventBridge supports cron(0 9 * * ? *) with 6 fields — the ? means "no specific value". Uses UTC.

Non-standard extensions to know

• Quartz (Java): 6 fields (seconds first), L (last), W (weekday nearest), # (nth weekday of month).
• Jenkins: H means "hash" — spreads jobs across builders to avoid the thundering-herd on 0 * * * *.
• node-cron: 6 fields with seconds.
• fcron / systemd: % for run-once conditions.

Debug your cron

• Build cron expressions with the visual builder
• Test the schedule: crontab -l lists your active crontab, tail -f /var/log/syslog | grep CRON shows executions.
• Nothing running? Check the user's crontab, not just root. Check paths — cron has a minimal PATH. Check that the script is executable.