Cron Cheatsheet

Cron Expression Format

┌───────────── minute (0-59)
│ ┌───────────── hour (0-23)
│ │ ┌───────────── day of month (1-31)
│ │ │ ┌───────────── month (1-12 or JAN-DEC)
│ │ │ │ ┌───────────── day of week (0-7 or SUN-SAT, 0 and 7 = Sunday)
│ │ │ │ │
* * * * *  command

Field Values

Field	Allowed Values	Special Characters
Minute	0-59	* , - /
Hour	0-23	* , - /
Day of Month	1-31	* , - / ? L W
Month	1-12 or JAN-DEC	* , - /
Day of Week	0-7 or SUN-SAT	* , - / ? L #

Special Characters

Character	Description	Example
*	Every value	* * * * * (every minute)
,	List separator	1,15 * * * * (minute 1 and 15)
-	Range	1-5 * * * * (minutes 1 through 5)
/	Step values	*/15 * * * * (every 15 minutes)
?	No specific value (day fields)	0 0 ? * MON
L	Last	0 0 L * * (last day of month)
W	Nearest weekday	0 0 15W * * (weekday nearest 15th)
#	Nth day of week	0 0 * * 5#3 (3rd Friday)

Special Strings (shorthand)

String	Equivalent	Description
@reboot	—	Run once at startup
@yearly	0 0 1 1 *	Once a year (Jan 1, midnight)
@annually	0 0 1 1 *	Same as @yearly
@monthly	0 0 1 * *	Once a month (1st, midnight)
@weekly	0 0 * * 0	Once a week (Sunday, midnight)
@daily	0 0 * * *	Once a day (midnight)
@midnight	0 0 * * *	Same as @daily
@hourly	0 * * * *	Once an hour (top of hour)

Common Schedules

Expression	Description
* * * * *	Every minute
*/5 * * * *	Every 5 minutes
*/15 * * * *	Every 15 minutes
0 * * * *	Every hour
0 */2 * * *	Every 2 hours
0 0 * * *	Every day at midnight
0 6 * * *	Every day at 6:00 AM
0 9-17 * * 1-5	Hourly, 9 AM–5 PM, Mon–Fri
0 0 * * 0	Every Sunday at midnight
0 0 * * 1-5	Every weekday at midnight
0 0 1 * *	First of every month
0 0 1 1 *	January 1st at midnight
30 4 1,15 * *	4:30 AM on 1st and 15th
0 0 * * 1	Every Monday at midnight
0 22 * * 5	Every Friday at 10:00 PM

Crontab Commands

Command	Description
crontab -e	Edit current user’s crontab
crontab -l	List current user’s crontab
crontab -r	Remove current user’s crontab
crontab -u user -e	Edit another user’s crontab

Environment & Tips

# Set shell
SHELL=/bin/bash

# Set PATH (cron has minimal PATH by default)
PATH=/usr/local/bin:/usr/bin:/bin

# Email output (set empty to disable)
MAILTO="user@example.com"
MAILTO=""

# Redirect output to log
* * * * * /path/script.sh >> /var/log/cron.log 2>&1

# Discard all output
* * * * * /path/script.sh > /dev/null 2>&1

# Use flock to prevent overlapping runs
* * * * * flock -n /tmp/job.lock /path/script.sh

System Cron Directories

Path	Description
/etc/crontab	System crontab (has user field)
/etc/cron.d/	Drop-in cron files
/etc/cron.daily/	Scripts run daily
/etc/cron.hourly/	Scripts run hourly
/etc/cron.weekly/	Scripts run weekly
/etc/cron.monthly/	Scripts run monthly