Cron cheatsheet

Crontab management

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 -l`	List another user's crontab (root)
`sudo crontab -e -u www-data`	Edit crontab as a specific user

Field syntax

Field	Values	Example
Minute	0–59	`*/5` every 5 minutes
Hour	0–23	`2` at 02:00
Day of month	1–31	`1` first of the month
Month	1–12	`*` every month
Day of week	0–7 (0 and 7 = Sunday)	`1-5` weekdays

Special strings

String	Equivalent	Meaning
`@reboot`	—	Run once at startup
`@yearly` / `@annually`	`0 0 1 1 *`	Once a year
`@monthly`	`0 0 1 * *`	First day of month
`@weekly`	`0 0 * * 0`	Every Sunday
`@daily` / `@midnight`	`0 0 * * *`	Every day at midnight
`@hourly`	`0 * * * *`	Every hour

Common schedule examples

# Every day at 3:15 AM
15 3 * * * /usr/local/bin/backup.sh

# Every 10 minutes
*/10 * * * * /opt/app/healthcheck.sh

# Weekdays at 9 AM
0 9 * * 1-5 /usr/bin/report.sh

# First of month at midnight
0 0 1 * * /usr/local/bin/monthly-cleanup.sh

System cron locations

Path	Description
`/etc/crontab`	System-wide crontab (includes user field)
`/etc/cron.d/`	Per-package drop-in files
`/etc/cron.hourly/`	Scripts run hourly
`/etc/cron.daily/`	Scripts run daily
`/var/spool/cron/crontabs/`	User crontabs (Debian/Ubuntu)
`/var/spool/cron/`	User crontabs (RHEL/CentOS)

Inspection & logs

Command	Description
`systemctl status cron`	Check cron service (Debian/Ubuntu)
`systemctl status crond`	Check cron service (RHEL/CentOS)
`grep CRON /var/log/syslog`	Cron run log (Debian/Ubuntu)
`grep CRON /var/log/cron`	Cron run log (RHEL/CentOS)
`journalctl -u cron`	systemd journal for cron unit

Crontab environment lines

MAILTO=ops@example.com
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
SHELL=/bin/bash

*/5 * * * * /usr/local/bin/job.sh >> /var/log/job.log 2>&1

Pro tips

Always use absolute paths for scripts and binaries in cron jobs
Redirect output to a log file — cron won't show errors on your terminal
Use flock to prevent overlapping runs of the same job
Test the exact command as the cron user: sudo -u www-data /path/to/script.sh

Practice scenarios

Hands-on Cron scenarios on live Linux VMs: cron