Cron expressions are the universal language for scheduling automated tasks — running database backups every night, sending weekly reports, polling APIs every 5 minutes. They look cryptic ("0 0 * * *") but follow simple rules once you understand the format.
This guide explains the 5-field cron syntax, common scheduling patterns, special characters, and tips for testing schedules safely before production.
Generate Cron Expressions — Free
Visual schedule builder with next-execution preview. Perfect for backups, reports, and automation.
Cron Syntax (5 Fields)
* * * * *
| | | | |
| | | | +---- Day of week (0-7, Sunday=0 or 7)
| | | +------ Month (1-12)
| | +-------- Day of month (1-31)
| +---------- Hour (0-23)
+------------ Minute (0-59)Special Characters
*— every value,— list (1,5,15)-— range (1-5)/— step (*/5 = every 5)?— no specific value (some systems)L— last day of month/weekW— weekday closest to date
Common Cron Patterns
| Schedule | Cron Expression |
|---|---|
| Every minute | * * * * * |
| Every 5 minutes | */5 * * * * |
| Every hour | 0 * * * * |
| Every day at midnight | 0 0 * * * |
| Every day at 3:30 AM | 30 3 * * * |
| Every Monday at 9 AM | 0 9 * * 1 |
| Every weekday at 6 PM | 0 18 * * 1-5 |
| 1st of every month | 0 0 1 * * |
| Every 15 minutes during work hours | */15 9-17 * * 1-5 |
| Twice daily (8 AM, 8 PM) | 0 8,20 * * * |
Special Cron Strings
| String | Meaning | Equivalent |
|---|---|---|
@yearly | Once a year | 0 0 1 1 * |
@monthly | Once a month | 0 0 1 * * |
@weekly | Once a week | 0 0 * * 0 |
@daily | Once a day | 0 0 * * * |
@hourly | Once an hour | 0 * * * * |
@reboot | At system startup | (varies) |
Common Cron Mistakes
- Forgetting time zone — cron uses server time; specify in code if needed
- Day of week 0 vs 7 — both = Sunday; 1=Monday in standard cron
- Long-running tasks overlapping — if task takes 6 minutes and runs every 5, multiple instances overlap
- Not redirecting output — silent failures; always log stderr/stdout
- PATH issues — cron has minimal PATH; use absolute paths
- Off-by-one in day-of-month — Feb 30 doesn't exist
A cron set to "*/1 * * * *" instead of "0 */1 * * *" runs every minute, not every hour — easy 60x oops. Use scheduling visualizers to verify intent before deploying.
How to Use the Tool (Step by Step)
- 1
Pick Schedule Frequency
Every X minutes, hourly, daily, weekly, monthly.
- 2
Set Specific Times
Hour, minute, day of week, day of month.
- 3
See Generated Expression
Tool builds cron string from your inputs.
- 4
Visualize Schedule
See next 5-10 execution times to verify intent.
- 5
Copy and Test
Add to crontab or scheduler. Test in staging before production.
Frequently Asked Questions
How do I add a cron job in Linux?+−
`crontab -e` opens your user crontab in editor. Add line, save. Job activates immediately.
Where do cron job logs go?+−
By default to system mail. Best practice: redirect output: `* * * * * /command >> /var/log/myjob.log 2>&1`
Can cron run jobs every second?+−
No, minimum is 1 minute. For sub-minute scheduling, use a script that loops with sleep, or systemd timers.
What if my server is down at scheduled time?+−
Standard cron skips missed runs. Use anacron for laptop/intermittent systems that should "catch up" on missed runs.
How to schedule based on time zone?+−
Standard cron uses server time. Set TZ environment variable in crontab: `TZ=Asia/Kolkata`
What is `@reboot`?+−
Runs the job once when system boots. Useful for starting daemons, cleaning temp files on startup.
Generate Cron Expressions — Free
Visual schedule builder with next-execution preview. Perfect for backups, reports, and automation.
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