Crontab Syntax, Schedule Expressions & Special Strings
Quick reference guide for Unix/Linux crontab schedule syntax, 5-field time breakdown, step values, special characters, and common cron presets.
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Crontab 5-Field Structure
Standard Linux/Unix crontab position breakdown.
| Syntax / Token | Name / Type | Description | Example / Notes |
|---|---|---|---|
┌───────────── minute (0 - 59)
│ ┌───────────── hour (0 - 23)
│ │ ┌───────────── day of month (1 - 31)
│ │ │ ┌───────────── month (1 - 12 or JAN-DEC)
│ │ │ │ ┌───────────── day of week (0 - 6 or SUN-SAT, 0=Sun)
│ │ │ │ │
* * * * * | 5-Field Syntax | Standard cron specification order: Minute, Hour, Day of Month, Month, Day of Week | — |
Special Characters & Operators
Allowed operators across crontab time fields.
| Syntax / Token | Name / Type | Description | Example / Notes |
|---|---|---|---|
* | Asterisk (Wildcard) | Matches every possible value in that field | * in minute = every minute |
, | Comma (Value List) | Specifies a list of discrete values | 1,15,30 in minute field |
- | Hyphen (Range) | Specifies an inclusive range of values | 1-5 in day-of-week = Mon to Fri |
/ | Slash (Step Values) | Specifies incremental steps over a range or wildcard | */15 in minute = every 15 minutes |
L | Last (Non-Standard) | Represents the last day of month or last specific weekday | 5L = last Friday of month |
W | Weekday (Non-Standard) | Nearest weekday (Mon-Fri) to given day of month | 15W = closest weekday to 15th |
Common Schedule Presets
Frequently used crontab schedules ready for production servers.
| Syntax / Token | Name / Type | Description | Example / Notes |
|---|---|---|---|
* * * * * | Every Minute | Executes command every 60 seconds | Health checks, queue polling |
*/5 * * * * | Every 5 Minutes | Runs at minute 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 | Telemetry batching |
*/15 * * * * | Every 15 Minutes | Runs at minute 0, 15, 30, 45 of every hour | Cache refreshes |
0 * * * * | Every Hour (Top of Hour) | Runs at minute 0 of every hour (00:00, 01:00, 02:00...) | Hourly syncs |
0 0 * * * | Every Day at Midnight | Runs at 00:00 (12:00 AM) every day | Daily log rotations |
0 2 * * * | Daily at 2:00 AM | Runs at low-traffic time 02:00 daily | Database backups |
0 0 * * 1 | Every Monday at Midnight | Runs at 00:00 every Monday | Weekly summary emails |
0 0 1 * * | 1st of Every Month | Runs at 00:00 on day 1 of every month | Monthly billing runs |
0 9-17 * * 1-5 | Business Hours (Mon-Fri) | Runs every hour from 9 AM to 5 PM on weekdays | Office notification jobs |
Crontab Special Strings (@shortcuts)
Human-readable shortcut aliases supported by modern cron daemons (Vixie Cron, systemd).
| Syntax / Token | Name / Type | Description | Example / Notes |
|---|---|---|---|
@reboot | Run at Startup | Executes once when the system boots up | @reboot /opt/app/start.sh |
@yearly / @annually | Once a Year (0 0 1 1 *) | Executes at midnight on January 1st | Annual archival |
@monthly | Once a Month (0 0 1 * *) | Executes at midnight on first day of month | Monthly reports |
@weekly | Once a Week (0 0 * * 0) | Executes at midnight on Sunday | Weekly vacuum |
@daily / @midnight | Once a Day (0 0 * * *) | Executes at midnight daily | Nightly builds |
@hourly | Once an Hour (0 * * * *) | Executes at the start of every hour | Hourly feed sync |
Frequently Asked Questions
Common questions and developer tips regarding crontab syntax & schedule reference.
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