Understand the 5 cron fields: minute, hour, day of month, month, day of week. Complete reference with examples.
A cron expression has 5 fields separated by spaces: minute (0-59), hour (0-23), day of month (1-31), month (1-12), day of week (0-6, where 0=Sunday). Cron expressions consist of five fields separated by spaces: minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-6, where 0 and 7 both represent Sunday). Each field can contain a single value, a range (1-5), a list (0,6), a step (*/5), or a wildcard (*). Understanding these operators is essential for writing correct cron schedules. The most common mistake is confusing the field order — remember the mnemonic "M H DOM MON DOW" (Minute, Hour, Day of Month, Month, Day of Week). When testing cron expressions, use an online validator like crontab.guru or our built-in cron validator to verify the schedule before deploying to production. Cron expressions consist of five fields separated by spaces: minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-6, where 0 and 7 both represent Sunday). Each field can contain a single value, a range (1-5), a list (0,6), a step (*/5), or a wildcard (*). Understanding these operators is essential for writing correct cron schedules. The most common mistake is confusing the field order — remember the mnemonic "M H DOM MON DOW" (Minute, Hour, Day of Month, Month, Day of Week). When testing cron expressions, use an online validator like crontab.guru or our built-in cron validator to verify the schedule before deploying to production.
The expression * * * * * means: at minute *, hour *, day-of-month *, month *, day-of-week *. Each field in the cron expression controls a different time component: minute, hour, day of month, month, and day of week.
Run crontab -e in your terminal to open your crontab editor. Add a new line: * * * * * /path/to/your/script.sh. Save and exit. Verify with crontab -l. Make sure your script is executable (chmod +x script.sh) and uses full paths for all commands.
Quartz Scheduler: 0 * * * ?. AWS EventBridge: cron(* * ? * * *). Kubernetes CronJob: schedule: "* * * * *" (standard 5-field format). Each platform has slight syntax differences — use our dialect switcher above to get the exact expression.
Common pitfalls: (1) Cron uses a minimal PATH — always use full paths to commands and scripts. (2) Percent signs (%) must be escaped with backslash in crontab. (3) Cron runs in the system timezone — set CRON_TZ=UTC at the top of your crontab for consistent UTC scheduling. (4) Redirect output to prevent email spam: * * * * * /path/command >> /var/log/myjob.log 2>&1. (5) Test your cron expression with crontab.guru or our validator above before deploying.
The cron expression * * * * * has different syntax on various scheduling platforms. Here is the equivalent expression for each:
| Platform | Expression |
|---|---|
| Unix / Linux crontab | * * * * * |
| Quartz Scheduler (Java) | 0 * * * ? |
| AWS EventBridge | cron(* * ? * * *) |
| Kubernetes CronJob | * * * * * |
| Vercel Cron | * * * * * |
| GitHub Actions | * * * * * (UTC) |
Key differences across platforms: Quartz uses 7 fields starting with seconds and supports L (last) and W (weekday) modifiers. AWS EventBridge requires a 6th year field and uses ? instead of * in day fields when the other day field is specified. Kubernetes uses standard 5-field Unix cron. Vercel Cron uses the same format but schedules are defined in vercel.json. GitHub Actions uses standard cron but runs in UTC timezone only, so adjust the hour field for your local timezone offset.
Follow these tips when setting up cron jobs in production: