What do the special characters mean in cron?

The asterisk (*) means 'every' value. The comma (,) separates list values (e.g., 1,3,5). The hyphen (-) defines ranges (e.g., 1-5 for Monday-Friday). The slash (/) defines step values (e.g., */5 means every 5 units). So '*/15 9-17 * * 1-5' means 'every 15 minutes between 9am and 5pm on weekdays'.

How do I monitor if my cron job ran successfully?

Use a cron job monitoring service like CronSignal. Add a curl command at the end of your cron job that pings a unique URL. If the ping doesn't arrive on schedule, you get alerted. This catches both jobs that fail silently and jobs that never start. Example: your-command && curl -s https://cronsignal.io/ping/your-id

What is the difference between 5-field and 6-field cron expressions?

Standard Unix cron uses 5 fields (minute, hour, day of month, month, day of week). Some systems like Quartz (Java), Spring, and AWS add a sixth field for seconds at the beginning. Some also add a seventh field for year. This tool generates standard 5-field expressions, which are compatible with crontab, most CI/CD systems, and cloud schedulers.

Cron Expression Generator - Free Crontab Builder

What is a Cron Expression?

A cron expression is a compact string that defines a recurring schedule. Originating from the Unix cron daemon (first introduced in Version 7 Unix in 1979), cron expressions are now used across virtually all scheduling systems: Linux crontab, CI/CD pipelines (GitHub Actions, GitLab CI), cloud schedulers (AWS EventBridge, GCP Cloud Scheduler), and application frameworks (Spring, Celery, node-cron).

The standard format uses five fields separated by spaces, each representing a time component. The cron daemon checks the current time against these fields every minute and runs the associated command when all fields match.

* * * * *

| | | | +-- Day of week (0-6, Sun-Sat)

| | | +---- Month (1-12)

| | +------ Day of month (1-31)

| +-------- Hour (0-23)

+---------- Minute (0-59)

Special Characters

Character	Meaning	Example
*	Any value	* * * * *
,	Value list	1,3,5 * * * *
-	Range	* 9-17 * * *
/	Step values	/5 * * *

Common Cron Expressions

Every minute* * * * *

Every 5 minutes*/5 * * * *

Every hour0 * * * *

Daily at midnight0 0 * * *

Weekdays at 9am0 9 * * 1-5

Every Sunday at 3am0 3 * * 0

1st of every month0 0 1 * *

Every 15 min, business hours*/15 9-17 * * 1-5

Frequently Asked Questions

How do I add a cron job on Linux?

Run crontab -e to open your user's crontab file. Add a line with the cron expression followed by the command to run. For example: 0 2 * * * /home/user/backup.sh runs backup.sh every day at 2:00 AM. Use crontab -l to list existing jobs. Always use full paths for commands and redirect output: >> /var/log/backup.log 2>&1.

What timezone does cron use?

By default, cron uses the system timezone. On most servers, this is UTC. You can set a specific timezone by adding CRON_TZ=America/New_York at the top of your crontab (supported on many modern systems). In cloud environments, AWS EventBridge supports timezone-aware scheduling, while Kubernetes CronJobs default to the kube-controller-manager timezone. Always verify your server's timezone with timedatectl or date.

How do I know if my cron job is running?

Check the system logs: grep CRON /var/log/syslog (Ubuntu) or journalctl -u cron (systemd). For reliable monitoring, use a dead man's switch service like CronSignal that alerts you if a job fails to run on schedule. This catches silent failures that log-checking might miss.

Can I use cron expressions in GitHub Actions?

Yes, GitHub Actions uses standard 5-field cron expressions with the schedule trigger. Example: on: schedule: - cron: '0 9 * * 1-5'. Note that GitHub Actions schedules run in UTC and may have a delay of up to 15-20 minutes during peak times. For time-sensitive tasks, consider using a dedicated scheduler.

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Monitor your cron jobs

Built a cron schedule? Make sure it actually runs. CronSignal monitors your cron jobs and alerts you if they fail to run on time. Need to monitor the endpoints your cron jobs hit? UptimeSignal has you covered.

Try CronSignal → Monitor endpoints →