What does * * * * * mean in cron?

The cron expression * * * * * means 'every minute'. Each asterisk represents a wildcard for minute, hour, day of month, month, and day of week respectively.

How do I schedule a cron job to run daily at midnight?

Use the cron expression 0 0 * * * which means 'at minute 0 of hour 0 (midnight), every day of month, every month, every day of week'.

What is the difference between cron and crontab?

Cron is the daemon (background service) that runs scheduled tasks. Crontab (cron table) is the file that contains the list of scheduled commands. You edit the crontab with 'crontab -e' to add or modify scheduled jobs.

⏰ Cron Expression Parser

Parse cron expressions into human-readable descriptions. See when your cron job will run next.

Cron Expression

Minute

Hour

Day (month)

Month

Day (week)

Presets:

Explanation

Next 5 Run Times

Understanding Cron Expressions – The Complete Crontab Syntax Guide

Cron expressions are the scheduling language used by Unix/Linux cron daemons, Kubernetes CronJobs, AWS CloudWatch Events, GitHub Actions, CI/CD pipelines, and countless task schedulers. A standard cron expression consists of 5 fields separated by spaces: minute hour day-of-month month day-of-week.

Cron Field Reference

Minute (0–59) — Which minute of the hour the job runs
Hour (0–23) — Which hour of the day (24-hour format)
Day of Month (1–31) — Which day of the month
Month (1–12 or JAN–DEC) — Which month of the year
Day of Week (0–6 or SUN–SAT) — Which day of the week (0 = Sunday)

Cron Special Characters and Operators

* — Any value. Matches every possible value for that field.
*/n — Step value. Runs every n intervals (e.g., */5 in minute = every 5 minutes).
1,3,5 — List. Runs at specific values (e.g., 1,15 in day = 1st and 15th).
1-5 — Range. Runs for every value in the range (e.g., 1-5 in day-of-week = Monday through Friday).

Common Cron Schedule Examples

* * * * * — Every minute (useful for testing, not recommended in production)
*/5 * * * * — Every 5 minutes (health checks, monitoring)
0 * * * * — Every hour at minute 0 (log rotation, cache clearing)
0 0 * * * — Daily at midnight (database backups, report generation)
0 9 * * 1-5 — Weekdays at 9:00 AM (business-hours notifications)
0 0 1 * * — First day of every month at midnight (billing, monthly reports)
0 2 * * 0 — Every Sunday at 2:00 AM (weekly maintenance window)

Where Cron Expressions Are Used

Linux/Unix crontab — The original cron scheduler (crontab -e)
Kubernetes CronJobs — Schedule containerized batch jobs in K8s clusters
GitHub Actions — schedule trigger in workflow YAML files
AWS CloudWatch Events / EventBridge — Trigger Lambda functions on a schedule
CI/CD pipelines — Jenkins, GitLab CI, CircleCI all support cron scheduling
Database maintenance — pg_cron for PostgreSQL, MySQL Event Scheduler