Cron FAQ

Clear answers for common cron expression, crontab, timezone, and scheduling questions.

What is a cron expression?

A cron expression is a five-field schedule format used to run tasks automatically. The fields represent minute, hour, day of month, month, and weekday.

What does * * * * * mean?

The cron expression * * * * * means every minute. Each asterisk allows every value for that field.

What is the difference between cron and crontab?

Cron is the scheduler service that runs jobs. Crontab is the table or file where cron jobs are defined.

Does cron use local time or server time?

Cron usually uses the server timezone unless the environment or cron implementation is configured differently. Always verify the timezone on the server running the job.

How do I run a cron job every 5 minutes?

Use */5 * * * *. This means every fifth minute of every hour, every day.

How do I run a cron job every hour?

Use 0 * * * *. This runs at minute 0 of every hour.

How do I run a cron job daily at midnight?

Use 0 0 * * *. This runs once per day at 00:00 according to the server timezone.

How do I run a cron job on weekdays only?

Use a weekday field of 1-5. For example, 0 9 * * 1-5 runs at 9 AM Monday through Friday.

What do the five cron fields mean?

The standard five fields are minute, hour, day of month, month, and weekday. Each field controls one part of the schedule.

Can cron run every few seconds?

Standard five-field cron does not support seconds. Some systems, such as Quartz cron, support an additional seconds field.

What does a slash mean in cron?

A slash defines a step value. For example, */15 in the minute field means every 15 minutes.

What does a comma mean in cron?

A comma lists multiple values. For example, 0,30 in the minute field means at minute 0 and minute 30.

What does a hyphen mean in cron?

A hyphen defines a range. For example, 1-5 in the weekday field means Monday through Friday.

Is Sunday 0 or 7 in cron?

Many cron implementations accept both 0 and 7 for Sunday. This tool treats 0 and 7 as Sunday.

Why does my cron job not run?

Common causes include the wrong server timezone, incorrect file permissions, missing environment variables, command path issues, or an invalid cron expression.

Can I use this cron generator for free?

Yes. Cron Generator is a free online tool for building, validating, explaining, and previewing cron expressions.