Question 1

What is a cron expression?

Accepted Answer

A cron expression is a string of 5 or 6 fields that define a schedule for automated tasks. The standard format is: minute hour day-of-month month day-of-week. For example, '0 9 * * 1-5' means 'at 9:00 AM, Monday through Friday'. Cron is built into Unix/Linux systems and supported by most job schedulers.

Question 2

What do the special characters mean in cron?

Accepted Answer

* means 'every'. / means 'every N' (*/5 = every 5 minutes). , separates multiple values (1,3,5). - defines a range (1-5). ? means 'no specific value' (in Quartz cron). L means 'last' (last day of month). # means 'Nth weekday' (2#3 = 3rd Tuesday).

Question 3

What is the difference between cron and crontab?

Accepted Answer

Cron is the daemon that runs scheduled tasks. Crontab (cron table) is the file that stores the schedule definitions. You edit crontabs with 'crontab -e'. Each line in a crontab is: expression command. For example: '0 * * * * /usr/bin/backup.sh'.

Question 4

How do I schedule a job every 15 minutes?

Accepted Answer

Use '*/15 * * * *' for every 15 minutes. Other examples: '0 * * * *' (hourly), '0 0 * * *' (daily at midnight), '0 9 * * 1' (weekly on Monday at 9am), '0 0 1 * *' (monthly on the 1st).

Question 5

What is the difference between Linux cron and Quartz cron?

Accepted Answer

Linux cron has 5 fields (minute through day-of-week). Quartz scheduler (used in Java/Spring) adds a seconds field at the start, making 6 fields. Kubernetes CronJobs use standard 5-field Linux cron syntax. AWS EventBridge supports both styles.

Question 6

How do I write a cron expression?

Accepted Answer

A cron expression has 5 fields: minute (0-59), hour (0-23), day of month (1-31), month (1-12), day of week (0-7). Use * for every value, */n for every n units, and commas for lists. Examples: '0 9 * * 1-5' runs at 9am Monday-Friday; '*/15 * * * *' runs every 15 minutes. Use the builder above to visually construct and validate expressions.

Question 7

What does '*/5 * * * *' mean in cron?

Accepted Answer

'*/5 * * * *' means 'every 5 minutes, every hour, every day.' The */ syntax means 'every n units of this field.' Common patterns: '0 * * * *' = every hour, '0 0 * * *' = daily at midnight, '0 0 * * 0' = weekly on Sunday. The builder above generates the expression from plain-language schedule descriptions.

Cron Generator — Free Online Cron Expression Builder

Frequently Asked Questions

Cron Expressions: Scheduling Automated Tasks in Linux

Related Tools

Unix Timestamp

UUID Generator

String Length

Diff Checker