A cron job is a time-based task scheduler in Unix-like operating systems. It allows you to run scripts or commands automatically at specified intervals — every minute, daily, weekly, or at any custom schedule defined by a cron expression.

What is crontab syntax?

Crontab uses a five-field expression: minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-6, where 0 is Sunday). An asterisk (*) means 'every' value. For example, '0 9 * * 1-5' means 'at 9:00 AM, Monday through Friday.'

Cron Job Generator

Q: How do I edit the crontab on Linux or macOS?

Run 'crontab -e' in your terminal to open the crontab editor. Add one line per scheduled task with the five-field cron expression followed by the command to run. Save and exit to activate. Use 'crontab -l' to list current jobs.

Q: What does */5 mean in a cron expression?

The /step syntax means 'every N intervals.' So */5 in the minute field means 'every 5 minutes,' */2 in the hour field means 'every 2 hours,' and so on. It is a shorthand for listing all matching values.

What Is a Cron Job?

A cron job is a time-based task scheduler built into Unix-like operating systems (Linux, macOS). It lets you automate repetitive tasks — running backups, clearing caches, sending reports, or deploying code — at precise intervals without human intervention.

The cron daemon runs in the background and checks the crontab (cron table) file every minute. When the current time matches a scheduled job, it executes the associated command. This makes cron one of the most reliable and widely-used scheduling tools in the developer ecosystem.

Crontab Syntax Explained

A cron expression consists of five fields separated by spaces. Each field represents a unit of time and accepts specific values or special characters.

* * * * *

min hour day month wday

Field	Values	Description
Minute	0–59	Minute of the hour
Hour	0–23	Hour of the day (24-hour format)
Day	1–31	Day of the month
Month	1–12	Month of the year
Weekday	0–6	Day of week (0 = Sunday)

Special Characters in Cron

* Wildcard

Matches every value in the field. * * * * * runs every minute.

, List

Specifies multiple values. 0 9,18 * * * runs at 9 AM and 6 PM.

- Range

Defines a range of values. 0 9 * * 1-5 runs at 9 AM Monday through Friday.

/ Step

Defines intervals. */15 * * * * runs every 15 minutes. */2 in the hour field means every 2 hours.

Common Cron Job Examples

Every minute * * * * *

Every day at midnight 0 0 * * *

Weekdays at 9 AM 0 9 * * 1-5

Every 15 minutes */15 * * * *

1st of every month at midnight 0 0 1 * *

Sundays at 2:30 AM 30 2 * * 0

Cron Job Best Practices

1
Log everything. Redirect output to a log file: 0 9 * * * /path/script.sh >> /var/log/myjob.log 2>&1
2
Use absolute paths. Cron runs with a minimal environment. Always use full paths for commands and files to avoid "command not found" errors.
3
Avoid overlapping jobs. If a job takes longer than its interval, use a lock file (flock) to prevent multiple instances from running simultaneously.
4
Test with short intervals first. Before setting a weekly job, test it with * * * * * (every minute) to confirm the command works in the cron environment.
5
Mind the timezone. Cron uses the system timezone by default. On servers, this is often UTC. Set the TZ variable in your crontab if needed.

Frequently Asked Questions

How do I edit the crontab on Linux or macOS?

Run crontab -e to open the editor, add your schedule line, and save. Use crontab -l to list current jobs.

What does */5 mean in a cron expression?

The step syntax */5 means "every 5 intervals." In the minute field, it triggers at minutes 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, and 55.

Can I schedule a cron job for a specific date?

Yes, combine the day and month fields. For example, 0 0 25 12 * runs at midnight on December 25th every year. For one-time tasks, consider using at instead.

What timezone does cron use?

Cron uses the system's default timezone, which is often UTC on servers. You can override it by adding TZ=America/New_York at the top of your crontab file.