Cron Expression Cheat Sheet — Complete Syntax, Examples & Schedule Guide

Cron is a time-based job scheduling daemon standard on Unix-like operating systems (Linux, macOS, BSD) and widely adopted across modern cloud systems like Kubernetes CronJobs, AWS CloudWatch Events, GitHub Actions, and Google Cloud Scheduler.

This cheat sheet provides a complete reference for cron syntax, special characters, predefined macros, copy-paste production schedules, and troubleshooting tips.

The 5-Field Standard Cron Syntax

A traditional cron schedule consists of five fields separated by whitespace:

┌───────────── Minute (0 - 59)
│ ┌───────────── Hour (0 - 23)
│ │ ┌───────────── Day of Month (1 - 31)
│ │ │ ┌───────────── Month (1 - 12 or JAN-DEC)
│ │ │ │ ┌───────────── Day of Week (0 - 6 or SUN-SAT) (Sunday = 0 or 7)
│ │ │ │ │
* * * * * <command-to-execute>

Field Descriptions & Allowed Ranges

Note on Sunday: In standard Unix cron, both 0 and 7 represent Sunday.

Special Operators Explained

Cron uses specific operators to represent intervals, lists, and wildcards:

1. Asterisk (*) — Every Value

Represents all possible values for that field.

• * * * * * = Every minute of every hour of every day.

2. Comma (,) — List of Values

Specifies multiple distinct values for a field.

• 0 9,12,15 * * * = At minute 0 of hours 9, 12, and 15 (9:00 AM, 12:00 PM, 3:00 PM every day).

3. Hyphen (-) — Range of Values

Defines an inclusive continuous range.

• 0 9-17 * * 1-5 = Every hour on the hour from 9:00 AM through 5:00 PM, Monday through Friday.

4. Slash (/) — Step / Interval Values

Specifies step increments through a range.

• */15 * * * * = Every 15 minutes (0, 15, 30, 45).
• 0 0-12/2 * * * = Every 2 hours starting from midnight until noon (0:00, 2:00, 4:00, ..., 12:00).

Quick Reference: Common Cron Patterns

Copy and paste these verified cron schedules directly into your configuration:

Predefined Special Macros

Many modern cron implementations (such as Vixie Cron and crontab) support convenient shortcut macros instead of the 5-field syntax:

Real-World Production Crontab Examples

1. PostgreSQL / MySQL Daily Backup

Run a database backup dump every night at 2:15 AM and redirect logs:

15 2 * * * /usr/local/bin/pg_dump -U postgres my_db > /var/backups/db_$(date +\%Y\%m\%d).sql 2>&1

2. Log Rotation & Cache Cleanup

Purge temporary files and rotate server logs every Sunday at 3:00 AM:

0 3 * * 0 /usr/sbin/logrotate /etc/logrotate.conf && find /tmp -type f -mtime +7 -delete

3. SSL Certificate Auto-Renewal (Certbot)

Attempt Let's Encrypt renewal twice daily at random minute offsets:

0 0,12 * * * /usr/bin/certbot renew --quiet

4. Health Check / Uptime Ping

Trigger an internal API health ping every 5 minutes:

*/5 * * * * /usr/bin/curl -fsS https://api.example.com/health > /dev/null

Troubleshooting & Best Practices

1. Always Use Absolute Binary Paths: Cron executes in a very minimal shell environment with a stripped down $PATH. Instead of typing python3 script.py, always write /usr/bin/python3 /opt/app/script.py.
2. Account for Timezones: Cron runs against the system clock (typically UTC in cloud environments like AWS EC2, GCP, and Kubernetes). Ensure your schedule accounts for UTC vs your local time.
3. Capture stdout and stderr: By default, cron attempts to email output to the user. Always redirect output to log files or null:

   0 4 * * * /path/to/job.sh >> /var/log/job.log 2>&1
   

4. Escape the % Character in Crontab: The percent sign (%) in crontab entries is treated as a newline unless escaped with a backslash (\%).