Cron Job Guide: Understanding Cron Expressions with Examples

Published April 4, 2026 · 8 min read · Try the Cron Builder Tool →

Cron is a time-based job scheduler in Unix-like operating systems. Whether you're automating backups, sending reports, or running maintenance scripts, understanding cron expressions is essential for any developer or sysadmin.

The Five-Field Cron Syntax

A standard cron expression has five fields, separated by spaces:

┌───────────── minute (0 - 59)
│ ┌───────────── hour (0 - 23)
│ │ ┌───────────── day of month (1 - 31)
│ │ │ ┌───────────── month (1 - 12)
│ │ │ │ ┌───────────── day of week (0 - 6, Sunday = 0)
│ │ │ │ │
* * * * *

Special Characters

Common Cron Schedule Examples

Frequent Intervals

* * * * *          # Every minute
*/5 * * * *        # Every 5 minutes
*/15 * * * *       # Every 15 minutes
*/30 * * * *       # Every 30 minutes
0 * * * *          # Every hour (at minute 0)
0 */2 * * *        # Every 2 hours
0 */6 * * *        # Every 6 hours

Daily Schedules

0 0 * * *          # Daily at midnight
0 6 * * *          # Daily at 6:00 AM
30 8 * * *         # Daily at 8:30 AM
0 12 * * *         # Daily at noon
0 23 * * *         # Daily at 11:00 PM

Weekly Schedules

0 0 * * 0          # Every Sunday at midnight
0 9 * * 1          # Every Monday at 9:00 AM
0 9 * * 1-5        # Weekdays at 9:00 AM
0 18 * * 5         # Every Friday at 6:00 PM
0 10 * * 6,0       # Weekends at 10:00 AM

Monthly and Yearly

0 0 1 * *          # First day of every month at midnight
0 9 15 * *         # 15th of every month at 9:00 AM
0 0 1 1 *          # January 1st at midnight (yearly)
0 0 1 */3 *        # First day of every quarter

Setting Up Cron Jobs

Edit Your Crontab

# Open the crontab editor
crontab -e

# List current cron jobs
crontab -l

# Remove all cron jobs (careful!)
crontab -r

Example: Backup Script

# Run backup every day at 2:00 AM
0 2 * * * /home/user/backup.sh >> /var/log/backup.log 2>&1

# Run database backup every 6 hours
0 */6 * * * /usr/local/bin/db-backup.sh

# Clean temp files every Sunday at 3:00 AM
0 3 * * 0 find /tmp -type f -mtime +7 -delete

Environment Variables in Cron

Cron runs with a minimal environment. Common issues arise because PATH is limited. Always use full paths:

# Bad (might not find the command)
0 * * * * python script.py

# Good (full paths)
0 * * * * /usr/bin/python3 /home/user/script.py

# Or set PATH at the top of crontab
PATH=/usr/local/bin:/usr/bin:/bin
0 * * * * python3 /home/user/script.py

Logging and Debugging

# Redirect output to a log file
0 * * * * /home/user/script.sh >> /var/log/myscript.log 2>&1

# Send output to /dev/null (suppress)
0 * * * * /home/user/script.sh > /dev/null 2>&1

# Check cron logs
grep CRON /var/log/syslog        # Debian/Ubuntu
grep cron /var/log/cron          # CentOS/RHEL

Common Mistakes

1. Forgetting output redirection — Cron sends stdout/stderr as email by default
2. Relative paths — Always use absolute paths for scripts and commands
3. Missing execute permissions — Run chmod +x script.sh
4. Wrong timezone — Cron uses system timezone by default
5. Percentage signs — % is special in crontab; escape with \%

Alternatives to Cron

• systemd timers — Modern alternative on systemd-based Linux
• at — One-time scheduled jobs
• GitHub Actions schedules — CI/CD cron schedules
• Cloud schedulers — AWS EventBridge, GCP Cloud Scheduler