How to Schedule Tasks with Cron Jobs (Linux)

Cron is the Linux task scheduler. It runs commands or scripts at specified times, dates, or intervals automatically.

Crontab Syntax

A cron job line has five time fields followed by the command:

* * * * * command
─ ─ ─ ─ ─
│ │ │ │ │
│ │ │ │ └── Day of week (0-7, 0=Sunday)
│ │ │ └──── Month (1-12)
│ │ └────── Day of month (1-31)
│ └──────── Hour (0-23)
└────────── Minute (0-59)

Common Examples

# Every day at 2:30 AM
30 2 * * * /home/user/backup.sh

# Every hour
0 * * * * /usr/bin/php /var/www/html/cron.php

# Every Monday at 9 AM
0 9 * * 1 /scripts/weekly-report.sh

# First day of every month at midnight
0 0 1 * * /scripts/monthly-cleanup.sh

# Every 15 minutes
*/15 * * * * /scripts/check-status.sh

# Every 5 minutes during business hours (9 AM - 5 PM)
*/5 9-17 * * 1-5 /scripts/notify.sh

# Twice a day (6 AM and 6 PM)
0 6,18 * * * /scripts/daily-digest.sh

Special Syntax

@reboot     # Runs once at system startup
@yearly     # 0 0 1 1 * (January 1st)
@monthly    # 0 0 1 * * (First of every month)
@weekly     # 0 0 * * 0 (Sunday)
@daily      # 0 0 * * * (Midnight)
@hourly     # 0 * * * * (Top of every hour)

Editing Crontab

crontab -e          # edit your cron jobs (opens in default editor)
crontab -l          # list your current cron jobs
crontab -r          # remove all cron jobs (careful!)

Viewing Cron Logs

# Ubuntu / Debian
grep CRON /var/log/syslog

# RHEL / Fedora
grep CRON /var/log/cron

# Check if a specific job ran
grep "backup.sh" /var/log/syslog

Common Pitfalls

1. Use absolute paths

Cron runs with a minimal environment. Paths may not include /usr/local/bin:

# Bad
*/5 * * * * python script.py

# Good
*/5 * * * * /usr/bin/python3 /home/user/script.py

2. Redirect output

Cron emails you if a command produces output. Redirect to a log file:

* * * * * /home/user/script.sh >> /var/log/script.log 2>&1

3. Environment variables

Cron doesn’t load your profile. Set PATH manually:

PATH=/usr/bin:/usr/local/bin:/home/user/.local/bin
*/5 * * * * mycommand

System Crontab

System-wide cron jobs go in /etc/crontab (requires sudo):

# /etc/crontab
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin

# Run weekly maintenance every Sunday at 3 AM
0 3 * * 0 root /usr/local/bin/maintenance.sh

Crontab Generator Tools

crontab.guru — best online tool for checking cron expressions
crontab-generator.org — visual crontab builder

Related: Learn Linux file permissions and our command cheat sheet.