Cron job patterns: syntax, common mistakes, and reliable execution

Cron jobs fail silently, run with a different environment than expected, or have scheduling syntax errors that are hard to debug.

Follow these patterns for reliable cron jobs:

# Edit crontab for current user
crontab -e

# Format: minute hour day month weekday command
# Run at 2:30 AM every day
30 2 * * * /opt/myapp/scripts/backup.sh >> /var/log/backup.log 2>&1

# Run every 5 minutes
*/5 * * * * /opt/myapp/scripts/health-check.sh

# Run on weekdays at 9 AM
0 9 * * 1-5 /opt/myapp/scripts/report.sh

Make scripts self-sufficient:

#!/bin/bash
# Always use absolute paths — cron has a minimal PATH
/usr/bin/node /opt/myapp/scripts/cleanup.js

# Source environment if needed
set -a
source /opt/myapp/.env
set +a

Verify cron is running and check logs:

systemctl status cron
grep CRON /var/log/syslog | tail -20

Cron runs with a minimal environment (PATH=/usr/bin:/bin). Scripts that work interactively fail in cron because they rely on a full shell environment.