Cron Manager Skill

Schedule and manage cron jobs.

When to Use

• Create new scheduled tasks
• List existing cron jobs
• Remove scheduled tasks
• Test cron expressions
• Convert human-readable schedules to cron

Cron Basics

Cron Expression Format

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

Common Patterns

Schedule	Cron	Description
Every minute	* * * * *	Run every minute
Every hour	0 * * * *	Run at minute 0 of every hour
Daily at midnight	0 0 * * *	Run at midnight
Daily at 9am	0 9 * * *	Run at 9am
Weekly on Sunday	0 0 * * 0	Run at midnight Sunday
Monthly	0 0 1 * *	Run at midnight on 1st
Every 5 minutes	*/5 * * * *	Run every 5 minutes
Every 30 minutes	*/30 * * * *	Run every 30 minutes

Manage Cron Jobs

List User Crontab

# List current crontab
crontab -l

# List for specific user
crontab -l -u username

Add Cron Job

# Edit crontab
crontab -e

# Add from command line
(crontab -l 2>/dev/null; echo "0 9 * * * /path/to/script.sh") | crontab -

Remove Cron Job

# Remove all crontabs
crontab -r

# Remove for specific user
crontab -r -u username

Specific Operations

# Run job immediately (test)
/path/to/script.sh

# Check cron service status
systemctl status cron  # or crond

# View cron logs
journalctl -u cron     # systemd
tail -f /var/log/cron # other systems

Cron Utilities

Validate Cron Expression

# Using Python
python3 -c "
from croniter import croniter
import sys
if len(sys.argv) > 1:
    expr = sys.argv[1]
    if croniter.is_valid(expr):
        print('Valid cron expression')
        # Show next 5 runs
        cron = croniter(expr)
        for i in range(5):
            print(cron.get_next())
    else:
        print('Invalid cron expression')
"

# Using online tools or crontab.guru
curl -s "https://crontab.guru/0+9+*+*+*" 

Human-Readable Conversion

# Using python-crontab
python3 -c "
from crontab import CronSitemap
c = CronSitemap('0 9 * * *')
print(c.human_readable)
"

Script Examples

Backup Script Schedule

# Add daily backup at 2am
(crontab -l 2>/dev/null; echo "0 2 * * * /usr/local/bin/backup.sh >> /var/log/backup.log 2>&1") | crontab -

Log Cleanup

# Clean logs older than 7 days, daily at 3am
(crontab -l 2>/dev/null; echo "0 3 * * * find /var/log -name '*.log' -mtime +7 -delete") | crontab -

Health Check

# Check every 5 minutes
(crontab -l 2>/dev/null; echo "*/5 * * * * curl -s https://example.com/health") | crontab -

Special Characters

Character	Meaning
*	Any value
,	List (1,3,5)
-	Range (1-5)
/	Step (*/15 = every 15)

Notes

• Cron jobs run with user's default shell
• Use absolute paths for scripts
• Redirect output to log files
• Consider timezone (cron uses system TZ)
• Thepopebot uses config/CRONS.json for job scheduling