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
