0 */4 * * *
│  │  │ │ │
│  │  │ │ └─── Day of week: * (every day)
│  │  │ └───── Month: * (every month)
│  │  └─────── Day of month: * (every day)
│  └────────── Hour: */4 (every 4 hours)
└───────────── Minute: 0 (at minute 0)

0 */4 * * * /usr/local/bin/backup.sh

0 */4 * * * /usr/bin/python3 /scripts/sync-data.py

0 */4 * * * /usr/bin/python3 /scripts/refresh-cache.py

0 */4 * * * /usr/local/bin/system-health-check.sh

#!/bin/bash
# /usr/local/bin/backup.sh

BACKUP_DIR="/var/backups/4hourly"
SOURCE_DIR="/var/data"
TIMESTAMP=$(date +%Y%m%d_%H%M%S)
LOG_FILE="/var/log/backups.log"

mkdir -p $BACKUP_DIR

tar -czf "$BACKUP_DIR/backup_$TIMESTAMP.tar.gz" \
    -C $(dirname $SOURCE_DIR) \
    $(basename $SOURCE_DIR) >> $LOG_FILE 2>&1

find $BACKUP_DIR -name "*.tar.gz" -mtime +14 -delete

echo "$(date): 4-hourly backup completed" >> $LOG_FILE

# sync-data.py
import requests
import json
from datetime import datetime
import sqlite3

def sync_data():
    try:
        response = requests.get(
            'https://api.external.com/data',
            timeout=180,
            headers={'Authorization': 'Bearer YOUR_TOKEN'}
        )
        response.raise_for_status()
        data = response.json()
        
        conn = sqlite3.connect('/var/data/app.db')
        cursor = conn.cursor()
        
        cursor.execute('''
            CREATE TABLE IF NOT EXISTS synced_data (
                id TEXT PRIMARY KEY,
                data TEXT,
                updated_at TIMESTAMP
            )
        ''')
        
        for item in data:
            cursor.execute('''
                INSERT OR REPLACE INTO synced_data 
                (id, data, updated_at) 
                VALUES (?, ?, ?)
            ''', (item['id'], json.dumps(item), datetime.now()))
        
        conn.commit()
        conn.close()
        
        print(f"{datetime.now()}: Synced {len(data)} records")
    except Exception as e:
        print(f"{datetime.now()}: Sync failed: {e}")

if __name__ == '__main__':
    sync_data()