🕒 Shell Scripting for Beginners – Part 9: Scheduling & Automation

• In DevOps and Middleware environments, automation isn't complete until it's scheduled.
• Here, we master cron, at, @reboot, and Jenkins integration — running scripts automatically for backups, restarts, monitoring, and cleanups.

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📑 Table of Contents

• 1️⃣ Automating with Cron
• 2️⃣ One-Time Tasks with At
• 3️⃣ Auto-Execute on System Reboot
• 4️⃣ Jenkins Scheduler Integration
• 5️⃣ Real Middleware Automation Examples
• 6️⃣ Tips & Troubleshooting
• 🏁 Summary

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⏰ 1️⃣ Automating with Cron

• cron executes scripts periodically.
• Perfect for recurring jobs like backups, cleanup, and health checks.

Example 1: Daily Jenkins Backup at 3 AM

0 3 * * * /opt/scripts/jenkins_backup.sh >> /var/log/jenkins_backup.log 2>&1

💬 Output (log):

[03:00] Jenkins backup started
[03:03] ✅ Jenkins backup completed

Example 2: Weekly Tomcat Log Cleanup

0 2 * * 0 /opt/scripts/cleanup_tomcat_logs.sh >> /var/log/tomcat_cleanup.log 2>&1

💬 Output:

🧹 Deleted old logs from /opt/tomcat/logs
✅ Weekly cleanup done

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🕐 2️⃣ One-Time Tasks with At

at executes a job once — ideal for maintenance windows, patches, or urgent restarts.

Example 3: Restart WebSphere at 11:30 PM

echo "/opt/IBM/WebSphere/AppServer/bin/stopServer.sh server1 && sleep 15 && /opt/IBM/WebSphere/AppServer/bin/startServer.sh server1" | at 23:30

💬 Output:

job 17 at Sat Nov 1 23:30:00 2025

Example 4: Run Backup Once in 2 Hours

echo "/opt/scripts/backup_db.sh" | at now + 2 hours

💬 Output:

job 18 at Sat Nov 1 05:30:00 2025

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🔄 3️⃣ Auto-Execute on System Reboot

The @reboot keyword in crontab ensures your scripts run every time Linux boots. Perfect for restarting services, mounting drives, or initializing environments.

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Example 5: Auto-Start Tomcat After Reboot

@reboot /opt/tomcat/bin/startup.sh >> /var/log/tomcat_reboot.log 2>&1

💬 Output (after reboot):

✅ Tomcat started automatically at boot.

Example 6: Health Check Script at Boot

@reboot /opt/scripts/health_check.sh >> /var/log/health_boot.log 2>&1

💬 Output (log):

[BOOT] Checking WebSphere, Jenkins, NGINX...
✅ All services active.

💡 To verify reboot jobs, check grep CRON /var/log/syslog after restart.

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⚙️ 4️⃣ Jenkins Scheduler Integration

In CI/CD, Jenkins provides cron-like scheduling for build pipelines.

Example 7: Daily Jenkins Build at 2 AM

pipeline {
  triggers { cron('H 2 * * *') }
  stages {
    stage('Nightly Build') {
      steps {
        sh '/opt/scripts/build_app.sh'
      }
    }
  }
}

💬 Output:

✅ Jenkins triggered build_app.sh
Build completed successfully.

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🧰 5️⃣ Real Middleware & DevOps Automation Examples

Example 8: NGINX Health Monitor Every 10 Minutes

*/10 * * * * /opt/scripts/nginx_health.sh >> /var/log/nginx_monitor.log 2>&1

💬 Output:

[02:40] 🌐 NGINX is active
[02:50] 🚨 NGINX down – restarted automatically.

Example 9: Database Backup Every 6 Hours

0 */6 * * * mysqldump -u root -pSecret middlewaredb > /backup/db_$(date +%F_%H).sql

💬 Output:

✅ Backup completed: db_2025-11-01_06.sql

Example 10: Restart Jenkins After Crash Detection

*/15 * * * * pgrep jenkins >/dev/null || systemctl restart jenkins

💬 Output:

[03:15] 🚨 Jenkins was down, restarted successfully.

Example 11: Auto-Remount Missing Volume

@reboot mount | grep /mnt/backup >/dev/null || mount /dev/sdb1 /mnt/backup

💬 Output:

✅ /mnt/backup auto-mounted on system startup.

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🧠 6️⃣ Tips & Troubleshooting

• 📄 Check logs → grep CRON /var/log/syslog
• 🔒 Ensure permissions → chmod +x /opt/scripts/*.sh
• ⚙️ Test reboot jobs manually → sudo run-parts /etc/cron.d/
• 📧 Use MAILTO in crontab for notifications
• 🚨 For Jenkins jobs, check /var/lib/jenkins/jobs/*/builds

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🏁 Summary

• Cron → Schedules recurring jobs
• At → Runs one-time tasks
• @reboot → Executes scripts on startup
• Jenkins → Manages enterprise-level schedules
• 💡 Combine them to create self-healing, auto-starting Middleware environments.

← Previous: Part 8 – Debugging & Logging Next: Part 10 – Middleware Health Monitoring →