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How to Detect and Block Malicious IPs on Your Ubuntu Linux Server in Real Time

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Intro:

If your Linux server is exposed to the internet, someone is scanning it right now. Most attackers don’t even need to break in — they just look for a weak point, like an open port or forgotten app. In this post, I’ll show you how to detect suspicious IPs in real time and block them automatically using tools built right into your Linux system.

1. Monitor Access Logs for Abuse

For Nginx:

sudo tail -f /var/log/nginx/access.log

For Apache:

sudo tail -f /var/log/apache2/access.log

Watch for:

  • Repeated requests from the same IP
  • Access to unusual URLs (/wp-login.php, /admin, /phpmyadmin)
  • Bots with weird user-agents

2. Use awk to Flag Suspicious IPs 

awk '{print $1}' /var/log/nginx/access.log | sort | uniq -c | sort -nr | head

This gives you the top IPs hitting your server.

3. Block Bad IPs with iptables or ufw

With iptables:

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