Closing a Specific Linux Port

Closing specific ports on Linux for Java/Spring Boot apps usually involves system-level commands, not direct Java code. Spring Boot manages application ports, not system ports.

Method 1: Using iptables (requires root privileges)

sudo iptables -A INPUT -p tcp --dport 8080 -j DROP #Blocks incoming TCP traffic on port 8080
sudo iptables -A OUTPUT -p tcp --sport 8080 -j DROP #Blocks outgoing TCP traffic on port 8080
sudo iptables-save > /etc/iptables/rules.v4  #Save rules (persist across reboots)

Replace 8080 with your target port. -A INPUT appends to the INPUT chain; -j DROP drops the packets. -p tcp specifies TCP protocol. iptables-save persists changes. Always back up your iptables rules before making significant changes.

Method 2: Using ufw (Uncomplicated Firewall, user-friendly)

Simpler than iptables.

sudo ufw allow ssh #Allow SSH (important!)
sudo ufw deny 8080/tcp #Deny port 8080
sudo ufw enable #Enable firewall
sudo ufw status #Verify changes

ufw provides a user-friendly interface. Remember to allow necessary ports (e.g., SSH) before denying others.

Important Considerations:

• Root privileges: Both methods require sudo (or root access).
• Persistence: Saving rules (iptables-save or ufw enable) ensures changes persist after reboots.
• Security: Incorrectly configuring firewalls can lock you out of your system. Proceed with caution and test thoroughly.
• Spring Boot: Spring Boot's port configuration (server.port in application.properties/yml) only affects the application's internal port, not system-level port access.

This approach manages system-level port access, independent of your Java/Spring Boot application's port configuration. Always prioritize secure practices when managing system firewalls.