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Stage 4: System Champion

Teach learners how to configure and manage networking, firewalls, and services in Linux. Build confidence in handling connectivity, securing systems, and managing active services - skills often tested in DevOps and SysAdmin interviews.


Hackbook Overview

  • Networking Basics: Commands like ifconfig, ip addr, ping, netstat, ss.
  • Firewall Management: Tools like iptables and firewalld for controlling traffic.
  • Service Management: Start, stop, restart, and enable services using systemctl.
  • Logs & Monitoring: Use journalctl and /var/log/ to troubleshoot services.
  • Why It Matters: Networking and service management are core to system reliability and security.

Hands‑On Practice

  • Check IP address: ip addr show.
  • Test connectivity: ping google.com.
  • View listening ports: ss -tuln.
  • Allow HTTP traffic with firewall: sudo firewall-cmd --add-service=http.
  • Restart a service: sudo systemctl restart nginx.
  • Check logs: journalctl -u nginx.

Interview Question Bank

Conceptual

  • Q1. How do you check the IP address of a Linux system?
    A1. Use ip addr show or ifconfig (if installed).
  • Q2. What is the purpose of a firewall in Linux?
    A2. A firewall controls incoming and outgoing traffic, protecting the system from unauthorized access.
  • Q3. What’s the difference between iptables and firewalld?
    A3. iptables is a traditional firewall tool, while firewalld provides a dynamic, easier‑to‑use interface for managing firewall rules.

Practical

  • Q4. How do you check if a service is running?
    A4. Run systemctl status <service>. Example: systemctl status ssh.
  • Q5. How do you open port 80 for HTTP traffic?
    A5. With firewalld: sudo firewall-cmd --add-service=http. With iptables: sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT.
  • Q6. How do you see which ports are currently open?
    A6. Run ss -tuln or netstat -tuln.

Scenario‑Based

  • Q7. A web server is not accessible. What steps would you take?
    A7. Check service status (systemctl status nginx), verify firewall rules (firewall-cmd --list-all), and test connectivity (ping or curl).
  • Q8. You need to ensure a service starts automatically on boot. How do you do it?
    A8. Run sudo systemctl enable <service>.
  • Q9. A port is blocked by firewall rules. How do you troubleshoot?
    A9. List rules with iptables -L or firewall-cmd --list-all, then adjust rules to allow the required port.

Behavioral Based

  • Q10. Tell me about a time you solved a networking or service issue.
    A10. Example: “I once fixed a production outage by identifying blocked HTTP traffic in firewall rules and reopening port 80.”

Cheatsheet (Quick Notes)

  • Networking: ip addr, ping, ss -tuln.
  • Firewall: iptables, firewalld.
  • Services: systemctl start|stop|restart|enable <service>.
  • Logs: journalctl -u <service>, /var/log/.

Updated on Dec 21, 2025