Stage 2: Troubleshoot Adventurer

Train learners to handle complex Linux problems that span multiple areas. Build confidence in diagnosing layered issues and applying systematic troubleshooting - a skill interviewers often test with “what if multiple things go wrong?” scenarios.

Hackbook Overview

• Layered Troubleshooting: Problems often involve more than one subsystem (e.g., service + firewall).
• Approach:
  1. Identify symptoms.
  2. Check logs and configs.
  3. Verify permissions and ownership.
  4. Test networking and connectivity.
• Common Complex Issues:
  • Service fails due to missing config + blocked port.
  • User access denied due to wrong group + file permissions.
  • Disk full causing service crashes.
• Why It Matters: Shows ability to think holistically, not just run single commands.

Hands‑On Practice

• Simulate a service failure by misconfiguring /etc/ssh/sshd_config, then fix it.
• Block port 80 with firewall and troubleshoot why Nginx isn’t accessible.
• Fill disk with dummy files, then clear space and restart services.
• Create a file with restricted permissions and troubleshoot user access.

Interview Question Bank

Conceptual

• Q1. Why is layered troubleshooting important in Linux?
  A1. Because issues often involve multiple subsystems — configs, permissions, networking — and require systematic diagnosis.
• Q2. What’s the difference between a simple error and a complex scenario?
  A2. A simple error has a single cause (e.g., missing permission), while a complex scenario involves multiple factors (e.g., config + firewall + disk space).

Practical

• Q3. A service fails to start after config changes. How do you troubleshoot?
  A3. Test config syntax (nginx -t or apachectl configtest), check logs (journalctl -u service), and verify permissions.
• Q4. A user cannot access a shared directory. What steps do you take?
  A4. Check ownership (ls -ld), group membership (groups user), and permissions (chmod/chown).
• Q5. A server is running but inaccessible externally. How do you investigate?
  A5. Verify firewall rules (firewall-cmd --list-all), confirm service status (systemctl status), and test connectivity (ping, curl).

Scenario‑Based

• Q6. Disk usage reaches 100% and services crash. What’s your approach?
  A6. Run df -h to confirm, clean logs or temp files, move large files, and restart services.
• Q7. SSH login fails for a user. How do you troubleshoot?
  A7. Check /etc/ssh/sshd_config, verify user permissions, and review logs in /var/log/auth.log.
• Q8. A web app fails because both config and firewall are misconfigured. How do you solve it?
  A8. Fix config syntax, reload service, then adjust firewall rules to open required ports.

Behavioral Based

• Q9. Tell me about a time you solved a multi‑layered Linux issue.
  A9. Example: “I once fixed a production outage by correcting a misconfigured Nginx file and reopening firewall ports, restoring service quickly.”

Cheatsheet (Quick Notes)

• Troubleshooting Steps: Symptoms → Logs → Configs → Permissions → Networking.
• Disk Issues: df -h, du -sh.
• Services: systemctl status, journalctl -u.
• Firewall: iptables -L, firewall-cmd --list-all.
• Configs: Test syntax (nginx -t, apachectl configtest).