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Chapter 4: Linux Advanced Commands

Practice Questions and Lab Exercises

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Come on, practice time! Do every lab on EC2 and type the commands by hand – copy-paste does not train your hands.

  1. Write a command to count how many times 404 appears in an Nginx access log.
  2. Find all .conf files under /etc that were modified in the last 2 days.
  3. Using awk, print the 1st and 9th columns (IP and status code) of an access log.
  4. Explain >, >>, 2>&1 and the pipe symbol with examples.
  5. What is the difference between service nginx restart and service nginx reload? Between service nginx start and systemctl enable nginx?
  6. Which command shows the ports on which a server is listening? How do you know whether an app is exposed to the internet?
  7. Write a cron entry that runs /home/ubuntu/backup.sh every Sunday at 11:00 PM.
  8. Lab: Write a script backup.sh that creates ~/backups/web-<date>.tar.gz of /var/www/html and deletes backups older than 7 days.
  9. Lab: Use scp to upload a folder to your EC2 instance and rsync to sync only changed files.

Quick Revision

  • grep (search text), find (search files), awk (columns), sed (replace).
  • Pipes, redirection > >> 2> 2>&1, tee for writing root-owned files, here-docs for multi-line files.
  • tar -czvf create, tar -xzvf extract.
  • sudo service <name> start|stop|restart|reload|status; boot-time with sudo systemctl enable <name>; logs with journalctl -u <name> -f.
  • Network: ip a, ss -tlnp, curl -I, dig, nc -zv. Disk: df -h, du -sh, lsblk -f, blkid, /etc/fstab.
  • crontab -e (5 fields). export VAR=value, ~/.bashrc. ssh -i, scp -r, rsync -avz.
  • Scripts: #!/bin/bash, chmod +x, variables, if, for, functions.

Got it? grep, awk, pipes, services, cron and scripts – these are a cloud engineer's everyday weapons. Now let's move on to the most important service in AWS – EC2.

Extended teaching notes

Why this lesson matters

Cloud security is mostly IAM, network exposure, logging and secure defaults. The shared responsibility model means the provider patches the metal; you patch what you configure.

  • No public databases or public admin panels.
  • Roles / OIDC instead of long-lived access keys.
  • CloudTrail / Activity Logs / Audit Logs on and retained.
  • S3/Blob/GCS: Block Public Access; encrypt; least privilege.

Mini case study

Suppose we are on a purple-team exercise for an Indian mid-size company (sample data). Red notes a technique from this lesson against a lab clone. Blue must show the control that stops it, the log that would have fired, and the ticket that hardens production. That is the standard this course trains you for.

Defender's worksheet (do this today)

  1. Write the lesson title, date and the exact lab target you are allowed to use.
  2. List three owned systems (VMs, apps, or cloud accounts) where this lesson applies.
  3. Run one safe check from the lesson on a lab system only. Paste the command and output.
  4. Write a two-sentence fix you would give a teammate.
  5. Name one related public advisory (CERT-In, CISA, NVD, or a vendor bulletin) with its date.

Indian workplace (sample data)

Suppose we are a junior analyst at Infosys, TCS, Wipro or a fintech SOC in Bengaluru/Pune. Turn this lesson into one checklist item with an owner, a due date and a place to store evidence (ticket + screenshot).

Global practice

Compare your notes with OWASP, CIS Benchmarks, NIST CSF/IR guidance or a cloud Well-Architected security question. Write five lines on what overlaps.

Everyday analogy

Explain the risk and the fix to a family member without jargon. If they can repeat the warning, you understand it well enough to teach juniors.

Key terms

  • Control: a safeguard (patch, config, process, detection).
  • Finding: a weakness backed by evidence.
  • Remediation: the fix plus how you verified it.
  • Scope: systems you have written permission to touch.
  • Least privilege: only the access the task needs.
  • Defence in depth: several layers so one failure does not end the story.

Common mistakes

  • Skipping written permission "just for a quick scan".
  • Practising on hostel, office or public targets without authorisation.
  • Collecting tool output without writing the fix.
  • Copying attack steps onto production to "verify". Defenders verify with versions, configs and patches.
  • Publishing screenshots that contain secrets, cookies or internal hostnames.

Recap

  • Evidence, fix, owner, date.
  • Own lab only.
  • Fix > spectacle.