Chapter 4: Linux Advanced Commands
Interview Questions
These questions on Linux advanced commands always come up in DevOps and cloud interviews. With every reply, say the command out loud – the interviewer understands that your hands work on the terminal.
Linux ॲडव्हान्स्ड कमांड्सवर हे प्रश्न DevOps आणि क्लाउड इंटरव्ह्यूमध्ये नेहमी येतात. प्रत्येक उत्तरासोबत कमांड बोलून दाखवा – इंटरव्ह्यूअरला कळतं की तुमचा हात टर्मिनलवर चालतो.
Linux एडवांस्ड कमांड्स पर ये सवाल DevOps और क्लाउड इंटरव्यू में हमेशा आते हैं. हर जवाब के साथ कमांड बोलकर दिखाओ – इंटरव्यूअर को पता चलता है कि आपका हाथ टर्मिनल पर चलता है.
- Q1. How do you find the top 10 IP addresses in an Nginx access log?
awk '{print $1}' access.log | sort | uniq -c | sort -rn | head- Q2. What is the difference between
>and>>? What does2>&1do? >overwrites a file,>>appends.2>&1redirects standard error to wherever standard output is going.- Q3. How do you check which ports a Linux server is listening on?
sudo ss -tlnp(or the oldernetstat -tlnp).- Q4. What is the difference between
service <name> restartandservice <name> reload? restartstops and starts the service (brief downtime).reloadasks the service to re-read its configuration without dropping existing connections (if supported).- Q5. What is the difference between
serviceandsystemctl? systemctlis the native systemd tool.serviceis an older wrapper that, on systemd systems, forwards start/stop/restart/reload/status tosystemctl. Enabling at boot (systemctl enable) anddaemon-reloadrequiresystemctl.- Q6. Explain the five fields of a cron expression.
- Minute, hour, day of month, month, day of week — e.g.
30 2 * * 1runs at 02:30 every Monday. - Q7. How do you see the logs of a systemd service?
journalctl -u <service>; add-fto follow live,-n 50for the last 50 lines,--since "1 hour ago"to filter by time.- Q8. What is the difference between
dfanddu? dfshows free/used space per mounted filesystem;dushows how much space specific files or directories use.
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)
- Write the lesson title, date and the exact lab target you are allowed to use.
- List three owned systems (VMs, apps, or cloud accounts) where this lesson applies.
- Run one safe check from the lesson on a lab system only. Paste the command and output.
- Write a two-sentence fix you would give a teammate.
- 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.