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Chapter 3: Linux Basic Commands

3.8 Processes

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Friends, every program running on a server is a process, and each one has a PID. When the website hangs or the CPU hits 100%, ps and top are your eyes.

A process is a running program. Each has a PID (process ID).

Command Purpose
ps aux All processes with user, CPU, memory
ps aux | grep nginx Find a specific process
pgrep -a node PIDs and command lines matching a name
top Live view (press q to quit, M sort by memory, P by CPU)
kill PID Politely ask process to stop (SIGTERM, 15)
kill -9 PID Force kill (SIGKILL) — last resort
pkill -f app.py Kill by name/pattern
command & Run in background
jobs, fg, bg Manage background jobs of the current shell
nohup command & Keep running after you log out
uptime Load average and how long the system has run
free -h RAM and swap usage

Ravindra Bagale's Tip

Many students kill every stuck process with kill -9. First send a plain kill PID (SIGTERM) – the program gets time to shut down cleanly. kill -9 is only the last resort. And if it is a service, use sudo service nginx restart instead of hunting for the PID.

Lab

Chala, sleep 300 & chalva, jobs aani pgrep -a sleep ne tyacha PID shodha, mag kill PID karun jobs madhe to gela ka te bagha. Mag top ughdun M aani P dabun sorting badla aani q ne baher ya.

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.