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5. Linux Basic Commands

5.8 Processes

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Also in the AWS course: this lesson is the same as 3.8 Processes in the AWS course, which is the main version of this page.

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 
ps aux --sort=-%cpu | head -5         # top CPU users
ps -ef --forest | less                # parent-child tree
sudo lsof -i :22                      # which process owns port 22?

Why this matters for security

Crypto-miners and reverse shells show up as strange processes: high CPU, odd names, running from /tmp, or a shell whose parent is the web server user. ps -ef --forest and lsof -i are standard first-response commands.

Ravindra Bagale's Tip

When a process hangs, many students immediately use kill -9. First send a plain kill PID (SIGTERM) – it gives the process time to clean up. -9 is only the last resort. Running kill -9 on a database can corrupt data.

Practice task

Start sleep 600 &, find it with pgrep -a sleep, view it in top, and stop it with kill. Then list the five processes using the most memory.

Extended teaching notes

Why this lesson matters

Use this lesson to strengthen systems you own: understand the risk, practise safely in a lab, then write and apply the fix.

Apply the fix across stacks

Same class of bug, same idea in every language.

Java / Spring Boot

Parameterise queries, encode output, CSRF tokens, limited Actuator, dependency scanning.

ASP.NET Core

EF Core / parameterised SQL, Razor encoding, HTTPS, Data Protection.

Node.js / Express

helmet, parameterised SQL, npm audit, avoid eval and shell concat.

Python / Django / Flask / FastAPI

ORM, autoescape, pip-audit, Bandit; never shell=True with user input.

PHP / Laravel

PDO/Eloquent, Blade escaping, composer audit.

Go / Ruby

database/sql placeholders / ActiveRecord; html/template / ERB escaping; govulncheck / Brakeman.

nginx / Apache / Tomcat

Hide versions, TLS, security headers, least-open ports.

MySQL / PostgreSQL / MongoDB / Redis

Private networks, auth on, least-privilege users, no 0.0.0.0/0.

AWS / Azure / GCP

Roles not long-lived keys, private data stores, cloud audit logs on.

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.