Ravindra BagaleCourses & study guides मराठी Track your progress

5. Linux Basic Commands

5.3 Working with Files and Directories

By Last updated:

Also in the AWS course: this lesson is the same as 3.3 Working with files and directories in the AWS course, which is the main version of this page.

Command Purpose Example
mkdir Make directory mkdir project, mkdir -p a/b/c (create parents)
touch Create empty file / update timestamp touch index.html
cp Copy cp a.txt b.txt, cp -​r site/ backup/
mv Move or rename mv old.txt new.txt, mv file.txt /tmp/
rm Remove file rm file.txt, rm -i *.log (ask first)
rm -r Remove directory recursively rm -r olddir
rmdir Remove empty directory rmdir emptydir
ln -s Create symbolic link (shortcut) ln -​s /​etc/​nginx/​sites-​available/​app /​etc/​nginx/​sites-​enabled/
file Show file type file /bin/ls
stat Detailed file info stat index.html 
mkdir -p ~/labs/site/css
cd ~/labs/site
touch index.html css/style.css
cp index.html index.bak
mv index.bak old-index.html
ls -R ~/labs
rm old-index.html

rm is permanent

There is no Recycle Bin on a Linux server. rm -rf /some/path deletes instantly and forever. Never run rm -rf with a variable that might be empty, and double-check the path before pressing Enter. Never run sudo rm -rf /.

Ravindra Bagale's Tip

Many students don't check the path before running rm -rf – and then there's trouble. First look at the same path with ls, then write rm. There's no Recycle Bin on a server; once it's gone, it's gone. For important files use rm -i – it asks before deleting.

Practice task

Create ~/labs/site/{css,js,img}, add index.html and css/style.css, copy the whole site to site-backup, rename it to site-old and finally delete it.

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.