Chapter 3: Linux Basic Commands
3.6 Users, groups and sudo
Friends, many people work on the same server – the Amul-style dairy's developer, the admin and the web server itself. A separate user for each, with only the rights they need – these are the rules of Linux.
मित्रांनो, एकाच सर्व्हरवर अनेक जण काम करतात – the Amul-style dairy चा डेव्हलपर, ॲडमिन आणि वेब सर्व्हर स्वतः. प्रत्येकाला वेगळा यूजर आणि फक्त गरजेचे अधिकार – हेच Linux चे नियम आहेत.
दोस्तों, एक ही सर्वर पर कई लोग काम करते हैं – the Amul-style dairy का डेवलपर, एडमिन और वेब सर्वर ख़ुद. हर एक को अलग यूज़र और सिर्फ़ ज़रूरी अधिकार – यही Linux के नियम हैं.
| Command | Purpose |
|---|---|
whoami |
Current user name |
id |
UID, GID and groups of the current user |
sudo useradd -m -s /bin/bash ravi |
Create user with home dir and bash shell (adduser ravi on Ubuntu is interactive) |
sudo passwd ravi |
Set password |
sudo usermod -aG wheel ravi |
Add to admin group (wheel on AL2023/CentOS, sudo on Ubuntu) |
sudo groupadd devops |
Create group |
sudo usermod -aG devops ravi |
Add user to extra group (-a = append — never forget it!) |
groups ravi |
Show user's groups |
sudo userdel -r ravi |
Delete user and home folder |
su - ravi |
Switch to another user |
sudo -i |
Become root (use carefully, type exit to return) |
User information lives in /etc/passwd (accounts), /etc/shadow (hashed passwords) and /etc/group (groups). Sudo rules live in /etc/sudoers — always edit with sudo visudo.
Why sudo instead of logging in as root?
sudo gives admin power only for one command, logs who did what (/var/log/secure or /var/log/auth.log), and reduces accidents. On EC2, the default user (ec2-user/ubuntu) has password-less sudo, and direct root login over SSH is disabled.
Ravindra Bagale's Tip
Many students run sudo usermod -G devops ravi and forget -a – then all of ravi's other groups (even wheel/sudo) are gone. Always write -aG: -a means append. Never forget it!
Ravindra Bagale's Tip – मराठी
बरेच students sudo usermod -G devops ravi चालवतात आणि -a विसरतात – मग ravi चे बाकी सगळे groups (wheel/sudo सुद्धा) जातात. नेहमी -aG लिहायचं: -a म्हणजे append. बिलकुल विसरू नका!
Ravindra Bagale's Tip – हिंदी
बहुत से students sudo usermod -G devops ravi चलाते हैं और -a भूल जाते हैं – फिर ravi के बाकी सारे groups (wheel/sudo भी) चले जाते हैं. हमेशा -aG लिखो: -a मतलब append. बिल्कुल मत भूलना!
Lab
Chala, sudo useradd -m -s /bin/bash maulidev ne user banva, sudo passwd maulidev ne password set kara, tyala wheel group madhe (Ubuntu var sudo group madhe) add kara aani groups maulidev ne check kara. Mag su - maulidev karun sudo whoami chalva – uttar root aala pahije.
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.