Linux Users, Groups, and Sudo Permissions¶

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User and permission management is a core responsibility of DevOps engineers.
This section explains how Linux handles users, groups, file ownership, and sudo access, which are critical for server security and access control.

`sudo` – Getting Root Permissions¶

sudo allows a normal user to execute commands with root (administrator) privileges.

ll /etc/passwd

Trying to edit system files as a normal user:

vi /etc/passwd    # Read-only, cannot write

Using sudo:

sudo vi /etc/passwd   # Able to write

📌 DevOps Tip: Avoid logging in directly as root. Use sudo instead.

Understanding User and Group Permissions¶

Each file in Linux has: - Owner - Group - Permissions

Example:

[opc@new-k8s etc]$ ll /etc/os-release
-rw-r--r--. 1 root root 452 Sep 30  2020 /etc/os-release

Breakdown: - root → owner - root → group - rw-r--r-- → permissions

Switching Users¶

sudo su

Switch to another user:

su vignesh

Switch with full environment:

su - vignesh

Creating a User¶

Ubuntu / Debian Based Systems¶

By default, useradd creates a user without a home directory.

useradd test

Create user with home directory:

useradd -m test1

Set Password for a User¶

passwd test

Verify User Creation¶

cat /etc/passwd

Test: User Installing a Package¶

sudo yum install tree

❌ This will fail because the user does not have sudo privileges.

Giving Sudo Permission to a User¶

To grant sudo access, add the user to the appropriate group.

CentOS / Oracle Linux / RHEL¶

usermod -aG wheel test

Group name: wheel

Ubuntu / Debian¶

usermod -aG sudo test

Group name: sudo

Verify Group Membership¶

id test

cat /etc/group

Test Again: Installing Package¶

sudo yum install tree

✅ This will now work because the user has sudo privileges.

Remove User from Group¶

gpasswd -d test wheel

Delete a User¶

Delete user without deleting files¶

userdel test

Delete user along with home directory¶

userdel -r test

Practice Tasks¶

Create a new user named devops
Set a password for the user
Try editing /etc/hosts without sudo
Add the user to sudo group
Verify sudo access
Remove the user

🧠 Quick Quiz — Users & Sudo Permissions¶

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Which group gives sudo access to users on Ubuntu systems?

📝 Want More Practice?¶

To strengthen your understanding and prepare for interviews, try the full 20-question practice quiz based on this chapter:

👉 Start Users & Sudo Permissions Quiz (20 Questions)

🚀

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