User Roles in Linux

Linux is a multi-user operating system. Each user has specific permissions and roles.

Types of Users:

a. Root User

The superuser with full control over the system.
Can read, write, and execute any file.
Username: root
Home directory: /root
Use with caution — root can break the system.

b. Regular User

Created by the system admin or during OS installation.
Limited privileges.
Can only access their own files and some shared resources.

c. System Users

Created by the OS for services (e.g., nobody, www-data, mysql).
Usually have no login access.
Run background services (daemons).

User Identification

Each user has:

Username – e.g., john
UID (User ID) – Unique number, root is 0
GID (Group ID) – Group membership
Home directory – e.g., /home/john
Shell – e.g., /bin/bash

User info is stored in:


/etc/passwd
/etc/shadow     # stores encrypted passwords

Sudo – Superuser Do

What is `sudo`?

Allows authorized users to run commands as root or another user.
Safer than logging in as root directly.
Tracks and logs actions for security.

Syntax


sudo command

Example


sudo apt update

Runs the apt update command with root privileges.

Granting Sudo Access

Only users in the sudo group (or wheel group in some distros) can use sudo.

Add a user to sudo group (Ubuntu/Debian)


sudo usermod -aG sudo username

On RedHat/CentOS/Fedora


sudo usermod -aG wheel username

Configuration File

/etc/sudoers – Defines who can use sudo and how.

Edit safely using:


sudo visudo

Example line:


john ALL=(ALL:ALL) ALL

john can run all commands as any user on any host.

Run as Another User

Use -u option:


sudo -u username command

Example:


sudo -u postgres psql

Security Tips

Avoid logging in as root directly.
Use sudo for elevated tasks only.
Log files: /var/log/auth.log or /var/log/secure
Limit sudo access using groups or command restrictions.