5.1 Basic Security and Identifying User Types (Weight: 2)

📘Linux Essentials (LPI 010-160)

1. Root User

The root user is the most powerful account in a Linux system. It is also known as the superuser.

The root account has complete control over the entire system. It can perform any operation without restrictions.

Characteristics of the Root User

User ID (UID) is 0
Has full administrative privileges
Can access all files and directories
Can create, modify, and delete any file
Can install or remove software
Can manage users and groups
Can control system services and processes
Can modify system configuration

In Linux systems, many important administrative tasks require root privileges.

Examples of Tasks Performed by Root

In an IT environment, system administrators often use root privileges to:

Install software packages
Update the operating system
Modify network configuration
Add or remove users
Change file permissions for system files
Manage system services
Configure security settings

Example command that requires root privileges:

apt install nginx

This command installs a web server package. Only root or a user with administrative privileges can perform this action.

Another example:

useradd student1

This command creates a new user account, which also requires administrative access.

Root Login and Security

Because root has complete control, using it carelessly can damage the system.

For example, the root user can:

Delete critical system files
Change security settings
Stop important services

To reduce risk, administrators usually avoid logging in directly as root.

Instead, they use the sudo command.

Example:

sudo apt update

The sudo command temporarily allows a standard user to perform administrative tasks.

Advantages of using sudo:

Better security
Activity logging
Reduced risk of mistakes

2. Standard Users (Regular Users)

A standard user is a normal user account created for everyday system usage.

These users have limited permissions compared to the root user.

Standard users cannot perform administrative tasks unless they are given permission.

Characteristics of Standard Users

Used by people who operate the system
Have limited access rights
Cannot modify system files
Cannot install system software (without permission)
Can only access their own files

Each standard user has a home directory where personal files are stored.

Example:

/home/student1

Inside this directory, the user can:

Create files
Modify files
Delete files
Organize directories

But they cannot access sensitive system directories like:

/etc
/root
/boot

Example of Standard User Activity

In an IT environment, a standard user might:

Log into a workstation
Write documents
Edit scripts
Run applications
Access shared resources
Use development tools

Example command used by a standard user:

touch notes.txt

This creates a file inside the user’s directory.

If the same user tries to modify a system file:

nano /etc/passwd

The system will deny permission unless elevated privileges are used.

User IDs for Standard Users

In most Linux systems:

Standard users usually start from UID 1000

Example:

student1 → UID 1000
student2 → UID 1001

These numbers help the system track permissions and ownership.

3. System Users

System users are special accounts created by the system or installed services.

These users are not meant for human login.

They exist so that services and applications can run securely.

Instead of running everything as root, Linux uses system users to limit the damage if a service is compromised.

Why System Users Are Important

If every service ran as root, a security vulnerability could give full system access to an attacker.

System users provide security isolation.

Each service runs under its own user account.

Examples of System Users

Many Linux services create their own system user.

Examples include:

www-data → web servers
mysql → database server
mail → mail service
daemon → background services
nobody → minimal permission account

These accounts allow services to run with limited privileges.

Example in an IT Environment

Consider a web server such as Apache or Nginx.

The web server process runs as:

www-data

This means:

The server can access website files
It cannot modify system configuration files
It cannot access other users’ data

If a website vulnerability occurs, the attacker only gains access to www-data privileges, not the entire system.

This protects the system from major damage.

System User ID Range

System users typically have lower UID numbers.

Common ranges:

0        → root
1–999    → system users
1000+    → standard users

These numbers may vary slightly depending on the Linux distribution.

Viewing Users in Linux

User accounts are stored in a system file:

/etc/passwd

You can view it using:

cat /etc/passwd

Example entry:

student1:x:1000:1000:Student User:/home/student1:/bin/bash

Explanation:

Field	Meaning
student1	Username
x	Password placeholder
1000	User ID (UID)
1000	Group ID (GID)
Student User	User description
/home/student1	Home directory
/bin/bash	Default shell

System users appear here as well.

Example:

www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin

Notice the shell:

/usr/sbin/nologin

This prevents interactive login.

Comparing Root, Standard, and System Users

User Type	Purpose	Permissions	Login Capability
Root User	System administration	Full access	Yes
Standard User	Regular system usage	Limited access	Yes
System User	Run services and processes	Restricted	Usually No

Security Best Practices

Understanding these user types is important for system security.

Common best practices include:

1. Avoid Using Root for Daily Tasks

Administrators should only use root when necessary.

2. Use sudo Instead of Root Login

This limits risks and records activity.

3. Use System Users for Services

Running services under dedicated accounts reduces security risks.

4. Apply Least Privilege Principle

Users should only have the permissions required for their tasks.

This prevents accidental or malicious changes to the system.

Key Points for the Linux Essentials Exam

You should remember the following:

Linux uses different user types for security and access control.
The root user has complete system control.
Standard users are regular accounts with limited permissions.
System users run services and applications.
Root has UID 0.
Standard users usually start at UID 1000.
System users typically use lower UID values.
User account information is stored in /etc/passwd.
Many services run under dedicated system users to improve security.
Administrators commonly use sudo instead of direct root login.