Linux Commands

File permissions and ownership

Learning Outcome

Use of File Permissions and Ownership

Protects files from unauthorized access

Why It Is Used?

Secure important files and directories

Restrict access to sensitive data

Allow controlled file sharing between users

Maintain system stability and security

What is file permission and Ownership

File ownership and permissions in Linux determine who owns a file and who has permission to read, write, or execute it.

Every file and directory is linked with a user owner, a group owner, and a set of permissions that apply to the owner, group members, and all other users. It defines “who is allowed to do what on a resource.”

Permissions Types

Linux file permissions types define the operations that can be performed on files and directories. The permission model consists fundamentally of three types: read (r), write (w) and execute (x) in combination control data access.

Linux mainly has 3 permission types:

Meaning of Permissions

Allows user to:

• Open file

• View contents

For folders: View files inside directory

 Network Layer (Layer 3): 

 Terminal Concept in Linux

A Terminal is a command-line interface used to communicate with the Linux operating system by typing commands.

It allows users to:

Run commands

Control the system

    Importance in Kali Linux

Most cybersecurity and penetration testing tools are commonly used through the terminal.

Shell Basics

A Shell is a program that interprets user commands and communicates with the operating system kernel.

  Functions of a Shell

Executes commands

Manages files and processes

Common Linux Shells

Bash

Zsh

Fish

User & Permission Concepts

Root User

The Root User is the administrator account in Kali Linux with full control over the entire system.

Features:

Can access all files and settings

Can install or remove software

Can modify system configurations

Has the highest privileges

Risk:

Wrong commands can damage the system.

Example:

Normal User

A Normal User is a regular account with limited permissions.

Features:

Can use applications

Can manage personal files

Cannot modify critical system files without permission

Benefits:

Safer for daily use

Reduces accidental system damage

File Permissions in Kali Linux

Linux controls access to files using permissions.

Main permission types:

 Ownership Concept in Kali Linux

Every file and directory in Linux has an owner and permission groups.

   User (Owner)

 Group

The user who created or owns the file.

Permissions Can have:

• Read

• Write

• Execute access

A collection of users who share similar access permissions.

Purpose :  Allows multiple users to access files together.

Others

All other users on the system who are not the owner or group members.

Usually Given Limited Access :  For security reasons.

Example:

File permissions in Kali Linux

Package & Software Management

What is a Package Manager?

A Package Manager is a software tool that helps users install, update, configure, and remove software packages in an operating system automatically.

In Linux, software is distributed in the form of packages. A package contains:

Application files

Configuration files

Libraries

Dependency information

Example:

• The package manager handles all these components and ensures the software works correctly after installation.

“This installs Nmap along with necessary dependencies.”

Main Functions of a Package Manager

1. Software Installation

Installs applications and required files automatically.

2. Dependency Management

Many programs need additional software libraries to work.

The package manager:

• Detects required dependencies

• Downloads them automatically

• Prevents missing-file errors

3. Software Updates

Package managers help keep software updated with:

• New features

• Bug fixes

• Security patches

4. Software Removal

Removes installed software cleanly from the system.

5. System Security

Repositories used by package managers usually provide trusted and verified software packages, reducing the risk of malicious software.

Benefits of Package Managers:

Faster software installation

Automatic dependency handling

Easy software updates

Better security

Centralized software management

APT Concept

APT stands for Advanced Package Tool. It is the default package management system used in Debian-based Linux distributions like Kali Linux.

Functions of APT:

Install software

Update packages

Upgrade the system

Remove software

Manage dependencies

Common APT Commands:

Example :

“This updates the package information from repositories.”

 Repositories

A Repository is an online storage location that contains software packages for Linux systems.

Linux downloads software from repositories instead of random websites.

Why Repositories are Important?

Provide trusted software

Make installation easier

Deliver updates and security patches

Manage software dependencies automatically

Repositories are used to store and provide software packages for Linux systems in a centralized and secure way.

Types of Repositories

Official repositories

Third-party repositories

Local repositories

Simple Working Process

User requests software

APT checks repositories

Package is downloaded

Software is installed automatically

Network Interface Concept in Kali

A Network Interface in Kali Linux is a hardware or virtual connection that allows the system to send and receive data over a network.

In Kali Linux, network interfaces are used for:

Internet access

Network communication

Security testing

Packet capturing

Each interface acts like a communication channel between the computer and the network.

It can be:

Wired (Ethernet)

Wireless (Wi-Fi)

Virtual network adapter

Each network interface has its own settings and IP address.

Loopback Interface (lo)

A special internal interface used for communication within the same system.

Example:  127.0.0.1

This is called the localhost address. Computers literally talk to themselves through a fake network interface.

IP Addressing in Linux

IP Addressing in Linux is the method of assigning unique numerical addresses to devices so they can communicate over a network. An IP address helps identify a device on a local network or the internet.

  Purpose of IP Addressing

IP addresses are used to:

Identify devices

Send and receive data

Enable network communication

Connect to the internet

Basic Idea of Connectivity in Linux Systems

Connectivity means the ability of Linux systems to communicate with:

Other computers

Networks

Internet services

Linux uses:

Network interfaces

IP addresses

Routing

DNS services

to establish communication.

Basic Connectivity Process

Device connects to a network

Receives an IP address

Sends data through network interfaces

Communicates with other systems

Common Connectivity Uses in Kali Linux

Internet access

Network scanning

Remote connections

Penetration testing

Packet analysis

Tools like:

• Nmap
• Wireshark

depend heavily on network connectivity.

Summary

Which desktop environment is the default in Kali Linux?

Which desktop environment is the default in Kali Linux?