Lesson 03 — Linux File System

Lesson Overview

Unlike Windows, Linux doesn’t use drive letters such as **C:*, **D:*, or **E:**.

Instead, Linux organizes everything into a single hierarchical directory structure that begins at the Root Directory (/).

In Linux:

Files
Directories
Hard disks
USB drives
Network storage
Running processes
Devices

are all represented as files within this hierarchy.

Understanding the Linux File System is one of the most important skills for Linux administrators, Cloud Engineers, DevOps Engineers, and Cybersecurity Professionals.

Throughout your Linux career, you’ll constantly work with directories, configuration files, logs, applications, and storage—all of which are organized within the Linux File System.

Learning Objectives

After completing this lesson, you will be able to:

Understand the Linux File System Hierarchy.
Navigate Linux directories.
Identify important system directories.
Understand absolute and relative paths.
Explore common file management commands.
Understand where Linux stores configuration files, logs, applications, and user data.

What is a File System?

A File System defines how an operating system stores, organizes, and retrieves files.

It provides a structured way to organize:

Files
Directories
Storage Devices
Permissions
Metadata

Without a file system, the operating system would not know where files are stored.

Linux File System Hierarchy

Linux follows the Filesystem Hierarchy Standard (FHS).

Everything begins from a single directory:

This is called the Root Directory.

Every other directory exists underneath it.

Linux Directory Structure

/

├── bin

├── boot

├── dev

├── etc

├── home

├── lib

├── media

├── mnt

├── opt

├── proc

├── root

├── run

├── sbin

├── srv

├── sys

├── tmp

├── usr

└── var

Understanding these directories is essential for Linux administration.

Root Directory (/)

The Root Directory is the top-level directory in Linux.

Everything starts here.

Example:

Think of it as the parent of every directory in the operating system.

/home

The /home directory stores user files.

Example:

/home

├── student

├── alice

└── bob

Each user has their own personal directory.

Typical contents include:

Documents
Downloads
Desktop
Pictures
Configuration Files

/root

The /root directory is the home directory of the root (administrator) user.

Example:

/root

Do not confuse / with /root.

They are completely different.

/etc

The /etc directory stores system configuration files.

Examples:

/etc/passwd

/etc/hosts

/etc/fstab

/etc/ssh/

Most Linux administration tasks involve modifying files in /etc.

/bin

Contains essential user commands.

Examples:

ls

cp

mv

cat

pwd

These commands are available even during system recovery.

/sbin

Contains essential administrative commands.

Examples:

reboot

shutdown

mount

fdisk

Primarily used by system administrators.

/usr

Stores applications and user programs.

Example:

/usr/bin

/usr/lib

/usr/share

Most installed software resides here.

/var

Stores data that changes frequently.

Examples:

Logs

Mail

Cache

Databases

Print Queues

One of the most important directories is:

/var/log

System logs are stored here.

/tmp

Temporary files.

Applications use this directory while running.

Files may be automatically removed after reboot.

/boot

Contains files required to start Linux.

Examples:

Linux Kernel
Boot Loader
Initial RAM Disk

Without /boot, Linux cannot start.

/dev

Linux treats hardware devices as files.

Examples:

/dev/sda

/dev/sdb

/dev/null

/dev/random

Hard disks, USB devices, and other hardware appear here.

/proc

A virtual file system containing information about running processes and the Linux kernel.

Examples:

/proc/cpuinfo

/proc/meminfo

/proc/version

Useful for troubleshooting and system monitoring.

/sys

Provides information about hardware devices and kernel settings.

System administrators use this directory for advanced hardware management.

/opt

Stores optional third-party applications.

Examples:

/opt/google

/opt/docker

/opt/customapp

Many enterprise applications install files here.

/media

Used when removable media is automatically mounted.

Examples:

USB Drives
DVDs
External Hard Drives

/mnt

Temporary mount point used by administrators.

Example:

/mnt/backup

/mnt/storage

Commonly used during maintenance.

Absolute Paths

An Absolute Path begins from the Root Directory.

Example:

/home/student/Documents/file.txt

Absolute paths always begin with:

Relative Paths

A Relative Path begins from the current directory.

Example:

Documents/file.txt

Relative paths do not begin with /.

Current Working Directory

Display your current location.

Command:

pwd

Example:

/home/student

Listing Files

Display files and directories.

Command:

ls

Display detailed information.

ls -l

Display hidden files.

ls -la

Changing Directories

Move into another directory.

cd /home

Return to your home directory.

cd

Move up one directory.

cd ..

Move to the previous directory.

cd -

Viewing Directory Contents

Display the contents of a directory.

Example:

ls /etc

Example output:

passwd

hosts

ssh

fstab

Hidden Files

Linux hides files beginning with a period.

Examples:

.bashrc

.profile

.gitconfig

Display hidden files:

ls -la

Linux File Types

Linux supports several file types.

Type	Description
Regular File	Standard file
Directory	Folder
Symbolic Link	Shortcut
Character Device	Keyboard, Terminal
Block Device	Hard Disk
Socket	Network Communication
Named Pipe	Process Communication

File System in Cloud Computing

Cloud virtual machines also use the Linux File System.

Example:

AWS EC2

↓

Ubuntu

↓

/etc

↓

Configuration Files

↓

Application Starts

Cloud administrators regularly manage these directories.

File System in Cybersecurity

Security professionals investigate:

Log Files
User Directories
SSH Configuration
Authentication Logs
Malware Files

Common investigation locations:

/var/log

/etc

/home

/tmp

Understanding the Linux File System is critical during incident response.

Common Commands

Display current directory:

pwd

List files:

ls

Change directory:

cd

Display directory tree (if installed):

tree

Display disk usage:

df -h

Display mounted file systems:

mount

These commands are used daily by Linux administrators.

Real-World Example

A Cloud Engineer deploys a web server.

Ubuntu Server

↓

/etc/nginx

(Configuration)

/var/log/nginx

(Log Files)

/usr/sbin/nginx

(Application Binary)

/var/www/html

(Website Files)

Knowing the Linux File System makes troubleshooting much easier.

Best Practices

As a Linux administrator:

Learn the purpose of each major directory.
Keep user data under /home.
Avoid modifying system files unnecessarily.
Store logs under /var/log.
Back up configuration files before making changes.
Use absolute paths in automation scripts.
Keep temporary files in /tmp.
Organize applications consistently.

A well-organized file system simplifies administration and troubleshooting.

Key Takeaways

After completing this lesson, you should understand:

The Linux File System Hierarchy Standard (FHS).
The purpose of major Linux directories.
Absolute vs relative paths.
Basic navigation commands.
Common file types.
How Linux organizes applications, configuration files, logs, and user data.

Summary

The Linux File System provides a standardized and organized way to store and manage files across the operating system.

Unlike Windows, Linux organizes everything beneath a single Root Directory, making navigation consistent across distributions.

Whether you’re managing cloud servers, troubleshooting applications, analyzing security incidents, or automating infrastructure, a solid understanding of the Linux File System is essential.

Mastering the Linux directory structure will make every future administration task easier.

Next Lesson

➡️ Lesson 04 — Linux Users & Groups

In the next lesson, you’ll learn how Linux manages users and groups, understand authentication and authorization, create user accounts, assign permissions, and explore best practices for identity management in Linux systems.