🐧 Linux Fundamentals¶

Understanding the foundations of Linux, the operating system at the heart of Born2beroot.

Table of Contents¶

What is Linux?
The Linux Philosophy
What is the Kernel?
User Space vs Kernel Space
Linux Distributions
Debian
Rocky Linux
Why So Many Distributions?
The Linux Boot Process
BIOS and UEFI
Bootloaders
systemd
The Shell
Common Shells
Terminal vs Shell
Commands and Utilities
Processes
Process Lifecycle
Foreground vs Background Processes
Process IDs (PID)
Files and Directories
Linux Filesystem Hierarchy
Important Directories
Paths
Hidden Files
Environment Variables
Package Managers
Why Linux Dominates Servers
Mental Model

1️⃣ What is Linux?¶

Linux is an operating system.

An operating system sits between:

Hardware
    ↓
Operating System
    ↓
Applications

Without an operating system, applications would need to communicate directly with hardware.

Linux provides a stable and secure layer that allows software to run efficiently.

2️⃣ The Linux Philosophy¶

Linux follows a simple philosophy:

Do one thing and do it well

Many Linux tools are intentionally small and focused.

Examples:

grep
cat
find
sort
chmod

Each solves a specific problem.

3️⃣ What is the Kernel?¶

The kernel is the core of Linux.

Think of it as the operating system's manager.

Responsibilities include:

CPU scheduling
memory management
hardware communication
process management
filesystem access

4️⃣ User Space vs Kernel Space¶

Linux separates the system into two worlds.

User Space¶

Applications run here.

Examples:

Firefox
VSCode
Python

Kernel Space¶

The kernel runs here.

Applications must ask permission before accessing hardware.

This separation improves security and stability.

5️⃣ Linux Distributions¶

Linux itself is only the kernel.

A distribution combines:

Linux kernel
package manager
utilities
configuration tools
documentation

Examples:

Debian
Ubuntu
Rocky Linux
Fedora
Arch Linux

6️⃣ Debian¶

Debian is one of the oldest and most respected Linux distributions.

Known for:

stability
reliability
large repositories
conservative updates

Many other distributions are based on Debian.

7️⃣ Rocky Linux¶

Rocky Linux focuses on enterprise environments.

Known for:

Red Hat compatibility
long-term support
server usage

It is commonly found in professional infrastructures.

8️⃣ Why So Many Distributions?¶

Different users have different goals.

Some prioritize:

stability
performance
security
ease of use
customization

This is why many Linux distributions exist.

9️⃣ The Linux Boot Process¶

A simplified boot sequence:

Power On
    ↓
BIOS / UEFI
    ↓
Bootloader
    ↓
Kernel
    ↓
systemd
    ↓
Services
    ↓
Login

Understanding this sequence helps explain how Linux starts.

🔟 BIOS and UEFI¶

These systems initialize hardware before Linux starts.

Responsibilities:

detect hardware
perform checks
locate boot devices

UEFI is the modern replacement for BIOS.

1️⃣1️⃣ Bootloaders¶

A bootloader loads the operating system.

One common example is:

GRUB

Its job is to locate and start the Linux kernel.

1️⃣2️⃣ systemd¶

systemd is responsible for managing the system after the kernel starts.

It handles:

service startup
dependencies
logging
process supervision

Modern Linux distributions rely heavily on systemd.

1️⃣3️⃣ The Shell¶

The shell is the interface between the user and the operating system.

You type commands:

ls
pwd
cd

The shell interprets them and communicates with the system.

1️⃣4️⃣ Common Shells¶

Examples include:

Bash
Zsh
Fish
Dash

Bash remains the most widely known shell.

1️⃣5️⃣ Terminal vs Shell¶

These terms are often confused.

Terminal¶

The application window.

Shell¶

The program running inside that window.

Example:

Terminal
    ↓
Bash

1️⃣6️⃣ Commands and Utilities¶

Linux provides many small tools.

Examples:

ls
pwd
cat
grep
find

Combining small tools is one of Linux's greatest strengths.

1️⃣7️⃣ Processes¶

A process is a running program.

Examples:

Python Script
Browser
SSH Server

Every running application becomes a process.

1️⃣8️⃣ Process Lifecycle¶

A process typically follows:

Created
   ↓
Running
   ↓
Waiting
   ↓
Finished

The kernel manages this lifecycle.

1️⃣9️⃣ Foreground vs Background Processes¶

Foreground¶

Runs directly in the terminal.

Background¶

Runs independently.

Examples include:

servers
monitoring services
daemons

2️⃣0️⃣ Process IDs (PID)¶

Every process receives a unique identifier.

Example:

PID 100
PID 250
PID 421

The kernel uses these IDs to manage processes.

2️⃣1️⃣ Files and Directories¶

Linux treats almost everything as a file.

Examples:

documents
devices
logs
configuration files

This creates a consistent environment.

2️⃣2️⃣ Linux Filesystem Hierarchy¶

Linux follows a standard structure.

/
├── home
├── etc
├── usr
├── var
├── boot
└── tmp

Everything starts from the root directory.

2️⃣3️⃣ Important Directories¶

/home¶

User files.

/etc¶

Configuration files.

/var¶

Logs and changing data.

/boot¶

Boot-related files.

/tmp¶

Temporary files.

2️⃣4️⃣ Paths¶

Linux uses paths to locate files.

Example:

/home/student/document.txt

Paths can be:

absolute
relative

2️⃣5️⃣ Hidden Files¶

Files beginning with:

are hidden by default.

Examples:

.bashrc
.profile
.gitignore

2️⃣6️⃣ Environment Variables¶

Environment variables store configuration values.

Examples:

PATH
HOME
USER
SHELL

Applications often rely on them.

2️⃣7️⃣ Package Managers¶

Package managers simplify software installation.

Examples:

apt
dnf
yum

They manage:

installation
updates
dependencies

2️⃣8️⃣ Why Linux Dominates Servers¶

Linux powers most servers because it offers:

✅ Stability

✅ Performance

✅ Security

✅ Flexibility

✅ Open-source development

Many cloud platforms rely heavily on Linux.

2️⃣9️⃣ Mental Model¶

Think of Linux as:

The operating system city

The kernel is:

The city manager

Processes are:

The citizens

The filesystem is:

The map

And the shell is:

Your way of communicating with the city