Fundamentals of Linux

What is Linux?

• Linux is not an operating system.
• Linux is an open-source unix-like operating system kernel.
• It was created by Linus Torvalds in 1991.
• It is the most popular operating system kernel in the world.
• It is used in wide range of devices from supercomputers to embedded systems.
• Android is based on Linux kernel.

What is an Operating System?

• An operating system is a software that manages computer hardware resources and provides common services for computer
  programs.
• It consists of a kernel and system programs.
• Generally, GNU/Linux is used to refer to the combination of Linux kernel and GNU system programs.
• There are many distributions of Linux that combine Linux kernel with different system programs.

Common Linux Distributions

What is an Operating System Kernel?

• A kernel (or operating system kernel) is a software that provides a bridge between applications and the actual hardware.
• It is responsible for managing system resources, such as memory, CPU, and I/O devices.
• It provides system calls for applications to interact with hardware.

Major Components of Linux

• Virtual File System
• Process Management
• Memory Management
• Device Drivers
• Network Stack
• Security

Root File System

File System Hierarchy

Common System Calls

Hello World in C

#include <stdio.h>

int main() {
    printf("Hello, World!\n");
    return 0;
}

Hello World in C (with system calls)

#include <unistd.h>

int main() {
    write(1, "Hello, World!\n", 14);
    return 0;
}

Hello World in x86 Assembly

.section .data
msg:
    .ascii "Hello, World!\n"
    len = . - msg

.section .text
.globl _start
_start:
    mov $4, %eax
    mov $1, %ebx
    mov $msg, %ecx
    mov $len, %edx
    int $0x80

    mov $1, %eax
    mov $0, %ebx
    int $0x80

Booting Process

Everything is a File

Stdout, Stdin, Stderr

Pipes

Signals

Threads

Sockets

IPC

Shell

Shell Scripting

Package Management

Systemd

Executables

Common Commands

Common Commands