Linux Basics Guide

What is Operating System ?

Operating system is an interface between user and the computer hardware. The hardware of the computer cannot understand the human readable language as it works on binaries i.e. O's and l's. Also it is very tough for humans to understand the binary language, in such case we need an interface which can translate human language to hardware and vice-versa for effective communication.

Types of Operating System:

Single User - Single Tasking Operating System
Single User - Multitasking Operating System
Multi User - Multitasking Operating System

Single User - Single Tasking Operating System:-in this type of operating system only one user can log into system and can perform only one task at a time.E.g.: MS-DOs
**Single User - Multi tasking operating System:-**This type of O/S supports only one user to log into the system but a user can perform multiple tasks at a time, browsing internet while playing songs etc.

E.g.: Windows -98,Xp,vista,Seven etc.
**Multi User - Multi Tasking Operating System:-**These type of O/S provides multiple users to log into the system and also each user can perform various tasks at a time. In a broader term multiple users can logged in to system and share the resources of the system at the same time.

E.g.: UNIX, LINUX etc.

HISTORY OF LINUX

Linus Torvalds had a dream. He wanted to create the coolest operating system in the world that was free for anyone to use and modify. Based on an obscure UNIX flavor called MINIX, Linus took the source code and created his own flavor, called Linux. Using the power of the Internet, he distributed copies of his OS all over the world, and fellow programmers improved upon his work. In 1999, with a dozen versions of the OS and many GUIs to choose from, Linux is causing a UNIX revival. Knowing that people are used to the Windows tools, Linux developers are making applications that combine the best of Windows with the best of UNIX.

LINUX PRINICIPLES

Everything is a file:
Small, Single-Purpose Programs
Ability to Chain Programs
Open Source and Free Software
Security and User Privileges
Portability and Multiuser Capability
Multitasking, Stability and Reliability
Community-Driven Development

LINUX ORIGIN

LINUS TORVALDS

a) Finnish college student in 1991
b) Created Linux Kernel
When Linux Kernel combined with GNU applications, complete free UNIX like OS was developed.

Why Linux?

Fresh implementation of UNIX APIs
Open source development model
Supports wide variety of hardware
Supports many networking protocols and Configurations

Fully supported

Linux is a UNIX like OS: Linux is a similar to UNIX as the various UNIX versions are to each other.
Multi-User and Multi-tasking: Linux is a multi-user and multi-tasking operating system. That means that more than one person can be logged on to the same Linux computer at the same time. The same user could even be logged into their account from two or more terminals at the same time; Linux is also Multi-Tasking. A user can have more than one program executing at the same time
Fully Supported: Red Hat Linux is a fully supported distribution Red Hat Inc. provides many support programs for the smallest to the largest companies.

Distributions of Linux (Linux Distros)

A distribution is a version of Linux that includes the Linux kernel + software + package manager + user interface.

Here are some popular Linux distributions:

ARCHITECTURE OF UNIX

The architecture of UNIX can be divided into three levels of functionality,

KERNEL
SHELL
UTILITY FUNCTIONS

as shown in Figure.

The lowest level is the kernel, which schedules tasks, manages resources, and controls security, device management, storage management.

1.What is Kernel in Linux?

The Kernel is the core part of the Linux operating system.

✅ Functions of the Kernel:

Manages hardware (CPU, RAM, hard disks, etc.).
Allocates resources to programs.
Handles processes, memory, and device drivers.
Acts as a bridge between hardware and software.

📌 You don’t interact directly with the kernel — it works in the background.

The next level is the shell, which acts as the user interface, interpreting user commands and starting applications.

2.What is Shell in Linux?

The Shell is the interface between the user and the kernel.

✅ Functions of the Shell:

Takes commands from the user.
Sends them to the kernel for execution.
Displays the output back to the user.

There are different types of shells in Linux:

Shell Name	Description
Bash	Most common shell (Bourne Again Shell)
Sh	Original Unix shell
Zsh	Advanced shell with more features
Ksh	Korn shell, used in scripting

📌 When you open a terminal and type commands, you're talking to the shell.

3.The highest level is utilities, which provides utility functions. In other words it is the USER level, as user is the one who operates those utilities.

1. File Types in Linux

In Linux, everything is treated as a file — including directories, hardware devices, and even processes. There are 7 basic file types:

File Type	Description	Symbol (ls -l)
Regular file	Normal files containing text, scripts, binary data	`-`
Directory	A folder that holds other files and directories	`d`
Symbolic link	Shortcut to another file	`l`
Character device	Represents devices like keyboard, mouse (char-by-char I/O)	`c`
Block device	Storage devices like hard drives (block-wise I/O)	`b`
Socket	For inter-process communication (like a network socket)	`s`
Named pipe (FIFO)	For communication between processes	`p`

Filesystem Hierarchy in Linux (FHS)

The Filesystem Hierarchy Standard (FHS) defines the directory structure and contents in Unix/Linux systems.

Here’s a simplified version of the Linux directory structure:

Linux File Hierarchy Structure | GeeksforGeeks

Day 1-Introduction To Linux

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