Linux - Documentation

1. Introduction

Linux is an open-source operating system widely used for servers, development, cloud computing, and embedded systems. It’s powerful due to its command-line interface (CLI), flexibility, and security.

2. Command Line Basics

The terminal or CLI is where you type commands to interact with the system.

Common Commands

Command	Description
`pwd`	Print current working directory
`ls`	List files and directories
`cd <dir>`	Change directory
`mkdir <dir>`	Create a directory
`touch <file>`	Create an empty file
`cp <src> <dest>`	Copy file/directory
`mv <src> <dest>`	Move/rename file/directory
`rm <file>`	Remove file
`rm -r <dir>`	Remove directory recursively
`cat <file>`	View file content
`less <file>`	View file content page by page
`echo "text"`	Display text or write to file
`find <path> -name <filename>`	Search files by name
`grep "text" <file>`	Search text in files
`history`	Show command history
`man <command>`	Show manual/help page

3. File Permissions

Linux is a multi-user OS. Every file/directory has permissions controlling who can read, write, or execute it.

Permission Structure

-rwxr-xr--

First character: (file) or d (directory)
Next 3 characters: owner permissions (r=read, w=write, x=execute)
Next 3 characters: group permissions
Last 3 characters: others/world permissions

Numeric Representation

Permission	Value
read (`r`)	4
write (`w`)	2
execute (`x`)	1

Sum values for each category: e.g., rwx = 4+2+1=7, rw- = 4+2=6
Example: chmod 755 file → rwxr-xr-x