Linux Overview Notes

Introduction

• 96% of viewers not using Linux; only 4% market share.
• Linux is popular on servers; essential for programmers and developers.
• Today’s focus: 101 essential concepts of Linux.

Historical Context

• Unix: Developed in the 70s at AT&T Bell Labs; led to POSIX standardization.
• Minix: Created in 1987 for academic use, inspired Linus Torvalds to develop Linux in 1991.
• Linux: Free, open-source under GPL 2.0; refers to the kernel, not the entire OS.

Linux Kernel

• Written in C; acts as an intermediary between software and hardware.
• Boot process: Bootloader (usually GRUB) loads the kernel into RAM.
• Kernel responsibilities:
  • Allocates/deallocates memory for processes.
  • Provides a virtual file system.
  • Interacts with hardware via drivers.

User Space vs Kernel Space

• Ring 0: Kernel (high privilege).
• Ring 3: User space (low privilege).
• System calls allow user applications to request kernel services.

GNU and Core Utilities

• GNU: Started in 1983 by Richard Stallman; provides core utilities for Linux.
• Shell: Allows command input; most common is Bash.

Basic Commands

• echo: Output text to console.
• man: Shows manuals for commands.
• ls: Lists files, with flags for details.
• touch: Creates a new file.
• cat: Reads file contents.
• stat: Displays file metadata.
• rm: Removes files.

Command Redirection and Piping

• Redirection: > to write output to a file, < for input.
• Piping: | sends output from one command to another (e.g., cat | sort | uniq).

Bash Scripting

• Use an editor (Nano, Vim) for scripts.
• Shebang: Indicates script interpreter.
• Scripts can automate command sequences.

User and File Management

• Users have unique UIDs; root user has UID 0.
• Use su or sudo for elevated privileges.
• Linux uses groups to manage permissions.

File System Structure

• Home directory: Personal workspace for logged-in user.
• Critical directories:
  • /boot: Contains Linux kernel.
  • /dev: External devices.
  • /etc: Configuration files.
  • /var: Log files.
  • /bin: Binaries.

Path and Environment Variables

• PATH: Environment variable for executable binary directories.
• Customize using export and .bashrc for persistent settings.

File Permissions

• Symbolic permissions: Read (r), Write (w), Execute (x).
• Changing permissions: chmod, changing ownership: chown, and groups: chgrp.

Process Management

• Each command execution creates a process.
• View processes with ps and htop.
• To kill processes, use kill or kill -9 for forceful termination.

Linux Distributions

• Varied based on target audience:
  • Slackware: Original classic.
  • Debian: Popular, open philosophy.
  • Red Hat: Enterprise-focused.
  • Arch: For advanced users.

Conclusion

• Familiarize with the terminal and commands for effectiveness.
• Explore further with resources available in the full course.
• Mastering Linux enhances programming and development skills.