Linux Overview Lecture Notes

Introduction

• Statistics: 96% of viewers not using Linux.
• Linux: A superior, free, open-source operating system with a 4% PC market share.
• Importance for Programmers: Essential for code development and server management.
• Goal: Understand 101 essential Linux concepts in 10 minutes.

History of Unix and Linux

• Unix: Developed in the 70s at AT&T Bell Labs, led to POSIX standardization for compatibility.
• POSIX Compliance: Influences macOS, Android, FreeBSD, and Linux distributions.
• Minix: Academic OS developed in 1987, inspired Linus Torvalds to create Linux in 1991.
• Linux Licensing: Free and open-source under GPL 2.0.

Linux Kernel

• Kernel vs Operating System: Linux is the kernel that interacts with hardware and software applications.
• Boot Process:
  • Bootloader (usually Grub) loads kernel into RAM.
  • Kernel detects hardware and starts the init system (commonly SystemD).
  • Initializes user applications.
• Memory Management: Allocates/deallocates memory, creates virtual memory using hard drive.
• File System: Provides a virtual file system, 4th Extended File System (ext4) is common.
• Device Interaction: Uses drivers to communicate with peripheral devices.

User Space and System Calls

• Privilege Rings:
  • Ring 0: Kernel, highest privilege level.
  • Ring 3: User space, lower privilege level.
• System Calls: Transition from user space to kernel, e.g., writing to a file.
• GNU Project: Started in 1983 by Richard Stallman, provides core utilities for Linux.

Exploring the Terminal

• Shell: Interface for sending commands to the kernel, most common: Bash.
• Basic Commands:
  • echo: Print output.
  • man: Access manual for commands.
  • touch: Create a new file.
  • ls: List files, cat: Read file contents.
  • stat: View file metadata.
  • rm: Remove files.

Combining Commands and Scripting

• Input/Output Redirection: Using angle brackets to redirect output/input.
• Pipes: Pass output from one command to another.
• Bash Scripts: Create scripts for repetitive tasks using text editors like Nano.

User Management and Permissions

• Users and UID: Each user has a unique UID, Root user has UID 0.
  • su to switch to root, sudo for elevated commands.
• Groups: Manage permissions easily.

File System Structure

• Home Directory: Personal workspace for the logged-in user.
• Critical Directories:
  • /boot: Linux kernel.
  • /dev: External devices.
  • /etc: Config files.
  • /var: Log files.
  • /bin: Executable binaries.

Environment Variables and Path

• Path Variable: Directories searched for executables.
• Customize with .bashrc: Run scripts before terminal sessions, modify terminal prompt.

File Permissions

• Symbolic Permissions: Read, write, execute privileges represented in triplets.
• Chmod/Chown Commands: Modify permissions and file ownership.

Process Management

• Processes: Created when commands are run, managed by the kernel.
  • Use ps to view processes, htop for interactive view.
• Killing Processes: Use kill command, with -9 flag for forceful termination.

Utilities and Distributions

• Common Utilities: grep, sed, gzip, tar.
• Linux Distributions: Varied based on target audience and package managers (e.g., apt, yum, pacman).
• Popular Distros:
  • Debian: Popular and user-friendly.
  • Red Hat: Enterprise-focused.
  • Arch: Emphasizes user control and customization.

Conclusion

• Exploring Linux: Beyond the basics, continuous learning recommended.
• Full Linux Course: Available for deeper exploration into Linux fundamentals.