Lecture 1: Introduction to Linux

What is an Operating System?

• The Operating System (OS) is the software that starts when the computer boots and manages all system operations.
• It acts as a manager, controlling resources such as the CPU, memory, and storage.

Main Functions:

1. Control Hardware: Coordinates all hardware components.
2. Run Applications: Executes application software (e.g., browsers, editors, games).
3. Manage Data and Files: Handles operations like copying, moving, deleting, and renaming data.

Before Linux

• 1980s: Microsoft DOS dominated personal computers.
• Apple MAC: Superior but expensive.
• UNIX: Advanced but highly costly.
• Users wanted a UNIX-like, affordable system that could run on PCs.

Linux Overview

• A UNIX-like, free, and open-source OS.
• Based on UNIX, designed initially for PCs but later used in servers, mainframes, and supercomputers.
• Runs on diverse hardware: PCs, phones, mainframes, and embedded devices.

Linux vs Unix vs Windows

Parameter	Linux	Unix	Windows
Inception Year	1991	1969	1985
Availability	Open-source and free	Proprietary	Paid
Developer	Linus Torvalds	AT&T Bell Labs	Microsoft
Security	Secure	Secure	Less secure
Virus Count	60–100	85–120	~60,000
Interface	GUI + CLI	Mostly CLI	GUI-focused
Language	C, Assembly	C, Assembly	C++, Assembly
License	GPL (open)	Closed	Proprietary

History of Linux

Linux was first released by Linus Torvalds on September 17, 1991.

• Origin: Linus developed Linux while he was a student at the University of Helsinki.
• Collaboration: The developers of the Free Open Source Foundation assisted in the development of Linux.
• Motivation: He created it for his computer because he could't afford a licensed operating system.
• GPL (General Public License): Ensures that Linux source code remains free to use, modify, and redistribute.

Linux Operating System

• Based on the Linux Kernel, which handles communication between hardware and software.
• A distribution combines the kernel with utilities and applications, forming a complete OS.
• Various Linux distributions cater to different users and needs.

Features of Linux OS

Open Source and Free

• Source code available to everyone.
• Users can modify and redistribute freely.

Multi-User & Multiprogramming

• Supports multiple users and simultaneous programs.

Security

• Resistant to most viruses; supports authentication, authorization, and encryption.
• No antivirus required.

Lightweight

• Requires minimal resources (4–8GB storage, low RAM usage).
• Supports numerous file formats.

Graphical User Interface

• CLI by default, but can include GUI environments (GNOME, KDE, etc.).

Stability & Performance

• Rarely crashes; supports many concurrent users efficiently.

Portability & Compatibility

• Runs on a wide range of hardware and supports extensive applications.

Community Support

• Backed by a large and active user/developer community.

Why Linux?

• Open-source flexibility, stability, and reliability make it ideal for developers, servers, and end users alike.

Linux Architecture

1. Kernel: Core component managing hardware and virtual resources.
2. System Libraries: Provide reusable functionality for developers.
3. Shell: Interface that interprets user commands.
4. Hardware Layer: Physical components (CPU, RAM, I/O devices).
5. System Utilities: Tools for managing system configurations, software, users, and performance.

Linux Distributions

Main componentes of a distribution:

• Kernel + device drivers
• Shell (bash, sch, etc.)
• GUI (X11, Xfree, X.org)
• Window mangers (KDE, Gnome, etc.)
• Boot managers (LILO, GRUB, systemd-boot)
• Application software
• Installation and maintenance tools

Examples: Ubuntu, Mint, Fedora, Arch, Debian

• Summary: A Linux distribution = Kernel + Libraries + Tools + GUI + Applications.

Linux Distribution Families

Check Distribution

cat /etc/issue      # Distribution name
uname -a            # Kernel version

Choosing the Right Distribution

• Hardware Compatibility: Ensure support for system architecture and devices.
• Application Requirements: Verify package availability.
• Security & Stability: Choose well-maintained distros.
• Community Support: Prefer active, documented communities.
• Customizability: Consider distros like Gentoo or Yocto for flexibility.
• User Experience: Evaluate desktop environments and usability.

Linux Licensing

• Licensed under GNU GPL v2, ensuring source code openness.
• GPL: Promotes free modification and distribution.
• Linus Torvalds declined GPL v3 for the kernel due to added restrictions.

Linux Commands

• Commands are instructions executed in the terminal.
• Case-sensitive.
• Processed by the shell, which interacts with the kernel.

Types:

• Built-in Commands: Integrated in the shell (e.g., cd, echo).
• External Commands: Separate executables (e.g., ls, cat).

Command Syntax:

command [ -options ] [ arguments ]

Shell

• Interface between user and kernel.
• Executes user commands and manages processes.
• Popular shells: sh, bash, csh, tcsh.
• Open terminal: Ctrl + Alt + T
• View default shell:

echo $SHELL

Bash (Bourne-Again Shell)

• Developed by Brian Fox for the GNU Project.
• Default shell for most Linux distributions.
• Functions as both a command interpreter and scripting language.
• Supports variables, conditionals, loops, and functions.
• Reads scripts directly from files.

Shell Scripts

• A script is a series of commands saved in a file.
• Executed by a shell interpreter.

Steps to Write:

1. Create a file with commands.
2. Add a shebang line (#!).
3. Make it executable:

chmod u+x script.sh

4. Run:

./script.sh

Alternative Execution:

• Run via shell: bash script.sh
• Source in current shell: source script.sh (any variables defined by the script remain in the current shell)

Example Script

#!/bin/bash

rm *.txt # remove all text files
ls -l

Man Command

• Access command manuals using:

man <command>

• Contains sections: NAME, SYNOPSIS, DESCRIPTION, OPTIONS, EXAMPLES.
• Exit manual: press q.

Manual Sections

1. General commands: Command used in the terminal.
2. System calls: Functions provided by the kernel.
3. Library functions: Functions within program libraries.
4. Special files: Devices are usually found in the /dev directory and corresponding drivers.
5. System administration commands
6. File formats and conventions
7. Kernel routines
8. Specs and interfaces
9. Games
10. Miscellaneous

Examples

man -aw     # View all sections of a topic
man -f      # Search by command name (whatis)
man -k      # Search by keyword
whereis -m  # Find man page location