Week 1: Unix/Linux Fundamentals

Introduction to the foundations of Unix and Linux systems

Modified

July 1, 2025

1 Unix/Linux Fundamentals

1.1 Learning Objectives

By the end of this module, you will be able to:

Explain the history and philosophy of Unix and Linux
Differentiate between major Linux distributions
Navigate the Linux file system hierarchy
Use essential command-line tools and utilities
Find help and documentation effectively
Perform basic system tasks from the command line

1.2 The Unix/Linux Heritage

1.2.1 Unix Origins and Philosophy

Unix was developed in the late 1960s and early 1970s at Bell Labs by Ken Thompson, Dennis Ritchie, and others. It embodied several key principles that continue to influence operating system design today:

Write programs that do one thing and do it well
Write programs to work together
Write programs to handle text streams

These principles led to the creation of a modular system where small, focused tools could be combined in powerful ways.

1.2.2 From Unix to Linux

Linux was created in 1991 by Linus Torvalds as a free and open-source alternative to Unix. Some key milestones:

1983: Richard Stallman announces the GNU Project to create a free Unix-like OS
1991: Linus Torvalds releases the Linux kernel
1992-1993: Early Linux distributions combine the kernel with GNU tools
1994-1995: Commercial Linux distributions begin to appear
2000s: Linux gains enterprise adoption
2010s: Linux dominates cloud computing and container technologies

1.2.3 Unix/Linux Today

Today, Unix and Linux systems power:

Most of the world’s web servers
The majority of cloud infrastructure
Android devices (Linux kernel)
Supercomputers and research systems
Embedded devices and IoT
Financial systems and critical infrastructure

1.3 Major Linux Distributions

1.3.1 Distribution Families

Linux distributions (“distros”) can be grouped into several major families:

1.3.1.1 Debian-based

Debian: Community-developed, highly stable
Ubuntu: User-friendly, popular for desktops and servers
Linux Mint: Designed for ease of use
Kali Linux: Security and penetration testing

1.3.1.2 Red Hat-based

Red Hat Enterprise Linux (RHEL): Commercial, enterprise-focused
CentOS/Rocky Linux/AlmaLinux: Free RHEL-compatible distributions
Fedora: Cutting-edge features, sponsored by Red Hat

1.3.1.3 SUSE-based

SUSE Linux Enterprise: Commercial enterprise distribution
openSUSE: Community version with Leap (stable) and Tumbleweed (rolling) variants

1.3.1.4 Arch-based

Arch Linux: Rolling release, minimalist philosophy
Manjaro: User-friendly version of Arch
EndeavourOS: Arch-based with simplified installation

1.3.1.5 Independent

Gentoo: Source-based, highly customizable
Slackware: One of the oldest distributions, minimalist
Alpine: Security-focused, lightweight

1.3.2 Choosing a Distribution

Factors to consider when selecting a distribution:

Stability vs. cutting-edge features
Release cycle (fixed vs. rolling releases)
Package management system
Community and commercial support
Default desktop environment
Specialized purpose (server, desktop, security, etc.)

1.4 System Architecture Overview

1.4.1 Linux Kernel

The kernel is the core of the operating system that:

Manages hardware resources
Provides process scheduling
Implements memory management
Handles file systems
Provides device drivers
Offers security and access control

1.4.2 User Space Components

Shell: Command interpreter (bash, zsh, etc.)
Core utilities: Basic commands and tools
System services: Background processes providing functionality
Package management: Installing and updating software
Desktop environment (if applicable): GUI and associated applications

1.4.3 Boot Process

BIOS/UEFI: Initial hardware initialization
Bootloader (GRUB, systemd-boot): Loads the kernel
Kernel initialization: Hardware detection and setup
Init system (systemd, SysV init): Starts system services
Login manager or shell prompt: User interaction begins

1.5 File System Hierarchy

1.5.1 The Filesystem Hierarchy Standard (FHS)

Linux follows a standardized directory structure:

/bin: Essential command binaries
/boot: Boot loader files and kernel
/dev: Device files
/etc: System configuration files
/home: User home directories
/lib: Essential shared libraries
/media: Mount points for removable media
/mnt: Temporary mount points
/opt: Optional application software
/proc: Virtual filesystem for process information
/root: Home directory for the root user
/run: Runtime variable data
/sbin: System binaries
/srv: Data for services provided by the system
/sys: Virtual filesystem for system information
/tmp: Temporary files
/usr: Secondary hierarchy (user programs, documentation)
/var: Variable data (logs, spool files, caches)

1.5.2 File Types in Linux

Regular files: Normal data files
Directories: Containers for other files
Symbolic links: Pointers to other files
Device files: Hardware device interfaces
Named pipes: FIFO (first-in, first-out) for inter-process communication
Sockets: Inter-process communication endpoints

1.6 Essential Command-Line Tools

1.6.1 Shell Basics

Terminal emulators: Programs that provide terminal functionality
Shell prompt: Where you type commands
Command structure: command [options] [arguments]
Command history: Access previous commands with up/down arrows
Tab completion: Press Tab to autocomplete commands and paths

1.6.2 File Navigation

# Print working directory
pwd

# List files and directories
ls
ls -l    # Long format with details
ls -a    # Show hidden files
ls -lh   # Human-readable file sizes

# Change directory
cd /path/to/directory
cd ~     # Go to home directory
cd ..    # Go up one level
cd -     # Go to previous directory

1.6.3 File Operations

# Create directories
mkdir directory_name
mkdir -p parent/child/grandchild   # Create parent directories as needed

# Create empty files
touch filename

# Copy files and directories
cp source destination
cp -r source_dir destination_dir   # Recursive copy for directories

# Move/rename files and directories
mv source destination

# Remove files and directories
rm filename
rm -r directory   # Recursive deletion
rm -i filename    # Interactive mode (asks for confirmation)
rm -f filename    # Force deletion without confirmation

# Be very careful with rm, especially rm -rf!

1.6.4 File Viewing

# View file contents
cat filename       # Display entire file
less filename      # Paginated viewing
head filename      # First 10 lines
head -n 20 filename  # First 20 lines
tail filename      # Last 10 lines
tail -f filename   # Follow file updates in real-time

# File information
file filename      # Determine file type
stat filename      # Detailed file information

1.6.5 Text Processing

# Search within files
grep pattern filename
grep -i pattern filename     # Case-insensitive
grep -r pattern directory    # Recursive search

# Stream editing
sed 's/old/new/g' filename   # Replace text

# Text manipulation
cut -d ',' -f 1,3 filename   # Extract columns from CSV
sort filename                # Sort lines
uniq filename                # Remove duplicate lines
wc filename                  # Count lines, words, characters

1.6.6 System Information

# User information
whoami         # Current username
id             # User and group IDs
who            # Who is logged in
w              # Who is logged in and what they're doing

# System information
uname -a       # Kernel and system information
hostname       # System hostname
uptime         # How long the system has been running
date           # Current date and time

# Resource usage
free -h        # Memory usage
df -h          # Disk usage
du -sh directory  # Directory size
top            # Process information (interactive)
ps aux         # Process listing

1.7 Getting Help and Documentation

1.7.1 Manual Pages

The man command provides detailed documentation for most commands:

man command_name
man 5 passwd     # Section 5 (file formats) entry for passwd
man -k keyword   # Search manual pages for keyword

Navigation in man pages: - Space/Page Down: Next page - b/Page Up: Previous page - /pattern: Search forward - n: Next search match - q: Quit

1.7.2 Info Pages

The GNU project’s documentation system:

info command_name

1.7.3 Command Help Options

Most commands offer built-in help:

command --help
command -h

1.7.4 Online Resources

Distribution documentation
The Linux Documentation Project (TLDP)
Stack Exchange sites
Command cheat sheets

1.8 Practical Exercise: Linux Exploration

1.8.1 Exercise 1: System Information Gathering

Create a script or series of commands to gather the following information about your Linux system:

Kernel version
Distribution name and version
Hostname
CPU information
Memory information
Disk usage
Currently logged-in users
Running processes
Network interfaces
Listening network ports

1.8.3 Exercise 3: Command Line Problem Solving

Solve the following tasks using command-line tools:

Find all files in your home directory modified in the last 24 hours
Count the number of lines containing the word “error” in a log file
Find the largest 5 files in a directory tree
Create a simple backup script that copies important configuration files to a backup directory with a timestamp
Extract a specific column from a CSV file

1.9 Additional Resources

1.10 Next Week

Next week, we’ll dive deeper into user and permission management, covering user accounts, groups, file permissions, access control lists, and security best practices.

1.11 Discussion Questions

How does the Unix philosophy influence modern software design beyond operating systems?
What factors would influence your choice of Linux distribution for different use cases?
How does the Linux file system hierarchy enhance organization and security?
What command-line tools do you find most useful, and why?
How might the skills learned in this module apply to cloud computing environments?