🔥Understanding Operating Systems (Theory & Hands-on) 🔥

We’ll break this down into structured learning with both theory and hands-on tasks to help you gain a deep understanding. Let's get started!

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1️⃣ What is an OS? How Does It Manage Hardware & Software?

Theory:

An Operating System (OS) is system software that acts as an intermediary between hardware and software. It manages system resources (CPU, Memory, Storage, I/O devices) and provides a user interface.

Key Responsibilities of an OS:

• Process Management: Handles multitasking, scheduling, and execution.
• Memory Management: Allocates RAM for processes and ensures efficient memory usage.
• File System Management: Organizes, stores, and retrieves files on disk.
• Device Management: Controls hardware like keyboards, printers, and network adapters.
• Security & User Management: Implements authentication, permissions, and access control.

🔹 Hands-on Task 1: Check OS Details

✅ Windows:
Open Command Prompt (Win + R → cmd) and run:

powershell

systeminfo | findstr /B /C:"OS Name" /C:"OS Version"

✅ Linux/macOS:
Open a terminal and run:

bash

uname -a
cat /etc/os-release

📝 Observe the OS name, version, and kernel details.

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2️⃣ Types of OS & Key Differences (Windows, Linux, macOS, Unix)

Theory:

Feature	Windows	Linux	macOS	Unix
Open Source?	No	Yes (Mostly)	No	Mostly
Kernel Type	Hybrid (Windows NT)	Monolithic (Linux Kernel)	Hybrid (XNU)	Monolithic
Command Shell	CMD/Powershell	Bash/Zsh/Fish	Bash/Zsh	Shell (csh, ksh)
Filesystem	NTFS, FAT32	EXT4, XFS, Btrfs	APFS, HFS+	UFS, ZFS
Security	Lower (More Malware)	High	Very High	High

🔹 Hands-on Task 2: Check System Type & Kernel

✅ Windows:

powershell

systeminfo | findstr /B /C:"System Type"

✅ Linux/macOS:

bash

uname -srm

📝 Compare the outputs of different OSes.

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3️⃣ OS Architecture: Kernel, User Space, System Calls, Libraries

Theory:

🔹 Kernel: Core of the OS that directly interacts with hardware. ( learn about kernel by clicking here)
🔹 User Space: Applications and processes running outside the kernel.
🔹 System Calls: Interface between applications and the kernel (e.g., open(), read(), write()).
🔹 Libraries: Precompiled functions that applications use (e.g., glibc for Linux, ntdll.dll for Windows).

🔹 Hands-on Task 3: Check Running Kernel & System Calls

✅ Windows:

powershell

Get-WmiObject Win32_OperatingSystem | Select-Object Version

✅ Linux/macOS:

bash

uname -r    # Kernel version
strace ls   # Trace system calls (Linux only)

📝 Compare kernel versions across different systems.

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4️⃣ Boot Process (Windows vs. Linux)

Theory:

🔹 Windows Boot Process:

The Windows Boot Process follows a structured sequence of events that leads from powering on the system to loading the Windows operating system fully into memory. 

1. BIOS/UEFI → click here
2. MBR/GPT → click here
3. Bootloader (Windows Boot Manager) → click here
4. NT Kernel (ntoskrnl.exe) → click here
5. User Space (Explorer, Apps).

🔹 Linux Boot Process:

The Linux boot process involves several key steps, similar to the Windows boot process, but with a few distinctions due to the nature of Linux. Below is a detailed breakdown of each phase in the process.

BIOS/UEFI →

• When the system is powered on, the BIOS (Basic Input/Output System) or UEFI (Unified Extensible Firmware Interface) firmware initializes the hardware components.
• Performs the Power-On Self-Test (POST) to check for hardware issues.
• Identifies the bootable device (HDD, SSD, USB, etc.).
• Loads the bootloader from the Master Boot Record (MBR) or EFI System Partition (ESP).

GRUB Bootloader →

• The bootloader is responsible for loading the Linux kernel into memory.
• The most commonly used bootloader is GRUB (Grand Unified Bootloader).
• GRUB presents a boot menu where users can choose:
  • Kernel versions
  • Different operating systems (if dual-boot is configured)
  • Recovery mode options
• GRUB loads the selected kernel into RAM and hands over control.

Init/Systemd →

• The init system (older Linux distros) or systemd (modern Linux) takes over.
• Systemd is the most commonly used initialization system today.
• It starts services based on predefined configurations.
• Executes scripts to mount filesystems, enable networking, and launch essential daemons.
• Systemd organizes processes using targets instead of traditional runlevels.

Kernel →

The Linux kernel is loaded into memory and starts executing.

It initializes hardware drivers and mounts the root filesystem.

The kernel loads essential modules required for system operation.

It executes initramfs (initial RAM filesystem), which provides necessary drivers to mount the root filesystem.

The kernel then starts the first process: init (or systemd in modern systems).

User Space (Shell, GUI).

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🔹 Hands-on Task 4: Check Boot Process Logs

✅ Windows:

powershell

Get-EventLog -LogName System -Newest 10 | Format-Table TimeGenerated, EntryType, Message

✅ Linux/macOS:

bash

dmesg | less
systemctl list-units --type=service --state=running

📝 Analyze how your system booted up.

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5️⃣ Filesystem Structure & Permissions

Theory:

🔹 Windows: Uses NTFS, FAT32.
🔹 Linux/macOS: Uses EXT4, XFS, Btrfs, APFS.
🔹 Key Directories in Linux:

• /home → User files
• /bin → Essential binaries
• /etc → Configuration files
• /var → Logs
• /boot → Kernel & bootloader files

🔹 File Permissions (Linux):

• r (read), w (write), x (execute)
• chmod (change file permissions)
• chown (change file ownership)

🔹 Hands-on Task 5: Check Filesystem & Modify Permissions

✅ Windows (Check File System):

powershell

fsutil fsinfo drives
fsutil fsinfo volumeinfo C:

✅ Linux/macOS (Check Filesystem & Permissions):

bash

df -hT
ls -l /etc/passwd
chmod 700 myfile.txt
chown user:user myfile.txt

📝 Observe the file structure and change permissions.

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6️⃣ Process & Memory Management

Theory:

🔹 Process: A running instance of a program.
🔹 Virtual Memory: Uses disk space as extra RAM (paging/swapping).
🔹 Context Switching: Switching between running processes.
🔹 Thread: A lightweight process (multiple threads run in a process).

🔹 Hands-on Task 6: Monitor Processes & Memory

✅ Windows (Check Processes & RAM Usage):

powershell

tasklist | Sort-Object WS -Descending | Select-Object -First 10

✅ Linux/macOS (Check Processes & RAM Usage):

bash

ps aux --sort=-%mem | head -10
top
htop   # (if installed)

📝 Observe running processes and memory usage.

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💯 Conclusion & Next Steps

🔥 You've learned:
✅ What an OS is & how it manages hardware/software.
✅ Different OS types and their differences.
✅ OS architecture, boot process, and system calls.
✅ Filesystem structure & permissions.
✅ Process & memory management.

🎯 Next Steps:

• Experiment with boot logs & system monitoring.
• Deep dive into privilege escalation in OS security.
• Learn kernel exploitation and OS hardening techniques.