Minimal OS - Educational Operating System

A simple, clean, and educational operating system designed for beginners to learn OS development concepts.

Features

• Basic I/O: Text output to VGA display and keyboard input
• Command Line Interface: Simple shell with built-in commands
• File System: Tree-based in-memory file system
• Clean Architecture: Well-organized code structure for learning

Project Structure

os/
├── src/
│   ├── boot/
│   │   └── boot.S          # Boot assembly code
│   └── kernel/
│       ├── kernel.c        # Main kernel entry point
│       ├── kernel.h        # Kernel header file
│       ├── io.c            # I/O functions (keyboard, screen)
│       ├── fs.c            # File system implementation
│       └── shell.c         # Command line interpreter
├── Makefile                # Build system (Linux/WSL)
├── linker.ld               # Linker script
├── grub.cfg                # GRUB configuration
├── build_linux.sh          # Build script for Linux/WSL
├── build_windows.bat       # Build script for Windows
├── BUILD_WINDOWS.md        # Windows-specific build instructions
└── README.md               # This file

Building

Prerequisites

• GCC (cross-compiler for i386 or host with 32-bit support)
• GNU Binutils (as, ld)
• GRUB tools (grub-mkrescue or grub2-mkrescue)
• Make

Build Commands

# Build the OS and create ISO image
make

# Clean build files
make clean

# Remove all generated files
make distclean

This will create minimal_os.iso which can be booted in a virtual machine.

Running

Using QEMU (Recommended)

# Build and run in QEMU
make run

# Or manually:
qemu-system-i386 -cdrom minimal_os.iso

Using VirtualBox

1. Create a new virtual machine
2. Set OS type: Other/Unknown
3. Mount minimal_os.iso as CD/DVD
4. Start the VM

Using VMware

Similar process to VirtualBox - mount the ISO and boot from it.

Available Commands

Once the OS boots, you'll see a command prompt. Type help to see available commands:

• help - Display available commands
• ls - List files in current directory
• cd <dir> - Change directory
• pwd - Print working directory
• cat <file> - Display file contents
• mkdir <dir> - Create directory
• touch <file> - Create empty file
• rm <name> - Remove file or directory
• clear - Clear screen
• reboot - Reboot system

Learning Resources

Code Organization

1. boot.S: Assembly code that sets up the stack and calls kernel main
2. kernel.c: Initializes subsystems and starts the shell
3. io.c: Low-level I/O operations for screen and keyboard
4. fs.c: Implements a simple tree-based file system
5. shell.c: Parses and executes commands

Key Concepts

• Multiboot Header: Required by GRUB to load the kernel
• VGA Text Mode: Direct memory access to video memory
• Keyboard Input: Reading from PS/2 keyboard port
• File System: In-memory tree structure for file management

Development

Adding New Commands

To add a new command:

1. Open src/kernel/shell.c
2. Add the command to the commands array
3. Implement the command function
4. Rebuild with make

Modifying the Kernel

The kernel is designed to be simple and educational:

• All code uses English comments
• Functions are well-documented
• Structure follows typical OS organization

System Requirements

• x86 or x86_64 processor
• 4MB RAM minimum
• Virtual machine (QEMU, VirtualBox, VMware)

License

This is an educational project. Feel free to use, modify, and learn from it.

Troubleshooting

Build Errors

• "grub-mkrescue not found": Install GRUB tools

  • Ubuntu/Debian: sudo apt install grub-common grub-pc-bin
  • Fedora: sudo dnf install grub2-tools
  • Arch: sudo pacman -S grub

• "cannot create regular file": Ensure you have write permissions

Boot Issues

• Make sure the ISO is properly generated
• Check virtual machine settings (enable legacy BIOS boot if needed)
• Try different virtualization software

Contributing

This is a learning project. Feel free to:

• Add new features
• Improve documentation
• Fix bugs
• Share your modifications

Author

PandaKing

Acknowledgments

• Inspired by various OS development tutorials
• Uses GRUB as bootloader
• Built with standard GNU toolchain