Bootable Linux Image via QEMU

This repository contains a shell script that creates a fully bootable AMD64 Linux disk image using QEMU. The image, once booted, prints "hello world" to the console and does not include any user/session management or login prompts.

Overview

The script is created by Kondreddy Rohith Sai Reddy and performs the following steps:

• Kernel Image Verification: Checks for a kernel image named vmlinuz in the current directory. If not found, it downloads a prebuilt AMD64 kernel image from a provided URL (update the URL as needed).
• Minimal Init Program: Creates and statically compiles a small C program that prints "hello world".
• Disk Image Creation:
  • Creates a 64 MB disk image.
  • Uses parted to partition the image with an MBR partition table.
  • Creates a primary ext4 partition and marks it as bootable.
• Filesystem Setup:
  • Formats the partition as ext4.
  • Mounts the partition and copies the kernel image and the init binary.
  • Sets up a minimal GRUB configuration.
• GRUB Bootloader Installation: Installs GRUB onto the disk image to make it fully bootable.
• QEMU Boot: Launches QEMU to boot the disk image, directing console output to the terminal.

Prerequisites

Ensure the following tools are installed on your system:

• qemu-system-x86_64
• gcc
• wget
• cpio
• gzip
• dd
• parted
• mkfs.ext4
• losetup
• mount
• umount
• grub-install

Note: Several operations (e.g., mounting, loop device management, GRUB installation) require superuser privileges. It is recommended to run the script using sudo.

Usage

1. Prepare the Environment:
   Verify that all required tools are installed. If not, install them using your package manager.

2. Kernel Image:
   Place a valid AMD64 Linux kernel image named vmlinuz in the current directory.
   Alternatively, update the KERNEL_URL variable in the script with a valid URL to download a kernel image automatically.

3. Run the Script:
   Execute the script (e.g., sudo ./script_name.sh).
   The script operates entirely within the current working directory and does not require any additional user input.

Script Details

• Kernel Image Verification:
  Checks for vmlinuz in the current directory and downloads it if missing.

• Minimal Init Program:
  A C program (hello.c) is created and compiled statically into an executable init that prints "hello world".

• Disk Image Creation and Partitioning:

  • A 64 MB disk image (disk.img) is created using dd.
  • The disk is partitioned with parted (MBR) and a primary partition is set as bootable.

• Filesystem and GRUB Setup:

  • The partition is formatted as ext4.
  • The kernel and init binary are copied to the appropriate locations.
  • A minimal GRUB configuration is created in /boot/grub/grub.cfg to boot the kernel with init=/init.
  • GRUB is installed onto the disk image with grub-install.

• Booting via QEMU:
  The disk image is booted with QEMU using the -nographic option so that all output is sent to the terminal.

Assumptions

• The script is designed for Ubuntu 20.04 LTS or 22.04 LTS (or similar Linux distributions).
• All operations are confined to the current working directory.
• Superuser privileges are required for certain operations such as mounting, loop device management, and GRUB installation.
• The placeholder kernel URL in the script must be updated to a valid URL if no local kernel image is provided.

Cleanup

The script automatically cleans up temporary files and unmounts any mounted partitions after installing GRUB.