Custom Lightweight Linux OS Build

This repository documents the process of building a custom, lightweight Linux operating system using Buildroot.
This project was completed as part of the Operating Systems Laboratory course.

---

Project Overview

The primary goal of this project was to create a minimal, bootable Linux distribution from scratch.
This involved:

• Setting up a build environment
• Configuring the Linux kernel and root filesystem
• Compiling the sources
• Deploying the resulting image to a bootable USB drive

---

Environment Setup & Prerequisites

The development environment was set up on an Ubuntu 64-bit system running on VMware Workstation.

1. System Update

First, the system's package list was updated, and all installed packages were upgraded to their latest versions.

sudo apt update && sudo apt upgrade

2. Installing Dependencies

Next, essential packages and build tools required by Buildroot were installed.

sudo apt install build-essential binutils rsync wget libncurses-dev libelf-dev libssl-dev

---

Building the Linux System with Buildroot

The core of this project involved using Buildroot to configure and build the custom Linux image.

1. Download and Extract Buildroot

Buildroot version 2025.02.3 was downloaded and extracted.

wget https://buildroot.org/downloads/buildroot-2025.02.3.tar.gz  
tar -xf buildroot-2025.02.3.tar.gz  
cd buildroot-2025.02.3

2. Configuration

The Buildroot configuration interface was launched using:

make menuconfig

The following key parameters were configured according to the project requirements:

• Target options: Set to x86_64 architecture
• System configuration: Hostname set to optional name, root password set to "optional name"
• Target packages: dropbear (an SSH server) selected
• Filesystem images: Generate an ext4 root filesystem with a size of 120M
• Bootloader: grub2 with support for x86-64-efi

These configurations were saved to the .config file.

3. Compilation

The build process was initiated with:

make

This step cross-compiles the toolchain, kernel, bootloader, and all selected userspace packages.
Upon completion, the final images were located in the output/images directory.
The total size of the generated OS was 30MB.

---

Deployment to USB Drive

After a successful build, the generated images were written to a USB drive to create a bootable device.

1. Partitioning the USB Drive

The target USB drive (identified as /dev/sdd) was partitioned with two primary partitions:

• Boot partition (FAT32) for the bootloader and kernel
• Root partition (ext4) for the root filesystem

2. Formatting and Mounting

The newly created partitions were formatted and mounted:

# Format the partitions  
sudo mkfs.vfat -F32 /dev/sdd1  
sudo mkfs.ext4 /dev/sdd2

# Mount the partitions  
sudo mount /dev/sdd1 /mnt/efi  
sudo mount /dev/sdd2 /mnt/root

3. Copying Files

The compiled artifacts were copied to the appropriate partitions on the USB drive:

# Copy boot files  
sudo cp output/images/bzImage /mnt/efi/boot/  
sudo cp -r output/images/efi-part/* /mnt/efi/

# Copy root filesystem  
sudo cp -a output/images/rootfs.ext4 /mnt/root/

4. GRUB Configuration

The GRUB configuration file (grub.cfg) was modified to point to the correct root partition (/dev/sda2 instead of /dev/sda1).

---

Booting the Custom OS

Finally, the target laptop's BIOS settings were adjusted to boot from the USB drive.

• Secure Boot was disabled to allow the custom-signed OS to load
• Upon booting, the system successfully loaded the custom Linux OS

Login credentials:

• Username: root
• Password: shabnam

---

Challenges Faced

The process was not without its difficulties:

• Insufficient Memory
  The initial build failed due to insufficient memory allocated to the virtual machine.
  Solution: Increased VM's disk space to 40GB.

• USB Detection Issues
  The virtual machine repeatedly failed to recognize the USB drive.
  Solution: Multiple troubleshooting attempts until the issue was resolved.

---