build.sh

#!/bin/bash

BUSYBOX_VERSION=1.32.1
LINUX_VERSION=5.15.6
BASH_VERSION=5.2.15

echo "Building for Busybox $BUSYBOX_VERSION, Linux $LINUX_VERSION, and Bash $BASH_VERSION"

echo "Cleaning up..."
rm -Rf bzImage
rm -Rf initrd
rm -Rf src
rm -Rf initrd.img
rm -Rf ez-admin.iso

mkdir -p src
cd src
    
    # Kernel
    echo "Downloading kernel $LINUX_VERSION..."
    LINUX_MAJOR=$(echo $LINUX_VERSION | sed 's/\([0-9]*\)[^0-9].*/\1/')
    wget https://mirrors.edge.kernel.org/pub/linux/kernel/v$LINUX_MAJOR.x/linux-$LINUX_VERSION.tar.xz
    echo "Extracting kernel..."
    tar -xf linux-$LINUX_VERSION.tar.xz
    echo "Building kernel..."
    cd linux-$LINUX_VERSION
        make defconfig
        make -j$(nproc) || exit
    cd ..

    # Busybox
    echo "Downloading busybox $BUSYBOX_VERSION..."
    wget https://www.busybox.net/downloads/busybox-$BUSYBOX_VERSION.tar.bz2  
    echo "Extracting busybox..."  
    tar -xf busybox-$BUSYBOX_VERSION.tar.bz2
    echo "Building busybox..."
    cd busybox-$BUSYBOX_VERSION
        make defconfig
        sed 's/^.*CONFIG_STATIC[^_].*$/CONFIG_STATIC=y/g' -i .config
        make -j$(nproc) || exit
    cd ..

cd ..

echo "Copying kernel..."
cp src/linux-$LINUX_VERSION/arch/x86_64/boot/bzImage ./

# initrd
mkdir initrd
cd initrd

    echo "Creating rootfs skeleton and installing busybox..."
    mkdir -p bin dev proc sys boot
    cd bin
        cp ../../src/busybox-$BUSYBOX_VERSION/busybox ./

        for prog in $(./busybox --list); do
            # Skip bash
            if [ "$prog" = "bash" ]; then
                continue
            fi
            ln -s /bin/busybox ./$prog
        done
    cd ..
cd ..

cd src
    echo "Downloading bash $BASH_VERSION..."
    wget https://ftp.gnu.org/gnu/bash/bash-$BASH_VERSION.tar.gz
    echo "Extracting bash..."
    tar -xf bash-$BASH_VERSION.tar.gz
    echo "Building bash..."
    cd bash-$BASH_VERSION
        ./configure --prefix=/usr --without-bash-malloc
        make -j$(nproc) || exit
        make install DESTDIR=../initrd
    cd ..
cd ..

cd initrd
    echo "Performing final config..."

    cat init.sh > init # Copy init file over

    chmod -R 777 .

    echo "Packing initrd..."
    find . | cpio -o -H newc > ../initrd.img
cd ..

echo "Creating iso..."

if ! command -v xorriso &> /dev/null
then
    echo "xorriso could not be found"
    exit
fi
if ! command -v grub-mkrescue &> /dev/null
then
    echo "grub-mkrescue could not be found"
    exit
fi

# Check if the kernel image and initrd(rootfs) exist
if [ ! -f bzImage ]; then
    echo "bzImage not found"
    exit
fi
if [ ! -d initrd ]; then
    echo "initrd not found"
    exit
fi

# Create the ISO image
xorriso -as mkisofs -iso-level 3 -full-iso9660-filenames -volid "ez-admin" -eltorito-boot boot/grub/eltorito.img -no-emul-boot -boot-load-size 4 -boot-info-table -eltorito-catalog boot/grub/boot.cat -output ez-admin.iso ./boot ./bzImage ./initrd

echo "Done!"