build-minimal.sh

#!/bin/bash

# Define variables for the Linux kernel version and BusyBox version
LINUX_KERNEL_VERSION="5.14.6"
BUSYBOX_VERSION="1.34.1"

# Extract the major kernel version (e.g., "5" from "5.14.6")
KERNEL_MAJOR=$(echo $LINUX_KERNEL_VERSION | cut -d '.' -f 1)

# Create the src directory and the subdirectories for kernel and busybox
SRC_DIR="src"
KERNEL_DIR="${SRC_DIR}/linux-${LINUX_KERNEL_VERSION}"
BUSYBOX_DIR="${SRC_DIR}/busybox-${BUSYBOX_VERSION}"

# Construct the URLs
KERNEL_URL="https://mirrors.edge.kernel.org/pub/linux/kernel/v${KERNEL_MAJOR}.x/linux-${LINUX_KERNEL_VERSION}.tar.xz"
BUSYBOX_URL="https://www.busybox.net/downloads/busybox-${BUSYBOX_VERSION}.tar.bz2"

WORKSPACE_DIRS=("initrd/bin" "initrd/sbin" "initrd/dev" "initrd/dev/pts" "initrd/tmp" "initrd/proc" "initrd/sys")
mkdir initrd

mkdir -p $SRC_DIR
cd $SRC_DIR
    if [ ! -d "linux-$LINUX_KERNEL_VERSION" ]; then  #linux-$LINUX_KERNEL_VERSION does not exists
        wget $KERNEL_URL
        tar -xf linux-$LINUX_KERNEL_VERSION.tar.xz
        cd linux-$LINUX_KERNEL_VERSION
            make defconfig
            make -j$(nproc) || exit
        cd ..
    fi

    # wget $BUSYBOX_URL
    # tar -xf busybox-$BUSYBOX_VERSION.tar.bz2
    # cd busybox-$BUSYBOX_VERSION
    #     make defconfig
    #     sed 's/^.*CONFIG_STATIC[^_].*$/CONFIG_STATIC=y/g' -i .config
    #     # sed -i "s|.*CONFIG_STATIC.*|CONFIG_STATIC=y|" .config  # this also works
    #     make CC=musl-gcc -j$(nproc) busybox
    # cd ..
    
    if [ ! -d "busybox-$BUSYBOX_VERSION" ]; then  #busybox-$BUSYBOX_VERSION does not exists
        wget $BUSYBOX_URL
        tar -xf busybox-$BUSYBOX_VERSION.tar.bz2
        cd busybox-$BUSYBOX_VERSION
            make defconfig
            sed -i "s|.*CONFIG_STATIC.*|CONFIG_STATIC=y|" .config
            make -j$(nproc)
            make CONFIG_PREFIX=../../initrd -j$(nproc) install
        cd ..
    fi
cd ..

cp $KERNEL_DIR/arch/x86/boot/bzImage ./

for DIR in "${WORKSPACE_DIRS[@]}"; do
    mkdir -p $DIR
done

cd initrd
    # cd bin
    #     cd ../../$BUSYBOX_DIR/busybox ./

    #     for cmd in $(./busybox --list); do
    #         ln -s /bin/busybox ./$cmd;
    #     done
    # cd ..

    ########## GENERATE INIT FILE ##########
    echo '#!/bin/sh' > init

    echo 'mount -t sysfs sysfs /sys' >> init
    echo 'mount -t proc proc /proc' >> init
    echo 'mount -t tmpfs none /tmp -o mode=1777' >> init
    echo 'mount -t devtmpfs udev /dev' >> init
    echo 'mount -t devpts none /dev/pts' >> init

    echo 'sysctl -w kernel.printk="2 4 1 7"' >> init
    echo 'clear' >> init
    echo 'echo -e "Welcome to \\e[34mWave \\e[32mLinux \\e[31mLive\\e[0m (/init)"' >> init
    echo '/bin/sh' >> init
    echo 'poweroff -f' >> init
    ########## GENERATE INIT FILE ##########

    chmod -R 777 .
    find . | cpio -o -H newc > ../initrd.img
cd ..