Minimal busybox & musl linux distro

gistfile1.txt

#!/usr/bin/env bash

set -e
BUSYBOX_URL="https://busybox.net/downloads/binaries/1.31.0-defconfig-multiarch-musl/busybox-x86_64"
MUSL_URL="https://musl.libc.org/releases/musl-1.2.4.tar.gz"
KERNEL_URL="https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.10.95.tar.xz"
OS_NAME="MinimalLinux.iso"
ROOTFS="/tmp/root"
KERNEL_VERSION="5.10.95"

[ -d ${ROOTFS} ] && rm -rf ${ROOTFS}

mkdir -p ${ROOTFS}/{bin,dev,etc,lib,mnt,proc,sbin,sys,tmp,var,boot/grub,usr/local/musl}

wget ${BUSYBOX_URL} -O ${ROOTFS}/bin/busybox
chmod +x ${ROOTFS}/bin/busybox
${ROOTFS}/bin/busybox --install -s ${ROOTFS}/bin

cat << 'EOF' > ${ROOTFS}/init
#!/bin/busybox sh
/bin/busybox --install -s /bin
mount -t devtmpfs devtmpfs /dev
mount -t proc proc /proc
mount -t sysfs sysfs /sys
mount -t tmpfs tmpfs /tmp
setsid cttyhack sh
exec /bin/sh
EOF
chmod +x ${ROOTFS}/init

cd ${ROOTFS}
find . | cpio -H newc -o | gzip -9 > boot/initramfs
cd -

cd /tmp
wget ${MUSL_URL}
tar xzf musl-1.2.4.tar.gz
cd musl-1.2.4
./configure --prefix=${ROOTFS}/usr/local/musl
make
make install
cd -

cd /tmp
wget ${KERNEL_URL}
tar xvf linux-${KERNEL_VERSION}.tar.xz
cd linux-${KERNEL_VERSION}
make defconfig
make -j$(nproc)
cp arch/x86/boot/bzImage ${ROOTFS}/boot/vmlinuz
cd -

cat << 'EOF' > ${ROOTFS}/boot/grub/grub.cfg
set default=0
set timeout=5

menuentry "Minimal Linux" {
    linux /boot/vmlinuz ro quiet
    initrd /boot/initramfs
}
EOF

grub-mkrescue -o ${OS_NAME} ${ROOTFS}