minimal.sh

#!/bin/sh
set -ex
KERNEL_VERSION=4.19.71
BUSYBOX_VERSION=1.31.0
SYSLINUX_VERSION=6.03

CORES=$(grep -c ^processor /proc/cpuinfo)
CORES=$((CORES + 1))

wget -O kernel.tar.xz http://kernel.org/pub/linux/kernel/v4.x/linux-$KERNEL_VERSION.tar.xz
wget -O busybox.tar.bz2 http://busybox.net/downloads/busybox-$BUSYBOX_VERSION.tar.bz2
wget -O syslinux.tar.xz http://kernel.org/pub/linux/utils/boot/syslinux/syslinux-$SYSLINUX_VERSION.tar.xz
tar -xvf kernel.tar.xz
tar -xvf busybox.tar.bz2
tar -xvf syslinux.tar.xz
mkdir isoimage
cd busybox-$BUSYBOX_VERSION
make distclean defconfig
sed -i 's/.*CONFIG_STATIC.*/CONFIG_STATIC=y/' .config
make -j${CORES} busybox install
cd _install
rm -f linuxrc
mkdir dev proc sys mnt
echo '#!/bin/sh' > init
echo 'dmesg -n 1' >> init
echo 'mount -t devtmpfs none /dev' >> init
echo 'mount -t proc none /proc' >> init
echo 'mount -t sysfs none /sys' >> init
echo 'setsid cttyhack /bin/sh' >> init
chmod +x init
find . | cpio -R root:root -H newc -o | gzip > ../../isoimage/rootfs.gz
cd ../../linux-$KERNEL_VERSION
make mrproper defconfig
sed -i 's/.*CONFIG_USB_XHCI_HCD.*/'\
'CONFIG_USB_XHCI_HCD=y\n'\
'CONFIG_USB_XHCI_DBGCAP=n\n'\
'CONFIG_USB_XHCI_PLATFORM=n'\
'/' .config
make -j${CORES} bzImage
cp arch/x86/boot/bzImage ../isoimage/kernel.gz
cd ../isoimage
cp ../syslinux-$SYSLINUX_VERSION/bios/core/isolinux.bin .
cp ../syslinux-$SYSLINUX_VERSION/bios/com32/elflink/ldlinux/ldlinux.c32 .
echo 'default kernel.gz initrd=rootfs.gz' > ./isolinux.cfg
xorriso \
  -as mkisofs \
  -o ../minimal_linux_live.iso \
  -b isolinux.bin \
  -c boot.cat \
  -no-emul-boot \
  -boot-load-size 4 \
  -boot-info-table \
  ./
cd ..
isohybrid minimal_linux_live.iso
set +ex