Linux bootable disk image using EXTLINUX, Busybox

Steps to create a minimal root filesystem using BusyBox and run Linux kernel using QEMU

• Download BusyBox and build with CONFIG_STATIC=y
• Create disk image

$ dd if=/dev/zero of=rootfs.img bs=1M count=10

• Make ext2 filesystem

$ mke2fs -j rootfs.img
$ tune2fs -c 0 -i 0 rootfs.img

• Mount disk image

$ sudo mount rootfs.img rootfs -o loop -t ext2

• Make boot directory

$ mkdir rootfs/boot

• Copy busybox to disk image

$ rsync -a busybox*/_install/ rootfs

• Create directories and files
  

$ cd rootfs
$ mkdir etc etc/init.d dev proc sys

$ cd etc
$ vi inittab
::sysinit:/etc/init.d/rcS
::askfirst:/bin/sh
$ chmod 644 inittab

$ cd init.d
$ vi rcS
#! /bin/sh
mount -a
$ chmod 744 rcS

$ cd ..
$ vi fstab
proc /proc proc defaults 0 0
$ chmod 644 fstab
$ cd ../..

• Unmount disk image
  

$ sudo umount rootfs

• Run in QEMU
  

$ qemu -hda rootfs.img -m 1024