Linux bootable disk image using EXTLINUX, debootstrap

Steps to create a bootable disk image using EXTLINUX, debootstrap, Linux kernel and run using QEMU

• Create disk image

$ dd if=/dev/zero of=rootfs.img bs=1M count=2560

• Create 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

• Run debootstrap

$ sudo debootstrap --arch i386 intrepid rootfs

• Copy Linux kernel and initial ramdisk to boot directory
  

$ cp vmlinuz rootfs/boot
$ cp initrd.img rootfs/boot

• Install EXTLINUX bootloader
  

$ extlinux --install rootfs/boot
$ vi rootfs/boot/extlinux.conf
default linux
timeout 10
prompt 1

label linux
kernel /boot/vmlinuz
append initrd=/boot/initrd.img root=/dev/sda clocksource=kvm-clock

• Unmount disk image

$ sudo umount rootfs

• Run in QEMU
  

$ qemu -hda rootfs.img -m 1024