docker2vm.sh

set -ve

OUTFILE=/tmp/disk
CONTAINER_NAME=alpine-x86-full

dd if=/dev/zero of=$OUTFILE bs=1k count=1M

(
echo o # Create a new empty DOS partition table
echo n # Add a new partition
echo p # Primary partition
echo 1 # Partition number
echo 2048 # First sector
echo   # Last sector (Accept default: varies)
echo a # make bootable
echo w # Write changes
echo q # quit
) | fdisk $OUTFILE

# 1048576 is 2048 (first sector) * 512 (sector size)
mkfs.ext4 -F -E offset=1048576 $OUTFILE

kpartx -a -v $OUTFILE
function finish_kpartx {
    kpartx -d $OUTFILE
}
trap finish_kpartx EXIT

# XXX: Assumes loop0

mount /dev/mapper/loop0p1 /mnt
function finish_mount {
    umount /mnt
    finish_kpartx
}
trap finish_mount EXIT

docker export $CONTAINER_NAME | tar -xvC /mnt/

grub-install --recheck --target=i386-pc --locales= --themes= --fonts= --root-directory /mnt/ /dev/loop0

cat > /mnt/boot/grub/grub.cfg << 'EOF'
set root='hd0' # XXX: I believe this has no significance, but is required to exist by grub

set timeout_style=menu
set timeout=0

menuentry 'Linux' {
    #insmod ext2
    #insmod gzio
    #insmod fat
    set root='hd0,msdos1'

    echo      'Loading Linux linux ...'
    linux    /boot/vmlinuz nosplash debug verbose rw root=/dev/sda1 rootfstype=ext4
    #linux     /boot/vmlinuz-virthardened nosplash debug verbose rw root=/dev/sda1 rootfstype=ext4

    echo      'Loading initial ramdisk ...'
    initrd   /boot/initramfs-vanilla
    #initrd    /boot/initramfs-virthardened
}
EOF

# sync should only necessary if the disk is left mounted, but we'll leave it
# here in case something goes wrong
sync

Dockerfile

FROM i386/alpine:latest

# https://wiki.gentoo.org/wiki/OpenRC/Baselayout_1_to_2_migration#Boot_runlevel
# https://wiki.alpinelinux.org/wiki/Installing_Alpine_Linux_in_a_chroot#Entering_your_chroot

RUN apk update && \
    apk upgrade && \
    apk add --no-cache linux-vanilla vim openrc && \
    rc-update add devfs sysinit && \
    rc-update add root boot && \
    rc-update add mtab boot && \
    rc-update add mount-ro shutdown && \
    rc-update add killprocs shutdown && \
    echo 'rc_sys=""' >> /etc/rc.conf

    #rc-update add mdev sysinit && \

COPY motd issue inittab fstab /etc/

fstab

/dev/sda1        /           ext4     rw,relatime,data=ordered    0 0
tmpfs            /tmp        tmpfs    nodev,nosuid                0 0

inittab

# /etc/inittab

::sysinit:/sbin/openrc sysinit
::sysinit:/sbin/openrc boot
::wait:/sbin/openrc default

# Set up a couple of getty's
tty1::respawn:/bin/sh
tty2::respawn:/sbin/getty 38400 tty2
tty3::respawn:/sbin/getty 38400 tty3
tty4::respawn:/sbin/getty 38400 tty4
tty5::respawn:/sbin/getty 38400 tty5
tty6::respawn:/sbin/getty 38400 tty6

# Put a getty on the serial port
#ttyS0::respawn:/sbin/getty -L ttyS0 115200 vt100
ttyS0::respawn:/bin/sh

# Stuff to do for the 3-finger salute
::ctrlaltdel:/sbin/reboot

# Stuff to do before rebooting
::shutdown:/sbin/openrc shutdown