mk-debian-image

#!/bin/bash
set -eu

# NOT FOR PRODUCTION USE
#
# This script shows how to prepare a bootable raw image
# from an appropriate docker image.
#
# For more information:
# https://github.com/0xef53/kvmrun/blob/master/scripts/README.md
#
# Dependencies: docker-ce, qemu-utils


declare DOCKER_IMAGE_TAG=""
declare GUEST_HOSTNAME=""
declare IMAGE_SIZE="2G"
declare IMAGE_FILE=""

declare TRAP_ACT=""

print_usage() {
    cat <<EOF
Usage:  ${0##*/} [OPTIONS]

    --t            docker image tag (latest, stretch, stretch-slim)
    --hostname     guest OS host name (will be generated if not set)
    --size         image file size (default: $IMAGE_SIZE)

Example:

    ${0##*/} -t stretch-slim --hostname alice --size 5G

EOF
    exit 2
}


#
# CHECK ARGUMENTS
#

if [[ $# -eq 0 ]]; then
    print_usage
fi

TEMP=$(getopt -o t: --long hostname:,size: -n ${0##*/} -- "$@")
if [[ $? -ne 0 ]]; then
    print_usage
fi

eval set -- "$TEMP"

while : ; do
    case "$1" in
        -t)
            DOCKER_IMAGE_TAG="$2"
            IMAGE_FILE="debian-${DOCKER_IMAGE_TAG//_/-}.img"
            shift 2
        ;;
        --hostname)
            GUEST_HOSTNAME="$2"
            shift 2
        ;;
        --size)
            IMAGE_SIZE="$2"
            shift 2
        ;;
        --)
            shift; break
        ;;
        *)
            print_usage
        ;;
    esac
done

if [[ -z "$DOCKER_IMAGE_TAG" ]]; then
    echo "Error: undefined docker image tag" >&2
    echo "" >&2
    print_usage
fi


#
# MAIN
#

declare -r TMPTAG="$(mcookie | head -c7)"
declare -r TMPDIR="$(mktemp -d)"

TRAP_ACT="rm -Rf ${TMPDIR}; $TRAP_ACT"
trap "$TRAP_ACT" 0


echo "==> Creating the raw image file: $IMAGE_FILE"

qemu-img create -f raw "$IMAGE_FILE" "$IMAGE_SIZE"
printf 'n\np\n1\n\n+256M\na\nn\np\n2\n\n\nwri\n' | >/dev/null fdisk "$IMAGE_FILE" || :
fdisk -l "$IMAGE_FILE" | awk '{if($1~"^Device"){x=1};if(x==1){print $0}}'

declare -r LOOPDEV="$(losetup -P --show -f $IMAGE_FILE)"

TRAP_ACT="losetup -d ${LOOPDEV}; $TRAP_ACT"
trap "$TRAP_ACT" 0


echo "==> Building the rootfs from debian:${DOCKER_IMAGE_TAG} (this may take a while)"

cat > "${TMPDIR}/Dockerfile" <<EOF
FROM debian:${DOCKER_IMAGE_TAG}

ARG DEBIAN_FRONTEND=noninteractive

RUN set -ex \\
    && rm -f /etc/apt/apt.conf.d/docker-* \\
    && rm -f /etc/dpkg/dpkg.cfg.d/docker-*

RUN set -ex \\
    && sed -i /etc/apt/sources.list \\
        -e 's/\ main/ main contrib non-free/g' \\
    && apt-get update \\
    && apt-get --no-install-recommends --yes install \\
        systemd systemd-sysv libpam-systemd udev kmod procps locales cron man-db netbase ucf \\
        util-linux rsyslog acpid acpi-support-base file psmisc whois dialog \\
        haveged ca-certificates apt-transport-https \\
    \\
    && apt-get --no-install-recommends --yes install \\
        grub2 initramfs-tools linux-image-amd64 \\
    \\
    && apt-get clean

CMD ["/bin/bash"]
EOF

docker build -q -t "debian:${TMPTAG}" "$TMPDIR" -f "${TMPDIR}/Dockerfile"

TRAP_ACT="docker image rm debian:${TMPTAG}; $TRAP_ACT"
trap "$TRAP_ACT" 0

>/dev/null docker container run --rm \
    --device "${LOOPDEV}p2" \
    "debian:${TMPTAG}" \
    mkfs.ext4 "${LOOPDEV}p2"

declare -r ROOTFS_UUID="$(blkid -s UUID -ovalue ${LOOPDEV}p2)"

install -d "${TMPDIR}/rootfs"
mount "${LOOPDEV}p2" "${TMPDIR}/rootfs"

TRAP_ACT=" 2>/dev/null umount ${TMPDIR}/rootfs || : ; $TRAP_ACT"
trap "$TRAP_ACT" 0

declare -r CID="$(docker container create debian:${TMPTAG})"

docker export ${CID} | tar -x -C "${TMPDIR}/rootfs"

umount "${TMPDIR}/rootfs"

if [[ -z "$GUEST_HOSTNAME" ]]; then
    GUEST_HOSTNAME="$(docker ps -a --filter id=$CID --format '{{.Names}}')"
    GUEST_HOSTNAME="${GUEST_HOSTNAME//_/-}"
fi

>/dev/null docker container rm --force "$CID"

echo


echo "==> Configuring the bootloader and guest OS"

declare -r GUEST_ROOT_PASSWORD="$(mcookie | head -c15)"

cat > "${TMPDIR}/configure_boot" <<EOF
#!/bin/bash
set -eu

mkfs.ext3 ${LOOPDEV}p1

install -d /mnt /mnt/boot
mount ${LOOPDEV}p2 /mnt
mount ${LOOPDEV}p1 /mnt/boot

cp -a /boot/. /mnt/boot

echo '(hd0) ${LOOPDEV}' >/mnt/boot/grub/device.map

install -d /mnt/dev /mnt/proc /mnt/sys
mount --bind /dev /mnt/dev
mount --bind /proc /mnt/proc
mount --bind /sys /mnt/sys

chroot /mnt \\
    grub-mkconfig -o /boot/grub/grub.cfg

sed -i /mnt/boot/grub/grub.cfg \\
    -e '/linux.*vmlinuz/s/ root=[^\ ]*/ root=UUID=${ROOTFS_UUID}/g'

chroot /mnt \\
    grub-install \\
        --no-floppy \\
        --modules='ext2 part_msdos' \\
        --skip-fs-probe \\
        $LOOPDEV

chroot /mnt \\
    /bin/bash -c 'echo root:${GUEST_ROOT_PASSWORD} | chpasswd --crypt-method=SHA512'

echo '$GUEST_HOSTNAME' >/mnt/etc/hostname

cat >/mnt/etc/fstab <<FSTAB
UUID=$ROOTFS_UUID   /       ext4    errors=remount-ro  0  1
UUID=\$(blkid -s UUID -ovalue ${LOOPDEV}p1)  /boot   ext4    defaults           0  2
FSTAB

exit 0
EOF

chmod 0755 "${TMPDIR}/configure_boot"

>/dev/null docker container run --rm -i \
    --privileged \
    --cap-add SYS_ADMIN \
    --device "${LOOPDEV}" \
    --device "${LOOPDEV}p1" \
    --device "${LOOPDEV}p2" \
    --volume "${TMPDIR}:/BUILD" \
    "debian:${TMPTAG}" \
    '/BUILD/configure_boot'

echo


echo "==> Successfully completed"
echo "Root password:  $GUEST_ROOT_PASSWORD"
echo

exit 0