Yet another wrapper for the debootstrap(8) command

debimage.sh

#!/bin/sh
# vim: set expandtab tabstop=4 shiftwidth=4 softtabstop=4 textwidth=80:

# Mathias J. Hennig wrote this script and it's manual page. As long as
# you retain this notice you can do whatever you want with this stuff.
# If we meet some day, and you think this stuff is worth it, you can buy
# me a beer in return.

# Ensure the script to abort on error
set -e

DI_BASENAME="`basename \"$0\"`"
DI_FORMAT="raw"
DI_INCLUDE="less"
DI_MIRROR="http://httpredir.debian.org/debian"
DI_RELEASE="stable"
DI_SIZE="4g"
DI_TEMPDIR="/tmp/$DI_BASENAME.$$"
DI_TRAP="trap - EXIT"

# Print the usage section of the CLI help message
di_usage() {
    cat <<END
Usage:  $DI_BASENAME [-f ...] [-i ...] [-s ...] \$target
        $DI_BASENAME -h
        $DI_BASENAME -f qcow2 -i vim,less -r stable debian.img
END
}

# Print the options section of the CLI help message
di_options() {
    cat <<END
Options:

    -f \$format
        The image format to use. Translates directly to the -f option of the
        qemu-img(1) executable. Defaults to "$DI_FORMAT".

    -h  Print this message and exit gracefully.

    -i \$packages
        A comma-separated list of packages to include. Translates to the -i
        option of debootstrap(8). Multiple occurences are concatenated, and the
        default "$DI_INCLUDE" is always included.

    -m \$mirror
        The APT source URL to fetch packages from. Used as the mirror option of
        of debootstrap(8). Defaults to "$DI_MIRROR".

    -r \$release
        The release code or symbolic name of the release within the mirror. Used
        as debootstrap(8) suite option. Defaults to "$DI_RELEASE".

    -s \$size
        The intended size of the image. Translates directly to the size option
        of the qemu-img(1) create command. Defaults to "$DI_SIZE".
END
}

# Print the composed CLI help message
di_help() {
    di_usage
    echo
    di_options
    echo
}

# Echo commands before execution, optionally with super-user privileges (-s)
# or within the image chroot(8) directory (-c)
di_call() {
    case "$1" in
        -c) shift; set -- sudo chroot "$DI_TEMPDIR" "$@";;
        -s) shift; set -- sudo "$@";;
    esac
    echo "\$" "$@"
    "$@"
}

# Run commands when the script ends, in reversed definition order. Supports
# the -c and -s options analogous to di_call
di_trap() {
    DI_TRAP="di_call $@; $DI_TRAP"
}

# Register cleanup commands to be scheduled with di_trap
trap "set +e; eval \"\$DI_TRAP\"" EXIT HUP INT QUIT PIPE TERM

# Option handling using standard shell builtins
while POSIXLY_CORRECT=1 getopts "f:hi:m:r:s" DI_OPTION; do
    case "$DI_OPTION" in
        f)  shift; DI_FORMAT="$1";;
        h)  di_help; exit;;
        i)  shift; DI_INCLUDE="$DI_INCLUDE,$1";;
        m)  shift; DI_MIRROR="$1";;
        r)  shift; DI_RELEASE="$1";;
        s)  shift; DI_SIZE="$1";;
        ?)  echo; di_help >&2; exit 1;;
    esac
    shift
done

# Fetch the image's target path from the remaining arguments
case $# in
    1)  DI_NAME="$1";;
    0)  echo "Missing image target path" >&2; di_usage >&2; exit 1;;
    *)  echo "Too many arguments" >&2; di_usage >&2; exit 1;;
esac

# Create the actual image file
di_call qemu-img create -f "$DI_FORMAT" "$DI_NAME" "$DI_SIZE"

# Ensure the NBD module is loaded
di_call -s modprobe nbd max_part=16

# Find a network block device to use with the image
for DI_DEVICE in /dev/nbd?; do
    if di_call -s qemu-nbd -f "$DI_FORMAT" -c "$DI_DEVICE" "$DI_NAME"; then
        di_trap -s qemu-nbd -d $DI_DEVICE
        break
    else
        DI_DEVICE=
    fi
done

# Abort in case no network block device worked out
if [ -z "$DI_DEVICE" ]; then
    echo "Failed to connect /dev/nbd\* device" >&2
    exit 2
fi

# Format the image (TODO: make this customizable)
di_call -s sfdisk "$DI_DEVICE" <<END
;
END

# Format the partition (TODO: make this customizable)
di_call -s mkfs.ext4 -L CORE -O ^metadata_csum "${DI_DEVICE}p1"

# Capture the partition's UUID for later reference
DI_UUID=`sudo blkid -s UUID -o value "${DI_DEVICE}p1"`

# Create a temporary directory for mounting & chrooting the partition, and
# ensure it is removed when the script ends
di_call mkdir "$DI_TEMPDIR"
di_trap rmdir "$DI_TEMPDIR"

# Mount the network block device partitiom to the directory and
# ensure it is unmounted when the script ents
di_call -s mount "${DI_DEVICE}p1" "$DI_TEMPDIR"
di_trap -s umount "$DI_TEMPDIR"

# The actual invocation of debootstrap, may require future extension as well
di_call -s debootstrap --include="$DI_INCLUDE" "$DI_RELEASE" "$DI_TEMPDIR" "$DI_MIRROR"

# Extend /etc/fstab to include the root file system
di_call -s tee -a "$DI_TEMPDIR/etc/fstab" <<END
UUID=$DI_UUID	/	ext4	errors=remount-ro	0	1
END

# Extend /etc/network/interfaces to include eth0 (TODO: make DHCP optional)
di_call -s tee -a "$DI_TEMPDIR/etc/network/interfaces" <<END
auto eth0
iface eth0 inet dhcp
END

# Bind the device index for use within chroot later
di_call -s mount --bind /dev "$DI_TEMPDIR/dev"
di_trap -s umount "$DI_TEMPDIR/dev"

# Bind the process FS for use within the chroot
di_call -c mount -t proc none /proc
di_trap -c umount /proc

# Bind the system FS for use within the chroot
di_call -c mount -t sysfs none /sys
di_trap -c umount /sys

# TODO: Avoid the creation of a root password entirely!
di_call -c passwd root <<END
changeme
changeme
END

# Manually ensure the UUID device mapping to be present, in order to allow for
# grub(8) to use UUIDs within the grub.cfg
di_call -s partx "$DI_DEVICE"
di_call -s ln -s "../../`basename \"$DI_DEVICE\"`p1" "/dev/disk/by-uuid/$DI_UUID"
di_trap -s rm "/dev/disk/by-uuid/$DI_UUID"

# The APT run requires a set of environment variables one cannot pass directly
# to chroot(8), hence the sudo(8) style is used here with some code duplication
di_call -s LANG=C DEBIAN_FRONTEND=noninteractive \
    chroot "$DI_TEMPDIR" apt-get -y install linux-image-amd64 grub-pc

# Finally install and configure grub(8) with required moduled and support for
# the serial console (for initial login with KVM)
di_call -c grub-install "$DI_DEVICE" --modules "biosdisk part_msdos"
di_call -c sed -i 's/GRUB_CMDLINE_LINUX_DEFAULT="/\0console=ttyS0,115200 /' /etc/default/grub
di_call -c update-grub