generates a squashfs from a docker image

docker2squash.sh

#!/usr/bin/fakeroot /bin/bash
set -o errexit
set -o nounset
set -o pipefail
OUTFILE=$2.squashfs
TMPDIR=$(mktemp -d -p .)

cleanup() {
  rm -fr $TMPDIR
}

trap cleanup EXIT

CONTAINER=$(docker create $1)
docker export $CONTAINER | tar -C $TMPDIR -p -s --same-owner -xv
docker rm $CONTAINER
mksquashfs $TMPDIR $OUTFILE -info -processors 1 -noappend -comp xz -Xdict-size 100%