Comment 4 for bug 1741300

Verified. on fresh xenial guest in openstack. See below.

$ lsb_release -sc
xenial
$ cat /etc/cloud/build.info
build_name: server
serial: 20180126

$ wget "$url" --progress=dot:giga -O xenial-server-cloudimg-amd64-disk1.img

$ dpkg -S `which mount-image-callback`
cloud-image-utils: /usr/bin/mount-image-callback

$ dpkg-query --show cloud-image-utils
cloud-image-utils 0.27-0ubuntu25

$ sha256sum < xenial-server-cloudimg-amd64-disk1.img
da7a59cbaf43eaaa83ded0b0588bdcee4e722d9355bd6b9bfddd01b2e7e372e2 -

$ cp -a xenial-server-cloudimg-amd64-disk1.img disk.img

$ sudo mount-image-callback -v disk.img -- true
waiting on pidfile for /dev/nbd0 in /sys/block/nbd0/pid
connected disk.img (qcow2) to /dev/nbd0. waiting for device.
partitioned disk.
mounted /dev/nbd0p1 via qemu-nbd /dev/nbd0
invoking: MOUNTPOINT=/tmp/mount-image-callback.XRd6Rk/mp true
cmd returned 0. unmounting /tmp/mount-image-callback.XRd6Rk/mp

$ sudo mount-image-callback --read-only disk.img -- \
     sh -c 'cd $MOUNTPOINT && cat etc/cloud/build.info'
mount: /dev/nbd0p1 is write-protected, mounting read-only
build_name: server
serial: 20180126