Daemonized processes inside the chroot cause image building to hang indefinitely

(This happened to me while performing a CFEngine bootstrap in a script while building the image which happens to start its own daemon processes, disregarding the init system and any policies.)

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For context, what I'm now doing is: config_space/scripts/ZDV/42-cfengine:

#!/bin/bash
set -ux
ROOTCMD="unshare --pid --fork --kill-child --mount-proc chroot $FAI_ROOT"
$ROOTCMD cf-agent -B config-01.zdv.uni-mainz.de
$ROOTCMD cf-agent -K -D bootstrap
$ROOTCMD cf-agent -K -D bootstrap

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My (updated) solution is to use the following in the script that does perform the problematic operations:

ROOTCMD="unshare --pid --fork --kill-child --mount-proc chroot $FAI_ROOT"

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My initial solution was to put something like this after the problematic script or in a finish hook:

PIDS="$(lsof -t +D $FAI_ROOT)"
if [[ -n ${PIDS} ]]; then
  for SIGNAL in TERM KILL; do
    kill -s ${SIGNAL} ${PIDS}
    sleep 1
  done
fi

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Now I have two questions:

• Do you think this would help others with similar problems if included in the Cloud images config_space or in FAI itself?
• Would you have come up with a better solution?