setup_hook.sh

#!/bin/bash

while read line
do
        echo $line > /tmp/myoutput
done < /dev/stdin

mkdir -p /var/log/journal/9876
mkdir -p /busybox/var/log/journal/9876

mount --bind /var/log/journal/9876 /busybox/var/log/journal/9876

mkdir -p /tmp/busybox/etc/
echo "9876" > /tmp/busybox/etc/machine-id
touch /busybox/etc/machine-id

mount --bind /tmp/busybox/etc/machine-id /busybox/etc/machine-id


echo "DONE"

You need to mount tmpfs at /run and /tmp, also, and we probably want to tar up the underlying layer.

Something like this untested snippet.

tar -xf  /tmp/run.tgz /busybox/run
mount -o tmpfs /busybox/run
tar cf /tmp/run.tgz -C /busybox/run .