Persisting a one-off hostname change

[Jason Heeris <jason.heeris@gmail.com>]

I have an image of a Debian Squeeze system that I want to put onto
multiple systems (flash-based disks for a single-board computer). I'd
like each system to have a different hostname, but have that hostname
persist across subsequent reboots.

My first thought was that I could remove "/etc/hostname" from the
image, and modify /etc/init.d/hostname.sh to something like:

    do_start () {
        if [ ! -f /etc/hostname ]; then
            RANDOM_MAGIC="$(cat /dev/urandom | tr -dc '0-9A-Z' | head -c 6)"
            echo "prefix-${RANDOM_MAGIC}" > /etc/hostname
        fi

        HOSTNAME="$(cat /etc/hostname)"

        [ "$VERBOSE" != no ] && log_action_begin_msg "Setting hostname
to '$HOSTNAME'"
        hostname "$HOSTNAME"
        ES=$?
        [ "$VERBOSE" != no ] && log_action_end_msg $ES
        exit $ES
    }

Then, upon the first boot AFTER imaging, this script would see that
there's no /etc/hostname, generate one, write the new value to the
file and I'd be done.

The problem is that the root FS is not mounted writeable at this stage
of the boot process! Is there another point in the rcS.d script
sequence where I can persist the current hostname? After
S10mountall.sh? Or is there a better way to achieve this that I'm
missing?

— Jason