/usr/sbin/oem-config-prepare is in oem-config 2.18.7.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 | #! /bin/sh
set -e
# Try to detect which frontend will be used by looking for a frontend
# module.
frontend=
for f in gtk_ui kde_ui debconf_ui; do
	if [ -f "/usr/lib/ubiquity/ubiquity/frontend/$f.py" ]; then
		frontend="$f"
		break
	fi
done
quiet=
if [ "$1" = --quiet ]; then
	quiet=1
	shift
fi
if [ "$(id -u)" = 0 ]; then
	# Machine-specific, so remove in case this system is going to be
	# cloned.  These will be regenerated on the first boot.
	rm -f /etc/udev/rules.d/70-persistent-cd.rules \
	      /etc/udev/rules.d/70-persistent-net.rules
	# Potentially sensitive.
	rm -f /home/oem/.ssh/known_hosts
	touch /var/lib/oem-config/run
else
	pkexec "$0" ${quiet:---quiet} "$@"
fi
if [ -z "$quiet" ]; then
	MESSAGE='oem-config will run the next time the system boots.'
	case $frontend in
		gtk_ui)
			if [ "$DISPLAY" ] && type zenity >/dev/null 2>&1; then
				zenity --title oem-config-prepare --info --text \
					"$MESSAGE"
				exit 0
			fi
			;;
		kde_ui)
			if [ "$DISPLAY" ] && type kdialog >/dev/null 2>&1; then
				kdialog --title oem-config-prepare --msgbox "$MESSAGE"
				exit 0
			fi
			;;
	esac
	echo "$MESSAGE"
fi
exit 0
 |