/usr/share/gdm/generate-config is in gdm3 3.28.0-0ubuntu1.
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  | #! /bin/sh
set -e
DEFAULTS_GENERATED=/var/lib/gdm3/greeter-dconf-defaults
DEFAULTS_DIR=/usr/share/gdm/dconf
if [ -d /var/lib/gdm3 ]; then
  needed=no
  if [ -f $DEFAULTS_GENERATED ]; then
    for f in \
        $DEFAULTS_DIR $DEFAULTS_DIR/*-settings \
        $DEFAULTS_DIR/locks $DEFAULTS_DIR/locks/*-locks \
        /etc/gdm3/greeter.dconf-defaults; do
      if [ "$f" -nt $DEFAULTS_GENERATED ]; then
        needed=yes
        break
      fi
    done
  else
    needed=yes
  fi
  if [ "$needed" = yes ]; then
    dconf compile $DEFAULTS_GENERATED $DEFAULTS_DIR
  fi
fi
for i in $(pidof dconf-service); do
  if [ "$(stat -c %U /proc/$i)" = gdm ]; then
    kill -HUP $i || true
  fi
done
exit 0
 |