Comment 2 for bug 1247905

WORKING SOLUTION
================

After encountering this problem, I developed a very simple solution:

nano /usr/sbin/grub-probe-overlay

-----[BEGIN]--------------------------------------------------------------
#!/bin/sh

ARGS=

for ARG in $@; do
 if [ "${ARG%%[!/]*}" = "/" ]; then

  OPTIONS=

  if FSTYPE=$( findmnt -n -o FSTYPE "$ARG" ); then
   if [ "$FSTYPE" = "overlay" ]; then
    OPTIONS=$(findmnt -n -o OPTIONS "$ARG")
   fi
  elif FSTYPE=$( findmnt -n -o FSTYPE / ); then
   if [ "$FSTYPE" = "overlay" ]; then
    OPTIONS=$(findmnt -n -o OPTIONS /)
   fi
  fi

  if LOWERDIR=$(echo "$OPTIONS" | grep -m 1 -oP 'lowerdir=\K[^,]+'); then
# echo "[DEBUG] Overlay filesystem detected \${ARG} --> \${LOWERDIR}\${ARG%*/}" 1>&2
   ARG="${LOWERDIR}${ARG%*/}"
  fi
 fi
 ARGS="$ARGS $ARG"
done

grub-probe-default $ARGS

exit $?
-----[END]----------------------------------------------------------------

mv /usr/sbin/grub-probe /usr/sbin/grub-probe-default

ln -s /usr/sbin/grub-probe-overlay /usr/sbin/grub-probe

OPTIONAL STEP:
==============

apt-mark hold grub-pc

NOTE: package name can also be "grub-efi-amd64" or "grub-efi-ia32" or something else, depending on what you use

PROS
====
- works perfectly with overlay filesystem
- shows a general solution (maybe someone can use it to fix the grub-probe source code)
- no patching of grub scripts required (some people tried patches as solution, but grub-probe is used in many grub scripts --> patching nightmare)

CONS
====
- grub-probe must be renamed (for this reason, I recommend that you set the status of your grub package to "hold")