I've pasted the content of /usr/share/grub/grub-mkconfig_lib underneath (pastebin was deleted as apparent from comment below). You can download it and place it in appropriate place, then retry.
Also, look for the file /usr/lib/grub/grub-mkconfig_lib. Generally, it's a symbolic link to /usr/share/grub/grub-mkconfig_lib. But do check if the original file is there. If in your case /usr/lib/grub/grub-mkconfig_lib is the original file then open the file /etc/grub.d/10_linux and change its 21st line from datarootdir="${prefix}/share" to datarootdir="${prefix}/lib" then complete the upgrade.
# Helper library for grub-mkconfig
# Copyright (C) 2007,2008,2009,2010 Free Software Foundation, Inc.
#
# GRUB is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# GRUB is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with GRUB. If not, see <http://www.gnu.org/licenses/>.
transform="s,x,x,"
prefix="/usr"
exec_prefix="${prefix}"
datarootdir="${prefix}/share"
datadir="${datarootdir}"
bindir="${exec_prefix}/bin"
sbindir="${exec_prefix}/sbin"
pkgdatadir="${datadir}/grub"
if test "x$grub_probe" = x; then
grub_probe="${sbindir}/`echo grub-probe | sed "${transform}"`"
fi
if test "x$grub_mkrelpath" = x; then
grub_mkrelpath="${bindir}/`echo grub-mkrelpath | sed "${transform}"`"
fi
if which gettext >/dev/null 2>/dev/null; then
:
else
gettext () {
printf "%s" "$@"
}
fi
grub_warn ()
{
echo "$(gettext "Warning:")" "$@" >&2
}
make_system_path_relative_to_its_root ()
{
"${grub_mkrelpath}" "$1"
}
is_path_readable_by_grub ()
{
path="$1"
# abort if path doesn't exist
if test -e "$path" ; then : ;else
return 1
fi
# abort if file is in a filesystem we can't read
if "${grub_probe}" -t fs "$path" > /dev/null 2>&1 ; then : ; else
return 1
fi
# ... or if we can't figure out the abstraction module, for example if
# memberlist fails on an LVM volume group.
if abstractions="`"${grub_probe}" -t abstraction "$path"`" 2> /dev/null ; then
:
else
return 1
fi
if [ x$GRUB_CRYPTODISK_ENABLE = xy ]; then
return 0
fi
for abstraction in $abstractions; do
if [ "x$abstraction" = xcryptodisk ]; then
return 1
fi
done
return 0
}
convert_system_path_to_grub_path ()
{
path="$1"
grub_warn "convert_system_path_to_grub_path() is deprecated. Use prepare_grub_to_access_device() instead."
# abort if GRUB can't access the path
if is_path_readable_by_grub "${path}" ; then : ; else
return 1
fi
if drive="`"${grub_probe}" -t drive "$path"`" ; then : ; else
return 1
fi
if relative_path="`make_system_path_relative_to_its_root "$path"`" ; then : ; else
return 1
fi
echo "${drive}${relative_path}"
}
save_default_entry ()
{
if [ "x${GRUB_SAVEDEFAULT}" = "xtrue" ] ; then
cat << EOF
savedefault
EOF
fi
}
prepare_grub_to_access_device ()
{
device="$1"
partmap="`"${grub_probe}" --device "${device}" --target=partmap`"
for module in ${partmap} ; do
case "${module}" in
netbsd | openbsd)
echo "insmod part_bsd";;
*)
echo "insmod part_${module}";;
esac
done
loop_file=
case ${device} in
/dev/loop/*|/dev/loop[0-9])
grub_loop_device="${device#/dev/}"
loop_file=`losetup "${device}" | sed -e "s/^[^(]*(\([^)]\+\)).*/\1/"`
case $loop_file in
/dev/*) ;;
*)
loop_device="${device}"
device=`"${grub_probe}" --target=device "${loop_file}"` || return 0
;;
esac
;;
esac
if dmsetup status $device 2>/dev/null | grep -q 'crypt[[:space:]]$'; then
grub_warn \
"$device is a crypto device, which GRUB cannot read directly. Some" \
"necessary modules may be missing from /boot/grub/grub.cfg. You may" \
"need to list them in GRUB_PRELOAD_MODULES in /etc/default/grub. See" \
"http://bugs.debian.org/542165 for details."
return 0
fi
# Abstraction modules aren't auto-loaded.
abstraction="`"${grub_probe}" --device "${device}" --target=abstraction`"
for module in ${abstraction} ; do
echo "insmod ${module}"
done
fs="`"${grub_probe}" --device "${device}" --target=fs`"
for module in ${fs} ; do
echo "insmod ${module}"
done
if [ x$GRUB_CRYPTODISK_ENABLE = xy ]; then
for uuid in "`"${grub_probe}" --device "${device}" --target=cryptodisk_uuid`"; do
echo "cryptomount -u $uuid"
done
fi
# If there's a filesystem UUID that GRUB is capable of identifying, use it;
# otherwise set root as per value in device.map.
fs_hint="`"${grub_probe}" --device "${device}" --target=compatibility_hint`"
if [ "x$fs_hint" != x ]; then
echo "set root='$fs_hint'"
fi
if fs_uuid="`"${grub_probe}" --device "${device}" --target=fs_uuid 2> /dev/null`" ; then
hints="`"${grub_probe}" --device "${device}" --target=hints_string 2> /dev/null`" || hints=
echo "if [ x\$feature_platform_search_hint = xy ]; then"
echo " search --no-floppy --fs-uuid --set=root ${hints} ${fs_uuid}"
echo "else"
echo " search --no-floppy --fs-uuid --set=root ${fs_uuid}"
echo "fi"
fi
if [ "x${loop_file}" != x ]; then
loop_mountpoint="$(awk '"'${loop_file}'" ~ "^"$2 && $2 != "/" { print $2 }' /proc/mounts | tail -n1)"
if [ "x${loop_mountpoint}" != x ]; then
echo "loopback ${grub_loop_device} ${loop_file#$loop_mountpoint}"
echo "set root=(${grub_loop_device})"
fi
fi
}
grub_get_device_id ()
{
device="$1"
if fs_uuid="`"${grub_probe}" --device "${device}" --target=fs_uuid 2> /dev/null`" ; then
echo "$fs_uuid";
else
echo "$device"
fi
}
grub_file_is_not_garbage ()
{
if test -f "$1" ; then
case "$1" in
*.dpkg-*) return 1 ;; # debian dpkg
*.rpmsave|*.rpmnew) return 1 ;;
README*|*/README*) return 1 ;; # documentation
esac
else
return 1
fi
return 0
}
version_sort ()
{
case $version_sort_sort_has_v in
yes)
LC_ALL=C sort -V;;
no)
LC_ALL=C sort -n;;
*)
if sort -V </dev/null > /dev/null 2>&1; then
version_sort_sort_has_v=yes
LC_ALL=C sort -V
else
version_sort_sort_has_v=no
LC_ALL=C sort -n
fi;;
esac
}
version_test_numeric ()
{
version_test_numeric_a="$1"
version_test_numeric_cmp="$2"
version_test_numeric_b="$3"
if [ "$version_test_numeric_a" = "$version_test_numeric_b" ] ; then
case "$version_test_numeric_cmp" in
ge|eq|le) return 0 ;;
gt|lt) return 1 ;;
esac
fi
if [ "$version_test_numeric_cmp" = "lt" ] ; then
version_test_numeric_c="$version_test_numeric_a"
version_test_numeric_a="$version_test_numeric_b"
version_test_numeric_b="$version_test_numeric_c"
fi
if (echo "$version_test_numeric_a" ; echo "$version_test_numeric_b") | version_sort | head -n 1 | grep -qx "$version_test_numeric_b" ; then
return 0
else
return 1
fi
}
version_test_gt ()
{
version_test_gt_sedexp="s/[^-]*-//;s/[._-]\(pre\|rc\|test\|git\|old\|trunk\)/~\1/g"
version_test_gt_a="`echo "$1" | sed -e "$version_test_gt_sedexp"`"
version_test_gt_b="`echo "$2" | sed -e "$version_test_gt_sedexp"`"
version_test_gt_cmp=gt
if [ "x$version_test_gt_b" = "x" ] ; then
return 0
fi
case "$version_test_gt_a:$version_test_gt_b" in
*.old:*.old) ;;
*.old:*) version_test_gt_a="`echo -n "$version_test_gt_a" | sed -e 's/\.old$//'`" ; version_test_gt_cmp=gt ;;
*:*.old) version_test_gt_b="`echo -n "$version_test_gt_b" | sed -e 's/\.old$//'`" ; version_test_gt_cmp=ge ;;
esac
dpkg --compare-versions "$version_test_gt_a" "$version_test_gt_cmp" "$version_test_gt_b"
return "$?"
}
version_find_latest ()
{
version_find_latest_a=""
for i in "$@" ; do
if version_test_gt "$i" "$version_find_latest_a" ; then
version_find_latest_a="$i"
fi
done
echo "$version_find_latest_a"
}
# One layer of quotation is eaten by "" and the second by
# sed; so this turns ' into \'. Note that you must use the output of
# this function in a printf format string.
grub_quote () {
sed "s/'/'\\\\''/g"
}
gettext_quoted () {
gettext "$@" | grub_quote
}
# Run the first argument through gettext, and then pass that and all
# remaining arguments to printf. This is a useful abbreviation and tends to
# be easier to type.
gettext_printf () {
gettext_printf_format="$1"
shift
printf "$(gettext "$gettext_printf_format")" "$@"
}
uses_abstraction () {
device="$1"
abstraction="`"${grub_probe}" --device "${device}" --target=abstraction`"
for module in ${abstraction}; do
if test "x${module}" = "x$2"; then
return 0
fi
done
return 1
}
print_option_help () {
if test x$print_option_help_wc = x; then
if wc -L </dev/null > /dev/null 2>&1; then
print_option_help_wc=-L
elif wc -m </dev/null > /dev/null 2>&1; then
print_option_help_wc=-m
else
print_option_help_wc=-b
fi
fi
if test x$grub_have_fmt = x; then
if fmt -w 40 </dev/null > /dev/null 2>&1; then
grub_have_fmt=y;
else
grub_have_fmt=n;
fi
fi
print_option_help_lead=" $1"
print_option_help_lspace="$(echo "$print_option_help_lead" | wc $print_option_help_wc)"
print_option_help_fill="$((26 - print_option_help_lspace))"
printf "%s" "$print_option_help_lead"
if test $print_option_help_fill -le 0; then
print_option_help_nl=y
echo
else
print_option_help_i=0;
while test $print_option_help_i -lt $print_option_help_fill; do
printf " "
print_option_help_i=$((print_option_help_i+1))
done
print_option_help_nl=n
fi
if test x$grub_have_fmt = xy; then
print_option_help_split="$(echo "$2" | fmt -w 50)"
else
print_option_help_split="$2"
fi
if test x$print_option_help_nl = xy; then
echo "$print_option_help_split" | awk \
'{ print " " $0; }'
else
echo "$print_option_help_split" | awk 'BEGIN { n = 0 }
{ if (n == 1) print " " $0; else print $0; n = 1 ; }'
fi
}
grub_fmt () {
if test x$grub_have_fmt = x; then
if fmt -w 40 < /dev/null > /dev/null; then
grub_have_fmt=y;
else
grub_have_fmt=n;
fi
fi
if test x$grub_have_fmt = xy; then
fmt
else
cat
fi
}
/usr/share/grub/grub-mkconfig_libexist? Is it readable?