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I have Ubuntu 20.04 installed as dual boot together with Windows 10. Until 1-2 weeks ago in the startup grub menu it listed Ubuntu together with Windows 10. But now it only shows Ubuntu on the startup.

I tried sudo update-grub command, checking the UEFI boot, and various solution on other threads, but seems nothing works..

1 Answer 1

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In the map /etc/grub.d/proxifiedScripts you should have a script (file) called OS Prober. If you don't have that file make it (as root). This is the code:
`

#! /bin/sh
set -e

# grub-mkconfig helper script.
# Copyright (C) 2006,2007,2008,2009  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/>.

prefix="/usr"
exec_prefix="/usr"
datarootdir="/usr/share"
quick_boot="1"

export TEXTDOMAIN=grub
export TEXTDOMAINDIR="${datarootdir}/locale"

. "$pkgdatadir/grub-mkconfig_lib"

found_other_os=

adjust_timeout () {
  if [ "$quick_boot" = 1 ] && [ "x${found_other_os}" != "x" ]; then
    cat << EOF
set timeout_style=menu
if [ "\${timeout}" = 0 ]; then
  set timeout=10
fi
EOF
  fi
}

if [ "x${GRUB_DISABLE_OS_PROBER}" = "xtrue" ]; then
  exit 0
fi

if [ -z "`which os-prober 2> /dev/null`" ] || [ -z "`which linux-boot-prober 2> /dev/null`" ] ; then
  # missing os-prober and/or linux-boot-prober
  exit 0
fi

OSPROBED="`os-prober | tr ' ' '^' | paste -s -d ' '`"
if [ -z "${OSPROBED}" ] ; then
  # empty os-prober output, nothing doing
  exit 0
fi

osx_entry() {
    found_other_os=1
    if [ x$2 = x32 ]; then
        # TRANSLATORS: it refers to kernel architecture (32-bit)
    bitstr="$(gettext "(32-bit)")"
    else
        # TRANSLATORS: it refers to kernel architecture (64-bit)
    bitstr="$(gettext "(64-bit)")"
    fi
    # TRANSLATORS: it refers on the OS residing on device %s
    onstr="$(gettext_printf "(on %s)" "${DEVICE}")"
        cat << EOF
menuentry '$(echo "${LONGNAME} $bitstr $onstr" | grub_quote)' --class osx --class darwin --class os \$menuentry_id_option 'osprober-xnu-$2-$(grub_get_device_id "${DEVICE}")'  {
EOF
    save_default_entry | grub_add_tab
    prepare_grub_to_access_device ${DEVICE} | grub_add_tab
    cat << EOF
        load_video
        set do_resume=0
        if [ /var/vm/sleepimage -nt10 / ]; then
           if xnu_resume /var/vm/sleepimage; then
             set do_resume=1
           fi
        fi
        if [ \$do_resume = 0 ]; then
           xnu_uuid ${OSXUUID} uuid
           if [ -f /Extra/DSDT.aml ]; then
              acpi -e /Extra/DSDT.aml
           fi
           if [ /kernelcache -nt /System/Library/Extensions ]; then
              $1 /kernelcache boot-uuid=\${uuid} rd=*uuid
           elif [ -f /System/Library/Kernels/kernel ]; then
              $1 /System/Library/Kernels/kernel boot-uuid=\${uuid} rd=*uuid
              xnu_kextdir /System/Library/Extensions
           else
              $1 /mach_kernel boot-uuid=\${uuid} rd=*uuid
              if [ /System/Library/Extensions.mkext -nt /System/Library/Extensions ]; then
                xnu_mkext /System/Library/Extensions.mkext
              else
                xnu_kextdir /System/Library/Extensions
              fi
           fi
           if [ -f /Extra/Extensions.mkext ]; then
              xnu_mkext /Extra/Extensions.mkext
           fi
           if [ -d /Extra/Extensions ]; then
              xnu_kextdir /Extra/Extensions
           fi
           if [ -f /Extra/devprop.bin ]; then
              xnu_devprop_load /Extra/devprop.bin
           fi
           if [ -f /Extra/splash.jpg ]; then
              insmod jpeg
              xnu_splash /Extra/splash.jpg
           fi
           if [ -f /Extra/splash.png ]; then
              insmod png
              xnu_splash /Extra/splash.png
           fi
           if [ -f /Extra/splash.tga ]; then
              insmod tga
              xnu_splash /Extra/splash.tga
           fi
        fi
}
EOF
}

used_osprober_linux_ids=

wubi=

for OS in ${OSPROBED} ; do
  DEVICE="`echo ${OS} | cut -d ':' -f 1`"
  LONGNAME="`echo ${OS} | cut -d ':' -f 2 | tr '^' ' '`"
  LABEL="`echo ${OS} | cut -d ':' -f 3 | tr '^' ' '`"
  BOOT="`echo ${OS} | cut -d ':' -f 4`"
  if UUID="`${grub_probe} --target=fs_uuid --device ${DEVICE%@*}`"; then
    EXPUUID="$UUID"

    if [ x"${DEVICE#*@}" != x ] ; then
      EXPUUID="${EXPUUID}@${DEVICE#*@}"
    fi

    if [ "x${GRUB_OS_PROBER_SKIP_LIST}" != "x" ] && [ "x`echo ${GRUB_OS_PROBER_SKIP_LIST} | grep -i -e '\b'${EXPUUID}'\b'`" != "x" ] ; then
      echo "Skipped ${LONGNAME} on ${DEVICE} by user request." >&2
      continue
    fi
    fi

    BTRFS="`echo ${OS} | cut -d ':' -f 5`"
    if [ "x$BTRFS" = "xbtrfs" ]; then
    BTRFSuuid="`echo ${OS} | cut -d ':' -f 6`"
    BTRFSsubvol="`echo ${OS} | cut -d ':' -f 7`"
    fi

    if [ -z "${LONGNAME}" ] ; then
    LONGNAME="${LABEL}"
    fi

    # os-prober returns text string followed by optional counter
    CLASS="--class $(echo "${LABEL}" | LC_ALL=C sed 's,[[:digit:]]*$,,' | cut     -d' ' -f1 | tr 'A-Z' 'a-z' | LC_ALL=C sed 's,[^[:alnum:]_],_,g')"

    gettext_printf "Found %s on %s\n" "${LONGNAME}" "${DEVICE}" >&2

    case ${BOOT} in
    chain)

      case ${LONGNAME} in
    Windows*)
      if [ -z "$wubi" ]; then
        if [ -x /usr/share/lupin-support/grub-mkimage ] && \
           /usr/share/lupin-support/grub-mkimage --test; then
          wubi=yes
        else
          wubi=no
        fi
      fi
      if [ "$wubi" = yes ]; then
        echo "Skipping ${LONGNAME} on Wubi system" >&2
        continue
      fi
      ;;
      esac

      found_other_os=1
      onstr="$(gettext_printf "(on %s)" "${DEVICE}")"
      cat << EOF
    menuentry '$(echo "${LONGNAME} $onstr" | grub_quote)' $CLASS --class os \$menuentry_id_option 'osprober-chain-$(grub_get_device_id "${DEVICE}")' {
    EOF
      save_default_entry | grub_add_tab
      prepare_grub_to_access_device ${DEVICE} | grub_add_tab

      if [ x"`${grub_probe} --device ${DEVICE} --target=partmap`" = xmsdos ];     then
      cat << EOF
    parttool \${root} hidden-
    EOF
      fi

      case ${LONGNAME} in
    Windows\ Vista*|Windows\ 7*|Windows\ Server\ 2008*)
    ;;
    *)
      cat << EOF
    drivemap -s (hd0) \${root}
EOF
    ;;
      esac

      cat <<EOF
    chainloader +1
}
EOF
    ;;
    efi)

    found_other_os=1
    EFIPATH=${DEVICE#*@}
    DEVICE=${DEVICE%@*}
    onstr="$(gettext_printf "(on %s)" "${DEVICE}")"
      cat << EOF
menuentry '$(echo "${LONGNAME} $onstr" | grub_quote)' $CLASS --class os \$menuentry_id_option 'osprober-efi-$(grub_get_device_id "${DEVICE}")' {
EOF
      save_default_entry | sed -e "s/^/\t/"
      prepare_grub_to_access_device ${DEVICE} | sed -e "s/^/\t/"

      cat <<EOF
    chainloader ${EFIPATH}
}
EOF
    ;;
    linux)
      if [ "x$BTRFS" = "xbtrfs" ]; then
         LINUXPROBED="`linux-boot-prober btrfs ${BTRFSuuid} ${BTRFSsubvol}  2> /dev/null | tr ' ' '^' | paste -s -d ' '`"
      else
         LINUXPROBED="`linux-boot-prober ${DEVICE} 2> /dev/null | tr ' ' '^' | paste -s -d ' '`"
      fi
      prepare_boot_cache=
      boot_device_id=
      is_top_level=true
      title_correction_code=
      OS="${LONGNAME}"

      for LINUX in ${LINUXPROBED} ; do
        LROOT="`echo ${LINUX} | cut -d ':' -f 1`"
        LBOOT="`echo ${LINUX} | cut -d ':' -f 2`"
        LLABEL="`echo ${LINUX} | cut -d ':' -f 3 | tr '^' ' '`"
        LKERNEL="`echo ${LINUX} | cut -d ':' -f 4`"
        LINITRD="`echo ${LINUX} | cut -d ':' -f 5`"
        LPARAMS="`echo ${LINUX} | cut -d ':' -f 6- | tr '^' ' '`"

        if [ -z "${LLABEL}" ] ; then
          LLABEL="${LONGNAME}"
        fi

    if [ "${LROOT}" != "${LBOOT}" ]; then
      LKERNEL="${LKERNEL#/boot}"
      LINITRD="${LINITRD#/boot}"
    fi

    if [ -z "${prepare_boot_cache}" ]; then
      prepare_boot_cache="$(prepare_grub_to_access_device ${LBOOT} | grub_add_tab)"
      [ "${prepare_boot_cache}" ] || continue
    fi

    found_other_os=1
    onstr="$(gettext_printf "(on %s)" "${DEVICE}")"
    recovery_params="$(echo "${LPARAMS}" | grep 'single\|recovery')" || true
    counter=1
    while echo "$used_osprober_linux_ids" | grep 'osprober-gnulinux-$LKERNEL-${recovery_params}-$counter-$boot_device_id' > /dev/null; do
        counter=$((counter+1));
    done
    if [ -z "$boot_device_id" ]; then
        boot_device_id="$(grub_get_device_id "${DEVICE}")"
    fi
    used_osprober_linux_ids="$used_osprober_linux_ids 'osprober-gnulinux-$LKERNEL-${recovery_params}-$counter-$boot_device_id'"

    if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xy ]; then
            cat << EOF
menuentry '$(echo "$OS $onstr" | grub_quote)' $CLASS --class gnu-linux --class gnu --class os \$menuentry_id_option 'osprober-gnulinux-simple-$boot_device_id' {
EOF
        save_default_entry | grub_add_tab
        printf '%s\n' "${prepare_boot_cache}"
        cat <<  EOF
    linux ${LKERNEL} ${LPARAMS}
EOF
            if [ -n "${LINITRD}" ] ; then
          cat << EOF
    initrd ${LINITRD}
EOF
            fi
        cat << EOF
}
EOF
        echo "submenu '$(gettext_printf "Advanced options for %s" "${OS} $onstr" | grub_quote)' \$menuentry_id_option 'osprober-gnulinux-advanced-$boot_device_id' {"
        is_top_level=false
    fi
    title="${LLABEL} $onstr"
        cat << EOF
    menuentry '$(echo "$title" | grub_quote)' --class gnu-linux --class gnu --class os \$menuentry_id_option 'osprober-gnulinux-$LKERNEL-${recovery_params}-$boot_device_id' {
EOF
    save_default_entry | sed -e "s/^/$grub_tab$grub_tab/"
    printf '%s\n' "${prepare_boot_cache}" | grub_add_tab
    cat <<  EOF
        linux ${LKERNEL} ${LPARAMS}
EOF
        if [ -n "${LINITRD}" ] ; then
            cat << EOF
        initrd ${LINITRD}
EOF
        fi
        cat << EOF
    }
EOF
    if [ x"$title" = x"$GRUB_ACTUAL_DEFAULT" ] || [ x"Previous Linux versions>$title" = x"$GRUB_ACTUAL_DEFAULT" ]; then
        replacement_title="$(echo "Advanced options for ${OS} $onstr" | sed 's,>,>>,g')>$(echo "$title" | sed 's,>,>>,g')"
        quoted="$(echo "$GRUB_ACTUAL_DEFAULT" | grub_quote)"
        title_correction_code="${title_correction_code}if [ \"x\$default\" = '$quoted' ]; then default='$(echo "$replacement_title" | grub_quote)'; fi;"
        grub_warn "$(gettext_printf "Please don't use old title \`%s' for GRUB_DEFAULT, use \`%s' (for versions before 2.00) or \`%s' (for 2.00 or later)" "$GRUB_ACTUAL_DEFAULT" "$replacement_title" "gnulinux-advanced-$boot_device_id>gnulinux-$version-$type-$boot_device_id")"
    fi
      done
      if [ x"$is_top_level" != xtrue ]; then
      echo '}'
      fi
      echo "$title_correction_code"
    ;;
    macosx)
      if [ "${UUID}" ]; then
    OSXUUID="${UUID}"
    osx_entry xnu_kernel 32
    osx_entry xnu_kernel64 64
      fi
    ;;
    hurd)
      found_other_os=1
      onstr="$(gettext_printf "(on %s)" "${DEVICE}")"
      cat << EOF
menuentry '$(echo "${LONGNAME} $onstr" | grub_quote)' --class hurd --class gnu --class os \$menuentry_id_option 'osprober-gnuhurd-/boot/gnumach.gz-false-$(grub_get_device_id "${DEVICE}")' {
EOF
      save_default_entry | grub_add_tab
      prepare_grub_to_access_device ${DEVICE} | grub_add_tab
      grub_device="`${grub_probe} --device ${DEVICE} --target=drive`"
      mach_device="`echo "${grub_device}" | sed -e 's/(\(hd.*\),msdos\(.*\))/\1s\2/'`"
      grub_fs="`${grub_probe} --device ${DEVICE} --target=fs`"
      case "${grub_fs}" in
    *fs)    hurd_fs="${grub_fs}" ;;
    *)  hurd_fs="${grub_fs}fs" ;;
      esac
      cat << EOF
    multiboot /boot/gnumach.gz root=device:${mach_device}
    module /hurd/${hurd_fs}.static ${hurd_fs} --readonly \\
            --multiboot-command-line='\${kernel-command-line}' \\
            --host-priv-port='\${host-port}' \\
            --device-master-port='\${device-port}' \\
            --exec-server-task='\${exec-task}' -T typed '\${root}' \\
            '\$(task-create)' '\$(task-resume)'
    module /lib/ld.so.1 exec /hurd/exec '\$(exec-task=task-create)'
}
EOF
    ;;
    minix)
      cat << EOF
menuentry "${LONGNAME} (on ${DEVICE}, Multiboot)" {
EOF
         save_default_entry | sed -e "s/^/\t/"
         prepare_grub_to_access_device ${DEVICE} | sed -e "s/^/\t/"
     cat << EOF
    multiboot /boot/image_latest
}
EOF
    ;;
    *)
      # TRANSLATORS: %s is replaced by OS name.
      gettext_printf "%s is not yet supported by grub-mkconfig.\n" "  ${LONGNAME}" >&2
    ;;
  esac
done

adjust_timeout
'


Then do a sudo update-grub in the terminal. Then you should have your Windows entry back in the grub-menu. If this doesn't work there is another problem.

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