This file is indexed.

/etc/grub.d/00_header is in grub-common 1.99-21ubuntu3.19.

This file is owned by root:root, with mode 0o755.

The actual contents of the file can be viewed below.

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#! /bin/sh
set -e

# grub-mkconfig helper script.
# Copyright (C) 2006,2007,2008,2009,2010  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"
locale_dir=`echo ${GRUB_PREFIX}/locale | sed ${transform}`
grub_lang=`echo $LANG | cut -d . -f 1`

. "${datarootdir}/grub/grub-mkconfig_lib"

# Do this as early as possible, since other commands might depend on it.
# (e.g. the `loadfont' command might need lvm or raid modules)
for i in ${GRUB_PRELOAD_MODULES} ; do
  echo "insmod $i"
done

if [ "x${GRUB_DEFAULT}" = "x" ] ; then GRUB_DEFAULT=0 ; fi
if [ "x${GRUB_DEFAULT}" = "xsaved" ] ; then GRUB_DEFAULT='${saved_entry}' ; fi
if [ "x${GRUB_TIMEOUT}" = "x" ] ; then GRUB_TIMEOUT=5 ; fi
if [ "x${GRUB_GFXMODE}" = "x" ] ; then GRUB_GFXMODE=auto ; fi

if [ "x${GRUB_DEFAULT_BUTTON}" = "x" ] ; then GRUB_DEFAULT_BUTTON="$GRUB_DEFAULT" ; fi
if [ "x${GRUB_DEFAULT_BUTTON}" = "xsaved" ] ; then GRUB_DEFAULT_BUTTON='${saved_entry}' ; fi
if [ "x${GRUB_TIMEOUT_BUTTON}" = "x" ] ; then GRUB_TIMEOUT_BUTTON="$GRUB_TIMEOUT" ; fi

cat << EOF
if [ -s \$prefix/grubenv ]; then
  set have_grubenv=true
  load_env
fi
EOF
if [ "x$GRUB_BUTTON_CMOS_ADDRESS" != "x" ]; then
    cat <<EOF
if cmostest $GRUB_BUTTON_CMOS_ADDRESS ; then
   set default="${GRUB_DEFAULT_BUTTON}"
else
   set default="${GRUB_DEFAULT}"
fi
EOF
else
    cat <<EOF
set default="${GRUB_DEFAULT}"
EOF
fi
cat <<EOF
if [ "\${prev_saved_entry}" ]; then
  set saved_entry="\${prev_saved_entry}"
  save_env saved_entry
  set prev_saved_entry=
  save_env prev_saved_entry
  set boot_once=true
fi

function savedefault {
  if [ -z "\${boot_once}" ]; then
    saved_entry="\${chosen}"
    save_env saved_entry
  fi
}

function recordfail {
  set recordfail=1
  if [ -n "\${have_grubenv}" ]; then if [ -z "\${boot_once}" ]; then save_env recordfail; fi; fi
}

function load_video {
EOF
if [ -n "${GRUB_VIDEO_BACKEND}" ]; then
    cat <<EOF
  insmod ${GRUB_VIDEO_BACKEND}
EOF
else
    # Insert all available backends; GRUB will use the most appropriate.
    have_video=0;
    for backend in $(cat "${GRUB_PREFIX}/video.lst"); do
	have_video=1;
	cat <<EOF
  insmod ${backend}
EOF
    done
    if [ x$have_video = x0 ]; then
	echo "true"
    fi
fi
cat <<EOF
}

EOF

serial=0;
gfxterm=0;
for x in ${GRUB_TERMINAL_INPUT} ${GRUB_TERMINAL_OUTPUT}; do
    if [ xserial = "x$x" ]; then
	serial=1;
    fi
    if [ xgfxterm = "x$x" ]; then
	gfxterm=1;
    fi
done

if [ "x$serial" = x1 ]; then
    if ! test -e "${GRUB_PREFIX}/serial.mod" ; then
	echo "Serial terminal not available on this platform." >&2 ; exit 1
    fi

    if [ "x${GRUB_SERIAL_COMMAND}" = "x" ] ; then
	grub_warn "Requested serial terminal but GRUB_SERIAL_COMMAND is unspecified. Default parameters will be used."
	GRUB_SERIAL_COMMAND=serial
    fi
    echo "${GRUB_SERIAL_COMMAND}"
fi

if [ "x$gfxterm" = x1 ]; then
    # Make the font accessible
    prepare_grub_to_access_device `${grub_probe} --target=device "${GRUB_FONT_PATH}"`

    cat << EOF
if loadfont `make_system_path_relative_to_its_root "${GRUB_FONT_PATH}"` ; then
  set gfxmode=${GRUB_GFXMODE}
  load_video
  insmod gfxterm
EOF

# Gettext variables and module
if [ "x${LANG}" != "xC" ] && [ -d "${locale_dir}" ] ; then
    prepare_grub_to_access_device $(${grub_probe} --target=device ${locale_dir}) | sed -e "s/^/  /"
  cat << EOF
  set locale_dir=(\$root)$(make_system_path_relative_to_its_root ${locale_dir})
  set lang=${grub_lang}
  insmod gettext
EOF
fi

cat <<EOF
fi
EOF
fi

case x${GRUB_TERMINAL_INPUT} in
  x)
    # Just use the native terminal
  ;;
  x*)
    cat << EOF
terminal_input ${GRUB_TERMINAL_INPUT}
EOF
  ;;
esac

case x${GRUB_TERMINAL_OUTPUT} in
  x)
    # Just use the native terminal
  ;;
  x*)
    cat << EOF
terminal_output ${GRUB_TERMINAL_OUTPUT}
EOF
  ;;
esac

if [ "x$gfxterm" = x1 ]; then
    if [ "x$GRUB_THEME" != x ] && [ -f "$GRUB_THEME" ] \
	&& is_path_readable_by_grub "$GRUB_THEME"; then
	echo "Found theme: $GRUB_THEME" >&2
	prepare_grub_to_access_device `${grub_probe} --target=device "$GRUB_THEME"`
	cat << EOF
insmod gfxmenu
EOF
	themedir="`dirname "$GRUB_THEME"`"
	for x in "$themedir"/*.pf2 "$themedir"/f/*.pf2; do
	    if [ -f "$x" ]; then
		cat << EOF
loadfont (\$root)`make_system_path_relative_to_its_root $x`
EOF
	    fi
	done
	if [ x"`echo "$themedir"/*.jpg`" != x"$themedir/*.jpg" ] || [ x"`echo "$themedir"/*.jpeg`" != x"$themedir/*.jpeg" ]; then
	    cat << EOF
insmod jpeg
EOF
	fi
	if [ x"`echo "$themedir"/*.png`" != x"$themedir/*.png" ]; then
	    cat << EOF
insmod png
EOF
	fi
	if [ x"`echo "$themedir"/*.tga`" != x"$themedir/*.tga" ]; then
	    cat << EOF
insmod tga
EOF
	fi
	    
	cat << EOF
set theme=(\$root)`make_system_path_relative_to_its_root $GRUB_THEME`
EOF
    elif [ "x$GRUB_BACKGROUND" != x ] && [ -f "$GRUB_BACKGROUND" ] \
	    && is_path_readable_by_grub "$GRUB_BACKGROUND"; then
	echo "Found background: $GRUB_BACKGROUND" >&2
	case "$GRUB_BACKGROUND" in 
	    *.png)         reader=png ;;
	    *.tga)         reader=tga ;;
	    *.jpg|*.jpeg)  reader=jpeg ;;
	    *)             echo "Unsupported image format" >&2; exit 1 ;;
	esac
	prepare_grub_to_access_device `${grub_probe} --target=device "$GRUB_BACKGROUND"`
	cat << EOF
insmod $reader
background_image -m stretch `make_system_path_relative_to_its_root "$GRUB_BACKGROUND"`
EOF
    fi
fi

make_timeout ()
{
    cat << EOF
if [ "\${recordfail}" = 1 ] ; then
  set timeout=${GRUB_RECORDFAIL_TIMEOUT:-30}
else
EOF
    if [ "x${1}${3}" != "x" ] ; then
	if [ "x${3}" != "x" ] ; then
	    timeout="${2}"
	    style="${3}"
	else
	    # Handle the deprecated GRUB_HIDDEN_TIMEOUT scheme.
	    timeout="${1}"
	    if [ "x${2}" != "x0" ] ; then
		grub_warn "$(gettext "Setting GRUB_TIMEOUT to a non-zero value when GRUB_HIDDEN_TIMEOUT is set is no longer supported.")"
	    fi
	    if [ "x${GRUB_HIDDEN_TIMEOUT_QUIET}" = "xtrue" ] ; then
		style="hidden"
	    else
		style="countdown"
	    fi
	fi
	if [ "x${style}" = "xcountdown" ] ; then
	    verbose=" --verbose"
	else
	    verbose=
	fi
	cat << EOF
  if [ x\$feature_timeout_style = xy ] ; then
    set timeout_style=${style}
    set timeout=${timeout}
EOF
	if [ "x${style}" != "xmenu" ] ; then
	    cat << EOF
  # Fallback hidden-timeout code in case the timeout_style feature is
  # unavailable.
  elif sleep${verbose} --interruptible ${timeout} ; then
    set timeout=0
EOF
	fi
	cat << EOF
  fi
EOF
    else
	cat << EOF
  set timeout=${2}
EOF
    fi
    cat << EOF
fi
EOF
}

if [ "x$GRUB_BUTTON_CMOS_ADDRESS" != "x" ]; then
    cat <<EOF
if cmostest $GRUB_BUTTON_CMOS_ADDRESS ; then
EOF
make_timeout "${GRUB_HIDDEN_TIMEOUT_BUTTON}" "${GRUB_TIMEOUT_BUTTON}" "${GRUB_TIMEOUT_STYLE_BUTTON}"
echo else
make_timeout "${GRUB_HIDDEN_TIMEOUT}" "${GRUB_TIMEOUT}" "${GRUB_TIMEOUT_STYLE}"
echo fi
else
make_timeout "${GRUB_HIDDEN_TIMEOUT}" "${GRUB_TIMEOUT}" "${GRUB_TIMEOUT_STYLE}"
fi

if [ "x$GRUB_BUTTON_CMOS_ADDRESS" != "x" ] && [ "x$GRUB_BUTTON_CMOS_CLEAN" = "xyes" ]; then
    cat <<EOF
cmosclean $GRUB_BUTTON_CMOS_ADDRESS
EOF
fi

# Play an initial tune
if [ "x${GRUB_INIT_TUNE}" != "x" ] ; then
  echo "play ${GRUB_INIT_TUNE}"
fi

if [ "x${GRUB_BADRAM}" != "x" ] ; then
  echo "badram ${GRUB_BADRAM}"
fi