En regardant un peu les scripts dans /etc/grub.d je vois dans 10_linux les lignes suivantes :
case x"$GRUBFS" in
xbtrfs)
rootsubvol="`make_system_path_relative_to_its_root /`"
rootsubvol="${rootsubvol#/}"
if [ "x${rootsubvol}" != x ]; then
GRUB_CMDLINE_LINUX="rootflags=subvol=${rootsubvol} ${GRUB_CMDLINE_LINUX}"
fi;;
xzfs)
rpool=`${grub_probe} --device ${GRUB_DEVICE} --target=fs_label 2>/dev/null || true`
bootfs="`make_system_path_relative_to_its_root / | sed -e "s,@$,,"`"
LINUX_ROOT_DEVICE="ZFS=${rpool}${bootfs}"
;;
esac
et
if [ "x${GRUB_DISABLE_SUBMENU}" = x ]; then
if [ "x$is_first_entry" = xtrue ]; then
linux_entry "${OS}" "${version}" simple \
"${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_LINUX_DEFAULT}"
submenu_indentation="$grub_tab"
if [ -z "$boot_device_id" ]; then
boot_device_id="$(grub_get_device_id "${GRUB_DEVICE}")"
fi
# TRANSLATORS: %s is replaced with an OS name
echo "submenu '$(gettext_printf "Advanced options for %s" "${OS}" | grub_quote)' \$menuentry_id_option 'gnulinux-advanced-$boot_device_id' {"
fi
fi
linux_entry "${OS}" "${version}" advanced \
"${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_LINUX_DEFAULT}"
if [ "x${GRUB_DISABLE_RECOVERY}" != "xtrue" ]; then
linux_entry "${OS}" "${version}" recovery \
"single ${GRUB_CMDLINE_LINUX}"
fi
C'est peut-çetre ce script qui génère GRUB_CMDLINE_LINUX.
