diff --git a/cluster/apt.check.update.sh b/cluster/apt.check.update.sh
index 5ecb5fb..9596608 100755
--- a/cluster/apt.check.update.sh
+++ b/cluster/apt.check.update.sh
@@ -137,54 +137,51 @@ SGE Master (${sge_master_uri}:${sge_master_port}) is not reachable from this hos
 
 }
 # }}}
-is_apt_upgrade_absent() {                                       # {{{
+
+APT_PACKAGE_LIST_IS_UP_TO_DATE='false'
+ensure_apt_package_list_is_up_to_date()
+{
+	if [ "$APT_PACKAGE_LIST_IS_UP_TO_DATE" = 'false' ]
+	then
+		apt	update &> /dev/null
+		APT_PACKAGE_LIST_IS_UP_TO_DATE='true'
+	fi
+}
+
+
+get_num_outdated_packages()
+{
+	# ensure that the package list is up to date, because "apt list --upgradable" doesn't automatically do it
+	ensure_apt_package_list_is_up_to_date
 
 	## Count the number of upgradable packages and substract 1 for the header
-	local_apt_upgrade_number="$(apt list --upgradable 2>/dev/null \
+	local num_outdated_packages="$(apt list --upgradable 2>/dev/null \
 		| wc -l \
 		| awk '{print $1-1}')"
 
-	case "${local_apt_upgrade_number}" in
-		0 ) ## No available upgrade
-			return_apt_upgrade_absent="0"
-			;;
-		* ) ## Upgrade seems available
-			return_apt_upgrade_absent="1"
-			;;
-esac
-
-	## Simple debug message to valid current variable
-	debug_message "is_apt_upgrade_absent − \
-APT upgrade available for this system: ${RED}${local_apt_upgrade_number:=/dev/null}${COLOR_DEBUG}."
-
-	return "${return_apt_upgrade_absent}"
-
+	echo "${num_outdated_packages}"
 }
-# }}}
-is_apt_upgrade_present() {                                      # {{{
 
-	## Count the number of upgradable packages and substract 1 for the header
-	local_apt_upgrade_number="$(apt list --upgradable 2>/dev/null \
-		| wc -l \
-		| awk '{print $1-1}')"
+some_packages_are_outdated()
+{
+	local num_outdated_packages=''
+	num_outdated_packages=$(get_num_outdated_packages)
+	debug_message "some_packages_are_outdated − \
+number of outdated packages on this system: ${RED}${num_outdated_packages:=/dev/null}${COLOR_DEBUG}."
 
-	case "${local_apt_upgrade_number}" in
-		0 ) ## No available upgrade
-			return_apt_upgrade_present="1"
+	local return_code=''
+	case "${num_outdated_packages}" in
+		0 )
+			return_code='1'   # some_packages_are_outdated = false
 			;;
-		* ) ## Upgrade seems available
-			return_apt_upgrade_present="0"
+		* )
+			return_code='0'   # some_packages_are_outdated = true
 			;;
-esac
-
-	## Simple debug message to valid current variable
-	debug_message "is_apt_upgrade_present − \
-APT upgrade available for this system: ${RED}${local_apt_upgrade_number:=/dev/null}${COLOR_DEBUG}."
-
-	return "${return_apt_upgrade_present}"
+	esac
 
+	return "${return_code}"
 }
-# }}}
+
 is_file_present() {                                             # {{{
 
 	local_file_present="${1}"
@@ -257,12 +254,15 @@ main() {                                                        # {{{
 	## Define all vars
 	define_vars
 
-	## If NO APT package upgrade is available {{{
+	## If NO APT packages are out of date {{{
 	### Ensure to remove any temp file related to APT upgrades
 	### AND Exit
-	is_apt_upgrade_absent \
-		&& rm -f -- "${APT_TMP_FILE}" \
+	if [ ! "$(some_packages_are_outdated)" ]
+	then
+		rm -f -- "${APT_TMP_FILE}" \
 		&& exit 0
+	fi
+
 	## }}}
 
 	## If APT temp file already exists {{{
@@ -276,7 +276,7 @@ main() {                                                        # {{{
 	### Create APT temp file
 	### AND Exit
 	is_file_present "${sge_queue_flag_pattern}" \
-		&& is_apt_upgrade_present \
+		&& some_packages_are_outdated \
 		&& touch "${APT_TMP_FILE}" && echo "APT upgrade is available." >> "${APT_TMP_FILE}" \
 		&& exit 0
 	## }}}
@@ -296,7 +296,7 @@ main() {                                                        # {{{
 	### Create APT temp file
 	### Disable SGE queue
 	### AND Exit
-	is_apt_upgrade_present \
+	some_packages_are_outdated \
 		&& touch "${APT_TMP_FILE}" && echo "APT upgrade is available." >> "${APT_TMP_FILE}" \
 		&& sh "${sge_disable_host_queue_script}" \
 		&& exit 0