diff --git a/README.md b/README.md
index 0c49e43..f780379 100755
--- a/README.md
+++ b/README.md
@@ -114,6 +114,7 @@ This repo contains two types of scripts, posix compatible and bash compatible.
 | sed              | Miscellaneous                                          |
 | mktemp           | To generate temporary files ( optional )               |
 | sleep            | Self explanatory                                       |
+| ps               | To manage different processes                          |
 
 <strong>If BASH is not available or BASH is available but version is less tham 4.x, then below programs are also required:</strong>
 
@@ -124,11 +125,10 @@ This repo contains two types of scripts, posix compatible and bash compatible.
 | cat                 | Miscellaneous                              |
 | stty or zsh or tput | To determine column size ( optional )      |
 
-<strong>These programs are needed for synchronisation script:</strong>
+<strong>These are the additional programs needed for synchronisation script:</strong>
 
 | Program       | Role In Script            |
 | ------------- | ------------------------- |
-| ps            | To manage background jobs |
 | tail          | To show indefinite logs   |
 
 ### Installation
diff --git a/bash/release/gupload b/bash/release/gupload
index 40a9d5f..386709f 100755
--- a/bash/release/gupload
+++ b/bash/release/gupload
@@ -1293,7 +1293,30 @@ _check_credentials() {
         fi
     }
 
-    [[ -z ${ACCESS_TOKEN} || ${ACCESS_TOKEN_EXPIRY} -lt "$(printf "%(%s)T\\n" "-1")" ]] && { _get_access_token_and_update || return 1; }
+    [[ -z ${ACCESS_TOKEN} || ${ACCESS_TOKEN_EXPIRY:-0} -lt "$(printf "%(%s)T\\n" "-1")" ]] && { _get_access_token_and_update || return 1; }
+
+    # launch a background service to check access token and update it
+    # checks ACCESS_TOKEN_EXPIRY, try to update before 5 mins of expiry, a fresh token gets 60 mins
+    # process will be killed when script exits
+    {
+        while :; do
+            CURRENT_TIME="$(printf "%(%s)T\\n" "-1")"
+            REMAINING_TOKEN_TIME="$((ACCESS_TOKEN_EXPIRY - CURRENT_TIME))"
+            if [[ ${REMAINING_TOKEN_TIME} -le 300 ]]; then
+                # timeout after 30 seconds, it shouldn't take too long anyway
+                _timeout 30 _get_access_token_and_update || :
+            else
+                TOKEN_PROCESS_TIME_TO_SLEEP="$(if [[ ${REMAINING_TOKEN_TIME} -le 301 ]]; then
+                    printf "0\n"
+                else
+                    printf "%s\n" "$((REMAINING_TOKEN_TIME - 300))"
+                fi)"
+                sleep "${TOKEN_PROCESS_TIME_TO_SLEEP}"
+            fi
+            sleep 1
+        done
+    } &
+    ACCESS_TOKEN_SERVICE_PID="${!}"
 
     return 0
 }
@@ -1566,6 +1589,16 @@ main() {
     _cleanup() {
         {
             [[ -n ${PARALLEL_UPLOAD} ]] && rm -f "${TMPFILE:?}"*
+
+            # grab all chidren processes of access token service
+            # https://askubuntu.com/a/512872
+            token_service_pids="$(ps --ppid="${ACCESS_TOKEN_SERVICE_PID}" -o pid=)"
+            # first kill parent id, then children processes
+            kill "${ACCESS_TOKEN_SERVICE_PID}"
+            for pid in ${token_service_pids}; do
+                kill "${pid}"
+            done
+
             export abnormal_exit && if [[ -n ${abnormal_exit} ]]; then
                 printf "\n\n%s\n" "Script exited manually."
                 kill -- -$$ &
diff --git a/bash/upload.bash b/bash/upload.bash
index 4e62821..ee574cb 100755
--- a/bash/upload.bash
+++ b/bash/upload.bash
@@ -367,7 +367,30 @@ _check_credentials() {
         fi
     }
 
-    [[ -z ${ACCESS_TOKEN} || ${ACCESS_TOKEN_EXPIRY} -lt "$(printf "%(%s)T\\n" "-1")" ]] && { _get_access_token_and_update || return 1; }
+    [[ -z ${ACCESS_TOKEN} || ${ACCESS_TOKEN_EXPIRY:-0} -lt "$(printf "%(%s)T\\n" "-1")" ]] && { _get_access_token_and_update || return 1; }
+
+    # launch a background service to check access token and update it
+    # checks ACCESS_TOKEN_EXPIRY, try to update before 5 mins of expiry, a fresh token gets 60 mins
+    # process will be killed when script exits
+    {
+        while :; do
+            CURRENT_TIME="$(printf "%(%s)T\\n" "-1")"
+            REMAINING_TOKEN_TIME="$((ACCESS_TOKEN_EXPIRY - CURRENT_TIME))"
+            if [[ ${REMAINING_TOKEN_TIME} -le 300 ]]; then
+                # timeout after 30 seconds, it shouldn't take too long anyway
+                _timeout 30 _get_access_token_and_update || :
+            else
+                TOKEN_PROCESS_TIME_TO_SLEEP="$(if [[ ${REMAINING_TOKEN_TIME} -le 301 ]]; then
+                    printf "0\n"
+                else
+                    printf "%s\n" "$((REMAINING_TOKEN_TIME - 300))"
+                fi)"
+                sleep "${TOKEN_PROCESS_TIME_TO_SLEEP}"
+            fi
+            sleep 1
+        done
+    } &
+    ACCESS_TOKEN_SERVICE_PID="${!}"
 
     return 0
 }
@@ -640,6 +663,16 @@ main() {
     _cleanup() {
         {
             [[ -n ${PARALLEL_UPLOAD} ]] && rm -f "${TMPFILE:?}"*
+
+            # grab all chidren processes of access token service
+            # https://askubuntu.com/a/512872
+            token_service_pids="$(ps --ppid="${ACCESS_TOKEN_SERVICE_PID}" -o pid=)"
+            # first kill parent id, then children processes
+            kill "${ACCESS_TOKEN_SERVICE_PID}"
+            for pid in ${token_service_pids}; do
+                kill "${pid}"
+            done
+
             export abnormal_exit && if [[ -n ${abnormal_exit} ]]; then
                 printf "\n\n%s\n" "Script exited manually."
                 kill -- -$$ &
diff --git a/sh/release/gupload b/sh/release/gupload
index b916df8..a3e2ddb 100755
--- a/sh/release/gupload
+++ b/sh/release/gupload
@@ -1286,7 +1286,30 @@ _check_credentials() {
         fi
     }
 
-    [ -z "${ACCESS_TOKEN}" ] || [ "${ACCESS_TOKEN_EXPIRY}" -lt "$(date +'%s')" ] && { _get_access_token_and_update || return 1; }
+    [ -z "${ACCESS_TOKEN}" ] || [ "${ACCESS_TOKEN_EXPIRY:-0}" -lt "$(date +'%s')" ] && { _get_access_token_and_update || return 1; }
+
+    # launch a background service to check access token and update it
+    # checks ACCESS_TOKEN_EXPIRY, try to update before 5 mins of expiry, a fresh token gets 60 mins
+    # process will be killed when script exits
+    {
+        while :; do
+            CURRENT_TIME="$(date +'%s')"
+            REMAINING_TOKEN_TIME="$((CURRENT_TIME - ACCESS_TOKEN_EXPIRY))"
+            if [ "${REMAINING_TOKEN_TIME}" -le 300 ]; then
+                # timeout after 30 seconds, it shouldn't take too long anyway
+                _timeout 30 _get_access_token_and_update || :
+            else
+                TOKEN_PROCESS_TIME_TO_SLEEP="$(if [ "${REMAINING_TOKEN_TIME}" -le 301 ]; then
+                    printf "0\n"
+                else
+                    printf "%s\n" "$((REMAINING_TOKEN_TIME - 300))"
+                fi)"
+                sleep "${TOKEN_PROCESS_TIME_TO_SLEEP}"
+            fi
+            sleep 1
+        done
+    } &
+    ACCESS_TOKEN_SERVICE_PID="${!}"
 
     return 0
 }
@@ -1575,6 +1598,16 @@ main() {
     _cleanup() {
         {
             [ -n "${PARALLEL_UPLOAD}" ] && rm -f "${TMPFILE:?}"*
+
+            # grab all chidren processes of access token service
+            # https://askubuntu.com/a/512872
+            token_service_pids="$(ps --ppid="${ACCESS_TOKEN_SERVICE_PID}" -o pid=)"
+            # first kill parent id, then children processes
+            kill "${ACCESS_TOKEN_SERVICE_PID}"
+            for pid in ${token_service_pids}; do
+                kill "${pid}"
+            done
+
             export abnormal_exit && if [ -n "${abnormal_exit}" ]; then
                 printf "\n\n%s\n" "Script exited manually."
                 kill -9 -$$ &
diff --git a/sh/upload.sh b/sh/upload.sh
index c059c6f..72394bf 100755
--- a/sh/upload.sh
+++ b/sh/upload.sh
@@ -377,7 +377,30 @@ _check_credentials() {
         fi
     }
 
-    [ -z "${ACCESS_TOKEN}" ] || [ "${ACCESS_TOKEN_EXPIRY}" -lt "$(date +'%s')" ] && { _get_access_token_and_update || return 1; }
+    [ -z "${ACCESS_TOKEN}" ] || [ "${ACCESS_TOKEN_EXPIRY:-0}" -lt "$(date +'%s')" ] && { _get_access_token_and_update || return 1; }
+
+    # launch a background service to check access token and update it
+    # checks ACCESS_TOKEN_EXPIRY, try to update before 5 mins of expiry, a fresh token gets 60 mins
+    # process will be killed when script exits
+    {
+        while :; do
+            CURRENT_TIME="$(date +'%s')"
+            REMAINING_TOKEN_TIME="$((CURRENT_TIME - ACCESS_TOKEN_EXPIRY))"
+            if [ "${REMAINING_TOKEN_TIME}" -le 300 ]; then
+                # timeout after 30 seconds, it shouldn't take too long anyway
+                _timeout 30 _get_access_token_and_update || :
+            else
+                TOKEN_PROCESS_TIME_TO_SLEEP="$(if [ "${REMAINING_TOKEN_TIME}" -le 301 ]; then
+                    printf "0\n"
+                else
+                    printf "%s\n" "$((REMAINING_TOKEN_TIME - 300))"
+                fi)"
+                sleep "${TOKEN_PROCESS_TIME_TO_SLEEP}"
+            fi
+            sleep 1
+        done
+    } &
+    ACCESS_TOKEN_SERVICE_PID="${!}"
 
     return 0
 }
@@ -666,6 +689,16 @@ main() {
     _cleanup() {
         {
             [ -n "${PARALLEL_UPLOAD}" ] && rm -f "${TMPFILE:?}"*
+
+            # grab all chidren processes of access token service
+            # https://askubuntu.com/a/512872
+            token_service_pids="$(ps --ppid="${ACCESS_TOKEN_SERVICE_PID}" -o pid=)"
+            # first kill parent id, then children processes
+            kill "${ACCESS_TOKEN_SERVICE_PID}"
+            for pid in ${token_service_pids}; do
+                kill "${pid}"
+            done
+
             export abnormal_exit && if [ -n "${abnormal_exit}" ]; then
                 printf "\n\n%s\n" "Script exited manually."
                 kill -9 -$$ &