diff --git a/bin/common_defs.sh b/bin/common_defs.sh
index 45d35eeb4..2757b7a27 100644
--- a/bin/common_defs.sh
+++ b/bin/common_defs.sh
@@ -5,8 +5,8 @@ if [ "$DEBUG" -eq 1 ]; then
     set -x
 fi
 
-ROOT_DIR="$(cd "$(dirname "$(readlink "$0" || echo "$0")")"/..; pwd -P)"
-# shellcheck disable=SC1090
+ROOT_DIR="$(cd "$(dirname "$(readlink "$0" || echo "$0")")"/.. || exit 1; pwd -P)"
+# shellcheck disable=SC1090,SC1091
 . "$ROOT_DIR"/releases/emqx_vars
 
 # defined in emqx_vars
@@ -14,15 +14,16 @@ export RUNNER_ROOT_DIR
 export RUNNER_ETC_DIR
 export REL_VSN
 
-RUNNER_SCRIPT="$RUNNER_BIN_DIR/$REL_NAME"
-CODE_LOADING_MODE="${CODE_LOADING_MODE:-embedded}"
-REL_DIR="$RUNNER_ROOT_DIR/releases/$REL_VSN"
-SCHEMA_MOD=emqx_conf_schema
+export RUNNER_SCRIPT="$RUNNER_BIN_DIR/$REL_NAME"
+export CODE_LOADING_MODE="${CODE_LOADING_MODE:-embedded}"
+export REL_DIR="$RUNNER_ROOT_DIR/releases/$REL_VSN"
+export SCHEMA_MOD=emqx_conf_schema
 
 WHOAMI=$(whoami)
+export WHOAMI
 
 # Make sure data/configs exists
-CONFIGS_DIR="$RUNNER_DATA_DIR/configs"
+export CONFIGS_DIR="$RUNNER_DATA_DIR/configs"
 
 # hocon try to read environment variables starting with "EMQX_"
 export HOCON_ENV_OVERRIDE_PREFIX='EMQX_'
@@ -33,7 +34,7 @@ export BINDIR="$ERTS_DIR/bin"
 export EMU="beam"
 export PROGNAME="erl"
 export ERTS_LIB_DIR="$ERTS_DIR/../lib"
-DYNLIBS_DIR="$RUNNER_ROOT_DIR/dynlibs"
+export DYNLIBS_DIR="$RUNNER_ROOT_DIR/dynlibs"
 
 ## backward compatible
 if [ -d "$ERTS_DIR/lib" ]; then
@@ -56,5 +57,6 @@ SED_REPLACE="sed -i "
 case $(sed --help 2>&1) in
     *GNU*) SED_REPLACE="sed -i ";;
     *BusyBox*) SED_REPLACE="sed -i ";;
-    *) SED_REPLACE="sed -i '' ";;
+    *) SED_REPLACE=(sed -i '' );;
 esac
+export SED_REPLACE
diff --git a/bin/common_defs2.sh b/bin/common_defs2.sh
index f699add3c..f1991b37d 100644
--- a/bin/common_defs2.sh
+++ b/bin/common_defs2.sh
@@ -7,6 +7,9 @@
 ## they require the variable `IS_BOOT_COMMAND` to be set to either
 ## `yes` or `no` for the name definition to be done properly.
 
+## This should be sourced after the calling script has define the
+## `$COMMAND` variable.
+
 ## make EMQX_NODE_COOKIE right
 if [ -n "${EMQX_NODE_NAME:-}" ]; then
     export EMQX_NODE__NAME="${EMQX_NODE_NAME}"
@@ -22,7 +25,7 @@ NAME="${EMQX_NODE__NAME:-}"
 if [ -z "$NAME" ]; then
     if [ "$IS_BOOT_COMMAND" = 'yes' ]; then
         # for boot commands, inspect emqx.conf for node name
-        NAME="$(call_hocon -s $SCHEMA_MOD -I "$CONFIGS_DIR/" -c "$RUNNER_ETC_DIR"/emqx.conf get node.name | tr -d \")"
+        NAME="$(call_hocon -s "$SCHEMA_MOD" -I "$CONFIGS_DIR/" -c "$RUNNER_ETC_DIR"/emqx.conf get node.name | tr -d \")"
     else
         vm_args_file="$(latest_vm_args 'EMQX_NODE__NAME')"
         NAME="$(grep -E '^-s?name' "${vm_args_file}" | awk '{print $2}')"
@@ -31,7 +34,7 @@ fi
 
 # force to use 'emqx' short name
 [ -z "$NAME" ] && NAME='emqx'
-MNESIA_DATA_DIR="$RUNNER_DATA_DIR/mnesia/$NAME"
+export MNESIA_DATA_DIR="$RUNNER_DATA_DIR/mnesia/$NAME"
 
 case "$NAME" in
     *@*)
@@ -40,6 +43,7 @@ case "$NAME" in
     *)
         NAME_TYPE='-sname'
 esac
+export NAME_TYPE
 SHORT_NAME="$(echo "$NAME" | awk -F'@' '{print $1}')"
 export ESCRIPT_NAME="$SHORT_NAME"
 
@@ -53,7 +57,7 @@ fi
 COOKIE="${EMQX_NODE__COOKIE:-}"
 if [ -z "$COOKIE" ]; then
     if [ "$IS_BOOT_COMMAND" = 'yes' ]; then
-        COOKIE="$(call_hocon -s $SCHEMA_MOD -I "$CONFIGS_DIR/" -c "$RUNNER_ETC_DIR"/emqx.conf get node.cookie | tr -d \")"
+        COOKIE="$(call_hocon -s "$SCHEMA_MOD" -I "$CONFIGS_DIR/" -c "$RUNNER_ETC_DIR"/emqx.conf get node.cookie | tr -d \")"
     else
         vm_args_file="$(latest_vm_args 'EMQX_NODE__COOKIE')"
         COOKIE="$(grep -E '^-setcookie' "${vm_args_file}" | awk '{print $2}')"
diff --git a/bin/common_functions.sh b/bin/common_functions.sh
index 2b740ce6e..5354fc58e 100644
--- a/bin/common_functions.sh
+++ b/bin/common_functions.sh
@@ -60,6 +60,7 @@ relx_rem_sh() {
     TICKTIME="$(relx_nodetool rpcterms net_kernel get_net_ticktime)"
 
     # shellcheck disable=SC2086 # $EPMD_ARG is supposed to be split by whitespace
+    # shellcheck disable=SC2153 # $NAME_TYPE is defined by `common_defs2.sh`, which runs before this is called
     # Setup remote shell command to control node
     exec "$BINDIR/erl" "$NAME_TYPE" "$id" -remsh "$NAME" -boot "$REL_DIR/start_clean" \
          -boot_var ERTS_LIB_DIR "$ERTS_LIB_DIR" \
@@ -90,7 +91,9 @@ relx_escript() {
     "$ERTS_DIR/bin/escript" "$ROOTDIR/$scriptpath" "$@"
 }
 
-# Output a start command for the last argument of run_erl
+# Output a start command for the last argument of run_erl.
+# The calling script defines `$START_OPTION`, when the command is to
+# start EMQX in the background.
 relx_start_command() {
     printf "exec \"%s\" \"%s\"" "$RUNNER_SCRIPT" \
            "$START_OPTION"
@@ -128,6 +131,7 @@ generate_config() {
     # This is needed by the Elixir scripts.
     # Do NOT append `.config`.
     RELEASE_SYS_CONFIG="$CONFIGS_DIR/app.$NOW_TIME"
+    export RELEASE_SYS_CONFIG
 
     CONFIG_ARGS="-config $CONF_FILE -args_file $HOCON_GEN_ARG_FILE"
 
@@ -212,6 +216,7 @@ latest_vm_args() {
         echo "$vm_args_file"
     else
         echoerr "node not initialized?"
+        # shellcheck disable=SC2153 # $COMMAND is defined by the calling script
         echoerr "Generated config file vm.*.args is not found for command '$COMMAND'"
         echoerr "in config dir: $CONFIGS_DIR"
         echoerr "In case the file has been deleted while the node is running,"
diff --git a/bin/emqx b/bin/emqx
index 6ca352214..21458cb53 100755
--- a/bin/emqx
+++ b/bin/emqx
@@ -5,7 +5,9 @@
 set -euo pipefail
 
 BASE="$(cd "$(dirname "$(readlink "$0" || echo "$0")")"/..; pwd -P)"
+# shellcheck disable=SC1090,SC1091
 source "$BASE/bin/common_defs.sh"
+# shellcheck disable=SC1090,SC1091
 source "$BASE/bin/common_functions.sh"
 
 # Make sure log directory exists
@@ -182,7 +184,9 @@ case "${COMMAND}" in
         IS_BOOT_COMMAND='no'
         ;;
 esac
+export IS_BOOT_COMMAND
 
+# shellcheck disable=SC1090,SC1091
 source "$BASE/bin/common_defs2.sh"
 
 cd "$ROOTDIR"
@@ -205,6 +209,7 @@ case "${COMMAND}" in
                 HEART_OPTION="start"
                 ;;
         esac
+        export START_OPTION
         RUN_PARAM="$*"
 
         # Set arguments for the heart command
diff --git a/bin/node_dump b/bin/node_dump
index c8f76841b..3640fada9 100755
--- a/bin/node_dump
+++ b/bin/node_dump
@@ -1,10 +1,11 @@
 #!/bin/sh
 set -eu
 
+# shellcheck disable=SC1090,SC1091
 ROOT_DIR="$(cd "$(dirname "$(readlink "$0" || echo "$0")")"/..; pwd -P)"
 echo "Running node dump in ${ROOT_DIR}"
 
-# shellcheck disable=SC1090
+# shellcheck disable=SC1090,SC1091
 . "$ROOT_DIR"/releases/emqx_vars
 
 cd "${ROOT_DIR}"
diff --git a/mix_release.sh b/mix_release.sh
index 1000b37b3..3770b3a9e 100755
--- a/mix_release.sh
+++ b/mix_release.sh
@@ -1,6 +1,4 @@
 #!/bin/bash
-# shellcheck disable=SC1000-SC9999
-
 set -ex
 
 mix release --overwrite
diff --git a/rel/overlays/bin/emqx b/rel/overlays/bin/emqx
index b0149f072..41e921abc 100755
--- a/rel/overlays/bin/emqx
+++ b/rel/overlays/bin/emqx
@@ -5,7 +5,9 @@
 set -euo pipefail
 
 BASE="$(cd "$(dirname "$(readlink "$0" || echo "$0")")"/..; pwd -P)"
+# shellcheck disable=SC1090,SC1091
 source "$BASE/bin/common_defs.sh"
+# shellcheck disable=SC1090,SC1091
 source "$BASE/bin/common_functions.sh"
 
 # Make sure log directory exists
@@ -30,12 +32,14 @@ case "${COMMAND}" in
         IS_BOOT_COMMAND='no'
         ;;
 esac
+export IS_BOOT_COMMAND
 
+# shellcheck disable=SC1090,SC1091
 source "$BASE/bin/common_defs2.sh"
 
 cd "$ROOTDIR"
 
-# FIXME!!!
+# FIXME!!! Create case for commands.
 generate_config "$NAME_TYPE" "$NAME"
 # Must be explicitly exported here in order to be picked up correctly
 export RELEASE_SYS_CONFIG
diff --git a/scripts/shellcheck.sh b/scripts/shellcheck.sh
index 5f8cdfd51..ee69d8787 100755
--- a/scripts/shellcheck.sh
+++ b/scripts/shellcheck.sh
@@ -3,7 +3,14 @@
 set -euo pipefail
 
 target_files=()
-while IFS='' read -r line; do target_files+=("$line"); done < <(grep -r -l --exclude-dir=.git --exclude-dir=_build "#!/bin/" .)
+while IFS='' read -r line;
+do
+  target_files+=("$line");
+done < <(grep -r -l \
+              --exclude-dir=.git \
+              --exclude-dir=_build \
+              --exclude-dir=deps \
+              "^#!/bin/" .)
 return_code=0
 for i in "${target_files[@]}"; do
   echo checking "$i" ...