diff --git a/build b/build
index a339f803b..b4c9d0548 100755
--- a/build
+++ b/build
@@ -18,7 +18,7 @@ cd -P -- "$(dirname -- "${BASH_SOURCE[0]}")"
 PKG_VSN="${PKG_VSN:-$(./pkg-vsn.sh)}"
 export PKG_VSN
 
-SYSTEM="$(./scripts/get-distro.sh)"
+SYSTEM="${SYSTEM:-$(./scripts/get-distro.sh)}"
 
 ##
 ## Support RPM and Debian based linux systems
diff --git a/scripts/pkg-full-vsn.sh b/scripts/pkg-full-vsn.sh
index de32e11ef..e118643c9 100755
--- a/scripts/pkg-full-vsn.sh
+++ b/scripts/pkg-full-vsn.sh
@@ -27,7 +27,7 @@ esac
 cd -P -- "$(dirname -- "${BASH_SOURCE[0]}")/.."
 
 OTP_VSN="${OTP_VSN:-$(./scripts/get-otp-vsn.sh)}"
-SYSTEM="$(./scripts/get-distro.sh)"
+SYSTEM="${SYSTEM:-$(./scripts/get-distro.sh)}"
 
 UNAME="$(uname -m)"
 case "$UNAME" in
diff --git a/scripts/relup-base-packages.sh b/scripts/relup-base-packages.sh
index 2a47b5135..070f3926a 100755
--- a/scripts/relup-base-packages.sh
+++ b/scripts/relup-base-packages.sh
@@ -62,10 +62,11 @@ pushd _upgrade_base
 for tag in $(../scripts/relup-base-vsns.sh $EDITION | xargs echo -n); do
     filename="$PROFILE-${tag#[e|v]}-otp$OTP_VSN-$SYSTEM-$ARCH.zip"
     url="https://www.emqx.com/downloads/$DIR/${tag#[e|v]}/$filename"
-    echo "downloading base package from ${url} ..."
     if [ ! -f "$filename" ] && curl -I -m 10 -o /dev/null -s -w "%{http_code}" "${url}" | grep -q -oE "^[23]+" ; then
+        echo "downloading base package from ${url} ..."
         curl -L -o "${filename}" "${url}"
         if [ "$SYSTEM" != "centos6" ]; then
+            echo "downloading sha256 sum from ${url}.sha256 ..."
             curl -L -o "${filename}.sha256" "${url}.sha256"
             SUMSTR=$(cat "${filename}.sha256")
             echo "got sha265sum: ${SUMSTR}"