diff --git a/tools/easzup b/tools/easzup
index b0f1e5e..ec53431 100755
--- a/tools/easzup
+++ b/tools/easzup
@@ -1,31 +1,52 @@
 #!/bin/bash
+#--------------------------------------------------
+# This script is for: 
+# 1. to download the scripts/binaries/images needed for installing a k8s cluster with kubeasz
+# 2. to run kubeasz in a container
+# @author:   gjmzj
+# @usage:    ./easzup
+# @repo:     https://github.com/easzlab/kubeasz
+# @ref:      https://github.com/kubeasz/dockerfiles
+#--------------------------------------------------
 
 set -o nounset
 set -o errexit
 #set -o xtrace
 
-function install_docker() {
-  systemctl status docker|grep Active|grep -q running && { echo "[WARN] dockerd already running!"; return 0; }
-  
-  systemctl status containerd|grep Active|grep -q running && { echo "[ERROR] containerd running, but unsupported!"; exit 1; }
+# default version, can be overridden by cmd line options
+export DOCKER_VER=18.09.6
+export KUBEASZ_VER=1.3.0
+export K8S_BIN_VER=v1.14.3
+export EXT_BIN_VER=0.3.0
+
+function install_docker() {
+  # check if a container runtime is already installed
+  systemctl status docker|grep Active|grep -q running && { echo "[WARN] docker is already running."; return 0; }
+  systemctl status containerd|grep Active|grep -q running && { echo "[ERROR] containerd is running, unsupported."; exit 1; }
+
+  DOCKER_URL=https://mirrors.tuna.tsinghua.edu.cn/docker-ce/linux/static/stable/x86_64/docker-${DOCKER_VER}.tgz
+  mkdir -p /opt/kube/bin /etc/docker /etc/ansible/down
+  if [[ -f "/etc/ansible/down/docker-${DOCKER_VER}.tgz" ]];then
+    echo "[INFO] docker binaries already existed"
+  else
+    echo -e "[INFO] \033[33mdownloading docker binaries\033[0m $DOCKER_VER"
+    wget -c -P /etc/ansible/down "$DOCKER_URL" || { echo "[ERROR] downloading docker failed"; exit 1; }
+  fi
+
+  tar zxf /etc/ansible/down/docker-${DOCKER_VER}.tgz -C /etc/ansible/down
+  mv /etc/ansible/down/docker/* /opt/kube/bin
+  ln -sf /opt/kube/bin/docker /bin/docker
 
-  mkdir -p /opt/kube/bin /etc/docker
-  echo -e "[INFO] \033[33mdownloading docker\033[0m $DOCKER_VER"
-  wget -c https://mirrors.tuna.tsinghua.edu.cn/docker-ce/linux/static/stable/x86_64/docker-$DOCKER_VER.tgz
-  tar zxf docker-$DOCKER_VER.tgz
-  mv docker/* /opt/kube/bin
-  rm -rf docker*
-  ln -sf /opt/kube/bin/docker /bin
-  
   echo "[INFO] generate docker service file"
-  echo '[Unit]
+  cat > /etc/systemd/system/docker.service << EOF
+[Unit]
 Description=Docker Application Container Engine
 Documentation=http://docs.docker.io
 [Service]
 Environment="PATH=/opt/kube/bin:/bin:/sbin:/usr/bin:/usr/sbin"
 ExecStart=/opt/kube/bin/dockerd
 ExecStartPost=/sbin/iptables -I FORWARD -s 0.0.0.0/0 -j ACCEPT
-ExecReload=/bin/kill -s HUP $MAINPID
+ExecReload=/bin/kill -s HUP \$MAINPID
 Restart=on-failure
 RestartSec=5
 LimitNOFILE=infinity
@@ -34,10 +55,12 @@ LimitCORE=infinity
 Delegate=yes
 KillMode=process
 [Install]
-WantedBy=multi-user.target' > /etc/systemd/system/docker.service
+WantedBy=multi-user.target
+EOF
 
   echo "[INFO] generate docker config file"
-  echo '{
+  cat > /etc/docker/daemon.json << EOF
+{
   "registry-mirrors": [
     "https://dockerhub.azk8s.cn",
     "https://docker.mirrors.ustc.edu.cn",
@@ -51,7 +74,8 @@ WantedBy=multi-user.target' > /etc/systemd/system/docker.service
     "max-file": "3"
     },
   "data-root": "/var/lib/docker"
-}' > /etc/docker/daemon.json
+}
+EOF
 
   echo "[INFO] enable and start docker"
   systemctl enable docker
@@ -59,55 +83,54 @@ WantedBy=multi-user.target' > /etc/systemd/system/docker.service
 }
 
 function get_kubeasz() {
-  if [ -d "/etc/ansible/roles/kube-node" ];then
-    echo "[WARN] kubeasz already Initialized."
-  else
-    echo -e "[INFO] \033[33mdownloading kubeasz\033[0m $KUBEASZ_VER"
-    rm -rf /etc/ansible
-    docker pull easzlab/kubeasz:$KUBEASZ_VER
-    echo "[INFO] run a temporary container"
-    docker run -d --name temp_easz easzlab/kubeasz:$KUBEASZ_VER
-    echo "[INFO] init kubeasz code"
-    docker cp temp_easz:/etc/ansible /etc/ansible
-    echo "[INFO] stop&remove temporary container"
-    docker rm -f temp_easz
-  fi
+  # check if kubeasz already existed
+  [[ -d "/etc/ansible/roles/kube-node" ]] && { echo "[WARN] kubeasz already existed"; return 0; }
+  # temporarily move docker binaries
+  [[ -f "/etc/ansible/down/docker-${DOCKER_VER}.tgz" ]] && mv "/etc/ansible/down/docker-${DOCKER_VER}.tgz" /tmp
+
+  rm -rf /etc/ansible && \
+  echo -e "[INFO] \033[33mdownloading kubeasz\033[0m $KUBEASZ_VER" && \
+  docker pull easzlab/kubeasz:${KUBEASZ_VER} && \
+  echo "[INFO] run a temporary container" && \
+  docker run -d --name temp_easz easzlab/kubeasz:${KUBEASZ_VER} && \
+  echo "[INFO] cp kubeasz code from the temporary container" && \
+  docker cp temp_easz:/etc/ansible /etc/ansible && \
+  echo "[INFO] stop&remove temporary container" && \
+  docker rm -f temp_easz && \
+  [[ -f "/tmp/docker-${DOCKER_VER}.tgz" ]] && mv "/tmp/docker-${DOCKER_VER}.tgz" /etc/ansible/down || true
 }
 
 function get_k8s_bin() {
-  if [ -f "/etc/ansible/bin/kubelet" ];then
-    echo "[WARN] kubernetes:$K8S_BIN_VER binaries already existed."
-  else
-    echo -e "[INFO] \033[33mdownloading kubernetes\033[0m $K8S_BIN_VER binaries"
-    docker pull easzlab/kubeasz-k8s-bin:$K8S_BIN_VER
-    echo "[INFO] run a temporary container"
-    docker run -d --name temp_k8s_bin easzlab/kubeasz-k8s-bin:$K8S_BIN_VER
-    echo "[INFO] cp k8s binaries"
-    docker cp temp_k8s_bin:/k8s /k8s_bin_tmp && mv /k8s_bin_tmp/* /etc/ansible/bin
-    echo "[INFO] stop&remove temporary container"
-    docker rm -f temp_k8s_bin
-    rm -rf /k8s_bin_tmp
-  fi
+  [[ -f "/etc/ansible/bin/kubelet" ]] && { echo "[WARN] kubernetes binaries existed"; return 0; }
+  
+  echo -e "[INFO] \033[33mdownloading kubernetes\033[0m $K8S_BIN_VER binaries"
+  docker pull easzlab/kubeasz-k8s-bin:${K8S_BIN_VER} && \
+  echo "[INFO] run a temporary container" && \
+  docker run -d --name temp_k8s_bin easzlab/kubeasz-k8s-bin:${K8S_BIN_VER} && \
+  echo "[INFO] cp k8s binaries" && \
+  docker cp temp_k8s_bin:/k8s /k8s_bin_tmp && \
+  mv /k8s_bin_tmp/* /etc/ansible/bin && \
+  echo "[INFO] stop&remove temporary container" && \
+  docker rm -f temp_k8s_bin && \
+  rm -rf /k8s_bin_tmp
 }
 
 function get_ext_bin() {
-  if [ -f "/etc/ansible/bin/etcdctl" ];then
-    echo "[WARN] extral binaries already existed."
-  else
-    echo -e "[INFO] \033[33mdownloading extral binaries\033[0m kubeasz-ext-bin:$EXT_BIN_VER"
-    docker pull easzlab/kubeasz-ext-bin:$EXT_BIN_VER
-    echo "[INFO] run a temporary container"
-    docker run -d --name temp_ext_bin easzlab/kubeasz-ext-bin:$EXT_BIN_VER
-    echo "[INFO] cp extral binaries"
-    docker cp temp_ext_bin:/extra /extra_bin_tmp && mv /extra_bin_tmp/* /etc/ansible/bin
-    echo "[INFO] stop&remove temporary container"
-    docker rm -f temp_ext_bin
-    rm -rf /extra_bin_tmp
-  fi
+  [[ -f "/etc/ansible/bin/etcdctl" ]] && { echo "[WARN] extral binaries existed"; return 0; }
+
+  echo -e "[INFO] \033[33mdownloading extral binaries\033[0m kubeasz-ext-bin:$EXT_BIN_VER"
+  docker pull easzlab/kubeasz-ext-bin:${EXT_BIN_VER} && \
+  echo "[INFO] run a temporary container" && \
+  docker run -d --name temp_ext_bin easzlab/kubeasz-ext-bin:${EXT_BIN_VER} && \
+  echo "[INFO] cp extral binaries" && \
+  docker cp temp_ext_bin:/extra /extra_bin_tmp && \
+  mv /extra_bin_tmp/* /etc/ansible/bin && \
+  echo "[INFO] stop&remove temporary container" && \
+  docker rm -f temp_ext_bin && \
+  rm -rf /extra_bin_tmp
 }
 
 function get_offline_image() {
-  
   calicoVer=v3.4.4
   corednsVer=1.5.0
   dashboardVer=v1.10.1
@@ -118,63 +141,60 @@ function get_offline_image() {
   traefikVer=v1.7.12
 
   imageDir=/etc/ansible/down
-  [ -d "$imageDir" ] || { echo "[ERROR] $imageDir not existed!"; exit 1; }
+  [[ -d "$imageDir" ]] || { echo "[ERROR] $imageDir not existed!"; exit 1; }
   
   echo -e "[INFO] \033[33mdownloading offline images\033[0m"
 
-  if [ ! -f "$imageDir/calico_${calicoVer}.tar" ];then
-    docker pull calico/cni:$calicoVer
-    docker pull calico/kube-controllers:$calicoVer
-    docker pull calico/node:$calicoVer
-    docker save -o $imageDir/calico_${calicoVer}.tar calico/cni:$calicoVer calico/kube-controllers:$calicoVer calico/node:$calicoVer
+  if [[ ! -f "$imageDir/calico_$calicoVer.tar" ]];then
+    docker pull calico/cni:${calicoVer} && \
+    docker pull calico/kube-controllers:${calicoVer} && \
+    docker pull calico/node:${calicoVer} && \
+    docker save -o ${imageDir}/calico_${calicoVer}.tar calico/cni:${calicoVer} calico/kube-controllers:${calicoVer} calico/node:${calicoVer}
   fi
-  if [ ! -f "$imageDir/coredns_${corednsVer}.tar" ];then
-    docker pull coredns/coredns:$corednsVer
-    docker save -o $imageDir/coredns_${corednsVer}.tar coredns/coredns:$corednsVer
+  if [[ ! -f "$imageDir/coredns_$corednsVer.tar" ]];then
+    docker pull coredns/coredns:${corednsVer} && \
+    docker save -o ${imageDir}/coredns_${corednsVer}.tar coredns/coredns:${corednsVer}
   fi
-  if [ ! -f "$imageDir/dashboard_${dashboardVer}.tar" ];then
-    docker pull mirrorgooglecontainers/kubernetes-dashboard-amd64:$dashboardVer
-    docker save -o $imageDir/dashboard_${dashboardVer}.tar mirrorgooglecontainers/kubernetes-dashboard-amd64:$dashboardVer
+  if [[ ! -f "$imageDir/dashboard_$dashboardVer.tar" ]];then
+    docker pull mirrorgooglecontainers/kubernetes-dashboard-amd64:${dashboardVer} && \
+    docker save -o ${imageDir}/dashboard_${dashboardVer}.tar mirrorgooglecontainers/kubernetes-dashboard-amd64:${dashboardVer}
   fi
-  if [ ! -f "$imageDir/flannel_${flannelVer}.tar" ];then
-    docker pull easzlab/flannel:$flannelVer
-    docker save -o $imageDir/flannel_${flannelVer}.tar easzlab/flannel:$flannelVer
+  if [[ ! -f "$imageDir/flannel_$flannelVer.tar" ]];then
+    docker pull easzlab/flannel:${flannelVer} && \
+    docker save -o ${imageDir}/flannel_${flannelVer}.tar easzlab/flannel:${flannelVer}
   fi
-  if [ ! -f "$imageDir/heapster_${heapsterVer}.tar" ];then
-    docker pull mirrorgooglecontainers/heapster-amd64:$heapsterVer
-    docker save -o $imageDir/heapster_${heapsterVer}.tar mirrorgooglecontainers/heapster-amd64:$heapsterVer
+  if [[ ! -f "$imageDir/heapster_$heapsterVer.tar" ]];then
+    docker pull mirrorgooglecontainers/heapster-amd64:${heapsterVer} && \
+    docker save -o ${imageDir}/heapster_${heapsterVer}.tar mirrorgooglecontainers/heapster-amd64:${heapsterVer}
   fi
-  if [ ! -f "$imageDir/metrics-server_${metricsVer}.tar" ];then
-    docker pull mirrorgooglecontainers/metrics-server-amd64:$metricsVer
-    docker save -o $imageDir/metrics-server_${metricsVer}.tar mirrorgooglecontainers/metrics-server-amd64:$metricsVer
+  if [[ ! -f "$imageDir/metrics-server_$metricsVer.tar" ]];then
+    docker pull mirrorgooglecontainers/metrics-server-amd64:${metricsVer} && \
+    docker save -o ${imageDir}/metrics-server_${metricsVer}.tar mirrorgooglecontainers/metrics-server-amd64:${metricsVer}
   fi
-  if [ ! -f "$imageDir/pause_${pauseVer}.tar" ];then
-    docker pull mirrorgooglecontainers/pause-amd64:$pauseVer
-    docker save -o $imageDir/pause_${pauseVer}.tar mirrorgooglecontainers/pause-amd64:$pauseVer
+  if [[ ! -f "$imageDir/pause_$pauseVer.tar" ]];then
+    docker pull mirrorgooglecontainers/pause-amd64:${pauseVer} && \
+    docker save -o ${imageDir}/pause_${pauseVer}.tar mirrorgooglecontainers/pause-amd64:${pauseVer}
   fi
-  if [ ! -f "$imageDir/traefik_${traefikVer}.tar" ];then
-    docker pull traefik:$traefikVer
-    docker save -o $imageDir/traefik_${traefikVer}.tar traefik:$traefikVer
+  if [[ ! -f "$imageDir/traefik_$traefikVer.tar" ]];then
+    docker pull traefik:${traefikVer} && \
+    docker save -o ${imageDir}/traefik_${traefikVer}.tar traefik:${traefikVer}
   fi
 }
 
 function download_all() {
-  install_docker
-  get_kubeasz
-  get_k8s_bin
-  get_ext_bin
+  install_docker && \
+  get_kubeasz && \
+  get_k8s_bin && \
+  get_ext_bin && \
   get_offline_image
 }
 
 function start_kubeasz_docker() {
-  if [ ! -d "/etc/ansible/roles/kube-node" ];then
-    echo "[ERROR] not initialized. try 'easzup -D' first."
-    exit 1
-  fi
+  [[ -d "/etc/ansible/roles/kube-node" ]] || { echo "[ERROR] not initialized. try 'easzup -D' first."; exit 1; }
 
   # get host's IP
   host_if=$(ip route|grep default|cut -d' ' -f5)
-  host_ip=$(ip a|grep $host_if|awk 'NR==2{print $2}'|cut -d'/' -f1)
+  host_ip=$(ip a|grep "$host_if"|awk 'NR==2{print $2}'|cut -d'/' -f1)
   echo "[INFO] get host IP: $host_ip"
   
   # run kubeasz docker container
@@ -182,13 +202,13 @@ function start_kubeasz_docker() {
   docker run --detach \
       --name kubeasz \
       --restart always \
-      --env HOST_IP=$host_ip \
+      --env HOST_IP="$host_ip" \
       --volume /etc/ansible:/etc/ansible \
       --volume /root/.kube:/root/.kube \
       --volume /root/.ssh/id_rsa:/root/.ssh/id_rsa:ro \
       --volume /root/.ssh/id_rsa.pub:/root/.ssh/id_rsa.pub:ro \
       --volume /root/.ssh/known_hosts:/root/.ssh/known_hosts:ro \
-      easzlab/kubeasz:$KUBEASZ_VER
+      easzlab/kubeasz:${KUBEASZ_VER}
 }
 
 function clean_container() {
@@ -212,61 +232,52 @@ see more at https://github.com/kubeasz/dockerfiles
 EOF
 } 
 
-function process_cmd() {
-    echo -e "[INFO] \033[33mAction begin\033[0m : $ACTION"
-    $ACTION || { echo -e "[ERROR] \033[31mAction failed\033[0m : $ACTION"; return 1; }
-    echo -e "[INFO] \033[32mAction successed\033[0m : $ACTION"
+### Main Lines ##################################################
+function main() {
+  # check if use bash shell
+  readlink /proc/$$/exe|grep -q "dash" && { echo "[ERROR] you should use bash shell, not sh"; exit 1; }
+  # check if use with root
+  [[ "$EUID" -ne 0 ]] && { echo "[ERROR] you should run this script as root"; exit 1; }
+  
+  [[ "$#" -eq 0 ]] && { usage >&2; exit 1; }
+  
+  ACTION=""
+  while getopts "CDSd:e:k:z:" OPTION; do
+      case "$OPTION" in
+        C)
+          ACTION="clean_container"
+          ;;
+        D)
+          ACTION="download_all"
+          ;;
+        S)
+          ACTION="start_kubeasz_docker"
+          ;;
+        d)
+          export DOCKER_VER="$OPTARG"
+          ;;
+        e)
+          export EXT_BIN_VER="$OPTARG"
+          ;;
+        k)
+          export K8S_BIN_VER="$OPTARG"
+          ;;
+        z)
+          export KUBEASZ_VER="$OPTARG"
+          ;;
+        ?)
+          usage
+          exit 1
+          ;;
+      esac
+  done
+  
+  [[ "$ACTION" == "" ]] && { echo "[ERROR] illegal option"; usage; exit 1; }
+  
+  # excute cmd "$ACTION" 
+  echo -e "[INFO] \033[33mAction begin\033[0m : $ACTION"
+  ${ACTION} || { echo -e "[ERROR] \033[31mAction failed\033[0m : $ACTION"; return 1; }
+  echo -e "[INFO] \033[32mAction successed\033[0m : $ACTION"
 }
 
-### Main Lines ##################################################
-if readlink /proc/$$/exe | grep -q "dash"; then
-  echo "[ERROR] This script needs to be run with bash, not sh"
-  exit 1
-fi
-
-if [[ "$EUID" -ne 0 ]]; then
-  echo "[ERROR] Sorry, you need to run this as root"
-  exit 1
-fi
-
-[ "$#" -gt 0 ] || { usage >&2; exit 2; }
-
-# default version, can be overridden by cmd line options
-export DOCKER_VER=18.09.6
-export KUBEASZ_VER=1.3.0
-export K8S_BIN_VER=v1.14.3
-export EXT_BIN_VER=0.3.0
-
-ACTION=""
-
-while getopts "CDSd:e:k:z:" OPTION; do
-    case $OPTION in
-      C)
-        ACTION="clean_container"
-        ;;
-      D)
-        ACTION="download_all"
-        ;;
-      S)
-        ACTION="start_kubeasz_docker"
-        ;;
-      d)
-        export DOCKER_VER=$OPTARG
-        ;;
-      e)
-        export EXT_BIN_VER=$OPTARG
-        ;;
-      k)
-        export K8S_BIN_VER=$OPTARG
-        ;;
-      z)
-        export KUBEASZ_VER=$OPTARG
-        ;;
-      ?)
-        usage
-        exit 1
-        ;;
-    esac
-done
-
-process_cmd
+main "$@"