diff --git a/README.md b/README.md
index c43b52c2..ee09d821 100644
--- a/README.md
+++ b/README.md
@@ -42,7 +42,7 @@ There are three scenarios to use KubeKey.
 
 * OS requirements:
   * `SSH` can access to all nodes.
-  *  `sudo` and `curl` can be used in all nodes.
+  *  `sudo`/`curl`/`openssl` can be used in all nodes.
   * `ebtables`/`socat`/`ipset`/`conntrack` should be installed on all nodes.
   * The [relevant client](./docs/storage-client.md) should be installed on all nodes, if NFS / Ceph / GlusterFS is used as persistent storage.
   * `docker` can be installed by yourself or by KubeKey. 
diff --git a/pkg/cluster/preinstall/tmpl/InitOS.go b/pkg/cluster/preinstall/tmpl/InitOS.go
index 135fc957..26d7413b 100644
--- a/pkg/cluster/preinstall/tmpl/InitOS.go
+++ b/pkg/cluster/preinstall/tmpl/InitOS.go
@@ -86,6 +86,9 @@ cat >>/etc/hosts<<EOF
 {{- end }}
 # kubekey hosts END
 EOF
+
+echo 3 > /proc/sys/vm/drop_caches
+
     `)))
 
 func InitOsScript(mgr *manager.Manager) (string, error) {