diff --git a/src/main/res/values-zh/strings.xml b/src/main/res/values-zh/strings.xml
index e405acba..02bd0674 100755
--- a/src/main/res/values-zh/strings.xml
+++ b/src/main/res/values-zh/strings.xml
@@ -56,7 +56,7 @@
   <string name="about">关于</string>
   <string name="about_title">影梭（shadowsocks）%s</string>
   <string name="flush_dnscache">刷新 DNS 缓存</string>
-  <string name="flush_dnscache_summary">需要 ROOT 权限</string>
+  <string name="flush_dnscache_summary_disabled">需要 ROOT 权限</string>
   <string name="flushing">刷新中……</string>
   <string name="qrcode">二维码</string>
   <string name="add_profile">添加配置文件</string>
diff --git a/src/main/res/values/strings.xml b/src/main/res/values/strings.xml
index e4c16cdc..cd88ddf2 100644
--- a/src/main/res/values/strings.xml
+++ b/src/main/res/values/strings.xml
@@ -80,7 +80,7 @@
   <string name="about_title">Shadowsocks %s</string>
   <string name="qrcode">QR Code</string>
   <string name="flush_dnscache">Flush DNS cache</string>
-  <string name="flush_dnscache_summary">Requires ROOT permission</string>
+  <string name="flush_dnscache_summary_disabled">Requires ROOT permission</string>
   <string name="flushing">Flushing</string>
   <string name="add_profile">Add Profile</string>
   <string name="action_export">Export to Clipboard</string>
diff --git a/src/main/res/xml/pref_all.xml b/src/main/res/xml/pref_all.xml
index f2a6af85..aa33012e 100644
--- a/src/main/res/xml/pref_all.xml
+++ b/src/main/res/xml/pref_all.xml
@@ -104,8 +104,7 @@
                                                                 android:summary="@string/nat_summary"/>
         <Preference android:key="recovery" android:title="@string/recovery"
             android:summary="@string/recovery_summary"/>
-        <Preference android:key="flush_dnscache" android:title="@string/flush_dnscache"
-                    android:summary="@string/flush_dnscache_summary"/>
+        <Preference android:key="flush_dnscache" android:title="@string/flush_dnscache"/>
         <Preference android:key="about" android:title="@string/about"/>
 
     </PreferenceCategory>
diff --git a/src/main/scala/com/github/shadowsocks/ShadowsocksSettings.scala b/src/main/scala/com/github/shadowsocks/ShadowsocksSettings.scala
index e7f9dfd6..79de4e4b 100644
--- a/src/main/scala/com/github/shadowsocks/ShadowsocksSettings.scala
+++ b/src/main/scala/com/github/shadowsocks/ShadowsocksSettings.scala
@@ -5,7 +5,7 @@ import java.util.Locale
 import android.app.AlertDialog
 import android.content.{DialogInterface, Intent}
 import android.net.Uri
-import android.os.Bundle
+import android.os.{Build, Bundle}
 import android.preference.{Preference, PreferenceFragment}
 import android.webkit.{WebViewClient, WebView}
 import com.github.shadowsocks.utils.Key
@@ -30,7 +30,11 @@ class ShadowsocksSettings extends PreferenceFragment {
       true
     })
 
-    findPreference("flush_dnscache").setOnPreferenceClickListener((preference: Preference) => {
+    val flush = findPreference("flush_dnscache")
+    if (Build.VERSION.SDK_INT >= 17 && !ShadowsocksApplication.isRoot) {
+      flush.setEnabled(false)
+      flush.setSummary(R.string.flush_dnscache_summary_disabled)
+    } else flush.setOnPreferenceClickListener((preference: Preference) => {
       ShadowsocksApplication.track(Shadowsocks.TAG, "flush_dnscache")
       activity.flushDnsCache()
       true
diff --git a/src/main/scala/com/github/shadowsocks/utils/Utils.scala b/src/main/scala/com/github/shadowsocks/utils/Utils.scala
index f2d5c981..1f1dceaf 100644
--- a/src/main/scala/com/github/shadowsocks/utils/Utils.scala
+++ b/src/main/scala/com/github/shadowsocks/utils/Utils.scala
@@ -55,7 +55,7 @@ import android.util.{DisplayMetrics, Base64, Log}
 import android.view.View.MeasureSpec
 import android.view.{Gravity, View, Window}
 import android.widget.Toast
-import com.github.shadowsocks.BuildConfig
+import com.github.shadowsocks.{ShadowsocksApplication, BuildConfig}
 import org.xbill.DNS._
 
 
@@ -155,24 +155,13 @@ object Utils {
 
   // Blocked > 3 seconds
   def toggleAirplaneMode(context: Context) {
-    if (Build.VERSION.SDK_INT >= 17) {
-      toggleAboveApiLevel17()
-    } else {
+    if (ShadowsocksApplication.isRoot) {
+      Console.runRootCommand(Array("ndc resolver flushdefaultif", "ndc resolver flushif wlan0"))
+    } else if (Build.VERSION.SDK_INT < 17) {
       toggleBelowApiLevel17(context)
     }
   }
 
-  private def toggleAboveApiLevel17() {
-    // Android 4.2 and above
-
-    Console.runRootCommand(Array("ndc resolver flushdefaultif", "ndc resolver flushif wlan0"))
-
-    //Utils.runRootCommand("settings put global airplane_mode_on 1\n"
-    //  + "am broadcast -a android.intent.action.AIRPLANE_MODE --ez state true\n"
-    //  + "settings put global airplane_mode_on 0\n"
-    //  + "am broadcast -a android.intent.action.AIRPLANE_MODE --ez state false\n")
-  }
-
   //noinspection ScalaDeprecation
   private def toggleBelowApiLevel17(context: Context) {
     // Android 4.2 below