diff --git a/app/build.gradle b/app/build.gradle
index c560d4c..d831a06 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -7,7 +7,7 @@ android {
     buildToolsVersion "25.0.2"
     defaultConfig {
         applicationId "org.itxtech.daedalus"
-        minSdkVersion 21
+        minSdkVersion 15
         targetSdkVersion 25
         versionCode 2
         versionName "1.0.1"
diff --git a/app/src/main/java/org/itxtech/daedalus/fragment/SettingsFragment.java b/app/src/main/java/org/itxtech/daedalus/fragment/SettingsFragment.java
index 3b99cd6..d91a5a8 100644
--- a/app/src/main/java/org/itxtech/daedalus/fragment/SettingsFragment.java
+++ b/app/src/main/java/org/itxtech/daedalus/fragment/SettingsFragment.java
@@ -2,10 +2,12 @@ package org.itxtech.daedalus.fragment;
 
 import android.content.Intent;
 import android.net.Uri;
+import android.os.Build;
 import android.os.Bundle;
 import android.preference.ListPreference;
 import android.preference.Preference;
 import android.preference.PreferenceFragment;
+import android.preference.SwitchPreference;
 import android.support.design.widget.Snackbar;
 import android.view.LayoutInflater;
 import android.view.View;
@@ -25,6 +27,7 @@ import org.itxtech.daedalus.util.DnsServer;
  * the Free Software Foundation, version 3.
  */
 public class SettingsFragment extends PreferenceFragment {
+    private View view = null;
     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
@@ -37,11 +40,17 @@ public class SettingsFragment extends PreferenceFragment {
         ListPreference secondaryServer = (ListPreference) findPreference("secondary_server");
         secondaryServer.setEntries(DnsServer.getDnsServerNames(Daedalus.getInstance()));
         secondaryServer.setEntryValues(DnsServer.getDnsServerIds());
+
+        if (Build.VERSION.SDK_INT < 21) {
+            SwitchPreference countQueryTimes = (SwitchPreference) findPreference("settings_count_query_times");
+            countQueryTimes.setChecked(false);
+            countQueryTimes.setEnabled(false);
+        }
     }
 
     @Override
     public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
-        final View view = super.onCreateView(inflater, container, savedInstanceState);
+        view = super.onCreateView(inflater, container, savedInstanceState);
 
         ListPreference checkUpdate = (ListPreference) findPreference("settings_check_update");
         checkUpdate.setOnPreferenceClickListener(new Preference.OnPreferenceClickListener() {
@@ -56,4 +65,20 @@ public class SettingsFragment extends PreferenceFragment {
 
         return view;
     }
+
+    @Override
+    public void onStart() {
+        super.onStart();
+        if (view != null && Build.VERSION.SDK_INT < 21) {
+            Snackbar.make(view, R.string.notice_legacy_api, Snackbar.LENGTH_LONG)
+                    .setAction("Action", null).show();
+        }
+    }
+
+    @Override
+    public void onDestroyView() {
+        super.onDestroyView();
+
+        view = null;
+    }
 }
diff --git a/app/src/main/java/org/itxtech/daedalus/service/DaedalusVpnService.java b/app/src/main/java/org/itxtech/daedalus/service/DaedalusVpnService.java
index 03be78e..a27e3af 100644
--- a/app/src/main/java/org/itxtech/daedalus/service/DaedalusVpnService.java
+++ b/app/src/main/java/org/itxtech/daedalus/service/DaedalusVpnService.java
@@ -143,8 +143,12 @@ public class DaedalusVpnService extends VpnService implements Runnable {
             if (this.mThread != null) {
                 this.running = false;
                 this.mThread.interrupt();
-                Os.close(mInterruptFd);
-                Os.close(mBlockFd);
+                if (mInterruptFd != null) {
+                    Os.close(mInterruptFd);
+                }
+                if (mBlockFd != null) {
+                    Os.close(mBlockFd);
+                }
                 this.mThread = null;
             }
             if (notification != null) {
@@ -166,10 +170,6 @@ public class DaedalusVpnService extends VpnService implements Runnable {
     @Override
     public void run() {
         try {
-            FileDescriptor[] pipes = Os.pipe();
-            mInterruptFd = pipes[0];
-            mBlockFd = pipes[1];
-
             Builder builder = new Builder();
             String format = null;
             for (String prefix : new String[]{"192.0.2", "198.51.100", "203.0.113", "10.0.0.", "192.168.50"}) {
@@ -185,7 +185,7 @@ public class DaedalusVpnService extends VpnService implements Runnable {
                 this.descriptor.close();
             }
 
-            boolean statisticQuery = PreferenceManager.getDefaultSharedPreferences(this).getBoolean("settings_query", false);
+            boolean statisticQuery = PreferenceManager.getDefaultSharedPreferences(this).getBoolean("settings_count_query_times", false);
             Log.d(TAG, "tun0 add " + format + " pServ " + primaryServer + " sServ " + secondaryServer);
             Inet4Address primaryDNSServer = InetAddressUtil.ipv4From(primaryServer);
             Inet4Address secondaryDNSServer = InetAddressUtil.ipv4From(secondaryServer);
@@ -194,13 +194,17 @@ public class DaedalusVpnService extends VpnService implements Runnable {
 
             if (statisticQuery) {
                 builder.addRoute(primaryDNSServer, primaryDNSServer.getAddress().length * 8)
-                        .addRoute(secondaryDNSServer, secondaryDNSServer.getAddress().length * 8);
+                        .addRoute(secondaryDNSServer, secondaryDNSServer.getAddress().length * 8)
+                        .setBlocking(true);
             }
 
-            this.descriptor = builder.setSession("Daedalus").setConfigureIntent(PendingIntent.getActivity(this, 0, new Intent(this, SettingsActivity.class), PendingIntent.FLAG_ONE_SHOT)).setBlocking(true).establish();
+            this.descriptor = builder.setSession("Daedalus").setConfigureIntent(PendingIntent.getActivity(this, 0, new Intent(this, SettingsActivity.class), PendingIntent.FLAG_ONE_SHOT)).establish();
 
             if (statisticQuery) {
                 Log.d(TAG, "Starting count queries");
+                FileDescriptor[] pipes = Os.pipe();
+                mInterruptFd = pipes[0];
+                mBlockFd = pipes[1];
                 FileInputStream inputStream = new FileInputStream(descriptor.getFileDescriptor());
                 FileOutputStream outputStream = new FileOutputStream(descriptor.getFileDescriptor());
 
diff --git a/app/src/main/res/values-zh/strings.xml b/app/src/main/res/values-zh/strings.xml
index 7f32eba..fcdc8bf 100644
--- a/app/src/main/res/values-zh/strings.xml
+++ b/app/src/main/res/values-zh/strings.xml
@@ -21,7 +21,7 @@
     <string name="test_domain">测试域名:</string>
     <string name="test_time_used">耗时:</string>
     <string name="test_dns_server">DNS 服务器:</string>
-    <string name="test_result_resolved">解析结果:</string>
+    <string name="test_result_resolved">解析地址:</string>
     <string name="test_failed">查询失败。超时或未知的主机。</string>
     <string name="test_test_domain">google.com</string>
     <string name="action_visit_cutedns">访问 CuteDNS!</string>
@@ -35,4 +35,5 @@
     <string name="notice_checking_update">正在前往 GitHub Releases 页面……</string>
     <string name="settings_count_number_of_queries">统计 DNS 查询次数</string>
     <string name="notification_queries">DNS 查询次数:</string>
+    <string name="notice_legacy_api">当前 Android API 无法支持所有功能。</string>
 </resources>
\ No newline at end of file
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 1a8e3cf..78d8d6c 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -20,7 +20,7 @@
     <string name="test_domain">Test domain:</string>
     <string name="test_time_used">Time used:</string>
     <string name="test_dns_server">DNS server:</string>
-    <string name="test_result_resolved">Resolved address:</string>
+    <string name="test_result_resolved">Address:</string>
     <string name="test_failed">Query failed. Timeout or unknown hostname.</string>
     <string name="test_test_domain">google.com</string>
     <string name="action_visit_itxtech">Visit iTXTech</string>
@@ -33,6 +33,7 @@
     <string name="settings_check_update">Check update</string>
     <string name="settings_update_summary">Check update via GitHub</string>
     <string name="notice_checking_update">Going to the GitHub Releases page …</string>
-    <string name="settings_count_number_of_queries">Count number of DNS queries</string>
+    <string name="settings_count_number_of_queries">Count DNS query times</string>
     <string name="notification_queries">DNS Query times:</string>
+    <string name="notice_legacy_api">The current Android API can not support all the features.</string>
 </resources>
diff --git a/app/src/main/res/xml/perf_settings.xml b/app/src/main/res/xml/perf_settings.xml
index f4386be..4982d36 100644
--- a/app/src/main/res/xml/perf_settings.xml
+++ b/app/src/main/res/xml/perf_settings.xml
@@ -26,7 +26,7 @@
                 android:title="@string/settings_boot"
                 android:defaultValue="false"/>
         <SwitchPreference
-                android:key="settings_query"
+                android:key="settings_count_query_times"
                 android:title="@string/settings_count_number_of_queries"
                 android:defaultValue="false"/>
         <SwitchPreference