diff --git a/lib/Controller/MainController.php b/lib/Controller/MainController.php
index 256e9f0..a6b2e5f 100644
--- a/lib/Controller/MainController.php
+++ b/lib/Controller/MainController.php
@@ -54,21 +54,38 @@ class MainController extends Controller
         // OC_Util::addStyle($this->appName, 'table');
         $params = array();
         $params['aria2_running'] = $this->aria2->isRunning();
-        $params['aria2_installed'] = $this->aria2->isInstalled();
-        $params['aria2_bin'] = $this->aria2->getBin();
-        $params['aria2_executable'] = $this->aria2->isExecutable();
-        $params['youtube_installed'] = $this->youtube->isInstalled();
-        $params['youtube_bin'] = $this->youtube->getBin();
-        $params['youtube_executable'] = $this->youtube->isExecutable();
+        $params['aria2_installed'] = $aria2_installed = $this->aria2->isInstalled();
+        $params['aria2_bin'] = $aria2_bin = $this->aria2->getBin();
+        $params['aria2_executable'] = $aria2_executable = $this->aria2->isExecutable();
+        $params['youtube_installed'] = $youtube_installed = $this->youtube->isInstalled();
+        $params['youtube_bin'] = $youtube_bin = $this->youtube->getBin();
+        $params['youtube_executable'] = $youtube_executable = $this->youtube->isExecutable();
         $params['ncd_hide_errors'] = $this->settings->get("ncd_hide_errors", false);
         $params['counter'] = $this->counters->getCounters();
+        $params['python_installed'] = $python_installed = Helper::pythonInstalled();
+
+        $errors = [];
+        if ($aria2_installed && !$aria2_executable) {
+            array_push($errors, sprintf("aria2 is installed but don't have the right permissions.Please execute command sudo chmod 755 %s", $aria2_bin));
+        }
+
+        if ($youtube_installed && (!$youtube_executable || !@is_readable($youtube_bin))) {
+            array_push($errors, sprintf("youtube-dl is installed but don't have the right permissions.Please execute command sudo chmod 755 %s", $youtube_bin));
+        } else if (!$youtube_installed) {
+            array_push($errors, "youtube-dl is not installed!");
+        }
+
+        if (!$python_installed) {
+            array_push($errors, "python is not installed!");
+        }
+        $params['errors'] = $errors;
 
         $params['settings'] = json_encode([
-            'is_admin' =>\OC_User::isAdminUser($this->uid),
+            'is_admin' => \OC_User::isAdminUser($this->uid),
             'admin_url' => $this->urlGenerator->linkToRoute("settings.AdminSettings.index", ['section' => 'ncdownloader']),
-            'personal_url' =>  $this->urlGenerator->linkToRoute("settings.PersonalSettings.index", ['section' => 'ncdownloader']),
-            'ncd_hide_errors' =>  $params['ncd_hide_errors'],
-         ]);
+            'personal_url' => $this->urlGenerator->linkToRoute("settings.PersonalSettings.index", ['section' => 'ncdownloader']),
+            'ncd_hide_errors' => $params['ncd_hide_errors'],
+        ]);
         $response = new TemplateResponse($this->appName, 'Index', $params);
 
         return $response;
diff --git a/lib/Tools/Aria2.php b/lib/Tools/Aria2.php
index 2801a9d..1860e32 100644
--- a/lib/Tools/Aria2.php
+++ b/lib/Tools/Aria2.php
@@ -44,7 +44,7 @@ class Aria2
             $this->bin = Helper::findBinaryPath('aria2c', __DIR__ . "/../../bin/aria2c");
         }
         if ($this->isInstalled() && !$this->isExecutable()) {
-            chmod($this->bin, 755);
+            chmod($this->bin, 0744);
         }
         $this->setDownloadDir($dir);
         $this->setTorrentsDir($torrents_dir);
diff --git a/lib/Tools/Helper.php b/lib/Tools/Helper.php
index e992e63..7becd2a 100644
--- a/lib/Tools/Helper.php
+++ b/lib/Tools/Helper.php
@@ -209,8 +209,10 @@ class Helper
         $exeSniffer = new ExecutableFinder();
         // Returns null if nothing is found
         $result = $exeSniffer->find($program, $default, $paths);
-        // store the value for 5 minutes
-        $memcache->set($program, $result, 300);
+        if ($result) {
+            // store the value for 5 minutes
+            $memcache->set($program, $result, 300);
+        }
         return $result;
     }
 
@@ -324,4 +326,9 @@ class Helper
         return self::doSignal($pid, 9);
     }
 
+    public static function pythonInstalled()
+    {
+        return (bool) self::findBinaryPath('python');
+    }
+
 }
diff --git a/lib/Tools/Youtube.php b/lib/Tools/Youtube.php
index 174968f..ca5a4d9 100644
--- a/lib/Tools/Youtube.php
+++ b/lib/Tools/Youtube.php
@@ -34,7 +34,7 @@ class Youtube
             $this->bin = Helper::findBinaryPath('youtube-dl', __DIR__ . "/../../bin/youtube-dl");
         }
         if ($this->isInstalled() && !$this->isExecutable()) {
-            chmod($this->bin, 755);
+            chmod($this->bin, 0744);
         }
         $this->setDownloadDir($downloadDir);
         if (!empty($settings)) {
@@ -246,6 +246,11 @@ class Youtube
         return @is_executable($this->bin);
     }
 
+    public function isReadable()
+    {
+        return @is_readable($this->bin);
+    }
+
     public function getBin()
     {
         return $this->bin;
diff --git a/templates/Navigation.php b/templates/Navigation.php
index 8c90758..b14c153 100644
--- a/templates/Navigation.php
+++ b/templates/Navigation.php
@@ -1,16 +1,5 @@
 <?php
 extract($_);
-$errors = [];
-if ($aria2_installed && !$aria2_executable) {
-    array_push($errors, sprintf("aria2 is installed but not executable.Please execute command sudo chmod 755 %s", $aria2_bin));
-}
-
-if ($youtube_installed && !$youtube_executable) {
-    array_push($errors, sprintf("youtube-dl is installed but not executable.Please execute command sudo chmod 755 %s", $youtube_bin));
-} else if (!$youtube_installed) {
-    array_push($errors, "youtube-dl is not installed!");
-}
-
 ?>
 <div id="app-navigation">
     <?php if (!$ncd_hide_errors): ?>