diff --git a/js/index.js b/js/index.js
index 4641951..5df1a39 100644
--- a/js/index.js
+++ b/js/index.js
@@ -28,7 +28,11 @@
           }).done(function (response) {
             term.echo('\n' + response).resume();
           }).fail(function (response, code) {
-            term.echo('\n' + response).resume();
+	    if (response.status === 403) {
+		term.echo(response.responseJSON.error).resume();
+	    } else {
+                term.echo('\n[[;red;]Error]\n' + response).resume();
+	    }
           });
         }
       }, {
diff --git a/lib/Controller/OccController.php b/lib/Controller/OccController.php
index 1df129b..4c62a13 100644
--- a/lib/Controller/OccController.php
+++ b/lib/Controller/OccController.php
@@ -21,13 +21,13 @@ class OccController extends Controller
 
   private $application;
   private $output;
-
+  private $blacklist;
   public function __construct(ILogger $logger, $AppName, IRequest $request, $userId)
   {
     parent::__construct($AppName, $request);
     $this->logger = $logger;
     $this->userId = $userId;
-
+    $this->blacklist = array("maintenance:mode on");
     $this->application = new Application(
       OC::$server->getConfig(),
       OC::$server->getEventDispatcher(),
@@ -58,8 +58,9 @@ class OccController extends Controller
       $this->application->run($input, $this->output);
       return $this->output->fetch();
     } catch (Exception $ex) {
-      $this->logger->logException($ex);
-      return "error: " . $ex->getMessage();
+      exceptionHandler($ex);
+    } catch (Error $ex) {
+      exceptionHandler($ex);
     }
   }
 
@@ -70,6 +71,10 @@ class OccController extends Controller
   public function cmd($command)
   {
     $this->logger->debug($command);
+    if (in_array($command, $this->blacklist)) {
+	$this->logger->debug("Command blacklist");
+	return new DataResponse(array("error" => "\n".'\u001b[37;41m                                 \u001b[39;49m'."\n".'\u001b[37;41m  Command blacklisted.        \u001b[39;49m'."\n".'\u001b[37;41m                                 \u001b[39;49m'."\n\n"), 403);
+    }
     $input = new StringInput($command);
     $response = $this->run($input);
     $this->logger->debug($response);
@@ -86,3 +91,9 @@ class OccController extends Controller
   }
 }
 
+function exceptionHandler($exception)
+{
+  echo "An unhandled exception has been thrown:" . PHP_EOL;
+  echo $exception;
+  exit(1);
+}