Check for OSError when starting the server.

gns3server/main.py

@@ -79,7 +79,7 @@ def parse_arguments():
     parser.add_argument("--ssl", action="store_true", help="run in SSL mode")
     parser.add_argument("--certfile", help="SSL cert file", default="")
     parser.add_argument("--certkey", help="SSL key file", default="")
-    parser.add_argument("-L", "--local", action="store_true", help="local mode (allow some insecure operations)")
+    parser.add_argument("-L", "--local", action="store_true", help="local mode (allows some insecure operations)")
     parser.add_argument("-A", "--allow", action="store_true", help="allow remote connections to local console ports")
     parser.add_argument("-q", "--quiet", action="store_true", help="do not show logs on stdout")
     parser.add_argument("-d", "--debug", action="store_true", help="show debug logs and enable code live reload")

gns3server/server.py

@@ -53,7 +53,12 @@ class Server:
     @asyncio.coroutine
     def _run_application(self, app, ssl_context=None):
 
-        server = yield from self._loop.create_server(app.make_handler(), self._host, self._port, ssl=ssl_context)
+        try:
+            server = yield from self._loop.create_server(app.make_handler(), self._host, self._port, ssl=ssl_context)
+        except OSError as e:
+            log.critical("Could not start the server: {}".format(e))
+            self._loop.stop()
+            return
         return server
 
     def _stop_application(self):