There was a typo in the setting file

nnmon/settings.py

@@ -206,7 +206,7 @@ DEFAULT_FROM_EMAIL = 'nnmon@nnmon.lqdn.fr'
 HAYSTACK_CONNECTIONS = {
         'default': {
             'ENGINE': 'haystack.backends.whoosh_backend.WhooshEngine',
-            'PATH': os.path.join(os.path.dirnam(__file__), 'whoosh_index'),
+            'PATH': os.path.join(os.path.dirname(__file__), 'whoosh_index'),
         },
 }