diff --git a/doc/source/cli/nova-manage.rst b/doc/source/cli/nova-manage.rst
index 862d8d4492f3..e27b151a2934 100644
--- a/doc/source/cli/nova-manage.rst
+++ b/doc/source/cli/nova-manage.rst
@@ -35,7 +35,7 @@ Run without arguments to see a list of available command categories::
 
   nova-manage
 
-You can also run with a category argument such as user to see a list of all
+You can also run with a category argument such as ``db`` to see a list of all
 commands in that category::
 
   nova-manage db
diff --git a/nova/cmd/common.py b/nova/cmd/common.py
index 684ae7ba2626..ab7b7c3ca205 100644
--- a/nova/cmd/common.py
+++ b/nova/cmd/common.py
@@ -124,6 +124,7 @@ def add_command_parsers(subparsers, categories):
         parser.set_defaults(command_object=command_object)
 
         category_subparsers = parser.add_subparsers(dest='action')
+        category_subparsers.required = True
 
         for (action, action_fn) in methods_of(command_object):
             parser = category_subparsers.add_parser(