rabbitmq cannot start after change config file - rabbitmq

Question

rabbitmq runs well, but cannot start after I change its config file according to the official doc.
I install openstack on opensuse13.2, following this doc:
http://docs.openstack.org/juno/install-guide/install/zypper/content/index.html
When reaching at 'Messaging server' section of 'Chapter 2. Basic environment`':
http://docs.openstack.org/juno/install-guide/install/zypper/content/ch_basic_environment.html#basics-messaging-server
Right here,some quote of this doc:
3. For RabbitMQ version 3.3.0 or newer, you must enable remote access for the guest account.
Check the RabbitMQ version:
A. # rabbitmqctl status | grep rabbit
Status of node 'rabbit#controller' ...
{running_applications,[{rabbit,"RabbitMQ","3.4.2"},
B. If necessary, edit the /etc/rabbitmq/rabbitmq.config file and configure loopback_users to reference an empty list:
[{rabbit, [{loopback_users, []}]}].
C. Restart the message broker service:
On openSUSE:
# systemctl restart rabbitmq-server.service
And I proceed like this:
a. controller:~ # rabbitmqctl status | grep rabbit
Status of node rabbit#controller ...
{running_applications,[{rabbit,"RabbitMQ","3.3.5"},
b.change config file:/etc/rabbitmq/rabbitmq.config,i.e. uncomment this line
%% {loopback_users, []},
c.controller:~ # systemctl start rabbitmq-server.service
Job for rabbitmq-server.service failed. See "systemctl status rabbitmq-server.service" and "journalctl -xn" for details.
d.controller:~ # systemctl status rabbitmq-server.service
rabbitmq-server.service - RabbitMQ broker
Loaded: loaded (/usr/lib/systemd/system/rabbitmq-server.service; enabled)
Active: failed (Result: exit-code) since 二 2015-04-14 14:27:59 CST; 30s ago
Process: 7387 ExecStopPost=/usr/bin/rm /var/run/rabbitmq/pid (code=exited, status=0/SUCCESS)
Process: 7345 ExecStop=/usr/sbin/rabbitmqctl stop (code=exited, status=2)
Process: 7219 ExecStartPost=/usr/sbin/rabbitmqctl wait /var/run/rabbitmq/pid (code=exited, status=2)
Process: 7218 ExecStart=/usr/sbin/rabbitmq-server (code=exited, status=1/FAILURE)
Main PID: 7218 (code=exited, status=1/FAILURE)
4月 14 14:27:59 controller rabbitmqctl[7345]: attempted to contact: [rabbit#controller]
4月 14 14:27:59 controller rabbitmqctl[7345]: rabbit#controller:
4月 14 14:27:59 controller rabbitmqctl[7345]: * connected to epmd (port 4369) on controller
4月 14 14:27:59 controller rabbitmqctl[7345]: * epmd reports: node 'rabbit' not running at all
4月 14 14:27:59 controller rabbitmqctl[7345]: no other nodes on controller
4月 14 14:27:59 controller rabbitmqctl[7345]: * suggestion: start the node
4月 14 14:27:59 controller rabbitmqctl[7345]: current node details:
4月 14 14:27:59 controller rabbitmqctl[7345]: - node name: rabbitmqctl7354#controller
4月 14 14:27:59 controller rabbitmqctl[7345]: - home dir: /var/lib/rabbitmq
4月 14 14:27:59 controller rabbitmqctl[7345]: - cookie hash: kBnKPRMCXBnfQlB8kipSdA==