I did some test:
When it's running:
$ /usr/lib/zookeeper/bin/zkServer.sh status
JMX enabled by default
Using config: /usr/lib/zookeeper/bin/../conf/zoo.cfg
Mode: follower
When it's stopped:
$ zkServer status
JMX enabled by default
Using config: /usr/local/etc/zookeeper/zoo.cfg
Error contacting service. It is probably not running.
I'm not running on the same machine, but you get the idea.