ZooKeeper responds to a small set of commands. Each command is composed of four letters. You issue the commands to ZooKeeper via telnet or nc, at the client port.

Three of the more interesting commands: "stat" gives some general information about the server and connected clients, while "srvr" and "cons" give extended details on server and connections respectively.

conf

New in 3.3.0: Print details about serving configuration.

cons

New in 3.3.0: List full connection/session details for all clients connected to this server. Includes information on numbers of packets received/sent, session id, operation latencies, last operation performed, etc...

crst

New in 3.3.0: Reset connection/session statistics for all connections.

dump

Lists the outstanding sessions and ephemeral nodes. This only works on the leader.

envi

Print details about serving environment

ruok

Tests if server is running in a non-error state. The server will respond with imok if it is running. Otherwise it will not respond at all.

A response of "imok" does not necessarily indicate that the server has joined the quorum, just that the server process is active and bound to the specified client port. Use "stat" for details on state wrt quorum and client connection information.

srst

Reset server statistics.

srvr

New in 3.3.0: Lists full details for the server.

stat

Lists brief details for the server and connected clients.

wchs

New in 3.3.0: Lists brief information on watches for the server.

wchc

New in 3.3.0: Lists detailed information on watches for the server, by session. This outputs a list of sessions(connections) with associated watches (paths). Note, depending on the number of watches this operation may be expensive (ie impact server performance), use it carefully.

wchp

New in 3.3.0: Lists detailed information on watches for the server, by path. This outputs a list of paths (znodes) with associated sessions. Note, depending on the number of watches this operation may be expensive (ie impact server performance), use it carefully.

mntr

New in 3.4.0: Outputs a list of variables that could be used for monitoring the health of the cluster.

$ echo mntr | nc localhost 2185  zk_version  3.4.0 zk_avg_latency  0 zk_max_latency  0 zk_min_latency  0 zk_packets_received 70 zk_packets_sent 69 zk_outstanding_requests 0 zk_server_state leader zk_znode_count   4 zk_watch_count  0 zk_ephemerals_count 0 zk_approximate_data_size    27 zk_followers    4                   - only exposed by the Leader zk_synced_followers 4               - only exposed by the Leader zk_pending_syncs    0               - only exposed by the Leader zk_open_file_descriptor_count 23    - only available on Unix platforms zk_max_file_descriptor_count 1024   - only available on Unix platforms 

The output is compatible with java properties format and the content may change over time (new keys added). Your scripts should expect changes.

ATTENTION: Some of the keys are platform specific and some of the keys are only exported by the Leader.

The output contains multiple lines with the following format:

key \t value

Here's an example of the ruok command:

$ echo ruok | nc 127.0.0.1 5111 imok