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8.0 Zookeeper Four-Letter Commands

Category Zookeeper Tutorial

Zookeeper supports certain specific four-letter commands for interaction, allowing users to obtain the current status and related information of the Zookeeper service. Users can submit corresponding commands to Zookeeper via telenet or nc (netcat) from the client.

Install nc command:

$ yum install nc                # CentOS
or
$ sudo apt install netcat       # Ubuntu

Four-letter command format:

echo [command] | nc [ip] [port]

Commonly used four-letter commands in ZooKeeper are as follows:

Four-Letter Command Functional Description
conf Introduced in version 3.3.0. Prints detailed information about service-related configurations.
cons Introduced in version 3.3.0. Lists all the connection/session details of clients connected to this server. Includes information such as "received/sent" packet counts, session ID, operation latency, last operation performed, etc.
crst Introduced in version 3.3.0. Resets connection and session statistics for all connections.
dump Lists important sessions and ephemeral nodes. This command is only useful on the leader node.
envi Prints detailed information about the service environment.
reqs Lists unprocessed requests.
ruok Tests whether the service is in the correct state. If so, the service returns "imok"; otherwise, it does not respond.
stat Outputs a list of clients about performance and connections.
srst Resets server statistics.
srvr Introduced in version 3.3.0. Lists detailed information about the server connections.
wchs Introduced in version 3.3.0. Lists detailed information about server watches.
wchc Introduced in version 3.3.0. Lists detailed information about server watches by session. Its output is a list of sessions related to watches.
wchp Introduced in version 3.3.0. Lists detailed information about server watches by path. It outputs a path related to a session.
mntr Introduced in version 3.4.0. Outputs a list of variables that can be used to detect the health status of the cluster.

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Refer to the official link: https://zookeeper.apache.org/doc/current/zookeeperAdmin.html#sc_4lw


Four-Letter Command Usage

stat Command

The stat command is used to view the status information of zk, example as follows:

$ echo stat | nc 192.168.3.38 2181

ruok Command

The ruok command is used to check if the current zkserver is started; if it returns imok, it indicates normal operation. Example as follows:

$ echo ruok | nc 192.168.3.38 2181

dump Command

The dump command is used to list unprocessed sessions and ephemeral nodes. Example as follows:

$ echo dump | nc 192.168.3.38 2181

conf Command

The conf command is used to view server configuration. Example as follows:

$ echo conf | nc 192.168.3.38 2181

cons Command

The cons command is used to display information about clients connected to the server. Example as follows:

$ echo cons | nc 192.168.3.38 2181

envi Command

The envi command is used to view environment variables. Example as follows:

$ echo envi | nc 192.168.3.38 2181
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