ZooKeeper Command Line Interface (CLI)

ZooKeeper commands

ZooKeeper Command Line Interface (CLI) is used to interact with the ZooKeeper ensemble which lets you perform simple, file-like operations. It is useful for debugging purposes.

• To perform ZooKeeper CLI operations, first start your ZooKeeper server and then, ZooKeeper client by “bin/zkCli.sh”. Once the client starts, from the shell, type help to get a listing of commands that can be executed from the client, as in:

  [zk: localhost:2181(CONNECTED) 0] help
  ZooKeeper -server host:port cmd args
          connect host:port
          get path [watch]
          ls path [watch]
          set path data [version]
          rmr path
          delquota [-n|-b] path
          quit
          printwatches on|off
          create [-s] [-e] path data acl
          stat path [watch]
          close
          ls2 path [watch]
          history
          listquota path
          setAcl path acl
          getAcl path
          sync path
          redo cmdno
          addauth scheme auth
          delete path [version]
          setquota -n|-b val path
  [zk: localhost:2181(CONNECTED) 1]
  

• From here, you can try a few commands to get a feel for this simple command line interface. First, start by issuing the list command, as in ls:

  [zk: localhost:2181(CONNECTED) 1] ls /
  [zookeeper]
  

• Next, create a new znode by running create /zk_test my_data. This creates a new znode and associates the string "my_data" with the node. You should see:

  [zk: localhost:2181(CONNECTED) 2] create /zk_test my_data
  Created /zk_test
  

• Issue another ls / command to see what the directory looks like:

  [zk: localhost:2181(CONNECTED) 3]  ls /
  [zookeeper, zk_test]
  

  Notice that the zk_test directory has now been created.

• Next, verify that the data was associated with the znode by running the get command, as in:

  [zk: localhost:2181(CONNECTED) 4] get /zk_test
  my_data
  cZxid = 0x8
  ctime = Mon Nov 30 18:41:06 IST 2015
  mZxid = 0x8
  mtime = Mon Nov 30 18:41:06 IST 2015
  pZxid = 0x8
  cversion = 0
  dataVersion = 0
  aclVersion = 0
  ephemeralOwner = 0x0
  dataLength = 7
  numChildren = 0
  

• We can change the data associated with zk_test by issuing the set command, as in:

  [zk: localhost:2181(CONNECTED) 5] set /zk_test junk
  cZxid = 0x8
  ctime = Mon Nov 30 18:41:06 IST 2015
  mZxid = 0x9
  mtime = Mon Nov 30 18:43:06 IST 2015
  pZxid = 0x8
  cversion = 0
  dataVersion = 1
  aclVersion = 0
  ephemeralOwner = 0x0
  dataLength = 4
  numChildren = 0
  

• Finally, let's delete the node by issuing:

  [zk: localhost:2181(CONNECTED) 6] delete /zk_test
  

Other important Zookeeper commands

Zookeeper Watch

Watches show a notification when the specified znode’s data get changed. You can set a watch only in get command, like:

get /path-to-znode [watch] 1

Lets run the watch command, as in:

[zk: localhost:2181(CONNECTED) 7] get /zk_test 1
my_data
cZxid = 0x8
ctime = Mon Nov 30 18:41:06 IST 2015
mZxid = 0x8
mtime = Mon Nov 30 18:41:06 IST 2015
pZxid = 0x8
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 7
numChildren = 0

The output is similar to get command, but it will wait for znode changes in the background.

Create Sub znode

You create sub-znode in a similar way as creating new znodes. The only difference is that the path of the child znode will have the parent path as well. Lets create a children of zk_test znode, like below:

[zk: localhost:2181(CONNECTED) 8] create /zk_test/Child1 “firstchild”
created /zk_test/Child1
[zk: localhost:2181(CONNECTED) 9] create /zk_test/Child2 “secondchild”
created /zk_test/Child2

List Children

Now to get the list of all children of our znode 'zk_test' type like below:

[zk: localhost:2181(CONNECTED) 10] ls /zk_test
[Child1, Child2]

Check Status

The metadata of a znode contains details such as Timestamp, Version number, ACL, Data length, and Children znode. If you want to view the metadata, use check status command like below:

[zk: localhost:2181(CONNECTED) 11] stat /zk_test
cZxid = 0x8
ctime = Mon Nov 30 18:41:06 IST 2015
mZxid = 0x8
mtime = Mon Nov 30 18:41:06 IST 2015
pZxid = 0x8
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 7
numChildren = 0

Quit

Finally to exit from command line interface, type quit:

[zk: localhost:2181(CONNECTED) 12] quit
Quitting...
[[email protected] bin]$

Zookeeper znode metadata

Using the get command we can view the data and metadata stored in our new znode.

[zk: localhost:2181(CONNECTED) 13] get /zk_test
my_data
cZxid = 0x8
ctime = Mon Nov 30 18:41:06 IST 2015
mZxid = 0x8
mtime = Mon Nov 30 18:41:06 IST 2015
pZxid = 0x8
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 7
numChildren = 0

Let’s examine the data and metadata that is returned:

• my_data :This line of text is the data that we stored in the znode.
• cZxid = 0x8 :The zxid (ZooKeeper Transaction Id) of the change that caused this znode to be created.
• ctime = Mon Nov 30 18:41:06 IST 2015 :The time when this znode was created.
• mZxid = 0x8 :The zxid of the change that last modified this znode.
• mtime = Mon Nov 30 18:41:06 IST 2015 :The time when this znode was last modified.
• pZxid = 0x8 :The zxid of the change that last modified children of this znode.
• cversion = 0 :The number of changes to the children of this znode.
• dataVersion = 0 :The number of changes to the data of this znode.
• aclVersion = 0 :The number of changes to the ACL of this znode.
• ephemeralOwner = 0x0: The session id of the owner of this znode if the znode is an ephemeral node. If it is not an ephemeral node, it will be zero.
• dataLength = 7 :The length of the data field of this znode.
• numChildren = 0 :The number of children of this znode.