ZooKeeper

https://zookeeper.apache.org/doc/current/
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### Install and start Dockerized Jepsen

Source: https://zookeeper.apache.org/doc/current/zookeeperTools.html

Clone the Jepsen repository, start the Dockerized environment with ./up.sh, and verify that one control node and five db nodes are up using docker ps. The first initialization may take a long time.

```bash
git clone git@github.com:jepsen-io/jepsen.git
cd docker
# maybe a long time for the first init.
./up.sh
# docker ps to check one control node and five db nodes are up
docker ps
     CONTAINER ID        IMAGE               COMMAND                 CREATED             STATUS              PORTS                     NAMES
     8265f1d3f89c        docker_control      "/bin/sh -c /init.sh"   9 hours ago         Up 4 hours          0.0.0.0:32769->8080/tcp   jepsen-control
     8a646102da44        docker_n5           "/run.sh"               9 hours ago         Up 3 hours          22/tcp                    jepsen-n5
     385454d7e520        docker_n1           "/run.sh"               9 hours ago         Up 9 hours          22/tcp                    jepsen-n1
     a62d6a9d5f8e        docker_n2           "/run.sh"               9 hours ago         Up 9 hours          22/tcp                    jepsen-n2
     1485e89d0d9a        docker_n3           "/run.sh"               9 hours ago         Up 9 hours          22/tcp                    jepsen-n3
     27ae01e1a0c5        docker_node         "/run.sh"               9 hours ago         Up 9 hours          22/tcp                    jepsen-node
     53c444b00ebd        docker_n4           "/run.sh"               9 hours ago         Up 9 hours          22/tcp                    jepsen-n4

```

--------------------------------

### start()

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/NIOServerCnxnFactory.html

Starts the server connection factory.

```APIDOC
## Method: start()

### Description
Starts the server connection factory.

### Signature
```java
public void start()
```

```

--------------------------------

### start()

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/metrics/MetricsProvider.html

Starts the provider, for example by starting a network endpoint. Throws MetricsProviderLifeCycleException if startup fails.

```APIDOC
## start()

### Description
Starts the provider, for example by starting a network endpoint. Throws MetricsProviderLifeCycleException if startup fails.

### Method
start

### Signature
void start() throws MetricsProviderLifeCycleException

### Throws
- **MetricsProviderLifeCycleException** - in case of failure.

```

--------------------------------

### start

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/ServerCnxnFactory.html

Starts the factory.

```APIDOC
## start

### Description
Starts the factory.

### Method
public abstract void start()
```

--------------------------------

### start()

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/embedded/ZooKeeperServerEmbedded.html

Starts the embedded ZooKeeper server.

```APIDOC
## start()

### Description
Starts the embedded ZooKeeper server.

### Method
start

### Signature
`void start() throws Exception`

### Throws
- `Exception` - If the server fails to start.
```

--------------------------------

### Example zoo.cfg with oraclePath

Source: https://zookeeper.apache.org/doc/current/zookeeperOracleQuorums.html

Example zoo.cfg showing required static parameters and the oraclePath entry.

```text
dataDir=/data
```

--------------------------------

### zkServer.sh usage and examples

Source: https://zookeeper.apache.org/doc/current/zookeeperTools.html

Shows the usage of zkServer.sh with commands like start, start-foreground, stop, restart, status, upgrade, print-cmd, and version. The status command output includes JMX enabled by default, config path, and mode. The version command outputs the ZooKeeper version.

```bash
Usage: ./zkServer.sh {start|start-foreground|stop|version|restart|status|upgrade|print-cmd}
# start the server
./zkServer.sh start

# start the server in the foreground for debugging
./zkServer.sh start-foreground

# stop the server
./zkServer.sh stop

# restart the server
./zkServer.sh restart

# show the status,mode,role of the server
./zkServer.sh status
JMX enabled by default
Using config: /data/software/zookeeper/conf/zoo.cfg
Mode: standalone

# Deprecated
./zkServer.sh upgrade

# print the parameters of the start-up
./zkServer.sh print-cmd

# show the version of the ZooKeeper server
./zkServer.sh version
Apache ZooKeeper, version 3.6.0-SNAPSHOT 06/11/2019 05:39 GMT

```

--------------------------------

### startup(ZooKeeperServer zks, boolean startServer)

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/NIOServerCnxnFactory.html

Starts up the server connection factory with the given ZooKeeperServer and whether to start the server. Throws IOException and InterruptedException.

```APIDOC
## Method: startup(ZooKeeperServer zks, boolean startServer)

### Description
Starts up the server connection factory with the given ZooKeeperServer and whether to start the server.

### Signature
```java
public void startup(ZooKeeperServer zks, boolean startServer) throws IOException, InterruptedException
```

### Parameters
- **zks** (ZooKeeperServer) - Required - The ZooKeeper server instance.
- **startServer** (boolean) - Required - Whether to start the server.

### Throws
- **IOException** - If an I/O error occurs.
- **InterruptedException** - If the operation is interrupted.

```

--------------------------------

### start(long startupTimeout)

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/embedded/ZooKeeperServerEmbedded.html

Starts the embedded ZooKeeper server with a specified startup timeout.

```APIDOC
## start(long startupTimeout)

### Description
Starts the embedded ZooKeeper server with a specified startup timeout.

### Method
start

### Signature
`void start(long startupTimeout) throws Exception`

### Parameters
- `startupTimeout` (long) - Required - Time to wait in milliseconds for the server to start.

### Throws
- `Exception` - If the server fails to start within the timeout.
```

--------------------------------

### Start ZooKeeper server (bin/zkServer.sh start)

Source: https://zookeeper.apache.org/doc/current/zookeeperStarted.html

Starts the ZooKeeper server in standalone mode. Run from the ZooKeeper root after creating the configuration file. Log messages appear on the console and/or a log file depending on the logback configuration.

```bash
bin/zkServer.sh start

```

--------------------------------

### zkCleanup.sh usage and example

Source: https://zookeeper.apache.org/doc/current/zookeeperTools.html

Shows the usage of zkCleanup.sh with arguments dataLogDir, snapDir, and count. The example keeps the latest 5 logs and snapshots.

```bash
Usage:
     * args dataLogDir [snapDir] -n count
     * dataLogDir -- path to the txn log directory
     * snapDir -- path to the snapshot directory
     * count -- the number of old snaps/logs you want to keep, value should be greater than or equal to 3
# Keep the latest 5 logs and snapshots
./zkCleanup.sh -n 5
```

--------------------------------

### Queue test: start a producer to create 100 elements

Source: https://zookeeper.apache.org/doc/current/zookeeperTutorial.html

Starts a producer for the queue test, creating 100 elements on the local ZooKeeper server.

```bash
java SyncPrimitive qTest localhost 100 p

```

--------------------------------

### connect command examples

Source: https://zookeeper.apache.org/doc/current/zookeeperCLI.html

Shows how to connect to a ZooKeeper server using the connect command. The first example connects to localhost:2181 and displays session establishment logs, then shows connecting to multiple servers. The second example connects to a remote server using remoteIP:2181.

```shell
[zkshell: 4] connect
	2019-03-09 06:43:33,179 [myid:localhost:2181] - INFO  [main-SendThread(localhost:2181):ClientCnxn$SendThread@986] - Socket connection established, initiating session, client: /127.0.0.1:35144, server: localhost/127.0.0.1:2181
	2019-03-09 06:43:33,189 [myid:localhost:2181] - INFO  [main-SendThread(localhost:2181):ClientCnxn$SendThread@1421] - Session establishment complete on server localhost/127.0.0.1:2181, sessionid = 0x10007ab7c550007, negotiated timeout = 30000
	connect "localhost:2181,localhost:2182,localhost:2183"

# connect a remote server
[zkshell: 5] connect remoteIP:2181
```

--------------------------------

### start()

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/common/FileChangeWatcher.html

Tells the background thread to start. Does not wait for it to be running. Calling this method more than once has no effect.

```APIDOC
## Method: start

### Description
Tells the background thread to start. Does not wait for it to be running. Calling this method more than once has no effect.

### Signature
```java
public void start()
```
```

--------------------------------

### Queue test: start a consumer to consume 100 elements

Source: https://zookeeper.apache.org/doc/current/zookeeperTutorial.html

Starts a consumer for the queue test, consuming 100 elements from the local ZooKeeper server.

```bash
java SyncPrimitive qTest localhost 100 c

```

--------------------------------

### Start ZooKeeper server with QuorumPeerMain

Source: https://zookeeper.apache.org/doc/current/zookeeperAdmin.html

Command to start a ZooKeeper server using QuorumPeerMain. Requires the configuration file (e.g., zoo.conf) and classpath including zookeeper.jar, lib/*, and conf. Registers JMX management beans.

```bash
$ java -cp zookeeper.jar:lib/*:conf org.apache.zookeeper.server.quorum.QuorumPeerMain zoo.conf

```

--------------------------------

### readTxnLog(long) - org.apache.zookeeper.server.persistence.FileTxnSnapLog

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/index-all.html

Get TxnIterator for iterating through txnlog starting at a given zxid.

```APIDOC
## readTxnLog(long)

### Description
Get TxnIterator for iterating through txnlog starting at a given zxid.

### Method
Instance method

### Class
org.apache.zookeeper.server.persistence.FileTxnSnapLog

### Parameters
- **zxid** (long) - The zxid to start from.

### Returns
- TxnIterator for iterating through txnlog.
```

--------------------------------

### startup

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/NettyServerCnxnFactory.html

Starts the server connection factory with a ZooKeeper server.

```APIDOC
## startup

### Description
Starts the server connection factory with a ZooKeeper server. This method is specified by the `startup` method in the `ServerCnxnFactory` class.

### Method
`startup`

### Signature
`public void startup(ZooKeeperServer zks, boolean startServer) throws IOException, InterruptedException`

### Parameters
- **zks** (ZooKeeperServer) - The ZooKeeper server to start.
- **startServer** (boolean) - Whether to start the server.

### Throws
- **IOException** - If an I/O error occurs.
- **InterruptedException** - If the current thread is interrupted.
```

--------------------------------

### readTxnLog(long, boolean) - org.apache.zookeeper.server.persistence.FileTxnSnapLog

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/index-all.html

Get TxnIterator for iterating through txnlog starting at a given zxid.

```APIDOC
## readTxnLog(long, boolean)

### Description
Get TxnIterator for iterating through txnlog starting at a given zxid.

### Method
Instance method

### Class
org.apache.zookeeper.server.persistence.FileTxnSnapLog

### Parameters
- **zxid** (long) - The zxid to start from.
- **fastForward** (boolean) - Whether to fast forward.

### Returns
- TxnIterator for iterating through txnlog.
```

--------------------------------

### main(String[] args)

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/quorum/QuorumPeerMain.html

Static entry point to start the ZooKeeper quorum peer server. The first argument is the path to the configuration file.

```APIDOC
## main(String[] args)

### Description
To start the replicated server specify the configuration file name on the command line.

### Method
main

### Signature
public static void main(String[] args)

### Parameters
- **args** (String[]) - Required - path to the configfile

### Throws
- QuorumPeerConfig.ConfigException
- IOException
- AdminServer.AdminServerException
```

--------------------------------

### Sample zoo.cfg configuration for Oracle

Source: https://zookeeper.apache.org/doc/current/zookeeperOracleQuorums.html

Example zoo.cfg configuration for a ZooKeeper instance with oraclePath set to /Volumes/Oracle/mastership. This configuration is used in the USB oracle setup.

```properties
dataDir=/data
dataLogDir=/datalog
tickTime=2000
initLimit=5
syncLimit=2
autopurge.snapRetainCount=3
autopurge.purgeInterval=0
maxClientCnxns=60
standaloneEnabled=true
admin.enableServer=true
oraclePath=/Volumes/Oracle/mastership
server.1=0.0.0.0:2888:3888;2181
server.2=hw1:2888:3888;2181
```

--------------------------------

### startup(ZooKeeperServer zkServer)

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/ServerCnxnFactory.html

Starts the factory with the given ZooKeeperServer.

```APIDOC
## startup(ZooKeeperServer zkServer)

### Description
Starts the factory with the given ZooKeeperServer.

### Method
public void startup(ZooKeeperServer zkServer) throws IOException, InterruptedException

### Parameters
- **zkServer** (ZooKeeperServer) - Required - The ZooKeeperServer to start.

### Throws
- **IOException** - If an I/O error occurs.
- **InterruptedException** - If the thread is interrupted.
```

--------------------------------

### Audit log entry for serverStart with OS user

Source: https://zookeeper.apache.org/doc/current/zookeeperAuditLogs.html

Example audit log entry for a system operation (serverStart) when no user is associated with the ZooKeeper server. The user who started the server (e.g., root) is used as the system user.

```text
user=root operation=serverStart result=success
```

--------------------------------

### initializeAndRun(String[] args)

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/ZooKeeperServerMain.html

Initializes and runs the server from command-line arguments.

```APIDOC
## initializeAndRun(String[] args)

### Description
Initializes and runs the server from command-line arguments.

### Method
initializeAndRun

### Signature
`protected void initializeAndRun(String[] args) throws QuorumPeerConfig.ConfigException, IOException, AdminServer.AdminServerException`

### Parameters
- **args** (String[]) - Required - Command-line arguments.

### Throws
- `QuorumPeerConfig.ConfigException`
- `IOException`
- `AdminServer.AdminServerException`
```

--------------------------------

### GET - org.apache.zookeeper.cli.CommandFactory.Command

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/index-all.html

Command constant for GET.

```APIDOC
## GET - org.apache.zookeeper.cli.CommandFactory.Command

### Description
Command constant for GET.
```

--------------------------------

### main(String[] args)

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/ZooKeeperServerMain.html

Static main method to start the ZooKeeper server from command-line arguments.

```APIDOC
## main(String[] args)

### Description
Static main method to start the ZooKeeper server from command-line arguments.

### Method
main

### Signature
`public static void main(String[] args)`

### Parameters
- **args** (String[]) - Required - Command-line arguments for server configuration.
```

--------------------------------

### FileChangeWatcher.State constant STARTING

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/common/FileChangeWatcher.State.html

Enum constant STARTING of FileChangeWatcher.State.

```java
public static final FileChangeWatcher.State STARTING
```

--------------------------------

### Connect to ZooKeeper with zkCli.sh

Source: https://zookeeper.apache.org/doc/current/zookeeperCLI.html

Shows how to start the ZooKeeper CLI (zkCli.sh) with different connection options: default localhost, remote server with timeout, waiting for connection, and a custom client configuration file.

```bash
# connect to the localhost with the default port:2181
bin/zkCli.sh
# connect to the remote host with timeout:3s
bin/zkCli.sh -timeout 3000 -server remoteIP:2181
# connect to the remote host with -waitforconnection option to wait for connection success before executing commands
bin/zkCli.sh -waitforconnection -timeout 3000 -server remoteIP:2181
# connect with a custom client configuration properties file
bin/zkCli.sh -client-configuration /path/to/client.properties
```

--------------------------------

### STARTED enum constant

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/DatadirCleanupManager.PurgeTaskStatus.html

Enum constant indicating the purge task has started.

```java
public static final DatadirCleanupManager.PurgeTaskStatus STARTED
```

--------------------------------

### get(int) - Method in class org.apache.zookeeper.server.util.BitMap

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/index-all.html

Method to get a value from the BitMap.

```APIDOC
## get(int) - Method in class org.apache.zookeeper.server.util.BitMap

### Description
Method to get a value from the BitMap.

### Parameters
- **int** - The index or key.
```

--------------------------------

### Run the SyncPrimitive example application

Source: https://zookeeper.apache.org/doc/current/zookeeperTutorial.html

Sets up the ZooKeeper environment and runs the SyncPrimitive Java application with the specified arguments: test type, ZooKeeper server, number of elements, and client type.

```bash
ZOOBINDIR="[path_to_distro]/bin"
. "$ZOOBINDIR"/zkEnv.sh
java SyncPrimitive [Test Type] [ZK server] [No of elements] [Client type]

```

--------------------------------

### get() - Method in class org.apache.zookeeper.server.metric.SimpleCounter

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/index-all.html

Method to get the current value of the SimpleCounter.

```APIDOC
## get() - Method in class org.apache.zookeeper.server.metric.SimpleCounter

### Description
Method to get the current value of the SimpleCounter.
```

--------------------------------

### main(String[] args)

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/ServerAdminClient.html

Main entry point for the ServerAdminClient command-line utility.

```APIDOC
## main(String[] args)

### Description
Main entry point for the ServerAdminClient command-line utility.

### Method
Static method

### Signature
`public static void main(String[] args)`

### Parameters
- **args** (String[]) - Required - Command-line arguments.
```

--------------------------------

### get() - Method in interface org.apache.zookeeper.metrics.Counter

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/index-all.html

Get the current value held by the counter.

```APIDOC
## get() - Method in interface org.apache.zookeeper.metrics.Counter

### Description
Get the current value held by the counter.
```

--------------------------------

### startMetricsProvider(String metricsProviderClassName, Properties configuration)

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/metrics/impl/MetricsProviderBootstrap.html

Starts a MetricsProvider using the given class name and configuration. This is a static method that returns a MetricsProvider instance and throws MetricsProviderLifeCycleException on failure.

```APIDOC
## startMetricsProvider(String metricsProviderClassName, Properties configuration)

### Description
Starts a MetricsProvider using the given class name and configuration. This is a static method that returns a MetricsProvider instance and throws MetricsProviderLifeCycleException on failure.

### Method
startMetricsProvider

### Signature
public static MetricsProvider startMetricsProvider(String metricsProviderClassName, Properties configuration) throws MetricsProviderLifeCycleException

### Parameters
- **metricsProviderClassName** (String) - Required - The fully qualified class name of the MetricsProvider to start.
- **configuration** (Properties) - Required - Configuration properties for the MetricsProvider.

### Returns
- **MetricsProvider** - The started MetricsProvider instance.

### Throws
- **MetricsProviderLifeCycleException** - If the MetricsProvider fails to start.
```

--------------------------------

### main(String[]) - org.apache.zookeeper.server.quorum.QuorumPeerMain

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/index-all.html

Starts the replicated server by specifying the configuration file name on the command line.

```APIDOC
## main(String[])

### Description
To start the replicated server specify the configuration file name on the command line.

### Method
main

### Parameters
- **args** (String[]) - Required - Command line arguments; expects the configuration file name as the first argument.
```

--------------------------------

### main(String[] args)

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/auth/KerberosName.html

Main entry point for command-line execution.

```APIDOC
## Method: main(String[] args)

### Description
Main method for command-line usage.

### Parameters
- `args` (String[]) - Required - Command-line arguments.

### Throws
- `Exception` - If an error occurs.
```

--------------------------------

### get(String, Stat) - Method in class org.apache.zookeeper.server.ResponseCache

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/index-all.html

Method to get a cached response.

```APIDOC
## get(String, Stat) - Method in class org.apache.zookeeper.server.ResponseCache

### Description
Method to get a cached response.

### Parameters
- **String** - The path.
- **Stat** - The stat object.
```

--------------------------------

### config command example

Source: https://zookeeper.apache.org/doc/current/zookeeperCLI.html

Shows the output of the config command, which displays the quorum membership configuration. The output lists server entries with their addresses and roles, along with a version number.

```shell
[zkshell: 17] config
	server.1=[2001:db8:1:0:0:242:ac11:2]:2888:3888:participant
	server.2=[2001:db8:1:0:0:242:ac11:2]:12888:13888:participant
	server.3=[2001:db8:1:0:0:242:ac11:2]:22888:23888:participant
	version=0
```

--------------------------------

### STARTED enum constant

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/NettyServerCnxn.HandshakeState.html

Declares the STARTED enum constant, indicating that the handshake process has begun.

```java
public static final NettyServerCnxn.HandshakeState STARTED
```

--------------------------------

### get(long) - Static method in enum org.apache.zookeeper.server.EphemeralTypeEmulate353

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/index-all.html

Static method to get an EphemeralTypeEmulate353 from a long value.

```APIDOC
## get(long) - Static method in enum org.apache.zookeeper.server.EphemeralTypeEmulate353

### Description
Static method to get an EphemeralTypeEmulate353 from a long value.

### Parameters
- **long** - The long value.
```

--------------------------------

### Backward-compatible configuration example (zoo_replicated1.cfg)

Source: https://zookeeper.apache.org/doc/current/zookeeperReconfig.html

Backward-compatible configuration that places server entries directly in the static file. During boot, a dynamic configuration file is created; the clientPort line remains in the static file because it is not redundant, but is removed if a reconfiguration sets the client port for server 1.

```properties
tickTime=2000
dataDir=/zookeeper/data/zookeeper1
initLimit=5
syncLimit=2
clientPort=2791
server.1=125.23.63.23:2780:2783:participant
server.2=125.23.63.24:2781:2784:participant
server.3=125.23.63.25:2782:2785:participant

```

--------------------------------

### runFromConfig(QuorumPeerConfig config)

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/quorum/QuorumPeerMain.html

Starts the quorum peer server using a pre-loaded configuration object. This method is part of the public API.

```APIDOC
## runFromConfig(QuorumPeerConfig config)

### Description
Runs the quorum peer server using the provided configuration object.

### Method
runFromConfig

### Signature
public void runFromConfig(QuorumPeerConfig config) throws IOException, AdminServer.AdminServerException

### Parameters
- **config** (QuorumPeerConfig) - Required - The configuration object containing server settings.

### Throws
- IOException
- AdminServer.AdminServerException
```

--------------------------------

### get(int) - Static method in enum org.apache.zookeeper.KeeperException.Code

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/index-all.html

Get the Code value for a particular integer error code.

```APIDOC
## get(int) - Static method in enum org.apache.zookeeper.KeeperException.Code

### Description
Get the Code value for a particular integer error code.

### Parameters
- **int** - The integer error code.
```

--------------------------------

### Get znode data with get

Source: https://zookeeper.apache.org/doc/current/zookeeperStarted.html

Retrieves the data and metadata of the '/zk_test' znode, showing the associated data and various znode properties.

```text
[zkshell: 12] get /zk_test
my_data
cZxid = 5
ctime = Fri Jun 05 13:57:06 PDT 2009
mZxid = 5
mtime = Fri Jun 05 13:57:06 PDT 2009
pZxid = 5
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0
dataLength = 7
numChildren = 0

```

--------------------------------

### version command example

Source: https://zookeeper.apache.org/doc/current/zookeeperCLI.html

Run the version command in the ZooKeeper CLI to display the version of the ZooKeeper client/CLI. The output shows the version string and build information.

```shell
[zkshell: 1] version
ZooKeeper CLI version: 3.6.0-SNAPSHOT-29f9b2c1c0e832081f94d59a6b88709c5f1bb3ca, built on 05/30/2019 09:26 GMT

```

--------------------------------

### main(String[] args)

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/SnapshotComparer.html

Entry point for the SnapshotComparer tool that loads and compares two snapshots with configurable threshold and various filters, and outputs information about the delta.

```APIDOC
## main(String[] args)

### Description
Entry point for the SnapshotComparer tool. Loads and compares two snapshots with configurable threshold and various filters, and outputs information about the delta. The delta includes specific znode paths added, updated, deleted comparing one snapshot to another. Only outputs information about permanent nodes, ignoring both sessions and ephemeral nodes.

### Method
main

### Signature
`public static void main(String[] args) throws Exception`

### Parameters
- **args** (String[]) - Required - Command-line arguments for the tool.

### Throws
- `Exception` - If an error occurs during snapshot loading or comparison.

### Usage
This method is the entry point for the SnapshotComparer tool. It is useful in use cases that involve snapshot analysis, such as offline data consistency checking, and data trending analysis (e.g. what's growing under which zNode path during when).
```

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### getStartTime

Source: https://zookeeper.apache.org/doc/current/apidocs/zookeeper-server/org/apache/zookeeper/server/ZooKeeperServerMXBean.html

Returns the time the server was started.

```APIDOC
## getStartTime

### Description
Returns the time the server was started.

### Method
String getStartTime()

### Returns
- **String** - time the server was started
```

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### Connect to Observer with zkCli.sh

Source: https://zookeeper.apache.org/doc/current/zookeeperObservers.html

Run this command to connect to the Observer as if it were an ordinary Follower. Replace localhost:2181 with the hostname and port of the Observer as specified in every config file. You should see a command line prompt to issue commands like ls.

```bash
$ bin/zkCli.sh -server localhost:2181

```
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