ZooKeeper ensemble fails to start

ZooKeeper might fail to start if the ZooKeeper ensemble is not configured correctly, or there are problems with file permissions, port conflicts, or disk corruption.

The following command indicates that the ZooKeeper server process did not start:
```
ps uxww | grep zookeeper
```
The streamtool getzkstate command indicates that the ZooKeeper ensemble is not running and serving.

ZooKeeper is not configured correctly.
- External ZooKeeper: The configuration file (ZooKeeper-installation-directory/conf/zoo.cfg) is not configured correctly or is missing.
- Embedded ZooKeeper: The bootstrap properties are not configured correctly.
File permissions are not set correctly for the dataDir and dataLogDir directories.
- If this error occurs for external ZooKeeper, messages similar to the following example are displayed at the command prompt:
```
  Using config: /home/zooadmin/zookeeper-3.4.8/bin/../conf/zoo.cfg
  Starting zookeeper ... ./zkServer.sh: line 113: /home/zooadmin/dataDir/zookeeper_server.pid: Permission denied
  FAILED TO WRITE PID
```
There is a network port conflict.
No quorum is formed.
The disk is corrupted.

Ensure that ZooKeeper is configured correctly.
- External ZooKeeper: Ensure that the configuration file (ZooKeeper-installation-directory/conf/zoo.cfg) is configured correctly. For more information, see the ZooKeeper Administrator’s Guide.
- Embedded ZooKeeper: Ensure that the bootstrap properties are configured correctly. For information about bootstrap properties, use the streamtool man bootproperties command. To check property values, use the streamtool getbootproperty -a command. To update property values, use the streamtool setbootproperty command.
Ensure that the file permissions for the dataDir and dataLogDir directories are set correctly.
- External ZooKeeper: If necessary, update the dataDir and dataLogDir configuration parameters in the ZooKeeper-installation-directory/conf/zoo.cfg file.
- Embedded ZooKeeper: Check the value of the streams.zookeeper.property.dataDir and streams.zookeeper.property.dataLogDir bootstrap properties by using the streamtool getbootproperty -a command. If necessary, update these properties by using the streamtool setbootproperty command.
Ensure that the specified network ports are available.
- External ZooKeeper: To change a port number, update the ZooKeeper configuration file.
- Embedded ZooKeeper: To change a port number, see Changing the port number for embedded ZooKeeper.
Ensure that there is a quorum that is formed for the ZooKeeper ensemble. For example, for a ZooKeeper ensemble that includes five resources, at least three resources need to be up and running to form a quorum. For reliability and availability, run ZooKeeper on at least three resources. Running ZooKeeper on five resources is preferred.
Embedded ZooKeeper: The streams.zookeeper.quorum bootstrap property indicates the host name of the embedded ZooKeeper server. Only a local host name is supported. When streamtool is first started, this property is populated with a local host name and persisted in the home directory of the user. If the home directory is on a shared file system and the user wants to start embedded ZooKeeper on a different resource, the streams.zookeeper.quorum property must first be updated with the new host name. The following example shows how to change the value of this property:
```
  streamtool setbootproperty streams.zookeeper.quorum=mynewhost.com
```
Ensure that there is a supervisory service for each ZooKeeper server.
Ensure that the disk device is healthy; reapply the latest archive or backup data to the ZooKeeper dataDir and dataLogDir directories; and restart ZooKeeper.