4. Configure and Start Apache ZooKeeper

	Tip
	If you are running a highly available cluster, upgrade Apache ZooKeeper before you upgrade HDFS. This best practice lets the upgraded ZKFC work with your primary NameNode and your Standby NameNode.

Replace your configuration after upgrading. Replace the ZooKeeper template configuration in /etc/zookeeper/conf.
Start ZooKeeper.
On all the ZooKeeper server host machines, run the following command to start ZooKeeper and the ZKFC:
su - zookeeper -c "export ZOOCFGDIR=/usr/hdp/current/zookeeper-server/conf ; export ZOOCFG=zoo.cfg; source /usr/hdp/current/zookeeper-server/conf/zookeeper-env.sh ; /usr/hdp/current/zookeeper-server/bin/zkServer.sh start"
/usr/hdp/current/hadoop-client/sbin/hadoop-daemon.sh start zkfc