8. Start Hadoop Core

If you are upgrading from an HA NameNode configuration, start all JournalNodes. On each JournalNode host, run the following command:

su -l $HDFS_USER -c "/usr/hdp/current/hadoop-hdfs-journalnode/../hadoop/sbin/hadoop-daemon.sh start journalnode"

	Important
	All JournalNodes must be running when performing the upgrade, rollback, or finalization operations. If any JournalNodes are down when running any such operation, the operation fails.

Start the NameNode. On the active NameNode host machine, run the following command:

su <HDFS_USER> -c "export HADOOP_LIBEXEC_DIR=/usr/hdp/current/hadoop-hdfs-namenode/../hadoop/sbin/hadoop-daemon.sh start namenode -upgrade"

On a large system, this can take a long time to complete.

	Note
	Run this command with the -upgrade option only once. After you have completed this step, you can bring up the NameNode using this command without including the -upgrade option.

Verify that the NameNode is up and running:

ps -ef|grep -i NameNode

Start the Secondary NameNode.

On the Secondary NameNode host machine, run the following commands:

su -l <HDFS_USER> -c "/usr/hdp/current/hadoop-client/sbin/hadoop-daemon.sh start secondarynamenode"

Verify that the Secondary NameNode is up and running:

ps -ef|grep SecondaryNameNode

If you are working on a non-secure DataNode, use $HDFS_USER. For a secure DataNode, use root.

Start DataNodes.

On all the DataNodes, run the following command:

export HADOOP_LIBEXEC_DIR=/usr/hdp/current/hadoop-hdfs-datanode/../hadoop/sbin/hadoop-daemon.sh start datanode

Verify that the DataNode process is up and running:

ps -ef|grep DataNode

Verify that Namenode can go out of safe mode.

su <HDFS_USER>

hdfs dfsadmin -safemode wait Safemode is OFF

In general, it takes 5-10 minutes to get out of safemode. For thousands of nodes with millions of data blocks, getting out of safemode could take up to 45 minutes.