8. Start Hadoop Core


Before you start HDFS on an HA cluster you must start the ZooKeeper service. If you do not start the ZKFC, there can be failures.

Start HDFS, executing commands as $HDFS_USER.

  1. 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"


    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.

  2. 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.


    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.

  3. Verify that the NameNode is up and running:

    ps -ef|grep -i NameNode

  4. Start the Secondary NameNode.

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

    su -l <HDFS_USER>

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

  5. 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.

  6. 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

  7. Verify that the DataNode process is up and running:

    ps -ef|grep DataNode

  8. 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.

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