5. Start HDFS

Start HDFS.

To start HDFS, run commands as the $HDFS_USER.

  1. Start the NameNode. On the NameNode host machine, execute the following command:

    su $HDFS_USER
     export HADOOP_LIBEXEC_DIR=/usr/lib/hadoop/libexec
    /usr/lib/hadoop/sbin/hadoop-daemon.sh start namenode -upgrade                 

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

    [Note]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.

  2. Verify that the NameNode is up and running:

    ps -ef|grep -i NameNode
  3. Start the Secondary NameNode. On the Secondary NameNode host machine, execute the following command:

    su $HDFS_USER
    export HADOOP_LIBEXEC_DIR=/usr/lib/hadoop/libexec
    /usr/lib/hadoop/sbin/hadoop-daemon.sh start secondarynamenode 

  4. Verify that the Secondary NameNode is up and running:

    ps -ef|grep  SecondaryNameNode
  5. [Note]Note

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

    Start DataNodes. On all the DataNodes, execute the following command:

    export HADOOP_LIBEXEC_DIR=/usr/lib/hadoop/libexec 
    /usr/lib/hadoop/sbin/hadoop-daemon.sh start datanode             
  6. Verify that the DataNode process is up and running:

    ps -ef|grep DataNode
  7. Verify that Namenode can go out of safe mode.

    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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