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This article mainly introduces the meaning of the prompt message when starting hadoop, it has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let the editor take you to understand it.

# start the hadoop distributed system (run on namenode) start-dfs.sh # enter the following information:

one. The following sentence illustrates the function of the current command: start namenode

Starting namenodes on [namenode.hadoop.ymxx]

two. Namenode feeds back the startup information and tells the startup namenode where to store the log files

Change out to log is the corresponding log file. Colon: the target node (IP or machine name) is in front of it, and colon: the feedback of the target node is followed by the colon.

Namenode.hadoop.ymxx: starting namenode, logging to / cluster/hadoop-2.2.0/logs/hadoop-root-namenode-namenode.hadoop.ymxx.out

three. Datanode feedback startup information, and also tell startup datanode log in which directory on the datanode node (I configured four datanode nodes here)

Datanode4nodemanager.hadoop.ymxx: starting datanode, logging to / cluster/hadoop-2.2.0/logs/hadoop-root-datanode-datanode4nodemanager.hadoop.ymxx.out datanodenodemanager.hadoop.ymxx: starting datanode, logging to / cluster/hadoop-2.2.0/logs/hadoop-root-datanode-datanodenodemanager.hadoop.ymxx.out datanode2nodemanager.hadoop.ymxx: starting datanode, logging to / cluster/hadoop-2.2.0/logs/hadoop-root-datanode-datanode2nodemanager.hadoop.ymxx.out datanode3nodemanager.hadoop.ymxx: starting datanode Logging to / cluster/hadoop-2.2.0/logs/hadoop-root-datanode-datanode3nodemanager.hadoop.ymxx.out

four. Start secondary namenode

Starting secondary namenodes [secondarynamenode.hadoop.ymxx]

five. Seconary namenode feedback startup information and inform log information

Secondarynamenode.hadoop.ymxx: starting secondarynamenode, logging to / cluster/hadoop-2.2.0/logs/hadoop-root-secondarynamenode-secondarynamenode.hadoop.ymxx.out

Note:

one. The log directory in the message is the directory on the target node, not the directory on the namenode

two. You can check whether the corresponding process is started by jps command on the target machine (usually, you can't tell whether the process has been started successfully from the information printed on the console at startup. You must check whether there are any related processes through jps).

three. If you find that it is not started, you should immediately check the log file on the target node and analyze the reason for the startup failure.

four. As explained here, many examples of building hadoop distributed computing platforms on the Internet put NameNode and ResoureManger on the same machine, so once built, you can run start-dfs.sh and start-yarn.sh on the same machine to start the entire distributed system, which gives people the illusion that start-dfs.sh,start-yarn.sh is executed on NameNode. In fact, this is a misunderstanding. It is important that start-dfs.sh should be executed on the same machine as NameNode, while start-yarn.sh should be executed on the same machine as ResourceManager. I was badly hurt by this misperception. I blamed myself for not taking a good look at the official documents. In fact, the official documents made it very clear:

Use the following command to start yarn and use yarn on the machine designated as the resource manager. The user runs # alas, blindly following Start the YARN with the following command, run on the designated ResourceManager as yarn: [yarn] $HADOOP_YARN_HOME/sbin/yarn-daemon.sh-- config $HADOOP_CONF_DIR start resourcemanager Thank you for reading this article carefully. I hope the article "what does the prompt message when starting hadoop" shared by the editor is helpful to everyone? at the same time, I also hope that you will support and pay attention to the industry information channel, and more related knowledge is waiting for you to learn!

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