What if hadoop2.5.2 starts up and finds that DataNode is not started?

This article mainly introduces the hadoop2.5.2 startup found that DataNode did not start how to do, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let Xiaobian with you to understand.

After hadoop2.5.2 starts successfully, check it with jps: it feels like DataNode is missing.

It is true that DataNode is missing.

View the log:

Judging from the journal, the underlined part illustrates the problem.

The clusterID of datanode does not match the clusterID of namenode.

Solution:

According to the path in the log, cd / home/hadoop/dfs

You can see the data and name folders

Copy the clusterID in VERSION under name/current to VERSION under data/current, overwriting the original clusterID

Keep the two in line

-> clusterID in name/current/VERSION: CID-da3018e4-2d0b-4ceb-9e7a-46319f0e32c8

Replace clusterID in data/current/VERSION.

Then restart, execute jps after startup, and view the process

The cause of the problem: after formatting dfs for the first time, hadoop is started and used, and then the format command (hdfs namenode-format) is re-executed, where the clusterID of namenode is regenerated and the clusterID of datanode remains unchanged.

Note: if you are in a cluster: modify the clusterID of the VERSION of each node to make it consistent with the clusterID in the master node (/ home/hadoop/dfs/name/current/VERSION).

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