Hadoop formatted namenode multiple times so that datanode could not start the problem.

Due to the previous installation of the hadoop-2.5.0 version, it has always been possible for related nodes to get up. Today, cheap formatting of namenode caused datanode to fail to start.

[root@xp hadoop-2.5.0] # sbin/hadoop namenode-format

After formatting, you want to start datanode as shown in the figure.

two。 Then check the datanode log

[root@xp logs] # tail-50 hadoop-root-datanode-xp.log

According to the contents of the log, the clusterID of namenode and datanode is inconsistent. I suddenly remembered that I formatted namenode twice before. It should be due to the clusterID inconsistency between namenode and datanode caused by multiple formatting of namenode! Namenode updates clusterID each time it is formatted, but datanode is only determined when it is formatted for the first time, resulting in inconsistencies.

3. Follow the log path prompt to find clusterID.

4. ClusterID replication in direct / opt/modules/hadoop-2.5.0/data/dfs/name/current/VERSION replaces clusterID in / opt/modules/hadoop-2.5.0/data/dfs/data/current/VERSION.

5. Finally, restart the hadoop-related node services, and finally DataNode has been running normally.