【hadoop】DataNode用jps查看无法启动解决办法

查看DataNode端口没有被其他进程占用，但是依旧用jps查看不了DataNode，此时打开hadoop，访问http://localhost:50070，点击页面中的Namenode logs链接，在logs页面点击hadoop-hadoop-datanode-ubuntu.log 链接，发现日志里面有如下错误：

ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: java.io.IOException: Incompatible namespaceIDs in

这导致了datanode启动不了。而且从本地文件中上传到DFS文件系统中，文件内容为空！！！

原因:每次namenode format会重新创建一个namenodeId,而dfs.data.dir参数配置的目录中包含的是上次format创建的id,和dfs.name.dir参数配置的目录中的id不一致。

hadoop namenode -format

清空了namenode下的数据,但是没有清空datanode下的数据,导致启动时失败,所要做的就是每次fotmat前,清空dfs.data.dir参数配置的目录（我这里的目录是在hdfs-site.xml里配置的），清空后运行

root@ubuntu:/opt/hadoop-0.20.2/bin# hadoop namenode -format 

15/07/20 00:25:42 INFO namenode.NameNode: STARTUP_MSG:  

/************************************************************ 

STARTUP_MSG: Starting NameNode 

STARTUP_MSG:   host = ubuntu/127.0.1.1 

STARTUP_MSG:   args = [-format] 

STARTUP_MSG:   version = 0.20.2 

STARTUP_MSG:   build = https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.20 -r 911707; compiled by 'chrisdo' on Fri Feb 19 08:07:34 UTC 2010 

************************************************************/ 

Re-format filesystem in /opt/hadoop-0.20.2/dfs/name ? (Y or N) Y 

15/07/20 00:25:45 INFO namenode.FSNamesystem: fsOwner=root,root 

15/07/20 00:25:45 INFO namenode.FSNamesystem: supergroup=supergroup 

15/07/20 00:25:45 INFO namenode.FSNamesystem: isPermissionEnabled=true 

15/07/20 00:25:45 INFO common.Storage: Image file of size 94 saved in 0 seconds. 

15/07/20 00:25:45 INFO common.Storage: Storage directory /opt/hadoop-0.20.2/dfs/name has been successfully formatted. 

15/07/20 00:25:45 INFO namenode.NameNode: SHUTDOWN_MSG:  

/************************************************************ 

SHUTDOWN_MSG: Shutting down NameNode at ubuntu/127.0.1.1 

************************************************************/ 

root@ubuntu:/opt/hadoop-0.20.2/bin# sh start-all.sh 

starting namenode, logging to /opt/hadoop-0.20.2/bin/../logs/hadoop-root-namenode-ubuntu.out 

localhost: starting datanode, logging to /opt/hadoop-0.20.2/bin/../logs/hadoop-root-datanode-ubuntu.out 

localhost: starting secondarynamenode, logging to /opt/hadoop-0.20.2/bin/../logs/hadoop-root-secondarynamenode-ubuntu.out 

starting jobtracker, logging to /opt/hadoop-0.20.2/bin/../logs/hadoop-root-jobtracker-ubuntu.out 

localhost: starting tasktracker, logging to /opt/hadoop-0.20.2/bin/../logs/hadoop-root-tasktracker-ubuntu.out 

root@ubuntu:/opt/hadoop-0.20.2/bin# jps 

79679 SecondaryNameNode 

79920 TaskTracker 

79521 DataNode 

79778 JobTracker 

79354 NameNode 

79979 Jps

就可以看到datanode了！！！