（转）无法启动namenode
（1）hadoop集群我维护有一段时间了，今天忽然出现了一个问题，当我stop-all.sh后hadoop的web页面无法显示，分析应该是namenode没有启动，检查后果然namenode没有启动，凭借经验，我猜想应该是配置文件的问题，于是仔细检查了conf下的每一个文件，但是配置文件配置无误，namenode依旧无法启动，这个问题困扰了我一天的时间，查看log日志后，发现时pid的问题，在网上查了相关资料后才知道原来我先前的03服务器搁置了一段时间没有添加到datanode，而后我添加后会有一个PID不匹配的问题，于是我着手开始做：
日志中显示的错误：
2010-02-09 21:52:49,343 INFO org.apache.hadoop.hdfs.server.namenode.NameNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting NameNode
STARTUP_MSG: host = yijian/192.168.0.13
STARTUP_MSG: args = []
STARTUP_MSG: version = 0.20.1
STARTUP_MSG: build =http://svn.apache.org/repos/asf/ ... /release-0.20.1-rc1-r 810220; compiled by 'oom' on Tue Sep 1 20:55:56 UTC 2009
************************************************************/
2010-02-09 21:52:49,531 INFO org.apache.hadoop.ipc.metrics.RpcMetrics: Initializing RPC Metrics with hostName=NameNode, port=8888
2010-02-09 21:52:49,531 INFO org.apache.hadoop.hdfs.server.namenode.NameNode: Namenode up at: 127.0.0.1/127.0.0.1:8888
2010-02-09 21:52:49,546 INFO org.apache.hadoop.metrics.jvm.JvmMetrics: Initializing JVM Metrics with processName=NameNode, sessionId=null
2010-02-09 21:52:49,546 INFO org.apache.hadoop.hdfs.server.namenode.metrics.NameNodeMetrics: Initializing NameNodeMeterics using context object:org.apache.hadoop.metrics.spi.NullContext
2010-02-09 21:52:50,250 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: fsOwner=jian,None,root,Administrators,Users
2010-02-09 21:52:50,250 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: supergroup=supergroup
2010-02-09 21:52:50,250 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: isPermissionEnabled=true
2010-02-09 21:52:50,265 INFO org.apache.hadoop.hdfs.server.namenode.metrics.FSNamesystemMetrics: Initializing FSNamesystemMetrics using context object:org.apache.hadoop.metrics.spi.NullContext
2010-02-09 21:52:50,265 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: Registered FSNamesystemStatusMBean
2010-02-09 21:52:50,359 ERROR org.apache.hadoop.hdfs.server.namenode.FSNamesystem: FSNamesystem initialization failed.
java.io.IOException:NameNode is not formatted.
at org.apache.hadoop.hdfs.server.namenode.FSImage.recoverTransitionRead(FSImage.java:317)
at org.apache.hadoop.hdfs.server.namenode.FSDirectory.loadFSImage(FSDirectory.java:87)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.initialize(FSNamesystem.java:311)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.<init>(FSNamesystem.java:292)
at org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:201)
at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:279)
at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:956)
at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:965)
2010-02-09 21:52:50,359 INFO org.apache.hadoop.ipc.Server: Stopping server on 8888
2010-02-09 21:52:50,359 ERROR org.apache.hadoop.hdfs.server.namenode.NameNode: java.io.IOException: NameNode is not formatted.
at org.apache.hadoop.hdfs.server.namenode.FSImage.recoverTransitionRead(FSImage.java:317)
at org.apache.hadoop.hdfs.server.namenode.FSDirectory.loadFSImage(FSDirectory.java:87)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.initialize(FSNamesystem.java:311)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.<init>(FSNamesystem.java:292)
at org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:201)
at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:279)
at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:956)
at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:965)
2010-02-09 21:52:50,359 INFO org.apache.hadoop.hdfs.server.namenode.NameNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at yijian/192.168.0.13
************************************************************/
处理错误：
将集群中每个datanode的/hdfs/data/current中的VERSION删掉，然后执行hadoop namenode -format
重启集群，错误消失。
link：http://hi.baidu.com/ren2200857/blog/item/3e14048ac30870e8503d9270.html