异常分析
1、“could only be replicated to 0 nodes, instead of 1”异常
（1）异常描述
上面配置都正确无误，并且，已经完成了如下运行步骤：
[root@localhost hadoop-0.20.0]# bin/hadoop namenode -format
[root@localhost hadoop-0.20.0]# bin/start-all.sh
这时，看到5个进程jobtracker、tasktracker、namenode、datanode、secondarynamenode已经给出了启动成功信息，但是运行jps命令查看进程的时候，发现并不是那样，如下所示：
4281 Jps
4007 SecondaryNameNode
3771 NameNode
可见，只有两个进程启动成功了，其它的并没有成功，如果你再继续向下执行，准备运行wordcount实例之前执行上传文件的命令：
[root@localhost hadoop-0.20.0]# bin/hadoop fs -put input in
现在就会抛出一堆异常了，如下所示：
10/08/02 15:36:04 INFO hdfs.DFSClient: org.apache.hadoop.ipc.RemoteException: java.io.IOException: File /user/root/in/LICENSE.txt could only be replicated to 0 nodes, instead of 1
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:1256)
at org.apache.hadoop.hdfs.server.namenode.NameNode.addBlock(NameNode.java:422)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:508)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:959)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:955)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:953)
at org.apache.hadoop.ipc.Client.call(Client.java:739)
at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:220)
at $Proxy0.addBlock(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:82)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:59)
at $Proxy0.addBlock(Unknown Source)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.locateFollowingBlock(DFSClient.java:2873)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.nextBlockOutputStream(DFSClient.java:2755)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.access$2000(DFSClient.java:2046)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream$DataStreamer.run(DFSClient.java:2232)
10/08/02 15:36:04 WARN hdfs.DFSClient: NotReplicatedYetException sleeping /user/root/in/LICENSE.txt retries left 4
10/08/02 15:36:04 INFO hdfs.DFSClient: org.apache.hadoop.ipc.RemoteException: java.io.IOException: File /user/root/in/LICENSE.txt could only be replicated to 0 nodes, instead of 1
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:1256)
at org.apache.hadoop.hdfs.server.namenode.NameNode.addBlock(NameNode.java:422)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:508)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:959)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:955)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:953)
at org.apache.hadoop.ipc.Client.call(Client.java:739)
at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:220)
at $Proxy0.addBlock(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:82)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:59)
at $Proxy0.addBlock(Unknown Source)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.locateFollowingBlock(DFSClient.java:2873)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.nextBlockOutputStream(DFSClient.java:2755)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.access$2000(DFSClient.java:2046)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream$DataStreamer.run(DFSClient.java:2232)
10/08/02 15:36:04 WARN hdfs.DFSClient: NotReplicatedYetException sleeping /user/root/in/LICENSE.txt retries left 3
10/08/02 15:36:05 INFO hdfs.DFSClient: org.apache.hadoop.ipc.RemoteException: java.io.IOException: File /user/root/in/LICENSE.txt could only be replicated to 0 nodes, instead of 1
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:1256)
at org.apache.hadoop.hdfs.server.namenode.NameNode.addBlock(NameNode.java:422)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:508)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:959)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:955)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:953)
at org.apache.hadoop.ipc.Client.call(Client.java:739)
at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:220)
at $Proxy0.addBlock(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:82)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:59)
at $Proxy0.addBlock(Unknown Source)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.locateFollowingBlock(DFSClient.java:2873)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.nextBlockOutputStream(DFSClient.java:2755)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.access$2000(DFSClient.java:2046)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream$DataStreamer.run(DFSClient.java:2232)
10/08/02 15:36:05 WARN hdfs.DFSClient: NotReplicatedYetException sleeping /user/root/in/LICENSE.txt retries left 2
10/08/02 15:36:07 INFO hdfs.DFSClient: org.apache.hadoop.ipc.RemoteException: java.io.IOException: File /user/root/in/LICENSE.txt could only be replicated to 0 nodes, instead of 1
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:1256)
at org.apache.hadoop.hdfs.server.namenode.NameNode.addBlock(NameNode.java:422)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:508)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:959)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:955)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:953)
at org.apache.hadoop.ipc.Client.call(Client.java:739)
at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:220)
at $Proxy0.addBlock(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:82)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:59)
at $Proxy0.addBlock(Unknown Source)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.locateFollowingBlock(DFSClient.java:2873)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.nextBlockOutputStream(DFSClient.java:2755)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.access$2000(DFSClient.java:2046)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream$DataStreamer.run(DFSClient.java:2232)
10/08/02 15:36:07 WARN hdfs.DFSClient: NotReplicatedYetException sleeping /user/root/in/LICENSE.txt retries left 1
10/08/02 15:36:10 WARN hdfs.DFSClient: DataStreamer Exception: org.apache.hadoop.ipc.RemoteException: java.io.IOException: File /user/root/in/LICENSE.txt could only be replicated to 0 nodes, instead of 1
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:1256)
at org.apache.hadoop.hdfs.server.namenode.NameNode.addBlock(NameNode.java:422)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:508)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:959)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:955)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:953)
at org.apache.hadoop.ipc.Client.call(Client.java:739)
at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:220)
at $Proxy0.addBlock(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:82)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:59)
at $Proxy0.addBlock(Unknown Source)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.locateFollowingBlock(DFSClient.java:2873)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.nextBlockOutputStream(DFSClient.java:2755)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.access$2000(DFSClient.java:2046)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream$DataStreamer.run(DFSClient.java:2232)
10/08/02 15:36:10 WARN hdfs.DFSClient: Error Recovery for block null bad datanode[0] nodes == null
10/08/02 15:36:10 WARN hdfs.DFSClient: Could not get block locations. Source file "/user/root/in/LICENSE.txt" - Aborting...
put: java.io.IOException: File /user/root/in/LICENSE.txt could only be replicated to 0 nodes, instead of 1
看到“could only be replicated to 0 nodes, instead of 1”这句信息的时候，你可能会首先想到是否hdfs-site.xml配置文件中的属性dfs.replication配置错误，但事实上并不是这样。
这时，就要查看启动日志了，我的是位于/root/hadoop-0.20.0/logs下面，如下所示：
hadoop-root-datanode-localhost.log hadoop-root-namenode-localhost.log hadoop-root-tasktracker-localhost.log
hadoop-root-datanode-localhost.out hadoop-root-namenode-localhost.out hadoop-root-tasktracker-localhost.out
hadoop-root-jobtracker-localhost.log hadoop-root-secondarynamenode-localhost.log history
hadoop-root-jobtracker-localhost.out hadoop-root-secondarynamenode-localhost.out
查看hadoop-root-datanode-localhost.log日志文件，看到异常信息：
2010-08-02 15:38:34,642 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting DataNode
STARTUP_MSG: host = localhost/127.0.0.1
STARTUP_MSG: args = []
STARTUP_MSG: version = 0.20.0
STARTUP_MSG: build = https://svn.apache.org/repos/asf/hadoop/core/branches/branch-0.20 -r 763504; compiled by 'ndaley' on Thu Apr 9 05:18:40 UTC 2009
************************************************************/
2010-08-02 15:38:35,381 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: java.io.IOException: Incompatible namespaceIDs in /tmp/hadoop-root/dfs/data: namenode namespaceID = 409052671; datanode namespaceID = 769845957
at org.apache.hadoop.hdfs.server.datanode.DataStorage.doTransition(DataStorage.java:233)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:148)
at org.apache.hadoop.hdfs.server.datanode.DataNode.startDataNode(DataNode.java:298)
at org.apache.hadoop.hdfs.server.datanode.DataNode.<init>(DataNode.java:216)
at org.apache.hadoop.hdfs.server.datanode.DataNode.makeInstance(DataNode.java:1283)
at org.apache.hadoop.hdfs.server.datanode.DataNode.instantiateDataNode(DataNode.java:1238)
at org.apache.hadoop.hdfs.server.datanode.DataNode.createDataNode(DataNode.java:1246)
at org.apache.hadoop.hdfs.server.datanode.DataNode.main(DataNode.java:1368)
2010-08-02 15:38:35,382 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down DataNode at localhost/127.0.0.1
************************************************************/
通过上面的信息，大致可以了解到，通过“Incompatible namespaceIDs in /tmp/hadoop-root/dfs/data”可知，是由于 /tmp/hadoop-root/dfs/data中的namespaceIDs不兼容导致的，也就是说，很可能是由于上次运行其它版本的Hadoop在/tmp/hadoop-root/dfs/data目录下有残留的不兼容的数据。事实上在我运行过程中出现这个问题就是由于，刚刚尝试了Hadoop-0.19.0版本的运行，运行后并没有清理这些数据。
（2）解决方法
清理对应目录 /tmp/hadoop-root/dfs/data的数据以后，就可以正常运行了，这时执行启动各个进程之后，通过jps命令可以查看到结果如下所示：
5386 JobTracker
5253 DataNode
5529 Jps
4874 SecondaryNameNode
5489 TaskTracker
4649 NameNode
上面5个进程都启动起来了，可以上传文件到HDFS，并执行wordcount例子
本篇文章来源于 Linux公社网站(www.linuxidc.com) 原文链接：http://www.linuxidc.com/Linux/2010-08/27484p3.htm
