Hadoop完全分布式环境下，DataNode进程正常启动，但是网页上不显示DataNode节点

Hadoop完全分布式环境下，上传文件到hdfs上时报错：

// :: WARN hdfs.DFSClient: DataStreamer Exception
org.apache.hadoop.ipc.RemoteException(java.io.IOException): File /wc_input/file1.txt._COPYING_ could only be replicated to 0 nodes instead of minReplication (=1).  There are 0 datanode(s) running and no node(s) are excluded in this operation.
    at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.chooseTarget4NewBlock(BlockManager.java:)
    at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getNewBlockTargets(FSNamesystem.java:)
    at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:)
    at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.addBlock(NameNodeRpcServer.java:)
    at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.addBlock(ClientNamenodeProtocolServerSideTranslatorPB.java:)
    at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$.callBlockingMethod(ClientNamenodeProtocolProtos.java)
    at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:)
    at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:)
    at org.apache.hadoop.ipc.Server$Handler$.run(Server.java:)
    at org.apache.hadoop.ipc.Server$Handler$.run(Server.java:)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:)
    at org.apache.hadoop.ipc.Server$Handler.run(Server.java:)

    at org.apache.hadoop.ipc.Client.call(Client.java:)
    at org.apache.hadoop.ipc.Client.call(Client.java:)
    at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:)
    at com.sun.proxy.$Proxy9.addBlock(Unknown Source)
    at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolTranslatorPB.addBlock(ClientNamenodeProtocolTranslatorPB.java:)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:)
    at java.lang.reflect.Method.invoke(Method.java:)
    at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:)
    at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:)
    at com.sun.proxy.$Proxy10.addBlock(Unknown Source)
    at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.locateFollowingBlock(DFSOutputStream.java:)
    at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.nextBlockOutputStream(DFSOutputStream.java:)
    at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:)
put: File /wc_input/file1.txt._COPYING_ could only be replicated to  nodes instead of minReplication (=).  There are  datanode(s) running and no node(s) are excluded in this operation.

报错指出我的DataNode一个都没有启动，但是通过jps查看得到所有节点的DataNode进程都成功启动，但在Hadoop页面上显示的Live Nodes个数却为0 。

解决方法：

step1：查看下etc/hosts是否配置了所有从节点的hostname到ip的映射关系，如果配置了请看步骤step2

step2：再namenode的机器上修改hdfs-site.xml文件，加入下面配置后，重新启动

<property>
     <name>dfs.namenode.datanode.registration.ip-hostname-check</name>
     <value>false</value>
</property>