INFO hdfs.DFSClient: Exception in createBlockOutputStream java.net解决办法
自己安装好Hadoop2.7.x之后，发现dfs中的/bin/hadoop fs -put命令不能够使用，报错如下：
[hadoop@master bin]$ ./hadoop fs -put ../logs/123 /wc/mytemp
16/07/27 01:29:26 INFO hdfs.DFSClient: Exception in createBlockOutputStream
java.net.NoRouteToHostException: No route to host
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717)
at org.apache.hadoop.net.SocketIOWithTimeout.connect(SocketIOWithTimeout.java:206)
at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:531)
at org.apache.hadoop.hdfs.DFSOutputStream.createSocketForPipeline(DFSOutputStream.java:1537)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.createBlockOutputStream(DFSOutputStream.java:1313)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.nextBlockOutputStream(DFSOutputStream.java:1266)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:449)
16/07/27 01:29:26 INFO hdfs.DFSClient: Abandoning BP-555863411-172.16.95.100-1469590594354:blk_1073741825_1001
16/07/27 01:29:26 INFO hdfs.DFSClient: Excluding datanode DatanodeInfoWithStorage[172.16.95.101:50010,DS-ee00e1f8-5143-4f06-9ef8-b0f862fce649,DISK]
16/07/27 01:29:26 INFO hdfs.DFSClient: Exception in createBlockOutputStream
java.net.NoRouteToHostException: No route to host
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717)
at org.apache.hadoop.net.SocketIOWithTimeout.connect(SocketIOWithTimeout.java:206)
at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:531)
at org.apache.hadoop.hdfs.DFSOutputStream.createSocketForPipeline(DFSOutputStream.java:1537)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.createBlockOutputStream(DFSOutputStream.java:1313)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.nextBlockOutputStream(DFSOutputStream.java:1266)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:449)
16/07/27 01:29:26 INFO hdfs.DFSClient: Abandoning BP-555863411-172.16.95.100-1469590594354:blk_1073741826_1002
16/07/27 01:29:26 INFO hdfs.DFSClient: Excluding datanode DatanodeInfoWithStorage[172.16.95.102:50010,DS-eea51eda-0a07-4583-9eee-acd7fc645859,DISK]
16/07/27 01:29:26 WARN hdfs.DFSClient: DataStreamer Exception
org.apache.hadoop.ipc.RemoteException(java.io.IOException): File /wc/mytemp/123._COPYING_ could only be replicated to 0 nodes instead of minReplication (=1). There are 2 datanode(s) running and 2 node(s) are excluded in this operation.
at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.chooseTarget4NewBlock(BlockManager.java:1547)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getNewBlockTargets(FSNamesystem.java:3107)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:3031)
at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.addBlock(NameNodeRpcServer.java:724)
at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.addBlock(ClientNamenodeProtocolServerSideTranslatorPB.java:492)
at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java)
at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:616)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:969)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2049)
at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2045)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:422)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1657)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2043)
at org.apache.hadoop.ipc.Client.call(Client.java:1475)
at org.apache.hadoop.ipc.Client.call(Client.java:1412)
at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:229)
at com.sun.proxy.$Proxy9.addBlock(Unknown Source)
at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolTranslatorPB.addBlock(ClientNamenodeProtocolTranslatorPB.java:418)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:191)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:102)
at com.sun.proxy.$Proxy10.addBlock(Unknown Source)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.locateFollowingBlock(DFSOutputStream.java:1459)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.nextBlockOutputStream(DFSOutputStream.java:1255)
at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:449)
put: File /wc/mytemp/123._COPYING_ could only be replicated to 0 nodes instead of minReplication (=1). There are 2 datanode(s) running and 2 node(s) are excluded in this operation.
[hadoop@master bin]$ service firewall
The service command supports only basic LSB actions (start, stop, restart, try-restart, reload, force-reload, status). For other actions, please try to use systemctl.
到网上找资料，好不统一找到几个解决的办法，感觉值的参考的是该文：hadoop常见错误解决办法 ，在其第14条，他给出的解决办法如下：
I have resolved the issue:
What i did:
1) '/etc/init.d/iptables stop' -->stopped firewall
2) SELINUX=disabled in '/etc/selinux/config' file.-->disabled selinux
I worked for me after these two changes
需要补充的地方：
（1）此处CentOS7中，防火墙的方式改变，关闭防火墙改成service firewalld stop
（2）不仅是master中的firewall要关闭，所有的从节点（slave）中的防火墙也要关闭。
（3）检查所有的主机，/etc/selinux/config下的SELINUX，设置SELINUX=disable。
（4）建议关闭防火墙之后，再使用systemctl disable firewalld.service #禁止firewall开机启动
然后在进行put的时候，就成功了。截图如下：
另外一个人博主给出的解决方法如下：hadoop报错：hdfs.DFSClient: Exception in createBlockOutputStream， 大家可以尝试一下，可以这样说，新手一般都会挂掉，因为格式化namenode的时候，slave中的文件会和namenode不一致，造成DataNode节点启动失败，解决办法就是删除slave和master中所有的data节点，然后重新执行namenode格式化操作。（不只是自己水平有限还是问题不一样，这种方法初步判定为坑人）
