hadoop中master能够启动datanode，但是datanode无法连接namenode 报 17/11/16 03:49:13 WARN ipc.Client: Failed to conn

datanode 执行  hadoop fs -ls / 报错

17/11/16 03:49:13 WARN ipc.Client: Failed to connect to server: hadoop-node-03/192.168.1.120:9000: try once and fail.

java.net.ConnectException: Connection refused
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.net.NetUtils.connect(NetUtils.java:495)
at org.apache.hadoop.ipc.Client$Connection.setupConnection(Client.java:682)
at org.apache.hadoop.ipc.Client$Connection.setupIOstreams(Client.java:778)
at org.apache.hadoop.ipc.Client$Connection.access$3500(Client.java:410)
at org.apache.hadoop.ipc.Client.getConnection(Client.java:1544)
at org.apache.hadoop.ipc.Client.call(Client.java:1375)
at org.apache.hadoop.ipc.Client.call(Client.java:1339)
at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:227)
at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:116)

at com.sun.proxy.$Proxy10.getFileInfo(Unknown Source)

at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolTranslatorPB.getFileInfo(ClientNamenodeProtocolTranslatorPB.java:792)

解决办法：

1.centos未关闭防火墙或hosts文件中未删除本地回环信息所致。