遇到拒绝连接的情况该怎么处理

ubuntu@rao2:~$ hadoop fs -ls /
17/07/26 21:20:51 WARN ipc.Client: Failed to connect to server: rao2/192.168.30.130:8020: 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$Connection.setupConnection(Client.java:681)
        at org.apache.hadoop.ipc.Client$Connection.setupIOstreams(Client.java:777)
        at org.apache.hadoop.ipc.Client$Connection.access$3500(Client.java:409)
        at org.apache.hadoop.ipc.Client.getConnection(Client.java:1542)
        at org.apache.hadoop.ipc.Client.call(Client.java:1373)
        at org.apache.hadoop.ipc.Client.call(Client.java:1337)
        at org.apache.hadoop.ipc.ProtobufRpcEngine$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:787)
        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:498)
        at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:398)
        at org.apache.hadoop.io.retry.RetryInvocationHandler$Call.invokeMethod(RetryInvocationHandler.java:163)
        at org.apache.hadoop.io.retry.RetryInvocationHandler$Call.invoke(RetryInvocationHandler.java:155)
        at org.apache.hadoop.io.retry.RetryInvocationHandler$Call.invokeOnce(RetryInvocationHandler.java:95)
        at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:335)
        at com.sun.proxy.$Proxy11.getFileInfo(Unknown Source)
        at org.apache.hadoop.hdfs.DFSClient.getFileInfo(DFSClient.java:1700)
        at org.apache.hadoop.hdfs.DistributedFileSystem$27.doCall(DistributedFileSystem.java:1436)
        at org.apache.hadoop.hdfs.DistributedFileSystem$27.doCall(DistributedFileSystem.java:1433)
        at org.apache.hadoop.fs.FileSystemLinkResolver.resolve(FileSystemLinkResolver.java:81)
        at org.apache.hadoop.hdfs.DistributedFileSystem.getFileStatus(DistributedFileSystem.java:1433)
        at org.apache.hadoop.fs.Globber.getFileStatus(Globber.java:64)
        at org.apache.hadoop.fs.Globber.doGlob(Globber.java:282)
        at org.apache.hadoop.fs.Globber.glob(Globber.java:148)
        at org.apache.hadoop.fs.FileSystem.globStatus(FileSystem.java:1685)
        at org.apache.hadoop.fs.shell.PathData.expandAsGlob(PathData.java:326)
        at org.apache.hadoop.fs.shell.Command.expandArgument(Command.java:235)
        at org.apache.hadoop.fs.shell.Command.expandArguments(Command.java:218)
        at org.apache.hadoop.fs.shell.FsCommand.processRawArguments(FsCommand.java:103)
        at org.apache.hadoop.fs.shell.Command.run(Command.java:165)
        at org.apache.hadoop.fs.FsShell.run(FsShell.java:315)
        at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:76)
        at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:90)
        at org.apache.hadoop.fs.FsShell.main(FsShell.java:378)
ls: Call From rao2/192.168.30.130 to rao2:8020 failed on connection exception: java.net.ConnectException: Connection refused; For more details see:  http://wiki.apache.org/hadoop/ConnectionRefused

以前是否成功过。集群启动了吗