ssh那些都已经搞了，跑一个书上的例子出现了Connection Refused异常，如下：
12/04/09 01:00:54 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:8020. Already tried 0 time(s).
12/04/09 01:00:56 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:8020. Already tried 1 time(s).
12/04/09 01:00:57 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:8020. Already tried 2 time(s).
12/04/09 01:00:58 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:8020. Already tried 3 time(s).
12/04/09 01:00:59 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:8020. Already tried 4 time(s).
12/04/09 01:01:00 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:8020. Already tried 5 time(s).
12/04/09 01:01:01 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:8020. Already tried 6 time(s).
12/04/09 01:01:02 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:8020. Already tried 7 time(s).
12/04/09 01:01:03 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:8020. Already tried 8 time(s).
12/04/09 01:01:04 INFO ipc.Client: Retrying connect to server: localhost/127.0.0.1:8020. Already tried 9 time(s).
Exception in thread "main" java.net.ConnectException: Call to localhost/127.0.0.1:8020 failed on connection exception: java.net.ConnectException: Connection refused
at org.apache.hadoop.ipc.Client.wrapException(Client.java:1095)
at org.apache.hadoop.ipc.Client.call(Client.java:1071)
at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:225)
at $Proxy1.getProtocolVersion(Unknown Source)
at org.apache.hadoop.ipc.RPC.getProxy(RPC.java:396)
at org.apache.hadoop.ipc.RPC.getProxy(RPC.java:379)
at org.apache.hadoop.hdfs.DFSClient.createRPCNamenode(DFSClient.java:119)
at org.apache.hadoop.hdfs.DFSClient.<init>(DFSClient.java:238)
at org.apache.hadoop.hdfs.DFSClient.<init>(DFSClient.java:203)
at org.apache.hadoop.hdfs.DistributedFileSystem.initialize(DistributedFileSystem.java:89)
at org.apache.hadoop.fs.FileSystem.createFileSystem(FileSystem.java:1386)
at org.apache.hadoop.fs.FileSystem.access$200(FileSystem.java:66)
at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:1404)
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:254)
at com.lan.hadoop.FileSystemCat.main(FileSystemCat.java:15)
.............................
记得以前也出过这个异常，当时是因为Namenode没有启动，今天的情况是使用hadoop的ls 、mkdir那些都正常，使用jps也发现有namenode进程，telnet localhost 8020失败，但是自己也不知道是为啥失败，最后董问我namenode的端口号是不是8020，我还没反应过来，最后看了下core-site.xml发现我将fs.default.name配置为
hdfs://localhost:9000了，果然是端口号不对。在代码中把端口号改为9000就OK了