搭建好hadoop集群后测试wordcount这个例子，执行到最后一步老是出现这样的错误，执行了hadoop namenode -format并没用，能ping通，貌似不是防火墙问题，请问是什么问题啊？急求大神答案！

15/10/29 09:30:05 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 0 time(s).
15/10/29 09:30:06 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 1 time(s).
15/10/29 09:30:07 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 2 time(s).
15/10/29 09:30:08 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 3 time(s).
15/10/29 09:30:09 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 4 time(s).
^Ctq@master:~$ hadoop jar hadoop/hadoop-0.20.2-examples.jar wordcount input output
15/10/29 09:30:15 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 0 time(s).
15/10/29 09:30:16 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 1 time(s).
15/10/29 09:30:17 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 2 time(s).
15/10/29 09:30:18 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 3 time(s).
15/10/29 09:30:19 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 4 time(s).
15/10/29 09:30:20 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 5 time(s).
15/10/29 09:30:21 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 6 time(s).
15/10/29 09:30:22 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 7 time(s).
15/10/29 09:30:23 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 8 time(s).
15/10/29 09:30:24 INFO ipc.Client: Retrying connect to server: /192.168.157.129:9001. Already tried 9 time(s).
java.net.ConnectException: Call to /192.168.157.129:9001 failed on connection exception: java.net.ConnectException: Connection refused
at org.apache.hadoop.ipc.Client.wrapException(Client.java:767)
at org.apache.hadoop.ipc.Client.call(Client.java:743)
at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:220)
at org.apache.hadoop.mapred.$Proxy0.getProtocolVersion(Unknown Source)
at org.apache.hadoop.ipc.RPC.getProxy(RPC.java:359)
at org.apache.hadoop.mapred.JobClient.createRPCProxy(JobClient.java:429)
at org.apache.hadoop.mapred.JobClient.init(JobClient.java:423)
at org.apache.hadoop.mapred.JobClient.<init>(JobClient.java:410)
at org.apache.hadoop.mapreduce.Job.<init>(Job.java:50)
at org.apache.hadoop.mapreduce.Job.<init>(Job.java:54)
at org.apache.hadoop.examples.WordCount.main(WordCount.java:58)
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.util.ProgramDriver$ProgramDescription.invoke(ProgramDriver.java:68)
at org.apache.hadoop.util.ProgramDriver.driver(ProgramDriver.java:139)
at org.apache.hadoop.examples.ExampleDriver.main(ExampleDriver.java:64)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.apache.hadoop.util.RunJar.main(RunJar.java:156)
Caused by: java.net.ConnectException: Connection refused
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717)
at org.apache.hadoop.net.SocketIOWithTimeout.connect(SocketIOWithTimeout.java:206)
at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:404)
at org.apache.hadoop.ipc.Client$Connection.setupIOstreams(Client.java:304)
at org.apache.hadoop.ipc.Client$Connection.access$1700(Client.java:176)
at org.apache.hadoop.ipc.Client.getConnection(Client.java:860)
at org.apache.hadoop.ipc.Client.call(Client.java:720)
... 21 more