採用C語言，利用libhdfs實現對hdfs的操作。但是在程序運行時報錯：
錯誤如下：
hadoop@node1:~/hadoop-1.2.1/sample$ ./test
十二月 17, 2013 11:44:38 上午 org.apache.hadoop.ipc.Client$Connection handleConnectionFailure
信息: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 0 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1 SECONDS)
十二月 17, 2013 11:44:39 上午 org.apache.hadoop.ipc.Client$Connection handleConnectionFailure
信息: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 1 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1 SECONDS)
十二月 17, 2013 11:44:40 上午 org.apache.hadoop.ipc.Client$Connection handleConnectionFailure
信息: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 2 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1 SECONDS)
十二月 17, 2013 11:44:41 上午 org.apache.hadoop.ipc.Client$Connection handleConnectionFailure
信息: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 3 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1 SECONDS)
十二月 17, 2013 11:44:42 上午 org.apache.hadoop.ipc.Client$Connection handleConnectionFailure
信息: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 4 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1 SECONDS)
十二月 17, 2013 11:44:43 上午 org.apache.hadoop.ipc.Client$Connection handleConnectionFailure
信息: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 5 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1 SECONDS)
十二月 17, 2013 11:44:44 上午 org.apache.hadoop.ipc.Client$Connection handleConnectionFailure
信息: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 6 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1 SECONDS)
十二月 17, 2013 11:44:45 上午 org.apache.hadoop.ipc.Client$Connection handleConnectionFailure
信息: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 7 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1 SECONDS)
十二月 17, 2013 11:44:46 上午 org.apache.hadoop.ipc.Client$Connection handleConnectionFailure
信息: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 8 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1 SECONDS)
十二月 17, 2013 11:44:47 上午 org.apache.hadoop.ipc.Client$Connection handleConnectionFailure
信息: Retrying connect to server: localhost/127.0.0.1:9000. Already tried 9 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1 SECONDS)
十二月 17, 2013 11:44:47 上午 org.apache.hadoop.security.UserGroupInformation doAs
嚴重: PriviledgedActionException as:hadoop cause:java.net.ConnectException: Call to localhost/127.0.0.1:9000 failed on connection exception: java.net.ConnectException: 拒絕連接
Exception in thread "main" java.net.ConnectException: Call to localhost/127.0.0.1:9000 failed on connection exception: java.net.ConnectException: 拒絕連接
at org.apache.hadoop.ipc.Client.wrapException(Client.java:1142)
at org.apache.hadoop.ipc.Client.call(Client.java:1118)
at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:229)
at com.sun.proxy.$Proxy1.getProtocolVersion(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:85)
at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:62)
at com.sun.proxy.$Proxy1.getProtocolVersion(Unknown Source)
at org.apache.hadoop.ipc.RPC.checkVersion(RPC.java:422)
at org.apache.hadoop.hdfs.DFSClient.createNamenode(DFSClient.java:183)
at org.apache.hadoop.hdfs.DFSClient.<init>(DFSClient.java:281)
at org.apache.hadoop.hdfs.DFSClient.<init>(DFSClient.java:245)
at org.apache.hadoop.hdfs.DistributedFileSystem.initialize(DistributedFileSystem.java:100)
at org.apache.hadoop.fs.FileSystem.createFileSystem(FileSystem.java:1446)
at org.apache.hadoop.fs.FileSystem.access$200(FileSystem.java:67)
at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:1464)
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:263)
at org.apache.hadoop.fs.FileSystem$1.run(FileSystem.java:118)
at org.apache.hadoop.fs.FileSystem$1.run(FileSystem.java:116)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1190)
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:116)
Caused by: java.net.ConnectException: 拒絕連接
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:735)
at org.apache.hadoop.net.SocketIOWithTimeout.connect(SocketIOWithTimeout.java:206)
at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:511)
at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:481)
at org.apache.hadoop.ipc.Client$Connection.setupConnection(Client.java:457)
at org.apache.hadoop.ipc.Client$Connection.setupIOstreams(Client.java:583)
at org.apache.hadoop.ipc.Client$Connection.access$2200(Client.java:205)
at org.apache.hadoop.ipc.Client.getConnection(Client.java:1249)
at org.apache.hadoop.ipc.Client.call(Client.java:1093)
... 24 more
Call to org.apache.hadoop.fs.Filesystem::get(URI, Configuration) failed!
Exception in thread "main" java.lang.NullPointerException
Call to get configuration object from filesystem failed!
Failed to open /tmp/testfile.txt for writing!
經過仔細分析，才知道問題所在。在c程序中：
hdfsConnect("127.0.0.1", 9000);而在core-site.xml等 配置文件中，寫的確是：
<configuration>
<property>
<name>fs.default.name</name>
<value>hdfs://localhost:9000</value>
</property>
</configuration>
解決辦法就是：把兩者修改一直，要不都用127.0.01，要不都用localhost。
問題得到解決。
