問題一
問題描述：
8/01/22 16:52:16 WARN Client: Failed to connect to server: master/192.168.217.128:10020: retries get failed due to exceeded maximum allowed retries number: 10
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$Invoker.invoke(ProtobufRpcEngine.java:116)
at com.sun.proxy.$Proxy15.getCounters(Unknown Source)
at org.apache.hadoop.mapreduce.v2.api.impl.pb.client.MRClientProtocolPBClientImpl.getCounters(MRClientProtocolPBClientImpl.java:166)
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.mapred.ClientServiceDelegate.invoke(ClientServiceDelegate.java:325)
at org.apache.hadoop.mapred.ClientServiceDelegate.getJobCounters(ClientServiceDelegate.java:381)
at org.apache.hadoop.mapred.YARNRunner.getJobCounters(YARNRunner.java:606)
at org.apache.hadoop.mapreduce.Job$8.run(Job.java:812)
at org.apache.hadoop.mapreduce.Job$8.run(Job.java:809)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:422)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1836)
at org.apache.hadoop.mapreduce.Job.getCounters(Job.java:809)
at org.apache.hadoop.mapreduce.Job.monitorAndPrintJob(Job.java:1434)
at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:1362)
at org.apache.mahout.text.SequenceFilesFromDirectory.runMapReduce(SequenceFilesFromDirectory.java:177)
at org.apache.mahout.text.SequenceFilesFromDirectory.run(SequenceFilesFromDirectory.java:90)
at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:76)
at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:90)
at org.apache.mahout.text.SequenceFilesFromDirectory.main(SequenceFilesFromDirectory.java:64)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.hadoop.util.ProgramDriver$ProgramDescription.invoke(ProgramDriver.java:71)
at org.apache.hadoop.util.ProgramDriver.run(ProgramDriver.java:144)
at org.apache.hadoop.util.ProgramDriver.driver(ProgramDriver.java:152)
at org.apache.mahout.driver.MahoutDriver.main(MahoutDriver.java:195)
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.util.RunJar.run(RunJar.java:234)
at org.apache.hadoop.util.RunJar.main(RunJar.java:148)
解決方案：
在mapred-site.xml配置文件中添加：
<property>
<name>mapreduce.jobhistory.address</name>
<value>${namenode hostname}:10020</value>
</property>
在namenode上執行命令：mr-jobhistory-daemon.sh start historyserver
這樣在namenode上會啓動JobHistoryServer服務，
參考文獻：hadoop運行mapreduce作業無法連接0.0.0.0/0.0.0.0:10020
問題二
問題描述
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/htrace/core/Tracer$Builder
at org.apache.hadoop.fs.FsTracer.get(FsTracer.java:42)
at org.apache.hadoop.fs.FileSystem.createFileSystem(FileSystem.java:2806)
at org.apache.hadoop.fs.FileSystem.access$200(FileSystem.java:100)
at org.apache.hadoop.fs.FileSystem$Cache.getInternal(FileSystem.java:2849)
at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:2831)
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:389)
at org.apache.hadoop.fs.Path.getFileSystem(Path.java:356)
at org.apache.mahout.classifier.df.mapreduce.TestForest.testForest(TestForest.java:170)
at org.apache.mahout.classifier.df.mapreduce.TestForest.run(TestForest.java:157)
at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:76)
at org.apache.mahout.classifier.df.mapreduce.TestForest.main(TestForest.java:505)
Caused by: java.lang.ClassNotFoundException: org.apache.htrace.core.Tracer$Builder
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
解決方案：
添加htrace-core4-4.1.0-incubating.jar （下載地址：http://mvnrepository.com/artifact/org.apache.htrace/htrace-core4/4.1.0-incubating）
問題三
問題描述：
這是一個血的教訓，以至於自己在這裏停了將近三天的時間。
我在本地環境運行mahout的程序時，總是顯示找不到自己寫的一個靜態的mapper子類，所報錯誤如下：
Error: java.lang.RuntimeException: java.lang.ClassNotFoundException: Class org.apache.mahout.classifier.df.mapreduce.Classifier$CMapper not found
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:2298)
at org.apache.hadoop.mapreduce.task.JobContextImpl.getMapperClass(JobContextImpl.java:186)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:745)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:341)
at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:175)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:422)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1836)
at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:169)
Caused by: java.lang.ClassNotFoundException: Class org.apache.mahout.classifier.df.mapreduce.Classifier$CMapper not found
at org.apache.hadoop.conf.Configuration.getClassByName(Configuration.java:2202)
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:2296)
... 8 more
解決方案：
如果不是在eclipse本地運行的話，可以參考http://techme.lofter.com/post/ccd6e_1e772b， 博主使用的是
((JobConf) job.getConfiguration()).setJar(jarFile.toString());
這行代碼代替job.setJarByClass（）。
但我是在eclipse本地運行，我的解決方案很簡單，就是不要把，hadoop的相關配置文件放在src目錄下！！！不然eclipse會把項目提交到hadoop集羣上去執行，而此時就牽扯到類加載和打jar包的相關問題。
把這三個文件移到別的目錄下就好了
之所以是血的教訓，是因爲，我在一開始學習的時候，就看到說不要把其他的相關配置文件放到src目錄下。┭┮﹏┭┮