自从上次调通hbase后很久没有碰hadoop了，今日想写一个mapreduce的小程序。于是先运行了下自带的wordcount示例程序，却报错了。

信息如下：

kevin@ubuntu:~/usr/hadoop/hadoop$ ./bin/hadoop jar hadoop-examples-1.2.1.jar wordcount readme.txt output15/05/11 08:20:04 INFO input.FileInputFormat: Total input paths to process : 115/05/11 08:20:04 INFO util.NativeCodeLoader: Loaded the native-hadoop library15/05/11 08:20:04 WARN snappy.LoadSnappy: Snappy native library not loaded15/05/11 08:20:05 INFO mapred.JobClient: Running job: job_201505110806_000315/05/11 08:20:06 INFO mapred.JobClient:  map 0% reduce 0%15/05/11 08:20:06 INFO mapred.JobClient: Task Id : attempt_201505110806_0003_m_000002_0, Status : FAILEDError initializing attempt_201505110806_0003_m_000002_0:java.io.IOException: Exception reading file:/~/usr/hadoop/hadoop/tmp/mapred/local/ttprivate/taskTracker/kevin/jobcache/job_201505110806_0003/jobToken    at org.apache.hadoop.security.Credentials.readTokenStorageFile(Credentials.java:135)    at org.apache.hadoop.mapreduce.security.TokenCache.loadTokens(TokenCache.java:178)    at org.apache.hadoop.mapred.TaskTracker.initializeJob(TaskTracker.java:1289)    at org.apache.hadoop.mapred.TaskTracker.localizeJob(TaskTracker.java:1226)    at org.apache.hadoop.mapred.TaskTracker$5.run(TaskTracker.java:2603)    at java.lang.Thread.run(Thread.java:745)Caused by: java.io.FileNotFoundException: File file:/~/usr/hadoop/hadoop/tmp/mapred/local/ttprivate/taskTracker/kevin/jobcache/job_201505110806_0003/jobToken does not exist.    at org.apache.hadoop.fs.RawLocalFileSystem.getFileStatus(RawLocalFileSystem.java:402)    at org.apache.hadoop.fs.FilterFileSystem.getFileStatus(FilterFileSystem.java:255)    at org.apache.hadoop.fs.ChecksumFileSystem$ChecksumFSInputChecker.
     
      (ChecksumFileSystem.java:125)    at org.apache.hadoop.fs.ChecksumFileSystem.open(ChecksumFileSystem.java:283)    at org.apache.hadoop.fs.FileSystem.open(FileSystem.java:436)    at org.apache.hadoop.security.Credentials.readTokenStorageFile(Credentials.java:129)    ... 5 more
     

错误是无法读取jobToken的文件，由于程序不会出错，推测是上次在配置hbase时修改hadoop的core-site.xml文件出错了。在stackoverflow上有一个同样的问题，有人建议删除 该配置文件中关于缓存文件目录的配置，因为这一部分是会被系统默认创建的，不需要手动配置。即下面这一部分：

1 
      2 
     
       3   
      
       hadoop.tmp.dir
       4   
      
       /app/hadoop/tmp
       5   
      
       A base for other temporary directories.
       6 
     

删掉这个问题就解决了。关闭hadoop，重启hadoop。出现新问题 JobTracker is in safe mode：

15/05/11 08:47:40 ERROR security.UserGroupInformation: PriviledgedActionException as:kevin cause:org.apache.hadoop.ipc.RemoteException: org.apache.hadoop.mapred.SafeModeException: JobTracker is in safe mode    at org.apache.hadoop.mapred.JobTracker.checkSafeMode(JobTracker.java:5188)    at org.apache.hadoop.mapred.JobTracker.getStagingAreaDir(JobTracker.java:3677)    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:483)    at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:587)    at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1432)    at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1428)    at java.security.AccessController.doPrivileged(Native Method)    at javax.security.auth.Subject.doAs(Subject.java:422)    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1190)    at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1426)

碰巧stackoverflow上也有相关的问题，应该是权限的问题，运行以下命令即可：

bin/hadoop dfsadmin -safemode leave

问题均解决，wordcount成功运行。