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伪分布模式下执行wordcount实例时报错解决办法

问题1、不能分配内存,错误提示如下:

FAILED
java.lang.RuntimeException: Error while running command to get file permissions : java.io.IOException: Cannot run program "/bin/ls": java.io.IOException: error=12, Cannot allocate memory
    at java.lang.ProcessBuilder.start(ProcessBuilder.java:488)
    at org.apache.hadoop.util.Shell.runCommand(Shell.java:200)
    at org.apache.hadoop.util.Shell.run(Shell.java:182)
    at org.apache.hadoop.util.Shell$ShellCommandExecutor.execute(Shell.java:375)
    at org.apache.hadoop.util.Shell.execCommand(Shell.java:461)
    at org.apache.hadoop.util.Shell.execCommand(Shell.java:444)
    at org.apache.hadoop.fs.FileUtil.execCommand(FileUtil.java:712)
    at org.apache.hadoop.fs.RawLocalFileSystem$RawLocalFileStatus.loadPermissionInfo(RawLocalFileSystem.java:448)



  解决把法:

  问题原因可能是机器内存太小(2G),安装Ubuntu时又没有使用交换空间。

  修改conf下的hadoop-env.sh

  # The maximum amount of heap to use, in MB. Default is 1000.
  export HADOOP_HEAPSIZE=2000



问题2:JobTracker处于安全模式


13/10/12 09:25:14 ERROR security.UserGroupInformation: PriviledgedActionException as:hadoop 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:5178)


  解决办法:

  解除安全模式,如下命令:

  bin/hadoop dfsadmin -safemode leave



  操作安全模式的参数:

  enter  进入安全模式

  leave  强制退出安全模式

  get  返回是否开启安全模式

  wait  等待,一直到安全模式结束

  

问题3:output文件夹已存在

  假如程序的输出路径为output,如果该文件夹已经存在,会提示此错误。

  ERROR security.UserGroupInformation: PriviledgedActionException as:hadoop cause:org.apache.hadoop.mapred.FileAlreadyExistsException: Output directory output already exists
org.apache.hadoop.mapred.FileAlreadyExistsException: Output directory output already exists
    at org.apache.hadoop.mapreduce.lib.output.FileOutputFormat.checkOutputSpecs(FileOutputFormat.java:137)


  解决办法:执行下面命令删除文件夹

  bin/hadoop dfs -rmr output


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