13/12/04 16:17:18 ERROR security.UserGroupInformation: PriviledgedActionException as:aolx (auth:SIMPLE) cause:org.apache.hadoop.mapred.FileAlreadyExistsException: Output directory hdfs://localhost:9000/out already exists
每次运行时，要保证output的目录为空，所以这时候必须去hdfs文件系统下把out以前的运行结果保存起来或者删除掉
可以用bin/hadoop fs -ls /
bin/hadoop fs -ls /
13/12/04 16:29:42 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
Found 2 items
drwxr-xr-x - aolx supergroup 0 2013-12-04 16:13 /in
drwxr-xr-x - aolx supergroup 0 2013-12-04 16:18 /out
删除out下的文件
bin/hadoop fs -rm -r /out