Centos ,rmr rhadoop, hadoop streaming failed with error code 1

When I download RMR and installed all dependency packages , try to run a simple mapreduce job on R, get an unknown error.

b=mapreduce(input=a,map=function(k,v) keyval(v,v^2))
packageJobJar: [/tmp/Rtmp8skozB/rmr-local-env, /tmp/Rtmp8skozB/rmr-global-env, /tmp/Rtmp8skozB/rhstr.map14f121ad6582, /var/lib/hadoop-0.20/cache/root/hadoop-unjar8292210935392046645/] [] /tmp/streamjob4219155535407733796.jar tmpDir=null
12/06/27 11:31:45 INFO mapred.FileInputFormat: Total input paths to process : 1
12/06/27 11:31:46 INFO streaming.StreamJob: getLocalDirs(): [/var/lib/hadoop-0.20/cache/root/mapred/local]
12/06/27 11:31:46 INFO streaming.StreamJob: Running job: job_201206271130_0001
12/06/27 11:31:46 INFO streaming.StreamJob: To kill this job, run:
12/06/27 11:31:46 INFO streaming.StreamJob: /usr/lib/hadoop/bin/hadoop job -Dmapred.job.tracker=localhost:8021 -kill job_201206271130_0001
12/06/27 11:31:46 INFO streaming.StreamJob: Tracking URL: http://localhost.localdomain:50030/jobdetails.jsp?jobid=job_201206271130_0001
12/06/27 11:31:47 INFO streaming.StreamJob: map 0% reduce 0%
12/06/27 11:32:07 INFO streaming.StreamJob: map 100% reduce 100%
12/06/27 11:32:07 INFO streaming.StreamJob: To kill this job, run:
12/06/27 11:32:07 INFO streaming.StreamJob: /usr/lib/hadoop/bin/hadoop job -Dmapred.job.tracker=localhost:8021 -kill job_201206271130_0001
12/06/27 11:32:07 INFO streaming.StreamJob: Tracking URL: http://localhost.localdomain:50030/jobdetails.jsp?jobid=job_201206271130_0001
12/06/27 11:32:07 ERROR streaming.StreamJob: Job not successful. Error: NA
12/06/27 11:32:07 INFO streaming.StreamJob: killJob...
Streaming Command Failed!
Error in mr(map = map, reduce = reduce, reduce.on.data.frame = reduce.on.data.frame, :
hadoop streaming failed with error code 1

I checked that 3 environments requried are all set ,

the error is very general, then I checked the jobtracker/tasktracker log.

Caused by: java.lang.RuntimeException: configuration exception
at org.apache.hadoop.streaming.PipeMapRed.configure(PipeMapRed.java:230)
at org.apache.hadoop.streaming.PipeMapper.configure(PipeMapper.java:66)
... 22 more
Caused by: java.io.IOException: Cannot run program "Rscript": java.io.IOException: error=2, No such file or directory
at java.lang.ProcessBuilder.start(ProcessBuilder.java:460)
at org.apache.hadoop.streaming.PipeMapRed.configure(PipeMapRed.java:214)
... 23 more
Caused by: java.io.IOException: java.io.IOException: error=2, No such file or directory
at java.lang.UNIXProcess.<init>(UNIXProcess.java:148)
at java.lang.ProcessImpl.start(ProcessImpl.java:65)
at java.lang.ProcessBuilder.start(ProcessBuilder.java:453)
... 24 more

it looks like I try run the Rscript, but failed, so for my first impression, it could be a permission issue.

then I run as the mapreduce user, try to locate the Rscript. all are ok, the permission are ok.

everyone has the execute access, so could it be a path issue? so I just give a try, make a link under /usr/bin/Rscript. then, all works. super!