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安装好hadoop集群之后，都会想着试一下自己的集群是否正常工作，最简单的方式就是运行hadoop提供的例子程序。
命令
hadoop jar hadoop-mapreduce-examples-2.6.4.jar pi 5 5
结果
[root@zk2 ~]# hadoop jar hadoop-mapreduce-examples-2.6.4.jar pi 5 5
Number of Maps = 5
Samples per Map = 5
Wrote input for Map #0
Wrote input for Map #1
Wrote input for Map #2
Wrote input for Map #3
Wrote input for Map #4
Starting Job
19/03/28 23:25:06 INFO client.RMProxy: Connecting to ResourceManager at /192.168.56.160:8032
19/03/28 23:25:07 INFO input.FileInputFormat: Total input paths to process : 5
19/03/28 23:25:07 INFO mapreduce.JobSubmitter: number of splits:5
19/03/28 23:25:08 INFO mapreduce.JobSubmitter: Submitting tokens for job: job_1553786668014_0001
19/03/28 23:25:08 INFO impl.YarnClientImpl: Submitted application application_1553786668014_0001
19/03/28 23:25:08 INFO mapreduce.Job: The url to track the job: http://zk1:8088/proxy/application_1553786668014_0001/
19/03/28 23:25:08 INFO mapreduce.Job: Running job: job_1553786668014_0001
19/03/28 23:25:20 INFO mapreduce.Job: Job job_1553786668014_0001 running in uber mode : false
19/03/28 23:25:20 INFO mapreduce.Job: map 0% reduce 0%
19/03/28 23:27:43 INFO mapreduce.Job: map 80% reduce 0%
19/03/28 23:27:45 INFO mapreduce.Job: map 100% reduce 0%
19/03/28 23:28:28 INFO mapreduce.Job: map 100% reduce 100%
19/03/28 23:28:29 INFO mapreduce.Job: Job job_1553786668014_0001 completed successfully
19/03/28 23:28:30 INFO mapreduce.Job: Counters: 49
File System Counters
FILE: Number of bytes read=116
FILE: Number of bytes written=642111
FILE: Number of read operations=0
FILE: Number of large read operations=0
FILE: Number of write operations=0
HDFS: Number of bytes read=1345
HDFS: Number of bytes written=215
HDFS: Number of read operations=23
HDFS: Number of large read operations=0
HDFS: Number of write operations=3
Job Counters
Launched map tasks=5
Launched reduce tasks=1
Data-local map tasks=5
Total time spent by all maps in occupied slots (ms)=734480
Total time spent by all reduces in occupied slots (ms)=36769
Total time spent by all map tasks (ms)=734480
Total time spent by all reduce tasks (ms)=36769
Total vcore-milliseconds taken by all map tasks=734480
Total vcore-milliseconds taken by all reduce tasks=36769
Total megabyte-milliseconds taken by all map tasks=752107520
Total megabyte-milliseconds taken by all reduce tasks=37651456
Map-Reduce Framework
Map input records=5
Map output records=10
Map output bytes=90
Map output materialized bytes=140
Input split bytes=755
Combine input records=0
Combine output records=0
Reduce input groups=2
Reduce shuffle bytes=140
Reduce input records=10
Reduce output records=0
Spilled Records=20
Shuffled Maps =5
Failed Shuffles=0
Merged Map outputs=5
GC time elapsed (ms)=19784
CPU time spent (ms)=14600
Physical memory (bytes) snapshot=676265984
Virtual memory (bytes) snapshot=12362330112
Total committed heap usage (bytes)=626020352
Shuffle Errors
BAD_ID=0
CONNECTION=0
IO_ERROR=0
WRONG_LENGTH=0
WRONG_MAP=0
WRONG_REDUCE=0
File Input Format Counters
Bytes Read=590
File Output Format Counters
Bytes Written=97
Job Finished in 204.801 seconds
Estimated value of Pi is 3.68000000000000000000
如果运行例子程序，出现以上结果，证明集群是正常工作的。