运行的命令：
[root@node1 ~]# cat wc.txt
hello tom
andy joy
hello rose
hello joy
mark andy
hello tom
andy rose
hello joy
[root@node1 ~]# hdfs dfs -mkdir -p /wordcount/input
21/11/03 13:28:24 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
[root@node1 ~]# hdfs dfs -put wc.txt /wordcount/input
21/11/03 13:28:47 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
[root@node1 ~]# hdfs dfs -ls /wordcount/input
21/11/03 13:30:00 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
Found 1 items
-rw-r--r-- 2 root supergroup 87 2021-11-03 13:28 /wordcount/input/wc.txt
[root@node1 ~]# cd /opt/hadoop-2.6.5/share/hadoop/mapreduce/
[root@node1 mapreduce]# ll
total 4880
-rw-rw-r-- 1 1000 1000 526732 Oct 3 2016 hadoop-mapreduce-client-app-2.6.5.jar
-rw-rw-r-- 1 1000 1000 686773 Oct 3 2016 hadoop-mapreduce-client-common-2.6.5.jar
-rw-rw-r-- 1 1000 1000 1535776 Oct 3 2016 hadoop-mapreduce-client-core-2.6.5.jar
-rw-rw-r-- 1 1000 1000 259326 Oct 3 2016 hadoop-mapreduce-client-hs-2.6.5.jar
-rw-rw-r-- 1 1000 1000 27489 Oct 3 2016 hadoop-mapreduce-client-hs-plugins-2.6.5.jar
-rw-rw-r-- 1 1000 1000 61309 Oct 3 2016 hadoop-mapreduce-client-jobclient-2.6.5.jar
-rw-rw-r-- 1 1000 1000 1514166 Oct 3 2016 hadoop-mapreduce-client-jobclient-2.6.5-tests.jar
-rw-rw-r-- 1 1000 1000 67762 Oct 3 2016 hadoop-mapreduce-client-shuffle-2.6.5.jar
-rw-rw-r-- 1 1000 1000 292710 Oct 3 2016 hadoop-mapreduce-examples-2.6.5.jar
drwxrwxr-x 2 1000 1000 4096 Oct 3 2016 lib
drwxrwxr-x 2 1000 1000 4096 Oct 3 2016 lib-examples
drwxrwxr-x 2 1000 1000 4096 Oct 3 2016 sources
[root@node1 mapreduce]# hadoop jar hadoop-mapreduce-examples-2.6.5.jar wordcount /wordcount/input /wordcount/output
21/11/03 13:31:43 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
21/11/03 13:31:48 INFO input.FileInputFormat: Total input paths to process : 1
21/11/03 13:31:48 INFO mapreduce.JobSubmitter: number of splits:1
21/11/03 13:31:49 INFO mapreduce.JobSubmitter: Submitting tokens for job: job_1635917251344_0001
21/11/03 13:31:50 INFO impl.YarnClientImpl: Submitted application application_1635917251344_0001
21/11/03 13:31:50 INFO mapreduce.Job: The url to track the job: http://node3:8088/proxy/application_1635917251344_0001/
21/11/03 13:31:50 INFO mapreduce.Job: Running job: job_1635917251344_0001
21/11/03 13:32:07 INFO mapreduce.Job: Job job_1635917251344_0001 running in uber mode : false
21/11/03 13:32:07 INFO mapreduce.Job: map 0% reduce 0%
21/11/03 13:32:23 INFO mapreduce.Job: map 100% reduce 0%
21/11/03 13:32:33 INFO mapreduce.Job: map 100% reduce 100%
21/11/03 13:32:33 INFO mapreduce.Job: Job job_1635917251344_0001 completed successfully
21/11/03 13:32:33 INFO mapreduce.Job: Counters: 49
File System Counters
FILE: Number of bytes read=71
FILE: Number of bytes written=218919
FILE: Number of read operations=0
FILE: Number of large read operations=0
FILE: Number of write operations=0
HDFS: Number of bytes read=191
HDFS: Number of bytes written=41
HDFS: Number of read operations=6
HDFS: Number of large read operations=0
HDFS: Number of write operations=2
Job Counters
Launched map tasks=1
Launched reduce tasks=1
Data-local map tasks=1
Total time spent by all maps in occupied slots (ms)=13217
Total time spent by all reduces in occupied slots (ms)=5760
Total time spent by all map tasks (ms)=13217
Total time spent by all reduce tasks (ms)=5760
Total vcore-milliseconds taken by all map tasks=13217
Total vcore-milliseconds taken by all reduce tasks=5760
Total megabyte-milliseconds taken by all map tasks=13534208
Total megabyte-milliseconds taken by all reduce tasks=5898240
Map-Reduce Framework
Map input records=8
Map output records=16
Map output bytes=144
Map output materialized bytes=71
Input split bytes=104
Combine input records=16
Combine output records=6
Reduce input groups=6
Reduce shuffle bytes=71
Reduce input records=6
Reduce output records=6
Spilled Records=12
Shuffled Maps =1
Failed Shuffles=0
Merged Map outputs=1
GC time elapsed (ms)=315
CPU time spent (ms)=3460
Physical memory (bytes) snapshot=293687296
Virtual memory (bytes) snapshot=4126777344
Total committed heap usage (bytes)=140374016
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=87
File Output Format Counters
Bytes Written=41
[root@node1 mapreduce]# hdfs dfs -ls /wordcount/output
21/11/03 13:41:39 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
Found 2 items
-rw-r--r-- 2 root supergroup 0 2021-11-03 13:32 /wordcount/output/_SUCCESS
-rw-r--r-- 2 root supergroup 41 2021-11-03 13:32 /wordcount/output/part-r-00000
[root@node1 mapreduce]# hdfs dfs -cat /wordcount/output/part-r-00000
21/11/03 13:42:34 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
andy 3
hello 5
joy 3
mark 1
rose 2
tom 2
[root@node1 mapreduce]# hdfs dfs -get /wordcount/output/part-r-00000
21/11/03 13:44:15 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
[root@node1 mapreduce]# ls
hadoop-mapreduce-client-app-2.6.5.jar hadoop-mapreduce-client-hs-2.6.5.jar hadoop-mapreduce-client-jobclient-2.6.5-tests.jar lib sources
hadoop-mapreduce-client-common-2.6.5.jar hadoop-mapreduce-client-hs-plugins-2.6.5.jar hadoop-mapreduce-client-shuffle-2.6.5.jar lib-examples
hadoop-mapreduce-client-core-2.6.5.jar hadoop-mapreduce-client-jobclient-2.6.5.jar hadoop-mapreduce-examples-2.6.5.jar part-r-00000
[root@node1 mapreduce]# cat part-r-00000
andy 3
hello 5
joy 3
mark 1
rose 2
tom 2*input:是 hdfs 文件系统中数据所在的目录
*ouput:是 hdfs 中不存在的目录，mr 程序运行的结果会输出到该目录
/_SUCCESS：是信号/标志文件
/part-r-00000：是 reduce 输出的数据文件
r：reduce 的意思，00000 是对应的 reduce 编号，多个 reduce 会有多个数据文件
