运行wordcount实例
在/tmp目录下生成两个文本文件，上面随便写两个单词。
cd /tmp/
mkdir file
cd file/
echo "Hello world" > file1.txt
cp file1.txt file2.txt在hadoop平台中新建 /input 目录，这里不是系统的 / 目录。
cd /usr/local/hadoop-2.6.5
./bin/hadoop fs -mkdir /input
hadoop fs -ls /
drwxr-xr-x - root supergroup 0 2018-01-04 09:32 /input执行 ./bin/hadoop fs -mkdir /input 可能会遇到一个错误：
报错：
mkdir: Cannot create directory /input. Name node is in safe mode.
# 解决办法
bin/hadoop dfsadmin -safemode leave
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leave - 强制NameNode离开安全模式
enter - 进入安全模式
get - 返回安全模式是否开启的信息
wait - 等待，一直到安全模式结束。把创建的文件放到hadoop平台的 /input中。
./bin/hadoop fs -put /tmp/file* /input
hadoop fs -ls /input/file
Found 2 items
-rw-r--r-- 1 root supergroup 12 2018-01-04 09:32 /input/file/file1.txt
-rw-r--r-- 1 root supergroup 12 2018-01-04 09:32 /input/file/file2.txt然后运行hadoop自带的example。
./bin/hadoop jar share/hadoop/mapreduce/hadoop-mapreduce-examples-2.6.5.jar wordcount /input/file/ /output/wordcount1
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18/01/04 09:54:09 INFO client.RMProxy: Connecting to ResourceManager at /0.0.0.0:8032
18/01/04 09:54:10 INFO input.FileInputFormat: Total input paths to process : 2
18/01/04 09:54:10 INFO mapreduce.JobSubmitter: number of splits:2
18/01/04 09:54:10 INFO mapreduce.JobSubmitter: Submitting tokens for job: job_1515028606802_0002
18/01/04 09:54:10 INFO impl.YarnClientImpl: Submitted application application_1515028606802_0002
18/01/04 09:54:10 INFO mapreduce.Job: The url to track the job: http://iz2ze31g42iypc75mm363gz:8088/proxy/application_1515028606802_0002/
18/01/04 09:54:10 INFO mapreduce.Job: Running job: job_1515028606802_0002
18/01/04 09:54:18 INFO mapreduce.Job: Job job_1515028606802_0002 running in uber mode : false
18/01/04 09:54:18 INFO mapreduce.Job: map 0% reduce 0%
18/01/04 09:54:27 INFO mapreduce.Job: map 100% reduce 0%
18/01/04 09:54:33 INFO mapreduce.Job: map 100% reduce 100%
18/01/04 09:54:33 INFO mapreduce.Job: Job job_1515028606802_0002 completed successfully
18/01/04 09:54:33 INFO mapreduce.Job: Counters: 49
File System Counters
FILE: Number of bytes read=54
FILE: Number of bytes written=322109
FILE: Number of read operations=0
FILE: Number of large read operations=0
FILE: Number of write operations=0
HDFS: Number of bytes read=238
HDFS: Number of bytes written=16
HDFS: Number of read operations=9
HDFS: Number of large read operations=0
HDFS: Number of write operations=2
Job Counters
Launched map tasks=2
Launched reduce tasks=1
Data-local map tasks=2
Total time spent by all maps in occupied slots (ms)=12913
Total time spent by all reduces in occupied slots (ms)=3521
Total time spent by all map tasks (ms)=12913
Total time spent by all reduce tasks (ms)=3521
Total vcore-milliseconds taken by all map tasks=12913
Total vcore-milliseconds taken by all reduce tasks=3521
Total megabyte-milliseconds taken by all map tasks=13222912
Total megabyte-milliseconds taken by all reduce tasks=3605504
Map-Reduce Framework
Map input records=2
Map output records=4
Map output bytes=40
Map output materialized bytes=60
Input split bytes=214
Combine input records=4
Combine output records=4
Reduce input groups=2
Reduce shuffle bytes=60
Reduce input records=4
Reduce output records=2
Spilled Records=8
Shuffled Maps =2
Failed Shuffles=0
Merged Map outputs=2
GC time elapsed (ms)=363
CPU time spent (ms)=1360
Physical memory (bytes) snapshot=499748864
Virtual memory (bytes) snapshot=6301630464
Total committed heap usage (bytes)=301146112
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=24
File Output Format Counters
Bytes Written=16查看结果
./bin/hdfs dfs -cat /output/wordcount1/*
Hello 2
world 2