1. 常见问题
（1）hostname设置问题。vi /etc/sysconfig/network
（2）集群/etc/hosts没有统一。
（3）yarn slave需要单独启动。./sbin/yarn-daemon.sh start resourcemanager
（4）namenode格式化需要逐个先启动journalnode。
（5）kerberos主从数据同步时获取不到ticket，一般和设置了多个hosts有关。建议hosts配置和hostname只配置一个。
（6）jsvc通过yum源安装，启动datanode会报错找不到org/apache/commons/daemon/support。改成手动编译安装后就OK了。
2. 测试
[root@master1 work]# hadoop jar wordcount-0.0.1-SNAPSHOT.jar com.javacodegeeks.examples.wordcount.WordCount hdfs://master1:9000/Input.txt output.txt
17/09/04 16:53:09 WARN mapreduce.JobResourceUploader: Hadoop command-line option parsing not performed. Implement the Tool interface and execute your application with ToolRunner to remedy this.
17/09/04 16:53:10 INFO input.FileInputFormat: Total input paths to process : 1
17/09/04 16:53:11 INFO mapreduce.JobSubmitter: number of splits:1
17/09/04 16:53:11 INFO mapreduce.JobSubmitter: Submitting tokens for job: job_1504514855214_0001
17/09/04 16:53:11 INFO impl.YarnClientImpl: Submitted application application_1504514855214_0001
17/09/04 16:53:11 INFO mapreduce.Job: The url to track the job: http://master1:8088/proxy/application_1504514855214_0001/
17/09/04 16:53:11 INFO mapreduce.Job: Running job: job_1504514855214_0001
17/09/04 16:53:19 INFO mapreduce.Job: Job job_1504514855214_0001 running in uber mode : false
17/09/04 16:53:19 INFO mapreduce.Job: map 0% reduce 0%
17/09/04 16:53:26 INFO mapreduce.Job: map 100% reduce 0%
17/09/04 16:53:32 INFO mapreduce.Job: map 100% reduce 100%
17/09/04 16:53:32 INFO mapreduce.Job: Job job_1504514855214_0001 completed successfully
17/09/04 16:53:32 INFO mapreduce.Job: Counters: 49
File System Counters
FILE: Number of bytes read=676
FILE: Number of bytes written=248505
FILE: Number of read operations=0
FILE: Number of large read operations=0
FILE: Number of write operations=0
HDFS: Number of bytes read=416
HDFS: Number of bytes written=339
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)=3592
Total time spent by all reduces in occupied slots (ms)=3048
Total time spent by all map tasks (ms)=3592
Total time spent by all reduce tasks (ms)=3048
Total vcore-milliseconds taken by all map tasks=3592
Total vcore-milliseconds taken by all reduce tasks=3048
Total megabyte-milliseconds taken by all map tasks=3678208
Total megabyte-milliseconds taken by all reduce tasks=3121152
Map-Reduce Framework
Map input records=4
Map output records=58
Map output bytes=554
Map output materialized bytes=676
Input split bytes=94
Combine input records=0
Combine output records=0
Reduce input groups=43
Reduce shuffle bytes=676
Reduce input records=58
Reduce output records=43
Spilled Records=116
Shuffled Maps =1
Failed Shuffles=0
Merged Map outputs=1
GC time elapsed (ms)=186
CPU time spent (ms)=1910
Physical memory (bytes) snapshot=442167296
Virtual memory (bytes) snapshot=4297965568
Total committed heap usage (bytes)=342884352
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=322
File Output Format Counters
Bytes Written=339
Job was successful