hadoop集群部署上后，在服务器中运行hadoop自带的jar包中的实例报错
异常一：
2018-01-09 03:25:37,250 INFO mapreduce.Job: Job job_1515468264727_0001 failed with state FAILED due to: Application application_1515468264727_0001 failed 2 times due to AM Container for appattempt_1515468264727_0001_000002 exited with exitCode: 1
Failing this attempt.Diagnostics: [2018-01-09 03:25:36.447]Exception from container-launch.
Container id: container_1515468264727_0001_02_000001
Exit code: 1
[2018-01-09 03:25:36.499]Container exited with a non-zero exit code 1. Error file: prelaunch.err.
Last 4096 bytes of prelaunch.err :
Last 4096 bytes of stderr :
Error: Could not find or load main class org.apache.hadoop.mapreduce.v2.app.MRAppMaster
Please check whether your etc/hadoop/mapred-site.xml contains the below configuration:
<property>
<name>yarn.app.mapreduce.am.env</name>
<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}</value>
</property>
<property>
<name>mapreduce.map.env</name>
<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}</value>
</property>
<property>
<name>mapreduce.reduce.env</name>
<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}</value>
</property>
解决方法：按错误提示，在mapred-site.xml配置文件中添加hadoop根目录
1.先运行hadoop classpath得到classpath
将得到的classpath全部复制到mapred-site.xml中，配置
<property>
<name>yarn.app.mapreduce.am.env</name>
<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}（将这一串红字用得到的classpath代替）</value>
</property>
<property>
<name>mapreduce.map.env</name>
<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}（将这一串红字用得到的classpath代替）</value>
</property>
<property>
<name>mapreduce.reduce.env</name>
<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}（将这一串红字用得到的classpath代替）</value>
</property>
配置结束关闭mapred-site.xml
重新启动集群，再在share文件中运行
得到结果：
测试成功！！
