4、利用hadoop自带的mr 示例测试运行任务失败: Could not find or load main class org.apache.hadoop.mapreduce.v2.app.MRAppMaster

• 报错信息截图

  

• 解决措施

  按提示所言，相关的类路径信息不全

  1. 获取所有的类路径

     hadoop classpath
     

  2. 然后在etc/hadoop/mapred-site.xml中加入下面这个标签。其中<value>里面的值就是上面hadoop classpath运行后的输出内容

     <property>
             <name>mapreduce.application.classpath</name>
             <value>/opt/software/hadoop-3.1.3/etc/hadoop:/opt/software/hadoop-3.1.3/share/hadoop/common/lib/*:/opt/software/hadoop-3.1.3/share/hadoop/common/*:/opt/software/hadoop-3.1.3/share/hadoop/hdfs:/opt/software/hadoop-3.1.3/share/hadoop/hdfs/lib/*:/opt/software/hadoop-3.1.3/share/hadoop/hdfs/*:/opt/software/hadoop-3.1.3/share/hadoop/mapreduce/lib/*:/opt/software/hadoop-3.1.3/share/hadoop/mapreduce/*:/opt/software/hadoop-3.1.3/share/hadoop/yarn:/opt/software/hadoop-3.1.3/share/hadoop/yarn/lib/*:/opt/software/hadoop-3.1.3/share/hadoop/yarn/*</value>
         </property>
     

  3. 完美解决