hadoop3.1.1：找不到或沒法加載主類 org.apache.hadoop.mapreduce.v2.app.MRAppMaster

yarn執行MapReduce任務時，找不到主類致使的

解決：

一、在命令行輸入：hadoop classpath

[hadoop@localhost ~]$ hadoop classpath /data/hadoop/hadoop//etc/hadoop:/data/hadoop/hadoop//share/hadoop/common/lib/*:/data/hadoop/hadoop//share/hadoop/common/*:/data/hadoop/hadoop//share/hadoop/hdfs:/data/hadoop/hadoop//share/hadoop/hdfs/lib/*:/data/hadoop/hadoop//share/hadoop/hdfs/*:/data/hadoop/hadoop//share/hadoop/mapreduce/lib/*:/data/hadoop/hadoop//share/hadoop/mapreduce/*:/data/hadoop/hadoop//share/hadoop/yarn:/data/hadoop/hadoop//share/hadoop/yarn/lib/*:/data/hadoop/hadoop//share/hadoop/yarn/*

二、把上述輸出的值添加到yarn-site.xml文件對應的屬性 <name>yarn.application.classpath</name>下面，eg：

<property>
         <name>yarn.application.classpath</name>
         <value>/data/hadoop/hadoop//etc/hadoop:/data/hadoop/hadoop//share/hadooo
p/common/lib/*:/data/hadoop/hadoop//share/hadoop/common/*:/data/hadoop/hadoop//ss hare/hadoop/hdfs:/data/hadoop/hadoop//share/hadoop/hdfs/lib/*:/data/hadoop/hadooo p//share/hadoop/hdfs/*:/data/hadoop/hadoop//share/hadoop/mapreduce/lib/*:/data/hh adoop/hadoop//share/hadoop/mapreduce/*:/data/hadoop/hadoop//share/hadoop/yarn:/dd ata/hadoop/hadoop//share/hadoop/yarn/lib/*:/data/hadoop/hadoop//share/hadoop/yarr n/*</value> </property>

三、重啓yarn，從新跑MapReduce任務。