Hadoop - 解决“找不到或无法加载主类 org.apache.hadoop.mapreduce.v2.app.MRAppMaster”问题

2024-08-20 发布：hangge 阅读：346

1，问题描述

最近我在 Hadoop 上执行一个 MapReduce 任务时，发现报“找不到或无法加载主类”错误，具体错误信息如下：

2024-01-26 09:45:52,652 INFO mapreduce.Job: map 0% reduce 0%

2024-01-26 09:45:52,671 INFO mapreduce.Job: Job job_1706233227329_0003 failed with state FAILED due to: Application application_1706233227329_0003 failed 2 times due to AM Container for appattempt_1706233227329_0003_000002 exited with exitCode: 1

Failing this attempt.Diagnostics: [2024-01-26 09:45:51.919]Exception from container-launch.

Container id: container_1706233227329_0003_02_000001

Exit code: 1

[2024-01-26 09:45:51.923]Container exited with a non-zero exit code 1. Error file: prelaunch.err.

Last 4096 bytes of prelaunch.err :

Last 4096 bytes of stderr :

错误: 找不到或无法加载主类 org.apache.hadoop.mapreduce.v2.app.MRAppMaster

[2024-01-26 09:45:51.924]Container exited with a non-zero exit code 1. Error file: prelaunch.err.

Last 4096 bytes of prelaunch.err :

Last 4096 bytes of stderr :

错误: 找不到或无法加载主类 org.apache.hadoop.mapreduce.v2.app.MRAppMaster

2，解决办法

（1）执行如下命令查看 hadoop 的 classpath：

hadoop classpath

（2）修改 hadoop 的 yarn-site.xml 配置文件（无论主节点还是从节点都要修改）：

vi $HADOOP_HOME/etc/hadoop/yarn-site.xml

（3）增加一个 yarn.application.classpath 配置项，其值就是前面我们查询到的 hadoop 的 classpath：

<property>
  <name>yarn.application.classpath</name>
  <value>/usr/local/hadoop/etc/hadoop:/usr/local/hadoop/share/hadoop/common/lib/*:/usr/local/hadoop/share/hadoop/common/*:/usr/local/hadoop/share/hadoop/hdfs:/usr/local/hadoop/share/hadoop/hdfs/lib/*:/usr/local/hadoop/share/hadoop/hdfs/*:/usr/local/hadoop/share/hadoop/mapreduce/*:/usr/local/hadoop/share/hadoop/yarn:/usr/local/hadoop/share/hadoop/yarn/lib/*:/usr/local/hadoop/share/hadoop/yarn/*</value>
</property>

（4）最后在修改好集群的配置后，需要重启 Hadoop 集群，这样配置才能生效。

cd $HADOOP_HOME
sbin/stop-all.sh
sbin/start-all.sh