hadoop运行mapreduce报错Error: Could not find or load main class org.apache.hadoop.mapreduce.v2.app.MRApp

小咪咪 2024-03-30 10:54 21阅读 0赞

异常问题：

今天运行word count单词统计示例，hadoop运行mapreduce报错Error: Could not find or load main class org.apache.hadoop.mapreduce.v2.app.MRAppMaster

详细错误信息如下：

1.  `Error: Could not find or load main class org.apache.hadoop.mapreduce.v2.app.MRAppMaster`
2.  
3.  `Please check whether your etc/hadoop/mapred-site.xml contains the below configuration:`
4.  `<property>`
5.  `<name>yarn.app.mapreduce.am.env</name>`
6.  `<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}</value>`
7.  `</property>`
8.  `<property>`
9.  `<name>mapreduce.map.env</name>`
10. `<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}</value>`
11. `</property>`
12. `<property>`
13. `<name>mapreduce.reduce.env</name>`
14. `<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}</value>`
15. `</property>`

解决办法：

先手hadoop classpath命令得到classpath:  
hadoop classpath  
如下：

1.  `[root@hd1 mapreduce]# hadoop classpath`
2.  `/home/hadoop-3.1.4/etc/hadoop:/home/hadoop-3.1.4/share/hadoop/common/lib/*:/home/hadoop-3.1.4/share/hadoop/common/*:/home/hadoop-3.1.4/share/hadoop/hdfs:/home/hadoop-3.1.4/share/hadoop/hdfs/lib/*:/home/hadoop-3.1.4/share/hadoop/hdfs/*:/home/hadoop-3.1.4/share/hadoop/mapreduce/lib/*:/home/hadoop-3.1.4/share/hadoop/mapreduce/*:/home/hadoop-3.1.4/share/hadoop/yarn:/home/hadoop-3.1.4/share/hadoop/yarn/lib/*:/home/hadoop-3.1.4/share/hadoop/yarn/*`

再修改mapred-site.xml配置，增加如下：

1.  `<property>`
2.  `<name>yarn.app.mapreduce.am.env</name> <value>HADOOP_MAPRED_HOME=/home/hadoop-3.1.4/etc/hadoop:/home/hadoop-3.1.4/share/hadoop/common/lib/*:/home/hadoop-3.1.4/share/hadoop/common/*:/home/hadoop-3.1.4/share/hadoop/hdfs:/home/hadoop-3.1.4/share/hadoop/hdfs/lib/*:/home/hadoop-3.1.4/share/hadoop/hdfs/*:/home/hadoop-3.1.4/share/hadoop/mapreduce/lib/*:/home/hadoop-3.1.4/share/hadoop/mapreduce/*:/home/hadoop-3.1.4/share/hadoop/yarn:/home/hadoop-3.1.4/share/hadoop/yarn/lib/*:/home/hadoop-3.1.4/share/hadoop/yarn/*</value>`
3.  `</property>`
4.  `<property>`
5.  `<name>mapreduce.map.env</name>`
6.  `<value>HADOOP_MAPRED_HOME=/home/hadoop-3.1.4/etc/hadoop:/home/hadoop-3.1.4/share/hadoop/common/lib/*:/home/hadoop-3.1.4/share/hadoop/common/*:/home/hadoop-3.1.4/share/hadoop/hdfs:/home/hadoop-3.1.4/share/hadoop/hdfs/lib/*:/home/hadoop-3.1.4/share/hadoop/hdfs/*:/home/hadoop-3.1.4/share/hadoop/mapreduce/lib/*:/home/hadoop-3.1.4/share/hadoop/mapreduce/*:/home/hadoop-3.1.4/share/hadoop/yarn:/home/hadoop-3.1.4/share/hadoop/yarn/lib/*:/home/hadoop-3.1.4/share/hadoop/yarn/*</value>`
7.  `</property>`
8.  `<property>`
9.  `<name>mapreduce.reduce.env</name>`
10. `<value>HADOOP_MAPRED_HOME=/home/hadoop-3.1.4/etc/hadoop:/home/hadoop-3.1.4/share/hadoop/common/lib/*:/home/hadoop-3.1.4/share/hadoop/common/*:/home/hadoop-3.1.4/share/hadoop/hdfs:/home/hadoop-3.1.4/share/hadoop/hdfs/lib/*:/home/hadoop-3.1.4/share/hadoop/hdfs/*:/home/hadoop-3.1.4/share/hadoop/mapreduce/lib/*:/home/hadoop-3.1.4/share/hadoop/mapreduce/*:/home/hadoop-3.1.4/share/hadoop/yarn:/home/hadoop-3.1.4/share/hadoop/yarn/lib/*:/home/hadoop-3.1.4/share/hadoop/yarn/*</value>`
11. `</property>`

注意：上面的配置的value都是上面命令得到的值，复制到value中即可