hadoop执行任务时常见exception

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hadoop.mapred.FileAlreadyExistsException

Exception in thread "main" org.apache.hadoop.mapred.FileAlreadyExistsException: Output directory hdfs://master:9000/mnt/hadoop/out already exists
	at org.apache.hadoop.mapreduce.lib.output.FileOutputFormat.checkOutputSpecs(FileOutputFormat.java:146)
	at org.apache.hadoop.mapreduce.JobSubmitter.checkSpecs(JobSubmitter.java:266)
	at org.apache.hadoop.mapreduce.JobSubmitter.submitJobInternal(JobSubmitter.java:139)
	at org.apache.hadoop.mapreduce.Job$10.run(Job.java:1290)
	at org.apache.hadoop.mapreduce.Job$10.run(Job.java:1287)
	at java.security.AccessController.doPrivileged(Native Method)
	at javax.security.auth.Subject.doAs(Subject.java:422)
	at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1754)
	at org.apache.hadoop.mapreduce.Job.submit(Job.java:1287)
	at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:1308)
	at com.bamboo.hbase.HbaseToMapreduce.main(HbaseToMapreduce.java:102)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.apache.hadoop.util.RunJar.run(RunJar.java:221)
	at org.apache.hadoop.util.RunJar.main(RunJar.java:136)

直接Hdfs删除该目录即可

 hadoop fs -rmr /mnt/hadoop/out

##　to 0.0.0.0:10020 failed on connection exception
执行mapreduc执行从habse查询数据然后排序，产生如下错误日志

Caused by: java.net.ConnectException: Call From master/192.168.1.101 to 0.0.0.0:10020 failed on connection exception: java.net.ConnectException: Connection refused; For more det
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	at org.apache.hadoop.net.NetUtils.wrapWithMessage(NetUtils.java:792)
	at org.apache.hadoop.net.NetUtils.wrapException(NetUtils.java:732)
	at org.apache.hadoop.ipc.Client.call(Client.java:1480)
	at org.apache.hadoop.ipc.Client.call(Client.java:1413)
	at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:229)
	at com.sun.proxy.$Proxy15.getJobReport(Unknown Source)
	at org.apache.hadoop.mapreduce.v2.api.impl.pb.client.MRClientProtocolPBClientImpl.getJobReport(MRClientProtocolPBClientImpl.java:133)
	at sun.reflect.GeneratedMethodAccessor9.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.apache.hadoop.mapred.ClientServiceDelegate.invoke(ClientServiceDelegate.java:325)
	... 17 more

修改配置文件
找到{HADOOP_HOME}/etc/hadoop/mapred-site.xml配置文件 ,增加如下配置：

<property>
    <name>mapreduce.jobhistory.address</name>
    <!-- 配置实际的主机名和端口-->
    <value>master:10020</value>
</property>

master修改为你自己的服务器地址ip或者hotname

启动 JobHistory 服务

{hadoop_dir}/sbin/mr-jobhistory-daemon.sh start historyserver

参考资料

作者：lazythinker
来源：CSDN
原文：https://blog.csdn.net/lazythinker/article/details/52064165
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