hadoop常见问题解决：

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WARN mapred.LocalJobRunner: job_local910166057_0001

org.apache.hadoop.security.AccessControlException: org.apache.hadoop.security.AccessControlException: Permission denied: user=***, access=WRITE, inode="wordcount":root:supergroup:rwxr-xr-x

sulution：added this entry to conf/hdfs-site.xml

<property>

<name>dfs.permissions</name>

<value>false</value>

</property>

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ERROR org.apache.hadoop.hdfs.server.namenode.SafeModeException:

Cannot create /mapreduce/wordcount/output/1. Name node is in

safe mode.

代码中添加

conf.set("dfs.permissions","false");

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ERROR security.UserGroupInformation: PriviledgedActionException as:bc_qi cause:org.apache.hadoop.mapred.FileAlreadyExistsException: Output directory /mapreduce/wordcount/output/1 already exists

执行

hadoop fs -rmr /mapreduce/wordcount/output

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提示连不上 50010 端口；

查看是不是防火墙的原因。

照样子添加 /etc/sysconfig/iptables 端口过滤

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Hadoop教程(二)讲解MapReduce用户编程接口

重谈下MapReduce框架中用户经常使用的一些接口或类的详细内容。了解这些会极大帮助你实现、配置和优化MR任务。当然javadoc中对每个class或接口都进行了更全面的陈述，这里只是一个指引教程。

Hadoop安装,Hadoop教程,MapReduce