20431011hadoop集群root启动hadoop带来问题及hive（hadoop_classpath）问题

1. 启动hadoop集群namenode起不来，

查看啟動情況

[Hadoop@CSCent43 ~]$ jps

4869 JobTracker

4983 Jps

4775 SecondaryNameNode

格式化后：

13/08/06
08:24:15 ERROR namenode.NameNode: java.io.IOException: Cannot remove current directory: /usr/hadoop-12/tmp/dfs/name/current

at org.apache.hadoop.hdfs.server.common.Storage$StorageDirectory.clearDirectory(Storage.java:292)

at org.apache.hadoop.hdfs.server.namenode.FSImage.format(FSImage.java:1333)

at org.apache.hadoop.hdfs.server.namenode.FSImage.format(FSImage.java:1352)

at org.apache.hadoop.hdfs.server.namenode.NameNode.format(NameNode.java:1261)

at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1467)

at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1488)

解决：之前用root启动过hadoop集群，导致tmp/dfs/name/current下的文件所属者为root，所以执行：chown
-R hadoopuser:hadoopuser tmp/dfs/name/

2.
启动hive报错：noclassdefFoudErr org/apache/hadoop/hive/conf/HiveConf

解决：在hadoop-env.sh添加hadoop_classpath

3.启动hive之前确保mysql已启动；