Hadoop部署在RedHat Linux 5上常见错误及解决方案
遇到的问题：
1、在hadoop conf下执行命令： hadoop-daemon.sh start datanode，无法启动hadoop datanode：
[hadoop@master conf]$ hadoop-daemon.sh start datanode
Warning: $HADOOP_HOME is deprecated.
starting datanode, logging to /opt/modules/hadoop/hadoop-1.1.2/libexec/../logs/hadoop-hadoop-datanode-master.out
[hadoop@master conf]$ jps
4662 NameNode
4819 Jps
[hadoop@master conf]$ tail -300f /opt/modules/hadoop/hadoop-1.1.2/libexec/../logs/hadoop-hadoop-datanode-master.log
报错：
Incompatible namespaceIDs in /data/hadoop/hdfs/data: namenode namespaceID = 573007068; datanode namespaceID = 1802250800
解决方法：用网上介绍的第一种：删除data目录（即是在hdfs-site.xml文件中配置的dfs.data.dir目录）然后重启datanode。
[hadoop@master conf]$ rm -rf /data/hadoop/hdfs/data
[hadoop@master conf]$ ll /data/hadoop/hdfs/
total 8
drwxrwxr-x 5 hadoop hadoop 4096 Jul 6 08:17 name
drwxrwxr-x 2 hadoop hadoop 4096 Jul 2 06:59 namesecondary
[hadoop@master conf]$ hadoop-daemon.sh start datanode
2、启动Jobtracker时报错：
2013-07-06 10:03:09,584 INFO org.apache.hadoop.mapred.JobTracker: problem cleaning system directory: hdfs://master:9000/data/hadoop/mapred/mrsystem
org.apache.hadoop.ipc.RemoteException: java.io.FileNotFoundException: Parent path is not a directory: /data
原因是：有个/data文件（注意不是文件夹，跟参数刚好不相匹配），也可以通过网页中看：
NameNode 'master:9000'
Started: Sat Jul 06 09:54:05 PDT 2013
Version: 1.1.2, r1440782
Compiled: Thu Jan 31 02:03:24 UTC 2013 by hortonfo
Upgrades: There are no upgrades in progress.
Browse the filesystem
Namenode Logs
解决方法：删除掉改文件：hadoop fs -rmr /data 即ok
3、在hadoop中编译eclipse导出的jar包时报错：
[hadoop@master hadoop-1.1.2]$ hadoop jar hdfs1.jar com.hadoop.hdfs.HDFSMkdir
Warning: $HADOOP_HOME is deprecated.
Exception in thread "main" java.lang.UnsupportedClassVersionError: com/hadoop/hdfs/HDFSMkdir : Unsupported major.minor version 51.0
原因：eclipse中所用java版本与hadoop所用java版本不一致。
解决方法：更改eclipse中的java版本重新导出jar包。