在配置hadoop1.x的集群时，如果我们在hdfs-site.xml里面，如果明确指定了dfs的路径，需要设置下dfs.data.dir的权限，下面是散仙在Hadoop1.2.0里面的配置：
class="xml" name="code"><configuration>
<property>
<name>dfs.replication</name>
<value>1</value>
</property>
<property>
<name>dfs.name.dir</name>
<value>/home/search/hadoop/hadoopnd</value>
</property>
<!-- 注意这个文件夹目录需要单独设置755权限，否则会报异常，在Hadoop2.2.0中不存在这个问题 -->
<property>
<name>dfs.data.dir</name>
<value>/home/search/hadoop/hadoopdd</value>
</property>
<property>
<name>dfs.tmp.dir</name>
<value>/home/search/hadoop/tmp</value>
</property>
<property>
<name>dfs.permissions</name>
<value>false</value>
</property>
</configuration>
异常详情：
[search@ph1 logs]$ tail -100f hadoop-search-datanode-ph1.log
2014-07-16 22:08:58,139 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting DataNode
STARTUP_MSG: host = ph1/192.168.46.23
STARTUP_MSG: args = []
STARTUP_MSG: version = 1.2.0
STARTUP_MSG: build = https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1.2 -r 1479473; compiled by 'hortonfo' on Mon May 6 06:59:37 UTC 2013
STARTUP_MSG: java = 1.7.0_25
************************************************************/
2014-07-16 22:08:58,463 INFO org.apache.hadoop.metrics2.impl.MetricsConfig: loaded properties from hadoop-metrics2.properties
2014-07-16 22:08:58,485 INFO org.apache.hadoop.metrics2.impl.MetricsSourceAdapter: MBean for source MetricsSystem,sub=Stats registered.
2014-07-16 22:08:58,487 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: Scheduled snapshot period at 10 second(s).
2014-07-16 22:08:58,487 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: DataNode metrics system started
2014-07-16 22:08:58,664 INFO org.apache.hadoop.metrics2.impl.MetricsSourceAdapter: MBean for source ugi registered.
2014-07-16 22:08:58,779 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Invalid directory in dfs.data.dir: Incorrect permission for /home/search/hadoop/hadoopdd, expected: rwxr-xr-x, while actual: rwxrwxr-x
2014-07-16 22:08:58,779 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: All directories in dfs.data.dir are invalid.
2014-07-16 22:08:58,779 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Exiting Datanode
2014-07-16 22:08:58,784 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down DataNode at ph1/192.168.46.23
************************************************************/
注意日志里面warn和error处的信息，
出现这个异常，会导致DataNode启动失败，解决办法：
使用root用户，给这个文件夹赋值755权限，执行命令如下：
chmod 755 -R /home/search/hadoop-1.2.0/hadoopdd
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