Datanode cannot start when Hadoop user creates data directory

Scenario: Centos 6.4 X64

Hadoop 0.20.205

Configuration file

Hdfs-site.xml

<?xml version= "1.0"?>
<?xml-stylesheet type= "text/xsl" href= "configuration.xsl"?>


<!--Put Site-specific property overrides in the this file. -
<configuration>
<property>
<name>dfs.name.dir</name>
<value>/usr/local/hadoop/hdfs/name</value>
</property>

<property>
<name>dfs.data.dir</name>
<value>/usr/local/hadoop/hdfs/data</value>
</property>

<property>
<name>dfs.replication</name>
<value>1</value>
</property>
</configuration>

When creating the data directory used by the Dfs.data.dir, it is created directly with the Hadoop user,

Mkidr-p/usr/local/hdoop/hdfs/data

The Namenode node can then be started when it is formatted and started.

When executing JPS on the Datanode,

[Hadoop@datanode1 local]# JPS
6763 Tasktracker
6816 Jps

No datanode process, no matter how it is formatted, cannot make the Datanode process appear

Back, go to view the logs on the DATANODE1 node

2013-04-10 20:50:49,100 WARN org.apache.hadoop.hdfs.server.datanode.DataNode:Invalid directory in Dfs.data.dir: Incorrect permission For/usr/local/hadoop/hdfs/data, expected:rwxr-xr-x, while Actual:rwxrwxr-x
2013-04-10 20:50:49,100 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode:All directories in Dfs.data.dir is Invalid.

Prompt permission does not meet the requirements

chmod 755/usr/local/hadoop/hdfs/data

Restart

[Hadoop@datanode1 data]$ JPS
7398 Tasktracker
7291 DataNode
7707 Jps

Datanode appears

To verify the difference between the root user and the Hadoop user's Create folder

[Root@namenode home]# mkdir data
[Root@namenode home]# LL
Total Dosage 24
Drwxr-xr-x. 2 root root 4096 April 21:03 data
DRWX------. 5 Hadoop hadoop 4096 April 20:45 Hadoop
DRWX------. 2 root root 16384 April 8 09:28 Lost+found

You can see that the root user created the folder permissions to meet the requirements

Then create a folder with Hadoop users

[Hadoop@namenode ~]$ mkdir Name
[Hadoop@namenode ~]$ LL
Total Dosage 4
Drwxrwxr-x. 2 Hadoop hadoop 4096 April 21:04 name
[Hadoop@namenode ~]$

Permissions have changed, causing Datanode to fail to start.

Conclusion: In order not to modify the owner of the folder, directly with the Hadoop user to create a folder, the result of a permissions problem, resulting in datanode cannot start.

Harvest: 1, understand the different user group permissions,

2, encounter problems, must be inquisitive, can not be specious, otherwise, wasted time, oneself but smattering, this state is the worst state.

3, multi-view logs, from the log to find the problem.