Hadoop环境变量
在/home/dbrg/HadoopInstall/hadoop-conf目录下的hadoop_env.sh中设置Hadoop需要的环境变量，其中JAVA_HOME是必须设定的变量。HADOOP_HOME变量可以设定也可以不设定，如果不设定，HADOOP_HOME默认的是bin目录的父目录，即本文中的/home/dbrg/HadoopInstall/hadoop。我的是这样设置的
export HADOOP_HOME=/home/dbrg/HadoopInstall/hadoop
export JAVA_HOME=/usr/java/jdk1.6.0
从这个地方就可以看出前面所述的创建hadoop0.12.0的链接hadoop的优点了，当以后更新hadoop的版本的时候，就不需要在改配置文件，只需要更改链接就可以了。
Hadoop配置文件
如前所述，在hadoop-conf/目录下，打开slaves文件，该文件用来指定所有的从节点，一行指定一个主机名。即本文中的dbrg-2，dbrg-3，因此slaves文件看起来应该是这样的
dbrg-2
dbrg-3
在conf/目录中的hadoop-default.xml中包含了Hadoop的所有配置项，但是不允许直接修改!可以在hadoop-conf/目录下的hadoop-site.xml里面定义我们需要的项，其值会覆盖hadoop-default.xml中的默认值。可以根据自己的实际需要来进行定制。以下是我的配置档：
<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>
<!-- Put site-specific property overrides in this file. -->
<configuration>
<property>
<name>fs.default.name</name>
<value>dbrg-1:9000</value>
<description>The name of the default file system. Either the literal string "local" or a host:port for DFS.</description>
</property>
<property>
<name>mapred.job.tracker</name>
<value>dbrg-1:9001</value>
<description>The host and port that the MapReduce job tracker runs at. If "local", then jobs are run in-process as a single map and reduce task.</description>
</property>
<property>
<name>hadoop.tmp.dir</name>
<value>/home/dbrg/HadoopInstall/tmp</value>
<description>A base for other temporary directories.</description>
</property>
<property>
<name>dfs.name.dir</name>
<value>/home/dbrg/HadoopInstall/filesystem/name</value>
<description>Determines where on the local filesystem the DFS name node should store the name table. If this is a comma-delimited list of directories then the name table is replicated in all of the directories, for redundancy. </description>
</property>
<property>
<name>dfs.data.dir</name>
<value>/home/dbrg/HadoopInstall/filesystem/data</value>
<description>Determines where on the local filesystem an DFS data node should store its blocks. If this is a comma-delimited list of directories, then data will be stored in all named directories, typically on different devices. Directories that do not exist are ignored.</description>
</property>
<property>
<name>dfs.replication</name>
<value>1</value>
<description>Default block replication. The actual number of replications can be specified when the file is created. The default is used if replication is not specified in create time.</description>
</property>
</configuration>
<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>
<!-- Put site-specific property overrides in this file. -->
<configuration>
<property>
<name>fs.default.name</name>
<value>dbrg-1:9000</value>
<description>The name of the default file system. Either the literal string "local" or a host:port for DFS.</description>
</property>
<property>
<name>mapred.job.tracker</name>
<value>dbrg-1:9001</value>
<description>The host and port that the MapReduce job tracker runs at. If "local", then jobs are run in-process as a single map and reduce task.</description>
</property>
<property>
<name>hadoop.tmp.dir</name>
<value>/home/dbrg/HadoopInstall/tmp</value>
<description>A base for other temporary directories.</description>
</property>
<property>
<name>dfs.name.dir</name>
<value>/home/dbrg/HadoopInstall/filesystem/name</value>
<description>Determines where on the local filesystem the DFS name node should store the name table. If this is a comma-delimited list of directories then the name table is replicated in all of the directories, for redundancy. </description>
</property>
<property>
<name>dfs.data.dir</name>
<value>/home/dbrg/HadoopInstall/filesystem/data</value>
<description>Determines where on the local filesystem an DFS data node should store its blocks. If this is a comma-delimited list of directories, then data will be stored in all named directories, typically on different devices. Directories that do not exist are ignored.</description>
</property>
<property>
<name>dfs.replication</name>
<value>1</value>
<description>Default block replication. The actual number of replications can be specified when the file is created. The default is used if replication is not specified in create time.</description>
</property>
</configuration>
