Hadoop系列：在Linux下部署hadoop 0.20.1

两台测试虚机，系统为REHL 5.3 x64，正常安装最新版本的JDK，正确设置SSH无密码登录。
服务器一：192.168.56.101 dev1
服务器二：192.168.56.102 dev2
从http://apache.freelamp.com/hadoop/core/hadoop-0.20.1/下载hadoop-0.20.1.tar.gz，把hadoop-0.20.1.tar.gz拷贝到dev1的“/usr/software/hadoop”目录下。登录dev1执行以下命令：
# cd /usr/software/hadoop
# tar zxvf hadoop-0.20.1.tar.gz
# cp -a hadoop-0.20.1 /usr/hadoop
# cd /usr/hadoop/conf
修改hadoop环境配置文件hadoop-env.sh
# vi hadoop-env.sh
添加以下内容：
export JAVA_HOME=/usr/java/jdk1.6.0_16
修改hadoop主要配置文件core-site.xml
# vi core-site.xml
添加以下内容（可以根据需求自行定义）：
<?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>hdfs://dev1</value>
    <description>The name of the default file system. Either the literal string "local" or a host:port for DFS.</description>
  </property>
  <property>
    <name>hadoop.tmp.dir</name>
    <value>/usr/hadoop/tmp</value>
    <description>A base for other temporary directories.</description>
  </property>
  <property>
    <name>dfs.name.dir</name>
    <value>/usr/hadoop/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>
    <