第一次安装hadoop 集群，记录其安装过程！
1 前期准备，配置所有的机器的/etc/hosts 文件
# cat /etc/hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1 rac localhost
::1 rac3 localhost
10.250.7.225 rac1
10.250.7.249 rac2
10.250.7.241 rac3
10.250.7.220 rac4
1 获取hadoop安装文件
可以从一下网址获取hadoop 安装文件 hadoop-0.20.2.tar.gz：
http://apache.etoak.com//hadoop/common/
http://mirror.bjtu.edu.cn/apache//hadoop/common/
http://labs.renren.com/apache-mirror//hadoop/common/
#tar zxvf hadoop-0.20.2.tar.gz
#mv hadoop-0.20.2.tar.gz hadoop
#cd hadoop/conf
配置conf文件夹里面的core-site.xml,hdfs-site.xml,mapread-site.xml,mapred-site.xml，hadoop-env.sh。具体各个配置的含义请参考Hadoop帮助文档。
core-site.xml文件
fs.default.name
hdfs://rac2:9000
2.其次编辑所有节点的hdfs-site.xml，命令如下：
#vi /root/hadoop/conf/hdfs-site.xml
dfs.name.dir
/opt/hadoop/NameData
dfs.permissions
false
dfs.replication
1
3 编辑所有节点mapred-site.xml文件：
#vi /home/hadoop/conf/mapred-site.xml
mapred.job.tracker
192.168.0.10:9001
4 在所有节点编辑hadoop-env.sh
export HADOOP_HOME=/root/hadoop
export HADOOP_CONF_DIR=$HADOOP_HOME/conf
export PATH=$PATH:$HADOOP_HOME/bin
export JAVA_HOME=/usr/java/jdk1.6.0_29
export CLASSHOME=/usr/java/jdk1.6.0_29/lib/tools.jar:/usr/java/jdk1.6.0_29/lib/dt.jar
5 在所有节点修改masters ，slaves 文件，其中masters 文件写入master 节点的ip，slaves 文件写入slaves 节点的ip
[root@rac1 conf]# cat masters
10.250.7.225
[root@rac1 conf]# cat slaves
10.250.7.220
10.250.7.249
10.250.7.241
6 启动hadoop
[root@rac1 bin]# sh start-all.sh
starting namenode, logging to /root/hadoop/logs/hadoop-root-namenode-rac1.out
10.250.7.220: starting datanode, logging to /root/hadoop/logs/hadoop-root-datanode-rac4.out
10.250.7.241: starting datanode, logging to /root/hadoop/logs/hadoop-root-datanode-rac3.out
10.250.7.249: starting datanode, logging to /root/hadoop/logs/hadoop-root-datanode-rac2.out
10.250.7.225: starting secondarynamenode, logging to /root/hadoop/logs/hadoop-root-secondarynamenode-rac1.out
jobtracker running as process 20175. Stop it first.
10.250.7.220: starting tasktracker, logging to /root/hadoop/logs/hadoop-root-tasktracker-rac4.out
10.250.7.241: starting tasktracker, logging to /root/hadoop/logs/hadoop-root-tasktracker-rac3.out
10.250.7.249: starting tasktracker, logging to /root/hadoop/logs/hadoop-root-tasktracker-rac2.out
