1、虚拟机环境html
见个人另外一篇博客http://www.cnblogs.com/xckk/p/6000881.html，java
须要安装JDK环境，centos下安装JDK可参考：node
http://www.centoscn.com/image-text/install/2014/0827/3585.htmllinux
注意三台机器均要配置，由于启动时，namenode会启动其它机器。apache
2、hadoop环境centos
hadoop1.2.1浏览器
idk7u79-linux-i586.tar.gzbash
3、开始搭彻底分布式hadoop分布式
三台机器，角色配置以下oop
| hostname | 角色配置 |
| centos1 | namenode |
| centos2 | datanode, secondaryNameNode |
| centos3 | datanode |
一、hadoop配置
分别在三台虚拟机内拷贝hadoop-1.2.1.tar.gz，并解压: tar -zxvf hadoop-1.2.1.tar.gz
conf目录文件配置
| conf目录下文件 | 配置项 | 备注 |
| core-site.xml | <configuration> <property> <name>fs.default.name</name> <value>hdfs://centos:9000</value> </property> <property> <name>hadoop.tmp.dir</name> <value>/opt/hadoop-tmp</value> </property> </configuration> |
一、fs.default.name：配置namenode站点地址。须要注意。9000端口是hdfs rpc协议端口，若是从浏览器访问，则是http协议，端口号是50070.例：http://cetnos:50070 |
| hadoop-env.sh | export JAVA_HOME=/usr/local/java/jdk1.7.0_79 | 配置jdk时在系统配置了JAVA_HOME,可是hadoop不认，必需要在这里修改为你如今的路径。 |
| hdfs-site.xml | <configuration> <property> <name>dfs.replication</name> <value>2</value> </property> </configuration> |
lock最大附本数，配置2台dataNode,此处填2. |
| masters | centos1 | master文件用来配置secondaryNameNod, 注意是secondaryNameNode,不是nameNode |
| slaves | centos1 |
slaves用来配置dataNode |
二、格式化dfs
cd /home/hadoop-1.2/bin/
./hadoop namenode -format (格式化成功后会在/opt/hadoop-tmp/dfs/name/下生成格式化文件)
三、hadoop路径每台机器要保持一致
配置完成后，NameNode机器上输入命令,便可完成hadoopo的hdfs分布式服务的启动。
root@centos bin]# ./start-dfs.sh
四、启动后结果
在浏览器中输入http://｛NameNode IP}:50070便可访问配置的hdfs环境
4、配置中常见问题
一、JAVA_HOME is not set.
错误日志：
root@centos bin]# ./start-dfs.sh
starting namenode, logging to /home/alvin/hadoop-1.2.1/libexec/../logs/hadoop-root-namenode-centos.out
centos1: bash: line 0: cd: /home/alvin/hadoop-1.2.1/libexec/..: No such file or directory
centos2: bash: line 0: cd: /home/alvin/hadoop-1.2.1/libexec/..: No such file or directory
centos2: starting datanode, logging to /opt/hadoop-1.2/libexec/../logs/hadoop-root-datanode-centos2.out
centos1: starting datanode, logging to /usr/hadoop-1.2.1/libexec/../logs/hadoop-root-datanode-centos1.out
centos2: Error: JAVA_HOME is not set.
centos1: Error: JAVA_HOME is not set.
centos1: bash: line 0: cd: /home/alvin/hadoop-1.2.1/libexec/..: No such file or directory
centos1: starting secondarynamenode, logging to /usr/hadoop-1.2.1/libexec/../logs/hadoop-root-secondarynamenode-centos1.out
centos1: Error: JAVA_HOME is not set.
产生缘由三种：
(1)、JDK未配置
解决方法：配置JDK解决，可参考
http://www.centoscn.com/image-text/install/2014/0827/3585.html
(2)、hadoop在每台机器路径不一致，会报JAVA_HOME is not set.问题
该问题首先会想到centos1, centos2两台机器JDK环境是否有配置JAVA_HOME，可是查看均已配了JDK环境。
仔细阅读日志，发现问题是No such file or directory
centos1: bash: line 0: cd: /home/alvin/hadoop-1.2.1/libexec/..: No such file or directory
centos2: bash: line 0: cd: /home/alvin/hadoop-1.2.1/libexec/..: No such file or directory
解决方法：hadoop在每台机器配置路径要一致
(3)、hadoop-env.sh里面没有配置JAVA_HOME
解决方法：配置jdk时在系统配置了JAVA_HOME,可是hadoop不认，必需要在这里修改为你如今的路径。
分析缘由：
因为centos1下hadoop路径在/home/alvin/hadoop-1.2.1/下，centos2与centos3路径在/opt/hadoop-1.2/下，
启动datanode或secondaryNameNode节点时，报No such file or directory.
能够看到centos2与centos3都是按照centos1机器的hadoop路径去读取文件的。所以报 No such file or directory
二、启动dfs服务时，jps命令查看，NameNode启动，DataNode和SecondaryNameNode未启动。
防火墙未关，输入命令service iptables stop关闭三台机器防火墙
三、org.apache.hadoop.security.AccessControlException
解决方法
在 hdfs-site.xml 添加参数：
<property>
<name>dfs.permissions</name>
<value>false</value>
</property>
</configuration>
四、org.apache.hadoop.hdfs.server.datanode.DataNode: java.io.IOException: Incompatible namespaceIDs in /opt/hadoop-tmp/dfs/data: namenode namespaceID = 1165565627; datanode namespaceID = 1468616188
解决方法：以name为准，将namenode节点上${hadoop-tmp}/hfs/data/current/VERSION文件的namespaceID改成${hadoop-tmp}/hfs/name/current/VERSION文件的namespaceID。同时将datanode节点上的${hadoop-tmp}/hfs/data/current/VERSION文件的namespaceID相应修改
五、org.apache.hadoop.hdfs.server.datanode.DataNode: All directories in dfs.data.dir are invalid
发生错误的缘由就是hdfs下的data文件夹权限设置错误，应为rwxr-xr-x，所以修改方式以下：
解决方法：chmod 755 /opt/hadoop-tmp/ –R
六、ERROR security.UserGroupInformation: PriviledgedActionException as:alvin cause:java.net.ConnectException: Call to 192.168.95.134/192.168.95.134:9091 failed on connection exception: java.net.ConnectException: Connection refused
java.net.ConnectException: Call to 192.168.95.134/192.168.95.134:9091 failed on connection exception: java.net.ConnectException: Connection refused
at org.apache.hadoop.ipc.Client.wrapException(Client.java:1142)
解决方法：确认IP和端口号是否正确，mapreduce端口号是9001，这里是9091.因此报错
七、启动hadoop时，log中出现：java.io.IOException: NameNode is not formatted.
解决方法：初始化namenode
./hadoop namenode –format
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