异常描述
在对HDFS格式化，执行hadoop namenode -format命令时，出现未知的主机名的问题，异常信息如下所示：
- [shirdrn@localhost bin]$ hadoop namenode -format
- 11/06/22 07:33:31 INFO namenode.NameNode: STARTUP_MSG:
- /************************************************************
- STARTUP_MSG: Starting NameNode
- STARTUP_MSG: host = java.net.UnknownHostException: localhost.localdomain: localhost.localdomain
- STARTUP_MSG: args = [-format]
- STARTUP_MSG: version = 0.20.0
- STARTUP_MSG: build = https://svn.apache.org/repos/asf/hadoop/core/branches/branch-0.20 -r 763504; compiled by 'ndaley' on Thu Apr 9 05:18:40 UTC 2009
- ************************************************************/
- Re-format filesystem in /tmp/hadoop/hadoop-shirdrn/dfs/name ? (Y or N) Y
- 11/06/22 07:33:36 INFO namenode.FSNamesystem: fsOwner=shirdrn,shirdrn
- 11/06/22 07:33:36 INFO namenode.FSNamesystem: supergroup=supergroup
- 11/06/22 07:33:36 INFO namenode.FSNamesystem: isPermissionEnabled=true
- 11/06/22 07:33:36 INFO metrics.MetricsUtil: Unable to obtain hostName
- java.net.UnknownHostException: localhost.localdomain: localhost.localdomain
- at java.net.InetAddress.getLocalHost(InetAddress.java:1353)
- at org.apache.hadoop.metrics.MetricsUtil.getHostName(MetricsUtil.java:91)
- at org.apache.hadoop.metrics.MetricsUtil.createRecord(MetricsUtil.java:80)
- at org.apache.hadoop.hdfs.server.namenode.FSDirectory.initialize(FSDirectory.java:73)
- at org.apache.hadoop.hdfs.server.namenode.FSDirectory.<init>(FSDirectory.java:68)
- at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.<init>(FSNamesystem.java:370)
- at org.apache.hadoop.hdfs.server.namenode.NameNode.format(NameNode.java:853)
- at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:947)
- at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:964)
- 11/06/22 07:33:36 INFO common.Storage: Image file of size 97 saved in 0 seconds.
- 11/06/22 07:33:36 INFO common.Storage: Storage directory /tmp/hadoop/hadoop-shirdrn/dfs/name has been successfully formatted.
- 11/06/22 07:33:36 INFO namenode.NameNode: SHUTDOWN_MSG:
- /************************************************************
- SHUTDOWN_MSG: Shutting down NameNode at java.net.UnknownHostException: localhost.localdomain: localhost.localdomain
- ************************************************************/
我们通过执行hostname命令可以看到：
- [shirdrn@localhost bin]# hostname
- localhost.localdomain
也就是说，Hadoop在格式化HDFS的时候，通过hostname命令获取到的主机名是localhost.localdomain，然后在/etc/hosts文件中进行映射的时候，没有找到，看下我的/etc/hosts内容：
- [root@localhost bin]# cat /etc/hosts
- # Do not remove the following line, or various programs
- # that require network functionality will fail.
- 127.0.0.1 localhost localhost
- 192.168.1.103 localhost localhost
也就说，通过localhost.localdomain根本无法映射到一个IP地址，所以报错了。
此时，我们查看一下/etc/sysconfig/network文件：
- NETWORKING=yes
- NETWORKING_IPV6=yes
- HOSTNAME=localhost.localdomain
可见，执行hostname获取到这里配置的HOSTNAME的值。
解决方法
修改/etc/sysconfig/network中HOSTNAME的值为localhost，或者自己指定的主机名，保证localhost在/etc/hosts文件中映射为正确的IP地址，然后重新启动网络服务：
- [root@localhost bin]# /etc/rc.d/init.d/network restart
- Shutting down interface eth0: [ OK ]
- Shutting down loopback interface: [ OK ]
- Bringing up loopback interface: [ OK ]
- Bringing up interface eth0:
- Determining IP information for eth0... done.
- [ OK ]
这时，再执行格式化HDFS命令，以及启动HDFS集群就正常了。
格式化：
- [shirdrn@localhost bin]$ hadoop namenode -format
- 11/06/22 08:02:37 INFO namenode.NameNode: STARTUP_MSG:
- /************************************************************
- STARTUP_MSG: Starting NameNode
- STARTUP_MSG: host = localhost/127.0.0.1
- STARTUP_MSG: args = [-format]
- STARTUP_MSG: version = 0.20.0
- STARTUP_MSG: build = https://svn.apache.org/repos/asf/hadoop/core/branches/branch-0.20 -r 763504; compiled by 'ndaley' on Thu Apr 9 05:18:40 UTC 2009
- ************************************************************/
- 11/06/22 08:02:37 INFO namenode.FSNamesystem: fsOwner=shirdrn,shirdrn
- 11/06/22 08:02:37 INFO namenode.FSNamesystem: supergroup=supergroup
- 11/06/22 08:02:37 INFO namenode.FSNamesystem: isPermissionEnabled=true
- 11/06/22 08:02:37 INFO common.Storage: Image file of size 97 saved in 0 seconds.
- 11/06/22 08:02:37 INFO common.Storage: Storage directory /tmp/hadoop/hadoop-shirdrn/dfs/name has been successfully formatted.
- 11/06/22 08:02:37 INFO namenode.NameNode: SHUTDOWN_MSG:
- /************************************************************
- SHUTDOWN_MSG: Shutting down NameNode at localhost/127.0.0.1
- ************************************************************/
启动：
- [shirdrn@localhost bin]$ start-all.sh
- starting namenode, logging to /home/shirdrn/eclipse/eclipse-3.5.2/hadoop/hadoop-0.20.0/logs/hadoop-shirdrn-namenode-localhost.out
- localhost: starting datanode, logging to /home/shirdrn/eclipse/eclipse-3.5.2/hadoop/hadoop-0.20.0/logs/hadoop-shirdrn-datanode-localhost.out
- localhost: starting secondarynamenode, logging to /home/shirdrn/eclipse/eclipse-3.5.2/hadoop/hadoop-0.20.0/logs/hadoop-shirdrn-secondarynamenode-localhost.out
- starting jobtracker, logging to /home/shirdrn/eclipse/eclipse-3.5.2/hadoop/hadoop-0.20.0/logs/hadoop-shirdrn-jobtracker-localhost.out
- localhost: starting tasktracker, logging to /home/shirdrn/eclipse/eclipse-3.5.2/hadoop/hadoop-0.20.0/logs/hadoop-shirdrn-tasktracker-localhost.out
查看：
- [shirdrn@localhost bin]$ jps
- 8192 TaskTracker
- 7905 DataNode
- 7806 NameNode
- 8065 JobTracker
- 8002 SecondaryNameNode
- 8234 Jps http://blog.csdn.net/shirdrn/article/details/6562292
