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：
[plain] view plain copy [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：
[plain] view plain copy [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：
[plain] view plain copy [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：
[plain] view plain copy NETWORKING=yes NETWORKING_IPV6=yes HOSTNAME=localhost.localdomain
可见，执行hostname获取到这里配置的HOSTNAME的值。
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：
[plain] view plain copy [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：
[plain] view plain copy [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： [plain] view plain copy [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： [plain] view plain copy [shirdrn@localhost bin]$ jps 8192 TaskTracker 7905 DataNode 7806 NameNode 8065 JobTracker 8002 SecondaryNameNode 8234 Jps
