Hadoop格式化HDFS报错java.net.UnknownHostException: localhost.localdomain: localhost.localdomain
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