異常描述

在對HDFS格式化，執行hadoop namenode -format命令時，出現未知的主機名的問題，異常信息如下所示：

1. [shirdrn@localhost bin]$ hadoop namenode -format
2. 11/06/22 07:33:31 INFO namenode.NameNode: STARTUP_MSG:
3. /************************************************************
4. STARTUP_MSG: Starting NameNode
5. STARTUP_MSG: host = java.net.UnknownHostException: localhost.localdomain: localhost.localdomain
6. STARTUP_MSG: args = [-format]
7. STARTUP_MSG: version = 0.20.0
8. 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
9. ************************************************************/
10. Re-format filesystem in /tmp/hadoop/hadoop-shirdrn/dfs/name ? (Y or N) Y
11. 11/06/22 07:33:36 INFO namenode.FSNamesystem: fsOwner=shirdrn,shirdrn
12. 11/06/22 07:33:36 INFO namenode.FSNamesystem: supergroup=supergroup
13. 11/06/22 07:33:36 INFO namenode.FSNamesystem: isPermissionEnabled=true
14. 11/06/22 07:33:36 INFO metrics.MetricsUtil: Unable to obtain hostName
15. java.net.UnknownHostException: localhost.localdomain: localhost.localdomain
16. at java.net.InetAddress.getLocalHost(InetAddress.java:1353)
17. at org.apache.hadoop.metrics.MetricsUtil.getHostName(MetricsUtil.java:91)
18. at org.apache.hadoop.metrics.MetricsUtil.createRecord(MetricsUtil.java:80)
19. at org.apache.hadoop.hdfs.server.namenode.FSDirectory.initialize(FSDirectory.java:73)
20. at org.apache.hadoop.hdfs.server.namenode.FSDirectory.<init>(FSDirectory.java:68)
21. at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.<init>(FSNamesystem.java:370)
22. at org.apache.hadoop.hdfs.server.namenode.NameNode.format(NameNode.java:853)
23. at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:947)
24. at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:964)
25. 11/06/22 07:33:36 INFO common.Storage: Image file of size 97 saved in 0 seconds.
26. 11/06/22 07:33:36 INFO common.Storage: Storage directory /tmp/hadoop/hadoop-shirdrn/dfs/name has been successfully formatted.
27. 11/06/22 07:33:36 INFO namenode.NameNode: SHUTDOWN_MSG:
28. /************************************************************
29. SHUTDOWN_MSG: Shutting down NameNode at java.net.UnknownHostException: localhost.localdomain: localhost.localdomain
30. ************************************************************/

我們通過執行hostname命令可以看到：

1. [shirdrn@localhost bin]# hostname
2. localhost.localdomain

也就是說，Hadoop在格式化HDFS的時候，通過hostname命令獲取到的主機名是localhost.localdomain，然後在/etc/hosts文件中進行映射的時候，沒有找到，看下我的/etc/hosts內容：

1. [root@localhost bin]# cat /etc/hosts
2. # Do not remove the following line, or various programs
3. # that require network functionality will fail.
4. 127.0.0.1 localhost localhost
5. 192.168.1.103 localhost localhost

也就說，通過localhost.localdomain根本無法映射到一個IP地址，所以報錯了。

此時，我們查看一下/etc/sysconfig/network文件：

1. NETWORKING=yes
2. NETWORKING_IPV6=yes
3. HOSTNAME=localhost.localdomain

可見，執行hostname獲取到這裏配置的HOSTNAME的值。

解決方法

修改/etc/sysconfig/network中HOSTNAME的值為localhost，或者自己指定的主機名，保證localhost在/etc/hosts文件中映射為正確的IP地址，然後重新啟動網絡服務：

1. [root@localhost bin]# /etc/rc.d/init.d/network restart
2. Shutting down interface eth0: [ OK ]
3. Shutting down loopback interface: [ OK ]
4. Bringing up loopback interface: [ OK ]
5. Bringing up interface eth0:
6. Determining IP information for eth0... done.
7. [ OK ]

這時，再執行格式化HDFS命令，以及啟動HDFS集群就正常了。

格式化：

1. [shirdrn@localhost bin]$ hadoop namenode -format
2. 11/06/22 08:02:37 INFO namenode.NameNode: STARTUP_MSG:
3. /************************************************************
4. STARTUP_MSG: Starting NameNode
5. STARTUP_MSG: host = localhost/127.0.0.1
6. STARTUP_MSG: args = [-format]
7. STARTUP_MSG: version = 0.20.0
8. 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
9. ************************************************************/
10. 11/06/22 08:02:37 INFO namenode.FSNamesystem: fsOwner=shirdrn,shirdrn
11. 11/06/22 08:02:37 INFO namenode.FSNamesystem: supergroup=supergroup
12. 11/06/22 08:02:37 INFO namenode.FSNamesystem: isPermissionEnabled=true
13. 11/06/22 08:02:37 INFO common.Storage: Image file of size 97 saved in 0 seconds.
14. 11/06/22 08:02:37 INFO common.Storage: Storage directory /tmp/hadoop/hadoop-shirdrn/dfs/name has been successfully formatted.
15. 11/06/22 08:02:37 INFO namenode.NameNode: SHUTDOWN_MSG:
16. /************************************************************
17. SHUTDOWN_MSG: Shutting down NameNode at localhost/127.0.0.1
18. ************************************************************/

啟動：

1. [shirdrn@localhost bin]$ start-all.sh
2. starting namenode, logging to /home/shirdrn/eclipse/eclipse-3.5.2/hadoop/hadoop-0.20.0/logs/hadoop-shirdrn-namenode-localhost.out
3. localhost: starting datanode, logging to /home/shirdrn/eclipse/eclipse-3.5.2/hadoop/hadoop-0.20.0/logs/hadoop-shirdrn-datanode-localhost.out
4. localhost: starting secondarynamenode, logging to /home/shirdrn/eclipse/eclipse-3.5.2/hadoop/hadoop-0.20.0/logs/hadoop-shirdrn-secondarynamenode-localhost.out
5. starting jobtracker, logging to /home/shirdrn/eclipse/eclipse-3.5.2/hadoop/hadoop-0.20.0/logs/hadoop-shirdrn-jobtracker-localhost.out
6. 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：

1. [shirdrn@localhost bin]$ jps
2. 8192 TaskTracker
3. 7905 DataNode
4. 7806 NameNode
5. 8065 JobTracker
6. 8002 SecondaryNameNode
7. 8234 Jps
8. from https://blog.csdn.net/shirdrn/article/details/6562292

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