hadoop 启动时namenode和datanode可以启动，使用jps命令也可以看到进程，但是在浏览器中输入master:50070却没有显示datanode
查看datanode的log日志：
2016- 05- 06 13: 22: 39, 899 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: master/ 192.168. 200.128: 9000. Already tried 1 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries= 10, sleepTime= 1 SECONDS) 2016- 05- 06 13: 22: 40, 901 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: master/ 192.168. 200.128: 9000. Already tried 2 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries= 10, sleepTime= 1 SECONDS) 2016- 05- 06 13: 22: 41, 903 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: master/ 192.168. 200.128: 9000. Already tried 3 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries= 10, sleepTime= 1 SECONDS) 2016- 05- 06 13: 22: 42, 905 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: master/ 192.168. 200.128: 9000. Already tried 4 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries= 10, sleepTime= 1 SECONDS) 2016- 05- 06 13: 22: 43, 907 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: master/ 192.168. 200.128: 9000. Already tried 5 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries= 10, sleepTime= 1 SECONDS) 2016- 05- 06 13: 22: 44, 908 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: master/ 192.168. 200.128: 9000. Already tried 6 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries= 10, sleepTime= 1 SECONDS) 2016- 05- 06 13: 22: 45, 910 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: master/ 192.168. 200.128: 9000. Already tried 7 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries= 10, sleepTime= 1 SECONDS) 2016- 05- 06 13: 22: 49, 236 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: master/ 192.168. 200.128: 9000. Already tried 8 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries= 10, sleepTime= 1 SECONDS) 2016- 05- 06 13: 22: 50, 238 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: master/ 192.168. 200.128: 9000. Already tried 9 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries= 10, sleepTime= 1 SECONDS)
2016-05-06 13:22:50,240 INFO org.apache.hadoop.ipc.RPC: Server at master/192.168.200.128:9000 not available yet, Zzzzz...
发现连接不上namenode。
所以在master（也就是namenode）中配置etc/hosts文件，将120.0.0.1 master注释掉，然后添加192.168.200.131 master（如果不注释可能会优先匹配），重新hadoop namenode -format 然后启动就可以了。