[ https://issues.apache.org/jira/browse/HADOOP-12734?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15113948#comment-15113948 ] 

Steve Loughran commented on HADOOP-12734:
-----------------------------------------

It's not a valid hostname: you can't use "_". Lots of networking software is going to fail.

see: https://cs.uwaterloo.ca/twiki/view/CF/HostNamingRules , and use a hyphen in your hostname "hdp-m1" instead. 



> NameNode with naming contained underline "_"  can not be started
> ----------------------------------------------------------------
>
>                 Key: HADOOP-12734
>                 URL: https://issues.apache.org/jira/browse/HADOOP-12734
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: conf
>    Affects Versions: 2.7.1
>            Reporter: Wei Guo
>            Priority: Minor
>
> I wrote core-site.xml with nameNode  contains "_" char , the nameNode will not be able to start up, which with error msg like:
> "Incorrect configuration: namenode address dfs.namenode.rpc-address is not configured"
> -->"hdp_m1:9000"
> --------------------
> <property>
> 	<name>fs.default.name</name>
> 	<value>hdfs://hdp_m1:9000</value>
> </property>
> --------------------
> NameNode starts up after removing "_".



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