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From "Allen Wittenauer (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-7198) Hadoop defaults for web UI ports often fall smack in the middle of Linux ephemeral port range
Date Thu, 17 Mar 2011 23:50:29 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7198?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13008226#comment-13008226
] 

Allen Wittenauer commented on HADOOP-7198:
------------------------------------------

We often run into this problem when the local named caching daemon fires up first.  The best
solution is to pretty much make sure that Hadoop comes up first or configure the other service
to use a limited set of ports.

Any port that is picked is going to conflict with *something* when talking above the 1k port
line.

> Hadoop defaults for web UI ports often fall smack in the middle of Linux ephemeral port
range
> ---------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-7198
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7198
>             Project: Hadoop Common
>          Issue Type: Wish
>            Reporter: Philip Zeyliger
>            Priority: Trivial
>
> It turns out (see http://en.wikipedia.org/wiki/Ephemeral_port and  /proc/sys/net/ipv4/ip_local_port_range)
that when you bind to port 0, Linux chooses an ephemeral port.  On my default-ridden Ubuntu
Maverick box and on CentOS 5.5, that range is 32768-61000.  So, when HBase binds to 60030
or when mapReduce binds to 50070, there's a small chance that you'll conflict with, say, an
FTP session, or with some other Hadoop daemon that's had a listening address configured as
:0.
> I don't know that there's a practical resolution here, since changing the defaults seems
like an ill-fated effort, but if you have any ephemeral port use, you can run into this. 
We've now run into it once.

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