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From "Harsh J (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 Sat, 08 Sep 2012 17:26:07 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7198?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13451374#comment-13451374
] 

Harsh J commented on HADOOP-7198:
---------------------------------

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

For Linux this may not hold true though, it seems to limit the ephemeral range from 32k onwards
these days. But yeah, thats non-standard.
                
> 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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