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From Steve Loughran <ste...@apache.org>
Subject Re: hostname in logs
Date Fri, 31 Oct 2008 10:58:13 GMT
Alex Loddengaard wrote:
> I'd like my log messages to display the hostname of the node that they were
> outputted on.  Sure, this information can be grabbed from the log filename,
> but I would like each log message to also have the hostname.  I don't think
> log4j provides support to include the hostname in a log, so I've tried
> programmatically inserting the hostname with the following three approaches.
>  These are all within a log4j Appender.
> -Using exec to run "hostname" from the command line.  This returns null.
> -Using InetAddress.getLocalHost().getHostName().  This returns null.
> -Using InetAddress.getLocalHost().getHostAddress().  This returns null.

You sure your real/virtual hosts networking is set up right? I've seen 
problems in hadoop there
https://issues.apache.org/jira/browse/HADOOP-3426
Have a look/apply that patch and see what happens

> Each of these approaches works in an isolated test, but they all return null
> when in Hadoop's context.  I believe I'd be able to get the hostname with a
> Java call to a Hadoop configuration method if I were in a Mapper or Reducer,
> but because I'm in a log4j Appender, I don't have access to any of Hadoop's
> configuration APIs.  How can I get the hostname?

Log4J appenders should have access to the hostname info, But you are 
going to risk time and trouble if you do that in every operation; every 
new process runs a risk of a 30s delay even if you cache it from then 
on. It is usually a lot faster/easier just to push out  the IP address, 
as that doesn't trigger a reverse DNS lookup or anything.

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