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From Colin McCabe <cmcc...@alumni.cmu.edu>
Date Thu, 22 May 2014 19:41:11 GMT
It's not always practical to edit the log4j.properties file.  For one
thing, if you're using a management system, there may be many log4j
properties sprinkled around the system, and it could be difficult to figure
out which is the one you need to edit.  For another, you may not (should
not?) have permission to do this on a production cluster.

Doing something like "HADOOP_ROOT_LOGGER="DEBUG,console" hadoop fs -cat
/foo" has helped me diagnose problems in the past.


On Thu, May 22, 2014 at 6:34 AM, Robert Rati <rrati@redhat.com> wrote:

> In my experience the default HADOOP_ROOT_LOGGER definition will override
> any root logger defined in log4j.properties, which is where the problems
> have arisen.  If the HADOOP_ROOT_LOGGER definition in hadoop-config.sh were
> removed, wouldn't the root logger defined in the log4j.properties file be
> used?  Or do the client commands not read that configuration file?
> I'm trying to understand why the root logger should be defined outside of
> the log4j.properties file.
> Rob
> On 05/22/2014 12:53 AM, Vinayakumar B wrote:
>> Hi Robert,
>> I understand your confusion.
>> HADOOP_ROOT_LOGGER is set to default value "INFO,console" if it hasn't set
>> for anything and logs will be displayed on the console itself.
>> This will be true for any client commands you run. For ex: "hdfs dfs -ls
>> /"
>> But for the server scripts (hadoop-daemon.sh, yarn-daemon.sh, etc)
>> variable is not defined.
>> So that all the log messages of the server daemons goto some log files and
>> this will be maintained by RollingFileAppender. If you want to override
>> all
>> these default and set your own loglevel then define that as env variable
>> For ex:
>>    export above env variable and then start server scripts or execute
>> client
>> commands, all logs goto files and will be maintained by
>> RollingFileAppender.
>> Regards,
>> Vinay
>> On Wed, May 21, 2014 at 6:42 PM, Robert Rati <rrati@redhat.com> wrote:
>>  I noticed in hadoop-config.sh there is this line:
>>> HADOOP_OPTS="$HADOOP_OPTS -Dhadoop.root.logger=${HADOOP_
>>> ROOT_LOGGER:-INFO,console}"
>>> which is setting a root logger if HADOOP_ROOT_LOGGER isn't set.  Why is
>>> this here.needed?  There is a log4j.properties file provided that
>>> defines a
>>> default logger.  I believe the line above will result in overriding
>>> whatever is set for the root logger in the log4j.properties file.  This
>>> has
>>> caused some confusion and hacks to work around this.
>>> Is there a reason not to remove the above code and just have all the
>>> logger definitions in the log4j.properties file?  Is there maybe a
>>> compatibility concern?
>>> Rob

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