Unix administration stuff that was hard to find out using Google and caused a lot of try and error. Hereby given back to the net...
Configure Hadoop to use Syslog on Ubuntu
Submitted by Lars Windolf on 24. July 2012 - 17:03.
If you come here and search for a good description on how to use syslog with Hadoop you might have run into this issue:
As documented on apache.org (HowToConfigurate) you have setup the log4j configuration similar to this
# Do not forward audit events to parent appenders (i.e. namenode)
# Configure local appender
# Configure syslog appender
It is important to have "SYSLOG" in the "...FSNamesystem.audit" definition at the top and to define such a "SYSLOG" appender below with "log4j.appender.SYSLOG". There you configure your loghost and facility.
Now it might be that you still do not get anything in syslog on your loghost when using Hadoop version 0.18 up to at least 0.20. I found a solution to this only at this Japanese blog post which suggested to modify the Hadoop start helper script /usr/lib/hadoop/bin/hadoop-daemon.sh to make it work.
You need to change the environment variables
to include "SYSLOG":
After making this change the syslog logging will work.