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##  ganglia-logtailer
##  ganglia-logtailer is a python script that will tail any log file,
##  crunch the data collected, and report summary data to ganglia.
##  This directory contains the script ganglia-logtailer, its required
##  helper classes, and two example classes, one generic and one for
##  parsing Apache logs.
##  Copyright Linden Lab, 2008
##  License to modify and redistribute granted under the GPL v2 or later

0. Table of Contents
1. Overview
2. Installation
3. License

1. Overview

Many metrics associated with ganglia and gmetric plugins are rather easy to
collect; you poll the relevant application for a value and report it.  Examples
are asking MySQL for the number of questions and calculating queries per
second, or asking iostat for the percentage disk I/O currently being used.
However, there are a large number of applications out there that don't support
being queried for interesting data, but do provide a log file which, when
properly parsed, yields the interesting data we desire.  An example of the
latter category is Apache, which does not furnish any interface for measuring
queries per second, yet has a log file allowing you to count how many queries
come in over a specific time period.

ganglia-logtailer is designed to make it easy to parse any log file, pull out
the information you desire, and plug it into ganglia to make pretty graphs.

ganglia-logtailer is comprised of three parts:
* ganglia-logtailer - the python script doing the real work
* and - supporting python classes
*,, etc. - user modifiable, log-file specific classes

You must modify or write new classes for
each of the log files you wish to parse.  As every log file has a specific
format, you must write the regular expression to properly pick out interesting
information for your specific application.  As each application has different
ways of expressing what might be interesting metrics to graph, you must write
the functions to collect the information present in each line of the log file. is an example file; it does nothing other than count the
number of lines present in the log file and report lines per second.  However,
it does have extensive comments explaining the purpose of each of the functions
present in the file.  I would recommend reading that file and modifying it to
do more interesting things. is a fully functional class parsing an Apache log.  At
Linden Lab, we use a custom log format (and include the very interesting %D -
time to execute the query in microseconds), so the regular expression included
there will probably have to be changed for your environment. defines and returns the number of Apache requests per
second, also broken out by return code (200, 300, 400, 500), and the average,
maximum, and 90th percentile run time of all queries caught during the sample

The rest of the * classes present are customized for different
types of logs (postfix, bind, etc.)

ganglia-logtailer can be invoked in two different modes, either as a daemon
(which tells it to run as a persistent process) or invoked from cron on a
regular basis.  I recommend using daemon mode for testing, but invoking it from
cron every 1-5 minutes for deploy.  I make this recommendation because (aside
from minimizing the number of running daemons), there are no start scripts to
invoke daemon mode on system boot, and there is no facility to relaunch the
process if it were to crash or raise an exception.

ganglia-logtailer will log certain bits of information to
/var/log/ganglia/ganglia_logtailer in case of error.  Log level is variable by
modfying ganglia-logtailer and editing the following line:
logger.setLevel(logging.INFO) Look up the 'logging' python module for valid
values.  (logging.DEBUG is a good bet)

2. Installation

ganglia-logtailer depends on the 'logtail' package
( when run in cron mode.

i.   Copy ganglia-logtailer to /usr/local/bin/ (or wherever you store
       unpackaged binaries)
ii.  Copy and to
       /usr/local/share/ganglia-logtailer (or somewhere in your python search 
iii. Copy and to /usr/local/share/ganglia-logtailer
       (or somewhere in your python search path)

Create the directory ganglia-logtailer uses to store state:

Test the installation by invoking ganglia-logtailer with the DummyLogtailer
class on a log file:
# ganglia-logtailer --classname DummyLogtailer --log_file /var/log/daemon.log --mode daemon
wait 30s to 1m, then check and see whether your new metric is present in

If all goes well, try out one of the real modules:
# ganglia-logtailer --classname PostfixLogtailer --log-file /var/log/mail.log --mode daemon

If that works as well, deploy!  Add the following to
* * * * * root /usr/local/bin/ganglia-logtailer --classname PostfixLogtailer --log-file /var/log/mail.log --mode cron

3. License

These scripts are all released under the GPL v2 or later.  For a full
description of the licence, please visit

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