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$Id: HOWTO-Customize-LogWatch,v 1.8 2006/02/28 19:34:24 bjorn Exp $

1. Table of Contents

  1. Table of Contents
  2. Introduction
  3. Directory Structure
        A. Configuration Structure
        B. Executable Structure
  4. Customizing the Configuration
  5. Customizing the Scripts
  6. Creating New Service Filters
	A. Logfile Groups
	B. Service Filter Configuration
	C. Service Filer Executable
  7. For More Information

This document describes the structure of the Logwatch files in the
distribution, how to modify the configuration files for your
system, and how to create new service filters.

2. Introduction

Logwatch is a system log analyzer and reporter.  Usage information
about Logwatch can be obtained through the man page:
	man logwatch

The section titled "MORE INFORMATION" in the man page lists
additional documentation files available with the distribution.

A summary of the command-line switches described in the man page
can be obtained with the '--help' option:
	logwatch --help

The rest of this document is intended for those that wish to
customize or enhance Logwatch beyond the capabilities provided
with the command-line switches.

3. Directory Structure

This section describes the subdirectories and files shipped
with the Logwatch distribution, using the names and locations
used by default.

The directory /usr/share/logwatch contains both the configuration
and (perl) executable files.  The contents of this directory are
the following subdirectories:

	default.conf:	Contains the default configuration files
			shipped with the Logwatch distribution

	dist.conf:	Contains the configuration files shipped
			with your specific Operating Systems

	lib:		Contains perl library files.

	scripts:	Contains the perl executables.

The /etc/logwatch directory contains the following subdirectories:

	conf:		Contains the configuration files specific
			to the system.

	scripts:	Contains the executable scripts specific
			to the system.

A. Configuration Structure

The contents of the three directories /usr/share/logwatch/default.conf,
/usr/share/logwatch/dist.conf, and /etc/logwatch/conf, all have the
same structure:

	services:	This subdirectory contains the configuration
			files specific to each service.  Logwatch
			determines which services are available by
			examining the contents of this directory.
			Each service configuration file is named by
			its service name with the ".conf" suffix.

	logfiles:	This subdirectory contains the logfile group
			configuration files.  Each logfile group
			configuration file contains information about
			one or more log files with the same format.
			Several services may use the same logfile
			group configuration file.  Each of these
			configuration files are named by the group
			name with the ".conf" suffix.  Many
			of the group names are taken from the name
			of a system log file (such as messages,
			maillog, secure, etc.), but not always.

	logwatch.conf:	This file contains the defaults for the
			overall execution of Logwatch, and affect all
			of its services.  Many of its parameters can
			be overridden by command-line switches when
			invoking the Logwatch executable, as described
			in the man page for Logwatch.

	ignore.conf:	This file specifies regular expressions that,
			when matched by the output of logwatch, will
			suppress the matching line, regardless of which
			service is being executed.

The /etc/logwatch/conf directory may also contain the file 'override.conf',
which is described in section 4, "Customizing the Configuration."

B. Executable Structure

The contents of the two directories /usr/share/logwatch/scripts
and /etc/logwatch/scripts have the same structure:

	services:	This subdirectory contains the executable
			for each service.  Unless otherwise specified
			in the configuration service file (see above),
			the executables are written in the perl language.

	shared:		This subdirectory contains executables that may
			be invoked by more than one configuration service

	logfiles:	This subdirectory may contain subdirectories with
			logfile group names.  The executables under each of
			these subdirectories are automatically invoked when
			running	a service that uses the corresponding
			logfile group name.

4. Customizing the Configuration

Logwatch can be, and has been, used on many variants of the Linux and
UNIX systems.  Some distributions that include Logwatch modify the
default configuration to comply with the settings of said
distributions.  Therefore, most people will not need to make any
modifications to Logwatch.

However, Logwatch, starting with version 7.0, implements a mechanism
to allow modifying the local system easier.  These modifications may
be needed either because the configuration of the service that writes
to the system log has been altered from its default, or because the
Logwatch user prefers what is reported or how it is reported by
Logwatch to be different.

You can customize the output of logwatch by modifying variables in the
/etc/logwatch/conf directory.

Default values are specified in the /usr/share/logwatch/default.conf
directory.  Your distribution may have set additional defaults in the
/usr/share/logwatch/dist.conf directory.  All the variables available
are declared in the files under these directories.  You can change the
default values to modify how or what is displayed with logwatch.

One variable available to all services, and which by default is not
specified, is the 'Detail' variable (note that it is not preceded by
a '$' symbol).  Specifying a Detail value will override the global
Detail level, for that service only.

There are two mechanisms for customizing the variables:

1. The /etc/logwatch/conf directory is first searched for files with the
   same name and relative location as the
   /usr/share/logwatch/default.conf directory.  Variables declared in
   these files override the defaults.

   For example, if file /etc/logwatch/conf/services/sendmail.conf has the
   single entry:
        $sendmail_unknownusersthreshold = 5
   then the threshold for unknown users is set to five instead of the
   default of one.  All other parameters are not modified.

   The configuration files have four different types of declarations,
   determined by the first character in each line:

      '#': Rest of line is a comment, and is ignored.
      '$': Rest of first field is a variable
      '*': Denotes the name of an executable script

      Other than blank lines, the only other declarations are
      reserved variable names, such as LogFile, Archive, etc.

   In general, setting a variable overrides any value previously set.
   However, the following variables are cumulative:
   - In logwatch.conf:  	    LogFile, Service
   - In services/service_name.conf: LogFile
   - In logfiles/service_name.conf: LogFile, Archive

   To remove all previous declarations of that variable, set the
   variable to the empty string.  Duplicate values in the cumulative
   variables are deleted.

   If an executable script is declared in an /etc/logwatch/conf file,
   all of the executable script declarations in the corresponding file
   in /usr/share/logwatch/default.conf or /usr/share/logwatch/dist.conf
   are ignored.

   Because of the way variables and executable scripts are declared,
   the files in /etc/logwatch/conf/ can be created in one of two ways:

   - you can create a file with only the modified variables (and
     new executable script declarations, if needed), as described
     above, or

   - you can copy an entire configuration file from
     /usr/share/logwatch/default.conf to its corresponding location in 
     /etc/logwatch/conf, and then modify those lines that require it.
     Because duplicates are removed from cumulative variables, and
     new executable script groups override the old ones, the output
     should be correct.

2. The /etc/logwatch/conf/override.conf file is then searched.  The first
   field in each line may be one of the following:

           This character indicates that the rest of the line is a
           comment, and is ignored.

           This string indicates that the rest of the line is a global
           configuration option, and uses the same syntax as the
           /usr/share/logwatch/default.conf/logwatch.conf file.

           (Where service_name is the name of a service.)  This string
           indicates that the rest of the line is a configuration
           option for the specified service, and uses the same syntax
           as the /usr/share/logwatch/default.conf/services files.

           (Where service_name is the name of a service.)  This string
           indicates that the rest of the line is a configuration
           option for the specified service, and uses the same syntax
           as the /usr/share/logwatch/default.conf/logfiles files.

   For example, if the file /etc/logwatch/conf/override.conf has the single
        logwatch: Detail = High
   then the default detail level for all services will be set to High.

   And, in file override.conf, the following declaration:
        logfiles/messages: LogFile = syslog

   will analyze the syslog file (in addition to the default messages file)
   for certain services.  But the following two declarations combined:

	logfiles/messages: LogFile = 
	logfiles/messages: LogFile = syslog

   will cause the messages file to be ignored for those same services,
   and only the syslog file will be used.

5. Customizing the Scripts

Similarly to the way you can customize the configuration, as
specified in section 4, you can override the default executable

This is accomplished by placing an executable file with the same
name and relative path (with respect to /usr/share/logwatch/scripts)
under the /etc/logwatch/scripts directory.  If such a file is
found in the /etc/logwatch/scripts directory, the corresponding
file under /usr/share/logwatch/scripts will be ignored.

6. Creating New Service Filters

New services may be created by creating new configuration and
executable files, described above, and placing them in the
/etc/logwatch directory.  This section provides additional
details and examples for creating new service filters, but
it might be easier to base the new files on the existing
configuration and script files under the /usr/share/logwatch

A. Logfile Groups

There is only one required line in the logfile group config file.  This
command is called 'LogFile'.

# This will be the logfile named 'messages' in the default logfile
# directory (probably /var/log).
LogFile = messages

# You can also give this command with an absolute path, like this:
LogFile = /var/log/messages

You can have as many LogFile entries as you wish.  All the files specified
will be merged into one input stream for any filters that use this logfile
group.  You can also use standard wildcards when you specify the filename.

Another command that is optional is called 'Archive'.  You can specify a
file to also include in the data stream if the '--archives' option is used.
If these files do not exist it is okay.  For example:

# These 2 'Archive' entries will allow users of most Red Hat Linux
# systems to access their archives of the 'messages' logfile:
Archive = messages.?
# If they configure Compression to be on in /etc/logrotate.conf:
Archive = messages.?.gz
# It is best just to include both of these so that the logfile group
# will work for most systems.

Now, the general theory is that the LogFile Group should apply the date
range requested.  If the logfile is in the standard syslog format, you can
use the shared script 'ApplyStdDate' to filter out only the appropriate log
entries.  The way to call shared scripts (located under
/usr/share/logwatch/scripts/shared) is:

*ApplyStdDate = 

Anything following the equal sign will be passed to the program as arguments
(the equal sign can be eliminated if no arguments are needed).  You should
look at the current logfile group config files for examples.

Finally, if the directory /usr/share/logwatch/scripts/logfiles//
exists, any scripts in that directory will be executed.  All of these
scripts take the contents of all the specified logfiles in through STDIN and
output the modified logfile trought STDOUT.

B. Service Filter Configuration File

Once you have defined one or more logfile groups (or decided on one or
more existing logfile groups), you need to define your service filter.

This file needs to be in /etc/logwatch/conf/services/ and it needs to be
named service_name.conf, where service_name is the name of the service.
You should probably copy an existing config for another service to create
a new one.  

There is only one required line.  This is the command 'LogFile'.  The
LogFile command allows you to specify one or more *LogFile Groups* (as
described above) that this filter will process.  Remember, any filter can
process any number of LogFile Groups, and any LogFile Group may contain the
data from any number of logfiles (and archives). 

For a service filter that needs messages from /var/log/messages you would
add this line:

LogFile = messages

NOTE:  This is *not* because the name of the logfile is 'messages', but it
is because the name of the LogFile Group that has been defined is

You can have commands in the form of:

*SharedScriptName = Arguments

that will execute a script found in the /usr/share/logwatch/scripts/shared/
directory named 'SharedScriptName' with arguments 'Arguments'.
This filter will modify the input to the service's filter.

You can also have commands in the form:

$EnvironmentVariable = Value

This command will set the 'EnvironmentVariable' environment variable to the
value 'Value'.  This environment variable will be accessable by your filter

You will also usually want to specify a title for your script (new in
Logwatch 4.0).  If specified, then a start and stop delimiter will be added
by Logwatch for your specific service (with your script's output between
those delimiters).  This will *only* happen if you produce output.  If you
produce no output, the headers will not be created.  Here is how you define
your title:

Title = "My Service Title"

C. Service Filter Executable

Once everything above has been done, you are ready to actually write
your filter.  This can be done in any language as all it does is:
1) Read logfile entries from STDIN
2) Access some environment variables
3) Generate a report on STDOUT

Before you try to write a filter, you should create the filter and make its
contents the test script given below.  The filter needs to be located in
/etc/logwatch/scripts/services/ and named service_name (because you named the
config file service_name.conf).

###################### Cut Here #########################
# This is as nice script that will show you the lines you will
# be processing and reporting on.  It will first display the
# standard environment variables and then it takes STDIN and
# dump it right back out to STDOUT.  

# These are the standard environment variables.  You can define
# more in your service config file (see above).
echo "Date Range: $LOGWATCH_DATE_RANGE"
echo "Detail Level: $LOGWATCH_DETAIL_LEVEL"
echo "Temp Dir: $LOGWATCH_TEMP_DIR"
echo "Debug Level: $LOGWATCH_DEBUG"

# Now take STDIN and dump it to STDOUT
###################### Cut Here #########################

If you temporarily replace a script such as 'pam' with the above, you will
notice that much has been cut out of /var/log/messages before it gets to
this filter.  

The value of the environment variable LOGWATCH_DETAIL_LEVEL can be any
integer.  In reality, it is usually 0 (for low), 5 (for medium), and 10
(for high). 

Your script should only produce output as appropriate.  If there are no
relevant log entries, no output should be produced.  Likewise, if you are
reporting two things, such as "Good Logins" and "Bad Logins", you should
only produce even the headers when appropriate.  For example:

Bad Logins:
   amber (2 time(s))
   kirk (3 time(s))

Good Logins:
   amber (5 time(s))
   kirk (10 time(s))

But, if no failed logins occur, you should only output:

Good Logins:
   amber (5 time(s))
   kirk (10 time(s))

Note that there is no "Bad Logins:" header as there were no bad logins.  You
should also use the detail environment variable when deciding what to
output.  Bad logins might always be displayed, but good logins might only be
displayed at higher detail levels.  Here is a guide on how you should
use the detail setting:

0 (Low): Display only errors and security-related issues
5 (Med): Display anything that a typical administator would be interested in
10 (High): Display anything that a paranoid administrator would want to see

In some cases, you can use a security setting higher than 10.  This would be
reserved for information so trivial that it would not even interest the US 

7. For More Information

The introduction of this document listed additional sources of information.
In addition, the website http://www.logwatch.org contains:
	- the current (and some archived) distributions of Logwatch
	- access to mailing lists where comments, suggestions, bug reports,
	  etc., are welcome.
	- access to the cvs repository, for the very latest code.

If you do create new services or enhancements that you feel would be useful
to other people, please send them to the logwatch-devel mailing list
at logwatch.org.

If you send patches, please make sure that you have the latest version
of the file from cvs, and send the patch file in unified format
(using 'cvs diff -u' or 'diff -u') as an attachment.

Enhancement suggestions are more likely to be implemented if patch files
implementing the change are sent.

This page last modified Sun Nov 13 08:49:40 2005 Copyright 2010 Kirk Bauer