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This is a part of the rsyslog.conf - documentation.
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<h2>Templates</h2>
Templates are a key feature of rsyslog. They allow to specify
any
format a user might want. They are also used for dynamic file name
generation. Every output in rsyslog uses templates - this holds true
for files, user messages and so on. The database writer expects its
template to be a proper SQL statement - so this is highly customizable
too. You might ask how does all of this work when no templates at all
are specified. Good question ;) The answer is simple, though. Templates
compatible with the stock syslogd formats are hardcoded into rsyslogd.
So if no template is specified, we use one of these hardcoded
templates. Search for "template_" in syslogd.c and you will find the
hardcoded ones.
Starting with 5.5.6, there are actually two differnt types of template:
<ul>
<li>string based
<li>string-generator module based
</ul>
<a href="rsyslog_conf_modules.html#sm">String-generator module</a> based templates
have been introduced in 5.5.6. They permit a string generator, actually a C "program",
the generate a format. Obviously, it is more work required to code such a generator,
but the reward is speed improvement. If you do not need the ultimate throughput, you
can forget about string generators (so most people never need to know what they are).
You may just be interested in learning that for the most important default formats, 
rsyslog already contains highly optimized string generators and these are called
without any need to configure anything. But if you have written (or purchased) a
string generator module, you need to know how to call it. Each such module has a name,
which you need to know (look it up in the module doc or ask the developer). Let's assume
that "mystrgen" is the module name. Then you can define a template for that strgen
in the following way:
<blockquote><code>$template MyTemplateName,=mystrgen</code></blockquote>
(Of course, you must have first loaded the module via $ModLoad).
The important part is the equal sign: it tells the rsyslog config parser that
no string follows but a strgen module name.
There are no additional parameters but the module name supported. This is because
there is no way to customize anything inside such a "template" other than by
modifying the code of the string generator.

So for most use cases, string-generator module based templates are not
the route to take. Usually, us use string based templates instead.
This is what the rest of the documentation now talks about.

A template consists of a template directive, a name, the
actual template text and optional options. A sample is:
<blockquote><code>$template MyTemplateName,"\7Text
%property% some more text\n",&lt;options&gt;</code></blockquote>
The "$template" is the template directive. It tells rsyslog
that this line contains a template. "MyTemplateName" is the template
name. All
other config lines refer to this name. The text within quotes is the
actual template text. The backslash is an escape character, much as it
is in C. It does all these "cool" things. For example, \7 rings the
bell (this is an ASCII value), \n is a new line. C programmers and perl
coders have the advantage of knowing this, but the set in rsyslog is a
bit restricted currently.

All text in the template is used literally, except for things
within percent signs. These are properties and allow you access to the
contents of the syslog message. Properties are accessed via the
<a href="property_replacer.html">property replacer</a>
(nice name, huh) and it can do cool things, too. For
example, it can pick a substring or do date-specific formatting. More
on this is below, on some lines of the property replacer. 
 
The &lt;options&gt; part is optional. It carries options
influencing the template as whole. See details below. Be sure NOT to
mistake template options with property options - the later ones are
processed by the property replacer and apply to a SINGLE property, only
(and not the whole template). 
 
Template options are case-insensitive. Currently defined are: 
sql - format the string suitable for a SQL
statement in MySQL format. This will replace single quotes ("'") and
the backslash character by their backslash-escaped counterpart ("\'"
and "\\") inside each field. Please note that in MySQL configuration,
the <code class="literal">NO_BACKSLASH_ESCAPES</code>
mode must be turned off for this format to work (this is the default).
stdsql - format the string suitable for a
SQL statement that is to be sent to a standards-compliant sql server.
This will replace single quotes ("'") by two single quotes ("''")
inside each field. You must use stdsql together with MySQL if in MySQL
configuration the
<code class="literal">NO_BACKSLASH_ESCAPES</code> is
turned on.
Either the sql or stdsql&nbsp;
option must be specified when a template is used
for writing to a database, otherwise injection might occur. Please note
that due to the unfortunate fact that several vendors have violated the
sql standard and introduced their own escape methods, it is impossible
to have a single option doing all the work.&nbsp; So you yourself
must make sure you are using the right format. If you choose
the wrong one, you are still vulnerable to sql injection. 
 
Please note that the database writer *checks* that the sql option is
present in the template. If it is not present, the write database
action is disabled. This is to guard you against accidental forgetting
it and then becoming vulnerable to SQL injection. The sql option can
also be useful with files - especially if you want to import them into
a database on another machine for performance reasons. However, do NOT
use it if you do not have a real need for it - among others, it takes
some toll on the processing time. Not much, but on a really busy system
you might notice it ;)
The default template for the write to database action has the
sql option set. As we currently support only MySQL and the sql option
matches the default MySQL configuration, this is a good choice.
However, if you have turned on
<code class="literal">NO_BACKSLASH_ESCAPES</code> in
your MySQL config, you need to supply a template with the stdsql
option. Otherwise you will become vulnerable to SQL injection. 
 
To escape: 
% = \% 
\ = \\ --&gt; '\' is used to escape (as in C) 
$template TraditionalFormat,"%timegenerated% %HOSTNAME% %syslogtag%%msg%\n" 
 
Properties can be accessed by the <a href="property_replacer.html">property
replacer</a> (see there for details).
Please note that templates can also by
used to generate selector lines with dynamic file names. For
example, if you would like to split syslog messages from different
hosts to different files (one per host), you can define the following
template:
<blockquote><code>$template
DynFile,"/var/log/system-%HOSTNAME%.log"</code></blockquote>
This template can then be used when defining an output
selector line. It will result in something like
"/var/log/system-localhost.log"
Template
names beginning with "RSYSLOG_" are reserved for rsyslog use. Do NOT
use them if, otherwise you may receive a conflict in the future (and
quite unpredictable behaviour). There is a small set of pre-defined
templates that you can use without the need to define it:
<ul>
<li>RSYSLOG_TraditionalFileFormat
- the "old style" default log file format with low-precision timestamps</li>
<li>RSYSLOG_FileFormat
- a modern-style logfile format similar to TraditionalFileFormat, buth
with high-precision timestamps and timezone information</li>
<li>RSYSLOG_TraditionalForwardFormat
- the traditional forwarding format with low-precision timestamps. Most
useful if you send&nbsp;messages to other syslogd's or rsyslogd
below
version 3.12.5.</li>
<li>RSYSLOG_SysklogdFileFormat
- sysklogd compatible log file format. If used with options: $SpaceLFOnReceive on;
$EscapeControlCharactersOnReceive off; $DropTrailingLFOnReception off,
the log format will conform to sysklogd log format.</li>
<li>RSYSLOG_ForwardFormat
- a new high-precision forwarding format very similar to the
traditional one, but with high-precision timestamps and timezone
information. Recommended to be used when sending messages to rsyslog
3.12.5 or above.</li>
<li>RSYSLOG_SyslogProtocol23Format
- the format specified in IETF's internet-draft
ietf-syslog-protocol-23, which is assumed to be come the new syslog
standard RFC. This format includes several improvements. The rsyslog
message parser understands this format, so you can use it together with
all relatively recent versions of rsyslog. Other syslogd's may get
hopelessly confused if receiving that format, so check before you use
it. Note that the format is unlikely to change when the final RFC comes
out, but this may happen.</li>
<li>RSYSLOG_DebugFormat
- a special format used for troubleshooting property problems. This format
is meant to be written to a log file. Do not use for production or remote
forwarding.</li>
</ul>
<h3>String-based Template Samples</h3>
This section provides some sample of what the default formats would
look as a text-based template. Hopefully, their description is self-explanatory.
Note that each $Template statement is on a single line, but probably broken
accross several lines for display purposes by your browsers. Lines are separated by
empty lines.
<code>
$template FileFormat,"%TIMESTAMP:::date-rfc3339% %HOSTNAME% %syslogtag%%msg:::sp-if-no-1st-sp%%msg:::drop-last-lf%\n"
 
$template TraditionalFileFormat,"%TIMESTAMP% %HOSTNAME% %syslogtag%%msg:::sp-if-no-1st-sp%%msg:::drop-last-lf%\n"
 
$template ForwardFormat,"<%PRI%>%TIMESTAMP:::date-rfc3339% %HOSTNAME% %syslogtag:1:32%%msg:::sp-if-no-1st-sp%%msg%"
 
$template TraditionalForwardFormat,"<%PRI%>%TIMESTAMP% %HOSTNAME% %syslogtag:1:32%%msg:::sp-if-no-1st-sp%%msg%"
 
$template StdSQLFormat,"insert into SystemEvents (Message, Facility, FromHost, Priority, DeviceReportedTime, ReceivedAt, InfoUnitID, SysLogTag) values ('%msg%', %syslogfacility%, '%HOSTNAME%', %syslogpriority%, '%timereported:::date-mysql%', '%timegenerated:::date-mysql%', %iut%, '%syslogtag%')",SQL
</code>

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This documentation is part of the
<a href="http://www.rsyslog.com/">rsyslog</a> project. 
Copyright &copy; 2008 by <a href="http://www.gerhards.net/rainer">Rainer Gerhards</a> and
<a href="http://www.adiscon.com/">Adiscon</a>. Released under the GNU GPL
version 2 or higher.
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