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<html><head>
<title>Recording the Priority of Syslog Messages</title>
<meta name="KEYWORDS" content="syslog, mysql, syslog to mysql, howto">
</head>
<body>
<h1>Recording the Priority of Syslog Messages</h1>
<P><small><i>Written by
<a href="http://www.adiscon.com/en/people/rainer-gerhards.php">Rainer
Gerhards</a> (2007-06-18)</i></small></P>
<h2>Abstract</h2>
<p><i><b>The so-called priority (PRI) is very important in syslog messages,
because almost all filtering in syslog.conf is based on it.</b> However, many
syslogds (including the Linux stock sysklogd) do not provide a way to record
that value. In this article, I'll give a brief overview of how PRI can be
written to a log file.</i></p>
<h2>Background</h2>
<p>The PRI value is a combination of so-called severity and facility. The
facility indicates where the message originated from (e.g. kernel, mail
subsystem) while the severity provides a glimpse of how important the message
might be (e.g. error or informational). Be careful with these values: they are
in no way consistent across applications (especially severity). However, they
still form the basis of most filtering in syslog.conf. For example, the
directive (aka "selector line)</p>
<p align="center">
<code>mail.* /var/log/mail.log</code>
</p>
<p>means that messages with the mail facility should be stored to
/var/log/mail.log, no matter which severity indicator they have (that is telling
us the asterisk). If you set up complex conditions, it can be annoying to find
out which PRI value a specific syslog message has. Most stock syslogds do not
provide any way to record them.</p>
<h2>How is it done?</h2>
<p>With <a href="http://www.rsyslog.com/">rsyslog</a>, PRI recording is simple.
All you need is the correct template. Even if you do not use rsyslog on a regular
basis, it might be a handy tool for finding out the priority.</p>
<p>Rsyslog provides a flexible system to specify the output formats. It is
template-based. A template with the traditional syslog format looks as follows:</p>
<p align="center">
<code>$template TraditionalFormat,"%timegenerated% %HOSTNAME% %syslogtag%%msg:::drop-last-lf%\n"</code>
</p>
<p>The part in quotes is the output formats. Things between percent-signs are
so-called <a href="property_replacer.html">messages properties</a>. They are replaced with the respective content
from the syslog message when output is written. Everything outside of the
percent signs is literal text, which is simply written as specified.</p>
<p>Thankfully, rsyslog provides message properties for the priority. These are
called "PRI", "syslogfacility" and "syslogpriority" (case is important!). They are numerical
values. Starting with rsyslog 1.13.4, there is also a property "pri-text", which
contains the priority in friendly text format (e.g. "syslog.info"). For the rest
of this article, I assume that you run version 1.13.4 or higher.</p>
<p>Recording the priority is now a simple matter of adding the respective field
to the template. It now looks like this:</p>
<p align="center">
<code>$template TraditionalFormatWithPRI,"%pri-text%: %timegenerated% %HOSTNAME% %syslogtag%%msg:::drop-last-lf%\n"</code>
</p>
<p>Now we have the right template - but how to write it to a file? You probably
have a line like this in your syslog.conf:</p>
<p align="center"><code>*.* -/var/log/messages.log</code></p>
<p>It does not specify a template. Consequently, rsyslog uses the traditional
format. In order to use some other format, simply specify the template after the
semicolon:</p>
<p align="center"><code>*.* -/var/log/messages.log;TraditionalFormatWithPRI</code></p>
<p>That's all you need to do. There is one common pitfall: you need to define
the template before you use it in a selector line. Otherwise, you will receive
an error.</p>
<p>Once you have applied the changes, you need to restart rsyslogd. It
will then pick the new configuration.</p>
<h2>What if I do not want rsyslogd to be the standard syslogd?</h2>
<p>If you do not want to switch to rsyslog, you can still use it as a setup aid.
A little bit of configuration is required.</p>
<ol>
<li>Download, make and install rsyslog</li>
<li>copy your syslog.conf over to rsyslog.conf</li>
<li>add the template described above to it; select the file that should use
it</li>
<li>stop your regular syslog daemon for the time being</li>
<li>run rsyslogd (you may even do this interactively by calling it with the
-n additional option from a shell)</li>
<li>stop rsyslogd (press ctrl-c when running interactively)</li>
<li>restart your regular syslogd</li>
</ol>
<p>That's it - you can now review the priorities.</p>
<h2>Some Sample Data</h2>
<p>Below is some sample data created with the template specified above. Note the
priority recording at the start of each line.</p>
<p>
<code>kern.info: Jun 15 18:10:38 host kernel: PCI: Sharing IRQ 11 with 00:04.0<br>
kern.info: Jun 15 18:10:38 host kernel: PCI: Sharing IRQ 11 with 01:00.0<br>
kern.warn: Jun 15 18:10:38 host kernel: Yenta IRQ list 06b8, PCI irq11<br>
kern.warn: Jun 15 18:10:38 host kernel: Socket status: 30000006<br>
kern.warn: Jun 15 18:10:38 host kernel: Yenta IRQ list 06b8, PCI irq11<br>
kern.warn: Jun 15 18:10:38 host kernel: Socket status: 30000010<br>
kern.info: Jun 15 18:10:38 host kernel: cs: IO port probe 0x0c00-0x0cff: clean.<br>
kern.info: Jun 15 18:10:38 host kernel: cs: IO port probe 0x0100-0x04ff: excluding 0x100-0x107 0x378-0x37f 0x4d0-0x4d7<br>
kern.info: Jun 15 18:10:38 host kernel: cs: IO port probe 0x0a00-0x0aff: clean.<br>
local7.notice: Jun 15 18:17:24 host dd: 1+0 records out<br>
local7.notice: Jun 15 18:17:24 host random: Saving random seed: succeeded<br>
local7.notice: Jun 15 18:17:25 host portmap: portmap shutdown succeeded<br>
local7.notice: Jun 15 18:17:25 host network: Shutting down interface eth1: succeeded<br>
local7.notice: Jun 15 18:17:25 host network: Shutting down loopback interface: succeeded<br>
local7.notice: Jun 15 18:17:25 host pcmcia: Shutting down PCMCIA services: cardmgr<br>
user.notice: Jun 15 18:17:25 host /etc/hotplug/net.agent: NET unregister event not supported<br>
local7.notice: Jun 15 18:17:27 host pcmcia: modules.<br>
local7.notice: Jun 15 18:17:29 host rc: Stopping pcmcia: succeeded<br>
local7.notice: Jun 15 18:17:30 host rc: Starting killall: succeeded<br>
syslog.info: Jun 15 18:17:33 host [origin software="rsyslogd" swVersion="1.13.3" x-pid="2464"] exiting on signal 15.<br>
syslog.info: Jun 18 10:55:47 host [origin software="rsyslogd" swVersion="1.13.3" x-pid="2367"][x-configInfo udpReception="Yes" udpPort="514" tcpReception="Yes" tcpPort="1470"] restart<br>
user.notice: Jun 18 10:55:50 host rger: test<br>
syslog.info: Jun 18 10:55:52 host [origin software="rsyslogd" swVersion="1.13.3" x-pid="2367"] exiting on signal 2.</code></p>
<h2>Feedback Requested</h2>
<P>I would appreciate feedback on this paper. If you have additional ideas,
comments or find bugs, please
<a href="mailto:rgerhards@adiscon.com">let me know</a>.</P>
<h2>References and Additional Material</h2>
<ul>
<li><a href="http://www.rsyslog.com">www.rsyslog.com</a> - the rsyslog site</li>
</ul>
<h2>Revision History</h2>
<ul>
<li>2007-06-18 *
<a href="http://www.adiscon.com/en/people/rainer-gerhards.php">Rainer Gerhards</a>
* initial version created</li>
</ul>
<h2>Copyright</h2>
<p>Copyright (c) 2007
<a href="http://www.adiscon.com/en/people/rainer-gerhards.php">Rainer Gerhards</a>
and <a href="http://www.adiscon.com/en/">Adiscon</a>.</p>
<p>Permission is granted to copy, distribute and/or modify this document under
the terms of the GNU Free Documentation License, Version 1.2 or any later
version published by the Free Software Foundation; with no Invariant Sections,
no Front-Cover Texts, and no Back-Cover Texts. A copy of the license can be
viewed at <a href="http://www.gnu.org/copyleft/fdl.html">
http://www.gnu.org/copyleft/fdl.html</a>.</p>
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