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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><title>Compatibility notes for rsyslog v3</title>
<meta name="KEYWORDS" content="syslog, mysql, syslog to mysql, howto">
</head>
<body>
<h1>Compatibility Notes for rsyslog v4</h1>
<p><small><i>Written by <a href="http://www.gerhards.net/rainer">Rainer Gerhards</a>
(2008-03-28)</i></small></p>
<p>Rsyslog aims to be a drop-in replacement for sysklogd.
However, version 3 has some considerable enhancements, which lead to
some backward compatibility issues both in regard to sysklogd and
rsyslog v1 and v2. Most of these issues are avoided by default by not
specifying the -c option on the rsyslog command line. That will enable
backwards-compatibility mode. However, please note that things may be
suboptimal in backward compatibility mode, so the advise is to work
through this document, update your rsyslog.conf, remove the no longer
supported startup options and then add -c4 as the first option to the
rsyslog command line. That will enable native mode.</p>
<p>Please note that rsyslogd helps you during that process by
logging appropriate messages about compatibility mode and
backwards-compatibility statemtents automatically generated. You may
want your syslogd log for those. They immediately follow rsyslogd's
startup message.</p>
<h2>Inputs</h2>
<p>With v2 and below, inputs were automatically started together
with rsyslog. In v3, inputs are optional! They come in the form of
plug-in modules.
<font color="#ff0000"><b>At least one input module
must be loaded to make rsyslog do any useful work.</b></font>
The config file directives doc briefly lists which config statements
are available by which modules.</p>
<p>It is suggested that input modules be loaded in the top part
of the config file. Here is an example, also highlighting the most
important modules:</p>
<p><b>$ModLoad immark # provides --MARK--
message capability<br>
$ModLoad imudp # provides UDP syslog reception<br>
$ModLoad imtcp # provides TCP syslog reception<br>
</b><b>$ModLoad imgssapi # provides GSSAPI syslog
reception<br>
</b><b>$ModLoad imuxsock # provides support for local
system logging (e.g.
via logger command)<br>
$ModLoad imklog # provides kernel logging support (previously done
by rklogd)</b></p>
<h2>Command Line Options</h2>
<p>A number of command line options have been removed. New config
file directives have been added for them. The -h and -e option have
been removed even in compatibility mode. They are ignored but an
informative message is logged. Please note that -h was never supported
in v2, but was silently ignored. It disappeared some time ago in the
final v1 builds. It can be replaced by applying proper filtering inside
syslog.conf.</p>
<h2>-c option</h2>
<p>The -c option is new and tell rsyslogd about the desired backward
compatibility mode. It must always be the first option on the command
line, as it influences processing of the other options. To use the
rsyslog v3 native
interface, specify -c4. To use compatibility mode ,
either do not use -c at all or use -c<vers> where vers is
the
rsyslog version that it shall be compatible to. Use -c0 to be
command-line compatible to sysklogd.</p>
<h2>-e Option</h2>This option is no longer supported, as the "last
message repeated n times" feature is now turned off by default. We
changed this default because this feature is causing a lot of trouble
and we need to make it either go away or change the way it works. For
more information, please see our dedicted <a href="http://www.rsyslog.com/PNphpBB2-viewtopic-p-1130.phtml">forum thread on "last message repeated n times"</a>.
This thread also contains information on how to configure rsyslogd so
that it continues to support this feature (as long as it is not totally
removed).<h2>-m Option</h2>
<p>The -m command line option is emulated in compatibiltiy mode.
To replace it, use the following config directives (compatibility mode
auto-generates them):</p>
<p><b>$ModLoad immark<br>
$MarkMessageInterval 1800 # 30 minutes</b></p>
<h2>-r Option</h2>
<p>Is no longer available in native mode. However, it
is
understood in compatibility mode (if no -c option is given). Use the <b>$UDPSeverRun
<port></b> config file directives. You can now also
set the local address the server should listen to via <b>$UDPServerAddress
<ip></b> config directive.</p>
<p>The following example configures an UDP syslog server at the
local address 192.0.2.1 on port 514:</p>
<p><b>$ModLoad imudp.so<br>
$UDPSeverAddress 192.0.2.1 # this MUST be before the $UDPServerRun
directive!<br>
$UDPServerRun 514</b></p>
<p>"$UDPServerAddress *" means listen on all local interfaces.
This is the default if no directive is specified.</p>
<p>Please note that now multiple listeners are supported. For
example, you can do the following:</p>
<p><b>$ModLoad imudp.so<br>
$UDPSeverAddress 192.0.2.1 # this MUST be before the $UDPServerRun
directive!<br>
$UDPServerRun 514<br>
$UDPSeverAddress * # all local interfaces<br>
$UDPServerRun 1514</b></p>
<p>These config file settings run two listeners: one
at 192.0.2.1:514 and one on port 1514, which listens on all local
interfaces.</p>
<h2>Default port for UDP (and TCP) Servers</h2>
<p>Please note that with pre-v3 rsyslogd, a service database
lookup was made when a UDP server was started and no port was
configured. Only if that failed, the IANA default of 514 was used. For
TCP servers, this lookup was never done and 514 always used if no
specific port was configured. For consitency, both TCP and UDP now use
port 514 as default. If a lookup is desired, you need to specify it in
the "Run" directive, e.g. "<i>$UDPServerRun syslog</i>".</p>
<h2>klogd</h2>
<p>klogd has (finally) been replaced by a loadable input module.
To enable klogd functionality, do</p>
<p><b>$ModLoad imklog.so</b></p>
<p>Note that this can not be handled by the compatibility layer,
as klogd was a separate binary.A limited set of klogd command line
settings is now supported
via rsyslog.conf. That set of configuration directives is to be
expanded. </p>
<h2>Output File Syncing</h2>
Rsyslogd tries to keep as compatible to
stock syslogd as possible. As such, it retained stock syslogd's default
of syncing every file write if not specified otherwise (by placing a
dash in front of the output file name). While this was a useful feature
in past days where hardware was much less reliable and UPS seldom, this
no longer is useful in today's worl. Instead, the syncing is a high
performace hit. With it, rsyslogd writes files around 50 *times* slower
than without it. It also affects overall system performance due to the
high IO activity. In rsyslog v3, syncing has been turned off by
default. This is done via a specific configuration directive
"$ActionFileEnableSync on/off" which is off by default. So even if
rsyslogd finds sync selector lines, it ignores them by default. In
order to enable file syncing, the administrator must specify
"$ActionFileEnableSync on" at the top of rsyslog.conf. This ensures
that syncing only happens in some installations where the administrator
actually wanted that (performance-intense) feature. In the fast
majority of cases (if not all), this dramatically increases rsyslogd
performance without any negative effects.
<h2>Queue Modes for the Main Message Queue</h2>
<p>Either "FixedArray" or "LinkedList" is recommended. "Direct"
is available, but should not be used except for a very good reason
("Direct" disables queueing and will potentially lead to message loss
on the input side).</p>
</body></html>
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