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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><title>Compatibility notes for rsyslog v6</title>
</head>
<body>
<h1>Compatibility Notes for rsyslog v6</h1>
<p><small><i>Written by <a href="http://www.gerhards.net/rainer">Rainer Gerhards</a>
(2011-07-13)</i></small></p>
<p>
This document describes things to keep in mind when moving from v5 to v6. It
does not list enhancements nor does it talk about compatibility concerns introduced
by earlier versions (for this, see their respective compatibility documents). Its focus
is primarily on what you need to know if you used a previous version and want to use the
current one without hassle. Note that versions prior to 6.3.3 did not have any notable compatibility
concerns. So all said here is for 6.3.3 and above.
<h2>RainerScript based rsyslog.conf</h2>
<p>A better config format was the main release target for rsyslog v6. It comes in the
flavor of so-called RainerScript
(<a href="http://blog.gerhards.net/2008/02/introducing-rainerscript-and-some.html">why the
name RainerScript?</a>). RainerScript supports legacy syslog.conf format, much as you know it
from other syslogd's (like sysklogd or the BSD syslogd's) as well as previous versions
of rsyslog. Initial work on RainerScript began in v4, and the if-construct was already
supported in v4 and v5. Version 6 has now taken this further. After long discussions we
decided to use the legacy format as a basis, and lightly extend it by native RainerScript
constructs. The main goal was to make sure that previous knowledge and config systems
could still be used while offering a much more intuitive and powerful way of configuring
rsyslog.
<p>RainerScript has been implemented from scratch and with new tools (flex/bison, for those in the
know). Starting with 6.3.3, this new config file processor replaces the legacy one. Note that
the new processor handles all formats, extended RainerScript as well as legacy syslog.conf format.
There are some legacy construct that were especially hard to translate. You'll read about them in
other parts of this document (especially outchannels, which require a format change).
<p>In v6, all legacy formats are supported. In the long term, we may remove some of the ugly
rsyslog-specific constructs. Good candidates are all configuration commands starting with
a dollar sign, like "$ActionFileDefaultTemplate"). However, this will not be the case before
rsyslog v7 or (much more likely) v8/9. Right now, you also need to use these commands, because
not all have already been converted to the new RainerScript format.
<p>In 6.3.3, the new parser is used, but almost none of the extended RainerScript capabilities
are available. They will incrementally be introduced with the following releases. Note that for
some features (most importantly if-then-else nested blocks), the v6 core engine is not
capable enough. It is our aim to provide a much better config language to as many rsyslog
users as quickly as possible. As such, we refrain from doing big engine changes in v6. This
in turn means we cannot introduce some features into RainerScript that we really want to see.
These features will come up with rsyslog v7, which will have even better flow control
capabilities inside the core engine. Note that v7 will fully support v6 RainerScript.
Let us also say that the v6 version is not a low-end quick hack: it offers full-fledged
syslog message processing control, capable of doing the best you can find inside the
industry. We just say that v7 will come up with even more advanced capabilites.
<p>Please note that we tried hard to make the RainerScript parser compatible with
all legacy config files. However, we may have failed in one case or another. So if you
experience problems during config processing, chances are there may be a problem
on the rsyslog side. In that case, please let us know.
<h2>compatibility mode</h2>
<p>Compatibility mode (specified via -c option) has been removed. This was a migration aid from
sysklogd and very early versions of rsyslog. As all major distros now have rsyslog as their
default, and thus ship rsyslog-compliant config files, there is no longer a need for
compatibility mode. Removing it provides easier to maintain code. Also, practice has shown
that many users were confused by compatibility mode (and even some package maintainers got
it wrong). So this not only cleans up the code but rather removes a frequent source of
error.
<p>It must be noted, though, that this means rsyslog is no longer a 100% drop-in replacement
for sysklogd. If you convert an extremely old system, you need to checks its config and
probably need to apply some very mild changes to the config file.
<h2>abort on config errors</h2>
<p>Previous versions accepted some malformedness inside the config file without aborting. This
could lead to some uncertainty about which configuration was actually running. In v6 there
are some situations where config file errors can not be ignored. In these cases rsyslog
emits error messages to stderr, and then exists with a non-zero exit code. It is important
to check for those cases as this means log data is potentially lost.
Please note that
the root problem is the same for earlier versions as well. With them, it was just harder
to spot why things went wrong (and if at all).
<h2>outchannels</h2>
<p>Outchannels are a to-be-removed feature of rsyslog, at least as far as the config
syntax is concerned. Nevertheless, v6 still supports it, but a new syntax is required
for the action. Let's assume your outchannel is named "channel". The previous syntax was
<blockquote><code>
*.* $channel
</code>
</blockquote>
This was deprecated in v5 and no longer works in v6. Instead, you need to specify
<blockquote><code>
*.* :omfile:$channel
</code></blockquote>
Note that this syntax is available starting with rsyslog v4. It is important to keep on your
mind that future versions of rsyslog will require different syntax and/or drop outchannel support
completely. So if at all possible, avoid using this feature. If you must use it, be prepared for
future changes and watch announcements very carefully.
<p>[<a href="manual.html">manual index</a>] [<a href="http://www.rsyslog.com/">rsyslog site</a>]</p>
<p><font size="2">This documentation is part of the
<a href="http://www.rsyslog.com/">rsyslog</a> project.<br>
Copyright © 2011 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.</font></p>
</body></html>
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