rsyslog vs. syslog-ng

Written by Rainer Gerhards (2008-05-06), slightly updated 2012-01-09

This comparison page is rooted nearly 5 years in the past and has become severely outdated since then. It was unmaintained for several years and contained false information on both syslog-ng and rsyslog as technology had advanced so much.

This page was initially written because so many people asked about a comparison when rsyslog was in its infancy. So I tried to create one, but it was hard to maintain as both projects grew and added feature after feature. I have to admit we did not try hard to keep it current -- there were many other priorities. I even had forgetten about this page, when I saw that Peter Czanik blogged about its incorrectness (it must be noted that Peter is wrong on RELP -- it is well alive). I now remember that he asked me some time ago about this page, what I somehow lost... I guess he must have been rather grumpy about that :-(

Visiting this page after so many years is interesting, because it shows how much has changed since then. Obviously, one of my main goals in regard to syslog-ng is reached: in 2007, I blogged that the world needs another syslogd in order to have healthy competition and a greate feature set in the free editions. In my opinion, the timeline clearly tells that rsyslog's competition has driven more syslog-ng features from the commercial to the free edition. Also, I found it interesting to see that syslog-ng has adapted rsyslog's licensing scheme, modular design and multi-threadedness. On the other hand, the Balabit folks have obviously done a quicker and better move on log normalization with what they call patterndb (it is very roughly equivalent to what rsyslog has just recently introduced with the help of liblognorm).

To that account, I think the projects are closer together than 5 years ago. I should now go ahead and create a new feature comparison. Given previous experience, I think this does not work out. In the future, we will probably focus on some top features, as Balabit does. However, that requires some time and I have to admit I do not like to drop this page that has a lot of inbound links. So I think I do the useful thing by providing these notes and removing the syslog-ng information. So it can't be wrong on syslog-ng any more. Note that it still contains some incorrect information about rsyslog (it's the state it had 5 years ago!). The core idea is to start with updating the rsyslog feature sheet and from there on work to a complete comparision. Of course, feel free to read on if you like to get some sense of history (and inspiration on what you can still do -- but more ;)).

Rainer Gerhards

Feature rsyslog syslog-ng

Input Sources
UNIX domain socket yes
UDP yes
TCP yes
RELP yes
RFC 3195/BEEP yes (via im3195)
kernel log yes
file yes
mark message generator as an optional input yes
Windows Event Log via a Windows event logging software such as EventReporter or MonitorWare Agent (both commercial software, both fund rsyslog development)

Network (Protocol) Support

support for (plain) tcp based syslog yes
support for GSS-API yes
ability to limit the allowed network senders (syslog ACLs) yes
support for syslog-transport-tls based framing on syslog/tcp connections yes
udp syslog yes
syslog over RELP
truly reliable message delivery (Why is plain tcp syslog not reliable?)
on the wire (zlib) message compression yes
support for receiving messages via reliable RFC 3195 delivery yes
support for TLS/SSL-protected syslog natively (since 3.19.0)
via stunnel
support for IETF's new syslog-protocol draft yes
support for IETF's new syslog-transport-tls draft yes
(since 3.19.0 - world's first implementation)
support for IPv6 yes
native ability to send SNMP traps yes
ability to preserve the original hostname in NAT environments and relay chains yes

Message Filtering
Filtering for syslog facility and priority yes
Filtering for hostname yes
Filtering for application yes
Filtering for message contents yes
Filtering for sending IP address yes
ability to filter on any other message field not mentioned above (including substrings and the like) yes
support for complex filters, using full boolean algebra with and/or/not operators and parenthesis yes
Support for reusable filters: specify a filter once and use it in multiple selector lines no
support for arbritrary complex arithmetic and string expressions inside filters yes
ability to use regular expressions in filters yes
support for discarding messages based on filters yes
ability to filter out messages based on sequence of appearing yes (starting with 3.21.3)
powerful BSD-style hostname and program name blocks for easy multi-host support yes

Supported Database Outputs
MySQL yes (native ommysql, omlibdbi)
PostgreSQL yes (native ompgsql, omlibdbi)
Oracle yes (omlibdbi)
SQLite yes (omlibdbi)
Microsoft SQL (Open TDS) yes (omlibdbi)
Sybase (Open TDS) yes (omlibdbi)
Firebird/Interbase yes (omlibdbi)
Ingres yes (omlibdbi)
mSQL yes (omlibdbi)

Enterprise Features
support for on-demand on-disk spooling of messages yes
ability to limit disk space used by spool files yes
each action can use its own, independant set of spool files yes
different sets of spool files can be placed on different disk yes
ability to process spooled messages only during a configured timeframe (e.g. process messages only during off-peak hours, during peak hours they are enqueued only) yes
(can independently be configured for the main queue and each action queue)
ability to configure backup syslog/database servers yes
Professional Support yes

Config File
config file format compatible to legacy syslogd but ugly
ability to include config file from within other config files yes
ability to include all config files existing in a specific directory yes

Functionality split in separately loadable modules yes
Support for third-party input plugins yes
Support for third-party output plugins yes

Other Features
ability to generate file names and directories (log targets) dynamically yes
control of log output format, including ability to present channel and priority as visible log data yes
native ability to send mail messages yes (ommail, introduced in 3.17.0)
good timestamp format control; at a minimum, ISO 8601/RFC 3339 second-resolution UTC zone yes
ability to reformat message contents and work with substrings yes
support for log files larger than 2gb yes
support for log file size limitation and automatic rollover command execution yes
support for running multiple syslogd instances on a single machine yes
ability to execute shell scripts on received messages yes
ability to pipe messages to a continously running program
massively multi-threaded for tomorrow's multi-core machines yes
ability to control repeated line reduction ("last message repeated n times") on a per selector-line basis yes
supports multiple actions per selector/filter condition yes
web interface phpLogCon
[also works with php-syslog-ng]
using text files as input source yes
rate-limiting output actions yes
discard low-priority messages under system stress yes
flow control (slow down message reception when system is busy) yes (advanced, with multiple ways to slow down inputs depending on individual input capabilities, based on watermarks)
rewriting messages yes
output data into various formats yes
ability to control "message repeated n times" generation yes
license GPLv3 (GPLv2 for v2 branch)
supported platforms Linux, BSD, anecdotical seen on Solaris; compilation and basic testing done on HP UX
DNS cache

While the rsyslog project was initiated in 2004, it is build on the main author's (Rainer Gerhards) 12+ years of logging experience. Rainer, for example, also wrote the first Windows syslog server in early 1996 and invented the eventlog-to-syslog class of applications in early 1997. He did custom logging development and consulting even before he wrote these products. Rsyslog draws on that vast experience and sometimes even on the code.

Based on a discussion I had, I also wrote about the political argument why it is good to have another strong syslogd besides syslog-ng. You may want to read it at my blog at "Why does the world need another syslogd?".

[manual index] [rsyslog.conf] [rsyslog site]

This documentation is part of the rsyslog project.
Copyright © 2008 by Rainer Gerhards and Adiscon. Released under the GNU GPL version 2 or higher.