rsyslog vs. syslog-ng - a comparison

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# 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This comparison page is rooted nearly 5 years in the past and has become severely outdated since then.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 ;)).
Thanks,
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?) | yes |
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 |
Extensibility
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.