rsyslog vs. syslog-ng

Written by Rainer Gerhards (2008-02-28)

We have often been asked about a comparison sheet between rsyslog and syslog-ng. Unfortunately, I do not know much about syslog-ng, I did not even use it once. Also, there seems to be no comprehensive feature sheet available for syslog-ng (that recently changed, see below). So I started this comparison, but it probably is not complete. For sure, I miss some syslog-ng features. This is not an attempt to let rsyslog shine more than it should. I just used the rsyslog feature sheet as a starting point, simply because it was available. If you would like to add anything to the chart, or correct it, please simply drop me a line. I would love to see a real honest and up-to-date comparison sheet, so please don't be shy ;)

Feature rsyslog syslog-ng

Input Sources
UNIX domain socket yes yes
UDP yes yes
TCP yes yes
RFC 3195/BEEP yes (needs separate build process) no
kernel log yes yes
file yes yes
mark message generator as an optional input yes no (?)
Windows Event Log via EventReporter or MonitorWare Agent (both commercial software) via separate Windows agent, paid edition only

Network (Protocol) Support

support for (plain) tcp based syslog yes yes
support for GSS-API yes no (?)
ability to limit the allowed network senders (syslog ACLs) yes yes (?)
support for syslog-transport-tls based framing on syslog/tcp connections yes no (?)
udp syslog yes yes
on the wire (zlib) message compression yes no (?)
support for receiving messages via reliable RFC 3195 delivery yes no
support for ssl-protected syslog via stunnel via stunnel
paid edition natively
support for IETF's new syslog-protocol draft yes no
support for IPv6 yes yes
native ability to send SNMP traps yes ?
ability to preserve the original hostname in NAT environments and relay chains yes yes

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

Supported Database Outputs
MySQL yes (native ommysql, omlibdbi) yes (via libdibi)
PostgreSQL yes (native ompgsql, omlibdbi) yes (via libdibi)
Oracle yes (omlibdbi) yes (via libdibi)
SQLite yes (omlibdbi) yes (via libdibi)
Microsoft SQL (Open TDS) yes (omlibdbi) no (?)
Sybase (Open TDS) yes (omlibdbi) no (?)
Firebird/Interbase yes (omlibdbi) no (?)
Ingres yes (omlibdbi) no (?)
mSQL yes (omlibdbi) no (?)

Enterprise Features
support for on-demand on-disk spooling of messages yes paid edition only
ability to limit disk space used by spool files yes yes
each action can use its own, independant set of spool files yes no
different sets of spool files can be placed on different disk yes no
ability to configure backup syslog/database servers yes no
Professional Support yes yes

Config File
config file format compatible to legacy syslogd but ugly clean but not backwards compatible
ability to include config file from within other config files yes no
ability to include all config files existing in a specific directory yes no

Extensibility
Functionality split in separately loadable modules yes no
Support for third-party input plugins yes no
Support for third-party output plugins yes no

Other Features
ability to generate file names and directories (log targets) dynamically yes yes
control of log output format, including ability to present channel and priority as visible log data yes not sure...
good timestamp format control; at a minimum, ISO 8601/RFC 3339 second-resolution UTC zone yes yes
ability to reformat message contents and work with substrings yes I think yes
support for log files larger than 2gb yes yes
support for log file size limitation and automatic rollover command execution yes yes
support for running multiple syslogd instances on a single machine yes ? (but I think yes)
ability to execute shell scripts on received messages yes yes
ability to pipe messages to a continously running program no yes
massively multi-threaded for tomorrow's multi-core machines yes no (only multithreaded with database destinations)
ability to control repeated line reduction ("last message repeated n times") on a per selector-line basis yes yes (?)
supports multiple actions per selector/filter condition yes yes
web interface phpLogCon
[also works with php-syslog-ng]
php-syslog-ng
using text files as input source yes yes
rate-limiting output actions yes yes
discard low-priority messages under system stress yes no (?)
flow control (slow down message reception when system is busy) limited (TCP Window, delay on queue full) yes (limited, too? "stops accepting messages")
rewriting messages yes yes (at least I think so...)
output data into various formats yes yes (looks somewhat limited to me)
ability to control "message repeated n times" generation yes no (?)
license GPLv3 (GPLv2 for v2 branch) GPL (paid edition is closed source)
supported platforms Linux, BSD, anecdotical seen on Solaris many popular *nixes
DNS cache no yes

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?".

Balabit, the vendor of syslog-ng, has just recently done a feature sheet. I have not yet been able to fully work through it. In the mean time, you may want to read it in parallel. It is available at Balabit's site.

This document is current as of 2008-02-28 and definitely incomplete (I did not yet manage to complete it!).