syslog-ng uses the quasi-standard BSD syslog protocol, specified in RFC 3164. As the text of RFC 3164 is vague and is just an informational description and not a standard, various incompatible extensions of it emerged. syslog-ng tries hard to interoperate with a wide variety of devices, and the format of relayed messages can be customized.
The most important extensions of the original protocol endorsed by syslog-ng are:
The syslog-ng project began in 1998, when Balázs Scheidler, the primary author of syslog-ng, ported the existing nsyslogd code to Linux. The 1.0.x branch of syslog-ng was still based on the nsyslogd sources and are available in the syslog-ng source archive.
Right after the release of syslog-ng 1.0.x, a reimplementation of the code base started to address some of the shortcomings of nsyslogd and to address the licensing concerns of Darren Reed, the original nsyslogd author. This reimplementation was named stable in the October of 1999 with the release of 1.2.0. This time around, syslog-ng depended on some code originally developed for lsh by Niels Möller.
Three major releases (1.2, 1.4 and 1.6) were using this code base, the last release of the 1.6.x branch in February 2007. In this period of about 8 years, syslog-ng became one of the most popular alternative syslog implementations.
In a volunteer based effort, yet another rewrite was started back in 2001, dropping lsh code and using the more widely available GLib library. This rewrite of the codebase took its time, the first stable release of 2.0.0 happened in October of 2006.
Development efforts are focused in improving the 2.0.x branch, support for 1.6.x is expected to be dropped in the near future (as of May 2007). BalaBit, the company behind syslog-ng started a parallel, commercial fork of syslog-ng, called syslog-ng Premium Edition. Portions of the commercial income are used to sponsor development of the free version.
syslog-ng is part of a number of different Linux and Unix distributions. Among others: