2.10. The structure of a log message The syslog-ng Premium Edition 7 Administrator Guide
The following sections describe the structure of log messages. Currently there are two standard syslog message formats:
The old standard described in RFC 3164 (also called the BSD-syslog or the legacy-syslog protocol): see Section 2.10.1, BSD-syslog or legacy-syslog messages
The new standard described in RFC 5424 (also called the IETF-syslog protocol): see Section 2.10.2, IETF-syslog messages
How messages are represented in syslog-ng PE: see Section 2.11, Message representation in syslog-ng PE.