The filters and default macros of syslog-ng work well on the headers and metainformation of the log messages, but are rather limited when processing the content of the messages. Parsers can segment the content of the messages into name-value pairs, and these names can be used as user-defined macros. Subsequent filtering or other type of processing of the message can use these custom macros to refer to parts of the message. Parsers are global objects most often used together with filters and rewrite rules.
The syslog-ng OSE application provides the following possibilities to parse the messages, or parts of the messages:
By default, syslog-ng OSE parses every message as a syslog message. To disable message parsing, use the flags(no-parse) option of the source. To explicitly parse a message as a syslog message, use the syslog parser. For details, see Parsing syslog messages.
To segment a message into columns using a CSV-parser, see Parsing messages with comma-separated and similar values.
To segment a message consisting of whitespace or comma-separated key=value pairs (for example, Postfix log messages), see Parsing key=value pairs.
To parse JSON-formatted messages, see The JSON parser The JSON parser.
To parse XML-formatted messages, see The XML parser.
To parse a specially-formatted date or timestamp, see Parsing dates and timestamps.
To write a custom parser in Python, see The Python Parser.
To identify and parse the messages using a pattern database, see db-parser: Process message content with a pattern database (patterndb).
The syslog-ng OSE application provides built-in parsers for the following application logs:
Apache HTTP server access logs. For details, see The Apache Access Log Parser.
Cisco devices. For details, see The Cisco Parser.
Linux Audit (auditd) logs. For details, see The Linux Audit Parser.
osquery result logs. For details, see osquery: Collect and parse osquery result logs.
SNMP traps of the Net-SNMP's snmptrapd application. For details, see snmptrap: Read Net-SNMP traps.
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