syslog-ng Open Source Edition 3.25 - Administration Guide

Literal string searches

Literal string searches have the following flags() options:

For the input string 'exam',
the following patterns will match:
'ex' (the pattern contains the initial characters of the input string in the exact same order)
'exam' (the pattern is an exact match for the input string)
the following patterns will not match:
'example' (the pattern is longer than the input string)
'hexameter' (the pattern's initial characters do not match the input string's characters in the exact same order, and the pattern is longer than the input string)

Glob patterns without regular expression support

There are no supported flags() options for glob patterns without regular expression support.

Optimizing regular expressions

The host(), match(), and program() filter functions and some other syslog-ng objects accept regular expressions as parameters. But evaluating general regular expressions puts a high load on the CPU, which can cause problems when the message traffic is very high. Often the regular expression can be replaced with simple filter functions and logical operators. Using simple filters and logical operators, the same effect can be achieved at a much lower CPU load.

xntpd[1567]: time error -1159.777379 is too large (set clock manually);

filter f_demo_regexp {
    program("demo_program") and
    match("time error .* is too large .* set clock manually");
};

filter f_demo_optimized_regexp {
    program("demo_program") and
    match("time error") and
    match("is too large") and
    match("set clock manually");
};

parser: Parse and segment structured messages

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 JSON parser.

• To parse XML-formatted messages, see XML parser.

• To identify and parse the messages using a pattern database, see db-parser: Process message content with a pattern database (patterndb).

• To parse a specially-formatted date or timestamp, see Parsing dates and timestamps.

• To write a custom parser in Python or Hy, see Python parser.

• To parse the tags sent by another syslog-ng host. For details, see Parsing tags.

The syslog-ng OSE application provides built-in parsers for the following application logs:

• Apache HTTP server access logs. For details, see Apache access log parser.

• Cisco devices. For details, see Cisco parser.

• Messages formatted using the enterprise-wide message model (EWMM) of syslog-ng OSE. For details, see Parsing enterprise-wide message model (EWMM) messages.

• Iptables logs. For details, see iptables parser.

• Linux Audit (auditd) logs. For details, see Linux audit parser.

• Netskope log messages. For details, see Netskope 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.

• sudo logs. For details, see Sudo parser.

• Websense Content Gateway (Raytheon|Websense, now Forcepoint) log messages. For details, see Websense parser.