Literal string searches have the following flags() options:
global
Usable only in rewrite rules, flags("global") matches for every occurrence of the expression, not only the first one.
ignore-case
Disables case-sensitivity.
prefix
During the matching process, patterns (also called search expressions) are matched against the input string starting from the beginning of the input string, and the input string is matched only for the maximum character length of the pattern. The initial characters of the pattern and the input string must be identical in the exact same order, and the pattern's length is definitive for the matching process (that is, if the pattern is longer than the input string, the match will fail).
Example: matching / non-matching patterns for the input string 'exam'
For the input string 'exam',
store-matches
Stores the matches of the regular expression into the $0, ... $255 variables. The $0 stores the entire match, $1 is the first group of the match (parentheses), and so on. Named matches (also called named subpatterns), for example, (?<name>...), are stored as well. Matches from the last filter expression can be referenced in regular expressions.
NOTE: To convert match variables into a syslog-ng OSE list, use the $* macro, which can be further manipulated using List manipulation, or turned into a list in type-aware destinations.
substring
The given literal string will match when the pattern is found within the input. Unlike flags("prefix"), the pattern does not have to be identical with the given literal string.
There are no supported flags() options for glob patterns without regular expression support.
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.
Example: Optimizing regular expressions in filters
Suppose you need a filter that matches the following error message logged by the xntpd NTP daemon:
xntpd[1567]: time error -1159.777379 is too large (set clock manually);
The following filter uses regular expressions and matches every instance and variant of this message.
filter f_demo_regexp {
program("demo_program") and
match("time error .* is too large .* set clock manually");
};
Segmenting the match() part of this filter into separate match() functions greatly improves the performance of the filter.
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.
