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syslog-ng Open Source Edition


13.2.1. Using parser results in filters and templates

The results of message classification and parsing can be used in custom filters and templates, for example, in file and database templates. The following built-in macros allow you to use the results of the classification:

  • The .classifier.class macro contains the class assigned to the message (for example violation, security, or unknown).

  • The .classifier.rule_id macro contains the identifier of the message pattern that matched the message.

  • The .classifier.context_id macro contains the identifier of the context for messages that were correlated. For details on correlating messages, see Section 13.3, Correlating log messages using pattern databases.

Example 13.3. Using classification results for filtering messages

To filter on a specific message class, create a filter that checks the .classifier_class macro, and use this filter in a log statement.

filter fi_class_violation {
log {

Filtering on the unknown class selects messages that did not match any rule of the pattern database. Routing these messages into a separate file allows you to periodically review new or unknown messages.

To filter on messages matching a specific classification rule, create a filter that checks the .classifier.rule_id macro. The unique identifier of the rule (for example e1e9c0d8-13bb-11de-8293-000c2922ed0a) is the id attribute of the rule in the XML database.

filter fi_class_rule {

Pattern database rules can assign tags to messages. These tags can be used to select tagged messages using the tags() filter function.


The syslog-ng OSE application automatically adds the class of the message as a tag using the .classifier.<message-class> format. For example, messages classified as "system" receive the .classifier.system tag. Use the tags() filter function to select messages of a specific class.

filter f_tag_filter {tags(".classifier.system");};

The message-segments parsed by the pattern parsers can also be used as macros as well. To accomplish this, you have to add a name to the parser, and then you can use this name as a macro that refers to the parsed value of the message.

Example 13.4. Using pattern parsers as macros

For example, you want to parse messages of an application that look like "Transaction: <type>.", where <type> is a string that has different values (for example refused, accepted, incomplete, and so on). To parse these messages, you can use the following pattern:

'Transaction: @ESTRING::.@'

Here the @ESTRING@ parser parses the message until the next full stop character. To use the results in a filter or a filename template, include a name in the parser of the pattern, for example:


After that, add a custom template to the log path that uses this template. For example, to select every accepted transaction, use the following custom filter in the log path:

match("accepted" value("TRANSACTIONTYPE"));

The above macros can be used in database columns and filename templates as well, if you create custom templates for the destination or logspace.

Use a consistent naming scheme for your macros, for example, APPLICATIONNAME_MACRONAME.