13.4. Triggering actions for identified messages

The syslog-ng OSE application can generate (trigger) messages automatically if certain events occur, for example, a specific log message is received, or the correlation timeout of a message expires. Basically, you can define messages for every pattern database rule that are emitted when a message matching the rule is received. Triggering messages is often used together with message correlation, but can also be used separately. When used together with message correlation, you can also create a new correlation context when a new message is received.

The generated message is injected into the same place where the db-parser() statement is referenced in the log path. To post the generated message into the internal() source instead, use the inject-mode() option in the definition of the parser.

Example 13.9. Sending triggered messages to the internal() source

To send the generated messages to the internal source, use the inject-mode(internal) option:

parser p_db {db-parser(
    file("mypatterndbfile.xml")
    inject-mode(internal)
);}; 

To inject the generated messages where the pattern database is referenced, use the inject-mode(pass-through) option:

parser p_db {db-parser(
    file("mypatterndbfile.xml")
    inject-mode(pass-through)
);}; 

The generated message must be configured in the pattern database rule. It is possible to create an entire message, use macros and values extracted from the original message with pattern database, and so on.

Example 13.10. Generating messages for pattern database matches

When inserted in a pattern database rule, the following example generates a message when a message matching the rule is received.

<actions>
    <action>
        <message>
            <values>
                <value name="MESSAGE">A log message from ${HOST} matched rule number $.classifier.rule_id</value>
            </values>
        </message>
    </action>
</actions>

To inherit the properties and values of the triggering message, set the inherit-properties attribute of the <message> element to TRUE. That way the triggering log message is cloned, including name-value pairs and tags. If you set any values for the message in the <action> element, they will override the values of the original message.

Example 13.11. Generating messages with inherited values

The following action generates a message that is identical to the original message, but its $PROGRAM field is set to overriding-original-program-name

<actions>
    <action>
        <message inherit-properties='TRUE'>
            <values>
                <value name="PROGRAM">overriding-original-program-name</value>
            </values>
        </message>
    </action>
</actions>
Example 13.12. Creating a new context from an action

In syslog-ng OSE version 3.8 and newer, you can create a new context as an action. For details, see Section 13.5.3.13, Element: create-context.

The following example creates a new context whenever the rule matches. The new context receives 1000 as ID, and program as scope, and the content set in the <message> element of the <create-context> element.

<rule provider='test' id='12' class='violation'>
  <patterns>
    <pattern>simple-message-with-action-to-create-context</pattern>
  </patterns>
  <actions>
    <action trigger='match'>
      <create-context context-id='1000' context-timeout='60' context-scope='program'>
        <message inherit-properties='context'>
          <values>
            <value name='MESSAGE'>context message</value>
          </values>
        </message>
      </create-context>
    </action>
  </actions>
</rule>

For details on configuring actions, see the description of the pattern database format.