OPTIONAL — A container element describing an action that is performed when a message matching the rule is received.
condition: A syslog-ng filter expression. The action is performed only if the message matches the filter. The filter can include macros and name-value pairs extracted from the message. When using actions together with message-correlation, you can also use the $(context-length) macro, which returns the number of messages in the current context. For example, this can be used to determine if the expected number of messages has arrived to the context: condition='"$(context-length)" >= "5"'
rate: Specifies maximum how many messages should be generated in the specified time period in the following format: <number-of-messages>/<period-in-seconds>. For example: 1/60 allows 1 message per minute. Rates apply within the scope of the context, that is, if context-scope="host" and rate="1/60", then maximum one message is generated per minute for every host that sends a log message matching the rule. Excess messages are dropped. Note that when applying the rate to the generated messages, syslog-ng OSE uses the timestamps of the log messages, similarly to calculating the context-timeout. That way rate is applied correctly even if the log messages are processed offline.
trigger: Specifies when the action is executed. The trigger attribute has the following possible values:
match: Execute the action immediately when a message matching the rule is received.
timeout: Execute the action when the correlation timer (context-timeout) of the pattern database rule expires. This is available only if actions are used together with correlating messages.
message: A container element storing the message to be sent when the action is executed. Currently syslog-ng OSE sends these messages to the internal() destination.
For details on the message context, see Correlating log messages using pattern databases and Actions and message correlation. For details on triggering messages, see Triggering actions for identified messages
inherit-mode: This attribute controls which name-value pairs and tags are propagated to the newly generated message.
context: syslog-ng OSE collects every name-value pair from each message stored in the context, and includes them in the generated message. If a name-value pair appears in multiple messages of the context, the value in the latest message will be used. Note that tags are not merged, the generated message will inherit the tags assigned to the last message of the context.
last-message: Only the name-value pairs appearing in the last message are copied. If the context contains only a single message, then it is the message that triggered the action.
none: An empty message is created, without inheriting any tags or name-value pairs.
This option is available in syslog-ng OSE 3.8 and later.
inherit-properties: This attribute is deprecated. Use the inherit-mode attribute instead.
If set to TRUE, the original message that triggered the action is cloned, including its name-value pairs and tags.
If set to context, syslog-ng OSE collects every name-value pair from each message stored in the context, and includes them in the generated message. If a name-value pair appears in multiple messages of the context, the value in the latest message will be used. Note that tags are not merged, the generated message will inherit the tags assigned to the last message of the context.
For details on the message context, see Correlating log messages using pattern databases and Actions and message correlation. For details on triggering messages, see Triggering actions for identified messages
values: A container element for values and fields that are used to create the message generated by the action.
value: Sets the value of the message field specified in the name attribute of the element. For example, to specify the body of the generated message, use the following syntax:
<value name="MESSAGE">A log message matched rule number $.classifier.rule_id</value>
Note that currently it is not possible to add DATE, FACILITY, or SEVERITY fields to the message.
When the action is used together with message correlation, the syslog-ng OSE application automatically adds fields to the message based on the context-scope parameter. For example, using context-scope="process" automatically fills the HOST, PROGRAM, and PID fields of the generated message.
name: Name of the message field set by the value element.
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.
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>OPTIONAL — Creates a new correlation context from the current message and its associated context. This can be used to "split" a context.
Available in syslog-ng OSE version
context-id: OPTIONAL — An identifier to group related log messages when using the pattern database to correlate events. The ID can be a descriptive string describing the events related to the log message (for example, ssh-sessions for log messages related to SSH traffic), but can also contain macros to generate IDs dynamically. When using macros in IDs, see also the context-scope attribute. Starting with syslog-ng OSE version
The syslog-ng OSE application determines the context of the message after the pattern matching is completed. This means that macros and name-value pairs created by the matching pattern database rule can be used as context-id macros.
context-timeout: OPTIONAL — The number of seconds the context is stored. Note that for high-traffic log servers, storing open contexts for long time can require significant amount of memory. For details on correlating messages, see Correlating log messages using pattern databases.
context-scope: OPTIONAL — Specifies which messages belong to the same context. This attribute is used to determine the context of the message if the context-id does not specify any macros. Usually, context-scope acts a filter for the context, with context-id refining the filtering if needed. The following values are available:
process: Only messages that are generated by the same process of a client belong to the same context, that is, messages that have identical ${HOST}, ${PROGRAM} and ${PID} values. This is the default behavior of syslog-ng OSE if context-scope is not specified.
program: Messages that are generated by the same application of a client belong to the same context, that is, messages that have identical ${HOST} and ${PROGRAM} values.
host: Every message generated by a client belongs to the same context, only the ${HOST} value of the messages must be identical.
global: Every message belongs to the same context.
Using the context-scope attribute is significantly faster than using macros in the context-id attribute.
For details on correlating messages, see Correlating log messages using pattern databases.
message: A container element storing the message that is added to the new context when the action is executed.
inherit-mode: This attribute controls which name-value pairs and tags are propagated to the newly generated message.
context: syslog-ng OSE collects every name-value pair from each message stored in the context, and includes them in the generated message. If a name-value pair appears in multiple messages of the context, the value in the latest message will be used. Note that tags are not merged, the generated message will inherit the tags assigned to the last message of the context.
last-message: Only the name-value pairs appearing in the last message are copied. If the context contains only a single message, then it is the message that triggered the action.
none: An empty message is created, without inheriting any tags or name-value pairs.
For details on the message context, see Correlating log messages using pattern databases and Actions and message correlation. For details on triggering messages, see Triggering actions for identified messages
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>OPTIONAL — An element containing custom keywords (tags) about the messages matching the patterns. The tags can be used to label specific events (for example, user logons). It is also possible to filter on these tags later (for details, see Tagging messages). Starting with syslog-ng Open Source Edition 3.2, the list of tags assigned to a message can be referenced with the ${TAGS} macro.
N/A
tag: OPTIONAL — A keyword or tags applied to messages matching the rule.
<tags><tag>UserLogin</tag></tags>
The syslog-ng OSE application can correlate log messages. Alternatively, you can also correlate log messages using pattern databases. For details, see Correlating log messages using pattern databases.
To group or correlate log messages that match a set of filters, use the grouping-by parser. This works similarly to SQL GROUP BY statements. For details, see Correlating messages using the grouping-by() parser.
You can correlate log messages identified using pattern databases. For details, see Correlating log messages using pattern databases.
Log messages are supposed to describe events, but applications often separate information about a single event into different log messages. For example, the Postfix email server logs the sender and recipient addresses into separate log messages, or in case of an unsuccessful login attempt, the OpenSSH server sends a log message about the authentication failure, and the reason of the failure in the next message. Of course, messages that are not so directly related can be correlated as well, for example, login-logout messages, and so on.
To correlate log messages with syslog-ng OSE, you can add messages into message-groups called contexts. A context consists of a series of log messages that are related to each other in some way, for example, the log messages of an SSH session can belong to the same context. As new messages come in, they may be added to a context. Also, when an incoming message is identified it can trigger actions to be performed, for example, generate a new message that contains all the important information that was stored previously in the context.
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