Chapter 14. Correlating log messages
The syslog-ng PE application can correlate log messages. Alternatively, you can also correlate log messages using pattern databases. For details, see Section 13.3, Correlating log messages using pattern databases.
To group or correlate log messages that match a set of filters, use the
grouping-byparser. This works similarly to SQL GROUP BY statements. For details, see Section 14.1, Correlating messages using the
You can correlate log messages identified using pattern databases. For details, see Section 13.3, 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 e-mail 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 PE, 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.