Chat now with support
Chat with Support

syslog-ng Premium Edition 7.0.33 - Administration Guide

Preface Introduction to syslog-ng The concepts of syslog-ng Installing syslog-ng PE The syslog-ng PE quick-start guide The syslog-ng PE configuration file Collecting log messages — sources and source drivers
How sources work default-network-drivers: Receive and parse common syslog messages internal: Collecting internal messages file: Collecting messages from text files google-pubsub: collecting messages from the Google Pub/Sub messaging service wildcard-file: Collecting messages from multiple text files linux-audit: Collecting messages from Linux audit logs mssql, oracle, sql: collecting messages from an SQL database network: Collecting messages using the RFC3164 protocol (network() driver) office365: Fetching logs from Office 365 osquery: Collect and parse osquery result logs pipe: Collecting messages from named pipes program: Receiving messages from external applications python: writing server-style Python sources python-fetcher: writing fetcher-style Python sources snmptrap: Read Net-SNMP traps syslog: Collecting messages using the IETF syslog protocol (syslog() driver) system: Collecting the system-specific log messages of a platform systemd-journal: Collecting messages from the systemd-journal system log storage systemd-syslog: Collecting systemd messages using a socket tcp, tcp6,udp, udp6: Collecting messages from remote hosts using the BSD syslog protocol udp-balancer: Receiving UDP messages at very high rate unix-stream, unix-dgram: Collecting messages from UNIX domain sockets windowsevent: Collecting Windows event logs
Sending and storing log messages — destinations and destination drivers
elasticsearch2>: Sending messages directly to Elasticsearch version 2.0 or higher (DEPRECATED) elasticsearch-http: Sending messages to Elasticsearch HTTP Event Collector file: Storing messages in plain-text files google_pubsub(): Sending logs to the Google Cloud Pub/Sub messaging service google_pubsub-managedaccount(): Sending logs to the Google Cloud Pub/Sub messaging service authenticated by Google Cloud managed service account hdfs: Storing messages on the Hadoop Distributed File System (HDFS) http: Posting messages over HTTP kafka(): Publishing messages to Apache Kafka (Java implementation) (DEPRECATED) kafka-c(): Publishing messages to Apache Kafka using the librdkafka client (C implementation) logstore: Storing messages in encrypted files mongodb: Storing messages in a MongoDB database network: Sending messages to a remote log server using the RFC3164 protocol (network() driver) pipe: Sending messages to named pipes program: Sending messages to external applications python: writing custom Python destinations sentinel(): Sending logs to the Microsoft Azure Sentinel cloud snmp: Sending SNMP traps smtp: Generating SMTP messages (email) from logs splunk-hec: Sending messages to Splunk HTTP Event Collector sql(): Storing messages in an SQL database stackdriver: Sending logs to the Google Stackdriver cloud syslog: Sending messages to a remote logserver using the IETF-syslog protocol syslog-ng(): Forward logs to another syslog-ng node tcp, tcp6, udp, udp6: Sending messages to a remote log server using the legacy BSD-syslog protocol (tcp(), udp() drivers) unix-stream, unix-dgram: Sending messages to UNIX domain sockets usertty: Sending messages to a user terminal — usertty() destination Client-side failover
Routing messages: log paths, flags, and filters Global options of syslog-ng PE TLS-encrypted message transfer Advanced Log Transport Protocol Reliability and minimizing the loss of log messages Manipulating messages parser: Parse and segment structured messages Processing message content with a pattern database Correlating log messages Enriching log messages with external data Monitoring statistics and metrics of syslog-ng Multithreading and scaling in syslog-ng PE Troubleshooting syslog-ng Best practices and examples The syslog-ng manual pages Glossary

Element: create-context




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 PE version 7 and later.

  • 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 PE version 7.0, if a message is added to a context, syslog-ng PE automatically adds the identifier of the context to the .classifier.context_id macro of the message. For details on correlating messages, see Correlating log messages using pattern databases.

    NOTE: The syslog-ng PE 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 PE 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.

    NOTE: 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 PE 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'>
    <action trigger='match'>
      <create-context context-id='1000' context-timeout='60' context-scope='program'>
        <message inherit-properties='context'>
            <value name='MESSAGE'>context message</value>

Element: tags




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 Premium Edition 3.2, the list of tags assigned to a message can be referenced with the ${TAGS} macro.



  • tag: OPTIONAL — A keyword or tags applied to messages matching the rule.


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 Correlating log messages using pattern databases.

Correlating messages using the grouping-by() parser

The syslog-ng PE application can correlate log messages that match a set of filters. This works similarly to SQL GROUP BY statements. Alternatively, you can also correlate log messages 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 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.

How the grouping-by() parser works

The grouping-by() parser has three options that determine if a message is added to a context: scope(), key(), and where().

  • The scope() option acts as an early filter, selecting messages sent by the same process (${HOST}${PROGRAM}${PID} is identical), application (${HOST}${PROGRAM} is identical), or host.

  • The key() identifies the context the message belongs to. (The value of the key must be the same for every message of the context.)

  • To use a filter to further limit the messages that are added to the context, you can use the where() option.

The timeout() option determines how long a context is stored, that is, how long syslog-ng PE waits for related messages to arrive. If the group has a specific log message that ends the context (for example, a logout message), you can specify it using the trigger() option.

When the context is closed, and the messages match the filter set in the having() option (or the having() option is not set), syslog-ng PE generates and sends the message set in the aggregate() option.

NOTE: Message contexts are persistent and are not lost when syslog-ng PE is reloaded (SIGHUP), but are lost when syslog-ng PE is restarted.

parser parser_name {

For the parser to work, you must set at least the following options: key(), aggregate(), and timeout().

Note the following points about timeout values:

  • When a new message is added to a context, syslog-ng PE will restart the timeout using the context-timeout set for the new message.

  • When calculating if the timeout has already expired or not, syslog-ng PE uses the timestamps of the incoming messages, not system time elapsed between receiving the two messages (unless the messages do not include a timestamp, or the keep-timestamp(no) option is set). That way syslog-ng PE can be used to process and correlate already existing log messages offline. However, the timestamps of the messages must be in chronological order (that is, a new message cannot be older than the one already processed), and if a message is newer than the current system time (that is, it seems to be coming from the future), syslog-ng PE will replace its timestamp with the current system time.

    Example: How syslog-ng PE calculates context-timeout

    Consider the following two messages:

    <38>1990-01-01T14:45:25 customhostname program6[1234]: program6 testmessage
    <38>1990-01-01T14:46:25 customhostname program6[1234]: program6 testmessage

    If the context-timeout is 10 seconds and syslog-ng PE receives the messages within 1 sec, the timeout event will occur immediately, because the difference of the two timestamps (60 sec) is larger than the timeout value (10 sec).

  • Avoid using unnecessarily long timeout values on high-traffic systems, as storing the contexts for many messages can require considerable memory. For example, if two related messages usually arrive within seconds, it is not needed to set the timeout to several hours.

Related Documents

The document was helpful.

Select Rating

I easily found the information I needed.

Select Rating