syslog-ng Open Source Edition 3.25 - Administration Guide

Preface Introduction to syslog-ng The concepts of syslog-ng Installing syslog-ng The syslog-ng OSE quick-start guide The syslog-ng OSE configuration file source: Read, receive, and collect log messages
How sources work default-network-drivers: Receive and parse common syslog messages internal: Collecting internal messages file: Collecting messages from text files wildcard-file: Collecting messages from multiple text files linux-audit: Collecting messages from Linux audit logs network: Collecting messages using the RFC3164 protocol (network() driver) nodejs: Receiving JSON messages from nodejs applications mbox: Converting local email messages to log messages osquery: Collect and parse osquery result logs pipe: Collecting messages from named pipes pacct: Collecting process accounting logs on Linux program: Receiving messages from external applications python: writing server-style Python sources python-fetcher: writing fetcher-style Python sources snmptrap: Read Net-SNMP traps sun-streams: Collecting messages on Sun Solaris 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— OBSOLETE unix-stream, unix-dgram: Collecting messages from UNIX domain sockets stdin: Collecting messages from the standard input stream
destination: Forward, send, and store log messages
amqp: Publishing messages using AMQP collectd: sending metrics to collectd elasticsearch2: Sending messages directly to Elasticsearch version 2.0 or higher (DEPRECATED) elasticsearch-http: Sending messages to Elasticsearch HTTP Bulk API file: Storing messages in plain-text files graphite: Sending metrics to Graphite Sending logs to Graylog hdfs: Storing messages on the Hadoop Distributed File System (HDFS) Posting messages over HTTP http: Posting messages over HTTP without Java kafka: Publishing messages to Apache Kafka (Java implementation) kafka: Publishing messages to Apache Kafka (C implementation, using the librdkafka client) loggly: Using Loggly logmatic: Using Logmatic.io mongodb: Storing messages in a MongoDB database network: Sending messages to a remote log server using the RFC3164 protocol (network() driver) osquery: Sending log messages to osquery's syslog table pipe: Sending messages to named pipes program: Sending messages to external applications pseudofile() python: writing custom Python destinations redis: Storing name-value pairs in Redis riemann: Monitoring your data with Riemann slack: Sending alerts and notifications to a Slack channel smtp: Generating SMTP messages (email) from logs snmp: Sending SNMP traps Splunk: Sending log messages to Splunk sql: Storing messages in an SQL database stomp: Publishing messages using STOMP 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) Telegram: Sending messages to Telegram unix-stream, unix-dgram: Sending messages to UNIX domain sockets usertty: Sending messages to a user terminal: usertty() destination Write your own custom destination in Java or Python Client-side failover
log: Filter and route log messages using log paths, flags, and filters Global options of syslog-ng OSE TLS-encrypted message transfer template and rewrite: Format, modify, and manipulate log messages parser: Parse and segment structured messages db-parser: Process message content with a pattern database (patterndb) Correlating log messages Enriching log messages with external data Statistics of syslog-ng Multithreading and scaling in syslog-ng OSE Troubleshooting syslog-ng Best practices and examples The syslog-ng manual pages Creative Commons Attribution Non-commercial No Derivatives (by-nc-nd) License Glossary

Element: action

Location

/patterndb/ruleset/actions/action

Description

OPTIONAL — A container element describing an action that is performed when a message matching the rule is received.

Attributes
  • 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.

Children
  • create-context

  • 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.

Example
Example: 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: 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>

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Element: create-context

Location

/patterndb/ruleset/actions/action/create-context

Description

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 3.8 and later.

Attributes
  • 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 3.5, if a message is added to a context, syslog-ng OSE 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 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.

    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.

Children
  • 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

Example

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>

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Element: tags

Location

/patterndb/ruleset/tags

Description

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.

Attributes

N/A

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

Example
<tags><tag>UserLogin</tag></tags>

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Correlating log messages

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.

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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