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syslog-ng Open Source Edition 3.33 - 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 mqtt() destination: sending messages from a local network to an MQTT broker 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 Sumo Logic destinations: sumologic-http() and sumologic-syslog() 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

Setting the facility field with the set-facility() rewrite function

It is possible to set the facility field with the set-facility() rewrite function. When set, the set-facility() rewrite function will only rewrite the $PRIORITY field in the message to the first parameter value specified in the function.

NOTE: If the parameter value is not a valid parameter value, the function ignores it and sends a debug message, but the application still sends the message.

Declaration
log {
source { system(); };
if (program("postfix")) {
rewrite { set-facility("mail"); };
};
destination { file("/var/log/mail.log"); };
flags(flow-control);
};
Parameters

The set-facility() rewrite function has a single, mandatory parameter that can be defined as follows:

set-facility( "parameter1" );
Accepted values

The set-facility() rewrite function accepts the following values:

  • numeric strings: [0-7]
  • named values: emerg, emergency, panic, alert, crit, critical, err, error, warning, warn, notice, info, informational, debug
Example usage for the set-facility() rewrite function

The following example can be used in production for the set-facility() rewrite function.

rewrite {
set-facility("info");
set-facility("6");
set-facility("${.json.severity}");};

Setting the priority of a message with the set-pri() rewrite function

You can set the PRI value of a BSD or IETF syslog message with the set-pri() rewrite function by specifying a template string. This is useful, for example, if incoming messages do not have a PRI value specified by default, but a PRI value is required for filtering purposes.

When configured, the set-pri() function will only rewrite the PRI value of the message field.

NOTE: If the specified parameter value is not a valid value, the function ignores it and sends a debug message. However, the syslog-ng Open Source Edition (syslog-ng OSE) application will still send the message.

Declaration
rewrite <rule-name> {
    set-pri("template-string");
};
Parameters

The set-pri() rewrite function expects a template string as its only parameter, for example:

  • set-pri("42");

  • set-pri("$.json.priority");

Accepted values

The template string specified for the set-pri() rewrite function must expand to a natural number in the interval of 0–1023, inclusive. This means that if you, for example, extract the value from a syslog <PRI> header (such as <42>), then you need to remove the opening and closing brackets (< >) in the specified template string.

Example: Temporarily raising the priority of an application

In the following example, the set-pri() rewrite function is used to temporarily raise the priority of the application myprogram:

log {
  source { system(); };
  if (program("myprogram")){
  rewrite { set-pri("92"); };
  };
  destination { file("/var/log/mail.log"); };
  flags(flow-control);
}
Example: Changing the priority of an application log message in JSON format

In the following example, an application sends log messages in the following JSON format:

{
"time": "2003-10-11T22:14:15.003Z",
"host": "mymachine",
"priority": "165",
"message": "An application event log entry."
}

You can parse these logs with the syslog-ng JSON parser function:

{
parser p_json {
json-parser (prefix(".json."));
}

As the application message contains a valid priority field, you can use the set-pri() rewrite function to modify the priority of the message:

set-pri("$.json.priority");

Unsetting message fields

You can unset macros or fields of the message, including any user-defined macros created using parsers (for details, see parser: Parse and segment structured messages and db-parser: Process message content with a pattern database (patterndb)). Note that the unset operation completely deletes any previous value of the field that you apply it on.

NOTE: Hard macros cannot be modified. For details on the hard and soft macros, see Hard versus soft macros).

Use the following syntax:

Declaration:
rewrite <name_of_the_rule> {
    unset(value("<field-name>"));
};
Example: Unsetting a message field

The following example unsets the HOST field of the message.

rewrite r_rewrite_unset{
    unset(value("HOST"));
};

To unset a group of fields, you can use the groupunset() rewrite rule.

Declaration:
rewrite <name_of_the_rule> {
    groupunset(values("<expression-for-field-names>"));
};
Example: Unsetting a group of fields

The following rule clears all SDATA fields:

rewrite r_rewrite_unset_SDATA{
    groupunset(values(".SDATA.*"));
};

Creating custom SDATA fields

If you use RFC5424-formatted (IETF-syslog) messages, you can also create custom fields in the SDATA part of the message (For details on the SDATA message part, see The STRUCTURED-DATA message part). According to RFC5424, the name of the field (its SD-ID) must not contain the @ character for reserved SD-IDs. Custom SDATA fields must be in the following format: .SDATA.group-name@<private enterprise number>.field-name, for example, .SDATA.mySDATA-field-group@18372.4.mySDATA-field. (18372.4 is the private enterprise number of One Identity LLC, the developer of syslog-ng OSE.)

Example: Rewriting custom SDATA fields

The following example sets the sequence ID field of the RFC5424-formatted (IETF-syslog) messages to a fixed value. This field is a predefined SDATA field with a reserved SD-ID, therefore its name does not contain the @ character.

rewrite r_sd {
    set("55555" value(".SDATA.meta.sequenceId"));
};

It is also possible to set the value of a field that does not exist yet, and create a new, custom name-value pair that is associated with the message. The following example creates the .SDATA.groupID.fieldID@18372.4 field and sets its value to yes. If you use the ${.SDATA.groupID.fieldID@18372.4} macro in a template or SQL table, its value will be yes for every message that was processed with this rewrite rule, and empty for every other message.

The next example creates a new SDATA field-group and field called custom and sourceip, respectively:

rewrite r_rewrite_set {
    set("${SOURCEIP}" value(".SDATA.custom@18372.4.sourceip"));
};

If you use the ${.SDATA.custom@18372.4.sourceip} macro in a template or SQL table, its value will be that of the SOURCEIP macro (as seen on the machine where the SDATA field was created) for every message that was processed with this rewrite rule, and empty for every other message.

You can verify whether or not the format is correct by looking at the actual network traffic. The SDATA field-group will be called custom@18372.4, and sourceip will become a field within that group. If you decide to set up several fields, they will be listed in consecutive order within the field-group's SDATA block.

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