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syslog-ng Open Source Edition 3.38 - 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 kubernetes: Collecting and parsing the Kubernetes CRI (Container Runtime Interface) format linux-audit: Collecting messages from Linux audit logs mqtt: receiving messages from an MQTT broker 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 discord: Sending alerts and notifications to Discord 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-c(): Publishing messages to Apache Kafka using the librdkafka client (C implementation) 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
Parsing syslog messages Parsing messages with comma-separated and similar values Parsing key=value pairs JSON parser XML parser Parsing dates and timestamps Python parser Parsing tags Apache access log parser Linux audit parser Cisco parser Parsing enterprise-wide message model (EWMM) messages iptables parser Netskope parser panos-parser(): parsing PAN-OS log messages Sudo parser MariaDB parser Websense parser Fortigate parser Check Point Log Exporter parser Regular expression (regexp) parser 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 The syslog-ng Open Source Edition Documentation License Glossary

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 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");

Setting match variables with the set-matches() rewrite rule

Match macros ($1, $2, ... $255) are temporary variables. You can use them for general purposes when operating with list-like items. For example, the match() filter stores capture group results in match variables when the store-matches flag is set, or the JSON parser produces match variables if the parsed JSON data is an array.

It is possible to set match variables in a single operation with the set-matches() rewrite function. set-matches() uses syslog-ng OSE list expressions to set $1, $2, ... $255, so it can be considered as a conversion function between syslog-ng OSE lists and match variables.

NOTE: To convert match variables into a syslog-ng OSE list, use the $* macro, which can be further manipulated using List manipulation, or turned into a list in type-aware destinations.

TIP: To reset match variables to be empty, use the unset-matches() rewrite rule.

Declaration
rewrite <name_of_the_rule> {
    set-matches("<list-expression or list-based template function>");
};
Example usage for the set-matches() rewrite function

In the following two examples, $1, $2, and $3 will be set to foo, bar, and baz, respectively.

Example using string:

rewrite {
    set-matches("foo,bar,baz");
};

Example using a list template function:

rewrite {
    set-matches("$(explode ':' 'foo:bar:baz')");
};

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.*"));
};

Renaming message fields

If you want to change the name of a field of a message, you can use rename() rewrite rules. This can be also achieved via using set() and unset() but those require extra conditions and two operation instead of one.

The rename() rewrite rule uses positional arguments and they are both required. It supports condition rewrite. For more information, see Conditional rewrites.

Declaration
rewrite r_rewrite_rename {
    rename("<string1>" "<string2>");
};
Example usage for the rename() rewrite function

The following example renames the .app.name into .container if the .app.name exists. Otherwise, it does nothing.

rewrite r_rewrite_rename {
    rename(".app.name" ".container");
};
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