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syslog-ng Open Source Edition 3.30 - 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 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 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

Adding metadata from an external file

In syslog-ng OSE version 3.8 and later, you can use an external database file to add additional metadata to your log messages. For example, you can create a database (or export it from an existing tool) that contains a list of hostnames or IP addresses, and the department of your organization that the host belongs to, the role of the host (mailserver, webserver, and so on), or similar contextual information.

The database file is a simple text file in comma-separated value (CSV) format, where each line contains the following information:

  • A selector or ID that appears in the log messages, for example, the hostname. To use shell-style globbing (wildcards) in selectors, see Shell-style globbing in the selector. You can also reference the name of a filter that matches the messages, see Using filters as selector

  • The name of the name-value pair that syslog-ng OSE adds to matching log messages.

  • The value of the name-value pairs. Starting with syslog-ng OSE version 3.22, the value of the name-value pair can be a template or a template function, for example, "selector3,name,$(echo $HOST_FROM)";

For example, the following csv-file contains three lines identified with the IP address, and adds the host-role field to the log message.,host-role,webserver,host-role,firewall,host-role,mailserver
The database file:

The database file must comply with the RFC4180 CSV format, with the following exceptions and limitations:

  • The values of the CSV-file cannot contain line-breaks

To add multiple name-value pairs to a message, include a separate line in the database for each name-value pair, for example:,host-role,webserver,contact-person,"John Doe",contact-email,

Technically, add-contextual-data() is a parser in syslog-ng OSE so you have to define it as a parser object.

parser p_add_context_data {

You can also add data to messages that do not have a matching selector entry in the database using the default-selector() option.

If you modify the database file, you have to reload syslog-ng OSE for the changes to take effect. If reloading syslog-ng OSE or the database file fails for some reason, syslog-ng OSE will keep using the last working database file.

Example: Adding metadata from a CSV file

The following example defines uses a CSV database to add the role of the host based on its IP address, and prefixes the added name-value pairs with .metadata. The destination includes a template that simply appends the added name-value pairs to the end of the log message.

@include "scl.conf"

source s_network {

destination d_local {
    template("$MSG Additional metadata:[${}]")};

parser p_add_context_data {
    add-contextual-data(selector("$SOURCEIP"), database("context-info-db.csv"), default-selector("unknown"), prefix(".metadata."));

log {

Using filters as selector

To better control to which log messages you add contextual data, you can use filters as selectors. In this case, the first column of the CSV database file must contain the name of a filter. For each message, syslog-ng OSE evaluates the filters in the order they appear in the database file. If a filter matches the message, syslog-ng OSE adds the name-value pair related to the filter.

For example, the database file can contain the entries. (For details on the accepted CSV-format, see database().)


Note that syslog-ng OSE does not evaluate other filters after the first match. For example, if you use the previous database file, and a message matches both the f_auth and f_localhost filters, syslog-ng OSE adds only the name-value pair of f_auth to the message.

To add multiple name-value pairs to a message, include a separate line in the database for each name-value pair, for example:

f_localhost,contact-person,"John Doe"

You can also add data to messages that do not have a matching selector entry in the database using the default-selector() option.

You must store the filters you reference in a database in a separate file. This file is similar to a syslog-ng OSE configuration file, but must contain only a version string and filters (and optionally comments). You can use the syslog-ng --syntax-only <filename> command to ensure that the file is valid. For example, the content of such a file can be:

@version: 3.30
filter f_localhost { host("") };
filter f_auth { facility(4) };
filter f_kern { facility(0) };
parser p_add_context_data_filter {

If you modify the database file, or the file that contains the filters, you have to reload syslog-ng OSE for the changes to take effect. If reloading syslog-ng OSE or the files fails for some reason, syslog-ng OSE will keep using the last working version of the file.

Shell-style globbing in the selector

Starting with in syslog-ng OSE3.24 and later, you can use shell-style globbing ('*' and '?' wildcards) in the selector.

To use globs in a selector

  1. Use the glob() option within the selector() option in your syslog-ng OSE configuration file, for example:

    parser p_add_context_data {
  2. Use globs and wildcards in the selector column of your CSV-file, for example:


Note the following points when using globbing in the selector:

  • The order of the patterns depends on the CSV-file. The order of entries in the database determines the matching order.

  • The globs are matched against the expanded template string sequentially.

  • Put more specific patterns to the top of the CSV-file. The syslog-ng OSE appication does not evaluate other entries after the first match.

  • In debug mode, syslog-ng OSE sends log messages to its internal() destination to help troubleshooting. For example:

    [2019-09-21T06:01:10.748237] add-contextual-data(): Evaluating glob against message; glob-template='$PROGRAM', string='postfix/smtpd', pattern='example-glob-entry1*', matched='0'
    [2019-09-21T06:01:10.748562] add-contextual-data(): Evaluating glob against message; glob-template='$PROGRAM', string='postfix/smtpd', pattern='example-glob-entry2*', matched='0'
    [2019-09-21T06:01:10.748697] add-contextual-data(): Evaluating glob against message; glob-template='$PROGRAM', string='postfix/smtpd', pattern='postfix*', matched='1'
    [2019-09-21T06:01:10.750084] add-contextual-data(): message lookup finished; message='almafa', resolved_selector='postfix*', selector='postfix*', msg='0x8e15320'

Options add-contextual-data()

The add-contextual-data() has the following options.

Required options:

The following options are required: selector(), database().

Type: <path-to-file>.csv

Description: Specifies the path to the CSV file, for example, /opt/syslog-ng/my-csv-database.csv. The extension of the file must be .csv, and can include Windows-style (CRLF) or UNIX-style (LF) linebreaks. You can use absolute path, or relative to the syslog-ng OSE binary.

Synopsis: default-selector()

Description: Specifies the ID of the entry (line) that is corresponds to log messages that do not have a selector that matches an entry in the database. For example, if you add name-value pairs from the database based on the hostname from the log message (selector("${HOST}")), then you can include a line for unknown hosts in the database, and set default-selector() to the ID of the line for unknown hosts. In the CSV file:


In the syslog-ng OSE configuration file:


Synopsis: ignore-case()



Description: Specifies if selectors are handled as case insensitive. If you set the ignore-case() option to yes, selectors are handled as case insensitive.

Synopsis: prefix()

Description: Insert a prefix before the name part of the added name-value pairs (including the pairs added by the default-selector()) to help further processing.

Synopsis: selector()

Description: Specifies the string or macro that syslog-ng OSE evaluates for each message, and if its value matches the ID of an entry in the database, syslog-ng OSE adds the name-value pair of every matching database entry to the log message. You can use the following in the selector() option.

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