syslog-ng Open Source Edition 3.16 - 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 network: Collecting messages using the RFC3164 protocol (network() driver) nodejs: Receiving JSON messages from nodejs applications mbox: Converting local e-mail 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 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 elasticsearch: Sending messages directly to Elasticsearch version 1.x elasticsearch2: Sending logs directly to Elasticsearch and Kibana 2.0 or higher 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 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() redis: Storing name-value pairs in Redis riemann: Monitoring your data with Riemann smtp: Generating SMTP messages (e-mail) from logs 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: Forwarding messages and tags 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
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 Third-party contributions Creative Commons Attribution Non-commercial No Derivatives (by-nc-nd) License About us

Customize message format using macros and templates

The following sections describe how to customize the names of logfiles, and also how to use templates, macros, and template functions.

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Formatting messages, filenames, directories, and tablenames

The syslog-ng OSE application can dynamically create filenames, directories, or names of database tables using macros that help you organize your log messages. Macros refer to a property or a part of the log message, for example, the ${HOST} macro refers to the name or IP address of the client that sent the log message, while ${DAY} is the day of the month when syslog-ng has received the message. Using these macros in the path of the destination log files allows you for example to collect the logs of every host into separate files for every day.

A set of macros can be defined as a template object and used in multiple destinations.

Another use of macros and templates is to customize the format of the syslog message, for example, to add elements of the message header to the message text.


If a message uses the IETF-syslog format (RFC5424), only the text of the message can be customized (that is, the $MESSAGE part of the log), the structure of the header is fixed.

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Templates and macros

The syslog-ng OSE application allows you to define message templates, and reference them from every object that can use a template. Templates can include strings, macros (for example date, the hostname, and so on), and template functions. For example, you can use templates to create standard message formats or filenames. For a list of macros available in syslog-ng Open Source Edition, see Macros of syslog-ng OSE. Fields from the structured data (SD) part of messages using the new IETF-syslog standard can also be used as macros.

template <template-name> {
    template("<template-expression>") <template-escape(yes)>;

Template objects have a single option called template-escape(), which is disabled by default (template-escape(no)). This behavior is useful when the messages are passed to an application that cannot handle escaped characters properly. Enabling template escaping (template-escape(yes)) causes syslog-ng to escape the ', ", and backslash characters from the messages.

If you do not want to enable the template-escape() option (which is rarely needed), you can define the template without the enclosing braces.

template <template-name> "<template-expression>";

You can also refer to an existing template from within a template. The result of the referred template will be pasted into the second template.

template first-template "sample-text";
template second-template "The result of the first-template is: $(template first-template)";

If you want to use a template only once, you can define the template inline, for example:

destination d_file {
    file ("/var/log/messages" template("${ISODATE} ${HOST} ${MESSAGE}\n") );

Macros can be included by prefixing the macro name with a $ sign, just like in Bourne compatible shells. Although using braces around macro names is not mandatory, and the "$MESSAGE" and "${MESSAGE}" formats are equivalent, using the "${MESSAGE}" format is recommended for clarity.

To use a literal $ character in a template, you have to escape it. In syslog-ng OSE versions 3.4 and earlier, use a backslash (\$). In version 3.5 and later, use $$.


To use a literal @ character in a template, use @@.

Default values for macros can also be specified by appending the :- characters and the default value of the macro. If a message does not contain the field referred to by the macro, or it is empty, the default value will be used when expanding the macro. For example, if a message does not contain a hostname, the following macro can specify a default hostname.


By default, syslog-ng sends messages using the following template: ${ISODATE} ${HOST} ${MSGHDR}${MESSAGE}\n. (The ${MSGHDR}${MESSAGE} part is written together because the ${MSGHDR} macro includes a trailing whitespace.)

Example: Using templates and macros

The following template (t_demo_filetemplate) adds the date of the message and the name of the host sending the message to the beginning of the message text. The template is then used in a file destination: messages sent to this destination (d_file) will use the message format defined in the template.

template t_demo_filetemplate {
    template("${ISODATE} ${HOST} ${MESSAGE}\n");
destination d_file {
    file("/var/log/messages" template(t_demo_filetemplate));

If you do not want to enable the template-escape() option (which is rarely needed), you can define the template without the enclosing braces. The following two templates are equivalent.

template t_demo_template-with-braces {
    template("${ISODATE} ${HOST} ${MESSAGE}\n");
template t_demo_template-without-braces "${ISODATE} ${HOST} ${MESSAGE}\n";

Templates can also be used inline, if they are used only at a single location. The following destination is equivalent with the previous example:

destination d_file {
    file ("/var/log/messages" template("${ISODATE} ${HOST} ${MESSAGE}\n") );

The following file destination uses macros to daily create separate logfiles for every client host.

destination d_file {


Macros can be used to format messages, and also in the name of destination files or database tables. However, they cannot be used in sources as wildcards, for example, to read messages from files or directories that include a date in their name.

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Date-related macros

The macros related to the date of the message (for example: ${ISODATE}, ${HOUR}, and so on) have three further variants each:

  • S_ prefix, for example, ${S_DATE}: The ${S_DATE} macro represents the date found in the log message, that is, when the message was sent by the original application.


    To use the S_ macros, the keep-timestamp() option must be enabled (this is the default behavior of syslog-ng OSE).

  • R_ prefix, for example, ${R_DATE}: ${R_DATE} is the date when syslog-ng OSE has received the message.

  • C_ prefix, for example, ${C_DATE}: ${C_DATE} is the current date, that is when syslog-ng OSE processes the message and resolves the macro.

The ${DATE} macro equals the ${S_DATE} macro.

The values of the date-related macros are calculated using the original timezone information of the message. To convert it to a different timezone, use the time-zone() option. You can set the time-zone() option as a global option, or per destination. For sources, it applies only if the original message does not contain timezone information. Converting the timezone changes the values of the following date-related macros (macros MSEC and USEC are not changed):

  • AMPM

  • DATE

  • DAY


  • HOUR

  • HOUR12


  • MIN





  • SEC


  • TZ



  • WEEK




  • YEAR


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