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syslog-ng Premium Edition 7.0.24 - Administration Guide

Preface Introduction to syslog-ng The concepts of syslog-ng Installing syslog-ng PE The syslog-ng PE quick-start guide The syslog-ng PE configuration file Collecting log messages — sources and source drivers
How sources work default-network-drivers: Receive and parse common syslog messages internal: Collecting internal messages file: Collecting messages from text files google-pubsub: collecting messages from the Google Pub/Sub messaging service wildcard-file: Collecting messages from multiple text files linux-audit: Collecting messages from Linux audit logs mssql, oracle, sql: collecting messages from an SQL database network: Collecting messages using the RFC3164 protocol (network() driver) office365: Fetching logs from Office 365 osquery: Collect and parse osquery result logs pipe: Collecting messages from named pipes program: Receiving messages from external applications python: writing server-style Python sources python-fetcher: writing fetcher-style Python sources snmptrap: Read Net-SNMP traps 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 udp-balancer: Receiving UDP messages at very high rate unix-stream, unix-dgram: Collecting messages from UNIX domain sockets windowsevent: Collecting Windows event logs
Sending and storing log messages — destinations and destination drivers
elasticsearch2: Sending messages directly to Elasticsearch version 2.0 or higher (DEPRECATED) elasticsearch-http: Sending messages to Elasticsearch HTTP Event Collector file: Storing messages in plain-text files google_pubsub: Sending logs to the Google Cloud Pub/Sub messaging service hdfs: Storing messages on the Hadoop Distributed File System (HDFS) http: Posting messages over HTTP kafka: Publishing messages to Apache Kafka logstore: Storing messages in encrypted files mongodb: Storing messages in a MongoDB database network: Sending messages to a remote log server using the RFC3164 protocol (network() driver) pipe: Sending messages to named pipes program: Sending messages to external applications python: writing custom Python destinations sentinel: Sending logs to the Microsoft Azure Sentinel cloud snmp: Sending SNMP traps smtp: Generating SMTP messages (email) from logs splunk-hec: Sending messages to Splunk HTTP Event Collector sql: Storing messages in an SQL database stackdriver: Sending logs to the Google Stackdriver cloud 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) unix-stream, unix-dgram: Sending messages to UNIX domain sockets usertty: Sending messages to a user terminal — usertty() destination Client-side failover
Routing messages: log paths, flags, and filters Global options of syslog-ng PE TLS-encrypted message transfer Advanced Log Transfer Protocol Reliability and minimizing the loss of log messages Manipulating messages parser: Parse and segment structured messages Processing message content with a pattern database Correlating log messages Enriching log messages with external data Monitoring statistics and metrics of syslog-ng Multithreading and scaling in syslog-ng PE Troubleshooting syslog-ng Best practices and examples The syslog-ng manual pages Glossary

Reusing configuration blocks

To create a reusable configuration snippet and reuse parts of a configuration file, you have to define the block (for example, a source) once, and reference it later. (Such reusable blocks are sometimes called a Source Configuration Library, or SCL.) Any syslog-ng object can be a block. Use the following syntax to define a block:

block type name() {<contents of the block>};

Type must be one of the following: destination, filter, log, parser, rewrite, root, source. The root blocks can be used in the "root" context of the configuration file, that is, outside any other statements.

Blocks may be nested into each other, so for example, a block can be built from other blocks. Blocks are somewhat similar to C++ templates.

The type and name combination of each block must be unique, that is, two blocks can have the same name if their type is different.

To use a block in your configuration file, you have to do two things:

  • Include the file defining the block in the syslog-ng.conf file — or a file already included into syslog-ng.conf. Version 7.0 and newer automatically includes the *.conf files from the <directory-where-syslog-ng-is-installed>/scl/*/ directories.

  • Reference the name of the block in your configuration file. This will insert the block into your configuration. For example, to use a block called myblock, include the following line in your configuration:


    Blocks may have parameters, but even if they do not, the reference must include opening and closing parentheses like in the previous example.

The contents of the block will be inserted into the configuration when syslog-ng PE is started or reloaded.

Example: Reusing configuration blocks

Suppose you are running an application on your hosts that logs into the /opt/var/myapplication.log file. Create a file (for example, myblocks.conf) that stores a source describing this file and how it should be read:

block source myappsource() {

Include this file in your main syslog-ng configuration file, reference the block, and use it in a logpath:

@version: 7.0
@include "<correct/path>/myblocks.conf"
source s_myappsource {
log {

To define a block that defines more than one object, use root as the type of the block, and reference the block from the main part of the syslog-ng PE configuration file.

Example: Defining blocks with multiple elements

The following example defines a source, a destination, and a log path to connect them.

block root mylogs() {
    source s_file {
    destination d_local {
    log {

TIP: Since the block is inserted into the syslog-ng PE configuration when syslog-ng PE is started, the block can be generated dynamically using an external script if needed. This is useful when you are running syslog-ng PE on different hosts and you want to keep the main configuration identical.

If you want to reuse more than a single configuration object, for example, a logpath and the definitions of its sources and destinations, use the include feature to reuse the entire snippet. For details, see Including configuration files.

Mandatory parameters

You can express in block definitons that a parameter is mandatory by defining it with empty brackets (). In this case, the parameter must be overridden in the reference block. Failing to do so will result in an error message and initialization failure.

To make a parameter expand into nothing (for example, because it has no default value, like hook-commands() or tls()), insert a pair of double quote marks inside the empty brackets: ("")

Example: Mandatory parameters

The following example defines a TCP source that can receive the following parameters: the port where syslog-ng PE listens (localport), and optionally source flags (flags).

block source my_tcp_source(localport() flags("")) {
    network(port(`localport`) transport(tcp) flags(`flags`));

Because localport is defined with empty brackets (), it is a mandatory parameter. However, the flags parameter is not mandatory, because it is defined with an empty double quote bracket pair (""). If you do not enter a specific value when referencing this parameter, the value will be an empty string. This means that in this case


will be expanded to:

network(port(8080) transport(tcp) flags());
Passing arguments to configuration blocks

Configuration blocks can receive arguments as well. The parameters the block can receive must be specified when the block is defined, using the following syntax:

block type block_name(argument1(<default-value-of-the-argument>) argument2(<default-value-of-the-argument>) argument3())

If an argument does not have a default value, use an empty double quote bracket pair ("") after the name of the argument. To refer the value of the argument in the block, use the name of the argument between backticks (for example, `argument1`).

Example: Passing arguments to blocks

The following sample defines a file source block, which can receive the name of the file as a parameter. If no parameter is set, it reads messages from the /var/log/messages file.

block source s_logfile (filename("messages")) {

source s_example {

If you reference the block with more arguments then specified in its definition, you can use these additional arguments as a single argument-list within the block. That way, you can use a variable number of optional arguments in your block. This can be useful when passing arguments to a template, or optional arguments to an underlying driver.

The three dots () at the end of the argument list refer to any additional parameters. It tells syslog-ng PE that this macro accepts `__VARARGS__`, therefore any name-value pair can be passed without validation. To reference this argument-list, insert `__VARARGS__` to the place in the block where you want to insert the argument-list. Note that you can use this only once in a block.

The following definition extends the logfile block from the previous example, and passes the optional arguments (follow-freq(1) flags(no-parse)) to the file() source.

block source s_logfile(filename("messages") ...) {
    file("/var/log/`filename`" `__VARARGS__`);

source s_example {

Generating configuration blocks from a script

The syslog-ng PE application can automatically execute scripts when it is started, and can include the output of such script in the configuration file. The following describes how to create and use a script that generates a part of the syslog-ng PE configuration file (actually, a configuration block). The steps include examples for collecting Apache access log files (access.log) from subdirectories, but you can create any script that creates a valid syslog-ng PE configuration snippet.

To create and use a script that generates a part of the syslog-ng PE configuration file (actually, a configuration block)

  1. Navigate to the directory where you have installed syslog-ng PE (for example, /opt/syslog-ng/share/include/scl/), and create a new directory, for example, apache-access-logs. The name of the directory will be used in the syslog-ng PE configuration file as well, so use a descriptive name.

  2. Create a file called plugin.conf in this new directory.

  3. Edit the plugin.conf file and add the following line:

    @module confgen context(source) name(<directory-name>) exec("`scl-root`/<directory-name>/<my-script>")

    Replace <directory-name> with the name of the directory (for example, apache-access-logs), and <my-script> with the filename of your script (for example, You can reference the script in your syslog-ng PE configuration file as a configuration block using the value name option.

    The context option determines the type of the configuration snippet that the script generates, and must be one of the following: destination, filter, log, parser, rewrite, root, source. The root blocks can be used in the "root" context of the configuration file, that is, outside any other statements. In the example, context(source) means that the output of the script will be used within a source statement.

  4. Write a script that generates the output you need, and formats it to a configuration snippet that syslog-ng PE can use. The filename of the script must match with the filename used in plugin.conf, for example,

    The following example checks the /var/log/apache2/ directory and its subdirectories, and creates a source driver for every directory that contains an access.log file.

    for i in `find /var/log/apache2/ -type d`; do
        echo "file(\"$i/access.log\" flags(no-parse) program_override(\"apache2\"));";

    The script generates an output similar to this one, where service* is the actual name of a subdirectory:

  5. Include the plugin.conf file in the syslog-ng.conf file — or a file already included into syslog-ng.conf. Version 7.0 and newer automatically includes the *.conf files from the <directory-where-syslog-ng-is-installed>/scl/*/ directories. For details on including configuration files, see Including configuration files.

  6. Add the block you defined in the plugin.conf file to your syslog-ng PE configuration file. You can reference the block using the value of the name option from the plugin.conf file, followed by parentheses, for example, apache-access-logs(). Make sure to use the block in the appropriate context of the configuration file, for example, within a source statement if the value of the context option in the plugin.conf file is source.

    @include "scl.conf"
    source s_apache {
    log {
  7. Check if your modified syslog-ng PE configuration file is syntactically correct using the syslog-ng --syntax-only command.

  8. If your modified configuration is syntactically correct, load the new configuration file using the syslog-ng-ctl reload command.

Python code in external files

You can extend and customize syslog-ng PE easily by writing destinations, parsers, template functions, and sources in Python.

Instead of writing Python code into your syslog-ng PE configuration file, you can store the Python code for your Python object in an external file. That way, it is easier to write, maintain, and debug the code. You can store the Python code in any directory in your system, but make sure to include it in your Python path.

When referencing a Python class from an external file in the class() option of a Python block in the syslog-ng PE configuration file, the class name must include the name of the Python file containing the class, without the path and the .py extension. For example, if the MyDestination class is available in the /etc/syslog-ng/etc/ file, use class("pythonexample.MyDestination"):

destination d_python_to_file {
log {

If you store the Python code in a separate Python file and only include it in the syslog-ng PE configuration file, make sure that the PYTHON_PATH environment variable includes the path to the Python file, and export the PYTHON_PATH environment variable. For example, if you start syslog-ng PE manually from a terminal and you store your Python files in the /opt/syslog-ng/etc directory, use the following command: export PYTHONPATH=/opt/syslog-ng/etc

In production, when syslog-ng PE starts on boot, you must configure your startup script to include the Python path. The exact method depends on your operating system. For recent Red Hat Enterprise Linux, Fedora, and CentOS distributions that use systemd, the systemctl command sources the /etc/sysconfig/syslog-ng file before starting syslog-ng PE. (On openSUSE and SLES, /etc/sysconfig/syslog file.) Append the following line to the end of this file: PYTHONPATH="<path-to-your-python-file>", for example, PYTHONPATH="/opt/syslog-ng/etc"

To help debugging and troubleshooting your Python code, you can send log messages to the internal() source of syslog-ng PE. For details, see Logging from your Python code.

Logging from your Python code

You can extend and customize syslog-ng PE easily by writing destinations, parsers, template functions, and sources in Python.

To debug and troubleshoot your Python code, syslog-ng PE allows you to use the logger() method to send log messages to the internal() source of syslog-ng PE. That way the diagnostic messages of your Python code are treated the same way as other such log messages of syslog-ng PE. This has the following benefits:

  • The logger() method respects the log level settings of syslog-ng PE. You can write error, warning, info, debug, and trace level messages.

  • You can follow what your Python code is doing even if syslog-ng PE is running as a daemon in the background.

Logging to the internal() source is available in syslog-ng PE version 7.0.14 and later.

To send log messages to the internal() source from Python

  1. Add the following import to your Python code:

    import syslogng
  2. Create a logger object:

    logger = syslogng.Logger()
  3. Use the logger object in your Python code, for example:"This is a sample log message send from the Python code.")

    You can use the following log levels: logger.error, logger.warning,, logger.debug, logger.trace

  4. Make sure that your syslog-ng PE configuration includes the internal() source, for example:

    source s_internal { internal(); };
    destination d_internal { file("/var/log/internal.txt"); };
    log {source(s_internal); destination(d_internal); };
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