Chat now with support
Chat with Support

syslog-ng Premium Edition 6.0.17 - Administration Guide

Preface Chapter 1. Introduction to syslog-ng Chapter 2. The concepts of syslog-ng Chapter 3. Installing syslog-ng Chapter 4. The syslog-ng PE quick-start guide Chapter 5. The syslog-ng PE configuration file Chapter 6. Collecting log messages — sources and source drivers Chapter 7. Sending and storing log messages — destinations and destination drivers Chapter 8. Routing messages: log paths, reliability, and filters Chapter 9. Global options of syslog-ng PE Chapter 10. TLS-encrypted message transfer Chapter 11. FIPS-compliant syslog-ng Chapter 12.  Reliable Log Transfer Protocol™ Chapter 13. Reliability and minimizing the loss of log messages Chapter 14. Manipulating messages Chapter 15. Parsing and segmenting structured messages Chapter 16. Processing message content with a pattern database Chapter 17. Statistics and metrics of syslog-ng Chapter 18. Multithreading and scaling in syslog-ng PE Chapter 19. Troubleshooting syslog-ng Chapter 20. Best practices and examples

Global and environmental variables

Starting with syslog-ng PE version 4 F1, it is possible to define global variables in the configuration file. Global variables are actually name-value pairs. When syslog-ng processes the configuration file during startup, it automatically replaces `name` with value. To define a global variable, use the following syntax:

@define name "value"

The value can be any string, but special characters must be escaped. To use the variable, insert the name of the variable enclosed between backticks (`, similarly to using variables in Linux or UNIX shells) anywhere in the configuration file. If backticks are meant literally, repeat the backticks to escape them. For example, ``not-substituted-value``.

The value of the global variable can be also specified using the following methods:

  • Without any quotes, as long as the value does not contain any spaces or special characters. In other word, it contains only the following characters: a-zA-Z0-9_..

  • Between apostrophes, in case the value does not contain apostrophes.

  • Between double quotes, in which case special characters must be escaped using backslashes (\).


The environmental variables of the host are automatically imported and can be used as global variables.

Example 5.3. Using global variables

For example, if an application is creating multiple log files in a directory, you can store the path in a global variable, and use it in your source definitions.

@define mypath "/opt/myapp/logs"
        source s_myapp_1 { file("`mypath`/access.log" follow-freq(1)); };
        source s_myapp_2 { file("`mypath`/error.log" follow-freq(1)); };
        source s_myapp_3 { file("`mypath`/debug.log" follow-freq(1)); };

The syslog-ng PE application will interpret this as:

@define mypath "/opt/myapp/logs"
        source s_myapp_1 { file("/opt/myapp/logs/access.log" follow-freq(1)); };
        source s_myapp_2 { file("/opt/myapp/logs/error.log" follow-freq(1)); };
        source s_myapp_3 { file("/opt/myapp/logs/debug.log" follow-freq(1)); };

Logging configuration changes

Every time syslog-ng is started, or its configuration is reloaded, it automatically logs the SHA-1 fingerprint of its configuration file using the internal() message source. That way any modification of the configuration of your syslog-ng clients is visible in the central logs. Note that the log message does not contain the exact change, nor can the configuration file be retrieved from the fingerprint. Only the fact of the configuration change can be detected.


Modular configuration files that are included in the main configuration file of syslog-ng PE are included when the fingerprint is calculated. However, other external files (for example, scripts used in program sources or destinations) are excluded, therefore their modifications do not change the fingerprint.

The fingerprint can be examined with the logchksign command-line application, which detects that the fingerprint was indeed generated by a syslog-ng application. Just paste the hashes from the log message after the logchksign command like in the following example:

bin/logchksign "cfg-fingerprint='832ef664ff79df8afc66cd955c0c8aaa3c343f31', cfg-nonce-ndx='0', cfg-signature='785223cfa19ad52b855550be141b00306347b0a9'"

Modules in syslog-ng PE

Modules in syslog-ng PE

The syslog-ng PE application is modular, to increase its flexibility and also to simplify the development of additional modules. Most of the functionality of syslog-ng PE is in separate modules. That way it becomes also possible to finetune the resource requirements of syslog-ng PE, for example, by loading only the modules that are actually used in the configuration, or simply omitting modules that are not used but require large amount of memory.

Each module contains one or more plugins, which add some functionality to syslog-ng PE, for example, a destination or a source driver.

  • To display the list of available modules, execute the syslog-ng --version command.

  • To the description of the available modules, execute the syslog-ng --module-registry command.

  • To customize which modules are loaded automatically when syslog-ng PE is started, use the --default-modules command-line option of syslog-ng PE.

  • To request loading a module from the syslog-ng PE configuration file, see the section called “Loading modules”.

For details on the command-line parameters of syslog-ng PE mentioned in the previous list, see the syslog-ng PE man page at syslog-ng(8).

Loading modules

The syslog-ng Premium Edition application loads every available module during startup, except the snmp() module, and Java-related modules like hdfs() (Java-related modules require the mod-java module). For details on using the snmp() destination driver, see the section called “Sending SNMP traps”, for details on the hdfs() driver, see the section called “Storing messages on the Hadoop Distributed File System (HDFS)”.

To load a module that is not loaded automatically, include the following statement in the syslog-ng PE configuration file:

@module <module-name>

Note the following points about the @module statement:

  • The @module statement is a top-level statement, that is, it cannot be nested into any other statement. Usually it is used immediately after the @version statement.

  • Every @module statement loads a single module: loading multiple modules requires a separate @module statement for every module.

  • In the configuration file, the @module statement of a module must be earlier than the module is used.

Managing complex syslog-ng configurations

The following sections describe some methods that can be useful to simplify the management of large-scale syslog-ng PE installations. If you are using Puppet to manage your IT infrastructure, you can use it to manage your syslog-ng PE configurations as well. For details, see Procedure 3.10, “Managing syslog-ng PE from Puppet”.

Including configuration files

The syslog-ng application supports including external files in its configuration file, so parts of its configuration can be managed separately. To include the contents of a file in the syslog-ng configuration, use the following syntax:

@include "<path to filename>"


If you enter only the filename, syslog-ng PE will search for the file in the default directory: /opt/syslog-ng/etc. If syslog-ng PE has been installed to a different directory, use the full path instead.

This imports the entire file into the configuration of syslog-ng PE, at the location of the include statement. The <filename> can be one of the following:

  • A filename, optionally with full path. The filename (not the path) can include UNIX-style wildcard characters (*, ?). When using wildcard characters, syslog-ng PE will include every matching file. For details on using wildcard characters, see the section called “glob”.

  • A directory. When including a directory, syslog-ng PE will try to include every file from the directory, except files beginning with a ~ (tilde) or a . (dot) character. Including a directory is not recursive. The files are included in alphabetic order, first files beginning with uppercase characters, then files beginning with lowercase characters. For example, if the directory contains the a.conf, B. conf, c.conf, D.conf files, they will be included in the following order: B.conf, D. conf, a.conf, c.conf.

When including configuration files, consider the following points:

  • If an object is defined twice (for example the original syslog-ng configuration file and the file imported into this configuration file both define the same option, source, or other object), then the object that is defined later in the configuration file will be effective. For example, if you set a global option at the beginning of the configuration file, and later include a file that defines the same option with a different value, then the option defined in the imported file will be used.

  • Files can be embedded into each other: the included files can contain include statements as well, up to a maximum depth of 15 levels.

  • You cannot include complete configuration files into each other, only configuration snippets can be included. This means that the included file cannot have a @version statement.

  • Include statements can only be used at top level of the configuration file. For example, the following is correct:

    @version: 6.0
    @include "example.conf"

    But the following is not:

    source s_example {
        @include "example.conf"


The syslog-ng application will not start if it cannot find a file that is to be included in its configuration. Always double-check the filenames, paths, and access rights when including configuration files, and use the --syntax-only command-line option to check your configuration.

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.

  • 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 5.4. 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() {
        file("/opt/var/myapplication.log" follow-freq(1) default-facility(syslog)); };

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

@version: 6.0
@include "<correct/path>/myblocks.conf"
source s_myappsource { myappsource(); };
log { source(s_myappsource); destination(...); };

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 5.5. 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 { file("/var/log/mylogs.log" follow-freq(1)); };
        destination d_local { file("/var/log/messages"); };
        log { source(s_file); destination(d_local); };


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 the section called “Including configuration files”.

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, add parentheses with empty quotes after the name of the argument, like this: example-option(""). To refer the value of the argument in the block, use the name of the argument between backticks (for example, `argument1`).

Example 5.6. 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")) {
  file("/var/log/`filename`" );

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. 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 {
  s_logfile(filename("logfile.log") follow-freq(1) flags(no-parse));
Related Documents

The document was helpful.

Select Rating

I easily found the information I needed.

Select Rating