Loading modules
The syslog-ng Open Source Edition application loads every available module during startup.
To load a module that is not loaded automatically, include the following statement in the syslog-ng OSE configuration file:
@module <module-name>
Note the following points about the @module statement:
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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.
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Every @module statement loads a single module: loading multiple modules requires a separate @module statement for every module.
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In the configuration file, the @module statement of a module must be earlier than the module is used.
Use the @requires statement to ensure that the specified module is loaded
To ensure that a module is loaded, include the following statement in the syslog-ng OSE configuration file or the external files included in the configuration file:
@requires <module-name>
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NOTE:
If you include the @requires statement in the:
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Managing complex syslog-ng configurations
The following sections describe some methods that can be useful to simplify the management of large-scale syslog-ng installations.
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 "<filename>"
This imports the entire file into the configuration of syslog-ng OSE, at the location of the include statement. The <filename> can be one of the following:
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A filename, optionally with full path. The filename (not the path) can include UNIX-style wildcard characters (*, ?). When using wildcard characters, syslog-ng OSE will include every matching file. For details on using wildcard characters, see glob.
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A directory. When including a directory, syslog-ng OSE 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:
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Defining an object twice is not allowed, unless you use the @define allow-config-dups 1 definition in the configuration file. 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.
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Files can be embedded into each other: the included files can contain include statements as well, up to a maximum depth of 15 levels.
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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.
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Include statements can only be used at top level of the configuration file. For example, the following is correct:
@version: 3.18 @include "example.conf"
But the following is not:
source s_example { @include "example.conf" };
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Caution:
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:
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Include the file defining the block in the syslog-ng.conf file — or a file already included into syslog-ng.conf. Version
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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:
myblock()
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 OSE 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() {
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: 3.18
@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 OSE 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 {
file("/var/log/mylogs.log" follow-freq(1));
};
destination d_local {
file("/var/log/messages");
};
log {
source(s_file); destination(d_local);
};
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TIP:
Since the block is inserted into the syslog-ng OSE configuration when syslog-ng OSE is started, the block can be generated dynamically using an external script if needed. This is useful when you are running syslog-ng OSE 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 OSE 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
my_tcp_source(localport(8080))
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")) {
file("/var/log/`filename`" );
};
source s_example {
s_logfile(filename("logfile.log"));
};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 OSE 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 {
s_logfile(
filename("logfile.log")
follow-freq(1)
flags(no-parse)
);
};
Example: Using arguments in blocks
The following example is the code of the pacct() source driver, which is actually a block that can optionally receive two arguments.
block source pacct(file("/var/log/account/pacct") follow-freq(1) ...) {
@module pacctformat
file("`file`" follow-freq(`follow-freq`) format("pacct") tags(".pacct") `__VARARGS__`);
};