syslog-ng Open Source Edition 3.30 - Administration Guide

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: ("")

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

my_tcp_source(localport(8080))

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`).

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)
    );
};

block source pacct(file("/var/log/account/pacct") follow-freq(1) ...) {
    file("`file`" follow-freq(`follow-freq`) format("pacct") tags(".pacct") `__VARARGS__`);
};

block options setup-dns(use-dns()) {
    keep-hostname(no);
    use-dns(`use-dns`);
    use-fqdn(`use-dns`);
dns-cache(`use-dns`);
};

options {
    setup-dns(use-dns(yes));
};

Purpose:

The syslog-ng OSE application can automatically execute scripts when it is started, and can include the output of such script in the configuration file. To create and use a script that generates a part of the syslog-ng OSE configuration file (actually, a configuration block), complete the following steps. 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 OSE configuration snippet.

Steps:

1. Navigate to the directory where you have installed syslog-ng OSE (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 OSE 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, apache-access-logs.sh). You can reference the script in your syslog-ng OSE 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.

   You can pass parameters to the script. In the script these parameters are available as environment variables, and have the confgen_ prefix. For example, passing the --myparameter parameter becomes available in the script as the confgen_myparameter environment variable.

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

   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.

   #!/bin/bash
   for i in `find /var/log/apache2/ -type d`; do
       echo "file(\"$i/access.log\" flags(no-parse) program-override(\"apache2\"));";
   done;

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

   file("/var/log/apache2/service1/access.log" flags(no-parse) program-override("apache2"));
   file("/var/log/apache2/service2/access.log" flags(no-parse) program-override("apache2"));
   

5. Include the plugin.conf file in the syslog-ng.conf file — or a file already included into syslog-ng.conf. Version 3.7 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 OSE 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 {
       file("/var/log/apache2/access.log" flags(no-parse) program-override("apache2"));
       file("/var/log/apache2/error.log" flags(no-parse) program-override("apache2"));
       file("/var/log/apache2/ssl.log" flags(no-parse) program-override("apache2"));
       apache-access-logs();
   };
   
   log {
       source(s_apache); destination(d_central);
   };
   ...

7. Check if your modified syslog-ng OSE 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.