syslog-ng Open Source Edition 3.25 - Administration Guide

Notes about the configuration syntax

When you are editing the syslog-ng configuration file, note the following points:

• The configuration file can contain a maximum of 6665 source / destination / log elements.

• When writing the names of options and parameters (or other reserved words), the hyphen (-) and underscore (_) characters are equivalent, for example, max-connections(10) and max_connections(10) are both correct.

• Numbers can be prefixed with + or - to indicate positive or negative values. Numbers beginning with zero (0) or 0x are treated as octal or hexadecimal numbers, respectively.

  Starting with syslog-ng OSE version 3.5, you can use suffixes for kilo-, mega-, and gigabytes. Use the Kb, Mb, or Gb suffixes for the base-10 version, and Kib, Mib, or Gib for the base-2 version. That is, 2MB means 2000000, while 2MiB means 2097152. For example, to set the log-msg-size() option to 2000000 bytes, use log-msg-size(2Mb).

• You can use commas (,) to separate options or other parameters for readability, syslog-ng completely ignores them. The following declarations are equivalent:

  source s_demo_stream {
      unix-stream("<path-to-socket>" max-connections(10) group(log));
  };
  source s_demo_stream {
      unix-stream("<path-to-socket>", max-connections(10), group(log));
  };

• When enclosing object IDs (for example, the name of a destination) between double-quotes ("mydestination"), the ID can include whitespace as well, for example:

  source "s demo stream" {
      unix-stream("<path-to-socket>" max-connections(10) group(log));
  };

• For notes on using regular expressions, see Regular expressions.

• You can use if {}, elif {}, and else {} blocks to configure conditional expressions. For details, see if-else-elif: Conditional expressions.

Defining configuration objects inline

Starting with syslog-ng OSE 3.4, you can define configuration objects inline, where they are actually used, without having to define them in a separate placement. This is useful if you need an object only once, for example, a filter or a rewrite rule. Every object can be defined inline: sources, destinations, filters, parsers, rewrite rules, and so on.

To define an object inline, use braces instead of parentheses. That is, instead of <object-type> (<object-id>);, you use <object-type> {<object-definition>};

source s_local {
    system();
    internal();
};
destination d_local {
    file("/var/log/messages");
};
log {
    source(s_local);
    destination(d_local);
};

log {
    source {
        system();
        internal();
    };
    destination {
        file("/var/log/messages");
    };
};

Using channels in configuration objects

Starting with syslog-ng OSE3.4, every configuration object is a log expression. Every configuration object is essentially a configuration block, and can include multiple objects. To reference the block, only the top-level object must be referenced. That way you can use embedded log statements, junctions and in-line object definitions within source, destination, filter, rewrite and parser definitions. For example, a source can include a rewrite rule to modify the messages received by the source, and that combination can be used as a simple source in a log statement. This feature allows you to preprocess the log messages very close to the source itself.

To embed multiple objects into a configuration object, use the following syntax. Note that you must enclose the configuration block between braces instead of parenthesis.

<type-of-top-level-object> <name-of-top-level-object> {
    channel {
        <configuration-objects>
    };
};

source s_apache {
    channel {
        source {
			file("/var/log/apache/error.log");
        };
        parser(p_apache_parser);
    };
};
log {
    source(s_apache); ...
};

parser demo-parser() {
    channel {
        junction {
            channel { ... };
            channel { ... };
        };
    };
};

source s_filtered_hosts {
    channel{
        source {
            pipe("/dev/pipe");
            syslog(ip(192.168.0.1) transport("tcp"));
            syslog(ip(127.0.0.1) transport("tcp"));
        };
        filter {
            netmask(10.0.0.0/16);
        };
    };
};

Global and environmental variables

You can 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 (for details, see Regular expressions). 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 (\).

@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));
};

@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));
};