syslog-ng Premium Edition 7.0.12 - Administration Guide

Defining configuration objects inline

Starting with syslog-ng PE 7.0, you can define configuration objects inline, where they are actually used, without having to define them in a separate object. This is useful if you need an object only once, for example, a filter or a rewrite rule, because it makes the configuration much easier to read. 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 PE 7.0, 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

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.

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)
        );
    };

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.

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'"