The `syslog-ng.conf` manual page

Name

syslog-ng.conf — configuration file

Synopsis

syslog-ng.conf

Description

The AxoSyslog application is a flexible and highly scalable system logging application. Typically, AxoSyslog is used to manage log messages and implement centralized logging, where the aim is to collect the log messages of several devices on a single, central log server. The different devices - called syslog-ng clients - all run AxoSyslog, and collect the log messages from the various applications, files, and other sources. The clients send all important log messages to the remote AxoSyslog server, where the server sorts and stores them.

Basic concepts of AxoSyslog

The AxoSyslog application reads incoming messages and forwards them to the selected destinations. The AxoSyslog application can receive messages from files, remote hosts, and other sources.

Log messages enter AxoSyslog in one of the defined sources, and are sent to one or more destinations.

Sources and destinations are independent objects, log paths define what AxoSyslog does with a message, connecting the sources to the destinations. A log path consists of one or more sources and one or more destinations: messages arriving from a source are sent to every destination listed in the log path. A log path defined in AxoSyslog is called a log statement.

Optionally, log paths can include filters. Filters are rules that select only certain messages, for example, selecting only messages sent by a specific application. If a log path includes filters, AxoSyslog sends only the messages satisfying the filter rules to the destinations set in the log path.

Other optional elements that can appear in log statements are parsers and rewriting rules. Parsers segment messages into different fields to help processing the messages, while rewrite rules modify the messages by adding, replacing, or removing parts of the messages.

Configuring AxoSyslog

• The main body of the configuration file consists of object definitions: sources, destinations, logpaths define which log message are received and where they are sent. All identifiers, option names and attributes, and any other strings used in the syslog-ng.conf configuration file are case sensitive. Object definitions (also called statements) have the following syntax:

      type-of-the-object identifier-of-the-object {<parameters>};
  

  • Type of the object: One of source, destination, log, filter, parser, rewrite rule, or template.

    Identifier of the object: A unique name identifying the object. When using a reserved word as an identifier, enclose the identifier in quotation marks ("").

    All identifiers, attributes, and any other strings used in the AxoSyslog configuration file are case sensitive.

    Note Use identifiers that refer to the type of the object they identify. For example, prefix source objects with s_, destinations with d_, and so on.

    Repeating a definition of an object (that is, defining the same object with the same id more than once) is not allowed, unless you use the @define allow-config-dups 1 definition in the configuration file.

  • Parameters: The parameters of the object, enclosed in braces {parameters}.

  • Semicolon: Object definitions end with a semicolon (;).

  For example, the following line defines a source and calls it s_internal.

      source s_internal { internal(); };
  

  The object can be later referenced in other statements using its ID, for example, the previous source is used as a parameter of the following log statement:

      log { source(s_internal); destination(d_file); };
  

• The parameters and options within a statement are similar to function calls of the C programming language: the name of the option followed by a list of its parameters enclosed within brackets and terminated with a semicolon.

      option(parameter1, parameter2); option2(parameter1, parameter2);
  

  For example, the file() driver in the following source statement has three options: the filename (/var/log/apache/access.log), follow-freq(), and flags(). The follow-freq() option also has a parameter, while the flags() option has two parameters.

      source s_tail { file("/var/log/apache/access.log"
      follow-freq(1) flags(no-parse, validate-utf8)); };
  

  Objects may have required and optional parameters. Required parameters are positional, meaning that they must be specified in a defined order. Optional parameters can be specified in any order using the option(value) format. If a parameter (optional or required) is not specified, its default value is used. The parameters and their default values are listed in the reference section of the particular object.

Example: Using required and optional parameters

The unix-stream() source driver has a single required argument: the name of the socket to listen on. Optional parameters follow the socket name in any order, so the following source definitions have the same effect:

source s_demo_stream1 {
    unix-stream("<path-to-socket>" max-connections(10) group(log)); };
    source s_demo_stream2 {
unix-stream("<path-to-socket>" group(log) max-connections(10)); };

• Some options are global options, or can be set globally, for example, whether AxoSyslog should use DNS resolution to resolve IP addresses.

      options { use-dns(no); };
  

  • Objects can be used before definition.

  • Objects can be defined inline as well. This is useful if you use the object only once (for example, a filter).

  • To add comments to the configuration file, start a line with # and write your comments. These lines are ignored by AxoSyslog.

    #Comment: This is a stream source
    source s_demo_stream {
    unix-stream("<path-to-socket>" max-connections(10) group(log)); };
    

The syntax of log statements is as follows:

   log {
        source(s1); source(s2); ...
    optional_element(filter1|parser1|rewrite1);
    optional_element(filter2|parser2|rewrite2);
                ...
    destination(d1); destination(d2); ...
    flags(flag1[, flag2...]);
            };

The following log statement sends all messages arriving to the localhost to a remote server.

source s_localhost { network(ip(127.0.0.1) port(1999)); };
destination d_tcp { network("10.1.2.3" port(1999) localport(999)); };
log { source(s_localhost); destination(d_tcp); };

The AxoSyslog application has a number of global options governing DNS usage, the timestamp format used, and other general points. Each option may have parameters, similarly to driver specifications. To set global options add an option statement to the AxoSyslog configuration file using the following syntax:

options { option1(params); option2(params); ... };

Example: Using global options

To disable domain name resolving, add the following line to the AxoSyslog configuration file:

options { use-dns(no); };

The sources, destinations, and filters available in AxoSyslog are listed below. For details, see the AxoSyslog documentation.

Table: Available source drivers

Table 2. Available destination drivers

Table 3. Filter functions

Files

/opt/syslog-ng/

/opt/syslog-ng/etc/syslog-ng.conf

See also

syslog-ng.8

Getting help

• The up-to-date documentation of AxoSyslog is available on the AxoSyslog documentation site.
• For news and notifications about AxoSyslog, visit the Axoflow blog.
• If you want to contact the developers directly to help with problems or report issues, contact us on Discord or GitHub.

This manual page is maintained by Axoflow