syslog-ng Open Source Edition 3.18 - Administration Guide

Setting message fields to specific values

To set a field of the message to a specific value, you have to:

• define the string to include in the message, and

• select the field where it should be included.

You can set the value of available macros, for example HOST, MESSAGE, PROGRAM, or any user-defined macros created using parsers (for details, see parser: Parse and segment structured messages and db-parser: Process message content with a pattern database (patterndb)). Hard macros cannot be modified. For details on the hard and soft macros, see Hard vs. soft macros). Note that the rewrite operation completely replaces any previous value of that field. Use the following syntax:

rewrite <name_of_the_rule> {
    set("<string to include>", value(<field name>));
};

rewrite r_rewrite_set{
    set("myhost", value("HOST"));
};

rewrite r_rewrite_set{
    set("$MESSAGE suffix", value("MESSAGE"));
};

You can also use the following options in rewrite rules that use the set() operator.

rewrite <name_of_the_rule> {
    set("<string to include>", value(<field name>), on-error("fallback-to-string");
};

frac-digits()

Description: The syslog-ng application can store fractions of a second in the timestamps according to the ISO8601 format. The frac-digits() parameter specifies the number of digits stored. The digits storing the fractions are padded by zeros if the original timestamp of the message specifies only seconds. Fractions can always be stored for the time the message was received. Note that syslog-ng can add the fractions to non-ISO8601 timestamps as well.

local-time-zone()

Description: Sets the timezone used when expanding filename and tablename templates.

The timezone can be specified by using the name, for example, time-zone("Europe/Budapest")), or as the timezone offset in +/-HH:MM format, for example, +01:00). On Linux and UNIX platforms, the valid timezone names are listed under the /usr/share/zoneinfo directory.

on-error()

Description: Controls what happens when type-casting fails and syslog-ng OSE cannot convert some data to the specified type. By default, syslog-ng OSE drops the entire message and logs the error. Currently the value-pairs() option uses the settings of on-error().

• drop-message: Drop the entire message and log an error message to the internal() source. This is the default behavior of syslog-ng OSE.

• drop-property: Omit the affected property (macro, template, or message-field) from the log message and log an error message to the internal() source.

• fallback-to-string: Convert the property to string and log an error message to the internal() source.

• silently-drop-message: Drop the entire message silently, without logging the error.

• silently-drop-property: Omit the affected property (macro, template, or message-field) silently, without logging the error.

• silently-fallback-to-string: Convert the property to string silently, without logging the error.

send-time-zone()

Description: Specifies the time zone associated with the messages sent by syslog-ng, if not specified otherwise in the message or in the destination driver. For details, see Timezones and daylight saving.

The timezone can be specified by using the name, for example, time-zone("Europe/Budapest")), or as the timezone offset in +/-HH:MM format, for example, +01:00). On Linux and UNIX platforms, the valid timezone names are listed under the /usr/share/zoneinfo directory.

time-zone()

Description: Convert timestamps to the timezone specified by this option. If this option is not set, then the original timezone information in the message is used. Converting the timezone changes the values of all date-related macros derived from the timestamp, for example, HOUR. For the complete list of such macros, see Date-related macros.

The timezone can be specified by using the name, for example, time-zone("Europe/Budapest")), or as the timezone offset in +/-HH:MM format, for example, +01:00). On Linux and UNIX platforms, the valid timezone names are listed under the /usr/share/zoneinfo directory.

ts-format()

Description: Override the global timestamp format (set in the global ts-format() parameter) for the specific destination. For details, see ts-format().

Unsetting message fields

You can unset macros or fields of the message, including any user-defined macros created using parsers (for details, see parser: Parse and segment structured messages and db-parser: Process message content with a pattern database (patterndb)). Hard macros cannot be modified. For details on hard and soft macros, see Hard vs. soft macros). Note that the unset operation completely deletes any previous value of the field that you apply it on. Use the following syntax:

rewrite <name_of_the_rule> {
    unset(value("<field-name>"));
};

rewrite r_rewrite_unset{
    unset(value("HOST"));
};

To unset a group of fields, you can use the groupunset() rewrite rule.

rewrite <name_of_the_rule> {
    groupunset(values("<expression-for-field-names>"));
};

rewrite r_rewrite_unset_SDATA{
    groupunset(values(".SDATA.*"));
};

Creating custom SDATA fields

If you use RFC5424-formatted (IETF-syslog) messages, you can also create custom fields in the SDATA part of the message (For details on the SDATA message part, see The STRUCTURED-DATA message part). According to RFC5424, the name of the field (its SD-ID) must not contain the @ character for reserved SD-IDs. Custom SDATA fields must be in the following format: .SDATA.group-name@<private enterprise number>.field-name, for example, .SDATA.mySDATA-field-group@18372.4.mySDATA-field. (18372.4 is the private enterprise number of &fullvendor;, the developer of &abbrev;.)

rewrite r_sd {
    set("55555" value(".SDATA.meta.sequenceId"));
};

rewrite r_rewrite_set {
    set("${SOURCEIP}" value(".SDATA.custom@18372.4.sourceip"));
};

Setting multiple message fields to specific values

The groupset() rewrite rule allows you to modify the value of multiple message fields at once, for example, to change the value of sensitive fields extracted using patterndb, or received in a JSON format. (If you want to modify the names of message fields, see map-value-pairs: Rename value-pairs to normalize logs.)

• The first parameter is the new value of the modified fields. This can be a simple string, a macro, or a template (which can include template functions as well).

• The second parameter (values()) specifies the fields to modify. You can explicitly list the macros or fields (a space-separated list with the values enclosed in double-quotes), or use wildcards and glob expressions to select multiple fields.

• Note that groupset() does not create new fields, it only modifies existing fields.

• You can refer to the old value of the field using the $_ macro. This is resolved to the value of the current field, and is available only in groupset() rules.

rewrite <name_of_the_rule> {
    groupset("<new-value-of-the-fields>", values("<field-name-or-glob>" ["<another-field-name-or-glob>"]));
};