syslog-ng Open Source Edition 3.30 - Administration Guide

Example: Unsetting a message field

The following example unsets the HOST field of the message.

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

Example: Unsetting a group of fields

The following rule clears all SDATA fields:

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

Example: Rewriting custom SDATA fields

The following example sets the sequence ID field of the RFC5424-formatted (IETF-syslog) messages to a fixed value. This field is a predefined SDATA field with a reserved SD-ID, therefore its name does not contain the @ character.

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

It is also possible to set the value of a field that does not exist yet, and create a new, custom name-value pair that is associated with the message. The following example creates the .SDATA.groupID.fieldID@18372.4 field and sets its value to yes. If you use the ${.SDATA.groupID.fieldID@18372.4} macro in a template or SQL table, its value will be yes for every message that was processed with this rewrite rule, and empty for every other message.

The next example creates a new SDATA field-group and field called custom and sourceip, respectively:

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

If you use the ${.SDATA.custom@18372.4.sourceip} macro in a template or SQL table, its value will be that of the SOURCEIP macro (as seen on the machine where the SDATA field was created) for every message that was processed with this rewrite rule, and empty for every other message.

You can verify whether or not the format is correct by looking at the actual network traffic. The SDATA field-group will be called custom@18372.4, and sourceip will become a field within that group. If you decide to set up several fields, they will be listed in consecutive order within the field-group's SDATA block.

Example: Using groupset rewrite rules

The following examples show how to change the values of multiple fields at the same time.

• Change the value of the HOST field to myhost.

  groupset ("myhost" values("HOST"))

• Change the value of the HOST and FULLHOST fields to myhost.

  groupset ("myhost" values("HOST" "FULLHOST"))

• Change the value of the HOST FULLHOST and fields to lowercase.

  groupset ("$(lowercase "$_")" values("HOST" "FULLHOST"))

• Change the value of each field and macro that begins with .USER to nobody.

  groupset ("nobody" values(".USER.*"))

• Change the value of each field and macro that begins with .USER to its SHA-1 hash (truncated to 6 characters).

  groupset ("$(sha1 --length 6 $_)" values(".USER.*"))

Example: Map name-value pairs

The following example creates a new name-value pair called username, adds the hashed value of the .apache.username to this new name-value pair, then adds the webserver prefix to the name of every name-value pair of the message that starts with .apache

parser p_remap_name_values {
    map-value-pairs(
        pair("username", "'($sha1 $.apache.username)")
        key('.apache.*' rekey(add-prefix("webserver")))
    );
};