Starting with
TIP: Using conditions in rewrite rules can simplify your syslog-ng PE configuration file, as you do not need to create separate log paths to modify certain messages.
Starting with
TIP: Using conditions in rewrite rules can simplify your syslog-ng PE configuration file, as you do not need to create separate log paths to modify certain messages.
The following procedure summarizes how conditional rewrite rules (rewrite rules that have the condition() parameter set) work. The following configuration snippet is used to illustrate the procedure:
rewrite r_rewrite_set{set("myhost", value("HOST") condition(program("myapplication")));};
log {
source(s1);
rewrite(r_rewrite_set);
destination(d1);};The log path receives a message from the source (s1).
The rewrite rule (r_rewrite_set) evaluates the condition. If the message matches the condition (the PROGRAM field of the message is "myapplication"), syslog-ng PE rewrites the log message (sets the value of the HOST field to "myhost"), otherwise it is not modified.
The next element of the log path processes the message (d1).
The following example sets the HOST field of the message to myhost only if the message was sent by the myapplication program.
rewrite r_rewrite_set{set("myhost", value("HOST") condition(program("myapplication")));};
The following example is identical to the previous one, except that the condition references an existing filter template.
filter f_rewritefilter {program("myapplication");};
rewrite r_rewrite_set{set("myhost", value("HOST") condition(filter(f_rewritefilter)));};Log messages of banking and e-commerce applications might include credit card numbers (Primary Account Number or PAN). According to privacy best practices and the requirements of the Payment Card Industry Data Security Standards (PCI-DSS), PAN must be rendered unreadable. The syslog-ng PE application uses a regular expression to detect credit card numbers, and provides two ways to accomplish this: you can either mask the credit card numbers, or replace them with a hash. To mask the credit card numbers, use the credit-card-mask() or the credit-card-hash() rewrite rules in a log path.
@include "scl/rewrite/cc-mask.conf"
rewrite { credit-card-mask(value("<message-field-to-process>")); };
By default, these rewrite rules process the MESSAGE part of the log message.
| Synopsis: | credit-card-hash(value("<message-field-to-process>")) |
Description: Process the specified message field (by default, ${MESSAGE}), and replace any credit card numbers (Primary Account Number or PAN) with its 16-character-long SHA-1 hash.
| Synopsis: | credit-card-mask(value("<message-field-to-process>")) |
Description: Process the specified message field (by default, ${MESSAGE}), and replace the 7-12th character of any credit card numbers (Primary Account Number or PAN) with asterisks (*). For example, syslog-ng PE replaces the number 5542043004559005 with 554204******9005.
Filters and substitution rewrite rules can use regular expressions. In regular expressions, the characters ()[].*?+^$|\ are used as special symbols. Depending on how you want to use these characters and which quotation mark you use, these characters must be used differently, as summarized below.
Strings between single quotes ('string') are treated literally and are not interpreted at all, you do not have to escape special characters. For example, the output of '\x41' is \x41 (characters as follows: backslash, x(letter), 4(number), 1(number)). This makes writing and reading regular expressions much more simple: it is recommended to use single quotes when writing regular expressions.
When enclosing strings between double-quotes ("string"), the string is interpreted and you have to escape special characters, that is, to precede them with a backslash (\) character if they are meant literally. For example, the output of the "\x41" is simply the letter a. Therefore special characters like \(backslash) or "(quotation mark) must be escaped (\\ and \"). The following expressions are interpreted: \a, \n, \r, \t, \v. For example, the \$40 expression matches the $40 string. Backslashes have to be escaped as well if they are meant literally, for example, the \\d expression matches the \d string.
TIP: If you use single quotes, you do not need to escape the backslash, for example, match("\\.") is equivalent to match('\.').
Enclosing alphanumeric strings between double-quotes ("string") is not necessary, you can just omit the double-quotes. For example, when writing filters, match("sometext") and match(sometext) will both match for the sometext string.
NOTE: Only strings containing alphanumerical characters can be used without quotes or double quotes. If the string contains whitespace or any special characters (()[].*?+^$|\ or ;:#), you must use quotes or double quotes.
When using the ;:# characters, you must use quotes or double quotes, but escaping them is not required.
By default, all regular expressions are case sensitive. To disable the case sensitivity of the expression, add the flags(ignore-case) option to the regular expression.
filter demo_regexp_insensitive { host("system" flags(ignore-case)); };
The regular expressions can use up to 255 regexp matches (${1} ... ${255}), but only from the last filter and only if the flags("store-matches") flag was set for the filter. For case-insensitive searches, use the flags("ignore-case") option.
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