Apache HTTP Server Version 1.3

Module mod_log_forensic

This module provides for forensic logging of the requests made to the server

Status: Extension
Source File: mod_log_forensic.c
Module Identifier: log_forensic_module
Compatibility: Available in Version 1.3.30 and later.

Summary

This module provides for forensic logging of client requests. Logging is done before and after processing a request, so the forensic log contains two log lines for each request. The forensic logger is very strict, which means:

The format is fixed. You cannot modify the logging format at runtime.
If it cannot write its data, the child process exits immediately and may dump core (depends on your CoreDumpDirectory configuration).

The check_forensic script, which can be found in the distribution's support directory, may be helpful in evaluating the forensic log output.

Directives

ForensicLog

Forensic Log Format

Each request is logged two times. The first time before it's processed further (that is, after receiving the headers). The second log entry is written after the request processing at the same time where normal logging occurs.

In order to identify each request, a unique request ID is assigned. This forensic ID can be cross logged in the normal transfer log using the %{forensic-id}n format string. If you're using mod_unique_id, its generated ID will be used.

The first line logs the forensic ID, the request line and all received headers, separated by pipe characters (|). A sample line looks like the following (all on one line):

+yQtJf8CoAB4AAFNXBIEAAAAA|GET /manual/de/images/down.gif HTTP/1.1|Host:localhost%3a8080|User-Agent:Mozilla/5.0 (X11; U; Linux i686; en-US; rv%3a1.6) Gecko/20040216 Firefox/0.8|Accept:image/png, etc...

The plus character at the beginning indicates that this is first log line of this request. The second line just contains a minus character and the id again:

-yQtJf8CoAB4AAFNXBIEAAAAA

The check_forensic script takes as its argument the name of the logfile. It looks for those +/- ID pairs and complains if a request was not completed.

Security Considerations

See the security tips document for details on why your security could be compromised if the directory where logfiles are stored is writable by anyone other than the user that starts the server.

ForensicLog directive

Syntax: ForensicLog filename|pipe
Context: server config, virtual host
Module: mod_log_forensic
Compatibility: Available in Version 1.3.30 and above

The ForensicLog directive is used to log requests to the server for forensic analysis. Each log entry is assigned unique ID which can be associated with the request using the normal CustomLog directive. mod_log_forensic creates a token called forensic-id, which can be added to the transfer log using the %{forensic-id}n format string.

The argument, which specifies the location to which the logs will be written, can take one of the following two types of values:

filename: A filename, relative to the ServerRoot.
pipe: The pipe character "|", followed by the path to a program to receive the log information on its standard input. Security: if a program is used, then it will be run as the user who started httpd. This will be root if the server was started by root; be sure that the program is secure.

Apache HTTP Server Version 1.3