Apache Module mod_log_forensic
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 (depending 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.
This module was backported from version 2.1 which uses a more powerful
APR version in order to generate the forensic IDs. If you want to run
mod_log_forensic in version 2.0, you need to include
mod_unique_id as well.
Directives
Topics
See also
Each request is logged two times. The first time is 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 the 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.
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.
The ForensicLog directive is used to
log requests to the server for forensic analysis. Each log entry
is assigned a unique ID which can be associated with the request
using the normal CustomLog
directive. mod_log_forensic takes the unique ID from
mod_unique_id, so you need to load this module as well.
(This requirement will not be necessary in version 2.1 and later, because
of a more powerful APR version.) The ID token is attached to the request
under the name 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. The program name can be specified relative to the ServerRoot directive.
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 or switches to a
less privileged user.
Note
When entering a file path on non-Unix platforms, care should be taken
to make sure that only forward slashed are used even though the platform
may allow the use of back slashes. In general it is a good idea to always
use forward slashes throughout the configuration files.
