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Apache HTTP Server Version 1.3
Module mod_log_config
This module provides for logging of the requests made to the server, using the Common Log
Format or a user-specified format.
Status:
Base
Source
File: mod_log_config.c
Module
Identifier: config_log_module
Compatibility:
Was an extension module prior to Apache 1.2.
Summary
This module provides for flexible logging of client requests. Logs are written in a
customizable format, and may be written directly to a file, or to an external program.
Conditional logging is provided so that individual requests may be included or excluded from
the logs based on characteristics of the request.
Three directives are provided by this module: TransferLog to create a log
file, LogFormat to set a custom format, and CustomLog to define a
log file and format in one step. The TransferLog and CustomLog
directives can be used multiple times in each server to cause each request to be logged to
multiple files.
See also: Apache Log Files.
Directives
The format argument to the LogFormat and CustomLog directives is
a string. This string is used to log each request to the log file. It can contain literal
characters copied into the log files and the C-style control characters "\n" and
"\t" to represent new-lines and tabs. Literal quotes and back-slashes should be
escaped with back-slashes.
The characteristics of the request itself are logged by placing "%"
directives in the format string, which are replaced in the log entry by the values as follows:
%...a: Remote IP-address
%...A: Local IP-address
%...B: Bytes sent, excluding HTTP headers.
%...b: Bytes sent, excluding HTTP headers. In CLF format
i.e. a '-' rather than a 0 when no bytes are sent.
%...c: Connection status when response was completed.
'X' = connection aborted before the response completed.
'+' = connection may be kept alive after the response is sent.
'-' = connection will be closed after the response is sent.
%...{FOOBAR}e: The contents of the environment variable FOOBAR
%...f: Filename
%...h: Remote host
%...H The request protocol
%...{Foobar}i: The contents of Foobar: header line(s) in the request
sent to the server.
%...l: Remote logname (from identd, if supplied)
%...m The request method
%...{Foobar}n: The contents of note "Foobar" from another module.
%...{Foobar}o: The contents of Foobar: header line(s) in the reply.
%...p: The canonical Port of the server serving the request
%...P: The process ID of the child that serviced the request.
%...q The query string (prepended with a ? if a query string exists,
otherwise an empty string)
%...r: First line of request
%...s: Status. For requests that got internally redirected, this is
the status of the *original* request --- %...>s for the last.
%...t: Time, in common log format time format (standard english format)
%...{format}t: The time, in the form given by format, which should
be in strftime(3) format. (potentially localized)
%...T: The time taken to serve the request, in seconds.
%...u: Remote user (from auth; may be bogus if return status (%s) is 401)
%...U: The URL path requested, not including any query string.
%...v: The canonical ServerName of the server serving the request.
%...V: The server name according to the UseCanonicalName setting.
The "..." can be nothing at all (e.g., "%h %u %r %s %b"),
or it can indicate conditions for inclusion of the item (which will cause it to be replaced
with "-" if the condition is not met). The forms of condition are a list of HTTP
status codes, which may or may not be preceded by "!". Thus,
"%400,501{User-agent}i" logs User-agent: on 400 errors and 501 errors (Bad Request,
Not Implemented) only; "%!200,304,302{Referer}i" logs Referer: on all requests which
did not return some sort of normal status.
Note that in versions previous to 1.3.25 no escaping was performed on the strings from %...r,
%...i and %...o. This was mainly to comply with the requirements of
the Common Log Format. This implied that clients could insert control characters into the log,
so you had to be quite careful when dealing with raw log files.
For security reasons starting with 1.3.25 non-printable and other special characters are
escaped mostly by using \xhh sequences, where hh stands for
the hexadecimal representation of the raw byte. Exceptions from this rule are "
and \ which are escaped by prepending a backslash, and all whitespace characters
that are written in their C-style notation (\n, \t, etc).
Some commonly used log format strings are:
- Common Log Format (CLF)
"%h %l %u %t \"%r\" %>s %b"
- Common Log Format with Virtual Host
"%v %h %l %u %t \"%r\" %>s %b"
- NCSA extended/combined log format
"%h %l %u %t \"%r\" %>s %b \"%{Referer}i\"
\"%{User-agent}i\""
- Referer log format
"%{Referer}i -> %U"
- Agent (Browser) log format
"%{User-agent}i"
Note that the canonical
ServerName
and Port of the server serving
the request are used for %v and %p respectively. This happens
regardless of the
UseCanonicalName
setting because otherwise log analysis programs would have to duplicate the entire vhost
matching algorithm in order to decide what host really served the request.
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.
Compatibility notes
- This module is based on mod_log_config distributed with previous Apache releases, now
updated to handle multiple logs. There is now no need to rebuild Apache to change
configuration log formats.
- The module also implements the
CookieLog directive, used to log
user-tracking information created by
mod_usertrack. The use of CookieLog
is deprecated, and a CustomLog should be defined to log user-tracking
information instead.
- As of Apache 1.3.5, this module allows conditional logging based upon the setting of
environment variables. That is, you can
control whether a request should be logged or not based upon whether an arbitrary
environment variable is defined or not. This is configurable on a per-logfile basis.
- Beginning with Apache 1.3.5, the mod_log_config module has also subsumed the
RefererIgnore
functionality from
mod_log_referer.
The effect of RefererIgnore can be achieved by combinations of
SetEnvIf
directives and conditional CustomLog definitions.
Syntax:
CookieLog filename
Context:
server config, virtual host
Module:
mod_cookies
Compatibility:
Only available in Apache 1.2 and above
The CookieLog directive sets the filename for logging of cookies. The filename is relative
to the ServerRoot. This
directive is included only for compatibility with
mod_cookies, and is deprecated.
Syntax:
CustomLog file|pipe format|nickname [env=[!]environment-variable]
Context:
server config, virtual host
Status:
Base
Compatibility:
Nickname only available in Apache 1.3 or later. Conditional logging available in 1.3.5 or
later.
Module:
mod_log_config
The CustomLog directive is used to log requests to the server. A log format is
specified, and the logging can optionally be made conditional on request characteristics using
environment variables.
The first argument, which specifies the location to which the logs will be written, can
take one of the following two types of values:
- file
- 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.
The second argument specifies what will be written to the log file. It can specify either a
nickname defined by a previous
LogFormat directive, or it
can be an explicit format string as described in the
log formats
section.
For example, the following two sets of directives have exactly the same effect:
# CustomLog with format nickname
LogFormat "%h %l %u %t \"%r\" %>s %b" common
CustomLog logs/access_log common
# CustomLog with explicit format string
CustomLog logs/access_log "%h %l %u %t \"%r\" %>s %b"
The third argument is optional and controls whether or not to log a particular request
based on the presence or absence of a particular variable in the server environment. If the
specified environment variable is set for
the request (or is not set, in the case of a 'env=!name' clause), then
the request will be logged.
Environment variables can be set on a per-request basis using the
mod_setenvif and/or
mod_rewrite modules. For example,
if you want to record requests for all GIF images on your server in a separate logfile but not
in your main log, you can use:
SetEnvIf Request_URI \.gif$ gif-image
CustomLog gif-requests.log common env=gif-image
CustomLog nongif-requests.log common env=!gif-image
Syntax:
LogFormat format|nickname [nickname]
Default:
LogFormat "%h %l %u %t \"%r\" %>s %b"
Context:
server config, virtual host
Status:
Base
Compatibility:
Nickname only available in Apache 1.3 or later
Module:
mod_log_config
This directive specifies the format of the access log file.
The LogFormat directive can take one of two forms. In the first form, where
only one argument is specified, this directive sets the log format which will be used by logs
specified in subsequent TransferLog directives. The single argument
can specify an explicit format as discussed in the
custom log
formats section above. Alternatively, it can use a nickname to refer to a log
format defined in a previous LogFormat directive as described below.
The second form of the LogFormat directive associates an explicit format
with a nickname. This nickname can then be used in subsequent LogFormat
or CustomLog directives rather than repeating the entire format
string. A LogFormat directive which defines a nickname does nothing else
-- that is, it only defines the nickname, it doesn't actually apply the format and
make it the default. Therefore, it will not affect subsequent
TransferLog
directives.
For example:
LogFormat "%v %h %l %u %t \"%r\" %>s %b" vhost_common
Syntax:
TransferLog file|pipe
Default:
none
Context:
server config, virtual host
Status:
Base
Module:
mod_log_config
This directive has exactly the same arguments and effect as the
CustomLog
directive, with the exception that it does not allow the log format to be specified explicitly
or for conditional logging of requests. Instead, the log format is determined by the most
recently specified LogFormat directive that does not define a
nickname. Common Log Format is used if no other format has been specified.
Example:
LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-agent}i\""
TransferLog logs/access_log
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