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Apache HTTP Server Version 2.0
Apache Module mod_log_config
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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.
Directives
See also
Custom Log Formats
The format argument to the LogFormat and
CustomLog directives is a string. This string is
logged to the log file for each request. It can contain literal
characters copied into the log files and the c-type 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 file 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. | ||
| %...{Foobar}C: | The contents of cookie "Foobar" in the request sent to the server. | ||
| %...D: | The time taken to serve the request, in microseconds. | ||
| %...{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. | ||
| %...X: | Connection status when response is completed.
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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 there is no escaping performed on the strings from %...r, %...i and %...o. This is mainly to comply with the requirements of the Common Log Format. This implies that clients can insert control characters into the log, so care should be taken when dealing with raw log files.
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 Listen 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.
CookieLog Directive
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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.
CustomLog Directive
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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 on 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 under 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 allows the decision on
whether or not to log a particular request to be 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
LogFormat Directive
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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 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
TransferLog Directive
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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
specified LogFormat directive (which
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
