Apache Module mod_log_config

Custom Log Formats

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 backslashes should be escaped with backslashes.

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:

Format String	Description
%%	The percent sign
%a	Remote IP-address
%A	Local IP-address
%B	Size of response in bytes, excluding HTTP headers.
%b	Size of response in bytes, 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. Only version 0 cookies are fully supported.
%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. Changes made by other modules (e.g. mod_headers) affect this. If you're interested in what the request header was prior to when most modules would have modified it, use mod_setenvif to copy the header into an internal environment variable and log that value with the %{VARNAME}e described above.
%k	Number of keepalive requests handled on this connection. Interesting if KeepAlive is being used, so that, for example, a '1' means the first keepalive request after the initial one, '2' the second, etc...; otherwise this is always 0 (indicating the initial request). Available in versions 2.2.11 and later.
%l	Remote logname (from identd, if supplied). This will return a dash unless mod_ident is present and IdentityCheck is set On.
%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
%{format}p	The canonical port of the server serving the request or the server's actual port or the client's actual port. Valid formats are canonical, local, or remote.
%P	The process ID of the child that serviced the request.
%{format}P	The process ID or thread id of the child that serviced the request. Valid formats are pid, tid, and hextid. hextid requires APR 1.2.0 or higher.
%q	The query string (prepended with a ? if a query string exists, otherwise an empty string)
%r	First line of request
%R	The handler generating the response (if any).
%s	Status. For requests that got internally redirected, this is the status of the *original* request --- %>s for the last.
%t	Time the request was received (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: 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. (This directive was %c in late versions of Apache 1.3, but this conflicted with the historical ssl %{var}c syntax.)
%I	Bytes received, including request and headers, cannot be zero. You need to enable mod_logio to use this.
%O	Bytes sent, including headers, cannot be zero. You need to enable mod_logio to use this.

Modifiers

Particular items can be restricted to print only for responses with specific HTTP status codes by placing a comma-separated list of status codes immediately following the "%". For example, "%400,501{User-agent}i" logs User-agent on 400 errors and 501 errors only. For other status codes, the literal string "-" will be logged. The status code list may be preceded by a "!" to indicate negation: "%!200,304,302{Referer}i" logs Referer on all requests that do not return one of the three specified codes.

The modifiers "<" and ">" can be used for requests that have been internally redirected to choose whether the original or final (respectively) request should be consulted. By default, the % directives %s, %U, %T, %D, and %r look at the original request while all others look at the final request. So for example, %>s can be used to record the final status of the request and %<u can be used to record the original authenticated user on a request that is internally redirected to an unauthenticated resource.

Some Notes

For security reasons, starting with version 2.0.46, non-printable and other special characters in %r, %i and %o are escaped 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, which are written in their C-style notation (\n, \t, etc). In versions prior to 2.0.46, no escaping was performed on these strings so you had to be quite careful when dealing with raw log files.

In httpd 2.0, unlike 1.3, the %b and %B format strings do not represent the number of bytes sent to the client, but simply the size in bytes of the HTTP response (which will differ, for instance, if the connection is aborted, or if SSL is used). The %O format provided by mod_logio will log the actual number of bytes sent over the network.

Note: mod_cache is implemented as a quick-handler and not as a standard handler. Therefore, the %R format string will not return any handler information when content caching is involved.

Examples

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"

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.