mod_log_config - Apache HTTP Server Version 2.5

mod_log_config - Apache HTTP Server Version 2.5
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Apache HTTP Server Version 2.5
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Version 2.5
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Apache Module mod_log_config
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Description:
Logging of the requests made to the server
Status:
Base
Module Identifier:
log_config_module
Source File:
mod_log_config.c
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.
Topics
Custom Log Formats
Security Considerations
Directives
BufferedLogs
CustomLog
GlobalLog
LogFormat
TransferLog
Bugfix checklist
httpd changelog
Known issues
Report a bug
See also
Apache Log Files
Comments
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
Client IP address of the request (see the
mod_remoteip
module).
%{c}a
Underlying peer IP address of the connection (see the
mod_remoteip
module).
%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.
%{
VARNAME
}C
The contents of cookie
VARNAME
in the request sent
to the server. Only version 0 cookies are fully supported.
%D
The time taken to serve the request, in microseconds. See %T for details.
%{
VARNAME
}e
The contents of the environment variable
VARNAME
%f
Filename.
%h
Remote hostname. Will log the IP address if
HostnameLookups
is set to
Off
, which is the default. If it logs the hostname
for only a few hosts, you probably have access control
directives mentioning them by name. See
the Require host
documentation
. This format is affected by modifications to the
remote hostname by modules like
mod_remoteip
%{c}h
Like
%h
, but always reports on the hostname of the
underlying TCP connection and not any modifications to the
remote hostname by modules like
mod_remoteip
%H
The request protocol.
%{
VARNAME
}i
The contents of
VARNAME
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).
%l
Remote logname (from identd, if supplied). This will return a
dash unless
mod_ident
is present and
IdentityCheck
is set
On
%L
The request log ID from the error log (or '-' if nothing has been
logged to the error log for this request). Look for the
matching error log line to see what request caused what error.
%{c}L
The connection log ID from the error log (or '-' if nothing has been
logged to the error log for this request). Look for the
matching error log line to see what request caused what error.
%m
The request method.
%{
VARNAME
}n
The contents of note
VARNAME
from another
module.
%{
VARNAME
}o
The contents of
VARNAME
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
%q
The query string (prepended with a
if a query
string exists, otherwise an empty string).
%r
First line of request. Does not adhere to
MergeSlashes
. (i.e. no merging
even if ON)
%R
The handler generating the response (if any).
%s
Status. For requests that have been internally redirected, this is
the status of the
original
request. Use
%>s
for the final status.
%t
Time the request was received, in the format
[18/Sep/2011:19:18:28 -0400]
The last number indicates the timezone offset from GMT
%{
format
}t
The time, in the form given by format, which should be in
an extended
strftime(3)
format (potentially localized).
If the format starts with
begin:
(default) the time is taken
at the beginning of the request processing. If it starts with
end:
it is the time when the log entry gets written,
close to the end of the request processing. In addition to the formats
supported by
strftime(3)
, the following format tokens are
supported:
sec
number of seconds since the Epoch
msec
number of milliseconds since the Epoch
usec
number of microseconds since the Epoch
msec_frac
millisecond fraction
usec_frac
microsecond fraction
These tokens can not be combined with each other or
strftime(3)
formatting in the same format string. You can use multiple
%{
format
}t
tokens instead.
%T
The time taken to serve the request, in seconds. The time measured
begins when the first line of the HTTP request is read from the host
operating system by the HTTP server and ends when the last byte of
the response is written by the HTTP server to the host operating system.
The time measured does
not
include any of the following:
Time spent in TCP or TLS handshakes.
The time before a webserver thread is able to read the first
line of the request.
Delays in the operating system putting the response data out
onto the network.
Time taken for the response to arrive at the client host.
Time taken for the the useragent to read and process the
response.
%{
UNIT
}T
The time taken to serve the request, in a time unit given by
UNIT
. Valid units are
ms
for milliseconds,
us
for microseconds, and
for seconds.
Using
gives the same result as
%T
without any format; using
us
gives the same result
as
%D
. Combining
%T
with a unit is
available in 2.4.13 and later.
%u
Remote user if the request was authenticated. May be bogus if return status
%s
) is 401 (unauthorized).
%U
The URL path requested, not including any query string.
Adheres to
MergeSlashes
(i.e. slashes are merged if
ON
%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:
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.
%I
Bytes received, including request and headers. Cannot be zero.
You need to enable
mod_logio
to use this.
%O
Bytes sent, including headers. May be zero in rare cases
such as when a request is aborted before a response is sent.
You need to enable
mod_logio
to use this.
%S
Bytes transferred (received and sent), including request and headers,
cannot be zero. This is the combination of %I and %O. You need to
enable
mod_logio
to use this.
%{
VARNAME
}^ti
The contents of
VARNAME
trailer line(s)
in the request sent to the server.
%{
VARNAME
}^to
The contents of
VARNAME
trailer line(s)
in the response sent from the server.
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
"%". The status code list may be preceded by a "
" to
indicate negation.
Format String
Meaning
%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.
%!200,304,302{Referer}i
Logs
Referer
on all requests that do
not
return one of the three specified codes,
" otherwise.
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
%can be used to record the
original authenticated user on a request that is internally
redirected to an unauthenticated resource.
Format Notes
For security reasons, starting with version 2.0.46,
non-printable and other special characters in format strings
that may contain arbitrary string data are escaped using
\x
hh
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.
Format
Description
Escaped
%c
SSL variable (shortcut)
Yes
%C
Cookie value
Yes
%e
Environment variable
Yes
%f
Request filename
Yes
%h
Remote hostname
Yes
%H
Request protocol
Yes
%i
Request header
Yes
%l
Remote logname
Yes
%m
Request method
Yes
%n
Note
Yes
%o
Response header
Yes
%q
Query string
Yes
%r
Request line
Yes
%R
Handler
Yes
%u
Remote user
Yes
%U
Request URI
Yes
%v
Server hostname
Yes
%V
Canonical server name
Yes
%x
SSL variable
Yes
%^ti
Request trailer
Yes
%^to
Response trailer
Yes
%a
Remote IP address
No (IP address)
%A
Local IP address
No (IP address)
%b
%B
Bytes sent
No (numeric)
%D
Request duration (microseconds)
No (numeric)
%F
Request flushed
No (single character)
%k
Requests on connection
No (numeric)
%L
Log ID
No (internally generated)
%p
Server port
No (numeric)
%P
PID/TID
No (numeric)
%s
Status code
No (numeric)
%t
Request time
No (formatted time)
%T
Request duration (seconds)
No (numeric)
%X
Connection status
No (single character)
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.
Note: The '^' character at the start of three-character formats
has no significance, but it must be the first character of any newly
added three-character format to avoid potential conflicts with log
formats that use literals adjacent to a format specifier, such as
"%Dus".
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"
You can use the
%{format}t
directive multiple
times to build up a time format using the extended format tokens
like
msec_frac
Timestamp including milliseconds
"%{%d/%b/%Y %T}t.%{msec_frac}t %{%z}t"
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.
BufferedLogs
Directive
Description:
Buffer log entries in memory before writing to disk
Syntax:
BufferedLogs On|Off
Default:
BufferedLogs Off
Context:
server config
Status:
Base
Module:
mod_log_config
The
BufferedLogs
directive causes
mod_log_config
to store several log entries in
memory and write them together to disk, rather than writing them
after each request. On some systems, this may result in more
efficient disk access and hence higher performance. It may be
set only once for the entire server; it cannot be configured
per virtual-host.
This directive should be used with caution as a crash might
cause loss of logging data.
CustomLog
Directive
Description:
Sets filename and format of log file
Syntax:
CustomLog
file
pipe
provider
format
nickname
[env=[!]
environment-variable
expr=
expression
Context:
server config, virtual host
Status:
Base
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. See the notes on
piped logs
for more information.
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.
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.
provider
Modules implementing ErrorLog providers can also be used as a target
for CustomLog messages. To use ErrorLog provider as a target,
"provider:argument" syntax must be used. You can for example use
mod_journald
or
mod_syslog
as a provider:
# CustomLog logging to journald
CustomLog "journald" "%h %l %u %t \"%r\" %>s %b"

# CustomLog logging to syslog with "user" facility
CustomLog "syslog:user" "%h %l %u %t \"%r\" %>s %b"
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. The condition can be the
presence or absence (in the case of a '
env=!
name
clause) of a particular variable in the server
environment
. Alternatively, the condition
can be expressed as arbitrary boolean
expression
. If the condition is not satisfied, the request
will not be logged. References to HTTP headers in the expression
will not cause the header names to be added to the Vary header.
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
Or, to reproduce the behavior of the old RefererIgnore
directive, you might use the following:
SetEnvIf Referer example\.com localreferer
CustomLog "referer.log" referer env=!localreferer
GlobalLog
Directive
Description:
Sets filename and format of log file
Syntax:
GlobalLog
file
pipe
provider
format
nickname
[env=[!]
environment-variable
expr=
expression
Context:
server config
Status:
Base
Module:
mod_log_config
Compatibility:
Available in Apache HTTP Server 2.4.19 and later
The
GlobalLog
directive defines a log shared
by the main server configuration and all defined virtual hosts.
The
GlobalLog
directive is identical to
the
CustomLog
directive, apart from the following
differences:
GlobalLog
is not valid in virtual host
context.
GlobalLog
is used by virtual hosts that
define their own
CustomLog
, unlike a
globally specified
CustomLog
LogFormat
Directive
Description:
Describes a format for use in a log file
Syntax:
LogFormat
format
nickname
nickname
Default:
LogFormat "%h %l %u %t \"%r\" %>s %b"
Context:
server config, virtual host
Status:
Base
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 that 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.
In addition,
LogFormat
cannot use one nickname
to define another nickname. Note that the nickname should not contain
percent signs (
).
Example
LogFormat "%v %h %l %u %t \"%r\" %>s %b" vhost_common
TransferLog
Directive
Description:
Specify location of a log file
Syntax:
TransferLog
file
pipe
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
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"
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Copyright 2026 The Apache Software Foundation.
Licensed under the
Apache License, Version 2.0
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