Apache HTTP Server Version 2.4

Description: | Logging of the requests made to the server |
---|---|

Status: | Base |

Module Identifier: | log_config_module |

Source File: | mod_log_config.c |


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.

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. | ||||||||||

`%{` |
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. | ||||||||||

`%{` |
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. | ||||||||||

`%{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. | ||||||||||

`%{` |
The contents of 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 `%{` 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. | ||||||||||

`%m` |
The request method. | ||||||||||

`%{` |
The contents of note VARNAME from another
module. | ||||||||||

`%{` |
The contents of header line(s)
in the reply. | ||||||||||

`%p` |
The canonical port of the server serving the request. | ||||||||||

`%{` |
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. | ||||||||||

`%{` |
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. | ||||||||||

`%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 | ||||||||||

`%{` |
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:
`strftime(3)`
formatting in the same format string. You can use multiple
`%{` tokens instead.
| ||||||||||

`%T` |
The time taken to serve the request, in seconds. | ||||||||||

`%{` |
The time taken to serve the request, in a time unit given by
`UNIT` . Valid units are `ms` for milliseconds,
`us` for microseconds, and `s` for seconds.
Using `s` 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. | ||||||||||

`%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:
| ||||||||||

`%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. | ||||||||||

`%{` |
The contents of trailer line(s)
in the request sent to the server. | ||||||||||

`%{` |
The contents of trailer line(s)
in the response sent from the server. |


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 `%<u`

can be used to record the
original authenticated user on a request that is internally
redirected to an unauthenticated resource.

For security reasons, starting with version 2.0.46,
non-printable and other special characters in `%r`

,
`%i`

and `%o`

are escaped using
`\x`

sequences, where `hh``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.

Since 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.

Some commonly used log format strings are:

`"%h %l %u %t \"%r\" %>s %b"`

`"%v %h %l %u %t \"%r\" %>s %b"`

```
"%h %l %u %t \"%r\" %>s %b \"%{Referer}i\"
\"%{User-agent}i\""
```

`"%{Referer}i -> %U"`

`"%{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`

:

`"%{%d/%b/%Y %T}t.%{msec_frac}t %{%z}t"`

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.

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.

Description: | Sets filename and format of log file |
---|---|

Syntax: | `CustomLog ` |

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:

`ServerRoot`

.`|`

", 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.
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.

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.

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=!`

'
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.`name`

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

Description: | Sets filename and format of log file |
---|---|

Syntax: | `GlobalLog` |

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`

.Description: | Describes a format for use in a log file |
---|---|

Syntax: | `LogFormat ` |

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 (`%`

).

LogFormat "%v %h %l %u %t \"%r\" %>s %b" vhost_common

Description: | Specify location of a log file |
---|---|

Syntax: | `TransferLog ` |

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.

LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-agent}i\"" TransferLog logs/access_log