Apache Core Features

AcceptFilter Directive

This directive enables operating system specific optimizations for a listening socket by the Protocol type. The basic premise is for the kernel to not send a socket to the server process until either data is received or an entire HTTP Request is buffered. Only FreeBSD's Accept Filters , Linux's more primitive TCP_DEFER_ACCEPT, and Windows' optimized AcceptEx() are currently supported.

Using none for an argument will disable any accept filters for that protocol. This is useful for protocols that require a server send data first, such as ftp: or nntp:

AcceptFilter nntp none

The default protocol names are https for port 443 and http for all other ports. To specify that another protocol is being used with a listening port, add the protocol argument to the Listen directive.

The default values on FreeBSD are:

AcceptFilter http httpready
AcceptFilter https dataready

The httpready accept filter buffers entire HTTP requests at the kernel level. Once an entire request is received, the kernel then sends it to the server. See the accf_http(9) man page for more details. Since HTTPS requests are encrypted, only the accf_data(9) filter is used.

The default values on Linux are:

AcceptFilter http data
AcceptFilter https data

Linux's TCP_DEFER_ACCEPT does not support buffering http requests. Any value besides none will enable TCP_DEFER_ACCEPT on that listener. For more details see the Linux tcp(7) man page.

The default values on Windows are:

AcceptFilter http connect
AcceptFilter https connect

Window's mpm_winnt interprets the AcceptFilter to toggle the AcceptEx() API, and does not support http protocol buffering. connect will use the AcceptEx() API, also retrieve the network endpoint addresses, but like none the connect option does not wait for the initial data transmission.

On Windows, none uses accept() rather than AcceptEx() and will not recycle sockets between connections. This is useful for network adapters with broken driver support, as well as some virtual network providers such as vpn drivers, or spam, virus or spyware filters.

See also

• Protocol

AcceptPathInfo Directive

This directive controls whether requests that contain trailing pathname information that follows an actual filename (or non-existent file in an existing directory) will be accepted or rejected. The trailing pathname information can be made available to scripts in the PATH_INFO environment variable.

For example, assume the location /test/ points to a directory that contains only the single file here.html. Then requests for /test/here.html/more and /test/nothere.html/more both collect /more as PATH_INFO.

The three possible arguments for the AcceptPathInfo directive are:

Off

A request will only be accepted if it maps to a literal path that exists. Therefore a request with trailing pathname information after the true filename such as /test/here.html/more in the above example will return a 404 NOT FOUND error.

On

A request will be accepted if a leading path component maps to a file that exists. The above example /test/here.html/more will be accepted if /test/here.html maps to a valid file.

Default

The treatment of requests with trailing pathname information is determined by the handler responsible for the request. The core handler for normal files defaults to rejecting PATH_INFO requests. Handlers that serve scripts, such as cgi-script and isapi-handler, generally accept PATH_INFO by default.

The primary purpose of the AcceptPathInfo directive is to allow you to override the handler's choice of accepting or rejecting PATH_INFO. This override is required, for example, when you use a filter, such as INCLUDES, to generate content based on PATH_INFO. The core handler would usually reject the request, so you can use the following configuration to enable such a script:

<Files "mypaths.shtml">
  Options +Includes
  SetOutputFilter INCLUDES
  AcceptPathInfo On
</Files>

AccessFileName Directive

While processing a request, the server looks for the first existing configuration file from this list of names in every directory of the path to the document, if distributed configuration files are enabled for that directory. For example:

AccessFileName .acl

Before returning the document /usr/local/web/index.html, the server will read /.acl, /usr/.acl, /usr/local/.acl and /usr/local/web/.acl for directives unless they have been disabled with:

<Directory "/">
    AllowOverride None
</Directory>

See also

• AllowOverride
• Configuration Files
• .htaccess Files

AddDefaultCharset Directive

This directive specifies a default value for the media type charset parameter (the name of a character encoding) to be added to a response if and only if the response's content-type is either text/plain or text/html. This should override any charset specified in the body of the response via a META element, though the exact behavior is often dependent on the user's client configuration. A setting of AddDefaultCharset Off disables this functionality. AddDefaultCharset On enables a default charset of iso-8859-1. Any other value is assumed to be the charset to be used, which should be one of the IANA registered charset values for use in Internet media types (MIME types). For example:

AddDefaultCharset utf-8

AddDefaultCharset should only be used when all of the text resources to which it applies are known to be in that character encoding and it is too inconvenient to label their charset individually. One such example is to add the charset parameter to resources containing generated content, such as legacy CGI scripts, that might be vulnerable to cross-site scripting attacks due to user-provided data being included in the output. Note, however, that a better solution is to just fix (or delete) those scripts, since setting a default charset does not protect users that have enabled the "auto-detect character encoding" feature on their browser.

See also

• AddCharset

AllowEncodedSlashes Directive

The AllowEncodedSlashes directive allows URLs which contain encoded path separators (%2F for / and additionally %5C for \ on accordant systems) to be used in the path info.

With the default value, Off, such URLs are refused with a 404 (Not found) error.

With the value On, such URLs are accepted, and encoded slashes are decoded like all other encoded characters.

With the value NoDecode, such URLs are accepted, but encoded slashes are not decoded but left in their encoded state.

Turning AllowEncodedSlashes On is mostly useful when used in conjunction with PATH_INFO.

See also

• AcceptPathInfo

AllowOverride Directive

When the server finds an .htaccess file (as specified by AccessFileName), it needs to know which directives declared in that file can override earlier configuration directives.

When this directive is set to None and AllowOverrideList is set to None, .htaccess files are completely ignored. In this case, the server will not even attempt to read .htaccess files in the filesystem.

When this directive is set to All, then any directive which has the .htaccess Context is allowed in .htaccess files.

The directive-type can be one of the following groupings of directives. (See the override class index for an up-to-date listing of which directives are enabled by each directive-type.)

AuthConfig

Allow use of the authorization directives ( AuthDBMGroupFile, AuthDBMUserFile, AuthGroupFile, AuthName, AuthType, AuthUserFile, Require, etc.).

FileInfo

Allow use of the directives controlling document types ( ErrorDocument, ForceType, LanguagePriority, SetHandler, SetInputFilter, SetOutputFilter, and mod_mime Add* and Remove* directives), document meta data ( Header, RequestHeader, SetEnvIf, SetEnvIfNoCase, BrowserMatch, CookieExpires, CookieDomain, CookieStyle, CookieTracking, CookieName), mod_rewrite directives ( RewriteEngine, RewriteOptions, RewriteBase, RewriteCond, RewriteRule), mod_alias directives ( Redirect, RedirectTemp, RedirectPermanent, RedirectMatch), and Action from mod_actions.

Indexes

Allow use of the directives controlling directory indexing ( AddDescription, AddIcon, AddIconByEncoding, AddIconByType, DefaultIcon, DirectoryIndex, FancyIndexing, HeaderName, IndexIgnore, IndexOptions, ReadmeName, etc.).

Limit

Allow use of the directives controlling host access ( Allow, Deny and Order).

Nonfatal=[Override|Unknown|All]

Allow use of AllowOverride option to treat syntax errors in .htaccess as nonfatal. Instead of causing an Internal Server Error, disallowed or unrecognised directives will be ignored and a warning logged:

• Nonfatal=Override treats directives forbidden by AllowOverride as nonfatal.
• Nonfatal=Unknown treats unknown directives as nonfatal. This covers typos and directives implemented by a module that's not present.
• Nonfatal=All treats both the above as nonfatal.

Note that a syntax error in a valid directive will still cause an internal server error.

Security

Nonfatal errors may have security implications for .htaccess users. For example, if AllowOverride disallows AuthConfig, users' configuration designed to restrict access to a site will be disabled.

Options[= Option,...]

Allow use of the directives controlling specific directory features ( Options and XBitHack). An equal sign may be given followed by a comma-separated list, without spaces, of options that may be set using the Options command.

Implicit disabling of Options

Even though the list of options that may be used in .htaccess files can be limited with this directive, as long as any Options directive is allowed any other inherited option can be disabled by using the non-relative syntax. In other words, this mechanism cannot force a specific option to remain set while allowing any others to be set.

AllowOverride Options=Indexes,MultiViews

Example:

AllowOverride AuthConfig Indexes

In the example above, all directives that are neither in the group AuthConfig nor Indexes cause an internal server error.

See also

• AccessFileName
• AllowOverrideList
• Configuration Files
• .htaccess Files
• Override Class Index for .htaccess

AllowOverrideList Directive

When the server finds an .htaccess file (as specified by AccessFileName), it needs to know which directives declared in that file can override earlier configuration directives.

When this directive is set to None and AllowOverride is set to None, then .htaccess files are completely ignored. In this case, the server will not even attempt to read .htaccess files in the filesystem.

Example:

AllowOverride None
AllowOverrideList Redirect RedirectMatch

In the example above, only the Redirect and RedirectMatch directives are allowed. All others will cause an internal server error.

Example:

AllowOverride AuthConfig
AllowOverrideList CookieTracking CookieName

In the example above, AllowOverride grants permission to the AuthConfig directive grouping and AllowOverrideList grants permission to only two directives from the FileInfo directive grouping. All others will cause an internal server error.

See also

• AccessFileName
• AllowOverride
• Configuration Files
• .htaccess Files

CGIMapExtension Directive

This directive is used to control how Apache httpd finds the interpreter used to run CGI scripts. For example, setting CGIMapExtension sys:\foo.nlm .foo will cause all CGI script files with a .foo extension to be passed to the FOO interpreter.

CGIPassAuth Directive

CGIPassAuth allows scripts access to HTTP authorization headers such as Authorization, which is required for scripts that implement HTTP Basic authentication. Normally these HTTP headers are hidden from scripts. This is to disallow scripts from seeing user ids and passwords used to access the server when HTTP Basic authentication is enabled in the web server. This directive should be used when scripts are allowed to implement HTTP Basic authentication.

This directive can be used instead of the compile-time setting SECURITY_HOLE_PASS_AUTHORIZATION which has been available in previous versions of Apache HTTP Server.

The setting is respected by any modules which use ap_add_common_vars(), such as mod_cgi, mod_cgid, mod_proxy_fcgi, mod_proxy_scgi, and so on. Notably, it affects modules which don't handle the request in the usual sense but still use this API; examples of this are mod_include and mod_ext_filter. Third-party modules that don't use ap_add_common_vars() may choose to respect the setting as well.

CGIVar Directive

This directive controls how some CGI variables are set.

REQUEST_URI rules:

original-uri (default)

The value is taken from the original request line, and will not reflect internal redirects or subrequests which change the requested resource.

current-uri

The value reflects the resource currently being processed, which may be different than the original request from the client due to internal redirects or subrequests.

ContentDigest Directive

This directive enables the generation of Content-MD5 headers as defined in RFC1864 respectively RFC2616.

MD5 is an algorithm for computing a "message digest" (sometimes called "fingerprint") of arbitrary-length data, with a high degree of confidence that any alterations in the data will be reflected in alterations in the message digest.

The Content-MD5 header provides an end-to-end message integrity check (MIC) of the entity-body. A proxy or client may check this header for detecting accidental modification of the entity-body in transit. Example header:

Note that this can cause performance problems on your server since the message digest is computed on every request (the values are not cached).

Content-MD5 is only sent for documents served by the core, and not by any module. For example, SSI documents, output from CGI scripts, and byte range responses do not have this header.

DefaultRuntimeDir Directive

The DefaultRuntimeDir directive sets the directory in which the server will create various run-time files (shared memory, locks, etc.). If set as a relative path, the full path will be relative to ServerRoot.

Example

DefaultRuntimeDir scratch/

The default location of DefaultRuntimeDir may be modified by changing the DEFAULT_REL_RUNTIMEDIR #define at build time.

Note: ServerRoot should be specified before this directive is used. Otherwise, the default value of ServerRoot would be used to set the base directory.

See also

• the security tips for information on how to properly set permissions on the ServerRoot

DefaultType Directive

This directive has been disabled. For backwards compatibility of configuration files, it may be specified with the value none, meaning no default media type. For example:

DefaultType None

DefaultType None is only available in httpd-2.2.7 and later.

Use the mime.types configuration file and the AddType to configure media type assignments via file extensions, or the ForceType directive to configure the media type for specific resources. Otherwise, the server will send the response without a Content-Type header field and the recipient may attempt to guess the media type.

Define Directive

In its one parameter form, Define is equivalent to passing the -D argument to httpd. It can be used to toggle the use of <IfDefine> sections without needing to alter -D arguments in any startup scripts.

In addition to that, if the second parameter is given, a config variable is set to this value. The variable can be used in the configuration using the ${VAR} syntax. The variable is always globally defined and not limited to the scope of the surrounding config section.

<IfDefine TEST>
  Define servername test.example.com
</IfDefine>
<IfDefine !TEST>
  Define servername www.example.com
  Define SSL
</IfDefine>

DocumentRoot "/var/www/${servername}/htdocs"

Variable names may not contain colon ":" characters, to avoid clashes with RewriteMap's syntax.

See also

• UnDefine
• IfDefine

<Directory> Directive

<Directory> and </Directory> are used to enclose a group of directives that will apply only to the named directory, sub-directories of that directory, and the files within the respective directories. Any directive that is allowed in a directory context may be used. Directory-path is either the full path to a directory, or a wild-card string using Unix shell-style matching. In a wild-card string, ? matches any single character, and * matches any sequences of characters. You may also use [] character ranges. None of the wildcards match a `/' character, so <Directory "/*/public_html"> will not match /home/user/public_html, but <Directory "/home/*/public_html"> will match. Example:

<Directory "/usr/local/httpd/htdocs">
  Options Indexes FollowSymLinks
</Directory>

Directory paths may be quoted, if you like, however, it must be quoted if the path contains spaces. This is because a space would otherwise indicate the end of an argument.

Regular expressions can also be used, with the addition of the ~ character. For example:

<Directory ~ "^/www/[0-9]{3}">

</Directory>

would match directories in /www/ that consisted of three numbers.

If multiple (non-regular expression) <Directory> sections match the directory (or one of its parents) containing a document, then the directives are applied in the order of shortest match first, interspersed with the directives from the .htaccess files. For example, with

<Directory "/">
  AllowOverride None
</Directory>

<Directory "/home">
  AllowOverride FileInfo
</Directory>

for access to the document /home/web/dir/doc.html the steps are:

• Apply directive AllowOverride None (disabling .htaccess files).
• Apply directive AllowOverride FileInfo (for directory /home).
• Apply any FileInfo directives in /home/.htaccess, /home/web/.htaccess and /home/web/dir/.htaccess in that order.

Regular expressions are not considered until after all of the normal sections have been applied. Then all of the regular expressions are tested in the order they appeared in the configuration file. For example, with

<Directory ~ "abc$">
  # ... directives here ...
</Directory>

the regular expression section won't be considered until after all normal <Directory>s and .htaccess files have been applied. Then the regular expression will match on /home/abc/public_html/abc and the corresponding <Directory> will be applied.

Note that the default access for <Directory "/"> is to permit all access. This means that Apache httpd will serve any file mapped from an URL. It is recommended that you change this with a block such as

<Directory "/">
  Require all denied
</Directory>

and then override this for directories you want accessible. See the Security Tips page for more details.

The directory sections occur in the httpd.conf file. <Directory> directives cannot nest, and cannot appear in a <Limit> or <LimitExcept> section.

See also

• How <Directory>, <Location> and <Files> sections work for an explanation of how these different sections are combined when a request is received

<DirectoryMatch> Directive

<DirectoryMatch> and </DirectoryMatch> are used to enclose a group of directives which will apply only to the named directory (and the files within), the same as <Directory>. However, it takes as an argument a regular expression. For example:

<DirectoryMatch "^/www/(.+/)?[0-9]{3}/">
    # ...
</DirectoryMatch>

matches directories in /www/ (or any subdirectory thereof) that consist of three numbers.

From 2.4.8 onwards, named groups and backreferences are captured and written to the environment with the corresponding name prefixed with "MATCH_" and in upper case. This allows elements of paths to be referenced from within expressions and modules like mod_rewrite. In order to prevent confusion, numbered (unnamed) backreferences are ignored. Use named groups instead.

<DirectoryMatch "^/var/www/combined/(?<sitename>[^/]+)">
    Require ldap-group cn=%{env:MATCH_SITENAME},ou=combined,o=Example
</DirectoryMatch>

See also

• <Directory> for a description of how regular expressions are mixed in with normal <Directory>s
• How <Directory>, <Location> and <Files> sections work for an explanation of how these different sections are combined when a request is received

DocumentRoot Directive

This directive sets the directory from which httpd will serve files. Unless matched by a directive like Alias, the server appends the path from the requested URL to the document root to make the path to the document. Example:

DocumentRoot "/usr/web"

then an access to http://my.example.com/index.html refers to /usr/web/index.html. If the directory-path is not absolute then it is assumed to be relative to the ServerRoot.

The DocumentRoot should be specified without a trailing slash.

See also

• Mapping URLs to Filesystem Locations

<Else> Directive

The <Else> applies the enclosed directives if and only if the most recent <If> or <ElseIf> section in the same scope has not been applied. For example: In

<If "-z req('Host')">
  # ...
</If>
<Else>
  # ...
</Else>

The <If> would match HTTP/1.0 requests without a Host: header and the <Else> would match requests with a Host: header.

See also

• <If>
• <ElseIf>
• How <Directory>, <Location>, <Files> sections work for an explanation of how these different sections are combined when a request is received. <If>, <ElseIf>, and <Else> are applied last.

<ElseIf> Directive

The <ElseIf> applies the enclosed directives if and only if both the given condition evaluates to true and the most recent <If> or <ElseIf> section in the same scope has not been applied. For example: In

<If "-R '10.1.0.0/16'">
  #...
</If>
<ElseIf "-R '10.0.0.0/8'">
  #...
</ElseIf>
<Else>
  #...
</Else>

The <ElseIf> would match if the remote address of a request belongs to the subnet 10.0.0.0/8 but not to the subnet 10.1.0.0/16.

See also

• Expressions in Apache HTTP Server, for a complete reference and more examples.
• <If>
• <Else>
• How <Directory>, <Location>, <Files> sections work for an explanation of how these different sections are combined when a request is received. <If>, <ElseIf>, and <Else> are applied last.

EnableMMAP Directive

This directive controls whether the httpd may use memory-mapping if it needs to read the contents of a file during delivery. By default, when the handling of a request requires access to the data within a file -- for example, when delivering a server-parsed file using mod_include -- Apache httpd memory-maps the file if the OS supports it.

This memory-mapping sometimes yields a performance improvement. But in some environments, it is better to disable the memory-mapping to prevent operational problems:

• On some multiprocessor systems, memory-mapping can reduce the performance of the httpd.
• Deleting or truncating a file while httpd has it memory-mapped can cause httpd to crash with a segmentation fault.

For server configurations that are vulnerable to these problems, you should disable memory-mapping of delivered files by specifying:

EnableMMAP Off

For NFS mounted files, this feature may be disabled explicitly for the offending files by specifying:

<Directory "/path-to-nfs-files">
  EnableMMAP Off
</Directory>

EnableSendfile Directive

This directive controls whether httpd may use the sendfile support from the kernel to transmit file contents to the client. By default, when the handling of a request requires no access to the data within a file -- for example, when delivering a static file -- Apache httpd uses sendfile to deliver the file contents without ever reading the file if the OS supports it.

This sendfile mechanism avoids separate read and send operations, and buffer allocations. But on some platforms or within some filesystems, it is better to disable this feature to avoid operational problems:

• Some platforms may have broken sendfile support that the build system did not detect, especially if the binaries were built on another box and moved to such a machine with broken sendfile support.
• On Linux the use of sendfile triggers TCP-checksum offloading bugs on certain networking cards when using IPv6.
• On Linux on Itanium, sendfile may be unable to handle files over 2GB in size.
• With a network-mounted DocumentRoot (e.g., NFS, SMB, CIFS, FUSE), the kernel may be unable to serve the network file through its own cache.

For server configurations that are not vulnerable to these problems, you may enable this feature by specifying:

EnableSendfile On

For network mounted files, this feature may be disabled explicitly for the offending files by specifying:

<Directory "/path-to-nfs-files">
  EnableSendfile Off
</Directory>

Please note that the per-directory and .htaccess configuration of EnableSendfile is not supported by mod_cache_disk. Only global definition of EnableSendfile is taken into account by the module.

Error Directive

If an error can be detected within the configuration, this directive can be used to generate a custom error message, and halt configuration parsing. The typical use is for reporting required modules which are missing from the configuration.

# Example
# ensure that mod_include is loaded
<IfModule !include_module>
  Error "mod_include is required by mod_foo.  Load it with LoadModule."
</IfModule>

# ensure that exactly one of SSL,NOSSL is defined
<IfDefine SSL>
<IfDefine NOSSL>
  Error "Both SSL and NOSSL are defined.  Define only one of them."
</IfDefine>
</IfDefine>
<IfDefine !SSL>
<IfDefine !NOSSL>
  Error "Either SSL or NOSSL must be defined."
</IfDefine>
</IfDefine>

ErrorDocument Directive

In the event of a problem or error, Apache httpd can be configured to do one of four things,

1. output a simple hardcoded error message
2. output a customized message
3. internally redirect to a local URL-path to handle the problem/error
4. redirect to an external URL to handle the problem/error

The first option is the default, while options 2-4 are configured using the ErrorDocument directive, which is followed by the HTTP response code and a URL or a message. Apache httpd will sometimes offer additional information regarding the problem/error.

From 2.4.13, expression syntax can be used inside the directive to produce dynamic strings and URLs.

URLs can begin with a slash (/) for local web-paths (relative to the DocumentRoot), or be a full URL which the client can resolve. Alternatively, a message can be provided to be displayed by the browser. Note that deciding whether the parameter is an URL, a path or a message is performed before any expression is parsed. Examples:

ErrorDocument 500 http://example.com/cgi-bin/server-error.cgi
ErrorDocument 404 /errors/bad_urls.php
ErrorDocument 401 /subscription_info.html
ErrorDocument 403 "Sorry, can't allow you access today"
ErrorDocument 403 Forbidden!
ErrorDocument 403 /errors/forbidden.py?referrer=%{escape:%{HTTP_REFERER}}

Additionally, the special value default can be used to specify Apache httpd's simple hardcoded message. While not required under normal circumstances, default will restore Apache httpd's simple hardcoded message for configurations that would otherwise inherit an existing ErrorDocument.

ErrorDocument 404 /cgi-bin/bad_urls.pl

<Directory "/web/docs">
  ErrorDocument 404 default
</Directory>

Note that when you specify an ErrorDocument that points to a remote URL (ie. anything with a method such as http in front of it), Apache HTTP Server will send a redirect to the client to tell it where to find the document, even if the document ends up being on the same server. This has several implications, the most important being that the client will not receive the original error status code, but instead will receive a redirect status code. This in turn can confuse web robots and other clients which try to determine if a URL is valid using the status code. In addition, if you use a remote URL in an ErrorDocument 401, the client will not know to prompt the user for a password since it will not receive the 401 status code. Therefore, if you use an ErrorDocument 401 directive, then it must refer to a local document.

Microsoft Internet Explorer (MSIE) will by default ignore server-generated error messages when they are "too small" and substitute its own "friendly" error messages. The size threshold varies depending on the type of error, but in general, if you make your error document greater than 512 bytes, then MSIE will show the server-generated error rather than masking it. More information is available in Microsoft Knowledge Base article Q294807 .

Although most error messages can be overridden, there are certain circumstances where the internal messages are used regardless of the setting of ErrorDocument. In particular, if a malformed request is detected, normal request processing will be immediately halted and the internal error message returned. This is necessary to guard against security problems caused by bad requests.

If you are using mod_proxy, you may wish to enable ProxyErrorOverride so that you can provide custom error messages on behalf of your Origin servers. If you don't enable ProxyErrorOverride, Apache httpd will not generate custom error documents for proxied content.

See also

• documentation of customizable responses

ErrorLog Directive

The ErrorLog directive sets the name of the file to which the server will log any errors it encounters. If the file-path is not absolute then it is assumed to be relative to the ServerRoot.

ErrorLog "/var/log/httpd/error_log"

If the file-path begins with a pipe character "|" then it is assumed to be a command to spawn to handle the error log.

ErrorLog "|/usr/local/bin/httpd_errors"

See the notes on piped logs for more information.

Using syslog instead of a filename enables logging via syslogd(8) if the system supports it. The default is to use syslog facility local7, but you can override this by using the syslog:facility syntax where facility can be one of the names usually documented in syslog(1). The facility is effectively global, and if it is changed in individual virtual hosts, the final facility specified affects the entire server. Same rules apply for the syslog tag, which by default uses the Apache binary name, httpd in most cases. You can also override this by using the syslog::tag syntax.

ErrorLog syslog:user
ErrorLog syslog:user:httpd.srv1
ErrorLog syslog::httpd.srv2

Additional modules can provide their own ErrorLog providers. The syntax is similar to the syslog example above.

SECURITY: See the security tips document for details on why your security could be compromised if the directory where log files are stored is writable by anyone other than the user that starts the server.

See also

• LogLevel
• Apache HTTP Server Log Files

ErrorLogFormat Directive

ErrorLogFormat allows to specify what supplementary information is logged in the error log in addition to the actual log message.

#Simple example
ErrorLogFormat "[%t] [%l] [pid %P] %F: %E: [client %a] %M"

Specifying connection or request as first parameter allows to specify additional formats, causing additional information to be logged when the first message is logged for a specific connection or request, respectively. This additional information is only logged once per connection/request. If a connection or request is processed without causing any log message, the additional information is not logged either.

It can happen that some format string items do not produce output. For example, the Referer header is only present if the log message is associated to a request and the log message happens at a time when the Referer header has already been read from the client. If no output is produced, the default behavior is to delete everything from the preceding space character to the next space character. This means the log line is implicitly divided into fields on non-whitespace to whitespace transitions. If a format string item does not produce output, the whole field is omitted. For example, if the remote address %a in the log format [%t] [%l] [%a] %M  is not available, the surrounding brackets are not logged either. Space characters can be escaped with a backslash to prevent them from delimiting a field. The combination '% ' (percent space) is a zero-width field delimiter that does not produce any output.

The above behavior can be changed by adding modifiers to the format string item. A - (minus) modifier causes a minus to be logged if the respective item does not produce any output. In once-per-connection/request formats, it is also possible to use the + (plus) modifier. If an item with the plus modifier does not produce any output, the whole line is omitted.

A number as modifier can be used to assign a log severity level to a format item. The item will only be logged if the severity of the log message is not higher than the specified log severity level. The number can range from 1 (alert) over 4 (warn) and 7 (debug) to 15 (trace8).

For example, here's what would happen if you added modifiers to the %{Referer}i token, which logs the Referer request header.

Some format string items accept additional parameters in braces.

The log ID format %L produces a unique id for a connection or request. This can be used to correlate which log lines belong to the same connection or request, which request happens on which connection. A %L format string is also available in mod_log_config to allow to correlate access log entries with error log lines. If mod_unique_id is loaded, its unique id will be used as log ID for requests.

#Example (default format for threaded MPMs)
ErrorLogFormat "[%{u}t] [%-m:%l] [pid %P:tid %T] %7F: %E: [client\ %a] %M% ,\ referer\ %{Referer}i"

This would result in error messages such as:

Notice that, as discussed above, some fields are omitted entirely because they are not defined.

#Example (similar to the 2.2.x format)
ErrorLogFormat "[%t] [%l] %7F: %E: [client\ %a] %M% ,\ referer\ %{Referer}i"

#Advanced example with request/connection log IDs
ErrorLogFormat "[%{uc}t] [%-m:%-l] [R:%L] [C:%{C}L] %7F: %E: %M"
ErrorLogFormat request "[%{uc}t] [R:%L] Request %k on C:%{c}L pid:%P tid:%T"
ErrorLogFormat request "[%{uc}t] [R:%L] UA:'%+{User-Agent}i'"
ErrorLogFormat request "[%{uc}t] [R:%L] Referer:'%+{Referer}i'"
ErrorLogFormat connection "[%{uc}t] [C:%{c}L] local\ %a remote\ %A"

See also

• ErrorLog
• LogLevel
• Apache HTTP Server Log Files

ExtendedStatus Directive

This option tracks additional data per worker about the currently executing request and creates a utilization summary. You can see these variables during runtime by configuring mod_status. Note that other modules may rely on this scoreboard.

This setting applies to the entire server and cannot be enabled or disabled on a virtualhost-by-virtualhost basis. The collection of extended status information can slow down the server. Also note that this setting cannot be changed during a graceful restart.

FileETag Directive

The FileETag directive configures the file attributes that are used to create the ETag (entity tag) response header field when the document is based on a static file. (The ETag value is used in cache management to save network bandwidth.) The FileETag directive allows you to choose which of these -- if any -- should be used. The recognized keywords are:

INode

The file's i-node number will be included in the calculation

MTime

The date and time the file was last modified will be included

Size

The number of bytes in the file will be included

All

All available fields will be used. This is equivalent to:

FileETag INode MTime Size

None

If a document is file-based, no ETag field will be included in the response

The INode, MTime, and Size keywords may be prefixed with either + or -, which allow changes to be made to the default setting inherited from a broader scope. Any keyword appearing without such a prefix immediately and completely cancels the inherited setting.

If a directory's configuration includes FileETag INode MTime Size, and a subdirectory's includes FileETag -INode, the setting for that subdirectory (which will be inherited by any sub-subdirectories that don't override it) will be equivalent to FileETag MTime Size.

<Files> Directive

The <Files> directive limits the scope of the enclosed directives by filename. It is comparable to the <Directory> and <Location> directives. It should be matched with a </Files> directive. The directives given within this section will be applied to any object with a basename (last component of filename) matching the specified filename. <Files> sections are processed in the order they appear in the configuration file, after the <Directory> sections and .htaccess files are read, but before <Location> sections. Note that <Files> can be nested inside <Directory> sections to restrict the portion of the filesystem they apply to.

The filename argument should include a filename, or a wild-card string, where ? matches any single character, and * matches any sequences of characters.

<Files "cat.html">
    # Insert stuff that applies to cat.html here
</Files>

<Files "?at.*">
    # This would apply to cat.html, bat.html, hat.php and so on.
</Files>

Regular expressions can also be used, with the addition of the ~ character. For example:

<Files ~ "\.(gif|jpe?g|png)$">
    #...
</Files>

would match most common Internet graphics formats. <FilesMatch> is preferred, however.

Note that unlike <Directory> and <Location> sections, <Files> sections can be used inside .htaccess files. This allows users to control access to their own files, at a file-by-file level.

See also

• How <Directory>, <Location> and <Files> sections work for an explanation of how these different sections are combined when a request is received

<FilesMatch> Directive

The <FilesMatch> directive limits the scope of the enclosed directives by filename, just as the <Files> directive does. However, it accepts a regular expression. For example:

<FilesMatch ".+\.(gif|jpe?g|png)$">
    # ...
</FilesMatch>

would match most common Internet graphics formats.

From 2.4.8 onwards, named groups and backreferences are captured and written to the environment with the corresponding name prefixed with "MATCH_" and in upper case. This allows elements of files to be referenced from within expressions and modules like mod_rewrite. In order to prevent confusion, numbered (unnamed) backreferences are ignored. Use named groups instead.

<FilesMatch "^(?<sitename>[^/]+)">
    Require ldap-group cn=%{env:MATCH_SITENAME},ou=combined,o=Example
</FilesMatch>

See also

• How <Directory>, <Location> and <Files> sections work for an explanation of how these different sections are combined when a request is received

ForceType Directive

When placed into an .htaccess file or a <Directory>, or <Location> or <Files> section, this directive forces all matching files to be served with the content type identification given by media-type. For example, if you had a directory full of GIF files, but did not want to label them all with .gif, you might want to use:

ForceType image/gif

Note that this directive overrides other indirect media type associations defined in mime.types or via the AddType.

You can also override more general ForceType settings by using the value of None:

# force all files to be image/gif:
<Location "/images">
  ForceType image/gif
</Location>

# but normal mime-type associations here:
<Location "/images/mixed">
  ForceType None
</Location>

This directive primarily overrides the content types generated for static files served out of the filesystem. For resources other than static files, where the generator of the response typically specifies a Content-Type, this directive has no effect.

GprofDir Directive

When the server has been compiled with gprof profiling support, GprofDir causes gmon.out files to be written to the specified directory when the process exits. If the argument ends with a percent symbol ('%'), subdirectories are created for each process id.

This directive currently only works with the prefork MPM.

HostnameLookups Directive

This directive enables DNS lookups so that host names can be logged (and passed to CGIs/SSIs in REMOTE_HOST). The value Double refers to doing double-reverse DNS lookup. That is, after a reverse lookup is performed, a forward lookup is then performed on that result. At least one of the IP addresses in the forward lookup must match the original address. (In "tcpwrappers" terminology this is called PARANOID.)

Regardless of the setting, when mod_authz_host is used for controlling access by hostname, a double reverse lookup will be performed. This is necessary for security. Note that the result of this double-reverse isn't generally available unless you set HostnameLookups Double. For example, if only HostnameLookups On and a request is made to an object that is protected by hostname restrictions, regardless of whether the double-reverse fails or not, CGIs will still be passed the single-reverse result in REMOTE_HOST.

The default is Off in order to save the network traffic for those sites that don't truly need the reverse lookups done. It is also better for the end users because they don't have to suffer the extra latency that a lookup entails. Heavily loaded sites should leave this directive Off, since DNS lookups can take considerable amounts of time. The utility logresolve, compiled by default to the bin subdirectory of your installation directory, can be used to look up host names from logged IP addresses offline.

Finally, if you have hostname-based Require directives, a hostname lookup will be performed regardless of the setting of HostnameLookups.

HttpProtocolOptions Directive

This directive changes the rules applied to the HTTP Request Line (RFC 7230 §3.1.1 ) and the HTTP Request Header Fields (RFC 7230 §3.2 ), which are now applied by default or using the Strict option. Due to legacy modules, applications or custom user-agents which must be deprecated the Unsafe option has been added to revert to the legacy behaviors.

These rules are applied prior to request processing, so must be configured at the global or default (first) matching virtual host section, by IP/port interface (and not by name) to be honored.

The directive accepts three parameters from the following list of choices, applying the default to the ones not specified:

Strict|Unsafe

Prior to the introduction of this directive, the Apache HTTP Server request message parsers were tolerant of a number of forms of input which did not conform to the protocol. RFC 7230 §9.4 Request Splitting and §9.5 Response Smuggling call out only two of the potential risks of accepting non-conformant request messages, while RFC 7230 §3.5 "Message Parsing Robustness" identify the risks of accepting obscure whitespace and request message formatting. As of the introduction of this directive, all grammar rules of the specification are enforced in the default Strict operating mode, and the strict whitespace suggested by section 3.5 is enforced and cannot be relaxed.

Security risks of Unsafe

Users are strongly cautioned against toggling the Unsafe mode of operation, particularly on outward-facing, publicly accessible server deployments. If an interface is required for faulty monitoring or other custom service consumers running on an intranet, users should toggle the Unsafe option only on a specific virtual host configured to service their internal private network.

Example of a request leading to HTTP 400 with Strict mode

# Missing CRLF
GET / HTTP/1.0\n\n

Command line tools and CRLF

Some tools need to be forced to use CRLF, otherwise httpd will return a HTTP 400 response like described in the above use case. For example, the OpenSSL s_client needs the -crlf parameter to work properly.

The DumpIOInput directive can help while reviewing the HTTP request to identify issues like the absence of CRLF.

RegisteredMethods|LenientMethods

RFC 7231 §4.1 "Request Methods" "Overview" requires that origin servers shall respond with a HTTP 501 status code when an unsupported method is encountered in the request line. This already happens when the LenientMethods option is used, but administrators may wish to toggle the RegisteredMethods option and register any non-standard methods using the RegisterHttpMethod directive, particularly if the Unsafe option has been toggled.

Forward Proxy compatibility

The RegisteredMethods option should not be toggled for forward proxy hosts, as the methods supported by the origin servers are unknown to the proxy server.

Example of a request leading to HTTP 501 with LenientMethods mode

# Unknown HTTP method
WOW / HTTP/1.0\r\n\r\n

# Lowercase HTTP method
get / HTTP/1.0\r\n\r\n


Allow0.9|Require1.0

RFC 2616 §19.6 "Compatibility With Previous Versions" had encouraged HTTP servers to support legacy HTTP/0.9 requests. RFC 7230 supersedes this with "The expectation to support HTTP/0.9 requests has been removed" and offers additional comments in RFC 7230 Appendix A . The Require1.0 option allows the user to remove support of the default Allow0.9 option's behavior.

Example of a request leading to HTTP 400 with Require1.0 mode

# Unsupported HTTP version
GET /\r\n\r\n

Reviewing the messages logged to the ErrorLog, configured with LogLevel debug level, can help identify such faulty requests along with their origin. Users should pay particular attention to the 400 responses in the access log for invalid requests which were unexpectedly rejected.

<If> Directive

The <If> directive evaluates an expression at runtime, and applies the enclosed directives if and only if the expression evaluates to true. For example:

<If "-z req('Host')">

would match HTTP/1.0 requests without a Host: header. Expressions may contain various shell-like operators for string comparison (==, !=, <, ...), integer comparison (-eq, -ne, ...), and others (-n, -z, -f, ...). It is also possible to use regular expressions,

<If "%{QUERY_STRING} =~ /(delete|commit)=.*?elem/">

shell-like pattern matches and many other operations. These operations can be done on request headers (req), environment variables (env), and a large number of other properties. The full documentation is available in Expressions in Apache HTTP Server.

Only directives that support the directory context can be used within this configuration section.

See also

• Expressions in Apache HTTP Server, for a complete reference and more examples.
• <ElseIf>
• <Else>
• How <Directory>, <Location>, <Files> sections work for an explanation of how these different sections are combined when a request is received. <If>, <ElseIf>, and <Else> are applied last.

<IfDefine> Directive

The <IfDefine test>...</IfDefine> section is used to mark directives that are conditional. The directives within an <IfDefine> section are only processed if the test is true. If test is false, everything between the start and end markers is ignored.

The test in the <IfDefine> section directive can be one of two forms:

• parameter-name
• !parameter-name

In the former case, the directives between the start and end markers are only processed if the parameter named parameter-name is defined. The second format reverses the test, and only processes the directives if parameter-name is not defined.

The parameter-name argument is a define as given on the httpd command line via -Dparameter at the time the server was started or by the Define directive.

<IfDefine> sections are nest-able, which can be used to implement simple multiple-parameter tests. Example:

<IfDefine ReverseProxy>
  LoadModule proxy_module   modules/mod_proxy.so
  LoadModule proxy_http_module   modules/mod_proxy_http.so
  <IfDefine UseCache>
    LoadModule cache_module   modules/mod_cache.so
    <IfDefine MemCache>
      LoadModule mem_cache_module   modules/mod_mem_cache.so
    </IfDefine>
    <IfDefine !MemCache>
      LoadModule cache_disk_module   modules/mod_cache_disk.so
    </IfDefine>
  </IfDefine>
</IfDefine>

<IfDirective> Directive

The <IfDirective test>...</IfDirective> section is used to mark directives that are conditional on the presence of a specific directive. The directives within an <IfDirective> section are only processed if the test is true. If test is false, everything between the start and end markers is ignored.

The test in the <IfDirective> section can be one of two forms:

• directive-name
• !directive-name

In the former case, the directives between the start and end markers are only processed if a directive of the given name is available at the time of processing. The second format reverses the test, and only processes the directives if directive-name is not available.

See also

• <IfSection>

<IfFile> Directive

The <IfFile filename>...</IfFile> section is used to mark directives that are conditional on the existence of a file on disk. The directives within an <IfFile> section are only processed if filename exists. If filename doesn't exist, everything between the start and end markers is ignored. filename can be an absolute path or a path relative to the server root.

The filename in the <IfFile> section directive can take the same forms as the test variable in the <IfDefine> section, i.e. the test can be negated if the ! character is placed directly before filename.

If a relative filename is supplied, the check is ServerRoot relative. In the case where this directive occurs before the ServerRoot, the path will be checked relative to the compiled-in server root or the server root passed in on the command line via the -d parameter.

<IfModule> Directive

The <IfModule test>...</IfModule> section is used to mark directives that are conditional on the presence of a specific module. The directives within an <IfModule> section are only processed if the test is true. If test is false, everything between the start and end markers is ignored.

The test in the <IfModule> section directive can be one of two forms:

• module
• !module

In the former case, the directives between the start and end markers are only processed if the module named module is included in Apache httpd -- either compiled in or dynamically loaded using LoadModule. The second format reverses the test, and only processes the directives if module is not included.

The module argument can be either the module identifier or the file name of the module, at the time it was compiled. For example, rewrite_module is the identifier and mod_rewrite.c is the file name. If a module consists of several source files, use the name of the file containing the string STANDARD20_MODULE_STUFF.

<IfModule> sections are nest-able, which can be used to implement simple multiple-module tests.

<IfSection> Directive

The <IfSection test>...</IfSection> section is used to mark directives that are conditional on the presence of a specific section directive. A section directive is any directive such as <VirtualHost> which encloses other directives, and has a directive name with a leading "<".

The directives within an <IfSection> section are only processed if the test is true. If test is false, everything between the start and end markers is ignored.

The section-name must be specified without either the leading "<" or closing ">". The test in the <IfSection> section can be one of two forms:

• section-name
• !section-name

In the former case, the directives between the start and end markers are only processed if a section directive of the given name is available at the time of processing. The second format reverses the test, and only processes the directives if section-name is not an available section directive.

For example:

<IfSection VirtualHost>
   ...
</IfSection>

See also

• <IfDirective>

Include Directive

This directive allows inclusion of other configuration files from within the server configuration files.

Shell-style (fnmatch()) wildcard characters can be used in the filename or directory parts of the path to include several files at once, in alphabetical order. In addition, if Include points to a directory, rather than a file, Apache httpd will read all files in that directory and any subdirectory. However, including entire directories is not recommended, because it is easy to accidentally leave temporary files in a directory that can cause httpd to fail. Instead, we encourage you to use the wildcard syntax shown below, to include files that match a particular pattern, such as *.conf, for example.

The Include directive will fail with an error if a wildcard expression does not match any file. The IncludeOptional directive can be used if non-matching wildcards should be ignored.

The file path specified may be an absolute path, or may be relative to the ServerRoot directory.

Examples:

Include /usr/local/apache2/conf/ssl.conf
Include /usr/local/apache2/conf/vhosts/*.conf

Or, providing paths relative to your ServerRoot directory:

Include conf/ssl.conf
Include conf/vhosts/*.conf

Wildcards may be included in the directory or file portion of the path. This example will fail if there is no subdirectory in conf/vhosts that contains at least one *.conf file:

Include conf/vhosts/*/*.conf

Alternatively, the following command will just be ignored in case of missing files or directories:

IncludeOptional conf/vhosts/*/*.conf

See also

• IncludeOptional
• apachectl

IncludeOptional Directive

This directive allows inclusion of other configuration files from within the server configuration files. It works identically to the Include directive, but it will be silently ignored (instead of causing an error) if wildcards are used and they do not match any file or directory or if a file path does not exist on the file system.

See also

• Include
• apachectl

KeepAlive Directive

The Keep-Alive extension to HTTP/1.0 and the persistent connection feature of HTTP/1.1 provide long-lived HTTP sessions which allow multiple requests to be sent over the same TCP connection. In some cases this has been shown to result in an almost 50% speedup in latency times for HTML documents with many images. To enable Keep-Alive connections, set KeepAlive On.

For HTTP/1.0 clients, Keep-Alive connections will only be used if they are specifically requested by a client. In addition, a Keep-Alive connection with an HTTP/1.0 client can only be used when the length of the content is known in advance. This implies that dynamic content such as CGI output, SSI pages, and server-generated directory listings will generally not use Keep-Alive connections to HTTP/1.0 clients. For HTTP/1.1 clients, persistent connections are the default unless otherwise specified. If the client requests it, chunked encoding will be used in order to send content of unknown length over persistent connections.

When a client uses a Keep-Alive connection, it will be counted as a single "request" for the MaxConnectionsPerChild directive, regardless of how many requests are sent using the connection.

See also

• MaxKeepAliveRequests

KeepAliveTimeout Directive

The number of seconds Apache httpd will wait for a subsequent request before closing the connection. By adding a postfix of ms the timeout can be also set in milliseconds. Once a request has been received, the timeout value specified by the Timeout directive applies.

Setting KeepAliveTimeout to a high value may cause performance problems in heavily loaded servers. The higher the timeout, the more server processes will be kept occupied waiting on connections with idle clients.

If KeepAliveTimeout is not set for a name-based virtual host, the value of the first defined virtual host best matching the local IP and port will be used.

<Limit> Directive

Access controls are normally effective for all access methods, and this is the usual desired behavior. In the general case, access control directives should not be placed within a <Limit> section.

The purpose of the <Limit> directive is to restrict the effect of the access controls to the nominated HTTP methods. For all other methods, the access restrictions that are enclosed in the <Limit> bracket will have no effect. The following example applies the access control only to the methods POST, PUT, and DELETE, leaving all other methods unprotected:

<Limit POST PUT DELETE>
  Require valid-user
</Limit>

The method names listed can be one or more of: GET, POST, PUT, DELETE, CONNECT, OPTIONS, PATCH, PROPFIND, PROPPATCH, MKCOL, COPY, MOVE, LOCK, and UNLOCK. The method name is case-sensitive. If GET is used, it will also restrict HEAD requests. The TRACE method cannot be limited (see TraceEnable).

The <Limit> and <LimitExcept> directives may be nested. In this case, each successive level of <Limit> or <LimitExcept> directives must further restrict the set of methods to which access controls apply.

For example, given the following configuration, all users will be authorized for POST requests, and the Require group editors directive will be ignored in all cases:

<LimitExcept GET>
  Require valid-user
</LimitExcept>
<Limit POST>
  Require group editors
</Limit>

<LimitExcept> Directive

<LimitExcept> and </LimitExcept> are used to enclose a group of access control directives which will then apply to any HTTP access method not listed in the arguments; i.e., it is the opposite of a <Limit> section and can be used to control both standard and nonstandard/unrecognized methods. See the documentation for <Limit> for more details.

For example:

<LimitExcept POST GET>
  Require valid-user
</LimitExcept>

LimitInternalRecursion Directive

An internal redirect happens, for example, when using the Action directive, which internally redirects the original request to a CGI script. A subrequest is Apache httpd's mechanism to find out what would happen for some URI if it were requested. For example, mod_dir uses subrequests to look for the files listed in the DirectoryIndex directive.

LimitInternalRecursion prevents the server from crashing when entering an infinite loop of internal redirects or subrequests. Such loops are usually caused by misconfigurations.

The directive stores two different limits, which are evaluated on per-request basis. The first number is the maximum number of internal redirects that may follow each other. The second number determines how deeply subrequests may be nested. If you specify only one number, it will be assigned to both limits.

LimitInternalRecursion 5

LimitRequestBody Directive

This directive specifies the number of bytes from 0 (meaning unlimited) to 2147483647 (2GB) that are allowed in a request body. See the note below for the limited applicability to proxy requests.

The LimitRequestBody directive allows the user to set a limit on the allowed size of an HTTP request message body within the context in which the directive is given (server, per-directory, per-file or per-location). If the client request exceeds that limit, the server will return an error response instead of servicing the request. The size of a normal request message body will vary greatly depending on the nature of the resource and the methods allowed on that resource. CGI scripts typically use the message body for retrieving form information. Implementations of the PUT method will require a value at least as large as any representation that the server wishes to accept for that resource.

This directive gives the server administrator greater control over abnormal client request behavior, which may be useful for avoiding some forms of denial-of-service attacks.

If, for example, you are permitting file upload to a particular location and wish to limit the size of the uploaded file to 100K, you might use the following directive:

LimitRequestBody 102400

LimitRequestFields Directive

Number is an integer from 0 (meaning unlimited) to 32767. The default value is defined by the compile-time constant DEFAULT_LIMIT_REQUEST_FIELDS (100 as distributed).

The LimitRequestFields directive allows the server administrator to modify the limit on the number of request header fields allowed in an HTTP request. A server needs this value to be larger than the number of fields that a normal client request might include. The number of request header fields used by a client rarely exceeds 20, but this may vary among different client implementations, often depending upon the extent to which a user has configured their browser to support detailed content negotiation. Optional HTTP extensions are often expressed using request header fields.

This directive gives the server administrator greater control over abnormal client request behavior, which may be useful for avoiding some forms of denial-of-service attacks. The value should be increased if normal clients see an error response from the server that indicates too many fields were sent in the request.

For example:

LimitRequestFields 50

LimitRequestFieldSize Directive

This directive specifies the number of bytes that will be allowed in an HTTP request header.

The LimitRequestFieldSize directive allows the server administrator to set the limit on the allowed size of an HTTP request header field. A server needs this value to be large enough to hold any one header field from a normal client request. The size of a normal request header field will vary greatly among different client implementations, often depending upon the extent to which a user has configured their browser to support detailed content negotiation. SPNEGO authentication headers can be up to 12392 bytes.

This directive gives the server administrator greater control over abnormal client request behavior, which may be useful for avoiding some forms of denial-of-service attacks.

For example:

LimitRequestFieldSize 4094

LimitRequestLine Directive

This directive sets the number of bytes that will be allowed on the HTTP request-line.

The LimitRequestLine directive allows the server administrator to set the limit on the allowed size of a client's HTTP request-line. Since the request-line consists of the HTTP method, URI, and protocol version, the LimitRequestLine directive places a restriction on the length of a request-URI allowed for a request on the server. A server needs this value to be large enough to hold any of its resource names, including any information that might be passed in the query part of a GET request.

This directive gives the server administrator greater control over abnormal client request behavior, which may be useful for avoiding some forms of denial-of-service attacks.

For example:

LimitRequestLine 4094

LimitXMLRequestBody Directive

Limit (in bytes) on maximum size of an XML-based request body. A value of 0 will disable any checking.

Example:

LimitXMLRequestBody 0

<Location> Directive

The <Location> directive limits the scope of the enclosed directives by URL. It is similar to the <Directory> directive, and starts a subsection which is terminated with a </Location> directive. <Location> sections are processed in the order they appear in the configuration file, after the <Directory> sections and .htaccess files are read, and after the <Files> sections.

<Location> sections operate completely outside the filesystem. This has several consequences. Most importantly, <Location> directives should not be used to control access to filesystem locations. Since several different URLs may map to the same filesystem location, such access controls may by circumvented.

The enclosed directives will be applied to the request if the path component of the URL meets any of the following criteria:

• The specified location matches exactly the path component of the URL.
• The specified location, which ends in a forward slash, is a prefix of the path component of the URL (treated as a context root).
• The specified location, with the addition of a trailing slash, is a prefix of the path component of the URL (also treated as a context root).

In the example below, where no trailing slash is used, requests to /private1, /private1/ and /private1/file.txt will have the enclosed directives applied, but /private1other would not.

<Location "/private1">
    #  ...
</Location>

In the example below, where a trailing slash is used, requests to /private2/ and /private2/file.txt will have the enclosed directives applied, but /private2 and /private2other would not.

<Location "/private2/">
    # ...
</Location>

For all origin (non-proxy) requests, the URL to be matched is a URL-path of the form /path/. No scheme, hostname, port, or query string may be included. For proxy requests, the URL to be matched is of the form scheme://servername/path, and you must include the prefix.

The URL may use wildcards. In a wild-card string, ? matches any single character, and * matches any sequences of characters. Neither wildcard character matches a / in the URL-path.

Regular expressions can also be used, with the addition of the ~ character. For example:

<Location ~ "/(extra|special)/data">
    #...
</Location>

would match URLs that contained the substring /extra/data or /special/data. The directive <LocationMatch> behaves identical to the regex version of <Location>, and is preferred, for the simple reason that ~ is hard to distinguish from - in many fonts.

The <Location> functionality is especially useful when combined with the SetHandler directive. For example, to enable status requests but allow them only from browsers at example.com, you might use:

<Location "/status">
  SetHandler server-status
  Require host example.com
</Location>

See also

• How <Directory>, <Location> and <Files> sections work for an explanation of how these different sections are combined when a request is received.
• LocationMatch

<LocationMatch> Directive

The <LocationMatch> directive limits the scope of the enclosed directives by URL, in an identical manner to <Location>. However, it takes a regular expression as an argument instead of a simple string. For example:

<LocationMatch "/(extra|special)/data">
    # ...
</LocationMatch>

would match URLs that contained the substring /extra/data or /special/data.

<LocationMatch "^/(extra|special)/data">

From 2.4.8 onwards, named groups and backreferences are captured and written to the environment with the corresponding name prefixed with "MATCH_" and in upper case. This allows elements of URLs to be referenced from within expressions and modules like mod_rewrite. In order to prevent confusion, numbered (unnamed) backreferences are ignored. Use named groups instead.

<LocationMatch "^/combined/(?<sitename>[^/]+)">
    Require ldap-group cn=%{env:MATCH_SITENAME},ou=combined,o=Example
</LocationMatch>

See also

• How <Directory>, <Location> and <Files> sections work for an explanation of how these different sections are combined when a request is received

LogLevel Directive

LogLevel adjusts the verbosity of the messages recorded in the error logs (see ErrorLog directive). The following levels are available, in order of decreasing significance:

When a particular level is specified, messages from all other levels of higher significance will be reported as well. E.g., when LogLevel info is specified, then messages with log levels of notice and warn will also be posted.

Using a level of at least crit is recommended.

For example:

LogLevel notice

Specifying a level without a module name will reset the level for all modules to that level. Specifying a level with a module name will set the level for that module only. It is possible to use the module source file name, the module identifier, or the module identifier with the trailing _module omitted as module specification. This means the following three specifications are equivalent:

LogLevel info ssl:warn
LogLevel info mod_ssl.c:warn
LogLevel info ssl_module:warn

It is also possible to change the level per directory:

LogLevel info
<Directory "/usr/local/apache/htdocs/app">
  LogLevel debug
</Directory>

See also

• ErrorLog
• ErrorLogFormat
• Apache HTTP Server Log Files

MaxKeepAliveRequests Directive

The MaxKeepAliveRequests directive limits the number of requests allowed per connection when KeepAlive is on. If it is set to 0, unlimited requests will be allowed. We recommend that this setting be kept to a high value for maximum server performance.

For example:

MaxKeepAliveRequests 500