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Apache > HTTP Server > Documentation > Version 2.5 > Modules

Apache Core Features

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Description:Core Apache HTTP Server features that are always available
Status:Core

Directives

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AcceptFilter Directive

Description:Configures optimizations for a Protocol's Listener Sockets
Syntax:AcceptFilter protocol accept_filter
Context:server config
Status:Core
Module:core

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 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 data
AcceptFilter https data

Window's mpm_winnt interprets the AcceptFilter to toggle the AcceptEx() API, and does not support http protocol buffering. There are two values which utilize the Windows AcceptEx() API and will recycle network sockets between connections. data waits until data has been transmitted as documented above, and the initial data buffer and network endpoint addresses are all retrieved from the single AcceptEx() invocation. 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

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AcceptPathInfo Directive

Description:Resources accept trailing pathname information
Syntax:AcceptPathInfo On|Off|Default
Default:AcceptPathInfo Default
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Core
Module:core

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>
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AccessFileName Directive

Description:Name of the distributed configuration file
Syntax:AccessFileName filename [filename] ...
Default:AccessFileName .htaccess
Context:server config, virtual host
Status:Core
Module:core

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

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AddDefaultCharset Directive

Description:Default charset parameter to be added when a response content-type is text/plain or text/html
Syntax:AddDefaultCharset On|Off|charset
Default:AddDefaultCharset Off
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Core
Module:core

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

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AllowEncodedSlashes Directive

Description:Determines whether encoded path separators in URLs are allowed to be passed through
Syntax:AllowEncodedSlashes On|Off|NoDecode
Default:AllowEncodedSlashes Off
Context:server config, virtual host
Status:Core
Module:core
Compatibility: NoDecode option available in 2.3.12 and later.

The AllowEncodedSlashes directive allows URLs which contain encoded path separators (%2F for / and additionally %5C for \ on according 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.

Note

If encoded slashes are needed in path info, use of NoDecode is strongly recommended as a security measure. Allowing slashes to be decoded could potentially allow unsafe paths.

See also

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AllowOverride Directive

Description:Types of directives that are allowed in .htaccess files
Syntax:AllowOverride All|None|directive-type [directive-type] ...
Default:AllowOverride None (2.3.9 and later), AllowOverride All (2.3.8 and earlier)
Context:directory
Status:Core
Module:core

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.

Only available in <Directory> sections

AllowOverride is valid only in <Directory> sections specified without regular expressions, not in <Location>, <DirectoryMatch> or <Files> sections.

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.

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, , FallbackResource,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 non-fatal: 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 non-fatal.
  • Nonfatal=Unknown treats unknown directives as non-fatal. This covers typos and directives implemented by a module that's not present.
  • Nonfatal=All treats both the above as non-fatal.

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 (but no spaces) separated lists 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.

For security and performance reasons, do not set AllowOverride to anything other than None in your <Directory /> block. Instead, find (or create) the <Directory> block that refers to the directory where you're actually planning to place a .htaccess file.

See also

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AllowOverrideList Directive

Description:Individual directives that are allowed in .htaccess files
Syntax:AllowOverrideList None|directive [directive-type] ...
Default:AllowOverrideList None
Context:directory
Status:Core
Module:core

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.

Only available in <Directory> sections

AllowOverrideList is valid only in <Directory> sections specified without regular expressions, not in <Location>, <DirectoryMatch> or <Files> sections.

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

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CGIMapExtension Directive

Description:Technique for locating the interpreter for CGI scripts
Syntax:CGIMapExtension cgi-path .extension
Context:directory, .htaccess
Override:FileInfo
Status:Core
Module:core
Compatibility:NetWare only

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.

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ContentDigest Directive

Description:Enables the generation of Content-MD5 HTTP Response headers
Syntax:ContentDigest On|Off
Default:ContentDigest Off
Context:server config, virtual host, directory, .htaccess
Override:Options
Status:Core
Module:core

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:

Content-MD5: AuLb7Dp1rqtRtxz2m9kRpA==

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.

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DefaultRuntimeDir Directive

Description:Base directory for the server run-time files
Syntax:DefaultRuntimeDir directory-path
Default:DefaultRuntimeDir DEFAULT_REL_RUNTIMEDIR (logs/)
Context:server config
Status:Core
Module:core
Compatibility:Available in Apache 2.4.2 and later

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

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DefaultType Directive

Description:This directive has no effect other than to emit warnings if the value is not none. In prior versions, DefaultType would specify a default media type to assign to response content for which no other media type configuration could be found.
Syntax:DefaultType media-type|none
Default:DefaultType none
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Core
Module:core
Compatibility:All choices except none are DISABLED for 2.3.x and later.

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.

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Define Directive

Description:Define a variable
Syntax:Define parameter-name [parameter-value]
Context:server config, virtual host, directory
Status:Core
Module:core

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.

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<Directory> Directive

Description:Enclose a group of directives that apply only to the named file-system directory, sub-directories, and their contents.
Syntax:<Directory directory-path> ... </Directory>
Context:server config, virtual host
Status:Core
Module:core

<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>

Be careful with the directory-path arguments: They have to literally match the filesystem path which Apache httpd uses to access the files. Directives applied to a particular <Directory> will not apply to files accessed from that same directory via a different path, such as via different symbolic links.

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:

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

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<DirectoryMatch> Directive

Description:Enclose directives that apply to the contents of file-system directories matching a regular expression.
Syntax:<DirectoryMatch regex> ... </DirectoryMatch>
Context:server config, virtual host
Status:Core
Module:core

<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>

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

Compatability

Prior to 2.3.9, this directive implicitly applied to sub-directories (like <Directory>) and could not match the end of line symbol ($). In 2.3.9 and later, only directories that match the expression are affected by the enclosed directives.

Trailing Slash

This directive applies to requests for directories that may or may not end in a trailing slash, so expressions that are anchored to the end of line ($) must be written with care.

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>

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DocumentRoot Directive

Description:Directory that forms the main document tree visible from the web
Syntax:DocumentRoot directory-path
Default:DocumentRoot /usr/local/apache/htdocs
Context:server config, virtual host
Status:Core
Module:core

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

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<Else> Directive

Description:Contains directives that apply only if the condition of a previous <If> or <ElseIf> section is not satisfied by a request at runtime
Syntax:<Else> ... </Else>
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Core
Module:core

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

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<ElseIf> Directive

Description:Contains directives that apply only if a condition is satisfied by a request at runtime while the condition of a previous <If> or <ElseIf> section is not satisfied
Syntax:<ElseIf expression> ... </ElseIf>
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Core
Module:core

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

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EnableMMAP Directive

Description:Use memory-mapping to read files during delivery
Syntax:EnableMMAP On|Off
Default:EnableMMAP On
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Core
Module:core

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:

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>
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EnableSendfile Directive

Description:Use the kernel sendfile support to deliver files to the client
Syntax:EnableSendfile On|Off
Default:EnableSendfile Off
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Core
Module:core
Compatibility:Default changed to Off in version 2.3.9.

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:

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.

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Error Directive

Description:Abort configuration parsing with a custom error message
Syntax:Error message
Context:server config, virtual host, directory, .htaccess
Status:Core
Module:core
Compatibility:2.3.9 and later

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>
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ErrorDocument Directive

Description:What the server will return to the client in case of an error
Syntax:ErrorDocument error-code document
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Core
Module:core

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.

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. Examples:

ErrorDocument 500 http://foo.example.com/cgi-bin/tester
ErrorDocument 404 /cgi-bin/bad_urls.pl
ErrorDocument 401 /subscription_info.html
ErrorDocument 403 "Sorry can't allow you access today"
ErrorDocument 403 Forbidden!

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

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ErrorLog Directive

Description:Location where the server will log errors
Syntax: ErrorLog file-path|syslog[:facility]
Default:ErrorLog logs/error_log (Unix) ErrorLog logs/error.log (Windows and OS/2)
Context:server config, virtual host
Status:Core
Module:core

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 and if mod_syslog is loaded. 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.

ErrorLog syslog:user

Additional modules can provide their own ErrorLog providers. The syntax is similar to 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.

Note

When entering a file path on non-Unix platforms, care should be taken to make sure that only forward slashes 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.

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ErrorLogFormat Directive

Description:Format specification for error log entries
Syntax: ErrorLogFormat [connection|request] format
Context:server config, virtual host
Status:Core
Module:core

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.

Modified TokenMeaning
%-{Referer}i Logs a - if Referer is not set.
%+{Referer}i Omits the entire line if Referer is not set.
%4{Referer}i Logs the Referer only if the log message severity is higher than 4.

Some format string items accept additional parameters in braces.

Format String Description
%% The percent sign
%a Client IP address and port of the request
%{c}a Underlying peer IP address and port of the connection (see the mod_remoteip module)
%A Local IP-address and port
%{name}e Request environment variable name
%E APR/OS error status code and string
%F Source file name and line number of the log call
%{name}i Request header name
%k Number of keep-alive requests on this connection
%l Loglevel of the message
%L Log ID of the request
%{c}L Log ID of the connection
%{C}L Log ID of the connection if used in connection scope, empty otherwise
%m Name of the module logging the message
%M The actual log message
%{name}n Request note name
%P Process ID of current process
%T Thread ID of current thread
%{g}T System unique thread ID of current thread (the same ID as displayed by e.g. top; currently Linux only)
%t The current time
%{u}t The current time including micro-seconds
%{cu}t The current time in compact ISO 8601 format, including micro-seconds
%v The canonical ServerName of the current server.
%V The server name of the server serving the request according to the UseCanonicalName setting.
(backslash space) Non-field delimiting space
(percent space) Field delimiter (no output)

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:

[Thu May 12 08:28:57.652118 2011] [core:error] [pid 8777:tid 4326490112] [client ::1:58619] File does not exist: /usr/local/apache2/htdocs/favicon.ico

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"

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ExtendedStatus Directive

Description:Keep track of extended status information for each request
Syntax:ExtendedStatus On|Off
Default:ExtendedStatus Off[*]
Context:server config
Status:Core
Module:core

This option tracks additional data per worker about the currently executing request, and 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.

Note that loading mod_status will change the default behavior to ExtendedStatus On, while other third party modules may do the same. Such modules rely on collecting detailed information about the state of all workers. The default is changed by mod_status beginning with version 2.3.6; the previous default was always Off.

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FileETag Directive

Description:File attributes used to create the ETag HTTP response header for static files
Syntax:FileETag component ...
Default:FileETag MTime Size
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Core
Module:core
Compatibility:The default used to be "INode MTime Size" in 2.3.14 and earlier.

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.

Warning

Do not change the default for directories or locations that have WebDAV enabled and use mod_dav_fs as a storage provider. mod_dav_fs uses MTime Size as a fixed format for ETag comparisons on conditional requests. These conditional requests will break if the ETag format is changed via FileETag.

Server Side Includes

An ETag is not generated for responses parsed by mod_include, since the response entity can change without a change of the INode, MTime, or Size of the static file with embedded SSI directives.
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<Files> Directive

Description:Contains directives that apply to matched filenames
Syntax:<Files filename> ... </Files>
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Core
Module:core

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.

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<FilesMatch> Directive

Description:Contains directives that apply to regular-expression matched filenames
Syntax:<FilesMatch regex> ... </FilesMatch>
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Core
Module:core

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>

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ForceType Directive

Description:Forces all matching files to be served with the specified media type in the HTTP Content-Type header field
Syntax:ForceType media-type|None
Context:directory, .htaccess
Override:FileInfo
Status:Core
Module:core

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.

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GprofDir Directive

Description:Directory to write gmon.out profiling data to.
Syntax:GprofDir /tmp/gprof/|/tmp/gprof/%
Context:server config, virtual host
Status:Core
Module:core

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.

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HostnameLookups Directive

Description:Enables DNS lookups on client IP addresses
Syntax:HostnameLookups On|Off|Double
Default:HostnameLookups Off
Context:server config, virtual host, directory
Status:Core
Module:core

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.

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<If> Directive

Description:Contains directives that apply only if a condition is satisfied by a request at runtime
Syntax:<If expression> ... </If>
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Core
Module:core

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.

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<IfDefine> Directive

Description:Encloses directives that will be processed only if a test is true at startup
Syntax:<IfDefine [!]parameter-name> ... </IfDefine>
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Core
Module:core

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:

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:

httpd -DReverseProxy -DUseCache -DMemCache ...

<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>
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<IfModule> Directive

Description:Encloses directives that are processed conditional on the presence or absence of a specific module
Syntax:<IfModule [!]module-file|module-identifier> ... </IfModule>
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Core
Module:core

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:

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.

This section should only be used if you need to have one configuration file that works whether or not a specific module is available. In normal operation, directives need not be placed in <IfModule> sections.
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Include Directive

Description:Includes other configuration files from within the server configuration files
Syntax:Include file-path|directory-path|wildcard
Context:server config, virtual host, directory
Status:Core
Module:core
Compatibility:Directory wildcard matching available in 2.3.6 and later

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

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IncludeOptional Directive

Description:Includes other configuration files from within the server configuration files
Syntax:IncludeOptional file-path|directory-path|wildcard
Context:server config, virtual host, directory
Status:Core
Module:core
Compatibility:Available in 2.3.6 and later

This directive allows inclusion of other configuration files from within the server configuration files. It works identically to the Include directive, with the exception that if wildcards do not match any file or directory, the IncludeOptional directive will be silently ignored instead of causing an error.

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KeepAlive Directive

Description:Enables HTTP persistent connections
Syntax:KeepAlive On|Off
Default:KeepAlive On
Context:server config, virtual host
Status:Core
Module:core

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.

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KeepAliveTimeout Directive

Description:Amount of time the server will wait for subsequent requests on a persistent connection
Syntax:KeepAliveTimeout num[ms]
Default:KeepAliveTimeout 5
Context:server config, virtual host
Status:Core
Module:core

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.

In a name-based virtual host context, the value of the first defined virtual host best matching the local IP and port will be used.

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<Limit> Directive

Description:Restrict enclosed access controls to only certain HTTP methods
Syntax:<Limit method [method] ... > ... </Limit>
Context:directory, .htaccess
Override:AuthConfig, Limit
Status:Core
Module:core

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).

A <LimitExcept> section should always be used in preference to a <Limit> section when restricting access, since a <LimitExcept> section provides protection against arbitrary methods.

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.

When using <Limit> or <LimitExcept> directives with the Require directive, note that the first Require to succeed authorizes the request, regardless of the presence of other Require directives.

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>
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<LimitExcept> Directive

Description:Restrict access controls to all HTTP methods except the named ones
Syntax:<LimitExcept method [method] ... > ... </LimitExcept>
Context:directory, .htaccess
Override:AuthConfig, Limit
Status:Core
Module:core

<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>
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LimitInternalRecursion Directive

Description:Determine maximum number of internal redirects and nested subrequests
Syntax:LimitInternalRecursion number [number]
Default:LimitInternalRecursion 10
Context:server config, virtual host
Status:Core
Module:core

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 deep subrequests may be nested. If you specify only one number, it will be assigned to both limits.

LimitInternalRecursion 5
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LimitRequestBody Directive

Description:Restricts the total size of the HTTP request body sent from the client
Syntax:LimitRequestBody bytes
Default:LimitRequestBody 0
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Core
Module:core

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

For a full description of how this directive is interpreted by proxy requests, see the mod_proxy documentation.

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LimitRequestFields Directive

Description:Limits the number of HTTP request header fields that will be accepted from the client
Syntax:LimitRequestFields number
Default:LimitRequestFields 100
Context:server config, virtual host
Status:Core
Module:core

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

Warning

When name-based virtual hosting is used, the value for this directive is taken from the default (first-listed) virtual host for the local IP and port combination.

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LimitRequestFieldSize Directive

Description:Limits the size of the HTTP request header allowed from the client
Syntax:LimitRequestFieldSize bytes
Default:LimitRequestFieldSize 8190
Context:server config, virtual host
Status:Core
Module:core

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
Under normal conditions, the value should not be changed from the default.

Warning

When name-based virtual hosting is used, the value for this directive is taken from the default (first-listed) virtual host best matching the current IP address and port combination.

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LimitRequestLine Directive

Description:Limit the size of the HTTP request line that will be accepted from the client
Syntax:LimitRequestLine bytes
Default:LimitRequestLine 8190
Context:server config, virtual host
Status:Core
Module:core

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
Under normal conditions, the value should not be changed from the default. Also, you can't set this higher than 8190 without modifying the source and rebuilding.

Warning

When name-based virtual hosting is used, the value for this directive is taken from the default (first-listed) virtual host best matching the current IP address and port combination.

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LimitXMLRequestBody Directive

Description:Limits the size of an XML-based request body
Syntax:LimitXMLRequestBody bytes
Default:LimitXMLRequestBody 1000000
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Core
Module:core

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

Example:

LimitXMLRequestBody 0
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<Location> Directive

Description:Applies the enclosed directives only to matching URLs
Syntax:<Location URL-path|URL> ... </Location>
Context:server config, virtual host
Status:Core
Module:core

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:

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>

When to use <Location>

Use <Location> to apply directives to content that lives outside the filesystem. For content that lives in the filesystem, use <Directory> and <Files>. An exception is <Location />, which is an easy way to apply a configuration to the entire server.

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>

Note about / (slash)

The slash character has special meaning depending on where in a URL it appears. People may be used to its behavior in the filesystem where multiple adjacent slashes are frequently collapsed to a single slash (i.e., /home///foo is the same as /home/foo). In URL-space this is not necessarily true. The <LocationMatch> directive and the regex version of <Location> require you to explicitly specify multiple slashes if that is your intention.

For example, <LocationMatch ^/abc> would match the request URL /abc but not the request URL //abc. The (non-regex) <Location> directive behaves similarly when used for proxy requests. But when (non-regex) <Location> is used for non-proxy requests it will implicitly match multiple slashes with a single slash. For example, if you specify <Location /abc/def> and the request is to /abc//def then it will match.

See also

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<LocationMatch> Directive

Description:Applies the enclosed directives only to regular-expression matching URLs
Syntax:<LocationMatch regex> ... </LocationMatch>
Context:server config, virtual host
Status:Core
Module:core

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.

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

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LogLevel Directive

Description:Controls the verbosity of the ErrorLog
Syntax:LogLevel [module:]level [module:level] ...
Default:LogLevel warn
Context:server config, virtual host, directory
Status:Core
Module:core
Compatibility:Per-module and per-directory configuration is available in Apache HTTP Server 2.3.6 and later

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:

Level Description Example
emerg Emergencies - system is unusable. "Child cannot open lock file. Exiting"
alert Action must be taken immediately. "getpwuid: couldn't determine user name from uid"
crit Critical Conditions. "socket: Failed to get a socket, exiting child"
error Error conditions. "Premature end of script headers"
warn Warning conditions. "child process 1234 did not exit, sending another SIGHUP"
notice Normal but significant condition. "httpd: caught SIGBUS, attempting to dump core in ..."
info Informational. "Server seems busy, (you may need to increase StartServers, or Min/MaxSpareServers)..."
debug Debug-level messages "Opening config file ..."
trace1 Trace messages "proxy: FTP: control connection complete"
trace2 Trace messages "proxy: CONNECT: sending the CONNECT request to the remote proxy"
trace3 Trace messages "openssl: Handshake: start"
trace4 Trace messages "read from buffered SSL brigade, mode 0, 17 bytes"
trace5 Trace messages "map lookup FAILED: map=rewritemap key=keyname"
trace6 Trace messages "cache lookup FAILED, forcing new map lookup"
trace7 Trace messages, dumping large amounts of data "| 0000: 02 23 44 30 13 40 ac 34 df 3d bf 9a 19 49 39 15 |"
trace8 Trace messages, dumping large amounts of data "| 0000: 02 23 44 30 13 40 ac 34 df 3d bf 9a 19 49 39 15 |"

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

Note

When logging to a regular file messages of the level notice cannot be suppressed and thus are always logged. However, this doesn't apply when logging is done using syslog.

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>
Per directory loglevel configuration only affects messages that are logged after the request has been parsed and that are associated with the request. Log messages which are associated with the server or the connection are not affected. The latter can be influenced by the LogLevelOverride directive, though.

See also

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LogLevelOverride Directive

Description:Override the verbosity of the ErrorLog for certain clients
Syntax:LogLevel ipaddress[/prefixlen] [module:]level [module:level] ...
Default:unset
Context:server config, virtual host
Status:Core
Module:core
Compatibility:Available in Apache HTTP Server 2.5.0 and later

LogLevelOverride adjusts the LogLevel for requests coming from certain client IP addresses. This allows to enable verbose logging only for certain test clients. The IP address is checked at a very early state in the connection processing. Therefore, LogLevelOverride allows to change the log level for things like the SSL handshake which happen before a LogLevel directive in an <If> container would be evaluated.

LogLevelOverride accepts either a single IP-address or a CIDR IP-address/len subnet specification. For the syntax of the loglevel specification, see the LogLevel directive.

For requests that match a LogLevelOverride directive, per-directory specifications of LogLevel are ignored.

Examples:

        LogLevelOverride 192.0.2.0/24 ssl:trace6
        LogLevelOverride 192.0.2.7 ssl:trace8
LogLevelOverride only affects log messages that are associated with the request or the connection. Log messages which are associated with the server not affected.

See also

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MaxKeepAliveRequests Directive

Description:Number of requests allowed on a persistent connection
Syntax:MaxKeepAliveRequests number
Default:MaxKeepAliveRequests 100
Context:server config, virtual host
Status:Core
Module:core

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
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MaxRangeOverlaps Directive

Description:Number of overlapping ranges (eg: 100-200,150-300) allowed before returning the complete resource
Syntax:MaxRangeOverlaps default | unlimited | none | number-of-ranges
Default:MaxRangeOverlaps 20
Context:server config, virtual host, directory
Status:Core
Module:core
Compatibility:Available in Apache HTTP Server 2.3.15 and later

The MaxRangeOverlaps directive limits the number of overlapping HTTP ranges the server is willing to return to the client. If more overlapping ranges than permitted are requested, the complete resource is returned instead.

default
Limits the number of overlapping ranges to a compile-time default of 20.
none
No overlapping Range headers are allowed.
unlimited
The server does not limit the number of overlapping ranges it is willing to satisfy.
number-of-ranges
A positive number representing the maximum number of overlapping ranges the server is willing to satisfy.
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MaxRangeReversals Directive

Description:Number of range reversals (eg: 100-200,50-70) allowed before returning the complete resource
Syntax:MaxRangeReversals default | unlimited | none | number-of-ranges
Default:MaxRangeReversals 20
Context:server config, virtual host, directory
Status:Core
Module:core
Compatibility:Available in Apache HTTP Server 2.3.15 and later

The MaxRangeReversals directive limits the number of HTTP Range reversals the server is willing to return to the client. If more ranges reversals than permitted are requested, the complete resource is returned instead.

default
Limits the number of range reversals to a compile-time default of 20.
none
No Range reversals headers are allowed.
unlimited
The server does not limit the number of range reversals it is willing to satisfy.
number-of-ranges
A positive number representing the maximum number of range reversals the server is willing to satisfy.
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MaxRanges Directive

Description:Number of ranges allowed before returning the complete resource
Syntax:MaxRanges default | unlimited | none | number-of-ranges
Default:MaxRanges 200
Context:server config, virtual host, directory
Status:Core
Module:core
Compatibility:Available in Apache HTTP Server 2.3.15 and later

The MaxRanges directive limits the number of HTTP ranges the server is willing to return to the client. If more ranges than permitted are requested, the complete resource is returned instead.

default
Limits the number of ranges to a compile-time default of 200.
none
Range headers are ignored.
unlimited
The server does not limit the number of ranges it is willing to satisfy.
number-of-ranges
A positive number representing the maximum number of ranges the server is willing to satisfy.
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MergeTrailers Directive

Description:Determins whether trailers are merged into headers
Syntax:MergeTrailers [on|off]
Default:MergeTrailers off
Context:server config, virtual host
Status:Core
Module:core
Compatibility:2.4.10 and later

This directive controls whether HTTP trailers are copied into the internal representation of HTTP headers. This mergeing occurs when the request body has been completely consumed, long after most header processing would have a chance to examine or modify request headers.

This option is provided for compatibility with releases prior to 2.4.10, where trailers were always merged.

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Mutex Directive

Description:Configures mutex mechanism and lock file directory for all or specified mutexes
Syntax:Mutex mechanism [default|mutex-name] ... [OmitPID]
Default:Mutex default
Context:server config
Status:Core
Module:core
Compatibility:Available in Apache HTTP Server 2.3.4 and later

The Mutex directive sets the mechanism, and optionally the lock file location, that httpd and modules use to serialize access to resources. Specify default as the first argument to change the settings for all mutexes; specify a mutex name (see table below) as the first argument to override defaults only for that mutex.

The Mutex directive is typically used in the following exceptional situations:

Supported modules

This directive only configures mutexes which have been registered with the core server using the ap_mutex_register() API. All modules bundled with httpd support the Mutex directive, but third-party modules may not. Consult the documentation of the third-party module, which must indicate the mutex name(s) which can be configured if this directive is supported.

The following mutex mechanisms are available:

Most mechanisms are only available on selected platforms, where the underlying platform and APR support it. Mechanisms which aren't available on all platforms are posixsem, sysvsem, sem, pthread, fcntl, flock, and file.

With the file-based mechanisms fcntl and flock, the path, if provided, is a directory where the lock file will be created. The default directory is httpd's run-time file directory, DefaultRuntimeDir. If a relative path is provided, it is relative to DefaultRuntimeDir. Always use a local disk filesystem for /path/to/mutex and never a directory residing on a NFS- or AFS-filesystem. The basename of the file will be the mutex type, an optional instance string provided by the module, and unless the OmitPID keyword is specified, the process id of the httpd parent process will be appended to to make the file name unique, avoiding conflicts when multiple httpd instances share a lock file directory. For example, if the mutex name is mpm-accept and the lock file directory is /var/httpd/locks, the lock file name for the httpd instance with parent process id 12345 would be /var/httpd/locks/mpm-accept.12345.

Security

It is best to avoid putting mutex files in a world-writable directory such as /var/tmp because someone could create a denial of service attack and prevent the server from starting by creating a lockfile with the same name as the one the server will try to create.

The following table documents the names of mutexes used by httpd and bundled modules.

Mutex name Module(s) Protected resource
mpm-accept prefork and worker MPMs incoming connections, to avoid the thundering herd problem; for more information, refer to the performance tuning documentation
authdigest-client mod_auth_digest client list in shared memory
authdigest-opaque mod_auth_digest counter in shared memory
ldap-cache mod_ldap LDAP result cache
rewrite-map mod_rewrite communication with external mapping programs, to avoid intermixed I/O from multiple requests
ssl-cache mod_ssl SSL session cache
ssl-stapling mod_ssl OCSP stapling response cache
watchdog-callback mod_watchdog callback function of a particular client module

The OmitPID keyword suppresses the addition of the httpd parent process id from the lock file name.

In the following example, the mutex mechanism for the MPM accept mutex will be changed from the compiled-in default to fcntl, with the associated lock file created in directory /var/httpd/locks. The mutex mechanism for all other mutexes will be changed from the compiled-in default to sysvsem.

Mutex sysvsem default
Mutex fcntl:/var/httpd/locks mpm-accept
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NameVirtualHost Directive

Description:DEPRECATED: Designates an IP address for name-virtual hosting
Syntax:NameVirtualHost addr[:port]
Context:server config
Status:Core
Module:core

Prior to 2.3.11, NameVirtualHost was required to instruct the server that a particular IP address and port combination was usable as a name-based virtual host. In 2.3.11 and later, any time an IP address and port combination is used in multiple virtual hosts, name-based virtual hosting is automatically enabled for that address.

This directive currently has no effect.

See also

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Options Directive

Description:Configures what features are available in a particular directory
Syntax:Options [+|-]option [[+|-]option] ...
Default:Options FollowSymlinks
Context:server config, virtual host, directory, .htaccess
Override:Options
Status:Core
Module:core
Compatibility:The default was changed from All to FollowSymlinks in 2.3.11

The Options directive controls which server features are available in a particular directory.

option can be set to None, in which case none of the extra features are enabled, or one or more of the following:

All
All options except for MultiViews.
ExecCGI
Execution of CGI scripts using mod_cgi is permitted.
FollowSymLinks
The server will follow symbolic links in this directory. This is the default setting.

Even though the server follows the symlink it does not change the pathname used to match against <Directory> sections.

The FollowSymLinks and SymLinksIfOwnerMatch Options work only in <Directory> sections or .htaccess files.

Omitting this option should not be considered a security restriction, since symlink testing is subject to race conditions that make it circumventable.

Includes
Server-side includes provided by mod_include are permitted.
IncludesNOEXEC
Server-side includes are permitted, but the #exec cmd and #exec cgi are disabled. It is still possible to #include virtual CGI scripts from ScriptAliased directories.
Indexes
If a URL which maps to a directory is requested, and there is no DirectoryIndex (e.g., index.html) in that directory, then mod_autoindex will return a formatted listing of the directory.
MultiViews
Content negotiated "MultiViews" are allowed using mod_negotiation.

Note

This option gets ignored if set anywhere other than <Directory>, as mod_negotiation needs real resources to compare against and evaluate from.

SymLinksIfOwnerMatch
The server will only follow symbolic links for which the target file or directory is owned by the same user id as the link.

Note

The FollowSymLinks and SymLinksIfOwnerMatch Options work only in <Directory> sections or .htaccess files.

This option should not be considered a security restriction, since symlink testing is subject to race conditions that make it circumventable.

Normally, if multiple Options could apply to a directory, then the most specific one is used and others are ignored; the options are not merged. (See how sections are merged.) However if all the options on the Options directive are preceded by a + or - symbol, the options are merged. Any options preceded by a + are added to the options currently in force, and any options preceded by a - are removed from the options currently in force.

Note

Mixing Options with a + or - with those without is not valid syntax, and will be rejected during server startup by the syntax check with an abort.

For example, without any + and - symbols:

<Directory "/web/docs">
  Options Indexes FollowSymLinks
</Directory>

<Directory "/web/docs/spec">
  Options Includes
</Directory>

then only Includes will be set for the /web/docs/spec directory. However if the second Options directive uses the + and - symbols:

<Directory "/web/docs">
  Options Indexes FollowSymLinks
</Directory>

<Directory "/web/docs/spec">
  Options +Includes -Indexes
</Directory>

then the options FollowSymLinks and Includes are set for the /web/docs/spec directory.

Note

Using -IncludesNOEXEC or -Includes disables server-side includes completely regardless of the previous setting.

The default in the absence of any other settings is FollowSymlinks.

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Protocol Directive

Description:Protocol for a listening socket
Syntax:Protocol protocol
Context:server config, virtual host
Status:Core
Module:core
Compatibility:On Windows only available from Apache 2.3.3 and later.

This directive specifies the protocol used for a specific listening socket. The protocol is used to determine which module should handle a request, and to apply protocol specific optimizations with the AcceptFilter directive.

You only need to set the protocol if you are running on non-standard ports, otherwise http is assumed for port 80 and https for port 443.

For example, if you are running https on a non-standard port, specify the protocol explicitly:

Protocol https

You can also specify the protocol using the Listen directive.

See also

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RegisterHttpMethod Directive

Description:Register non-standard HTTP methods
Syntax:RegisterHttpMethod method [method [...]]
Context:server config
Status:Core
Module:core

HTTP Methods that are not conforming to the relvant RFCs are normally rejected by request processing in Apache HTTPD. To avoid this, modules can register non-standard HTTP methods they support. The RegisterHttpMethod allows to register such methods manually. This can be useful for if such methods are forwared for external processing, e.g. to a CGI script.

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RLimitCPU Directive

Description:Limits the CPU consumption of processes launched by Apache httpd children
Syntax:RLimitCPU seconds|max [seconds|max]
Default:Unset; uses operating system defaults
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Core
Module:core

Takes 1 or 2 parameters. The first parameter sets the soft resource limit for all processes and the second parameter sets the maximum resource limit. Either parameter can be a number, or max to indicate to the server that the limit should be set to the maximum allowed by the operating system configuration. Raising the maximum resource limit requires that the server is running as root, or in the initial startup phase.

This applies to processes forked off from Apache httpd children servicing requests, not the Apache httpd children themselves. This includes CGI scripts and SSI exec commands, but not any processes forked off from the Apache httpd parent such as piped logs.

CPU resource limits are expressed in seconds per process.

See also

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RLimitMEM Directive

Description:Limits the memory consumption of processes launched by Apache httpd children
Syntax:RLimitMEM bytes|max [bytes|max]
Default:Unset; uses operating system defaults
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Core
Module:core

Takes 1 or 2 parameters. The first parameter sets the soft resource limit for all processes and the second parameter sets the maximum resource limit. Either parameter can be a number, or max to indicate to the server that the limit should be set to the maximum allowed by the operating system configuration. Raising the maximum resource limit requires that the server is running as root, or in the initial startup phase.

This applies to processes forked off from Apache httpd children servicing requests, not the Apache httpd children themselves. This includes CGI scripts and SSI exec commands, but not any processes forked off from the Apache httpd parent such as piped logs.

Memory resource limits are expressed in bytes per process.

See also

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RLimitNPROC Directive

Description:Limits the number of processes that can be launched by processes launched by Apache httpd children
Syntax:RLimitNPROC number|max [number|max]
Default:Unset; uses operating system defaults
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Core
Module:core

Takes 1 or 2 parameters. The first parameter sets the soft resource limit for all processes and the second parameter sets the maximum resource limit. Either parameter can be a number, or max to indicate to the server that the limit should be set to the maximum allowed by the operating system configuration. Raising the maximum resource limit requires that the server is running as root, or in the initial startup phase.

This applies to processes forked off from Apache httpd children servicing requests, not the Apache httpd children themselves. This includes CGI scripts and SSI exec commands, but not any processes forked off from the Apache httpd parent such as piped logs.

Process limits control the number of processes per user.

Note

If CGI processes are not running under user ids other than the web server user id, this directive will limit the number of processes that the server itself can create. Evidence of this situation will be indicated by cannot fork messages in the error_log.

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ScriptInterpreterSource Directive

Description:Technique for locating the interpreter for CGI scripts
Syntax:ScriptInterpreterSource Registry|Registry-Strict|Script
Default:ScriptInterpreterSource Script
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Core
Module:core
Compatibility:Win32 only.

This directive is used to control how Apache httpd finds the interpreter used to run CGI scripts. The default setting is Script. This causes Apache httpd to use the interpreter pointed to by the shebang line (first line, starting with #!) in the script. On Win32 systems this line usually looks like:

#!C:/Perl/bin/perl.exe

or, if perl is in the PATH, simply:

#!perl

Setting ScriptInterpreterSource Registry will cause the Windows Registry tree HKEY_CLASSES_ROOT to be searched using the script file extension (e.g., .pl) as a search key. The command defined by the registry subkey Shell\ExecCGI\Command or, if it does not exist, by the subkey Shell\Open\Command is used to open the script file. If the registry keys cannot be found, Apache httpd falls back to the behavior of the Script option.

Security

Be careful when using ScriptInterpreterSource Registry with ScriptAlias'ed directories, because Apache httpd will try to execute every file within this directory. The Registry setting may cause undesired program calls on files which are typically not executed. For example, the default open command on .htm files on most Windows systems will execute Microsoft Internet Explorer, so any HTTP request for an .htm file existing within the script directory would start the browser in the background on the server. This is a good way to crash your system within a minute or so.

The option Registry-Strict which is new in Apache HTTP Server 2.0 does the same thing as Registry but uses only the subkey Shell\ExecCGI\Command. The ExecCGI key is not a common one. It must be configured manually in the windows registry and hence prevents accidental program calls on your system.

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SeeRequestTail Directive

Description:Determine if mod_status displays the first 63 characters of a request or the last 63, assuming the request itself is greater than 63 chars.
Syntax:SeeRequestTail On|Off
Default:SeeRequestTail Off
Context:server config
Status:Core
Module:core

mod_status with ExtendedStatus On displays the actual request being handled. For historical purposes, only 63 characters of the request are actually stored for display purposes. This directive controls whether the 1st 63 characters are stored (the previous behavior and the default) or if the last 63 characters are. This is only applicable, of course, if the length of the request is 64 characters or greater.

If Apache httpd is handling GET /disk1/storage/apache/htdocs/images/imagestore1/food/apples.jpg HTTP/1.1 mod_status displays as follows:

Off (default) GET /disk1/storage/apache/htdocs/images/imagestore1/food/apples
On orage/apache/htdocs/images/imagestore1/food/apples.jpg HTTP/1.1
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ServerAdmin Directive

Description:Email address that the server includes in error messages sent to the client
Syntax:ServerAdmin email-address|URL
Context:server config, virtual host
Status:Core
Module:core

The ServerAdmin sets the contact address that the server includes in any error messages it returns to the client. If the httpd doesn't recognize the supplied argument as an URL, it assumes, that it's an email-address and prepends it with mailto: in hyperlink targets. However, it's recommended to actually use an email address, since there are a lot of CGI scripts that make that assumption. If you want to use an URL, it should point to another server under your control. Otherwise users may not be able to contact you in case of errors.

It may be worth setting up a dedicated address for this, e.g.

ServerAdmin www-admin@foo.example.com

as users do not always mention that they are talking about the server!

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ServerAlias Directive

Description:Alternate names for a host used when matching requests to name-virtual hosts
Syntax:ServerAlias hostname [hostname] ...
Context:virtual host
Status:Core
Module:core

The ServerAlias directive sets the alternate names for a host, for use with name-based virtual hosts. The ServerAlias may include wildcards, if appropriate.

<VirtualHost *:80>
  ServerName server.example.com
  ServerAlias server server2.example.com server2
  ServerAlias *.example.com
  UseCanonicalName Off
  # ...
</VirtualHost>

Name-based virtual hosts for the best-matching set of <virtualhost>s are processed in the order they appear in the configuration. The first matching ServerName or ServerAlias is used, with no different precedence for wildcards (nor for ServerName vs. ServerAlias).

The complete list of names in the VirtualHost directive are treated just like a (non wildcard) ServerAlias.

See also

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ServerName Directive

Description:Hostname and port that the server uses to identify itself
Syntax:ServerName [scheme://]fully-qualified-domain-name[:port]
Context:server config, virtual host
Status:Core
Module:core

The ServerName directive sets the request scheme, hostname and port that the server uses to identify itself. This is used when creating redirection URLs.

Additionally, ServerName is used (possibly in conjunction with ServerAlias) to uniquely identify a virtual host, when using name-based virtual hosts.

For example, if the name of the machine hosting the web server is simple.example.com, but the machine also has the DNS alias www.example.com and you wish the web server to be so identified, the following directive should be used:

ServerName www.example.com

The ServerName directive may appear anywhere within the definition of a server. However, each appearance overrides the previous appearance (within that server).

If no ServerName is specified, then the server attempts to deduce the hostname by performing a reverse lookup on the IP address. If no port is specified in the ServerName, then the server will use the port from the incoming request. For optimal reliability and predictability, you should specify an explicit hostname and port using the ServerName directive.

If you are using name-based virtual hosts, the ServerName inside a <VirtualHost> section specifies what hostname must appear in the request's Host: header to match this virtual host.

Sometimes, the server runs behind a device that processes SSL, such as a reverse proxy, load balancer or SSL offload appliance. When this is the case, specify the https:// scheme and the port number to which the clients connect in the ServerName directive to make sure that the server generates the correct self-referential URLs.

See the description of the UseCanonicalName and UseCanonicalPhysicalPort directives for settings which determine whether self-referential URLs (e.g., by the mod_dir module) will refer to the specified port, or to the port number given in the client's request.

Failure to set ServerName to a name that your server can resolve to an IP address will result in a startup warning. httpd will then use whatever hostname it can determine, using the system's hostname command. This will almost never be the hostname you actually want.

httpd: Could not reliably determine the server's fully qualified domain name, using rocinante.local for ServerName

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ServerPath Directive

Description:Legacy URL pathname for a name-based virtual host that is accessed by an incompatible browser
Syntax:ServerPath URL-path
Context:virtual host
Status:Core
Module:core

The ServerPath directive sets the legacy URL pathname for a host, for use with name-based virtual hosts.

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ServerRoot Directive

Description:Base directory for the server installation
Syntax:ServerRoot directory-path
Default:ServerRoot /usr/local/apache
Context:server config
Status:Core
Module:core

The ServerRoot directive sets the directory in which the server lives. Typically it will contain the subdirectories conf/ and logs/. Relative paths in other configuration directives (such as Include or LoadModule, for example) are taken as relative to this directory.

ServerRoot "/home/httpd"

The default location of ServerRoot may be modified by using the --prefix argument to configure, and most third-party distributions of the server have a different default location from the one listed above.

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ServerSignature Directive

Description:Configures the footer on server-generated documents
Syntax:ServerSignature On|Off|EMail
Default:ServerSignature Off
Context:server config, virtual host, directory, .htaccess
Override:All
Status:Core
Module:core

The ServerSignature directive allows the configuration of a trailing footer line under server-generated documents (error messages, mod_proxy ftp directory listings, mod_info output, ...). The reason why you would want to enable such a footer line is that in a chain of proxies, the user often has no possibility to tell which of the chained servers actually produced a returned error message.

The Off setting, which is the default, suppresses the footer line (and is therefore compatible with the behavior of Apache-1.2 and below). The On setting simply adds a line with the server version number and ServerName of the serving virtual host, and the EMail setting additionally creates a "mailto:" reference to the ServerAdmin of the referenced document.

After version 2.0.44, the details of the server version number presented are controlled by the ServerTokens directive.

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ServerTokens Directive

Description:Configures the Server HTTP response header
Syntax:ServerTokens Major|Minor|Min[imal]|Prod[uctOnly]|OS|Full
Default:ServerTokens Full
Context:server config
Status:Core
Module:core

This directive controls whether Server response header field which is sent back to clients includes a description of the generic OS-type of the server as well as information about compiled-in modules.

ServerTokens Full (or not specified)
Server sends (e.g.): Server: Apache/2.4.2 (Unix) PHP/4.2.2 MyMod/1.2
ServerTokens Prod[uctOnly]
Server sends (e.g.): Server: Apache
ServerTokens Major
Server sends (e.g.): Server: Apache/2
ServerTokens Minor
Server sends (e.g.): Server: Apache/2.4
ServerTokens Min[imal]
Server sends (e.g.): Server: Apache/2.4.2
ServerTokens OS
Server sends (e.g.): Server: Apache/2.4.2 (Unix)

This setting applies to the entire server, and cannot be enabled or disabled on a virtualhost-by-virtualhost basis.

After version 2.0.44, this directive also controls the information presented by the ServerSignature directive.

Setting ServerTokens to less than minimal is not recommended because it makes it more difficult to debug interoperational problems. Also note that disabling the Server: header does nothing at all to make your server more secure; the idea of "security through obscurity" is a myth and leads to a false sense of safety.

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SetHandler Directive

Description:Forces all matching files to be processed by a handler
Syntax:SetHandler handler-name|None
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Core
Module:core

When placed into an .htaccess file or a <Directory> or <Location> section, this directive forces all matching files to be parsed through the handler given by handler-name. For example, if you had a directory you wanted to be parsed entirely as imagemap rule files, regardless of extension, you might put the following into an .htaccess file in that directory:

SetHandler imap-file

Another example: if you wanted to have the server display a status report whenever a URL of http://servername/status was called, you might put the following into httpd.conf:

<Location "/status">
  SetHandler server-status
</Location>

You could also use this directive to configure a particular handler for files with a particular file extension. For example:

<FilesMatch \.php$>
    SetHandler application/x-httpd-php
</FilesMatch>

You can override an earlier defined SetHandler directive by using the value None.

Note

Because SetHandler overrides default handlers, normal behavior such as handling of URLs ending in a slash (/) as directories or index files is suppressed.

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SetInputFilter Directive

Description:Sets the filters that will process client requests and POST input
Syntax:SetInputFilter filter[;filter...]
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Core
Module:core

The SetInputFilter directive sets the filter or filters which will process client requests and POST input when they are received by the server. This is in addition to any filters defined elsewhere, including the AddInputFilter directive.

If more than one filter is specified, they must be separated by semicolons in the order in which they should process the content.

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SetOutputFilter Directive

Description:Sets the filters that will process responses from the server
Syntax:SetOutputFilter filter[;filter...]
Context:server config, virtual host, directory, .htaccess
Override:FileInfo
Status:Core
Module:core

The SetOutputFilter directive sets the filters which will process responses from the server before they are sent to the client. This is in addition to any filters defined elsewhere, including the AddOutputFilter directive.

For example, the following configuration will process all files in the /www/data/ directory for server-side includes.

<Directory "/www/data/">
  SetOutputFilter INCLUDES
</Directory>

If more than one filter is specified, they must be separated by semicolons in the order in which they should process the content.

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TimeOut Directive

Description:Amount of time the server will wait for certain events before failing a request
Syntax:TimeOut seconds
Default:TimeOut 60
Context:server config, virtual host
Status:Core
Module:core

The TimeOut directive defines the length of time Apache httpd will wait for I/O in various circumstances:

  1. When reading data from the client, the length of time to wait for a TCP packet to arrive if the read buffer is empty.
  2. When writing data to the client, the length of time to wait for an acknowledgement of a packet if the send buffer is full.
  3. In mod_cgi and mod_cgid, the length of time to wait for output from a CGI script.
  4. In mod_ext_filter, the length of time to wait for output from a filtering process.
  5. In mod_proxy, the default timeout value if ProxyTimeout is not configured.
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TraceEnable Directive

Description:Determines the behavior on TRACE requests
Syntax:TraceEnable [on|off|extended]
Default:TraceEnable on
Context:server config, virtual host
Status:Core
Module:core

This directive overrides the behavior of TRACE for both the core server and mod_proxy. The default TraceEnable on permits TRACE requests per RFC 2616, which disallows any request body to accompany the request. TraceEnable off causes the core server and mod_proxy to return a 405 (Method not allowed) error to the client.

Finally, for testing and diagnostic purposes only, request bodies may be allowed using the non-compliant TraceEnable extended directive. The core (as an origin server) will restrict the request body to 64k (plus 8k for chunk headers if Transfer-Encoding: chunked is used). The core will reflect the full headers and all chunk headers with the response body. As a proxy server, the request body is not restricted to 64k.

Note

Despite claims to the contrary, TRACE is not a security vulnerability and there is no viable reason for it to be disabled. Doing so necessarily makes your server non-compliant.

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UnDefine Directive

Description:Undefine the existence of a variable
Syntax:UnDefine parameter-name
Context:server config
Status:Core
Module:core

Undoes the effect of a Define or of passing a -D argument to httpd.

This directive can be used to toggle the use of <IfDefine> sections without needing to alter -D arguments in any startup scripts.

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UseCanonicalName Directive

Description:Configures how the server determines its own name and port
Syntax:UseCanonicalName On|Off|DNS
Default:UseCanonicalName Off
Context:server config, virtual host, directory
Status:Core
Module:core

In many situations Apache httpd must construct a self-referential URL -- that is, a URL that refers back to the same server. With UseCanonicalName On Apache httpd will use the hostname and port specified in the ServerName directive to construct the canonical name for the server. This name is used in all self-referential URLs, and for the values of SERVER_NAME and SERVER_PORT in CGIs.

With UseCanonicalName Off Apache httpd will form self-referential URLs using the hostname and port supplied by the client if any are supplied (otherwise it will use the canonical name, as defined above). These values are the same that are used to implement name-based virtual hosts, and are available with the same clients. The CGI variables SERVER_NAME and SERVER_PORT will be constructed from the client supplied values as well.

An example where this may be useful is on an intranet server where you have users connecting to the machine using short names such as www. You'll notice that if the users type a shortname, and a URL which is a directory, such as http://www/splat, without the trailing slash then Apache httpd will redirect them to http://www.example.com/splat/. If you have authentication enabled, this will cause the user to have to authenticate twice (once for www and once again for www.example.com -- see the FAQ on this subject for more information). But if UseCanonicalName is set Off, then Apache httpd will redirect to http://www/splat/.

There is a third option, UseCanonicalName DNS, which is intended for use with mass IP-based virtual hosting to support ancient clients that do not provide a Host: header. With this option Apache httpd does a reverse DNS lookup on the server IP address that the client connected to in order to work out self-referential URLs.

Warning

If CGIs make assumptions about the values of SERVER_NAME they may be broken by this option. The client is essentially free to give whatever value they want as a hostname. But if the CGI is only using SERVER_NAME to construct self-referential URLs then it should be just fine.

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UseCanonicalPhysicalPort Directive

Description:Configures how the server determines its own port
Syntax:UseCanonicalPhysicalPort On|Off
Default:UseCanonicalPhysicalPort Off
Context:server config, virtual host, directory
Status:Core
Module:core

In many situations Apache httpd must construct a self-referential URL -- that is, a URL that refers back to the same server. With UseCanonicalPhysicalPort On Apache httpd will, when constructing the canonical port for the server to honor the UseCanonicalName directive, provide the actual physical port number being used by this request as a potential port. With UseCanonicalPhysicalPort Off Apache httpd will not ever use the actual physical port number, instead relying on all configured information to construct a valid port number.

Note

The ordering of the lookup when the physical port is used is as follows:

UseCanonicalName On
  1. Port provided in Servername
  2. Physical port
  3. Default port
UseCanonicalName Off | DNS
  1. Parsed port from Host: header
  2. Physical port
  3. Port provided in Servername
  4. Default port

With UseCanonicalPhysicalPort Off, the physical ports are removed from the ordering.

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<VirtualHost> Directive

Description:Contains directives that apply only to a specific hostname or IP address
Syntax:<VirtualHost addr[:port] [addr[:port]] ...> ... </VirtualHost>
Context:server config
Status:Core
Module:core

<VirtualHost> and </VirtualHost> are used to enclose a group of directives that will apply only to a particular virtual host. Any directive that is allowed in a virtual host context may be used. When the server receives a request for a document on a particular virtual host, it uses the configuration directives enclosed in the <VirtualHost> section. Addr can be any of the following, optionally followed by a colon and a port number (or *):

<VirtualHost 10.1.2.3:80>
  ServerAdmin webmaster@host.example.com
  DocumentRoot /www/docs/host.example.com
  ServerName host.example.com
  ErrorLog logs/host.example.com-error_log
  TransferLog logs/host.example.com-access_log
</VirtualHost>

IPv6 addresses must be specified in square brackets because the optional port number could not be determined otherwise. An IPv6 example is shown below:

<VirtualHost [2001:db8::a00:20ff:fea7:ccea]:80>
  ServerAdmin webmaster@host.example.com
  DocumentRoot /www/docs/host.example.com
  ServerName host.example.com
  ErrorLog logs/host.example.com-error_log
  TransferLog logs/host.example.com-access_log
</VirtualHost>

Each Virtual Host must correspond to a different IP address, different port number or a different host name for the server, in the former case the server machine must be configured to accept IP packets for multiple addresses. (If the machine does not have multiple network interfaces, then this can be accomplished with the ifconfig alias command -- if your OS supports it).

Note

The use of <VirtualHost> does not affect what addresses Apache httpd listens on. You may need to ensure that Apache httpd is listening on the correct addresses using Listen.

A ServerName should be specified inside each <VirtualHost> block. If it is absent, the ServerName from the "main" server configuration will be inherited.

When a request is received, the server first maps it to the best matching <VirtualHost> based on the local IP address and port combination only. Non-wildcards have a higher precedence. If no match based on IP and port occurs at all, the "main" server configuration is used.

If multiple virtual hosts contain the best matching IP address and port, the server selects from these virtual hosts the best match based on the requested hostname. If no matching name-based virtual host is found, then the first listed virtual host that matched the IP address will be used. As a consequence, the first listed virtual host for a given IP address and port combination is default virtual host for that IP and port combination.

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.

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Warning Directive

Description:Warn from configuration parsing with a custom message
Syntax:Warning message
Context:server config, virtual host, directory, .htaccess
Status:Core
Module:core
Compatibility:2.5 and later

If an issue can be detected from within the configuration, this directive can be used to generate a custom warning message. The configuration parsing is not halted. The typical use it to check whether some user define options are set, and warn if not.

# Example
# tell when ReverseProxy is not set
<IfDefine !ReverseProxy>
  Warning "reverse proxy is not started, hope this is okay!"
</IfDefine>

<IfDefine ReverseProxy>
  # define custom proxy configuration
</IfDefine>

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Comments

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