Apache Core Features

Directives

• AcceptFilter
• AcceptPathInfo
• AccessFileName
• AddDefaultCharset
• AllowEncodedSlashes
• AllowOverride
• AllowOverrideList
• CGIMapExtension
• CGIPassAuth
• CGIVar
• ContentDigest
• DefaultRuntimeDir
• DefaultType
• Define
• <Directory>
• <DirectoryMatch>
• DocumentRoot
• <Else>
• <ElseIf>
• EnableMMAP
• EnableSendfile
• Error
• ErrorDocument
• ErrorLog
• ErrorLogFormat
• ExtendedStatus
• FileETag
• <Files>
• <FilesMatch>
• FlushMaxPipelined
• FlushMaxThreshold
• ForceType
• GprofDir
• HostnameLookups
• HttpProtocolOptions
• <If>
• <IfDefine>
• <IfDirective>
• <IfFile>
• <IfModule>
• <IfSection>
• Include
• IncludeOptional
• KeepAlive
• KeepAliveTimeout
• <Limit>
• <LimitExcept>
• LimitInternalRecursion
• LimitRequestBody
• LimitRequestFields
• LimitRequestFieldSize
• LimitRequestLine
• LimitXMLRequestBody
• <Location>
• <LocationMatch>
• LogLevel
• MaxKeepAliveRequests
• MaxRangeOverlaps
• MaxRangeReversals
• MaxRanges
• MergeSlashes
• MergeTrailers
• Mutex
• NameVirtualHost
• Options
• Protocol
• Protocols
• ProtocolsHonorOrder
• QualifyRedirectURL
• ReadBufferSize
• RegexDefaultOptions
• RegisterHttpMethod
• RLimitCPU
• RLimitMEM
• RLimitNPROC
• ScriptInterpreterSource
• SeeRequestTail
• ServerAdmin
• ServerAlias
• ServerName
• ServerPath
• ServerRoot
• ServerSignature
• ServerTokens
• SetHandler
• SetInputFilter
• SetOutputFilter
• StrictHostCheck
• TimeOut
• TraceEnable
• UNCList
• UnDefine
• UseCanonicalName
• UseCanonicalPhysicalPort
• <VirtualHost>

Bugfix checklist

• httpd changelog
• Known issues
• Report a bug

See also

• Comments

AcceptFilterDirective

This directive enables operating system specific optimizations for a listening socket by theProtocol 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 primitiveTCP_DEFER_ACCEPT, and Windows' optimized AcceptEx() are currently supported.

Usingnone for an argument will disable any accept filters for that protocol. This is useful for protocols that require a server send data first, such asftp: ornntp:

AcceptFilter nntp none

The default protocol names arehttps for port 443 andhttp for all other ports. To specify that another protocol is being used with a listening port, add theprotocol argument to theListen directive.

The default values on FreeBSD are:

AcceptFilter http httpreadyAcceptFilter https dataready

Thehttpready 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 dataAcceptFilter https data

Linux'sTCP_DEFER_ACCEPT does not support buffering http requests. Any value besidesnone will enableTCP_DEFER_ACCEPT on that listener. For more details see the Linux tcp(7) man page.

The default values on Windows are:

AcceptFilter http connectAcceptFilter https connect

Window's mpm_winnt interprets the AcceptFilter to toggle the AcceptEx() API, and does not support http protocol buffering.connect will use the AcceptEx() API, also retrieve the network endpoint addresses, but likenone theconnect option does not wait for the initial data transmission.

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

See also

• Protocol

AcceptPathInfoDirective

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 thePATH_INFO environment variable.

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

The three possible arguments for theAcceptPathInfo 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 thehandler responsible for the request. The core handler for normal files defaults to rejectingPATH_INFO requests. Handlers that serve scripts, such ascgi-script andisapi-handler, generally acceptPATH_INFO by default.

The primary purpose of theAcceptPathInfo directive is to allow you to override the handler's choice of accepting or rejectingPATH_INFO. This override is required, for example, when you use afilter, such asINCLUDES, to generate content based onPATH_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>

AccessFileNameDirective

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 areenabled for that directory. For example:

AccessFileName .acl

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

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

See also

• AllowOverride
• Configuration Files
• .htaccess Files

AddDefaultCharsetDirective

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 eithertext/plain ortext/html. This should override any charset specified in the body of the response via aMETA element, though the exact behavior is often dependent on the user's client configuration. A setting ofAddDefaultCharset Off disables this functionality.AddDefaultCharset On enables a default charset ofiso-8859-1. Any other value is assumed to be thecharset to be used, which should be one of theIANA registered charset values for use in Internet media types (MIME types). For example:

AddDefaultCharset utf-8

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

See also

• AddCharset

AllowEncodedSlashesDirective

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

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

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

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

TurningAllowEncodedSlashesOn is mostly useful when used in conjunction withPATH_INFO.

See also

• AcceptPathInfo

AllowOverrideDirective

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

When this directive is set toNone andAllowOverrideList is set toNone,.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 toAll, then any directive which has the .htaccessContext is allowed in.htaccess files.

Thedirective-type can be one of the following groupings of directives. (See theoverride class index for an up-to-date listing of which directives are enabled by eachdirective-type.)

AuthConfig

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

FileInfo

Allow use of the directives controlling document types (ErrorDocument,ForceType,LanguagePriority,SetHandler,SetInputFilter,SetOutputFilter, andmod_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), andAction frommod_actions.

Indexes

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

Limit

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

Nonfatal=[Override|Unknown|All]

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

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

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

Security

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

Options[=Option,...]

Allow use of the directives controlling specific directory features (Options andXBitHack). An equal sign may be given followed by a comma-separated list, without spaces, of options that may be set using theOptions 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 anyOptions 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 remainset 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 groupAuthConfig norIndexes cause an internal server error.

See also

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

AllowOverrideListDirective

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

When this directive is set toNone andAllowOverride is set toNone, then.htaccess files are completely ignored. In this case, the server will not even attempt to read.htaccess files in the filesystem.

Example:

AllowOverride NoneAllowOverrideList Redirect RedirectMatch

In the example above, only theRedirect andRedirectMatch directives are allowed. All others will cause an internal server error.

Example:

AllowOverride AuthConfigAllowOverrideList CookieTracking CookieName

In the example above,AllowOverride grants permission to theAuthConfig directive grouping andAllowOverrideList grants permission to only two directives from theFileInfo directive grouping. All others will cause an internal server error.

See also

• AccessFileName
• AllowOverride
• Configuration Files
• .htaccess Files

CGIMapExtensionDirective

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

CGIPassAuthDirective

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

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

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

CGIVarDirective

This directive controls how some CGI variables are set.

REQUEST_URI rules:

original-uri (default)

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

current-uri

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

ContentDigestDirective

This directive enables the generation ofContent-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.

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

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

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

DefaultRuntimeDirDirective

TheDefaultRuntimeDir 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 toServerRoot.

Example

DefaultRuntimeDir scratch/

The default location ofDefaultRuntimeDir may be modified by changing theDEFAULT_REL_RUNTIMEDIR #define at build time.

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

See also

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

DefaultTypeDirective

This directive has been disabled. For backwards compatibility of configuration files, it may be specified with the valuenone, 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 theAddType to configure media type assignments via file extensions, or theForceType 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.

DefineDirective

In its one parameter form,Define is equivalent to passing the-D argument tohttpd. 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 withRewriteMap's syntax.

See also

• UnDefine
• IfDefine

<Directory>Directive

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

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

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

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

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

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

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

<Directory "/">  AllowOverride None</Directory><Directory "/home">  AllowOverride FileInfo</Directory>

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

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

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

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

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

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

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

and then override this for directories youwant accessible. See theSecurity Tips page for more details.

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

See also

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

<DirectoryMatch>Directive

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

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

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

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

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

See also

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

DocumentRootDirective

This directive sets the directory from whichhttpd will serve files. Unless matched by a directive likeAlias, 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 tohttp://my.example.com/index.html refers to/usr/web/index.html. If thedirectory-path is not absolute then it is assumed to be relative to theServerRoot.

TheDocumentRoot should be specified without a trailing slash.

See also

• Mapping URLs to FilesystemLocations

<Else>Directive

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

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

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

See also

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

<ElseIf>Directive

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

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

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

See also

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

EnableMMAPDirective

This directive controls whether thehttpd 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 usingmod_include -- Apache httpd memory-maps the file if the OS supports it.

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

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

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

EnableMMAP Off

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

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

EnableSendfileDirective

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

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

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

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

EnableSendfile On

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

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

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

ErrorDirective

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>

ErrorDocumentDirective

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 localURL-path to handle the problem/error
4. redirect to an externalURL to handle the problem/error

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

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

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

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

Additionally, the special valuedefault 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 existingErrorDocument.

ErrorDocument 404 /cgi-bin/bad_urls.pl<Directory "/web/docs">  ErrorDocument 404 default</Directory>

Note that when you specify anErrorDocument that points to a remote URL (ie. anything with a method such ashttp 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 anErrorDocument 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 anErrorDocument 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 articleQ294807.

Although most error messages can be overridden, there are certain circumstances where the internal messages are used regardless of the setting ofErrorDocument. 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 enableProxyErrorOverride so that you can provide custom error messages on behalf of your Origin servers. If you don't enable ProxyErrorOverride, Apache httpd will not generate custom error documents for proxied content.

See also

• documentation of customizable responses

ErrorLogDirective

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

ErrorLog "/var/log/httpd/error_log"

If thefile-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 onpiped logs for more information.

Usingsyslog instead of a filename enables logging via syslogd(8) if the system supports it. The default is to use syslog facilitylocal7, but you can override this by using thesyslog:facility syntax wherefacility can be one of the names usually documented in syslog(1). The facility is effectively global, and if it is changed in individual virtual hosts, the final facility specified affects the entire server. Same rules apply for the syslog tag, which by default uses the Apache binary name,httpd in most cases. You can also override this by using thesyslog::tag syntax.

ErrorLog syslog:userErrorLog syslog:user:httpd.srv1ErrorLog syslog::httpd.srv2

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

See also

• LogLevel
• Apache HTTP Server Log Files

ErrorLogFormatDirective

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

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

Specifyingconnection orrequest 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 theReferer request header.

Some format string items accept additional parameters in braces.

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

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

This would result in error messages such as:

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

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

#Advanced example with request/connection log IDsErrorLogFormat "[%{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] remote\ %a local\ %A"

See also

• ErrorLog
• LogLevel
• Apache HTTP Server Log Files

ExtendedStatusDirective

This option tracks additional data per worker about the currently executing request and creates a utilization summary. You can see these variables during runtime by configuringmod_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.

FileETagDirective

TheFileETag directive configures the file attributes that are used to create theETag (entity tag) response header field when the document is based on a static file. (TheETag value is used in cache management to save network bandwidth.) TheFileETag 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

Digest

If a document is file-based, theETag field will be calculated by taking the digest over the file.

None

If a document is file-based, noETag field will be included in the response

TheINode,MTime,Size andDigest 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 includesFileETag INode MTime Size, and a subdirectory's includesFileETag -INode, the setting for that subdirectory (which will be inherited by any sub-subdirectories that don't override it) will be equivalent toFileETag MTime Size.

<Files>Directive

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

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

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

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

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

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

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

See also

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

<FilesMatch>Directive

The<FilesMatch> directive limits the scope of the enclosed directives by filename, just as the<Files> directive does. However, it accepts aregular 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 withinexpressions and modules likemod_rewrite. In order to prevent confusion, numbered (unnamed) backreferences are ignored. Use named groups instead.

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

See also

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

FlushMaxPipelinedDirective

This directive allows to configure the maximum number of pipelined responses, which remain pending so long as pipelined request are received. When the limit is reached, responses are forcibly flushed to the network in blocking mode, until passing under the limit again.

FlushMaxPipelined helps constraining memory usage. When set to0 pipelining is disabled, when set to-1 there is no limit (FlushMaxThreshold still applies).

FlushMaxThresholdDirective

This directive allows to configure the threshold for pending output data (in bytes). When the limit is reached, data are forcibly flushed to the network in blocking mode, until passing under the limit again.

FlushMaxThreshold helps constraining memory usage. When set to0 or a too small value there are actually no pending data, but for threaded MPMs there can be more threads busy waiting for the network thus less ones available to handle the other simultaneous connections.

ForceTypeDirective

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 bymedia-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 theAddType.

You can also override more generalForceType settings by using the value ofNone:

# 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.

GprofDirDirective

When the server has been compiled with gprof profiling support,GprofDir causesgmon.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 theprefork MPM.

HostnameLookupsDirective

This directive enables DNS lookups so that host names can be logged (and passed to CGIs/SSIs inREMOTE_HOST). The valueDouble 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 calledPARANOID.)

Regardless of the setting, whenmod_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 setHostnameLookups Double. For example, if onlyHostnameLookups 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 inREMOTE_HOST.

The default isOff 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 directiveOff, since DNS lookups can take considerable amounts of time. The utilitylogresolve, compiled by default to thebin subdirectory of your installation directory, can be used to look up host names from logged IP addresses offline.

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

HttpProtocolOptionsDirective

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

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

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

Strict|Unsafe

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

Security risks of Unsafe

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

Example of a request leading to HTTP 400 with Strict mode

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

Command line tools and CRLF

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

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

RegisteredMethods|LenientMethods

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

Forward Proxy compatibility

TheRegisteredMethods option shouldnot be toggled for forward proxy hosts, as the methods supported by the origin servers are unknown to the proxy server.

Example of a request leading to HTTP 501 with LenientMethods mode

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

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


Allow0.9|Require1.0

RFC 2616 §19.6 "Compatibility With Previous Versions" had encouraged HTTP servers to support legacy HTTP/0.9 requests. RFC 7230 supersedes this with "The expectation to support HTTP/0.9 requests has been removed" and offers additional comments inRFC 7230 Appendix A. TheRequire1.0 option allows the user to remove support of the defaultAllow0.9 option's behavior.

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

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

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

<If>Directive

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

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

would match HTTP/1.0 requests without aHost: 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 inExpressions in Apache HTTP Server.

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

See also

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

<IfDefine>Directive

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

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

• parameter-name
• !parameter-name

In the former case, the directives between the start and end markers are only processed if the parameter namedparameter-name is defined. The second format reverses the test, and only processes the directives ifparameter-name isnot defined.

Theparameter-name argument is a define as given on thehttpd command line via-Dparameter at the time the server was started or by theDefine directive.

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

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

<IfDirective>Directive

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

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

• directive-name
• !directive-name

In the former case, the directives between the start and end markers are only processed if a directive of the given name is available at the time of processing. The second format reverses the test, and only processes the directives ifdirective-name isnot available.

See also

• <IfSection>

<IfFile>Directive

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

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

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

<IfModule>Directive

The<IfModuletest>...</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 thetest is true. Iftest is false, everything between the start and end markers is ignored.

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

• module
• !module

In the former case, the directives between the start and end markers are only processed if the module namedmodule is included in Apache httpd -- either compiled in or dynamically loaded usingLoadModule. The second format reverses the test, and only processes the directives ifmodule isnot included.

Themodule 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 andmod_rewrite.c is the file name. If a module consists of several source files, use the name of the file containing the stringSTANDARD20_MODULE_STUFF.

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

<IfSection>Directive

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

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

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

• section-name
• !section-name

In the former case, the directives between the start and end markers are only processed if a section directive of the given name is available at the time of processing. The second format reverses the test, and only processes the directives ifsection-name isnot an available section directive.

For example:

<IfSection VirtualHost>   ...</IfSection>

See also

• <IfDirective>

IncludeDirective

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, ifInclude 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 causehttpd 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.

TheInclude directive willfail with an error if a wildcard expression does not match any file. TheIncludeOptional 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 theServerRoot directory.

Examples:

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

Or, providing paths relative to yourServerRoot directory:

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

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

Include conf/vhosts/*/*.conf

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

IncludeOptional conf/vhosts/*/*.conf

See also

• IncludeOptional
• apachectl

IncludeOptionalDirective

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

See also

• Include
• apachectl

KeepAliveDirective

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, setKeepAlive 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 theMaxConnectionsPerChild directive, regardless of how many requests are sent using the connection.

See also

• MaxKeepAliveRequests

KeepAliveTimeoutDirective

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 theTimeout directive applies.

SettingKeepAliveTimeout 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.

IfKeepAliveTimeout isnot set for a name-based virtual host, the value of the first defined virtual host best matching the local IP and port will be used.

<Limit>Directive

Access controls are normally effective forall 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> bracketwill have no effect. The following example applies the access control only to the methodsPOST,PUT, andDELETE, 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, andUNLOCK.The method name is case-sensitive. IfGET is used, it will also restrictHEAD requests. TheTRACE method cannot be limited (seeTraceEnable).

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

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

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

<LimitExcept>Directive

<LimitExcept> and</LimitExcept> are used to enclose a group of access control directives which will then apply to any HTTP access methodnot 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>

LimitInternalRecursionDirective

An internal redirect happens, for example, when using theAction 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 theDirectoryIndex 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 firstnumber is the maximum number of internal redirects that may follow each other. The secondnumber determines how deeply subrequests may be nested. If you specify only onenumber, it will be assigned to both limits.

LimitInternalRecursion 5

LimitRequestBodyDirective

This directive specifies the number ofbytes that are allowed in a request body. A value of0 means unlimited.

TheLimitRequestBody 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 thePUT 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

LimitRequestFieldsDirective

Settingnumber at 0 means unlimited. The default value is defined by the compile-time constantDEFAULT_LIMIT_REQUEST_FIELDS (100 as distributed).

TheLimitRequestFields 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

LimitRequestFieldSizeDirective

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

TheLimitRequestFieldSize 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

LimitRequestLineDirective

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

TheLimitRequestLine 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, theLimitRequestLine 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 aGET 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

LimitXMLRequestBodyDirective

Limit (in bytes) on the maximum size of an XML-based request body. A value of0 will apply a hard limit (depending on 32bit vs 64bit system) allowing for XML escaping within the bounds of the system addressable memory, but it exists for compatibility only and is not recommended since it does not account for memory consumed elsewhere or concurrent requests, which might result in an overall system out-of-memory.

Example:

# Limit of 1 MiBLimitXMLRequestBody 1048576

<Location>Directive

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

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

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

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

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

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

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

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

For all origin (non-proxy) requests, the URL to be matched is a URL-path of the form/path/.No scheme, hostname, port, or query string may be included. For proxy requests, the URL to be matched is of the formscheme://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 theSetHandler directive. For example, to enable status requests but allow them only from browsers atexample.com, you might use:

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

See also

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

<LocationMatch>Directive

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

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

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

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

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

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

See also

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

LogLevelDirective

LogLevel adjusts the verbosity of the messages recorded in the error logs (seeErrorLog directive). The followinglevels are available, in order of decreasing significance:

When a particular level is specified, messages from all other levels of higher significance will be reported as well.E.g., whenLogLevel info is specified, then messages with log levels ofnotice andwarn will also be posted.

Using a level of at leastcrit is recommended.

For example:

LogLevel notice

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

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

It is also possible to change the level per directory:

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

See also

• ErrorLog
• ErrorLogFormat
• Apache HTTP Server Log Files

MaxKeepAliveRequestsDirective

TheMaxKeepAliveRequests directive limits the number of requests allowed per connection whenKeepAlive is on. If it is set to0, unlimited requests will be allowed. We recommend that this setting be kept to a high value for maximum server performance.

For example:

MaxKeepAliveRequests 500

MaxRangeOverlapsDirective

TheMaxRangeOverlaps 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.

MaxRangeReversalsDirective

TheMaxRangeReversals 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.

MaxRangesDirective

TheMaxRanges 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.

MergeSlashesDirective

By default, the server merges (or collapses) multiple consecutive slash ('/') characters in the path component of the request URL.

When mapping URL's to the filesystem, these multiple slashes are not significant. However, URL's handled other ways, such as by CGI or proxy, might prefer to retain the significance of multiple consecutive slashes. In these casesMergeSlashes can be set toOFF to retain the multiple consecutive slashes, which is the legacy behavior.

When set to "OFF", regular expressions used in the configuration file that match the path component of the URL (LocationMatch,RewriteRule, ...) need to take into account multiple consecutive slashes. Non regular expression basedLocation always operate against a URL with merged slashes and cannot differentiate between multiple slashes.

MergeTrailersDirective

This directive controls whether HTTP trailers are copied into the internal representation of HTTP headers. This merging 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 2.4.11, where trailers were always merged.

MutexDirective

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

TheMutex directive is typically used in the following exceptional situations:

• change the mutex mechanism when the default mechanism selected byAPR has a functional or performance problem
• change the directory used by file-based mutexes when the default directory does not support locking

The following mutexmechanisms are available:

• default | yes

  This selects the default locking implementation, as determined byAPR. The default locking implementation can be displayed by runninghttpd with the-V option.

• none | no

  This effectively disables the mutex, and is only allowed for a mutex if the module indicates that it is a valid choice. Consult the module documentation for more information.

• posixsem

  This is a mutex variant based on a Posix semaphore.

  Warning

  The semaphore ownership is not recovered if a thread in the process holding the mutex segfaults, resulting in a hang of the web server.

• sysvsem

  This is a mutex variant based on a SystemV IPC semaphore.

  Warning

  It is possible to "leak" SysV semaphores if processes crash before the semaphore is removed.

  Security

  The semaphore API allows for a denial of service attack by any CGIs running under the same uid as the webserver (i.e., all CGIs, unless you use something likesuexec orcgiwrapper).

• sem

  This selects the "best" available semaphore implementation, choosing between Posix and SystemV IPC semaphores, in that order.

• pthread

  This is a mutex variant based on cross-process Posix thread mutexes.

  Warning

  On most systems, if a child process terminates abnormally while holding a mutex that uses this implementation, the server will deadlock and stop responding to requests. When this occurs, the server will require a manual restart to recover.

  Solaris and Linux are notable exceptions as they provide a mechanism which usually allows the mutex to be recovered after a child process terminates abnormally while holding a mutex.

  If your system is POSIX compliant or if it implements thepthread_mutexattr_setrobust_np() function, you may be able to use thepthread option safely.

• fcntl:/path/to/mutex

  This is a mutex variant where a physical (lock-)file and thefcntl() function are used as the mutex.

  Warning

  When multiple mutexes based on this mechanism are used within multi-threaded, multi-process environments, deadlock errors (EDEADLK) can be reported for valid mutex operations iffcntl() is not thread-aware, such as on Solaris.

• flock:/path/to/mutex

  This is similar to thefcntl:/path/to/mutex method with the exception that theflock() function is used to provide file locking.

• file:/path/to/mutex

  This selects the "best" available file locking implementation, choosing betweenfcntl andflock, in that order.

Most mechanisms are only available on selected platforms, where the underlying platform andAPR support it. Mechanisms which aren't available on all platforms areposixsem,sysvsem,sem,pthread,fcntl,flock, andfile.

With the file-based mechanismsfcntl andflock, the path, if provided, is a directory where the lock file will be created. The default directory is httpd's run-time file directory relative toServerRoot. 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 theOmitPID keyword is specified, the process id of the httpd parent process will be appended to make the file name unique, avoiding conflicts when multiple httpd instances share a lock file directory. For example, if the mutex name ismpm-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.

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

TheOmitPID 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 tofcntl, 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 tosysvsem.

Mutex sysvsem defaultMutex fcntl:/var/httpd/locks mpm-accept

NameVirtualHostDirective

Prior to 2.3.11,NameVirtualHost was requiredto instruct the server that a particular IP address and port combinationwas 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 virtualhosts, name-based virtual hosting is automatically enabled for that address.

This directive currently has no effect.

See also

• Virtual Hostsdocumentation

OptionsDirective

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

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

All

All options except forMultiViews.

ExecCGI

Execution of CGI scripts usingmod_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 doesnot change the pathname used to match against<Directory> sections.

TheFollowSymLinks andSymLinksIfOwnerMatchOptions 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 bymod_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 fromScriptAliased directories.

Indexes

If a URL which maps to a directory is requested and there is noDirectoryIndex (e.g.,index.html) in that directory, thenmod_autoindex will return a formatted listing of the directory.

MultiViews

Content negotiated "MultiViews" are allowed usingmod_negotiation.

Note

This option gets ignored if set anywhere other than<Directory>, asmod_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

TheFollowSymLinks andSymLinksIfOwnerMatchOptions 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 multipleOptions could apply to a directory, then the most specific one is used and others are ignored; the options are not merged. (Seehow sections are merged.) However ifall the options on theOptions 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.

For example, without any+ and- symbols:

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

then onlyIncludes will be set for the/web/docs/spec directory. However if the secondOptions directive uses the+ and- symbols:

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

then the optionsFollowSymLinks andIncludes are set for the/web/docs/spec directory.

The default in the absence of any other settings isFollowSymlinks.

ProtocolDirective

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 theAcceptFilter directive.

This directive not required for most configurations. If not specified,https is the default for port 443 andhttp the default for all other ports. The protocol is used to determine which module should handle a request, and to apply protocol specific optimizations with theAcceptFilter directive.

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

Protocol https

You can also specify the protocol using theListen directive.

See also

• AcceptFilter
• Listen

ProtocolsDirective

This directive specifies the list of protocols supported for a server/virtual host. The list determines the allowed protocols a client may negotiate for this server/host.

You need to set protocols if you want to extend the available protocols for a server/host. By default, only the http/1.1 protocol (which includes the compatibility with 1.0 and 0.9 clients) is allowed.

For example, if you want to support HTTP/2 for a server with TLS, specify:

Protocols h2 http/1.1

Valid protocols arehttp/1.1 for http and https connections,h2 on https connections andh2c for http connections. Modules may enable more protocols.

It is safe to specify protocols that are unavailable/disabled. Such protocol names will simply be ignored.

Protocols specified in base servers are inherited for virtual hosts only if the virtual host has no own Protocols directive. Or, the other way around, Protocols directives in virtual hosts replace any such directive in the base server.

See also

• ProtocolsHonorOrder

ProtocolsHonorOrderDirective

This directive specifies if the server should honor the order in which theProtocols directive lists protocols.

If configured Off, the client supplied list order of protocols has precedence over the order in the server configuration.

WithProtocolsHonorOrder set toon (default), the client ordering does not matter and only the ordering in the server settings influences the outcome of the protocol negotiation.

See also

• Protocols

QualifyRedirectURLDirective

This directive controls whether the server will ensure that the REDIRECT_URL environment variable is fully qualified. By default, the variable contains the verbatim URL requested by the client, such as "/index.html". WithQualifyRedirectURL On, the same request would result in a value such as "http://www.example.com/index.html".

Even without this directive set, when a request is issued against a fully qualified URL, REDIRECT_URL will remain fully qualified.

ReadBufferSizeDirective

This directive allows to configure the size (in bytes) of the memory buffer used to read data from the network or files.

A larger buffer can increase peformances with larger data, but consumes more memory per connection. The minimum configurable size is1024.

RegexDefaultOptionsDirective

This directive adds some default behavior to ANY regular expression used afterwards.

Any option preceded by a '+' is added to the already set options.
Any option preceded by a '-' is removed from the already set options.
Any option without a '+' or a '-' will be set, removing any other already set option.
Thenone keyword resets any already set options.

option can be:

ICASE

Use a case-insensitive match.

EXTENDED

Perl's /x flag, ignore (unescaped-)spaces and comments in the pattern.

DOTALL

Perl's /s flag, '.' matches newline characters.

DOLLAR_ENDONLY

'$' matches at end of subject string only.

# Add the ICASE option for all regexes by defaultRegexDefaultOptions +ICASE...# Remove the default DOLLAR_ENDONLY option, but keep any other oneRegexDefaultOptions -DOLLAR_ENDONLY...# Set the DOTALL option only, resetting any other oneRegexDefaultOptions DOTALL...# Reset all defined optionsRegexDefaultOptions none...

RegisterHttpMethodDirective

This directive may be used to register additional HTTP methods. This isnecessary if non-standard methods need to be used with directives that accept method names as parameters, or to allow particular non-standard methods to be used via proxy or CGI script when the server has been configured to only pass recognized methods to modules.

See also

• HTTPProtocolOptions
• AllowMethods

RLimitCPUDirective

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, ormax 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 asroot or in the initial startup phase.

This applies to processes forked 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 from the Apache httpd parent, such as piped logs.

CPU resource limits are expressed in seconds per process.

See also

• RLimitMEM
• RLimitNPROC

RLimitMEMDirective

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, ormax 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 asroot or in the initial startup phase.

This applies to processes forked 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 from the Apache httpd parent, such as piped logs.

Memory resource limits are expressed in bytes per process.

See also

• RLimitCPU
• RLimitNPROC

RLimitNPROCDirective

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, ormax 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 asroot or in the initial startup phase.

This applies to processes forked 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 from the Apache httpd parent, such as piped logs.

Process limits control the number of processes per user.

See also

• RLimitMEM
• RLimitCPU

ScriptInterpreterSourceDirective

This directive is used to control how Apache httpd finds the interpreter used to run CGI scripts. The default setting isScript. 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, ifperl is in thePATH, simply:

#!perl

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

The optionRegistry-Strict does the same thing asRegistry but uses only the subkeyShell\ExecCGI\Command. TheExecCGI key is not a common one. It must be configured manually in the windows registry and hence prevents accidental program calls on your system.

SeeRequestTailDirective

mod_status withExtendedStatus 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 first 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 handlingGET /disk1/storage/apache/htdocs/images/imagestore1/food/apples.jpg HTTP/1.1mod_status displays as follows:

ServerAdminDirective

TheServerAdmin sets the contact address that the server includes in any error messages it returns to the client. If thehttpd doesn't recognize the supplied argument as an URL, it assumes, that it's anemail-address and prepends it withmailto: 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!

ServerAliasDirective

TheServerAlias directive sets the alternate names for a host, for use withname-based virtual hosts. TheServerAlias 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 matchingServerName orServerAlias 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

• UseCanonicalName
• Apache HTTP Server Virtual Host documentation

ServerNameDirective

TheServerName directive sets the request scheme, hostname and port that the server uses to identify itself.

ServerName is used (possibly in conjunction withServerAlias) to uniquely identify a virtual host, when usingname-based virtual hosts.

Additionally, this is used when creating self-referential redirection URLs whenUseCanonicalName is set to a non-default value.

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

ServerName www.example.com

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

If noServerName is specified, the server attempts to deduce the client visible hostname by first asking the operating system for the system hostname, and if that fails, performing a reverse lookup on an IP address present on the system.

If no port is specified in theServerName, 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 theServerName directive.

If you are usingname-based virtual hosts, theServerName inside a<VirtualHost> section specifies what hostname must appear in the request'sHost: 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 thehttps:// scheme and the port number to which the clients connect in theServerName directive to make sure that the server generates the correct self-referential URLs.

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

See also

• Issues Regarding DNS and Apache HTTP Server
• Apache HTTP Server virtual host documentation
• UseCanonicalName
• UseCanonicalPhysicalPort
• ServerAlias

ServerPathDirective

TheServerPath directive sets the legacy URL pathname for a host, for use withname-based virtual hosts.

See also

• Apache HTTP Server Virtual Host documentation

ServerRootDirective

TheServerRoot directive sets the directory in which the server lives. Typically it will contain the subdirectoriesconf/ andlogs/. Relative paths in other configuration directives (such asInclude orLoadModule, for example) are taken as relative to this directory.

ServerRoot "/home/httpd"

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

See also

• the-d option tohttpd
• the security tips for information on how to properly set permissions on theServerRoot

ServerSignatureDirective

TheServerSignature 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.

TheOff setting, which is the default, suppresses the footer line. TheOn setting simply adds a line with the server version number andServerName of the serving virtual host, and theEMail setting additionally creates a "mailto:" reference to theServerAdmin of the referenced document.

The details of the server version number presented are controlled by theServerTokens directive.

See also

• ServerTokens

ServerTokensDirective

This directive controls whetherServer 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.

This directive also controls the information presented by theServerSignature directive.

See also

• ServerSignature

SetHandlerDirective

When placed into an.htaccess file or a<Directory> or<Location> section, this directive forces all matching files to be parsed through thehandler given byhandler-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 ofhttp://servername/status was called, you might put the following intohttpd.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>

String-valued expressions can be used to reference per-request variables, including backreferences to named regular expressions:

<LocationMatch ^/app/(?<sub>[^/]+)/>     SetHandler "proxy:unix:/var/run/app_%{env:MATCH_sub}.sock|fcgi://localhost:8080"</LocationMatch>

You can override an earlier definedSetHandler directive by using the valueNone.

See also

• AddHandler

SetInputFilterDirective

TheSetInputFilter 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 theAddInputFilter directive.

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

See also

• Filters documentation

SetOutputFilterDirective

TheSetOutputFilter 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 theAddOutputFilter 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.

See also

• Filters documentation

StrictHostCheckDirective

By default, the server will respond to requests for any hostname, including requests addressed to unexpected or unconfigured hostnames. While this is convenient, it is sometimes desirable to limit what hostnames a backend application handles since it will often generate self-referential responses.

By settingStrictHostCheck toON, the server will return an HTTP 400 error if the requested hostname hasn't been explicitly listed by eitherServerName orServerAlias in the virtual host that best matches the details of the incoming connection.

This directive also allows matching of the requested hostname to hostnames specified within the openingVirtualHost tag, which is a relatively obscure configuration mechanism that acts like additionalServerAlias entries.

This directive has no affect in non-default virtual hosts. The value inherited from the global server configuration, or the default virtualhost for the ip:port the underlying connection, determine the effective value.

TimeOutDirective

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

• When reading data from the client, the length of time to wait for a TCP packet to arrive if the read buffer is empty.

  For initial data on a new connection, this directive doesn't take effect until after any configured AcceptFilter has passed the new connection to the server.

• When writing data to the client, the length of time to wait for an acknowledgement of a packet if the send buffer is full.
• Inmod_cgi andmod_cgid, the length of time to wait for any individual block of output from a CGI script.
• Inmod_ext_filter, the length of time to wait for output from a filtering process.
• Inmod_proxy, the default timeout value ifProxyTimeout is not configured.

TraceEnableDirective

This directive overrides the behavior ofTRACE for both the core server andmod_proxy. The defaultTraceEnable on permitsTRACE requests per RFC 2616, which disallows any request body to accompany the request.TraceEnable off causes the core server andmod_proxy to return a405 (Method not allowed) error to the client.

Finally, for testing and diagnostic purposes only, request bodies may be allowed using the non-compliantTraceEnable extended directive. The core (as an origin server) will restrict the request body to 64Kb (plus 8Kb for chunk headers ifTransfer-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 64Kb.

UNCListDirective

During request processing, requests to access a filesystem path that resolves to a UNC path will fail unless the hostname in the UNC path has been specified by this directive. The intent is to limit access to paths derived from untrusted inputs.

UNCList example.com other.example.com

UnDefineDirective

Undoes the effect of aDefine or of passing a-D argument tohttpd.

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

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

See also

• Define
• IfDefine

UseCanonicalNameDirective

In many situations Apache httpd must construct aself-referential URL -- that is, a URL that refers back to the same server. WithUseCanonicalName On Apache httpd will use the hostname and port specified in theServerName directive to construct the canonical name for the server. This name is used in all self-referential URLs, and for the values ofSERVER_NAME andSERVER_PORT in CGIs.

WithUseCanonicalName 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 implementname-based virtual hosts and are available with the same clients. The CGI variablesSERVER_NAME andSERVER_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 aswww. You'll notice that if the users type a shortname and a URL which is a directory, such ashttp://www/splat,without the trailing slash, then Apache httpd will redirect them tohttp://www.example.com/splat/. If you have authentication enabled, this will cause the user to have to authenticate twice (once forwww and once again forwww.example.com -- see the FAQ on this subject for more information). But ifUseCanonicalName is setOff, then Apache httpd will redirect tohttp://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 aHost: 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.

See also

• UseCanonicalPhysicalPort
• ServerName
• Listen

UseCanonicalPhysicalPortDirective

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

See also

• UseCanonicalName
• ServerName
• Listen

<VirtualHost>Directive

<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 *):

• The IP address of the virtual host;
• A fully qualified domain name for the IP address of the virtual host (not recommended);
• The character*, which acts as a wildcard and matches any IP address.
• The string_default_, which is an alias for*

<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 theifconfig alias command -- if your OS supports it).

AServerName should be specified inside each<VirtualHost> block. If it is absent, theServerName 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 the default virtual host for that IP and port combination.

See also

• Apache HTTP Server Virtual Host documentation
• Issues Regarding DNS and Apache HTTP Server
• Setting which addresses and ports Apache HTTP Server uses
• How <Directory>, <Location> and <Files> sections work for an explanation of how these different sections are combined when a request is received