core
Core Apache HTTP Server features that are always available
Core
AcceptPathInfo
Controls whether requests can contain trailing pathname information
AcceptPathInfo On|Off|Default
AcceptPathInfo Default
server config
virtual host
directory
.htaccess
Available in Apache 2.0.30 and later

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

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

The three possible arguments for the AcceptPathInfo directive are:

`off`
  A request will only be accepted if it maps to a literal path that exists. Therefore a request with trailing pathname information after the true filename such as `/test/here.html/more` in the above example will return a 404 NOT FOUND error.
`on`
  A request will be accepted if a leading path component maps to a file that exists. The above example `/test/here.html/more` will be accepted if `/test/here.html` maps to a valid file.
`default`
  The treatment of requests with trailing pathname information is determined by the handler responsible for the request. The core handler for normal files defaults to rejecting PATH_INFO. Handlers that serve scripts, such as cgi-script and isapi-isa, generally accept PATH_INFO by default.

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

<Files "mypaths.shtml">
Options +Includes
SetOutputFilter INCLUDES
AcceptPathInfo on
</Files>
AccessFileName
Sets the name of the .htaccess file
AccessFileName filename [filename] ...
AccessFileName .htaccess
server config
virtual host

When returning a document to the client the server looks for the first existing access control file from this list of names in every directory of the path to the document, if access control files are enabled for that directory. For example:

AccessFileName .acl

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

<Directory />
AllowOverride None
</Directory>
AllowOverride
Configuration Files
AddDefaultCharset
Specifies the default character set to be added for a response without an explicit character set
AddDefaultCharset On|Off|charset
AddDefaultCharset Off
server config
virtual host
directory
.htaccess

This directive specifies the name of the character set that will be added to any response that does not have any parameter on the content type in the HTTP headers. This will override any character set specified in the body of the document via a `META` tag. A setting of `AddDefaultCharset Off` disables this functionality. `AddDefaultCharset On` enables Apache's internal default charset of `iso-8859-1` as required by the directive. You can also specify an alternate charset to be used. For example:

AddDefaultCharset utf-8
AddModule
AddModule module [module] ...
server config

The server can have modules compiled in which are not actively in use. This directive can be used to enable the use of those modules. The server comes with a pre-loaded list of active modules; this list can be cleared with the ClearModuleList directive.

For example:

AddDefaultCharset utf-8
AllowOverride
Sets the types of directives that are allowed in .htaccess files
AllowOverride All|None|directive-type [directive-type] ...
AllowOverride All
directory

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

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

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

The directive-type can be one of the following groupings of directives.

AuthConfig

  Allow use of the authorization directives (AuthDBMGroupFile, AuthDBMUserFile, AuthGroupFile, AuthName, AuthType, AuthUserFile, Require, etc.).
FileInfo
  Allow use of the directives controlling document types (DefaultType, ErrorDocument, ForceType, LanguagePriority, SetHandler, SetInputFilter, SetOutputFilter, and mod_mime Add* and Remove* directives, etc.).
Indexes
  Allow use of the directives controlling directory indexing (AddDescription, AddIcon, AddIconByEncoding, AddIconByType, DefaultIcon, DirectoryIndex, FancyIndexing, HeaderName, IndexIgnore, IndexOptions, ReadmeName, etc.).
Limit
  Allow use of the directives controlling host access (Allow, Deny and Order).
Options
  Allow use of the directives controlling specific directory features (Options and XBitHack).

Example:

AllowOverride AuthConfig Indexes
AccessFileName
Configuration Files
AuthName
Sets the authorization realm for use in HTTP authentication
AuthName auth-domain
directory
.htaccess
AuthConfig

This directive sets the name of the authorization realm for a directory. This realm is given to the client so that the user knows which username and password to send. AuthName takes a single argument; if the realm name contains spaces, it must be enclosed in quotation marks. It must be accompanied by AuthType and Require directives, and directives such as AuthUserFile and AuthGroupFile to work.

For example:

AuthName "Top Secret"

The string provided for the `AuthRealm` is what will appear in the password dialog provided by most browsers.

Authentication, Authorization, and Access Control
AuthType
Selects the type of user authentication
AuthType Basic|Digest
directory
.htaccess
AuthConfig

This directive selects the type of user authentication for a directory. Only `Basic` and `Digest` are currently implemented.

It must be accompanied by AuthName and Require directives, and directives such as AuthUserFile and AuthGroupFile to work.

Authentication, Authorization, and Access Control
ContentDigest
Enables the generation of Content-MD5 HTTP Response headers
ContentDigest on|off
ContentDigest off
server config
virtual host
directory
.htaccess
Options
Experimental
Available in Apache 1.1 and later

This directive enables the generation of `Content-MD5` headers as defined in RFC1864 respectively RFC2068.

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

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

Content-MD5: AuLb7Dp1rqtRtxz2m9kRpA==

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

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

DefaultType
Sets the MIME content-type that will be sent if the server cannot determine a type in any other way
DefaultType MIME-type
DefaultType text/html
server config
virtual host
directory
.htaccess
FileInfo

There will be times when the server is asked to provide a document whose type cannot be determined by its MIME types mappings.

The server must inform the client of the content-type of the document, so in the event of an unknown type it uses the `DefaultType`. For example:

DefaultType image/gif

would be appropriate for a directory which contained many gif images with filenames missing the .gif extension.

Note that unlike ForceType, this directive is only provides the default mime-type. All other mime-type definitions, including filename extensions, that might identify the media type will override this default.

Directory
Enclose a group of directives that apply only to the named file-system directory and sub-directories
<Directory directory-path> ... </Directory>
server config
virtual host

Directory and `</Directory>` are used to enclose a group of directives which will apply only to the named directory and sub-directories of that directory. Any directive which is allowed in a directory context may be used. Directory-path is either the full path to a directory, or a wild-card string. In a wild-card string, `?' matches any single character, and `*' matches any sequences of characters. You may also use `[]' character ranges like in the shell. Also as of Apache 1.3 none of the wildcards match a `/' character, which more closely mimics the behavior of Unix shells. Example:

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

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

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

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

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

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

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

- Apply directive `AllowOverride None` (disabling `.htaccess` files).
- Apply directive `AllowOverride FileInfo` (for directory `/home/web`).
- Apply any FileInfo directives in `/home/web/.htaccess`

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 be applied.

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

<Directory />
Order Deny,Allow
Deny from All
</Directory>

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

The directory sections typically occur in the access.conf file, but they may appear in any configuration file. Directory directives cannot nest, and cannot appear in a Limit or LimitExcept section.

How Directory, Location and Files sections work for an explanation of how these different sections are combined when a request is received
DirectoryMatch
Enclose a group of directives that apply only to file-system directories that match a regular expression and their subdirectories
<Directory regex> ... </Directory>
server config
virtual host

DirectoryMatch and `</DirectoryMatch>` are used to enclose a group of directives which will apply only to the named directory and sub-directories of that directory, the same as Directory. However, it takes as an argument a regular expression. For example:

<DirectoryMatch "^/www/.*/[0-9]{3}">

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

Directory
for a description of how regular expressions are mixed in with normal `<Directory>`s
How Directory, Location and Files sections work for an explanation of how these different sections are combined when a request is received
DocumentRoot
Sets the directory that forms the main document tree visible from the web
DocumentRoot directory-path
DocumentRoot /usr/local/apache/htdocs
server config
virtual host

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

DocumentRoot /usr/web

then an access to `http://www.my.host.com/index.html` refers to `/usr/web/index.html`.

The DocumentRoot should be specified without a trailing slash.

Mapping URLs to Filesystem Location
ErrorDocument
Specifies what the server will return to the client in case of an error
ErrorDocument error-code document
server config
virtual host
directory
.htaccess
FileInfo
Quoting syntax for text messages is different in Apache 2.0

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

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

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

URLs can begin with a slash (/) for local URLs, or be a full URL which the client can resolve. Alternatively, a message can be provided to be displayed by the browser. Examples:

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

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

Prior to version 2.0, messages were indicated by prefixing them with a single unmatched double quote character.

documentation of customizable responses
ErrorLog
Sets the name of the file to which the server will log errors
ErrorLog file-path|syslog[:facility]
ErrorLog logs/error_log (Unix) ErrorLog logs/error.log (Windows and OS/2)
server config
virtual host

The ErrorLog directive sets the name of the file to which the server will log any errors it encounters. If the file-path does not begin with a slash (/) then it is assumed to be relative to the ServerRoot. If the file-path begins with a pipe (|) then it is assumed to be a command to spawn to handle the error log.

Using `syslog` instead of a filename enables logging via syslogd(8) if the system supports it. The default is to use syslog facility `local7`, but you can override this by using the `syslog:`facility syntax where facility can be one of the names usually documented in syslog(1).

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

LogLevel
Apache Log Files
FileETag
Configures the file attributes used to create the ETag HTTP response header
FileETag component ...
server config
virtual host
directory
.htaccess
FileInfo

The FileETag directive configures the file attributes that are used to create the ETag (entity tag) response header field when the document is based on a file. (The ETag value is used in cache management to save network bandwidth.) In Apache 1.3.22 and earlier, the ETag value was always formed from the file's inode, size, and last-modified time (mtime). The FileETag directive allows you to choose which of these -- if any -- should be used. The recognized keywords are:

INode
  The file's i-node number will be included in the calculation
MTime
  The date and time the file was last modified will be included
Size
  The number of bytes in the file will be included
All
  All available fields will be used (equivalent to '`FileETag INode MTime Size`')
None
  If a document is file-based, no ETag field will be included in the response

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

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

Files
Contains that directives that apply to matched filenames
<Files filename> ... </Files>
server config
virtual host
directory
.htaccess

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

The filename argument should include a filename, or a wild-card string, where `?' matches any single character, and `*' matches any sequences of characters. Extended regular expressions can also be used, with the addition of the `~` character. For example:

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

would match most common Internet graphics formats. In Apache 1.3 and later, 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.

How Directory, Location and Files sections work for an explanation of how these different sections are combined when a request is received
FilesMatch
Contains that directives that apply to regular-expression matched filenames
<FilesMatch regex> ... </FilesMatch>
server config
virtual host
directory
.htaccess

The FilesMatch directive provides for access control by filename, just as the Files directive does. However, it accepts a regular expression. For example:

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

would match most common Internet graphics formats.

How Directory, Location and Files sections work for an explanation of how these different sections are combined when a request is received
ForceType
Forces all matching files to be served with the specified MIME content-type
ForceType mime-type
directory
.htaccess
Moved to the core in Apache 2.0

When placed into an `.htaccess` file or a Directory, or Location or Files section, this directive forces all matching files to be served with the content type identification given by mime-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 unlike DefaultType, this directive overrides all mime-type associations, including filename extensions, that might identify the media type.

HostnameLookups
Enables DNS lookups on client IP addresses
HostnameLookups on|off|double
HostnameLookups off
server config
virtual host
directory

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

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

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

IdentityCheck
Enables logging of the RFC1413 identity of the remote user
IdentityCheck on|off
IdentityCheck off

This directive enables RFC1413-compliant logging of the remote user name for each connection, where the client machine runs identd or something similar. This information is logged in the access log.

The information should not be trusted in any way except for rudimentary usage tracking.

Note that this can cause serious latency problems accessing your server since every request requires one of these lookups to be performed. When firewalls are involved each lookup might possibly fail and add 30 seconds of latency to each hit. So in general this is not very useful on public servers accessible from the Internet.

IfDefine
Encloses directives that will be processed only if a test is true at startup
<IfDefine [!]parameter-name> ... </IfDefine>
server config
virtual host
directory
.htaccess

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

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

- parameter-name
- `!` parameter-name

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

The parameter-name argument is a define as given on the `httpd` command line via `-D` parameter-, at the time the server was started.

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

      $ httpd -DReverseProxy ...

      # httpd.conf
      <IfDefine ReverseProxy>
      LoadModule rewrite_module modules/mod_rewrite.so
      LoadModule proxy_module   modules/libproxy.so
      </IfDefine>

IfModule
Encloses directives that are processed conditional on the presence of absence of a specific module
<IfModule [!]module-name> ... </IfModule>
server config
virtual host
directory
.htaccess

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

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

- module name
- !module name

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

The module name argument is the file name of the module, at the time it was compiled. For example, `mod_rewrite.c`.

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

Include
Includes other configuration files from within the server configuration files
Include file-path|directory-path
server config

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

If Include points to a directory, rather than a file, Apache will read all files in that directory, and any subdirectory, and parse those as configuration files.

The file path specified may be a fully qualified path (i.e. starting with a slash), or may be relative to the ServerRoot directory.

Examples:

Include /usr/local/apache/conf/ssl.conf
Include /usr/local/apache/conf/vhosts/

Or, providing paths relative to your `ServerRoot` directory:

Include conf/ssl.conf
Include conf/vhosts/

Make sure that an included directory does not contain any stray files, such as editor temporary files, for example, as Apache will attempt to read them in and use the contents as configuration directives, which may cause the server to fail on start up. Running `apachectl configtest` will give you a list of the files that are being processed during the configuration check:

     root@host# apachectl configtest
      Processing config directory: /usr/local/apache/conf/vhosts
      Processing config file: /usr/local/apache/conf/vhosts/vhost1
      Processing config file: /usr/local/apache/conf/vhosts/vhost2
     Syntax OK

This will help in verifying that you are getting only the files that you intended as part of your configuration.

apachectl
KeepAlive
Turns on or off HTTP persistent connections.
KeepAlive on|off
KeepAlive On
server config

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 in Apache 1.2 and later, set `KeepAlive On`.

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

MaxKeepAliveRequests
KeepAliveTimeout
Sets the amount of time the server will wait for subsequent requests on a persistent connection
KeepAliveTimeout seconds
KeepAliveTimeout 15
server config

The number of seconds Apache will wait for a subsequent request before closing the connection. Once a request has been received, the timeout value specified by the Timeout directive applies.

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

Limit
Restrict access controls to only certain HTTP methods
<Limit method [method] ... > ... </Limit>
server config
virtual host
directory
.htaccess

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

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

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

The method names listed can be one or more of: GET, POST, PUT, DELETE, CONNECT, OPTIONS, TRACE, PATCH, PROPFIND, PROPPATCH, MKCOL, COPY, MOVE, LOCK, and UNLOCK. The method name is case-sensitive. If GET is used it will also restrict HEAD requests.

LimitExcept
Restrict access controls to all HTTP methods except the named ones
<LimitExcept method [method] ... > ... </LimitExcept>
server config
virtual host
directory
.htaccess

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

For example:

<LimitExcept POST GET>
Require valid-user
<LimitExcept>
LimitRequestBody
Restricts the total size of the HTTP request body sent from the client
LimitRequestBody bytes
LimitRequestBody 0
server config
virtual host
directory
.htaccess

This directive specifies the number of bytes from 0 (meaning unlimited) to 2147483647 (2GB) that are allowed in a request body. The default value is defined by the compile-time constant `DEFAULT_LIMIT_REQUEST_BODY` (0 as distributed).

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

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

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

LimitRequestBody 102400
LimitRequestFields
Limits the number of HTTP request header fields that will be accepted from the client
LimitRequestFields number
LimitRequestFields 100
server config

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

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

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

For example:

LimitRequestFields 50
LimitRequestFieldSize
Limits the size of the HTTP request header allowed from the client
LimitRequestFieldsize bytes
LimitRequestFieldsize 8190
server config

This directive specifies the number of bytes from 0 to the value of the compile-time constant `DEFAULT_LIMIT_REQUEST_FIELDSIZE` (8190 as distributed) that will be allowed in an HTTP request header.

The LimitRequestFieldsize directive allows the server administrator to reduce the limit on the allowed size of an HTTP request header field below the normal input buffer size compiled with the server. 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.

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 16380

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

LimitRequestLine
Limit the size of the HTTP request line that will be accepted from the client
LimitRequestLine bytes
LimitRequestLine 8190
server config

This directive sets the number of bytes from 0 to the value of the compile-time constant `DEFAULT_LIMIT_REQUEST_LINE` (8190 as distributed) that will be allowed on the HTTP request-line.

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

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

For example:

LimitRequestLine 16380

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

LimitXMLRequestBody
Limits the size of an XML-based request body
LimitXMLRequestBody number
LimitXMLRequestBody 1000000
server config

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

Example:

LimitXMLRequestBody 0
Location
Applies the enclosed directives only to matching URLs
<Location URL-path|URL> ... </Location>
server config
virtual host

The Location directive provides for access control 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.

Note that URLs do not have to line up with the filesystem at all, it should be emphasized that <Location> operates completely outside the filesystem.

For all origin (non-proxy) requests, the URL to be matched is of the form `/path/`, and you should not include any `http://servername` prefix. For proxy requests, the URL to be matched is of the form `scheme://servername/path`, and you must include the prefix.

The URL may use wildcards In a wild-card string, `?' matches any single character, and `*' matches any sequences of characters.

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

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

would match URLs that contained the substring "/extra/data" or "/special/data". In Apache 1.3 and above, a new directive LocationMatch exists which behaves identical to the regex version of Location.

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

<Location /status>
SetHandler server-status
Order Deny,Allow
Deny from all
Allow from .foo.com
</Location>

# Note about / (slash)

The slash character has special meaning depending on where in a URL it appears. People may be used to its behavior in the filesystem where multiple adjacent slashes are frequently collapsed to a single slash (i.e., `/home///foo` is the same as `/home/foo`). In URL-space this is not necessarily true. The LocationMatch directive and the regex version of Location require you to explicitly specify multiple slashes if that is your intention. For example, `<LocationMatch ^/abc>` would match the request URL `/abc` but not the request URL `//abc`. The (non-regex) Location directive behaves similarly when used for proxy requests. But when (non-regex) Location is used for non-proxy requests it will implicitly match multiple slashes with a single slash. For example, if you specify `<Location /abc/def>` and the request is to `/abc//def` then it will match.

How Directory, Location and Files sections work for an explanation of how these different sections are combined when a request is received
LocationMatch
Applies the enclosed directives only to regular-expression matching URLs
<LocationMatch regex> ... </Location>
server config
virtual host

The LocationMatch directive provides for access control by URL, in an identical manner to Location. However, it takes a regular expression as an argument instead of a simple string. For example:

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

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

How Directory, Location and Files sections work for an explanation of how these different sections are combined when a request is received
LogLevel
Controls the verbosity of the ErrorLog
LogLevel level
LogLevel warn
server config
virtual host

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

Level | Description | Example
--- | --- | ---
`emerg` | Emergencies - system is unusable. | "Child cannot open lock file. Exiting"
`alert` | Action must be taken immediately. | "getpwuid: couldn't determine user name from uid"
`crit` | Critical Conditions. | "socket: Failed to get a socket, exiting child"
`error` | Error conditions. | "Premature end of script headers"
`warn` | Warning conditions. | "child process 1234 did not exit, sending another SIGHUP"
`notice` | Normal but significant condition. | "httpd: caught SIGBUS, attempting to dump core in ..."
`info` | Informational. | "Server seems busy, (you may need to increase StartServers, or Min/MaxSpareServers)..."
`debug` | Debug-level messages | "Opening config file ..."

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

Using a level of at least `crit` is recommended.

For example:

LogLevel notice
MaxKeepAliveRequests
Sets the number of requests allowed on a persistent connection
MaxKeepAliveRequests number
MaxKeepAliveRequests 100
server config

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

For example:

MaxKeepAliveRequests 500
NameVirtualHost
Configures an IP address for name-virtual hosting
NameVirtualHost addr[:port]
server config

The NameVirtualHost directive is a required directive if you want to configure name-based virtual hosts.

Although addr can be hostname it is recommended that you always use an IP address, e.g.

NameVirtualHost 111.22.33.44

With the NameVirtualHost directive you specify the IP address on which the server will receive requests for the name-based virtual hosts. This will usually be the address to which your name-based virtual host names resolve. In cases where a firewall or other proxy receives the requests and forwards them on a different IP address to the server, you must specify the IP address of the physical interface on the machine which will be servicing the requests. If you have multiple name-based hosts on multiple addresses, repeat the directive for each address.

Note: the "main server" and any _default_ servers will never be served for a request to a NameVirtualHost IP Address (unless for some reason you specify NameVirtualHost but then don't define any VirtualHosts for that address).

Optionally you can specify a port number on which the name-based virtual hosts should be used, e.g.

NameVirtualHost 111.22.33.44:8080

IPv6 addresses must be enclosed in square brackets, as shown in the following example:

NameVirtualHost [fe80::a00:20ff:fea7:ccea]:8080
See also: Virtual Hosts documentation
Options
Configures what features are available in a particular directory
Options [+|-]option [[+|-]option] ...
Options All
server config
virtual host
directory
.htaccess
Options

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

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

All
  All options except for MultiViews. This is the default setting.
ExecCGI
  Execution of CGI scripts is permitted.
FollowSymLinks

  The server will follow symbolic links in this directory.
  Note: even though the server follows the symlink it does not change the pathname used to match against Directory sections.
  Note: this option gets ignored if set inside a Location section.
Includes
  Server-side includes are permitted.
IncludesNOEXEC

  Server-side includes are permitted, but the #exec command and #exec CGI are disabled. It is still possible to #include virtual CGI scripts from ScriptAliase'd directories.
Indexes
  If a URL which maps to a directory is requested, and the there is no DirectoryIndex (e.g., index.html) in that directory, then the server will return a formatted listing of the directory.
MultiViews
  Content negotiated MultiViews are allowed.
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: this option gets ignored if set inside a Location section.

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

For example, without any + and - symbols:

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

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

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

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

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

The default in the absence of any other settings is `All`.

Require
Selects which authenticated users can access a resource
Require entity-name [entity-name] ...
directory
.htaccess
AuthConfig

This directive selects which authenticated users can access a directory. The allowed syntaxes are:

- Require user userid [userid] ...

  Only the named users can access the directory.

- Require group group-name [group-name] ...

  Only users in the named groups can access the directory.

- Require valid-user

  All valid users can access the directory.

Require must be accompanied by AuthName and AuthType directives, and directives such as AuthUserFile and AuthGroupFile (to define users and groups) in order to work correctly. Example:

AuthType Basic
AuthName "Restricted Directory"
AuthUserFile /web/users
AuthGroupFile /web/groups
Require group admin

Access controls which are applied in this way are effective for all methods. This is what is normally desired. If you wish to apply access controls only to specific methods, while leaving other methods unprotected, then place the Require statement into a Limit section.

Satisfy
mod_access
RLimitCPU
Limits the CPU consumption of processes launched by Apache children
RLimitCPU number|max [number|max]
Unset; uses operating system defaults
server config
virtual host
Moved in version 2.0 to the MPMs

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

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

CPU resource limits are expressed in seconds per process.

RLimitMEM
RLimitNPROC
RLimitMEM
Limits the memory consumption of processes launched by Apache children
RLimitMEM number|max [number|max]
Unset; uses operating system defaults
server config
virtual host
Moved in version 2.0 to the MPMs.

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

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

Memory resource limits are expressed in bytes per process.

RLimitCPU
RLimitNPROC
RLimitNPROC
Limits the number of processes that can be launched by processes launched by Apache children
RLimitNPROC number|max [number|max]
Unset; uses operating system defaults
server config
virtual host
Moved in version 2.0 to the MPMs.

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

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

Process limits control the number of processes per user.

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

RLimitMEM
RLimitCPU
Satisfy
Configures how host-level access control and user authentication interact
Satisfy any|all
Satisfy all
directory
.htaccess

Access policy if both Allow and Require used. The parameter can be either 'all' or 'any'. This directive is only useful if access to a particular area is being restricted by both username/password and client host address. In this case the default behavior ("all") is to require that the client passes the address access restriction and enters a valid username and password. With the "any" option the client will be granted access if they either pass the host restriction or enter a valid username and password. This can be used to password restrict an area, but to let clients from particular addresses in without prompting for a password.

For example, if you wanted to let people on your network have unrestricted access to a portion of your website, but require that people outside of your network provide a password, you could use a configuration similar to the following:

Require valid-user
Allow from 192.168.1
Satisfy any
Allow
Require
ScriptInterpreterSource
Controls how the interpreter for CGI scripts is located
ScriptInterpreterSource registry|script
ScriptInterpreterSource script
directory
.htaccess
Win32 only

This directive is used to control how Apache finds the interpreter used to run CGI scripts. The default technique is to use the interpreter pointed to by the #! line in the script. Setting `ScriptInterpreterSource registry` will cause the Windows Registry to be searched using the script file extension (e.g., .pl) as a search key.

ServerAdmin
Sets the email address that the server includes in error messages sent to the client
ServerAdmin email-address
server config
virtual host

The ServerAdmin sets the e-mail address that the server includes in any error messages it returns to the client.

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

ServerAdmin www-admin@foo.bar.com

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

ServerAlias
Sets alternate names for a host used when matching requests to name-virtual hosts
ServerAlias hostname [hostname] ...
virtual host

The ServerAlias directive sets the alternate names for a host, for use with name-based virtual hosts.

<VirtualHost *>
ServerName server.domain.com
ServerAlias server server2.domain.com server2
...
</VirtualHost>
Apache Virtual Host documentation
ServerName
Sets the hostname and port that the server uses to identify itself
ServerName fully-qualified-domain-name[:port]
server config
virtual host
In version 2.0, this directive supersedes the functionality of the Port directive from version 1.3.

The ServerName directive sets the hostname and port that the server uses to identify itself. This is used when creating redirection URLs. For example, if the name of the machine hosting the webserver is `simple.example.com`, but the machine also has the DNS alias `www.example.com` and you wish the webserver to be so identified, the following directive should be used:

ServerName www.example.com:80

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

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

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

DNS Issues
Apache virtual host documentation
UseCanonicalName
NameVirtualHost
ServerAlias
ServerPath
Sets the legacy URL pathname for a name-virtual host that is accessed by an incompatible browser
ServerPath directory-path
virtual host

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

Apache Virtual Host documentation
ServerRoot
Sets the base directory for the server installation
ServerRoot directory-path
ServerRoot /usr/local/apache
server config

The ServerRoot directive sets the directory in which the server lives. Typically it will contain the subdirectories `conf/` and `logs/`. Relative paths for other configuration files are taken as relative to this directory.

the `-d` option to `httpd`
the security tips for information on how to properly set permissions on the ServerRoot
ServerSignature
Configures the footer on server-generated documents
ServerSignature On|Off|EMail
ServerSignature Off
server config
virtual host
directory
.htaccess

The ServerSignature directive allows the configuration of a trailing footer line under server-generated documents (error messages, mod_proxy ftp directory listings, mod_info output, ...). The reason why you would want to enable such a footer line is that in a chain of proxies, the user often has no possibility to tell which of the chained servers actually produced a returned error message.
The `Off` setting, which is the default, suppresses the error line (and is therefore compatible with the behavior of Apache-1.2 and below). The `On` setting simply adds a line with the server version number and ServerName of the serving virtual host, and the `EMail` setting additionally creates a "mailto:" reference to the ServerAdmin of the referenced document.

ServerTokens
Configures the Server HTTP response header
ServerTokens Minimal|ProductOnly|OS|Full
ServerTokens Full
server config

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

`ServerTokens Prod[uctOnly]`
  Server sends (e.g.): `Server: Apache`
`ServerTokens Min[imal]`
  Server sends (e.g.): `Server: Apache/1.3.0`
`ServerTokens OS`
  Server sends (e.g.): `Server: Apache/1.3.0 (Unix)`
`ServerTokens Full` (or not specified)
  Server sends (e.g.): `Server: Apache/1.3.0 (Unix) PHP/3.0 MyMod/1.2`

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

SetHandler
Forces all matching files to be processed by a handler
SetHandler handler-name
server config
virtual host
directory
.htaccess
Moved into the core in Apache 2.0

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

SetHandler imap-file

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

<Location /status>
SetHandler server-status
</Location>
SetInputFilter
Sets the filters that will process client requests and POST input
SetInputFilter filter[;filter...]
server config
virtual host
directory
.htaccess

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

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

Filters documentation
SetOutputFilter
Sets the filters that will process responses from the server
SetOutputFilter filter [filter] ...
server config
virtual host
directory
.htaccess

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

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

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

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

Filters documentation
TimeOut
Defines the amount of time the server will wait for certain events before failing a request
TimeOut number
TimeOut 300
server config

The TimeOut directive currently defines the amount of time Apache will wait for three things:

1. The total amount of time it takes to receive a GET request.
2. The amount of time between receipt of TCP packets on a POST or PUT request.
3. The amount of time between ACKs on transmissions of TCP packets in responses.

We plan on making these separately configurable at some point down the road. The timer used to default to 1200 before 1.2, but has been lowered to 300 which is still far more than necessary in most situations. It is not set any lower by default because there may still be odd places in the code where the timer is not reset when a packet is sent.

UseCanonicalName
Configures how the server determines its own name and port
UseCanonicalName on|off|dns
UseCanonicalName on
server config
virtual host
directory
.htaccess
Options

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

With `UseCanonicalName off` Apache 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). These values are the same that are used to implement name based virtual hosts, and are available with the same clients. The CGI variables `SERVER_NAME` and `SERVER_PORT` will be constructed from the client supplied values as well.

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

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

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

ServerName
Listen
VirtualHost
Contains directives that apply only to a specific hostname or IP address
<VirtualHost addr[:port] [addr[:port]] ...> ... </VirtualHost>
server config

VirtualHost and `</VirtualHost>` are used to enclose a group of directives which will apply only to a particular virtual host. Any directive which 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

- The IP address of the virtual host
- A fully qualified domain name for the IP address of the virtual host.

# Example

<VirtualHost 10.1.2.3>
ServerAdmin webmaster@host.foo.com
DocumentRoot /www/docs/host.foo.com
ServerName host.foo.com
ErrorLog logs/host.foo.com-error_log
TransferLog logs/host.foo.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 [fe80::a00:20ff:fea7:ccea]>
ServerAdmin webmaster@host.foo.com
DocumentRoot /www/docs/host.foo.com
ServerName host.foo.com
ErrorLog logs/host.foo.com-error_log
TransferLog logs/host.foo.com-access_log
</VirtualHost>

Each Virtual Host must correspond to a different IP address, different port number or a different host name for the server, in the former case the server machine must be configured to accept IP packets for multiple addresses. (If the machine does not have multiple network interfaces, then this can be accomplished with the `ifconfig alias` command (if your OS supports it), or with kernel patches like VIF (for SunOS(TM) 4.1.x)).

The special name `_default_` can be specified in which case this virtual host will match any IP address that is not explicitly listed in another virtual host. In the absence of any _default_ virtual host the "main" server config, consisting of all those definitions outside any VirtualHost section, is used when no match occurs.

You can specify a `:port` to change the port that is matched. If unspecified then it defaults to the same port as the most recent Listen statement of the main server. You may also specify `:*` to match all ports on that address. (This is recommended when used with `_default_`.)

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

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

Apache Virtual Host documentation
Warnings about DNS and Apache
Setting which addresses and ports Apache uses
How Directory, Location and Files sections work for an explanation of how these different sections are combined when a request is received