Apache HTTP Server Version 1.3

Apache Core Features

These configuration parameters control the core Apache features, and are always available.

Directives

• AcceptFilter
• AcceptMutex
• AccessConfig
• AccessFileName
• AddDefaultCharset
• AddModule
• AllowOverride
• AuthName
• AuthType
• BindAddress
• BS2000Account
• ClearModuleList
• ContentDigest
• CoreDumpDirectory
• DefaultType
• <Directory>
• <DirectoryMatch>
• DocumentRoot
• EBCDICConvert
• EBCDICConvertByType
• EBCDICKludge
• ErrorDocument
• ErrorLog
• <Files>
• <FilesMatch>
• Group
• HostNameLookups
• IdentityCheck
• <IfDefine>
• <IfModule>
• Include
• KeepAlive
• KeepAliveTimeout
• <Limit>
• <LimitExcept>
• LimitRequestBody
• LimitRequestFields
• LimitRequestFieldsize
• LimitRequestLine
• Listen
• ListenBacklog
• <Location>
• <LocationMatch>
• LockFile
• LogLevel
• MaxClients
• MaxKeepAliveRequests
• MaxRequestsPerChild
• MaxSpareServers
• MinSpareServers
• NameVirtualHost
• Options
• PidFile
• Port
• Require
• ResourceConfig
• RLimitCPU
• RLimitMEM
• RLimitNPROC
• Satisfy
• ScoreBoardFile
• ScriptInterpreterSource
• SendBufferSize
• ServerAdmin
• ServerAlias
• ServerName
• ServerPath
• ServerRoot
• ServerSignature
• ServerTokens
• ServerType
• StartServers
• ThreadsPerChild
• ThreadStackSize
• TimeOut
• UseCanonicalName
• User
• <VirtualHost>

AcceptFilter directive

AcceptFilter controls a BSD specific filter optimization. It is compiled in by default - and switched on by default if your system supports it (setsocketopt() option SO_ACCEPTFILTER). Currently only FreeBSD supports this.

See the filter section on performance hints for more information.

The compile time flag AP_ACCEPTFILTER_OFF can be used to change the default to 'off'. httpd -V and httpd -L will show compile time defaults and whether or not SO_ACCEPTFILTER was defined during the compile.

AcceptMutex directive

AcceptMutex controls which accept() mutex method Apache will use. Not all methods are available on all platforms, since the suite of methods is determined at compile-time. For a list of which methods are available for your particular build, the httpd -L command line option will list them out.

The compile time flags -D HAVE_METHOD_SERIALIZED_ACCEPT can be used to add different methods to your build, or one can edit the include/ap_config.h file for your particular platform.

See the performance tuning guide for more information.

AccessConfig directive

The server will read this file for more directives after reading the ResourceConfig file. File-path is relative to the ServerRoot. This feature can be disabled using:

AccessConfig /dev/null

AccessConfig nul

New in Apache 1.3.13 is the feature that if AccessConfig 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.

See also ResourceConfig.

AccessFileName directive

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

<Directory />
AllowOverride None
</Directory>

See Also: AllowOverride

AddDefaultCharset directive

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; e.g. AddDefaultCharset utf-8.

AddModule directive

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.

AllowOverride directive

When the server finds an .htaccess file (as specified by AccessFileName) it needs to know which directives declared in that file can override earlier 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 (AddEncoding, AddLanguage, AddType, DefaultType, ErrorDocument, LanguagePriority, 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).

See Also: AccessFileName

AuthName directive

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.

AuthType directive

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.

BindAddress directive

A Unix® http server can either listen for connections to every IP address of the server machine, or just one IP address of the server machine. If the argument to this directive is *, then the server will listen for connections on every IP address. Otherwise, the server can listen to only a specific IP-address or a fully-qualified Internet domain-name.

Only one BindAddress directive can be used. For more control over which address and ports Apache listens to, use the Listen directive instead of BindAddress.

BindAddress can be used as an alternative method for supporting virtual hosts using multiple independent servers, instead of using <VirtualHost> sections.

See Also: DNS Issues
See Also: Setting which addresses and ports Apache uses

BS2000Account directive

The BS2000Account directive is available for BS2000 hosts only. It must be used to define the account number for the non-privileged apache server user (which was configured using the User directive). This is required by the BS2000 POSIX subsystem (to change the underlying BS2000 task environment by performing a sub-LOGON) to prevent CGI scripts from accessing resources of the privileged account which started the server, usually SYSROOT.
Only one BS2000Account directive can be used.

See Also: Apache EBCDIC port

ClearModuleList directive

The server comes with a built-in list of active modules. This directive clears the list. It is assumed that the list will then be re-populated using the AddModule directive.

ContentDigest directive

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.

CoreDumpDirectory directive

This controls the directory to which Apache attempts to switch before dumping core. The default is in the ServerRoot directory, however since this should not be writable by the user the server runs as, core dumps won't normally get written. If you want a core dump for debugging, you can use this directive to place it in a different location.

DefaultType directive

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

<Directory> directive

<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. As of Apache 1.3, 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>

Apache 1.2 and above: Extended regular expressions can also be used, with the addition of the ~ character. For example:

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

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>

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

Regular expression directory sections are handled slightly differently by Apache 1.2 and 1.3. In Apache 1.2 they are interspersed with the normal directory sections and applied in the order they appear in the configuration file. They are applied only once, and apply when the shortest match possible occurs. In Apache 1.3 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>


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.

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>

<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.

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

DocumentRoot directive

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

DocumentRoot /usr/web

There appears to be a bug in mod_dir which causes problems when the DocumentRoot has a trailing slash (i.e., "DocumentRoot /usr/web/") so please avoid that.

EBCDICConvert

The EBCDICConvert directive maps the given filename extensions to the specified conversion setting (On or Off). File extensions may be specified with or without a leading dot.

If the optional format On=direction (or Off=direction) is used, where direction is one of In, Out or InOut, then the directive only applies to the specified transfer direction (In: uploaded content in a PUT or POST request, Out: returned content in a GET or POST request, and InOut: conversion in both directions).
Otherwise, InOut (conversion in both directions) is implied.

Conversion configuration based on file extension is tested prior to configuration based on MIME type, to allow for generic MIME based rules to be overridden by a more specific file extension (several file extensions may exist for the same MIME type).

Example:
With a configuration like the following, the normal *.html files contain HTML text in EBCDIC encoding, while *.ahtml files contain HTML text in ASCII encoding:

    # *.html and *.ahtml contain HTML text:
    AddType  text/html  .html .ahtml

    # *.ahtml is not converted (contains ASCII text already):
    EBCDICConvert       Off .ahtml

    # All other text/html files presumably contain EBCDIC text:
    EBCDICConvertByType On  text/html

See also: EBCDICConvertByType and Overview of the EBCDIC Conversion Functions

EBCDICConvertByType

The EBCDICConvertByType directive maps the given MIME type (optionally containing wildcards) to the specified conversion setting (On or Off).

If the optional format On=direction (or Off=direction) is used, where direction is one of In, Out or InOut, then the directive only applies to the specified transfer direction (In: uploaded content in a PUT or POST request, Out: returned content in a GET or POST request, and InOut: conversion in both directions).
Otherwise, InOut (conversion in both directions) is implied.

Example:
A useful standard configuration should at least contain the following defaults:

    # All text documents are stored as EBCDIC files:
    EBCDICConvertByType On  text/* message/* multipart/*
    EBCDICConvertByType On  application/x-www-form-urlencoded \
                model/vrml application/postscript
    # All other files are assumed to be binary:
    EBCDICConvertByType Off */*

    # All documents are ASCII already:
    EBCDICConvertByType Off */*

See also: EBCDICConvert and Overview of the EBCDIC Conversion Functions

EBCDICKludge

The EBCDICKludge is provided for the backward compatible behavior with apache versions 1.3.0 through 1.3.18. In these versions, all files with MIME types starting with "text/", "message/" or "multipart/" or with type "application/x-www-form-urlencoded" would be converted by default, all other documents were returned unconverted. Only if a MIME type "text/x-ascii-subtype" was configured for a certain document, the document was assumed to be in ASCII format already, and was not converted again. Instead, the "x-ascii-" was removed from the type, resulting in the MIME type "text/subtype" being returned for the document.

If the EBCDICKludge directive is set to On, and if none of the file extensions configured with the EBCDICConvert directive matches in the current context, then the server tests for a MIME type of the format type/x-ascii-subtype. If the document has such a type, then the "x-ascii-" substring is removed and the conversion set to Off. This allows for overriding the implicit assumption that all text files are stored in EBCDIC format, for example when serving documents from an NFS mounted directory with ASCII documents.
By using the EBCDICKludge, there is no way to force one of the other MIME types (e.g., model/vrml) to be treated as an EBCDIC text file. Use of the EBCDICConvertByType directive mentioned above is the preferred way to configure such a conversion. (Before Apache version 1.3.19, there was no way at all to force these binary documents to be treated as EBCDIC text files.)

See also: EBCDICConvert, EBCDICConvertByType and Overview of the EBCDIC Conversion Functions

ErrorDocument directive

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 message or URL.

Messages in this context begin with a single double-quote character ("), which does not form part of the message itself. 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. 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.

See Also: documentation of customizable responses.

ErrorLog directive

The error log 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.

Apache 1.3 and above: 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.

See also: LogLevel and Apache Log Files

<Files> directive

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)$">

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>

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.

Group directive

The Group directive sets the group under which the server will answer requests. In order to use this directive, the stand-alone server must be run initially as root. Unix-group is one of:

A group name

Refers to the given group by name.

# followed by a group number.

Refers to a group by its number.

Note: if you start the server as a non-root user, it will fail to change to the specified group, and will instead continue to run as the group of the original user.

Special note: Use of this directive in <VirtualHost> requires a properly configured suEXEC wrapper. When used inside a <VirtualHost> in this manner, only the group that CGIs are run as is affected. Non-CGI requests are still processed as the group specified in the main Group directive.

SECURITY: See User for a discussion of the security considerations.

HostNameLookups directive

This directive enables DNS lookups so that host names can be logged (and passed to CGIs/SSIs in REMOTE_HOST). The value double refers to doing double-reverse DNS. 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 for this directive was previously on in versions of Apache prior to 1.3. It was changed to 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 directive

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. Boolean is either on or off.

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> directive

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

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

• parameter-name
• !parameter-name

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

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

<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 libexec/mod_rewrite.so
  LoadModule proxy_module   libexec/libproxy.so
  </IfDefine>

<IfModule> directive

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 compiled in to Apache. The second format reverses the test, and only processes the directives if module name is not compiled in.

The module name argument is a module name as given as 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 directive

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

New in Apache 1.3.13 is the feature that 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.

KeepAlive directive

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

Apache 1.1 only: Set max-requests to the maximum number of requests you want Apache to entertain per connection. A limit is imposed to prevent a client from hogging your server resources. Set this to 0 to disable support. In Apache 1.2 and 1.3, this is controlled through the MaxKeepAliveRequests directive instead.

See also MaxKeepAliveRequests.

KeepAliveTimeout directive

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> directive

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

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

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

<LimitExcept> directive

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

LimitRequestBody directive

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.

LimitRequestFields directive

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

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

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

LimitRequestFieldsize directive

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

LimitRequestLine directive

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

Listen directive

The Listen directive instructs Apache to listen to more than one IP address or port; by default it responds to requests on all IP interfaces, but only on the port given by the Port directive.

Note that you may still require a Port directive so that URLs that Apache generates that point to your server still work.

Multiple Listen directives may be used to specify a number of addresses and ports to listen to. The server will respond to requests from any of the listed addresses and ports.

For example, to make the server accept connections on both port 80 and port 8000, use:

   Listen 80
   Listen 8000

   Listen 192.170.2.1:80
   Listen 192.170.2.5:8000

See Also: DNS Issues
See Also: Setting which addresses and ports Apache uses
See Also: Known Bugs

ListenBacklog directive

The maximum length of the queue of pending connections. Generally no tuning is needed or desired, however on some systems it is desirable to increase this when under a TCP SYN flood attack. See the backlog parameter to the listen(2) system call.

This will often be limited to a smaller number by the operating system. This varies from OS to OS. Also note that many OSes do not use exactly what is specified as the backlog, but use a number based on (but normally larger than) what is set.

<Location> directive

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.

Apache 1.2 and above: 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>

Apache 1.3 and above note about / (slash): The slash character has special meaning depending on where in a URL it appears. People may be used to its behavior in the filesystem where multiple adjacent slashes are frequently collapsed to a single slash (i.e., /home///foo is the same as /home/foo). In URL-space this is not necessarily true. The <LocationMatch> directive and the regex version of <Location> require you to explicitly specify multiple slashes if that is your intention. For example, <LocationMatch ^/abc> would match the request URL /abc but not the request URL //abc. The (non-regex) <Location> directive behaves similarly when used for proxy requests. But when (non-regex) <Location> is used for non-proxy requests it will implicitly match multiple slashes with a single slash. For example, if you specify <Location /abc/def> and the request is to /abc//def then it will match.

See also: How Directory, Location and Files sections work for an explanation of how these different sections are combined when a request is received

<LocationMatch>

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".

LockFile directive

The LockFile directive sets the path to the lockfile used when Apache is compiled with either USE_FCNTL_SERIALIZED_ACCEPT or USE_FLOCK_SERIALIZED_ACCEPT. This directive should normally be left at its default value. The main reason for changing it is if the logs directory is NFS mounted, since the lockfile must be stored on a local disk. The PID of the main server process is automatically appended to the filename.

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

LogLevel directive

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

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

Using a level of at least crit is recommended.

MaxClients directive

The MaxClients directive sets the limit on the number of simultaneous requests that can be supported; not more than this number of child server processes will be created. To configure more than 256 clients, you must edit the HARD_SERVER_LIMIT entry in httpd.h and recompile.

Any connection attempts over the MaxClients limit will normally be queued, up to a number based on the ListenBacklog directive. Once a child process is freed at the end of a different request, the connection will then be serviced.

MaxKeepAliveRequests directive

The MaxKeepAliveRequests directive limits the number of requests allowed per connection when KeepAlive is on. If it is set to "0", unlimited requests will be allowed. We recommend that this setting be kept to a high value for maximum server performance. In Apache 1.1, this is controlled through an option to the KeepAlive directive.

MaxRequestsPerChild directive

The MaxRequestsPerChild directive sets the limit on the number of requests that an individual child server process will handle. After MaxRequestsPerChild requests, the child process will die. If MaxRequestsPerChild is 0, then the process will never expire.

Setting MaxRequestsPerChild to a non-zero limit has two beneficial effects:

• it limits the amount of memory that process can consume by (accidental) memory leakage;
• by giving processes a finite lifetime, it helps reduce the number of processes when the server load reduces.

However, on Win32, It is recommended that this be set to 0. If it is set to a non-zero value, when the request count is reached, the child process exits, and is respawned, at which time it re-reads the configuration files. This can lead to unexpected behavior if you have modified a configuration file, but are not expecting the changes to be applied yet. See also ThreadsPerChild.

NOTE: For KeepAlive requests, only the first request is counted towards this limit. In effect, it changes the behavior to limit the number of connections per child.

MaxSpareServers directive

The MaxSpareServers directive sets the desired maximum number of idle child server processes. An idle process is one which is not handling a request. If there are more than MaxSpareServers idle, then the parent process will kill off the excess processes.

Tuning of this parameter should only be necessary on very busy sites. Setting this parameter to a large number is almost always a bad idea.

This directive has no effect when used with the Apache Web server on a Microsoft Windows platform.

See also MinSpareServers and StartServers.

MinSpareServers directive

The MinSpareServers directive sets the desired minimum number of idle child server processes. An idle process is one which is not handling a request. If there are fewer than MinSpareServers idle, then the parent process creates new children at a maximum rate of 1 per second.

Tuning of this parameter should only be necessary on very busy sites. Setting this parameter to a large number is almost always a bad idea.

This directive has no effect on Microsoft Windows.

See also MaxSpareServers and StartServers.

NameVirtualHost directive

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 or wildcard, e.g.

NameVirtualHost 111.22.33.44

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

See also: Apache Virtual Host documentation

Options directive

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.

For example, without any + and - symbols:

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

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

PidFile directive

The PidFile directive sets the file to which the server records the process id of the daemon. If the filename does not begin with a slash (/) then it is assumed to be relative to the ServerRoot. The PidFile is only used in standalone mode.

It is often useful to be able to send the server a signal, so that it closes and then reopens its ErrorLog and TransferLog, and re-reads its configuration files. This is done by sending a SIGHUP (kill -1) signal to the process id listed in the PidFile.

The PidFile is subject to the same warnings about log file placement and security.

Port directive

Number is a number from 0 to 65535; some port numbers (especially below 1024) are reserved for particular protocols. See /etc/services for a list of some defined ports; the standard port for the http protocol is 80.

The Port directive has two behaviors, the first of which is necessary for NCSA backwards compatibility (and which is confusing in the context of Apache).

• In the absence of any Listen or BindAddress directives specifying a port number, a Port directive given in the "main server" (i.e., outside any <VirtualHost> section) sets the network port on which the server listens. If there are any Listen or BindAddress directives specifying :number then Port has no effect on what address the server listens at.
• The Port directive sets the SERVER_PORT environment variable (for CGI and SSI), and is used when the server must generate a URL that refers to itself (for example when creating an external redirect to itself). This behavior is modified by UseCanonicalName.

Port 80 is one of Unix's special ports. All ports numbered below 1024 are reserved for system use, i.e., regular (non-root) users cannot make use of them; instead they can only use higher port numbers. To use port 80, you must start the server from the root account. After binding to the port and before accepting requests, Apache will change to a low privileged user as set by the User directive.

If you cannot use port 80, choose any other unused port. Non-root users will have to choose a port number higher than 1023, such as 8000.

SECURITY: if you do start the server as root, be sure not to set User to root. If you run the server as root whilst handling connections, your site may be open to a major security attack.

Require directive

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


See also Satisfy and mod_access.

ResourceConfig directive

The server will read this file for more directives after reading the httpd.conf file. File-path is relative to the ServerRoot. This feature can be disabled using:

ResourceConfig /dev/null

ResourceConfig nul

New in Apache 1.3.13 is the feature that if ResourceConfig 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.

See also AccessConfig.

RLimitCPU directive

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.

See also RLimitMEM or RLimitNPROC.

RLimitMEM directive

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.

See also RLimitCPU or RLimitNPROC.

RLimitNPROC directive

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.

See also RLimitMEM or RLimitCPU.

Satisfy directive

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.

See also Require and Allow.

ScoreBoardFile directive

The ScoreBoardFile directive is required on some architectures to place a file that the server will use to communicate between its children and the parent. The easiest way to find out if your architecture requires a scoreboard file is to run Apache and see if it creates the file named by the directive. If your architecture requires it then you must ensure that this file is not used at the same time by more than one invocation of Apache.

If you have to use a ScoreBoardFile then you may see improved speed by placing it on a RAM disk. But be careful that you heed the same warnings about log file placement and security.

Apache 1.2 and above:

Linux 1.x users might be able to add -DHAVE_SHMGET -DUSE_SHMGET_SCOREBOARD to the EXTRA_CFLAGS in your Configuration. This might work with some 1.x installations, but won't work with all of them. (Prior to 1.3b4, HAVE_SHMGET would have sufficed.)

SVR4 users should consider adding -DHAVE_SHMGET -DUSE_SHMGET_SCOREBOARD to the EXTRA_CFLAGS in your Configuration. This is believed to work, but we were unable to test it in time for 1.2 release. (Prior to 1.3b4, HAVE_SHMGET would have sufficed.)

See Also: Stopping and Restarting Apache

ScriptInterpreterSource directive

This directive is used to control how Apache 1.3.5 and later 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.

SendBufferSize directive

The server will set the TCP buffer size to the number of bytes specified. Very useful to increase past standard OS defaults on high speed high latency (i.e., 100ms or so, such as transcontinental fast pipes)

ServerAdmin directive

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

ServerAlias directive

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

See also: Apache Virtual Host documentation

ServerName directive

The ServerName directive sets the hostname of the server; this is used when creating redirection URLs. If it is not specified, then the server attempts to deduce it from its own IP address; however this may not work reliably, or may not return the preferred hostname. For example:

ServerName www.example.com

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 Also:
DNS Issues
Apache virtual host documentation
UseCanonicalName
NameVirtualHost
ServerAlias

ServerPath directive

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

See also: Apache Virtual Host documentation

ServerRoot directive

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.

See also the -d option to httpd.

See also the security tips for information on how to properly set permissions on the ServerRoot.

ServerSignature directive

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 directive

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.

ServerType directive

The ServerType directive sets how the server is executed by the system. Type is one of

inetd

The server will be run from the system process inetd; the command to start the server is added to /etc/inetd.conf

standalone

The server will run as a daemon process; the command to start the server is added to the system startup scripts. (/etc/rc.local or /etc/rc3.d/....)

Standalone is the most common setting for ServerType since it is far more efficient. The server is started once, and services all subsequent connections. If you intend running Apache to serve a busy site, standalone will probably be your only option.

StartServers directive

The StartServers directive sets the number of child server processes created on startup. As the number of processes is dynamically controlled depending on the load, there is usually little reason to adjust this parameter.

When running under Microsoft Windows, this directive has no effect. There is always one child which handles all requests. Within the child requests are handled by separate threads. The ThreadsPerChild directive controls the maximum number of child threads handling requests, which will have a similar effect to the setting of StartServers on Unix.

See also MinSpareServers and MaxSpareServers.

ThreadsPerChild

This directive tells the server how many threads it should use. This is the maximum number of connections the server can handle at once; be sure and set this number high enough for your site if you get a lot of hits.

This directive has no effect on Unix systems. Unix users should look at StartServers and MaxRequestsPerChild.

ThreadStackSize

This directive tells the server what stack size to use for each of the running threads. If you ever get a stack overflow you will need to bump this number to a higher setting.

This directive has no effect on other systems.

TimeOut directive

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.

UseCanonicalName directive

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 (and in all versions prior to 1.3) Apache will use the ServerName and Port directives 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.

See also: ServerName, Port

User directive

The User directive sets the userid as which the server will answer requests. In order to use this directive, the standalone server must be run initially as root. Unix-userid is one of:

A username

Refers to the given user by name.

# followed by a user number.

Refers to a user by their number.

Notes: If you start the server as a non-root user, it will fail to change to the lesser privileged user, and will instead continue to run as that original user. If you do start the server as root, then it is normal for the parent process to remain running as root.

Special note: Use of this directive in <VirtualHost> requires a properly configured suEXEC wrapper. When used inside a <VirtualHost> in this manner, only the user that CGIs are run as is affected. Non-CGI requests are still processed with the user specified in the main User directive.

SECURITY: Don't set User (or Group) to root unless you know exactly what you are doing, and what the dangers are.

<VirtualHost> directive

<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.

<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>

You can specify more than one IP address. This is useful if a machine responds to the same name on two different interfaces. For example, if you have a VirtualHost that is available to hosts on an internal (intranet) as well as external (internet) network. Example:

<VirtualHost 192.168.1.2 204.255.176.199>
DocumentRoot /www/docs/host.foo.com
ServerName host.foo.com
ServerAlias host
</VirtualHost>

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 Port 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 either BindAddress or Listen.

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

Apache HTTP Server Version 1.3