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
• CGICommandArgs
• ClearModuleList
• ContentDigest
• CoreDumpDirectory
• DefaultType
• <Directory>
• <DirectoryMatch>
• DocumentRoot
• EBCDICConvert
• EBCDICConvertByType
• EBCDICKludge
• ErrorDocument
• ErrorLog
• FileETag
• <Files>
• <FilesMatch>
• Group
• HostnameLookups
• IdentityCheck
• <IfDefine>
• <IfModule>
• Include
• KeepAlive
• KeepAliveTimeout
• <Limit>
• <LimitExcept>
• LimitInternalRecursion
• LimitRequestBody
• LimitRequestFields
• LimitRequestFieldsize
• LimitRequestLine
• Listen
• ListenBacklog
• <Location>
• <LocationMatch>
• LockFile
• LogLevel
• MaxClients
• MaxKeepAliveRequests
• MaxRequestsPerChild
• MaxSpareServers
• MinSpareServers
• NameVirtualHost
• Options
• PidFile
• Port
• ProtocolReqCheck
• Require
• ResourceConfig
• RLimitCPU
• RLimitMEM
• RLimitNPROC
• Satisfy
• ScoreBoardFile
• ScriptInterpreterSource
• SendBufferSize
• ServerAdmin
• ServerAlias
• ServerName
• ServerPath
• ServerRoot
• ServerSignature
• ServerTokens
• ServerType
• ShmemUIDisUser
• 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 -V 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.

This directive has no effect on Microsoft Windows.

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

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.

Alternatively you can use a wildcard to limit the scope; i.e to only *.conf files.

Note that by default any file in the specified directory will be loaded as a configuration file.

So make sure that you don't have stray files in this directory by mistake, such as temporary files created by your editor, for example.

See also: Include and 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 and Configuration Files

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.

For example:

AddDefaultCharset utf-8

Note: This will not have any effect on the Content-Type and character set for default Apache-generated status pages (such as '404 Not Found' or '301 Moved Permanently') because those have an actual character set (that in which the hard-coded page content is written) and don't need to have a default applied.

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.

For example:

AddModule mod_include.c

The ordering of AddModule lines is important. Modules are listed in reverse priority order --- the ones that come later can override the behavior of those that come earlier. This can have visible effects; for instance, if UserDir followed Alias, you couldn't alias out a particular user's home directory. For more information and a recommended ordering, see src/Configuration.tmpl in the Apache source distribution.

See also: ClearModuleList and LoadModule

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.

Note: AllowOverride is only valid in <Directory> sections, not in <Location> or <Files> sections, as implied by the Context section above.

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).

Example:

AllowOverride AuthConfig Indexes

See Also: AccessFileName and Configuration Files

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.

For example:

AuthName "Top Secret"

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

See also: Authentication, Authorization, and Access Control

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.

See also: Authentication, Authorization, and Access Control

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.

For example:

Only one BindAddress directive can be used.

This directive is deprecated and will be eliminated in Apache 2.0. Equivalent functionality and more control over the address and ports Apache listens to is available using the Listen directive.

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

CGICommandArgs directive

Way back when the internet was a safer, more naive place, it was convenient for the server to take a query string that did not contain an '=' sign and to parse and pass it to a CGI program as command line args. For example, <IsIndex> generated searches often work in this way. The default behavior in Apache is to maintain this behavior for backwards compatibility, although it is generally regarded as unsafe practice today. Most CGI programs do not take command line parameters, but among those that do, many are unaware of this method of passing arguments and are therefore vulnerable to malicious clients passing unsafe material in this way. Setting CGICommandArgs Off is recommended to protect such scripts with little loss in functionality.

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.

See also: AddModule and LoadModule

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.

For example:

CoreDumpDirectory /tmp

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

See also: AddType and TypesConfig.

<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.

If you have mod_proxy enabled, you can use the proxy: syntax to apply configuration directives to proxied content. The syntax for this is to specify the proxied URLs to which you wish to apply the configuration, or to specify * to apply to all proxied content:

To apply to all proxied content:

   <Directory proxy:*>
     ... directives here ...
   </Directory>
   

To apply to just a subset of proxied content:

   <Directory proxy:http://www.example.com/>
     ... directives here ...
   </Directory>
   

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

See also: DirectoryMatch

<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. See the HTTP specification for a complete list of the status codes and their meanings.

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.

Examples

ErrorLog logs/vhost1.error

ErrorLog |/usr/local/bin/errorlog.pl

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).

For example:

ErrorLog syslog

ErrorLog syslog:user

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

FileETag directive

The FileETag directive configures the file attributes that are used to create the ETag (entity tag) response header field when the document is based on a 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> 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. For example, to password protect a single file within a particular directory, you might add the following to your .htaccess file:

    <Files admin.cgi>
    Require group admin
    </Files>

Remember that directives apply to subdirectories as well, so this will also protect files called admin.cgi in subdirectories, unless specifically overridden.

(See Require for details on using the Require directive)

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.

It is recommended that you set up a new group specifically for running the server. Some admins use user nobody, but this is not always possible or desirable.

Example:

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.

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 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 directive

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

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.

By using a wildcard this can be further limited to, say, just the '*.conf' files.

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.

See also: apachectl

KeepAlive directive

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

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

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

<LimitExcept> directive

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

For example:

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

LimitInternalRecursion directive

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

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

The directive stores two different limits, which are evaluated on per-request basis. The first number is the maximum number of internal redirects, that may follow each other. The second number determines, how deep subrequests may be nested. If you specify only one number, it will be assigned to both limits. A value of 0 means "unlimited".

Example

    LimitInternalRecursion 5
    

LimitRequestBody directive

This directive specifies the number of bytes from 0 (meaning unlimited) to 2147483647 (2GB) that are allowed in a request body.

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 directive

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

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

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

For example:

LimitRequestFields 50

LimitRequestFieldsize directive

This directive specifies the number of bytes 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 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.

For example:

LimitRequestLine 16380

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.

For example:

LogLevel notice

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

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.

For example

MaxKeepAliveRequests 500

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 behavio