core - Apache HTTP Server

Apache HTTP Server Version 2.2

Apache > HTTP Server > Documentation > Version 2.2 > Modules

# Apache Core Features

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

### Directives

## AcceptFilter Directive

Description: | Configures optimizations for a Protocol's Listener Sockets
Syntax: | `AcceptFilter protocol accept_filter`
Context: | server config
Status: | Core
Module: | core
Compatibility: | Available in Apache 2.1.5 and later

This directive enables operating system specific optimizations for a listening socket by the Protocol type. The basic premise is for the kernel to not send a socket to the server process until either data is received or an entire HTTP Request is buffered. Only FreeBSD's Accept Filters and Linux's more primitive `TCP_DEFER_ACCEPT` are currently supported.

The default values on FreeBSD are:

`AcceptFilter http httpready
AcceptFilter https dataready`

The `httpready` accept filter buffers entire HTTP requests at the kernel level. Once an entire request is received, the kernel then sends it to the server. See the accf_http(9) man page for more details. Since HTTPS requests are encrypted only the accf_data(9) filter is used.

The default values on Linux are:

`AcceptFilter http data
AcceptFilter https data`

Linux's `TCP_DEFER_ACCEPT` does not support buffering http requests. Any value besides `none` will enable `TCP_DEFER_ACCEPT` on that listener. For more details see the Linux tcp(7) man page.

Using `none` for an argument will disable any accept filters for that protocol. This is useful for protocols that require a server send data first, such as `nntp`:

`AcceptFilter nntp none`

### See also

- `Protocol`

## AcceptPathInfo Directive

Description: | Resources accept trailing pathname information
Syntax: | `AcceptPathInfo On|Off|Default`
Default: | `AcceptPathInfo Default`
Context: | server config, virtual host, directory, .htaccess
Override: | FileInfo
Status: | Core
Module: | core
Compatibility: | Available in Apache 2.0.30 and later

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

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

The three possible arguments for the `AcceptPathInfo` directive are:

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

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

`<Files "mypaths.shtml">
Options +Includes
SetOutputFilter INCLUDES
AcceptPathInfo On
</Files>`

## AccessFileName Directive

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

While processing a request the server looks for the first existing configuration file from this list of names in every directory of the path to the document, if distributed configuration files are enabled for that directory. For example:

`AccessFileName .acl`

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

`<Directory />
AllowOverride None
</Directory>`

### See also

- `AllowOverride`
- Configuration Files
- .htaccess Files

## AddDefaultCharset Directive

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

This directive specifies a default value for the media type charset parameter (the name of a character encoding) to be added to a response if and only if the response's content-type is either `text/plain` or `text/html`. This should override any charset specified in the body of the response via a `META` element, though the exact behavior is often dependent on the user's client configuration. A setting of `AddDefaultCharset Off` disables this functionality. `AddDefaultCharset On` enables a default charset of `iso-8859-1`. Any other value is assumed to be the charset to be used, which should be one of the IANA registered charset values for use in MIME media types. For example:

`AddDefaultCharset utf-8`

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

### See also

- `AddCharset`

## AddOutputFilterByType Directive

Description: | assigns an output filter to a particular MIME-type
Syntax: | `AddOutputFilterByType filter[;filter...] MIME-type [MIME-type] ...`
Context: | server config, virtual host, directory, .htaccess
Override: | FileInfo
Status: | Core
Module: | core
Compatibility: | Available in Apache 2.0.33 and later; deprecated in Apache 2.1 and later

This directive activates a particular output filter for a request depending on the response MIME-type. Because of certain problems discussed below, this directive is deprecated. The same functionality is available using `mod_filter`.

The following example uses the `DEFLATE` filter, which is provided by `mod_deflate`. It will compress all output (either static or dynamic) which is labeled as `text/html` or `text/plain` before it is sent to the client.

`AddOutputFilterByType DEFLATE text/html text/plain`

If you want the content to be processed by more than one filter, their names have to be separated by semicolons. It's also possible to use one `AddOutputFilterByType` directive for each of these filters.

The configuration below causes all script output labeled as `text/html` to be processed at first by the `INCLUDES` filter and then by the `DEFLATE` filter.

`<Location /cgi-bin/>
Options Includes
AddOutputFilterByType INCLUDES;DEFLATE text/html
</Location>`

### Note

Enabling filters with `AddOutputFilterByType` may fail partially or completely in some cases. For example, no filters are applied if the MIME-type could not be determined and falls back to the `DefaultType` setting, even if the `DefaultType` is the same.

However, if you want to make sure, that the filters will be applied, assign the content type to a resource explicitly, for example with `AddType` or `ForceType`. Setting the content type within a (non-nph) CGI script is also safe.

### See also

- `AddOutputFilter`
- `SetOutputFilter`
- filters

## AllowEncodedSlashes Directive

Description: | Determines whether encoded path separators in URLs are allowed to be passed through
Syntax: | `AllowEncodedSlashes On|Off|NoDecode`
Default: | `AllowEncodedSlashes Off`
Context: | server config, virtual host
Status: | Core
Module: | core
Compatibility: | Available in Apache httpd 2.0.46 and later. NoDecode option available in 2.2.18 and later.

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

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

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

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

Turning `AllowEncodedSlashes` `On` is mostly useful when used in conjunction with `PATH_INFO`.

### Note

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

### See also

- `AcceptPathInfo`

## AllowOverride Directive

Description: | Types of directives that are allowed in `.htaccess` files
Syntax: | `AllowOverride All|None|directive-type [directive-type] ...`
Default: | `AllowOverride All`
Context: | directory
Status: | Core
Module: | core

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

### Only available in <Directory> sections

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

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

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

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

AuthConfig
  Allow use of the authorization directives (`AuthDBMGroupFile`, `AuthDBMUserFile`, `AuthGroupFile`, `AuthName`, `AuthType`, `AuthUserFile`, `Require`, etc.).
FileInfo
  Allow use of the directives controlling document types (`DefaultType`, `ErrorDocument`, `ForceType`, `LanguagePriority`, `SetHandler`, `SetInputFilter`, `SetOutputFilter`, and `mod_mime` Add* and Remove* directives, etc.), document meta data (`Header`, `RequestHeader`, `SetEnvIf`, `SetEnvIfNoCase`, `BrowserMatch`, `CookieExpires`, `CookieDomain`, `CookieStyle`, `CookieTracking`, `CookieName`), `mod_rewrite` directives `RewriteEngine`, `RewriteOptions`, `RewriteBase`, `RewriteCond`, `RewriteRule`) and `Action` from `mod_actions`.
Indexes
  Allow use of the directives controlling directory indexing (`AddDescription`, `AddIcon`, `AddIconByEncoding`, `AddIconByType`, `DefaultIcon`, `DirectoryIndex`, `FancyIndexing`, `HeaderName`, `IndexIgnore`, `IndexOptions`, `ReadmeName`, etc.).
Limit
  Allow use of the directives controlling host access (`Allow`, `Deny` and `Order`).
Options[=Option,...]
  Allow use of the directives controlling specific directory features (`Options` and `XBitHack`). An equal sign may be given followed by a comma (but no spaces) separated lists of options that may be set using the `Options` command.

Example:

`AllowOverride AuthConfig Indexes`

In the example above all directives that are neither in the group `AuthConfig` nor `Indexes` cause an internal server error.

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

### See also

- `AccessFileName`
- Configuration Files
- .htaccess Files

## AuthName Directive

Description: | Authorization realm for use in HTTP authentication
Syntax: | `AuthName auth-domain`
Context: | directory, .htaccess
Override: | AuthConfig
Status: | Core
Module: | core

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

Description: | Type of user authentication
Syntax: | `AuthType Basic|Digest`
Context: | directory, .htaccess
Override: | AuthConfig
Status: | Core
Module: | core

This directive selects the type of user authentication for a directory. The authentication types available are `Basic` (implemented by `mod_auth_basic`) and `Digest` (implemented by `mod_auth_digest`).

To implement authentication, you must also use the `AuthName` and `Require` directives. In addition, the server must have an authentication-provider module such as `mod_authn_file` and an authorization module such as `mod_authz_user`.

### See also

- Authentication, Authorization, and Access Control

## CGIMapExtension Directive

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

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

## ContentDigest Directive

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

This directive enables the generation of `Content-MD5` headers as defined in RFC1864 respectively RFC2616.

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

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

`Content-MD5: AuLb7Dp1rqtRtxz2m9kRpA==`

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

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

## DefaultType Directive

Description: | MIME content-type that will be sent if the server cannot determine a type in any other way
Syntax: | `DefaultType MIME-type|none`
Default: | `DefaultType text/plain`
Context: | server config, virtual host, directory, .htaccess
Override: | FileInfo
Status: | Core
Module: | core
Compatibility: | The argument `none` is available in Apache 2.2.7 and later

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 SHOULD inform the client of the content-type of the document. If the server is unable to determine this by normal means, it will set it to the configured `DefaultType`. For example:

`DefaultType image/gif`

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

In cases where it can neither be determined by the server nor the administrator (e.g. a proxy), it is preferable to omit the MIME type altogether rather than provide information that may be false. This can be accomplished using

`DefaultType None`

`DefaultType None` is only available in httpd-2.2.7 and later.

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

## <Directory> Directive

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

### See also

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

## <DirectoryMatch> Directive

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

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

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

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

### End-of-line character

The end-of-line character ($) cannot be matched with this directive.

### See also

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

## DocumentRoot Directive

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

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

`DocumentRoot /usr/web`

then an access to `http://www.my.host.com/index.html` refers to `/usr/web/index.html`. If the directory-path is not absolute then it is assumed to be relative to the `ServerRoot`.

The `DocumentRoot` should be specified without a trailing slash.

### See also

- Mapping URLs to Filesystem Locations

## EnableMMAP Directive

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

This directive controls whether the `httpd` may use memory-mapping if it needs to read the contents of a file during delivery. By default, when the handling of a request requires access to the data within a file -- for example, when delivering a server-parsed file using `mod_include` -- Apache memory-maps the file if the OS supports it.

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

- On some multiprocessor systems, memory-mapping can reduce the performance of the `httpd`.
- Deleting or truncating a file while `httpd` has it memory-mapped can cause `httpd` to crash with a segmentation fault.

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

`EnableMMAP Off`

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

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

## EnableSendfile Directive

Description: | Use the kernel sendfile support to deliver files to the client
Syntax: | `EnableSendfile On|Off`
Default: | `EnableSendfile On`
Context: | server config, virtual host, directory, .htaccess
Override: | FileInfo
Status: | Core
Module: | core
Compatibility: | Available in version 2.0.44 and later

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

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

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

For server configurations that are vulnerable to these problems, you should disable this feature by specifying:

`EnableSendfile Off`

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

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

Please note that the per-directory and .htaccess configuration of `EnableSendfile` is not supported by `mod_disk_cache`. Only global definition of `EnableSendfile` is taken into account by the module.

## ErrorDocument Directive

Description: | What the server will return to the client in case of an error
Syntax: | `ErrorDocument error-code document`
Context: | server config, virtual host, directory, .htaccess
Override: | FileInfo
Status: | Core
Module: | core
Compatibility: | Quoting syntax for text messages is different in Apache 2.0

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

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

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

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

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

Additionally, the special value `default` can be used to specify Apache's simple hardcoded message. While not required under normal circumstances, `default` will restore Apache's simple hardcoded message for configurations that would otherwise inherit an existing `ErrorDocument`.

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

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

Microsoft Internet Explorer (MSIE) will by default ignore server-generated error messages when they are "too small" and substitute its own "friendly" error messages. The size threshold varies depending on the type of error, but in general, if you make your error document greater than 512 bytes, then MSIE will show the server-generated error rather than masking it. More information is available in Microsoft Knowledge Base article Q294807.

Although most error messages can be overriden, there are certain circumstances where the internal messages are used regardless of the setting of `ErrorDocument`. In particular, if a malformed request is detected, normal request processing will be immediately halted and the internal error message returned. This is necessary to guard against security problems caused by bad requests.

If you are using mod_proxy, you may wish to enable `ProxyErrorOverride` so that you can provide custom error messages on behalf of your Origin servers. If you don't enable ProxyErrorOverride, Apache will not generate custom error documents for proxied content.

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

### See also

- documentation of customizable responses

## ErrorLog Directive

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

The `ErrorLog` directive sets the name of the file to which the server will log any errors it encounters. If the file-path is not absolute then it is assumed to be relative to the `ServerRoot`.

### Example

`ErrorLog /var/log/httpd/error_log`

If the file-path begins with a pipe character "`|`" then it is assumed to be a command to spawn to handle the error log.

### Example

`ErrorLog "|/usr/local/bin/httpd_errors"`

See the notes on piped logs for more information.

Using `syslog` instead of a filename enables logging via syslogd(8) if the system supports it. 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).

### Example

`ErrorLog syslog:user`

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

### Note

When entering a file path on non-Unix platforms, care should be taken to make sure that only forward slashes are used even though the platform may allow the use of back slashes. In general it is a good idea to always use forward slashes throughout the configuration files.

### See also

- `LogLevel`
- Apache Log Files

## FileETag Directive

Description: | File attributes used to create the ETag HTTP response header for static files
Syntax: | `FileETag component ...`
Default: | `FileETag INode MTime Size`
Context: | server config, virtual host, directory, .htaccess
Override: | FileInfo
Status: | Core
Module: | core

The `FileETag` directive configures the file attributes that are used to create the `ETag` (entity tag) response header field when the document is based on a static file. (The `ETag` value is used in cache management to save network bandwidth.) 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. This is equivalent to:

  `FileETag INode MTime Size`

None
  If a document is file-based, no `ETag` field will be included in the response

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

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

### Warning

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

### Server Side Includes

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

## <Files> Directive

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

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

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

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

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

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

### See also

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

## <FilesMatch> Directive

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

The `<FilesMatch>` directive limits the scope of the enclosed directives by filename, just as the `<Files>` directive does. However, it accepts a regular expression. For example:

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

would match most common Internet graphics formats.

### See also

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

## ForceType Directive

Description: | Forces all matching files to be served with the specified MIME content-type
Syntax: | `ForceType MIME-type|None`
Context: | directory, .htaccess
Override: | FileInfo
Status: | Core
Module: | core
Compatibility: | Moved to the core in Apache 2.0

When placed into an `.htaccess` file or a `<Directory>`, or `<Location>` or `<Files>` section, this directive forces all matching files to be served with the content type identification given by MIME-type. For example, if you had a directory full of GIF files, but did not want to label them all with `.gif`, you might want to use:

`ForceType image/gif`

Note that unlike `DefaultType`, this directive overrides all mime-type associations, including filename extensions, that might identify the media type.

You can override any `ForceType` setting by using the value of `None`:

`# force all files to be image/gif:
<Location /images>
ForceType image/gif
</Location>
# but normal mime-type associations here:
<Location /images/mixed>
ForceType None
</Location>`

## GprofDir Directive

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

When the server has been compiled with gprof profiling suppport, `GprofDir` causes `gmon.out` files to be written to the specified directory when the process exits. If the argument ends with a percent symbol ('%'), subdirectories are created for each process id.

This directive currently only works with the `prefork` MPM.

## HostnameLookups Directive

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

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

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

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

## <IfDefine> Directive

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

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

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

- 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 -DUseCache -DMemCache ...
# httpd.conf
<IfDefine ReverseProxy>
LoadModule proxy_module modules/mod_proxy.so
LoadModule proxy_http_module modules/mod_proxy_http.so
<IfDefine UseCache>
LoadModule cache_module modules/mod_cache.so
<IfDefine MemCache>
LoadModule mem_cache_module modules/mod_mem_cache.so
</IfDefine>
<IfDefine !MemCache>
LoadModule disk_cache_module modules/mod_disk_cache.so
</IfDefine> </IfDefine> </IfDefine>`

## <IfModule> Directive

Description: | Encloses directives that are processed conditional on the presence or absence of a specific module
Syntax: | `<IfModule [!]module-file|module-identifier> ... </IfModule>`
Context: | server config, virtual host, directory, .htaccess
Override: | All
Status: | Core
Module: | core
Compatibility: | Module identifiers are available in version 2.1 and later.

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

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

- module
- !module

In the former case, the directives between the start and end markers are only processed if the module named module 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 is not included.

The module argument can be either the module identifier or the file name of the module, at the time it was compiled. For example, `rewrite_module` is the identifier and `mod_rewrite.c` is the file name. If a module consists of several source files, use the name of the file containing the string `STANDARD20_MODULE_STUFF`.

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

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

## Include Directive

Description: | Includes other configuration files from within the server configuration files
Syntax: | `Include file-path|directory-path`
Context: | server config, virtual host, directory
Status: | Core
Module: | core
Compatibility: | Wildcard matching available in 2.0.41 and later

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

Shell-style (`fnmatch()`) wildcard characters can be used to include several files at once, in alphabetical order. In addition, if `Include` points to a directory, rather than a file, Apache will read all files in that directory and any subdirectory. But including entire directories is not recommended, because it is easy to accidentally leave temporary files in a directory that can cause `httpd` to fail.

The file path specified may be an absolute path, or may be relative to the `ServerRoot` directory.

Examples:

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

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

`Include conf/ssl.conf
Include conf/vhosts/*.conf`

### See also

- `apachectl`

## KeepAlive Directive

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

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

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

When a client uses a Keep-Alive connection it will be counted as a single "request" for the MaxRequestsPerChild directive, regardless of how many requests are sent using the connection.

### See also

- `MaxKeepAliveRequests`

## KeepAliveTimeout Directive

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

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.

In a name-based virtual host context, the value of the first defined virtual host (the default host) in a set of `NameVirtualHost` will be used. The other values will be ignored.

## <Limit> Directive

Description: | Restrict enclosed access controls to only certain HTTP methods
Syntax: | `<Limit method [method] ... > ... </Limit>`
Context: | server config, virtual host, directory, .htaccess
Override: | All
Status: | Core
Module: | core

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

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

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

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

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

Description: | Restrict access controls to all HTTP methods except the named ones
Syntax: | `<LimitExcept method [method] ... > ... </LimitExcept>`
Context: | server config, virtual host, directory, .htaccess
Override: | All
Status: | Core
Module: | core

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

For example:

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

## LimitInternalRecursion Directive

Description: | Determine maximum number of internal redirects and nested subrequests
Syntax: | `LimitInternalRecursion number [number]`
Default: | `LimitInternalRecursion 10`
Context: | server config, virtual host
Status: | Core
Module: | core
Compatibility: | Available in Apache 2.0.47 and later

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.

### Example

`LimitInternalRecursion 5`

## LimitRequestBody Directive

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

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

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

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

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

`LimitRequestBody 102400`

Note: not applicable to proxy requests.

## LimitRequestFields Directive

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

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

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

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

For example:

`LimitRequestFields 50`

### Warning

When name-based virtual hosting is used, the value for this directive is taken from the default (first-listed) virtual host for the `NameVirtualHost` the connection was mapped to.

## LimitRequestFieldSize Directive

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

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

The `LimitRequestFieldSize` directive allows the server administrator to reduce or increase the limit on the allowed size of an HTTP request header field. A server needs this value to be large enough to hold any one header field from a normal client request. The size of a normal request header field will vary greatly among different client implementations, often depending upon the extent to which a user has configured their browser to support detailed content negotiation. SPNEGO authentication headers can be up to 12392 bytes.

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

For example:

`LimitRequestFieldSize 4094`

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

### Warning

When name-based virtual hosting is used, the value for this directive is taken from the default (first-listed) virtual host for the `NameVirtualHost` the connection was mapped to.

## LimitRequestLine Directive

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

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

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

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

For example:

`LimitRequestLine 4094`

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

### Warning

When name-based virtual hosting is used, the value for this directive is taken from the default (first-listed) virtual host for the `NameVirtualHost` the connection was mapped to.

## LimitXMLRequestBody Directive

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

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

Example:

`LimitXMLRequestBody 0`

## <Location> Directive

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

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

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

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

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

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

`<Location /private1> ...`

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

`<Location /private2/> ...`

### When to use `<Location>`

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

For all origin (non-proxy) requests, the URL to be matched is a URL-path of the form `/path/`. No scheme, hostname, port, or query string may be included. For proxy requests, the URL to be matched is of the form `scheme://servername/path`, and you must include the prefix.

The URL may use wildcards. In a wild-card string, `?` matches any single character, and `*` matches any sequences of characters. Neither wildcard character matches a / in the URL-path.

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

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

would match URLs that contained the substring `/extra/data` or `/special/data`. The directive `<LocationMatch>` 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 `example.com`, you might use:

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

### Note about / (slash)

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

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

### See also

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

## <LocationMatch> Directive

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

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

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

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

### See also

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

## LogLevel Directive

Description: | Controls the verbosity of the ErrorLog
Syntax: | `LogLevel level`
Default: | `LogLevel warn`
Context: | server config, virtual host
Status: | Core
Module: | core

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

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

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

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

For example:

`LogLevel notice`

### 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`.

## MaxKeepAliveRequests Directive

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

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

For example:

`MaxKeepAliveRequests 500`

## NameVirtualHost Directive

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

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

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

`NameVirtualHost 111.22.33.44`

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

### Note

Note, that 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 `VirtualHost`s for that address).

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

`NameVirtualHost 111.22.33.44:8080`

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

`NameVirtualHost [2001:db8::a00:20ff:fea7:ccea]:8080`

To receive requests on all interfaces, you can use an argument of `*:80`, or, if you are listening on multiple ports and really want the server to respond on all of them with a particular set of virtual hosts, `*`

`NameVirtualHost *:80`

### Argument to `<VirtualHost>` directive

Note that the argument to the `<VirtualHost>` directive must exactly match the argument to the `NameVirtualHost` directive.

`NameVirtualHost 1.2.3.4
<VirtualHost 1.2.3.4>
# ...
</VirtualHost>
`

### See also

- Virtual Hosts documentation

## Options Directive

Description: | Configures what features are available in a particular directory
Syntax: | `Options [+|-]option [[+|-]option] ...`
Default: | `Options All`
Context: | server config, virtual host, directory, .htaccess
Override: | Options
Status: | Core
Module: | core

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 using `mod_cgi` is permitted.
`FollowSymLinks`
  The server will follow symbolic links in this directory.

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

  Note also, that this option gets ignored if set inside a `<Location>` section.

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

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

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

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

### Warning

Mixing `Options` with a `+` or `-` with those without is not valid syntax, and is likely to cause unexpected results.

For example, without any `+` and `-` symbols:

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

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

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

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

### Note

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

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

## Protocol Directive

Description: | Protocol for a listening socket
Syntax: | `Protocol protocol`
Context: | server config, virtual host
Status: | Core
Module: | core
Compatibility: | Available in Apache 2.1.5 and later. On Windows from Apache 2.3.3 and later.

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

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

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

`Protocol https`

You can also specify the protocol using the `Listen` directive.

### See also

- `AcceptFilter`
- `Listen`

## Require Directive

Description: | Selects which authenticated users can access a resource
Syntax: | `Require entity-name [entity-name] ...`
Context: | directory, .htaccess
Override: | AuthConfig
Status: | Core
Module: | core

This directive selects which authenticated users can access a resource. Multipe instances of this directive are combined with a logical "OR", such that a user matching any `Require` line is granted access. The restrictions are processed by authorization modules. Some of the allowed syntaxes provided by `mod_authz_user` and `mod_authz_groupfile` are:

`Require user userid [userid] ...`
  Only the named users can access the resource.
`Require group group-name [group-name] ...`
  Only users in the named groups can access the resource.
`Require valid-user`
  All valid users can access the resource.

Other authorization modules that implement require options include `mod_authnz_ldap`, `mod_authz_dbm`, and `mod_authz_owner`.

`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 Resource"
AuthUserFile /web/users
AuthGroupFile /web/groups
Require group admin`

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

If `Require` is used together with the `Allow` or `Deny` directives, then the interaction of these restrictions is controlled by the `Satisfy` directive.

### Removing controls in subdirectories

The following example shows how to use the `Satisfy` directive to disable access controls in a subdirectory of a protected directory. This technique should be used with caution, because it will also disable any access controls imposed by `mod_authz_host`.

`<Directory /path/to/protected/>
Require user david
</Directory>
<Directory /path/to/protected/unprotected>
# All access controls and authentication are disabled
# in this directory
Satisfy Any
Allow from all
</Directory>
`

### See also

- Authentication, Authorization, and Access Control
- `Satisfy`
- `mod_authz_host`

## RLimitCPU Directive

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

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

This applies to processes forked off from Apache 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`
- `RLimitNPROC`

## RLimitMEM Directive

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

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

This applies to processes forked off from Apache 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`
- `RLimitNPROC`

## RLimitNPROC Directive

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

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

This applies to processes forked off from Apache 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 user ids other than the web server user id, this directive will limit the number of processes that the server itself can create. Evidence of this situation will be indicated by `cannot fork` messages in the `error_log`.

### See also

- `RLimitMEM`
- `RLimitCPU`

## Satisfy Directive

Description: | Interaction between host-level access control and user authentication
Syntax: | `Satisfy Any|All`
Default: | `Satisfy All`
Context: | directory, .htaccess
Override: | AuthConfig
Status: | Core
Module: | core
Compatibility: | Influenced by `<Limit>` and `<LimitExcept>` in version 2.0.51 and later

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

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

`Require valid-user
Order allow,deny
Allow from 192.168.1
Satisfy Any`

Since version 2.0.51 `Satisfy` directives can be restricted to particular methods by `<Limit>` and `<LimitExcept>` sections.

### See also

- `Allow`
- `Require`

## ScriptInterpreterSource Directive

Description: | Technique for locating the interpreter for CGI scripts
Syntax: | `ScriptInterpreterSource Registry|Registry-Strict|Script`
Default: | `ScriptInterpreterSource Script`
Context: | server config, virtual host, directory, .htaccess
Override: | FileInfo
Status: | Core
Module: | core
Compatibility: | Win32 only; option `Registry-Strict` is available in Apache 2.0 and later

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

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

or, if `perl` is in the `PATH`, simply:

`#!perl`

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

For example, the registry setting to have a script with the .pl extension processed via perl would be:

``HKEY_CLASSES_ROOT\.pl\Shell\ExecCGI\Command\(Default) => C:\Perl\bin\perl.exe -wT``

### Security

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

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

## ServerAdmin Directive

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

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

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

`ServerAdmin www-admin@foo.example.com`

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

## ServerAlias Directive

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

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

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

### See also

- `UseCanonicalName`
- Apache Virtual Host documentation

## ServerName Directive

Description: | Hostname and port that the server uses to identify itself
Syntax: | `ServerName [scheme://]fully-qualified-domain-name[:port]`
Context: | server config, virtual host
Status: | Core
Module: | core
Compatibility: | In version 2.0, this directive supersedes the functionality of the `Port` directive from version 1.3.

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

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

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

`ServerName www.example.com`

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

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

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

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

### See also

- Issues Regarding DNS and Apache
- Apache virtual host documentation
- `UseCanonicalName`
- `UseCanonicalPhysicalPort`
- `NameVirtualHost`
- `ServerAlias`

## ServerPath Directive

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

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

### See also

- Apache Virtual Host documentation

## ServerRoot Directive

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

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

### Example

`ServerRoot /home/httpd`

### See also

- the `-d` option to `httpd`
- the security tips for information on how to properly set permissions on the `ServerRoot`

## ServerSignature Directive

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

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

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

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

### See also

- `ServerTokens`

## ServerTokens Directive

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

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

`ServerTokens Prod[uctOnly]`
  Server sends (e.g.): `Server: Apache`
`ServerTokens Major`
  Server sends (e.g.): `Server: Apache/2`
`ServerTokens Minor`
  Server sends (e.g.): `Server: Apache/2.0`
`ServerTokens Min[imal]`
  Server sends (e.g.): `Server: Apache/2.0.41`
`ServerTokens OS`
  Server sends (e.g.): `Server: Apache/2.0.41 (Unix)`
`ServerTokens Full` (or not specified)
  Server sends (e.g.): `Server: Apache/2.0.41 (Unix) PHP/4.2.2 MyMod/1.2`

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

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

### See also

- `ServerSignature`

## SetHandler Directive

Description: | Forces all matching files to be processed by a handler
Syntax: | `SetHandler handler-name|None`
Context: | server config, virtual host, directory, .htaccess
Override: | FileInfo
Status: | Core
Module: | core
Compatibility: | Moved into the core in Apache 2.0

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

`SetHandler imap-file`

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

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

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

### See also

- `AddHandler`

## SetInputFilter Directive

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

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

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

### See also

- Filters documentation

## SetOutputFilter Directive

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

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

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

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

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

### See also

- Filters documentation

## Suexec Directive

Description: | Enable or disable the suEXEC feature
Syntax: | `Suexec On|Off`
Default: | `On if suexec binary exists with proper owner and mode, Off otherwise`
Context: | server config
Status: | Core
Module: | core
Compatibility: | Available in Apache httpd 2.2.18 and later

When On, startup will fail if the suexec binary doesn't exist or has an invalid owner or file mode.

When Off, suEXEC will be disabled even if the suexec binary exists and has a valid owner and file mode.

## TimeOut Directive

Description: | Amount of time the server will wait for certain events before failing a request
Syntax: | `TimeOut seconds`
Default: | `TimeOut 300`
Context: | server config, virtual host
Status: | Core
Module: | core

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

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

## TraceEnable Directive

Description: | Determines the behaviour on `TRACE` requests
Syntax: | `TraceEnable [on|off|extended]`
Default: | `TraceEnable on`
Context: | server config
Status: | Core
Module: | core
Compatibility: | Available in Apache 1.3.34, 2.0.55 and later

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

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

## UseCanonicalName Directive

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

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

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

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

- `UseCanonicalPhysicalPort`
- `ServerName`
- `Listen`

## UseCanonicalPhysicalPort Directive

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

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

### Note

The ordering of when the physical port is used is as follows:
`UseCanonicalName On`

- Port provided in `Servername`
- Physical port
- Default port

`UseCanonicalName Off | DNS`

- Parsed port from `Host:` header
- Physical port
- Port provided in `Servername`
- Default port

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

### See also

- `UseCanonicalName`
- `ServerName`
- `Listen`

## <VirtualHost> Directive

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

`<VirtualHost>` and `</VirtualHost>` are used to enclose a group of directives that will apply only to a particular virtual host. Any directive that is allowed in a virtual host context may be used. When the server receives a request for a document on a particular virtual host, it uses the configuration directives enclosed in the `<VirtualHost>` section. Addr can be:

- The IP address of the virtual host;
- A fully qualified domain name for the IP address of the virtual host (not recommended);
- The character `*`, which is used only in combination with `NameVirtualHost *` to match all IP addresses; or
- The string `_default_`, which is used only with IP virtual hosting to catch unmatched IP addresses.

### Example

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

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

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

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

### Note

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

When using IP-based virtual hosting, the special name `_default_` can be specified in which case this virtual host will match any IP address that is not explicitly listed in another virtual host. In the absence of any `_default_` virtual host the "main" server config, consisting of all those definitions outside any VirtualHost section, is used when no IP-match occurs. (But note that any IP address that matches a `NameVirtualHost` directive will use neither the "main" server config nor the `_default_` virtual host. See the name-based virtual hosting documentation for further details.)

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

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

### Security

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

### See also

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

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