Apache HTTP Server Version 2.2
Apache HTTP Server Version 2.2
This document refers to the 2.2 version of Apache httpd, which is no longer maintained. The active release is documented here. If you have not already upgraded, please follow this link for more information.
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| Description: | Provides for mapping different parts of the host filesystem in the document tree and for URL redirection |
|---|---|
| Status: | Base |
| Module Identifier: | alias_module |
| Source File: | mod_alias.c |
The directives contained in this module allow for manipulation and control of URLs as requests arrive at the server. The Alias and ScriptAlias directives are used to map between URLs and filesystem paths. This allows for content which is not directly under the DocumentRoot served as part of the web document tree. The ScriptAlias directive has the additional effect of marking the target directory as containing only CGI scripts.
The Redirect directives are used to instruct clients to make a new request with a different URL. They are often used when a resource has moved to a new location.
mod_alias is designed to handle simple URL manipulation tasks. For more complicated tasks such as manipulating the query string, use the tools provided by mod_rewrite.
Aliases and Redirects occurring in different contexts are processed like other directives according to standard merging rules. But when multiple Aliases or Redirects occur in the same context (for example, in the same <VirtualHost> section) they are processed in a particular order.
First, all Redirects are processed before Aliases are processed, and therefore a request that matches a Redirect or RedirectMatch will never have Aliases applied. Second, the Aliases and Redirects are processed in the order they appear in the configuration files, with the first match taking precedence.
For this reason, when two or more of these directives apply to the same sub-path, you must list the most specific path first in order for all the directives to have an effect. For example, the following configuration will work as expected:
Alias /foo/bar /baz
Alias /foo /gaq
But if the above two directives were reversed in order, the /fooAlias would always match before the /foo/barAlias, so the latter directive would be ignored.
| Description: | Maps URLs to filesystem locations |
|---|---|
| Syntax: | Alias URL-pathfile-path|directory-path |
| Context: | server config, virtual host |
| Status: | Base |
| Module: | mod_alias |
The Alias directive allows documents to be stored in the local filesystem other than under the DocumentRoot. URLs with a (%-decoded) path beginning with URL-path will be mapped to local files beginning with directory-path. The URL-path is case-sensitive, even on case-insensitive file systems.
Alias /image /ftp/pub/image
A request for http://example.com/image/foo.gif would cause the server to return the file /ftp/pub/image/foo.gif. Only complete path segments are matched, so the above alias would not match a request for http://example.com/imagefoo.gif. For more complex matching using regular expressions, see the AliasMatch directive.
Note that if you include a trailing / on the URL-path then the server will require a trailing / in order to expand the alias. That is, if you use
Alias /icons/ /usr/local/apache/icons/
then the URL /icons will not be aliased, as it lacks that trailing /. Likewise, if you omit the slash on the URL-path then you must also omit it from the file-path.
Note that you may need to specify additional <Directory> sections which cover the destination of aliases. Aliasing occurs before <Directory> sections are checked, so only the destination of aliases are affected. (Note however <Location> sections are run through once before aliases are performed, so they will apply.)
In particular, if you are creating an Alias to a directory outside of your DocumentRoot, you may need to explicitly permit access to the target directory.
Alias /image /ftp/pub/image
<Directory /ftp/pub/image>
Order allow,deny
Allow from all
</Directory>
Any number of slashes in the URL-path parameter matches any number of slashes in the requested URL-path.
| Description: | Maps URLs to filesystem locations using regular expressions |
|---|---|
| Syntax: | AliasMatch regexfile-path|directory-path |
| Context: | server config, virtual host |
| Status: | Base |
| Module: | mod_alias |
This directive is equivalent to Alias, but makes use of regular expressions, instead of simple prefix matching. The supplied regular expression is matched against the URL-path, and if it matches, the server will substitute any parenthesized matches into the given string and use it as a filename. For example, to activate the /icons directory, one might use:
AliasMatch ^/icons(.*) /usr/local/apache/icons$1
The full range of regular expression power is available. For example, it is possible to construct an alias with case-insensitive matching of the URL-path:
AliasMatch (?i)^/image(.*) /ftp/pub/image$1
One subtle difference between Alias and AliasMatch is that Alias will automatically copy any additional part of the URI, past the part that matched, onto the end of the file path on the right side, while AliasMatch will not. This means that in almost all cases, you will want the regular expression to match the entire request URI from beginning to end, and to use substitution on the right side.
In other words, just changing Alias to AliasMatch will not have the same effect. At a minimum, you need to add ^ to the beginning of the regular expression and add (.*)$ to the end, and add $1 to the end of the replacement.
For example, suppose you want to replace this with AliasMatch:
Alias /image/ /ftp/pub/image/
This is NOT equivalent - don't do this! This will send all requests that have /image/ anywhere in them to /ftp/pub/image/:
AliasMatch /image/ /ftp/pub/image/
This is what you need to get the same effect:
AliasMatch ^/image/(.*)$ /ftp/pub/image/$1
Of course, there's no point in using AliasMatch where Alias would work. AliasMatch lets you do more complicated things. For example, you could serve different kinds of files from different directories:
AliasMatch ^/image/(.*)\.jpg$ /files/jpg.images/$1.jpg
AliasMatch ^/image/(.*)\.gif$ /files/gif.images/$1.gif
Multiple leading slashes in the requested URL are discarded by the server before directives from this module compares against the requested URL-path.
| Description: | Sends an external redirect asking the client to fetch a different URL |
|---|---|
| Syntax: | Redirect [status] URL-pathURL |
| Context: | server config, virtual host, directory, .htaccess |
| Override: | FileInfo |
| Status: | Base |
| Module: | mod_alias |
| Compatibility: | Support for specifying a URL-path as the final argument was added in Apache HTTP Server 2.2.6 |
The Redirect directive maps an old URL into a new one by asking the client to refetch the resource at the new location.
The old URL-path is a case-sensitive (%-decoded) path beginning with a slash. A relative path is not allowed. The new URL should be an absolute URL beginning with a scheme and hostname. In Apache HTTP Server 2.2.6 and later, a URL-path beginning with a slash may also be used, in which case the scheme and hostname of the current server will be added.
Then any request beginning with URL-path will return a redirect request to the client at the location of the target URL. Additional path information beyond the matched URL-path will be appended to the target URL.
Redirect /service http://foo2.example.com/service
If the client requests http://example.com/service/foo.txt, it will be told to access http://foo2.example.com/service/foo.txt instead. Only complete path segments are matched, so the above example would not match a request for http://example.com/servicefoo.txt. For more complex matching using regular expressions, see the RedirectMatch directive.
Redirect directives take precedence over Alias and ScriptAlias directives, irrespective of their ordering in the configuration file.
If no status argument is given, the redirect will be "temporary" (HTTP status 302). This indicates to the client that the resource has moved temporarily. The status argument can be used to return other HTTP status codes:
Other status codes can be returned by giving the numeric status code as the value of status. If the status is between 300 and 399, the URL argument must be present, otherwise it must be omitted. Note that the status must be known to the Apache code (see the function send_error_response in http_protocol.c).
Redirect permanent /one http://example.com/two
Redirect 303 /three http://example.com/other
| Description: | Sends an external redirect based on a regular expression match of the current URL |
|---|---|
| Syntax: | RedirectMatch [status] regexURL |
| Context: | server config, virtual host, directory, .htaccess |
| Override: | FileInfo |
| Status: | Base |
| Module: | mod_alias |
This directive is equivalent to Redirect, but makes use of regular expressions, instead of simple prefix matching. The supplied regular expression is matched against the URL-path, and if it matches, the server will substitute any parenthesized matches into the given string and use it as a filename. For example, to redirect all GIF files to like-named JPEG files on another server, one might use:
RedirectMatch (.*)\.gif$ http://www.anotherserver.com$1.jpg
| Description: | Sends an external permanent redirect asking the client to fetch a different URL |
|---|---|
| Syntax: | RedirectPermanent URL-pathURL |
| Context: | server config, virtual host, directory, .htaccess |
| Override: | FileInfo |
| Status: | Base |
| Module: | mod_alias |
This directive makes the client know that the Redirect is permanent (status 301). Exactly equivalent to Redirect permanent.
| Description: | Sends an external temporary redirect asking the client to fetch a different URL |
|---|---|
| Syntax: | RedirectTemp URL-pathURL |
| Context: | server config, virtual host, directory, .htaccess |
| Override: | FileInfo |
| Status: | Base |
| Module: | mod_alias |
This directive makes the client know that the Redirect is only temporary (status 302). Exactly equivalent to Redirect temp.
| Description: | Maps a URL to a filesystem location and designates the target as a CGI script |
|---|---|
| Syntax: | ScriptAlias URL-pathfile-path|directory-path |
| Context: | server config, virtual host |
| Status: | Base |
| Module: | mod_alias |
The ScriptAlias directive has the same behavior as the Alias directive, except that in addition it marks the target directory as containing CGI scripts that will be processed by mod_cgi's cgi-script handler. URLs with a case-sensitive (%-decoded) path beginning with URL-path will be mapped to scripts beginning with the second argument, which is a full pathname in the local filesystem.
ScriptAlias /cgi-bin/ /web/cgi-bin/
A request for http://example.com/cgi-bin/foo would cause the server to run the script /web/cgi-bin/foo. This configuration is essentially equivalent to:
Alias /cgi-bin/ /web/cgi-bin/
<Location /cgi-bin >
SetHandler cgi-script
Options +ExecCGI
</Location>
DocumentRoot in order to avoid accidentally revealing their source code if the configuration is ever changed. The ScriptAlias makes this easy by mapping a URL and designating CGI scripts at the same time. If you do choose to place your CGI scripts in a directory already accessible from the web, do not use ScriptAlias. Instead, use <Directory>, SetHandler, and Options as in: <Directory /usr/local/apache2/htdocs/cgi-bin >
SetHandler cgi-script
Options ExecCGI
</Directory>
ScriptAlias and revealing the source code of the CGI scripts if they are not restricted by a Directory section.| Description: | Maps a URL to a filesystem location using a regular expression and designates the target as a CGI script |
|---|---|
| Syntax: | ScriptAliasMatch regexfile-path|directory-path |
| Context: | server config, virtual host |
| Status: | Base |
| Module: | mod_alias |
This directive is equivalent to ScriptAlias, but makes use of regular expressions, instead of simple prefix matching. The supplied regular expression is matched against the URL-path, and if it matches, the server will substitute any parenthesized matches into the given string and use it as a filename. For example, to activate the standard /cgi-bin, one might use:
ScriptAliasMatch ^/cgi-bin(.*) /usr/local/apache/cgi-bin$1
As for AliasMatch, the full range of regular expression power is available. For example, it is possible to construct an alias with case-insensitive matching of the URL-path:
ScriptAliasMatch (?i)^/cgi-bin(.*) /usr/local/apache/cgi-bin$1
The considerations related to the difference between Alias and AliasMatch also apply to the difference between ScriptAlias and ScriptAliasMatch. See AliasMatch for details.
