Apache Module mod_alias

Summary

The directives contained in this module allow for manipulation and control of URLs as requests arrive at the server. TheAlias andScriptAlias directives are used to map between URLs and filesystem paths. This allows for content which is not directly under theDocumentRoot served as part of the web document tree. TheScriptAlias directive has the additional effect of marking the target directory as containing only CGI scripts.

TheRedirect 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.

When theAlias,ScriptAlias andRedirect directives are used within a<Location> or<LocationMatch> section,expression syntax can be used to manipulate the destination path or URL.

mod_alias is designed to handle simple URL manipulation tasks. For more complicated tasks such as manipulating the query string, use the tools provided bymod_rewrite.

Topics

• Order of Processing

Directives

• Alias
• AliasMatch
• AliasPreservePath
• Redirect
• RedirectMatch
• RedirectPermanent
• RedirectRelative
• RedirectTemp
• ScriptAlias
• ScriptAliasMatch

Bugfix checklist

• httpd changelog
• Known issues
• Report a bug

See also

• mod_rewrite
• Mapping URLs to the filesystem
• Comments

Order of Processing

Aliases and Redirects occurring in different contexts are processed like other directives according to standardmerging 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 aRedirect orRedirectMatch 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.

When theAlias,ScriptAlias andRedirect directives are used within a<Location> or<LocationMatch> section, these directives will take precedence over any globally definedAlias,ScriptAlias andRedirect directives.

AliasDirective

TheAlias directive allows documents to be stored in the local filesystem other than under theDocumentRoot. URLs with a (%-decoded) path beginning withURL-path will be mapped to local files beginning withdirectory-path. TheURL-path is case-sensitive, even on case-insensitive file systems.

Alias "/image" "/ftp/pub/image"

A request forhttp://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 forhttp://example.com/imagefoo.gif. For more complex matching using regular expressions, see theAliasMatch directive.

Note that if you include a trailing / on theURL-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 theURL-path then you must also omit it from thefile-path.

Note that you may need to specify additional<Directory> sections which cover thedestination 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 anAlias to a directory outside of yourDocumentRoot, you may need to explicitly permit access to the target directory.

Alias "/image" "/ftp/pub/image"<Directory "/ftp/pub/image">    Require all granted</Directory>

Any number slashes in theURL-path parameter matches any number of slashes in the requested URL-path.

If theAlias directive is used within a<Location> or<LocationMatch> section the URL-path is omitted, and the file-path is interpreted usingexpression syntax.
This syntax is available in Apache 2.4.19 and later.

<Location "/image">    Alias "/ftp/pub/image"</Location><LocationMatch "/error/(?<NUMBER>[0-9]+)">    Alias "/usr/local/apache/errors/%{env:MATCH_NUMBER}.html"</LocationMatch>

Note that when theAliasPreservePath directive is on, the full path is mapped to the destination. When the directive is off, all URLs are mapped to the single target URL.

# /files/foo and /files/bar mapped to /ftp/pub/files/foo and /ftp/pub/files/bar<Location "/files">    AliasPreservePath on    Alias "/ftp/pub/files"</Location># /errors/foo and /errors/bar mapped to /var/www/errors.html<Location "/errors">    AliasPreservePath off    Alias "/var/www/errors.html"</Location>

AliasMatchDirective

This directive is equivalent toAlias, but makes use ofregular 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$2"

The full range ofregular 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 betweenAlias andAliasMatch is thatAlias 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, whileAliasMatch 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 changingAlias toAliasMatch 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 usingAliasMatch whereAlias 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.

AliasPreservePathDirective

When using the two parameter version of theAlias directive, the full path after the alias is preserved. When using the one parameter version of theAlias directive inside aLocation directive, the full path is dropped, and all URLs are mapped to the target expression.

To make the one parameter version of theAlias directive preserve paths in the same way that the two parameter version of theAlias directive, enable this setting.

RedirectDirective

TheRedirect directive maps an old URL into a new one by asking the client to refetch the resource at the new location.

The oldURL-path is a case-sensitive (%-decoded) path beginning with a slash. A relative path is not allowed.

The newURL may be either an absolute URL beginning with a scheme and hostname, or a URL-path beginning with a slash. In this latter case the scheme and hostname of the current server will be added.

Then any request beginning withURL-path will return a redirect request to the client at the location of the targetURL. Additional path information beyond the matchedURL-path will be appended to the target URL.

# Redirect to a URL on a different hostRedirect "/service" "http://foo2.example.com/service"# Redirect to a URL on the same hostRedirect "/one" "/two"

If the client requestshttp://example.com/service/foo.txt, it will be told to accesshttp://foo2.example.com/service/foo.txt instead. This includes requests withGET parameters, such ashttp://example.com/service/foo.pl?q=23&a=42, it will be redirected tohttp://foo2.example.com/service/foo.pl?q=23&a=42. Note thatPOSTs will be discarded.
Only complete path segments are matched, so the above example would not match a request forhttp://example.com/servicefoo.txt. For more complex matching using theexpression syntax, omit the URL-path argument as described below. Alternatively, for matching using regular expressions, see theRedirectMatch directive.

If nostatus argument is given, the redirect will be "temporary" (HTTP status 302). This indicates to the client that the resource has moved temporarily. Thestatus argument can be used to return other HTTP status codes:

permanent

Returns a permanent redirect status (301) indicating that the resource has moved permanently.

temp

Returns a temporary redirect status (302). This is the default.

seeother

Returns a "See Other" status (303) indicating that the resource has been replaced.

gone

Returns a "Gone" status (410) indicating that the resource has been permanently removed. When this status is used theURL argument should be omitted.

Other status codes can be returned by giving the numeric status code as the value ofstatus. If the status is between 300 and 399, theURL argument must be present. If the status isnot between 300 and 399, theURL argument must be omitted. The status must be a valid HTTP status code, known to the Apache HTTP Server (see the functionsend_error_response in http_protocol.c).

Redirect permanent "/one" "http://example.com/two"Redirect 303 "/three" "http://example.com/other"

If theRedirect directive is used within a<Location> or<LocationMatch> section with theURL-path omitted, then theURL parameter will be interpreted usingexpression syntax.
This syntax is available in Apache 2.4.19 and later.

<Location "/one">    Redirect permanent "http://example.com/two"</Location><Location "/three">    Redirect 303 "http://example.com/other"</Location><LocationMatch "/error/(?<NUMBER>[0-9]+)">    Redirect permanent "http://example.com/errors/%{env:MATCH_NUMBER}.html"</LocationMatch>

RedirectMatchDirective

This directive is equivalent toRedirect, but makes use ofregular 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://other.example.com$1.jpg"

The considerations related to the difference betweenAlias andAliasMatch also apply to the difference betweenRedirect andRedirectMatch. SeeAliasMatch for details.

RedirectPermanentDirective

This directive makes the client know that the Redirect is permanent (status 301). Exactly equivalent toRedirect permanent.

RedirectRelativeDirective

By default, if the target URL of aRedirect directive is a relative URL beginning with a '/' character, the server converts it to an absolute URL before responding to the client. By settingRedirectRelative to the value "On", the relative URL is presented to the client directly.

RedirectTempDirective

This directive makes the client know that the Redirect is only temporary (status 302). Exactly equivalent toRedirect temp.

ScriptAliasDirective

TheScriptAlias directive has the same behavior as theAlias directive, except that in addition it marks the target directory as containing CGI scripts that will be processed bymod_cgi's cgi-script handler. URLs with a case-sensitive (%-decoded) path beginning withURL-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 forhttp://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>

ScriptAlias can also be used in conjunction with a script or handler you have. For example:

ScriptAlias "/cgi-bin/" "/web/cgi-handler.pl"

In this scenario all files requested in/cgi-bin/ will be handled by the file you have configured, this allows you to use your own custom handler. You may want to use this as a wrapper for CGI so that you can add content, or some other bespoke action.

<Directory "/usr/local/apache2/htdocs/cgi-bin">    SetHandler cgi-script    Options ExecCGI</Directory>

If theScriptAlias directive is used within a<Location> or<LocationMatch> section with the URL-path omitted, then the URL parameter will be interpreted usingexpression syntax.
This syntax is available in Apache 2.4.19 and later.

<Location "/cgi-bin">    ScriptAlias "/web/cgi-bin/"</Location><LocationMatch "/cgi-bin/errors/(?<NUMBER>[0-9]+)">    ScriptAlias "/web/cgi-bin/errors/%{env:MATCH_NUMBER}.cgi"</LocationMatch>

See also

• CGI Tutorial

ScriptAliasMatchDirective

This directive is equivalent toScriptAlias, but makes use ofregular 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 ofregular 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 betweenAlias andAliasMatch also apply to the difference betweenScriptAlias andScriptAliasMatch. SeeAliasMatch for details.