Types of Configuration Section Containers
core
mod_version
mod_proxy
Directory
DirectoryMatch
Files
FilesMatch
If
IfDefine
IfModule
IfVersion
Location
LocationMatch
Proxy
ProxyMatch
VirtualHost
There are two basic types of containers. Most containers are
evaluated for each request. The enclosed directives are applied only
for those requests that match the containers. The IfDefine, IfModule, and
IfVersion
containers, on the other hand, are evaluated only at server startup
and restart. If their conditions are true at startup, then the
enclosed directives will apply to all requests. If the conditions are
not true, the enclosed directives will be ignored.
The IfDefine directive
encloses directives that will only be applied if an appropriate
parameter is defined on the httpd command line. For example,
with the following configuration, all requests will be redirected
to another site only if the server is started using
httpd -DClosedForNow
:
<IfDefine ClosedForNow>
Redirect / http://otherserver.example.com/
</IfDefine>
The IfModule
directive is very similar, except it encloses directives that will
only be applied if a particular module is available in the server.
The module must either be statically compiled in the server, or it
must be dynamically compiled and its LoadModule line must be earlier in the
configuration file. This directive should only be used if you need
your configuration file to work whether or not certain modules are
installed. It should not be used to enclose directives that you want
to work all the time, because it can suppress useful error messages
about missing modules.
In the following example, the MimeMagicFiles directive will be
applied only if mod_mime_magic is available.
<IfModule mod_mime_magic.c>
MimeMagicFile conf/magic
</IfModule>
The IfVersion
directive is very similar to IfDefine and IfModule, except it encloses directives that will
only be applied if a particular version of the server is executing. This
module is designed for the use in test suites and large networks which have to
deal with different httpd versions and different configurations.
<IfVersion >= 2.1>
# this happens only in versions greater or
# equal 2.1.0.
</IfVersion>
IfDefine,
IfModule, and the
IfVersion
can apply negative conditions by preceding their test with "!".
Also, these sections can be nested to achieve more complex
restrictions.
Filesystem and Webspace
The most commonly used configuration section containers are the
ones that change the configuration of particular places in the
filesystem or webspace. First, it is important to understand the
difference between the two. The filesystem is the view of your disks
as seen by your operating system. For example, in a default install,
Apache resides at /usr/local/apache2
in the Unix
filesystem or "c:/Program Files/Apache Group/Apache2"
in
the Windows filesystem. (Note that forward slashes should always be
used as the path separator in Apache, even for Windows.) In contrast,
the webspace is the view of your site as delivered by the web server
and seen by the client. So the path /dir/
in the
webspace corresponds to the path
/usr/local/apache2/htdocs/dir/
in the filesystem of a
default Apache install on Unix. The webspace need not map directly to
the filesystem, since webpages may be generated dynamically
from databases or other locations.
Filesystem Containers
The Directory
and Files
directives, along with their regex
counterparts, apply directives to
parts of the filesystem. Directives enclosed in a Directory section apply to
the named filesystem directory and all subdirectories of that
directory. The same effect can be obtained using .htaccess files. For example, in the
following configuration, directory indexes will be enabled for the
/var/web/dir1
directory and all subdirectories.
<Directory /var/web/dir1>
Options +Indexes
</Directory>
Directives enclosed in a Files section apply to any file with
the specified name, regardless of what directory it lies in.
So for example, the following configuration directives will,
when placed in the main section of the configuration file,
deny access to any file named private.html
regardless
of where it is found.
<Files private.html>
Order allow,deny
Deny from all
</Files>
To address files found in a particular part of the filesystem, the
Files and
Directory sections
can be combined. For example, the following configuration will deny
access to /var/web/dir1/private.html
,
/var/web/dir1/subdir2/private.html
,
/var/web/dir1/subdir3/private.html
, and any other instance
of private.html
found under the /var/web/dir1/
directory.
<Directory /var/web/dir1>
<Files private.html>
Order allow,deny
Deny from all
</Files>
</Directory>
Webspace Containers
The Location
directive and its regex counterpart, on
the other hand, change the
configuration for content in the webspace. For example, the following
configuration prevents access to any URL-path that begins in /private.
In particular, it will apply to requests for
http://yoursite.example.com/private
,
http://yoursite.example.com/private123
, and
http://yoursite.example.com/private/dir/file.html
as well
as any other requests starting with the /private
string.
<Location /private>
Order Allow,Deny
Deny from all
</Location>
The Location
directive need not have anything to do with the filesystem.
For example, the following example shows how to map a particular
URL to an internal Apache handler provided by mod_status.
No file called server-status
needs to exist in the
filesystem.
<Location /server-status>
SetHandler server-status
</Location>
Wildcards and Regular Expressions
The Directory,
Files, and
Location
directives can each use shell-style wildcard characters as in
fnmatch
from the C standard library. The character "*"
matches any sequence of characters, "?" matches any single character,
and "[seq]" matches any character in seq. The "/"
character will not be matched by any wildcard; it must be specified
explicitly.
If even more flexible matching is required, each
container has a regular expression (regex) counterpart DirectoryMatch, FilesMatch, and LocationMatch that allow
perl-compatible
regular expressions
to be used in choosing the matches. But see the section below on
configuration merging to find out how using regex sections will change
how directives are applied.
A non-regex wildcard section that changes the configuration of
all user directories could look as follows:
<Directory /home/*/public_html>
Options Indexes
</Directory>
Using regex sections, we can deny access to many types of image files
at once:
<FilesMatch \.(?i:gif|jpe?g|png)$>
Order allow,deny
Deny from all
</FilesMatch>
What to use When
Choosing between filesystem containers and webspace containers is
actually quite easy. When applying directives to objects that reside
in the filesystem always use Directory or Files. When applying directives to objects
that do not reside in the filesystem (such as a webpage generated from
a database), use Location.
It is important to never use Location when trying to restrict
access to objects in the filesystem. This is because many
different webspace locations (URLs) could map to the same filesystem
location, allowing your restrictions to be circumvented.
For example, consider the following configuration:
<Location /dir/>
Order allow,deny
Deny from all
</Location>
This works fine if the request is for
http://yoursite.example.com/dir/
. But what if you are on
a case-insensitive filesystem? Then your restriction could be easily
circumvented by requesting
http://yoursite.example.com/DIR/
. The Directory directive, in
contrast, will apply to any content served from that location,
regardless of how it is called. (An exception is filesystem links.
The same directory can be placed in more than one part of the
filesystem using symbolic links. The Directory directive will follow the symbolic
link without resetting the pathname. Therefore, for the highest level
of security, symbolic links should be disabled with the appropriate
Options directive.)
If you are, perhaps, thinking that none of this applies to you
because you use a case-sensitive filesystem, remember that there are
many other ways to map multiple webspace locations to the same
filesystem location. Therefore you should always use the filesystem
containers when you can. There is, however, one exception to this
rule. Putting configuration restrictions in a <Location
/>
section is perfectly safe because this section will apply
to all requests regardless of the specific URL.
What Directives are Allowed?
To find out what directives are allowed in what types of
configuration sections, check the Context of the directive.
Everything that is allowed in
Directory
sections is also syntactically allowed in
DirectoryMatch,
Files,
FilesMatch,
Location,
LocationMatch,
Proxy,
and ProxyMatch
sections. There are some exceptions, however:
- The AllowOverride directive
works only in Directory
sections.
- The
FollowSymLinks
and
SymLinksIfOwnerMatch
Options work only in Directory sections or
.htaccess
files.
- The Options directive cannot
be used in Files
and FilesMatch
sections.
How the sections are merged
The configuration sections are applied in a very particular order.
Since this can have important effects on how configuration directives
are interpreted, it is important to understand how this works.
The order of merging is:
- Directory (except regular expressions)
and
.htaccess
done simultaneously (with
.htaccess
, if allowed, overriding
Directory)
- DirectoryMatch
(and
<Directory ~>
)
- Files and FilesMatch done
simultaneously
- Location
and LocationMatch done simultaneously
Apart from Directory, each group is processed in
the order that they appear in the configuration files. Directory (group 1 above)
is processed in the order shortest directory component to longest.
So for example, <Directory /var/web/dir>
will
be processed before <Directory
/var/web/dir/subdir>
. If multiple Directory sections apply
to the same directory they are processed in the configuration file
order. Configurations included via the Include directive will be treated as if
they were inside the including file at the location of the
Include directive.
Sections inside VirtualHost sections
are applied after the corresponding sections outside
the virtual host definition. This allows virtual hosts to
override the main server configuration.
When the request is served by mod_proxy, the
Proxy
container takes the place of the Directory container in the processing
order.
Later sections override earlier ones.
Technical Note
There is actually a
<Location>
/<LocationMatch>
sequence performed just before the name translation phase
(where Aliases
and DocumentRoots
are used to map URLs to filenames). The results of this
sequence are completely thrown away after the translation has
completed.
Some Examples
Below is an artificial example to show the order of
merging. Assuming they all apply to the request, the directives in
this example will be applied in the order A > B > C > D >
E.
<Location />
E
</Location>
<Files f.html>
D
</Files>
<VirtualHost *>
<Directory /a/b>
B
</Directory>
</VirtualHost>
<DirectoryMatch "^.*b$">
C
</DirectoryMatch>
<Directory /a/b>
A
</Directory>
For a more concrete example, consider the following. Regardless of
any access restrictions placed in Directory sections, the Location section will be
evaluated last and will allow unrestricted access to the server. In
other words, order of merging is important, so be careful!
<Location />
Order deny,allow
Allow from all
</Location>
# Woops! This <Directory> section will have no effect
<Directory />
Order allow,deny
Allow from all
Deny from badguy.example.com
</Directory>