How-To / Tutorials

# Apache Tutorial: .htaccess files

`.htaccess` files provide a way to make configuration changes on a per-directory basis.

# .htaccess files

core
mod_auth
mod_cgi
mod_include
mod_mime
AccessFileName
AllowOverride
Options
AddHandler
SetHandler
AuthType
AuthName
AuthUserFile
AuthGroupFile
Require

# What they are/How to use them

`.htaccess` files (or "distributed configuration files") provide a way to make configuration changes on a per-directory basis. A file, containing one or more configuration directives, is placed in a particular document directory, and the directives apply to that directory, and all subdirectories thereof.

## Note:

If you want to call your `.htaccess` file something else, you can change the name of the file using the AccessFileName directive. For example, if you would rather call the file `.config` then you can put the following in your server configuration file:

AccessFileName .config

In general, `.htaccess` files use the same syntax as the main configuration files. What you can put in these files is determined by the AllowOverride directive. This directive specifies, in categories, what directives will be honored if they are found in a `.htaccess` file. If a directive is permitted in a `.htaccess` file, the documentation for that directive will contain an Override section, specifying what value must be in AllowOverride in order for that directive to be permitted.

For example, if you look at the documentation for the AddDefaultCharset directive, you will find that it is permitted in `.htaccess` files. (See the Context line in the directive summary.) The Override line reads `FileInfo`. Thus, you must have at least `AllowOverride FileInfo` in order for this directive to be honored in `.htaccess` files.

## Example:

Context: | server config, virtual host, directory, .htaccess
Override: | FileInfo

If you are unsure whether a particular directive is permitted in a `.htaccess` file, look at the documentation for that directive, and check the Context line for ".htaccess".

# When (not) to use .htaccess files

In general, you should never use `.htaccess` files unless you don't have access to the main server configuration file. There is, for example, a prevailing misconception that user authentication should always be done in `.htaccess` files. This is simply not the case. You can put user authentication configurations in the main server configuration, and this is, in fact, the preferred way to do things.

`.htaccess` files should be used in a case where the content providers need to make configuration changes to the server on a per-directory basis, but do not have root access on the server system. In the event that the server administrator is not willing to make frequent configuration changes, it might be desirable to permit individual users to make these changes in `.htaccess` files for themselves. This is particularly true, for example, in cases where ISPs are hosting multiple user sites on a single machine, and want their users to be able to alter their configuration.

However, in general, use of `.htaccess` files should be avoided when possible. Any configuration that you would consider putting in a `.htaccess` file, can just as effectively be made in a Directory section in your main server configuration file.

There are two main reasons to avoid the use of `.htaccess` files.

The first of these is performance. When AllowOverride is set to allow the use of `.htaccess` files, Apache will look in every directory for `.htaccess` files. Thus, permitting `.htaccess` files causes a performance hit, whether or not you actually even use them! Also, the `.htaccess` file is loaded every time a document is requested.

Further note that Apache must look for `.htaccess` files in all higher-level directories, in order to have a full complement of directives that it must apply. (See section on how directives are applied.) Thus, if a file is requested out of a directory `/www/htdocs/example`, Apache must look for the following files:

/.htaccess
/www/.htaccess
/www/htdocs/.htaccess
/www/htdocs/example/.htaccess

And so, for each file access out of that directory, there are 4 additional file-system accesses, even if none of those files are present. (Note that this would only be the case if `.htaccess` files were enabled for `/`, which is not usually the case.)

The second consideration is one of security. You are permitting users to modify server configuration, which may result in changes over which you have no control. Carefully consider whether you want to give your users this privilege. Note also that giving users less privileges than they need will lead to additional technical support requests. Make sure you clearly tell your users what level of privileges you have given them. Specifying exactly what you have set AllowOverride to, and pointing them to the relevant documentation, will save yourself a lot of confusion later.

Note that it is completely equivalent to put a `.htaccess` file in a directory `/www/htdocs/example` containing a directive, and to put that same directive in a Directory section `<Directory /www/htdocs/example>` in your main server configuration:

`.htaccess` file in `/www/htdocs/example`:

## Contents of .htaccess file in `/www/htdocs/example`

AddType text/example .exm

## Section from your `httpd.conf` file

<Directory /www/htdocs/example>
AddType text/example .exm
</Directory>

However, putting this configuration in your server configuration file will result in less of a performance hit, as the configuration is loaded once when Apache starts, rather than every time a file is requested.

The use of `.htaccess` files can be disabled completely by setting the AllowOverride directive to `none`:

AllowOverride None

# How directives are applied

The configuration directives found in a `.htaccess` file are applied to the directory in which the `.htaccess` file is found, and to all subdirectories thereof. However, it is important to also remember that there may have been `.htaccess` files in directories higher up. Directives are applied in the order that they are found. Therefore, a `.htaccess` file in a particular directory may override directives found in `.htaccess` files found higher up in the directory tree. And those, in turn, may have overridden directives found yet higher up, or in the main server configuration file itself.

Example:

In the directory `/www/htdocs/example1` we have a `.htaccess` file containing the following:

Options +ExecCGI

(Note: you must have "`AllowOverride Options`" in effect to permit the use of the "Options" directive in `.htaccess` files.)

In the directory `/www/htdocs/example1/example2` we have a `.htaccess` file containing:

Options Includes

Because of this second `.htaccess` file, in the directory `/www/htdocs/example1/example2`, CGI execution is not permitted, as only `Options Includes` is in effect, which completely overrides any earlier setting that may have been in place.

# Authentication example

If you jumped directly to this part of the document to find out how to do authentication, it is important to note one thing. There is a common misconception that you are required to use `.htaccess` files in order to implement password authentication. This is not the case. Putting authentication directives in a Directory section, in your main server configuration file, is the preferred way to implement this, and `.htaccess` files should be used only if you don't have access to the main server configuration file. See above for a discussion of when you should and should not use `.htaccess` files.

Having said that, if you still think you need to use a `.htaccess` file, you may find that a configuration such as what follows may work for you.

You must have "`AllowOverride AuthConfig`" in effect for these directives to be honored.

`.htaccess` file contents:

AuthType Basic
AuthName "Password Required"
AuthUserFile /www/passwords/password.file
AuthGroupFile /www/passwords/group.file
Require Group admins

Note that `AllowOverride AuthConfig` must be in effect for these directives to have any effect.

Please see the authentication tutorial for a more complete discussion of authentication and authorization.

# Server Side Includes example

Another common use of `.htaccess` files is to enable Server Side Includes for a particular directory. This may be done with the following configuration directives, placed in a `.htaccess` file in the desired directory:

Options +Includes
AddType text/html shtml
AddHandler server-parsed shtml

Note that `AllowOverride Options` and `AllowOverride FileInfo` must both be in effect for these directives to have any effect.

Please see the SSI tutorial for a more complete discussion of server-side includes.

# CGI example

Finally, you may wish to use a `.htaccess` file to permit the execution of CGI programs in a particular directory. This may be implemented with the following configuration:

Options +ExecCGI
AddHandler cgi-script cgi pl

Alternately, if you wish to have all files in the given directory be considered to be CGI programs, this may be done with the following configuration:

Options +ExecCGI
SetHandler cgi-script

Note that `AllowOverride Options` and `AllowOverride FileInfo` must both be in effect for these directives to have any effect.

Please see the CGI tutorial for a more complete discussion of CGI programming and configuration.

# Troubleshooting

When you put configuration directives in a `.htaccess` file, and you don't get the desired effect, there are a number of things that may be going wrong.

Most commonly, the problem is that AllowOverride is not set such that your configuration directives are being honored. Make sure that you don't have a `AllowOverride None` in effect for the file scope in question. A good test for this is to put garbage in your `.htaccess` file and reload. If a server error is not generated, then you almost certainly have `AllowOverride None` in effect.

If, on the other hand, you are getting server errors when trying to access documents, check your Apache error log. It will likely tell you that the directive used in your `.htaccess` file is not permitted. Alternately, it may tell you that you had a syntax error, which you will then need to fix.