Apache .htaccess file

.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. It is widely used by ISP to provide users with control of their environment which shared hosting environment. Among typical usages:

• Provide customized HTTP 404 error page
• Prevent folder listing with IndexIgnore *
• Blocking crazy Bots run by script kiddies either by name or by attempting to file .dll, .php or other executable in all directories

• Blocking bad referrers. A lot of jerk insert some crazy referrer strings in their requests and make analysis of 404 errors difficult or impossible. There is not sure way to fight those jerks but usually they demonstrate some pattern that can be used to guess that particular requests comes from them

• Block bad apples. You can block "champions" of bad requests directly by blocking their IPs
• You can block hotlinking for images if it consume considerable bandwidth (otherwise it does not make sense to bother)

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

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.

Performance hit. 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.)

• New set of problems to troubleshoot. Changes in .htaccess can result in configuration  which Web site stops to  be visible on the Web. Some capability also have security implications -- good example is  automatic indexing of files...

Note that it is completely equivalent to put a .htaccess directives is the appropriate Directory section <Directory /www/htdocs/example> in your main server configuration if of couse you have access to it. Id you use Web services provider you don't and have no choice.

Here is an example of two equivalent directives

• In .htaccess file in /www/htdocs/example:

  AddType text/example .exm

• in httpd.conf

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

As we mentioned before 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 in server configuration file 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 its subdirectories.

However, if there are  .htaccess files in subdirectories they will overwrite settings of the .htaccess file in a particular directory. 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 must 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.