Apache Tutorial: .htaccess files

Available Languages: en | + ja | + ko

+ +

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

.htaccess files
What they are/How to use them
When (not) to use .htaccess files
How directives are applied
Authentication example
Server Side Includes example
CGI example
Troubleshooting

Related Modules	Related Directives
`core` `mod_auth` `mod_cgi` `mod_include` `mod_mime`	`AccessFileName` `AllowOverride` `Options` `AddHandler` `SetHandler` `AuthType` `AuthName` `AuthUserFile` `AuthGroupFile` `Require`

.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.

+ +

Merging of .htaccess with the main + configuration files

+ +

As discussed in the documentation on Configuration Sections, + .htaccess files can override the <Directory> sections for + the corresponding directory, but will be overriden by other types + of configuration sections from the main configuration files. This + fact can be used to enforce certain configurations, even in the + presence of a liberal AllowOverride setting. For example, to + prevent script execution while allowing anything else to be set in + .htaccess you can use:

+ +

+<Directory /> + +Allowoverride All + +</Directory> + +<Location /> + +Options +IncludesNoExec -ExecCGI + +</Location> +

+ + +

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.

+ +

Apache Tutorial: .htaccess files

Note:

Example:

Contents of .htaccess file in + /www/htdocs/example

Section from your httpd.conf + file

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

Section from your `httpd.conf` + file