Apache HTTP Server Tutorial: .htaccess files

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+ +

.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
Rewrite Rules in .htaccess files
CGI example
Troubleshooting

.htaccess files

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

+ + +

You should avoid using .htaccess files completely if you have access to + httpd main server config file. Using .htaccess files slows down your Apache http server. + Any directive that you can include in a .htaccess file is better set in a Directory block, as it will have the same effect with better performance.

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 only use .htaccess files when + you don't have access to the main server configuration file. There is, + for example, a common misconception that user authentication should + always be done in .htaccess files, and, in more recent years, + another misconception that mod_rewrite directives + must go 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. Likewise, mod_rewrite directives work better, + in many respects, in the main server configuration.

+ +

.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, httpd 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 httpd 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, httpd 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.)

+ +

In the case of RewriteRule directives, in + .htaccess context these regular expressions must be + re-compiled with every request to the directory, whereas in main + server configuration context they are compiled once and cached. + Additionally, the rules themselves are more complicated, as one must + work around the restrictions that come with per-directory context + and mod_rewrite. Consult the Rewrite Guide for more + detail on this subject.

+ +

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 httpd 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 overridden 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 "/www/htdocs">
+    AllowOverride All
+</Directory>
+
+<Location "/">
+    Options +IncludesNoExec -ExecCGI
+</Location>

+ + +

This example assumes that your DocumentRoot is /www/htdocs.

+ + +

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.

+ +

.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.

Rewrite Rules in .htaccess files

When using RewriteRule in +.htaccess files, be aware that the per-directory context +changes things a bit. In particular, rules are taken to be relative to +the current directory, rather than being the original requested URI. +Consider the following examples:

+ +

# In httpd.conf
+RewriteRule "^/images/(.+)\.jpg" "/images/$1.png"
+
+# In .htaccess in root dir
+RewriteRule "^images/(.+)\.jpg" "images/$1.png"
+
+# In .htaccess in images/
+RewriteRule "^(.+)\.jpg" "$1.png"

+ + +

In a .htaccess in your document directory, the leading +slash is removed from the value supplied to RewriteRule, and in the +images subdirectory, /images/ is removed from +it. Thus, your regular expression needs to omit that portion as +well.

+ +

Consult the mod_rewrite documentation for +further details on using mod_rewrite.

+ +

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 the page. 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 httpd error log. It will likely tell you + that the directive used in your .htaccess file is not + permitted.

+ +

+ [Fri Sep 17 18:43:16 2010] [alert] [client 192.168.200.51] /var/www/html/.htaccess: DirectoryIndex not allowed here +

+ +

This will indicate either that you've used a directive that is + never permitted in .htaccess files, or that you simply + don't have AllowOverride set to + a level sufficient for the directive you've used. Consult the + documentation for that particular directive to determine which is + the case.

+ +

Alternately, it may tell you that you had a syntax error in your + usage of the directive itself.

+ +

+ [Sat Aug 09 16:22:34 2008] [alert] [client 192.168.200.51] /var/www/html/.htaccess: RewriteCond: bad flag delimiters +

+ +

In this case, the error message should be specific to the + particular syntax error that you have committed.

+ +

Apache HTTP Server Tutorial: .htaccess files

See also

.htaccess files

What they are/How to use them

Note:

Example:

When (not) to use .htaccess files

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

Section from your `httpd.conf` + file

How directives are applied

Merging of .htaccess with the main + configuration files

Authentication example

Server Side Includes example

Rewrite Rules in .htaccess files

CGI example

Troubleshooting

Comments

Apache HTTP Server Tutorial: .htaccess files

See also

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