Understanding htaccess

by Sangeetha Naik

.htaccess (Hypertext Access) is the default name of Apache's directory-level configuration file. It allows webmasters to customize configuration directives, normally available in the main httpd.conf.

htaccess allows webmasters to do a range of customization to a webservers behaviour in a directory, including password protecting them, denying access, error handlers, redirects and a lot more. htaccess is particularly useful when you don't have root access to the server. For example, in virtual Web Hosting and ISPs.

Before making any of these configurations, however, the following points need to be kept in mind.

  • Your webserver Administrator should allow you to make these changes by using ``AllowOverride All'' in the main configuration file(httpd.conf)
  • You need to make sure that you are not using Microsoft Frontpage on your website. Frontpage uses htaccess for its own directives. Changing the .htaccess files to insert new directives ``will'' break your website.
  • Test, Test, Test. Test new htaccess configurations on an empty directory before making it LIVE.

A .htaccess file controls the directory it is in, plus all subdirectories. However, by placing additional .htaccess files in the subdirectories, this can be overruled. Therefore, if you have an .htaccess file in a subdirectory and another one in a parent directory, the one in the subdirectory will be followed.

Showing error pages

Error handlers are setup so that custom pages can be displayed to users, should they encounter an error on your website. For example, if they should encounter a ``Not found'' 404 error, they could get directed to a good looking page, rather than the boring default error page.

To achieve this, simply put this little snippet in your .htaccess file.

ErrorDocument 400 /errors/404.html
ErrorDocument 403 /errors/403.html
ErrorDocument 404 /errors/404.html
ErrorDocument 500 /errors/500.html

You can name the pages anything you want, provided it is linked correctly in the .htaccess file.

The most common error pages are

404 - Page not found error
400 - Bad Request
403 - Forbidden error
500 - Internal server error

Password protect

Password protecting a web directory can be achieved by putting this little snippet in your .htaccess file in the directory you want to protect.

AuthType Basic
AuthName "Password Required"
AuthUserFile /www/passwords/.htpasswd

In order for the password protect to work, you should create a .htpasswd file. You can create it by doing these steps.

[root@localhost ~]# cd /var/passwords
[root@localhost ~]# htpasswd -c .passwd username
New password:
Re-type new password:
Adding password for user username
[root@localhost ~]# cat .passwd
username:wLU7nnYVpdXO2
[root@localhost ~]#

In order for this to work, your Web administrator should have allowed ``AllowOverride AuthConfig'' in the server wide httpd.conf.

Denying users by IP or domain

You can deny users based on IP or IP block by putting in this snippet in your .htaccess.

order allow,deny
deny from 98.654.321.12
deny from 98.654.322.
allow from all

The second line, specifically denies one IP 98.654.321.12. The third line denies all the IPs starting with 98.654.322. . This is particularly useful if you have seen strange activity on your website by unknown IPs in your access logs.

Some webmasters use this feature to deny whole ISPs or datacenters access, especially if they find credit card fraud or increased attempts from poorly secured servers.

You can also deny by domain name. For example ``deny from .madguy.com'', denies all users from www.madguy.com or abc.madguy.com .

Changing the default page

Assume you are using index.php instead of index.html as your main home page. But the webserver is configured to access index.html first. All you need to do is to add this to your .htaccess.

DirectoryIndex index.php index.html

This makes the php file the default file. In case the php file is not around, it will look for the index.html file.

Controlling PHP using htaccess

The good thing about htaccess is that I can use it to control the php variables as well. PHP's behaviour is controlled a large extent by the /etc/php.ini file. In a server shared by many websites, it may not be possible to change the php.ini file for everyone's special needs. Thats where the .htaccess file comes in.

For example, if you want to turn the register globals off, simply put this in the .htaccess file

php_flag register_globals Off

In this way, you can override any php.ini variable, by putting such entries in the .htaccess file. Of course, this works only if it is allowed by the administrator.

Redirects

Webmasters use Redirects during maintenance(to redirect from index.html to tempmessage.html) or to redirect from an old file to a new file.

In order to redirect from http://yoursite.com/old/file.html to http://yoursite.com/new/file.html, simply put this line in your .htaccess file.

Redirect /old/file.html http://yoursite.com/new/file.html

The /old is relative to the root of your website. i.e at http://yoursite.com/old.

SSI

In order to allow SSI(Server Side Includes) in one directory, simply include this snippet in the .htaccess file in that directory.

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

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