When using a UNIX system it is sometimes necessary to enable certain HTML files executable for the purpose of using SSI. Server Side Includes are often used to run a cgi script. An include is called with an example such as this: <!--#exec cgi="/cgi-bin/example.cgi"--> After you insert your include, you must mark the HTML file as executable so the server will parse the file. This is done using the following:
Renaming the file to .shtml: On our server any file name .shtml will be parsed. So instead of having an index.html file, you would name it index.shtml. This is the easiest way of enabling includes.

Reasons for Using SSI:
SSI is often used to include something into an HTML page. You can insert the contents of one HTML page into another page. An example of a practical usage for this would be to include your e-mail address at the bottom of each page. If you do this as an include, then when your e-mail address changes, you will only have to update it on one page and not your entire web site. Another usage is to call cgi scripts into action. Many counters, clocks, and other scripts are called using SSI. The command used will most likely be provided in the documentation of your cgi script.