When working on UNIX system, sometimes it is necessary to enable certain HTML files executable for the purpose of using SSI. They are used to run a cgi script. Refer the example: After you insert your include, you must mark the HTML file as executable, so that the server will parse the file. This is done using one of two options.
1.) 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.
2.) chmod the file to 777: With CHMOD 777 you can also mark a file as executable. It is important to only make the files which you want parsed executable.


Basic usage of ssi:
SSI is used to include something into an HTML page. You can insert the contents of one HTML page into another page. For example ,include your e-mail address at the bottom of each page. If you do this as an include and when your e-mail address gets changed, 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.