When you've setup suPHP on your ISPConfig server, you are able to run the PHP scripts under the admin user of the website instead of www-data.
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With this howto I explain how to set up suPHP on a Debian based ISPConfig server with php4. Mainly, it is based on Falko's howto http://www.howtoforge.com/apache2_suphp_php4_php5. Within the forums on Howtoforge, lots of information about “setting up suphp” can be found.
However, this information is spread all over the forums, so it is not very clear how to set up suphp on an ISPConfig server. It was the reason for me to write this howto.