Are there any common pitfalls when running PHP 4 and PHP 5 on the same server?

One common pitfall when running PHP 4 and PHP 5 on the same server is that they may have conflicting configurations or dependencies, leading to compatibility issues. To solve this, you can use a tool like FastCGI to run PHP 4 and PHP 5 in separate processes, ensuring they do not interfere with each other.

AddHandler php4-cgi .php
Action php4-cgi /cgi-bin/php4.cgi

AddHandler php5-cgi .php
Action php5-cgi /cgi-bin/php5.cgi