PHP Warning: exec() unable to fork

Question

So here is a little background info on my setup. Running Centos with apache and php 5.2.17. I have a website that lists products from many different retailers websites. I

Answer 1

For anyone else who comes across this issue, it could be several problems as outlined in this question's answer.

However, my problem was my nginx user did not have a proper shell to execute the commands I wanted. Adding .bashrc to the nginx user's home directory fixed this.