Where can I find php.ini?

Question

A few years ago I installed Apache 2.2x and PHP 5.3.1 on a Linux server I maintain. I used .tar.gz\'s and built them as instructed (instead of rpms and what-have-you). And

Answer 1

Best way to find this is: create a php file and add the following code:

and open it in browser, it will show the file which is actually being read!

Updates by OP:

1. The previously accepted answer is likely to be faster and more convenient for you, but it is not always correct. See comments on that answer.
2. Please also note the more convenient alternative mentioned in this answer.