Well, I have a linux box too, but you may find your thing in the php.ini, like hmerril mentioned.
The parameter you have to look is 'error_reporting' and it may have a bit-value.
If it has the bit-value 8, PHP displays
warnings that can be ignored (but often give hints about possible error-sources).
4: Parse-Errors
2: Normal Warnings
1: Normal Errors
Hope it helps!