GPL

I read the GPL a few times and tried to understand it.

I am sure there have been discussions and interpretations

of it, and I am wondering whether there is someone who

understands it better than I do?

If for instance you use CentOS and MySql and TomCat and do development

with them, and you make a product which uses them, and you want to sell

this product, what do you need to do?

From what I understand, it is OK if you sell the product as long as you give them

the source code for it?  Is that true?  Or would it just be source code for

MySql, Tomcat, Linux?  And you have to provide them the same notices?

And you can't modify anything?

Is this right, or do you also need licenses?  It just wasn't clear to me.

If I decide to make a product using things like MySql I want to be sure I am doing

it correctly.

Thanks