inhouse forking?

Dear community
I do have a basic question about the GPL: If I download a software
(source code, for example linux) licensed under GPL and I change some
code (for example because I dislike something) but do not plan to sell
or distribute it: I just want to use my changes on my computer: Do I
have to make my changes public anyway? Although I think nobody would
ever like my changes? 
Thank you very much!
\\fogelsharp