What Joe says is that Linux isn't programmed in a single language.
You'll find parts done in any of the following (and probably a lot more): C C++ Assembly (several dialects) Pascal Perl Python Ruby Fortran Java
Forgot to add: Redhat is NOT Linux. It's nothing more than a company packaging Linux with some of their own stuff and selling it under their own name. Linux as such doesn't even exist... It's the whole of all the distributions out there.
To make your own distro you'll probably need mainly shellscripting for a ton of applications, plus whatever language you decide to use for your installers. [ June 17, 2004: Message edited by: Jeroen Wenting ]
One of the strengths of open source software like Linux and the GNU applications is that one can build on the work of others. If you want to make your own Linux distribution, there's a bootable CD Linux distribution called Morphix that claims to make it easy. Since it's a bootable CD, you don't have to install it on your computer. Take the CD out of your drive, reboot and your computer is back to normal.