I am just starting to use UML. I created a root filesystem using umlbuilder_gui for redhat 7.3 (kernel 2.4.18-3). I was able to successfully get uml running with the created rootfs following the documentation on the uml page. It boots up with kernel "2.4.18-36um".
However, now I want to be able to start UML with my own modified image. I followed the directions on the web as to how to compile the kernel and apply the uml patch to it. I was able to compile the kernel (get the linux image build). But I did not find any documentation as to how to start the UML with this compiled image.