UML
This site provides ready-made UML kernels to help you getting started.
You may also want to check fs.devloop.org.uk for filesystem images in raw disk format.
Kernels
These binary kernel images are updated fairly regularly.The latest version available is
4.3.5:
Many more versions are available here.
Howto
Running a UML instance is as simple as running:./kernel ubda=root_fs rw mem=256m
