Chapter 11. Compiling UML from Source

So far we have been playing with a UML kernel binary that we had no hand in creating. Now we will see what's involved with building a UML binary from source.

The process is exactly the same as building a kernel for the host download the source, configure it, and then build it. The kernel build procedure can be daunting for someone who has never done it before; if the kernel isn't configured correctly, it is reasonably likely not to recognize all of the system's hardware. If one of the unrecognized devices is the boot disk, the kernel won't even boot.

With UML, things are simpler. There are far fewer configuration options because there is a much greater variety of physical devices possibly present on the host than there are virtual devices available for UML. For example, there is one UML block driver, which can be used to access anything on the host that looks like a filenormal files, disks and disk partitions, CD and DVD drives, floppies, and so on. This one driver is the functional equivalent of a large menu hierarchy on the host. As a result, the number of choices and the depth of menus are far less for UML than for the host architecture, and the configuration process is much less complicated.

A further benefit is that the default UML configuration will build and boot. It may not be exactly what you want, but it will work. To get what you want may take some tweaking of the configuration and rebuilding. If you get a nonworking configuration at some point, you know what change you need to undo in order to get back to a working configuration.