Kernel paremeter may be needed to be passed to a Xen DomU. For example, when the DomU fails to boot and we want to check it in 'single' mode.
We can simply start the DomU with the "extra=" syntax. For example, to add 'single' to the kernel parameters of DomU:
# xm create domu-vm.cfg extra="single"
To make it permanent for the VM, we can add
to the VM's configuration file domu-vm.cfg.