I am trying to compile xen 3.1.3 from source . The existing OS in my machine is ubuntu 8.04. The make world and make install were successfull. I then made a initrd image using update-initramfs command (at /lib/modules) with -k linux version 18.104.22.168 (since that is the linux kernel version corresponding to xen 3.1.3). Then I make the change in the boot/grub/menu.lst to point to the compiled images. But while booting after a particular point ( usb: 3 ports detected ) . It is giving the error. Check root = boot arg cat /proc/cmdline or missing modules , devices. cat /proc/modules ls dev ALERT! /dev/disk/by-uuid/<uuid> does not exist dropping to a shell. - I am sure the uuid given in menu.lst is right since it works for the original ubuntu installation . I changed uuid with /dev/sdax but then the error is /dev/sdax missing dropping to..(rest of the error is same) .My machine config is AMD Phenom(tm) 9550 quad core processor. 64 bit. Cpu Mhz :2204 . One suggestion I got for this problem was to compile the driver for the disk controller. Can someone guide me as to how to compile the driver for disk controller with xen. I may be wrong, Can I just copy the /lib/modules of generic linux to the xen folder and then do an update-initramfs. Are there other possible reasons for the above error ?