I checked the .config file of Dom0 kernel source, I found CONFIG_XEN_NETDEV_FRONTEND=m CONFIG_XEN_NETDEV_BACKEND=m It seems should be =y,so I modify to =y, and rebuild the kernel. When I start DomU again, get the error message below: [ 0.472203] IP-Config: Complete: [ 0.472207] device=eth0, addr=10.0.1.183, mask=255.255.255.0, gw=10.0.1.254, [ 0.472215] host=nfsclient, domain=, nis-domain=(none), [ 0.472219] bootserver=10.0.1.198, rootserver=10.0.1.198, rootpath[ 0.472524] Freeing unused kernel memory: 936k freed [ 0.472660] Write protecting the kernel read-only data: 12288k [ 0.476451] Freeing unused kernel memory: 900k freed [ 0.476884] Freeing unused kernel memory: 1096k freed Loading, please wait... Begin: Loading essential drivers ... done. [ 0.506404] udevd[82]: starting version 173 Begin: Running /scripts/init-premount ... done. Begin: Mounting root file system ... Begin: Running /scripts/local-top ... done. Gave up waiting for root device. Common problems: - Boot args (cat /proc/cmdline) - Check rootdelay= (did the system wait long enough?) - Check root= (did the system wait for the right device?) - Missing modules (cat /proc/modules; ls /dev) ALERT! /dev/nfs does not exist. Dropping to a shell! BusyBox v1.18.4 (Ubuntu 1:1.18.4-2ubuntu2) built-in shell (ash) Enter ''help'' for a list of built-in commands. (initramfs) cat /proc/cmdline root=/dev/nfs ip=10.0.1.183:10.0.1.198:10.0.1.254:255.255.255.0:nfsclient:eth0:off (initramfs) -- View this message in context: http://xen.1045712.n5.nabble.com/Anyone-use-xen-4-x-root-on-nfsv4-tp5635483p5635507.html Sent from the Xen - User mailing list archive at Nabble.com.