I think I see a bug in libvirt. Here is step-by-step instructions how to reproduce: 1. Create domain from XML (note vnc port): <domain type="xen"> <name>lvnc</name> <os> <type>linux</type> <kernel>/boot/vmlinuz-2.6.15-1.43_FC5guest</kernel> <initrd>/boot/initrd-2.6.15-1.43_FC5guest.img</initrd> <root>/dev/sda1</root> <cmdline> ro selinux=0 3</cmdline> </os> <memory>10</memory> <vcpu>1</vcpu> <on_poweroff>destroy</on_poweroff> <on_reboot>restart</on_reboot> <on_crash>restart</on_crash> <devices> <graphics type="vnc" port="5905"/> </devices> </domain> 2. Examine s-expr definition: sudo /usr/sbin/xm list -l lvnc (domain (on_crash restart) (uuid 5c56456a-1f19-d996-35e3-f5e514b79601) (bootloader_args ) (vcpus 1) (name lvnc) (on_poweroff destroy) (on_reboot restart) (bootloader ) (maxmem 128) (memory 128) (shadow_memory 0) (features ) (on_xend_start ignore) (on_xend_stop ignore) (image (linux (kernel /boot/vmlinuz-2.6.15-1.43_FC5guest) (ramdisk /boot/initrd-2.6.15-1.43_FC5guest.img) (args 'root=/dev/sda1 ro selinux=0 3') (device_model /usr/lib/xen/bin/qemu-dm) ) ) (status 0) (device (vkbd (uuid c1ea89ea-903c-ba5b-603d-7b5c7bc25654))) (device (vfb (type vnc) (vncdisplay 5) (uuid bc92b909-8ca3-eece-8ef5-7551eaccda6e) ) ) ) So far, so good: vncdisplay 5 3. dumpxml lvnc <domain type='xen' id='-1'> <name>lvnc</name> <uuid>5c56456a-1f19-d996-35e3-f5e514b79601</uuid> <bootloader/> <os> <type>linux</type> <kernel>/boot/vmlinuz-2.6.15-1.43_FC5guest</kernel> <initrd>/boot/initrd-2.6.15-1.43_FC5guest.img</initrd> <cmdline>root=/dev/sda1 ro selinux=0 3</cmdline> </os> <memory>131072</memory> <vcpu>1</vcpu> <on_poweroff>destroy</on_poweroff> <on_reboot>restart</on_reboot> <on_crash>restart</on_crash> <devices> <emulator>/usr/lib/xen/bin/qemu-dm</emulator> <input type='mouse' bus='xen'/> <graphics type='vnc' port='-1'/> </devices> </domain> As you can see, port is now -1 instead of expected 5905. Looks like the problem around 'vncunused' variable handling in xml_internal.c. (I think it should be assigned 0 not 1 by default and if 'vncunused' config keyword is not found. I tried to fix it myself, but without much luck so far. By the way, what would be a good way to do logging in libvirt code? Sincerely, Vadim -- "La perfection est atteinte non quand il ne reste rien a ajouter, mais quand il ne reste rien a enlever." (Antoine de Saint-Exupery)