How to find which screen (and thus port) the VNC UI for a kvm guest has? Or how to assign it

Question

Is there a straightforward way to find the VNC screen (i.e. port number minus 5900) onto which a KVM guest is bound?

My guests are all configured to run with VNC enabled, but the order in which they occupy the ports is random.

Alternately, is there a way to assign them in the configuration (of guest or host), so that each respective guest will occupy a predefined port?!

Answer 1

Since you're using libvirt, you can just ask it!

root@onhost1:~# virsh list
 Id Name                 State
----------------------------------
  1 one-34               running
  2 one-36               running
  3 one-38               running

root@onhost1:~# virsh vncdisplay one-34
:34

root@onhost1:~# virsh vncdisplay 1
:34

(my particular correlation of name to VNC display port is due to the use of Open Nebula)

---

Here's a one-liner to execute this for all running guests at once:

for i in $(virsh list|tail -n +3|awk '{print $2}'|sort); do
  echo -e "\033[01;31m$i\033[00m -> $(virsh vncdisplay $i)"
done

Also made it into a function that sorts output by port number:

function vnc-list
{
  for i in $(virsh list|tail -n +3|awk '{print $2}'|sort); do
    PORTNUM=$(virsh vncdisplay $i|cut -f 2 -d ':')
    printf "% 2d: \033[01;32m%.20s\033[00m\n" "$PORTNUM" "$i";
  done | sort -n
}

Answer 2

I would run :

ps aux | grep "VM name/config"

Note the process ID and then

netstat -apn | grep "process ID"

This should show you are port open by that process.

Answer 3

To set the display, simply explicitly provide the -vnc <ip:display> option to qemu-kvm. See the man page to qemu-kvm, especially the -vnc parameter section for details.

Answer 4

I dont have linux box right now but I remember that folder named ".vnc" is created at home directory which has subfolders according to all the displays created. This subfolders will have the information you are looking for