Change screen resolution of Xenserver Console for a CentOS VM

In Gentoo I was able to solve this problem by adding

GRUB_CMDLINE_XEN_DEFAULT="vga=gfx-1920x1080x16"

at the end of the file /etc/default/grub

It is important that you add the prefix gfx- in front of the actual resolution. Otherwise this won't work.

If you want to find out which resolutions are possible, you might want to start with

GRUB_CMDLINE_XEN_DEFAULT="vga=ask"

Actually my Xen command line configuration looks like this:

GRUB_CMDLINE_XEN_DEFAULT="dom0_mem=2048M,max:2048M vga=gfx-1920x1080x16"

However, the first parameters are not necessary for the display resolution

Beyound the SSH X11Forwading way I succeeded in XDMCP!

Use Xnest or Xephyr in Domain0:

Xnest :1 -geometry 1280x800 -query 10.0.1.x

Xephyr :1 -screen 1280x1024 -query 192.168.1.x

The only thing you have to do is to enable remote login in your VM or DomainU by manually editing /etc/gdm/custom.cfg or using the gdmsetup GUI program. Here CentOS 5 DomainU is taken as an example. In Ubuntu things will be a little different.

This approach is very different to VNC which is like Microsoft's RDP (screen capture) while XDMCP utilizes your Domain0's graphic power to assist DomainU system. That is comparable to Xen VGA pass-through in terms of performance.

Remember X11 was specifically designed to be used over network connections rather than on an integral or attached display device. X features network transparency: the machine where an application (the client application, for instance Firefox in your VM or DomainU) runs can differ from the user's local machine (the display server, that is the X11 in your Domain0). This approach allows both 2D and 3D operations to be fully accelerated on the user's local X server.