« “Could not find any loop device.” WTF?
Don’t Ask »

Increasing the X resolution for KVM guests

Today I wondered again, why my KVM guests get only 800×600 display resolution, even though the framebuffer console is configured for 1024×768. While most of the time this does not matter for testing, it does once you want to evalutate desktop environments or such in a VM.
I checked the xorg log file and found, that the Cirrus card emulation apparently has no DDC channel implemented, thus cannot detect the monitor and then X.org falls back to a plain SVGA monitor. From the logfile: 

Using default hsync range of 31.50-37.90 kHz
Using default vrefresh range of 50.00-70.00 Hz

Simply setting those ranges to something reasonable (I got my values from “hwinfo --monitor“) helps quite a lot. Put this into /etc/X11/xorg.conf.d/50-monitor.conf: 

  HorizSync   31 - 61
  VertRefresh 50 - 90

and you get a much more usable 1024×768 resolution.

This entry was posted on Monday, January 17th, 2011 at 14:34 and is filed under linux. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

2 Responses to “Increasing the X resolution for KVM guests”

  1. Andreas Schneider says:
    January 17, 2011 at 15:37

    Why don’t you simply use the vmware graphics driver?

  2. seife says:
    January 17, 2011 at 16:38

    The VGA / VESA framebuffer emulation of vmvga (which is used during GRUB / system boot) is very slow, I’d say unusably slow, but yes, for guests that are used mainly for testing desktops, this might be an option.
    Maybe someone will write a vmvga KMS driver, then this will be the best option for sure ;)