Blurry Linux KVM screen fix

QEMU/KVM scales the guest's screen to fit a re-sized window. This is one of the small "paper cuts" that I've been living with since moving to KVM for my virtualization needs.

Having the screen get resized fine for occasions where you want to lessen the screen real-estate of a VM but still keep an eye want is going on. The problem is once you try drag the window back to it's 1:1 size. With a free hand you won't be able to get the window size exactly back to a 1:1 ratio so the everything in the VM will look slightly blurry.

Here's an example of my trying to get this 1152 x 864 Windows XP KVM back to actual screen resolution. It's close but still blurry.

I've lived with this blurriness for months now but today I came across Al Dimond's post about the problem. He took the time to investigate the problem and found a quick workaround using xdotool to resize the KVM window to a width and height one pixel less than the guest.

First get the window ID of your KVM

xdotool search --title QEMU

Then use the windowsize option to set the window to an exact size. The window ID in my example is 90177539.

xdotool windowsize 90177539 1151 863

Following the one pixel less workaround, you would use this command for a 1024x768 guest.

xdotool windowsize 90177539 1023 767

Now the guest screen is sharp and crisp again.

Run Windows virtual machines on Ubuntu/Debian desktop with KVM

Both at home and at work, I use Ubuntu as my operating system. There are times when I'm forced use Windows for some reason and there are several solutions for host Windows OS virtual machines on an Ubuntu laptop. Several years ago, I used what I most understood, VMware's workstation offering for Linux. Later when Virtualbox-ose (open source edition) caught up with VMware's features and hosted from Ubuntu's repositories, I switched to it.

These days, I'm much more technically adept with FOSS virtualization technologies and made the switch to using Linux KVM on my newer machines which support Intel's VT and AMD's AMD-V acceleration. I don't have any Phoronix style detailed comparisons but KVM feels faster and lighter than Virtualbox or VMware.

Quick Setup

Install the qemu-kvm package

sudo apt-get install qemu-kvm

Create a directory to hold your virtual machines.

mkdir -p ~/VM/WinXP

Move to that directory and create a disk image file.

cd ~/VM/WinXP
qemu-img create -f raw windows_xp.img 12G

Options:
-f raw = creates raw IO driver format image (You could also use the qcow2 mode. It has more features but doesn't perform as fast as raw)
windows_xp.img = name of the image file
12G = The virtual disk size.

Now create a bash script using your favourite text editor. I like vim but you could just as easily use gedit from GNOME.

vim Windows_XP.sh

Here's how my script looks:

#!/bin/bash
#
# Description: Launches Windows XP QEMU64
#
# Verion: 1
# Author: Clayton Kramer clayton.kramer @ gmail.com
# Modified: Fri 23 Apr 2010 11:43:35 AM EDT 
#

# Ubuntu Karmic tweek - Prepare audio to use Pulse driver instead of ALSA 
export QEMU_AUDIO_DRV=pa

# Launch Windows XP KVM
kvm  \
    -name "Windows XP Guest" \
    -m 1024 \
    -smp 1 \
    -localtime \
    -drive file=~/VM/WinXP/windows_xp.img,if=virtio,index=0,boot=on,cache=writeback \
    -drive file=~/ISO/windows_xp_sp2.iso,if=ide,media=cdrom,index=2 \
    -fda ~/ISO/viostor-31-03-2010-floppy.img \
    -net nic,model=virtio \
    -net user \
    -soundhw ac97 \
    -usb \
    -usbdevice tablet 

By default Ubuntu 9.10's qemu-kvm will use ALSA drivers which can lead to some choppy sound. You can change this behavior by setting the QEMU_AUDIO_DRV environmental variable to pa before launching the KVM.

I am using the VirtIO drivers in the script above. They improve the IO performance for Windows guests. Haydn Solomon provides some detailed instructions on setting them up in his KVM blog. I've decided to live a little dangerous and enabled the writeback option for the block driver.

http://www.linux-kvm.com/content/block-driver-updates-install-drivers-during-windows-installation

After the Windows installation is complete you can ommit the virtual floppy disk device line.

You may also want to take note that my script also configures the paravirtualized network device. You'll need to get the latest driver for that from:

http://www.linux-kvm.org/page/WindowsGuestDrivers/Download_Drivers

If you wanted wanted to get a Windows XP install going without using the VirtIO drivers you can use this compatibility script. It uses IDE for the IO controller bus and Intel e1000 driver for the NIC.

# Launch Windows XP KVM (compatibility)
kvm  \
    -name "Windows XP Guest" \
    -m 1024 \
    -smp 1 \
    -localtime \
    -drive file=~/VM/WinXP/windows_xp.img,if=ide,index=0,boot=on \
    -drive file=~/ISO/windows_xp_sp2.iso,if=ide,media=cdrom,index=2 \
    -net nic,model=e1000 \
    -net user \
    -soundhw ac97 \
    -usb \
    -usbdevice tablet