How to Use QEMU GTK as Display for Libvirt Virtual Machines

Learn how to use QEMU GTK as a display for libvirt virtual machines, and how to troubleshoot common issues with this setup.

Problem

One of the advantages of using QEMU GTK as a display for libvirt virtual machines is that it allows you to use your host’s graphics card and drivers for better performance and compatibility. However, setting up QEMU GTK as a display for libvirt virtual machines can be tricky, and you may encounter some issues along the way.

In this blog post, we will show you how to use QEMU GTK as a display for libvirt virtual machines, and how to troubleshoot common issues with this setup. We will assume that you have already installed QEMU, libvirt, and virt-manager on your Linux system, and that you have a working virtual machine that you want to use QEMU GTK as a display for.

Step 1: Add QEMU command line arguments to the virtual machine XML file

The first step is to add QEMU command line arguments to the virtual machine XML file. These arguments will tell QEMU to use GTK as a display, enable OpenGL acceleration, and disable zooming to fit. To do this, you need to edit the XML file of your virtual machine using virt-manager or a text editor.

To edit the XML file using virt-manager:

1. Open virt-manager and select your virtual machine from the list.

2. Click on the “Open” button to open the virtual machine console.

3. Click on the “Show virtual hardware details” button on the toolbar.

4. Click on the “XML” tab at the bottom of the window.

5. Scroll down to the end of the XML file and look for the <qemu:commandline> element. If it doesn’t exist, create it before the closing </domain> tag.

6. Inside the <qemu:commandline> element, add the following sub-elements:

<qemu:arg value="-display"/>
<qemu:arg value="gtk,gl=on,zoom-to-fit=off"/>
<qemu:env name="DISPLAY" value=":0"/>

7. Click on the “Apply” button to save the changes.

To edit the XML file using a text editor:

1. Open a terminal and run the following command to dump the XML file of your virtual machine to a text file:

virsh dumpxml <vm-name> > vm.xml

Replace <vm-name> with the name of your virtual machine.

2. Open the text file with your preferred text editor and look for the <qemu:commandline> element. If it doesn’t exist, create it before the closing </domain> tag.

3. Inside the <qemu:commandline> element, add the following sub-elements:

<qemu:arg value="-display"/>
<qemu:arg value="gtk,gl=on,zoom-to-fit=off"/>
<qemu:env name="DISPLAY" value=":0"/>

4. Save the text file and run the following command to redefine the virtual machine with the modified XML file:

virsh define vm.xml

Step 2: Start the virtual machine and check the QEMU GTK display

The next step is to start the virtual machine and check the QEMU GTK display. To do this, you can use virt-manager or the command line.

To start the virtual machine using virt-manager:

1. Open virt-manager and select your virtual machine from the list.

2. Click on the “Run” button to start the virtual machine.

3. Click on the “Open” button to open the virtual machine console.

4. You should see the QEMU GTK display with the virtual machine screen.

To start the virtual machine using the command line:

1. Open a terminal and run the following command to start the virtual machine:

virsh start <vm-name>

Replace <vm-name> with the name of your virtual machine.

2. Run the following command to open the QEMU GTK display:

virt-viewer -c qemu:///system <vm-name>

Replace <vm-name> with the name of your virtual machine.

3. You should see the QEMU GTK display with the virtual machine screen.

Step 3: Troubleshoot common issues with QEMU GTK display

If you encounter any issues with QEMU GTK display, here are some possible solutions:

If you see a black screen or a message saying “No protocol specified”, it means that QEMU cannot connect to the X server on your host. To fix this, you need to allow QEMU to access the X server by running the following command on your host:

xhost +SI:localuser:root

This command will grant access to the X server for the root user, which is the user that QEMU runs as by default. If you want to grant access to a different user, replace root with the username.

If you see a message saying “Could not initialize SDL(No available video device) – exiting”, it means that QEMU cannot find the SDL library on your host. To fix this, you need to install the SDL library by running the following command on your host:

sudo apt install libsdl2-2.0-0

This command will install the SDL library for Ubuntu and Debian systems. If you are using a different Linux distribution, use the appropriate package manager and package name.

If you see a message saying “Failed to initialize GTK: Could not open display”, it means that QEMU cannot find the GTK library on your host. To fix this, you need to install the GTK library by running the following command on your host:

sudo apt install libgtk-3-0

This command will install the GTK library for Ubuntu and Debian systems. If you are using a different Linux distribution, use the appropriate package manager and package name.

If you see a message saying “Failed to initialize GLX: GLX extension not found”, it means that QEMU cannot use OpenGL acceleration on your host. To fix this, you need to install the OpenGL drivers for your graphics card by following the instructions for your specific hardware and operating system.

Frequently Asked Questions (FAQs)

Question: What is QEMU GTK?

Answer: QEMU GTK is a graphical user interface (GUI) for QEMU that supports OpenGL acceleration and zooming. It allows you to use your host’s graphics card and drivers for better performance and compatibility with your virtual machines.

Question: What is libvirt?

Answer: Libvirt is a toolkit that provides a common API for managing virtual machines and other virtualization resources. It supports various hypervisors, including QEMU, KVM, Xen, VMware, VirtualBox, and more.

Question: What is virt-manager?

Answer: Virt-manager is a graphical application that uses libvirt to create and manage virtual machines. It allows you to configure the virtual hardware, network, storage, and display of your virtual machines.

Question: How to use QEMU GTK as a display for libvirt virtual machines?

Answer: To use QEMU GTK as a display for libvirt virtual machines, you need to add QEMU command line arguments to the virtual machine XML file, start the virtual machine, and check the QEMU GTK display. You also need to troubleshoot common issues with QEMU GTK display if you encounter any.

Summary

In this blog post, we have shown you how to use QEMU GTK as a display for libvirt virtual machines, and how to troubleshoot common issues with this setup. We hope that this guide has been helpful and informative for you. If you have any questions or feedback, please leave a comment below.

Disclaimer: This blog post is for informational purposes only and does not constitute professional advice. We are not responsible for any damages or losses that may result from following the instructions or using the tools mentioned in this blog post. Always backup your data and test your setup before making any changes.