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179 lines
4.3 KiB
Markdown
179 lines
4.3 KiB
Markdown
---
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title: Display
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description: How to access a virtual machine's display
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published: true
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date: 2023-10-15T15:11:00.161Z
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tags:
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editor: markdown
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dateCreated: 2022-07-31T09:22:05.854Z
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---
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# Display
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A virtual display can be attached to a virtual machine. It is a must-have for non-headless scenarios.
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## Display types
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### SDL display
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The [Simple DirectMedia Layer](https://www.libsdl.org/) (SDL)-powered display is a local-only low-latency display.
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> The SDL display is only avalable with virtual machines created using the QEMU/KVM **User Session**
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{.is-info}
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> Mouse grab does not currently work with the SDL display
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{.is-warning}
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> The display resolution of your guest display should not exceed that of your physical screen
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{.is-info}
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#### SELinux-related configuration
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By default, SELinux will block access to X Windows Server for the virtualization stack. An exception has to be set.
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* Set new rule
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```
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sudo setsebool -P virt_use_xserver 1
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```
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* Do some magic trick
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```
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sudo ausearch -c 'qemu-system-x86' --raw | audit2allow -M my-qemusystemx86
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k
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```
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* And another one
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```
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sudo semodule -X 300 -i my-qemusystemx86.pp
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```
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#### SDL XML configuration
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* The default display can be identified using `echo $DISPLAY`.
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```
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$ echo $DISPLAY
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:0
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```
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The same applies to `xauth`. On Wayland, it would look like that.
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```
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$ echo $XAUTHORITY
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/run/user/1000/.mutter-Xwaylandauth.ARIY51
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```
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* Example of an XML SDL configuration, with OpenGL enabled. This example requires a 3D-capable graphic card to be attached to the guest computer, such as `virtio-gpu`.
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```
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<graphics type="sdl" display=":0" xauth="/run/user/1000/.mutter-Xwaylandauth.ARIY51" fullscreen="yes">
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<gl enable="yes"/>
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</graphics>
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```
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> The fullscreen attribute is not honored at the moment
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{.is-warning}
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### D-Bus display
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[D-Bus](https://www.freedesktop.org/wiki/Software/dbus/) is a desktop-oriented middleware that can be used to create a display for a virtual machine.
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#### Libvirt
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* Add a D-Bus video backend and add enable for OpenGL:
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```
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<graphics type="dbus">
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<gl enable="yes"/>
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</graphics>
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```
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> This equates to `-display dbus,gl=on` in QEMU
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>
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{.is-info}
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When the virtual machine is launched, a specific D-Bus address will be choosen, as well as a rendering device:
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```
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<graphics type="dbus" address="unix:path=/run/user/1000/libvirt/qemu/run/dbus/8-user-d-bus-dbus.sock">
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<gl enable="yes" rendernode="/dev/dri/renderD128"/>
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</graphics>
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```
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* Add a D-Bus audio backend:
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```
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<graphics type="dbus">
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<audio id="1">
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</graphics>
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```
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#### Connect to the D-Bus display
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A third-party tool is required to interact to the D-Bus display.
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[Libmks](https://gitlab.gnome.org/GNOME/libmks), which is under development, is such a tool.
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> Due to [a bug](https://gitlab.gnome.org/GNOME/libmks/-/issues/16), it is currenlty only possible to connect a D-Bus display with plain QEMU
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{.is-warning}
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Libmks has to be built from source.
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- Clone the repository
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```
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git clone https://gitlab.gnome.org/GNOME/libmks
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```
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- Change directory
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```
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cd libmks
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```
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- Build it
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```
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meson setup build
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cd build
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ninja
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```
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- Launch a diskless virtual machine
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```
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qemu-system-x86_64 \
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-enable-kvm \
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-machine q35 \
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-drive if=pflash,format=raw,readonly=on,file=/usr/share/edk2-ovmf/x64/OVMF_CODE.fd \
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-cpu host \
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-device virtio-vga-gl \
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-m 4G \
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-smp 2,sockets=1,dies=1,cores=2,threads=1 \
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-display dbus,gl=on \
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-device virtio-tablet-pci \
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-device virtio-keyboard-pci \
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```
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- From another terminal tab or window, launch the previously built MKS using the following command
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```
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./build/tools/mks
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```
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As there is no Live ISO or disk attached to the virtual machine, you will eventually land in the UEFI shell.
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## Resources
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* [Detailed presentation](https://bootlin.com/pub/conferences/2016/meetup/dbus/josserand-dbus-meetup.pdf) on D-Bus
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* [Official resource](https://libvirt.org/formatdomain.html#graphical-framebuffers) for libvirt-compatible displays, including various XML examples
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* [Libmks](https://gitlab.gnome.org/chergert/libmks) provides a "Mouse, Keyboard, and Screen" to QEMU using the D-Bus device support in QEMU and GTK 4.
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* [QEMU D-Bus display experiment](https://gitlab.com/marcandre.lureau/qemu-display/) is a WIP Rust crates to interact with a -display dbus QEMU
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* [SDL graphics](https://fedoraproject.org/wiki/How_to_debug_Virtualization_problems#SDL_Graphics)
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---
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*[**Go to parent page**](https://wiki.phyllo.me/)* |