Adding a second monitor to a QEMU VM

In progress and possibly untested; take everything with a pinch of salt.

command line - Adding a second monitor on qemu virtual machine - Super User

First Answer

I recently tried to set up a virtual machine with several video heads (e.g., two monitors).

I found a series of blog articles that explain how to do that: https://linux-blog.anracom.com/2017/07/06/kvmqemu-mit-qxl-hohe-aufloesungen-und-virtuelle-monitore-im-gastsystem-definieren-und-nutzen-i/

Unfortunately, it is written in German, a language I can’t read. But an online translater helped me, and I finally succeeded running a virtual machine with two heads.

As I understand it, you are missing two things:

1. You need to configure the qxl-vga device to enable two heads with the max_outputs=2 option (you can use values up to 4).
2. You have to use a spice client that supports multiple displays over a single connection. (On my Debian host, remote-viewer, from the virt-viewer package does, but spicy does not.)

For the reference, here is the command I used to start an Ubuntu guest, with dual-head support:

qemu-system-x86_64 -machine q35,accel=kvm -cpu host -smp 1 -m size=4G \
-audiodev driver=spice,id=audio -device intel-hda -device hda-duplex,audiodev=audio \
-blockdev driver=raw,node-name=ubuntu,file.driver=file,file.filename=Downloads/ubuntu-22.04.1-desktop-amd64.iso \
-device ide-cd,drive=ubuntu \
-vga none -device qxl-vga,vgamem_mb=64,ram_size_mb=256,vram_size_mb=128,max_outputs=2 \
-device piix4-usb-uhci -device usb-tablet \
-display none -spice port=5900,addr=127.0.0.1,disable-ticketing \
-chardev spicevmc,id=charchannel0,name=vdagent \
-device virtio-serial-pci,id=virtio-serial0 -device virtserialport,bus=virtio-serial0