QEMU is pretty neat, particularly when combined with KVM for hardware-accelerated virtualization. I’m currently using it with an Ubuntu guest for research purposes and missed a few convenience features that just magically work in VMware and VirtualBox: Seamless resizing and copy/paste between guest and host. I’ve found a few guides online telling me to use SPICE, but nearly all of them assumed you start the VM via virt-manager, a nice frontend with an ugly XML configuration format. Personally I prefer writing a small shell script, so here’s mine, adapted from the relevant Arch Wiki article:
#!/bin/bash socket='/tmp/vm_spice.socket' qemu-system-x86_64 \ -m 2G -enable-kvm -drive file=disk.qcow2,format=qcow2 \ -vga qxl -device virtio-serial-pci \ -device virtserialport,chardev=spicechannel0,name=com.redhat.spice.0 \ -chardev spicevmc,id=spicechannel0,name=vdagent \ -spice "unix,addr=$socket,disable-ticketing" & sleep 5 remote-viewer -f "spice+unix://$socket"
The first line of options is stuff specific to my setup. The guest won’t work comfortably without at least 2G of RAM, KVM makes virtualization run close to native speed and the drive points to a qcow2 file. The remaining options are for setting up SPICE with a QXL video device and all the guest interop jazz, listening on a UNIX socket. After waiting for a while, remote-viewer is spawned against the UNIX socket in full-screen mode. You might want to experiment here, for example you can configure it to use your favorite mouse cursor release key combination.
Inside the guest you’ll have to do a few more things:
[wasa@box ~]# apt-get install spice-vdagent xserver-xorg-video-qxl [wasa@box ~]# systemctl enable spice-vdagentd [wasa@box ~]# systemctl start spice-vdagentd [wasa@box ~]$ spice-vdagent
The last line is about running the client which communicates clipboard requests and alike to the daemon. I discovered the hard way that the spice-vdagent package comes with autorun entries for popular desktop environments, so instead I went for launching it inside i3 as soon as my session starts.
To see changes to screen resolution you’ll have to restart your session and check /var/log/Xorg.0.log to correctly detect and use the QXL driver. If that’s indeed the case, xrandr will show a Virtual-0 device and xrandr --output Virtual-0 --auto changes its resolution to the best fitting one.
Finally, there’s one more underappreciated feature this setup gives you, changing focus is seamless so you’ll no longer need a dedicated key combination for releasing or capturing the mouse cursor. If you’re in windowed mode focus is back to the host once you hover over anything outside the VM’s screen, in fullscreen mode you can hover over the top middle part of its screen, an OSD appears (with options such as disabling fullscreen mode) and focus is back to the host again. Switching focus between host and guest no longer sends spurious keys to the guest, for example pressing $mod+3 to switch to a VM on workspace 3 used to enter the number 3 into whatever application had focus inside the VM. This is no longer the case with remote-viewer and makes for a smooth user experience.