19 hours ago, togbabe said:

Without needing to start the array, nor stop all the dockers, just go into your 'Libvirt storage location.'  Which - in my case is "/mnt/user/system/libvirt/libvirt.img" - and change the ownership of the libvirt.img file to root.

That doesn't work for me, you may be having a different issue, the problem is usually caused by the loop device not being detached, and changing the ownership of libvirt.img doesn't help with that, at least not for me.

I just came across this with a different error, although I had the same symptoms (libvirt img showing up in losetup -l and fuser -c showing all the docker containers). After stopping the VM service, starting it gave this error:

Apr 17 20:47:46 Media emhttpd: shcmd (2867675): /usr/local/sbin/mount_image '/mnt/user/system/libvirt/libvirt.img' /etc/libvirt 1
Apr 17 20:47:46 Media root: '/mnt/windows/system/libvirt/libvirt.img' attached to loop device, cannot mount
Apr 17 20:47:46 Media emhttpd: shcmd (2867675): exit status: 1

The workaround of stopping the docker service was successful, it released libvirt from the loop device immediately without any extra messages in the syslog.

Ran into the same issue today, also on Unraid 7.3.0-rc.1.
I was unable to start up libvirt until I had shut down docker. Once docker was disabled, libvirt started up fine, and I re-enabled docker.

I have the same issue. Need to stop docker before re-starting vm service. Pretty annoying...