Context: The baremetal host previously had QEMU 2.11. But I manually downgraded the QEMU version (via `dnf downgrade qemu-system-x86`); now it is at 2.10: $ rpm -q qemu-system-x86 qemu-system-x86-2.10.2-1.fc27.x86_64 The guest is offline. Let's see (in a couple of ways) what machine type it has while it is dormant: # virsh dumpxml cirros | grep -i machine= <type arch='x86_64' machine='pc-i440fx-2.10'>hvm</type> # grep machine= /etc/libvirt/qemu/cirros.xml <type arch='x86_64' machine='pc-i440fx-2.10'>hvm</type> Okay, now edit the guest XML and carefully remove the "machine='pc-i440fx-2.10'" bit---to see what machine type will libvirt (libvirt-daemon-kvm-4.0.0-2.fc27.x86_64) default to: # virsh edit cirros Domain cirros XML configuration edited. Now check the machine type again. Bizarrely enough, libvirt "helpfully" auto-adds QEMU *2.11* machine type, which is obviously no longer on the system! # grep machine= /etc/libvirt/qemu/cirros.xml <type arch='x86_64' machine='pc-i440fx-2.11'>hvm</type> # virsh dumpxml cirros | grep -i machine= <type arch='x86_64' machine='pc-i440fx-2.11'>hvm</type> How to explain this? Is this even a "valid test"? (To undo the nuisance, obviously, I had to `virsh edit cirros` again and change it to 2.10.) Note, I *don't* have 2.11 QEMU on the system: # rpm -qa | grep -E 'qemu.*2.11' # echo $? 1 * * * It's getting late, and I should stop staring at screens.

On Sun, Oct 14, 2018 at 02:28:07PM +0200, Andrea Bolognani wrote: > If I had to guess, I would say the <emulator> element of your guest > is probably pointing to a custom-built QEMU 2.11 binary rather than > the default one installed from RPMs. Your guess made me curious enough to check the remote machine one last time before I went to sleep, but unfortunately the <emulator> element is pointing to the plain `/usr/bin/qemu-kvm`, which in turn exec()'s `/usr/bin/qemu-system-x86_64`. (I attached the nothing-special, full guest XML.)

On Mon, Oct 15, 2018 at 09:05:16AM +0200, Andrea Bolognani wrote: > Interesting. What is the output of 'virsh capabilities'? In attachment.

> More interesting still is the fact that the guest XML you shared > looks like an *active* XML, ie. one taken from a running guest... > Does that mean the guest can start even though it's using the 2.11 > machine type? No, of course it doesn't; the guest is running because I `virsh-edit`ed it to use 2.10 machine type :-)