Fails to start VM after Jaunty upgrade: Failed to add tap interface 'vnet%d' to bridge 'virbr%d'

[Thierry Carrez]

After upgrading from Intrepid to Jaunty, my VMs fail to start with the following error:

$ virsh start jaunty-test
Connecting to uri: qemu:///system
error: Failed to start domain jaunty-test
error: internal error Failed to add tap interface 'vnet%d' to bridge 'virbr%d' : No such device
$ virsh net-list --all
Name State Autostart
-----------------------------------------
default inactive yes
$ virsh net-start default
error: Failed to start network default
error: cannot create bridge 'virbr0': File exists

libvirt 0.6.1-0ubuntu4
kvm 1:84+dfsg-0ubuntu9

[Thierry Carrez (ttx)]

Apparently I had dnsmasq running which prevented virbr0 setup. Probably a leftover of some test... properly purging dnsmasq solved the issue. Please ignore the noise, that would be a duplicate of bug 231060.