I hosed up the configuration of libvirt on Cinnamon, trying to change the network definition.
It was so fouled up I decided to remove and reinstall libvirtd-bin, qemu, and virt-manager.
After the reinstall, the default network did not reappear, and I went looking for how to reinstall it. In the end I had to piece together various information, but the upshot is that the definition of networks for libvirt is in /usr/share/libvirt/networks. This directory was missing for me, and I had to recreated it:
root@cinnamon:~# mkdir /usr/share/libvirt/networks
root@cinnamon:~# cd /usr/share/libvirt/networks
root@cinnamon:/usr/share/libvirt/networks# touch default.xml
root@cinnamon:/usr/share/libvirt/networks# chmod 0777 default.xml
root@cinnamon:/usr/share/libvirt/networks# emacs default.xml
What I put into the file was:
<network>
<name>internal</name>
<bridge name=”virbr0″ />
<forward/>
<ip address=”192.168.122.1″ netmask=”255.255.255.0″>
<dhcp>
<range start=”192.168.122.2″ end=”192.168.122.254″/>
</dhcp>
</ip>
</network>