If you install libvirt from ubuntu software library like this
sudo apt-get install libvirt-bin
The default version is 1.2.2 for Ubuntu Trusty.
However, after you upgrade it to version 2.5.0 from its source codes (restart the libvirtd service), you will see following error if you want to install vm with virt-install.
ERROR Failed to connect socket to '/var/run/libvirt/virtlogd-sock': No such file or directory
Domain installation does not appear to have been successful.
If it was, you can restart your domain by running:
virsh --connect qemu:///system start kvm1
otherwise, please restart your installation.