check file
$ file trusty64_vagrant_box_image.img
trusty64_vagrant_box_image.img: QEMU QCOW Image (unknown version)
init
apt-get install -qqy lvm2
modprobe nbd
attach
cd /var/lib/libvirt/images
qemu-nbd -c /dev/nbd0 `pwd`/trusty64_vagrant_box_image.img
vgscan
vgchange -ay
mount /dev/mapper/vagrant--vg-root /mnt
detach
cd /
umount /mnt
vgchange -an vagrant-vg
qemu-nbd -d /dev/nbd0