Useful for data recovery. As per this Reddit post:
[dom0] sudo lvcreate --size 1G --snapshot --name tempsnap /dev/mapper/qubes_dom0-vm--untrusted--private
[dom0] readlink /dev/mapper/qubes_dom0-tempsnap
[dom0] qvm-start --hddisk dom0:/dev/[from previous command] viewervm
(Attaching to a running viewervm was not possible)
[viewervm] mkdir -v /tmp/stuff
[viewervm] sudo mount /dev/xvdi /tmp/stuff
If the original VM has more than one partition, have to pick the right one, such as xvdi1 or xvdi2, etcetera.
Could be unmounted, but no commands or options we tried allowed to detach the viewervm until it was stopped. (qvm-block still seems bugged)
Couldn't lvremove until the machine was restarted.