I have ploop disk image created by dumping an OpenVZ container. There are two files:
791 DiskDescriptor.xml 2.4G root.hdd
Is there any way to extract the whole root file system from there on a non-OpenVZ machine?
You don't need to spin up the container, you can simply mount the filesystem image according the manual https://openvz.org/Man/ploop.8
[-r] [-F] [-d device] [-m mount_point] [-o mount_options] [-t fstype] [-u uuid] DiskDescriptor.xml
You can use ploop_userspace.
./ploop_userspace root.hdd & mount -r -o noload /dev/nbd0p1 /mnt