[ubuntu] [16.04] domfsfreeze not working

I'm setting up Ubuntu 16.04 as a host server. I've installed qemu-guest-agent onto the server and configured the chael however when I try to do domfsfreeze on the server I get:

error: Unable to freeze filesystems
error: Guest agent is not responding: Guest agent not available for now

To explain the situation, we're trying out qcow images and trying to do snapshot backups by freezing the os and then doing a snapshot of the image. If you have any solutions or alteative ways of freezing the OS any help would be great, thanks.