Ubuntu 18.04 disk full

I am running HASSIO on an Intel NUC with 8Gb ram and a 120Gb disk. The back end is Ubuntu 18.04 running docker.
I previously had a critical space issue which could only be resolved by deleting through command line some of the held snapshots.
I am now faced a few months later with a bit of a catch 22. My system does not start as it says that the docker container service failed. I can’t do an update to fix because I have no space left on the disk. So I thought i would go back to command and free up some space. I can’t use prune command because it says that i cannot connect to the Docker Daemon.
I am slowly losing my mind over this. i have not worked out how a hassio image on ubuntu can go from a maybe 5g install to blow out a 120Gb disk so quickly (I’m not doing snapshots every day)
help (said with little mouse voice)

OK so weird issue partly solved. In my hassio I have 4 cctv cameras that I view using the rtsp feed in motioneye addon. for some reason over the past week i have had folders created in a subdirectory that were using about 80Gb of space. I don’t have the cameras set to record to any file or directory as I had issues with this previously crashing my NAS from too much data going in too quick. Anyway space is back on the disk and everything starts. Now to work out where and how those camera folders appeared and were populated. Any ideas welcome. Wouuld be interested to know how others set up their cctv camera and storage systems.