I’m totally sure all of those tips are valid and right, and @danielabc is lacking free space. However — I’ve been on that situation once and anything wasn’t broken, even I was on too small VPS (the 5USD droplet from DO is very problematic in many ways). I rebooted VPS and docker didn’t restart. That’s it, and errors were very similar, or totally same, than showed here.
But if everything is because of lack free space/memory, wouldn’t then the only solution be increasing size of VPS? Even shortly just to find out if the issue is lacking of resources? Because if it so, then OP is just using bandage that doesn’t hold too long and she will be at same situation again?
Because I’m just another end-user I love easy solutions. Knowing how to clean and keep everything nice and tidy is something that we have to learn. But it is not a solution, it is short time fix, where one can break places before that fix works.