Ok found out what the problem is…
Ubuntu comes with a default /tmp size of 100Mb. Now the chain is 180Mb. I don’t get why the GRIN node is going through the /tmp directory instead of directly writing into the ~/.grin/main/ directory, or why it doesn’t write it piece by piece, but that’s definitely a pain. And this problem might increase with time. Not a lot of people has a 1Gb mounted on /tmp