How to find out what is taking up space in Ubuntu?

Question

linux

The picture is as follows:

All the space in the root is occupied, but it's not clear what is occupied...
You can't restart the server, the application is very critical, and after mashing it may not start on a busy disk.

Answer 1

lsof + grep deleted
Try to find processes that "hold" deleted files (most often these are logs)

Answer 2

try sudo ncdu

Answer 3

scan folders like sudo du -sh /*
and then see what exactly

Answer 4

man du