Install this simple tool ncdu for linux
sudo apt install ncdu
After this simply run the command:
sudo ncdu -x /
you will enter into navigation mode in the terminal using which you can find which directories are eating up space on your linux system.
sample output
4,0GiB [##########] /usr
579,3MiB [# ] /root
487,4MiB [# ] /opt
41,7MiB [ ] /lib
22,7MiB [ ] /sbin
21,2MiB [ ] /boot
18,6MiB [ ] /etc
9,1MiB [ ] /bin
3,6MiB [ ] core
260,0KiB [ ] /build
88,0KiB [ ] /tmp
e 16,0KiB [ ] /lost+found
8,0KiB [ ] /media
4,0KiB [ ] /lib64
e 4,0KiB [ ] /srv
e 4,0KiB [ ] /mnt
> 0,0 B [ ] /var
> 0,0 B [ ] /sys
> 0,0 B [ ] /run
> 0,0 B [ ] /proc
> 0,0 B [ ] /ovhbackup
> 0,0 B [ ] /home
> 0,0 B [ ] /dev