Как освободить место на диске в Ubuntu?

sudo du -h --max-depth=1


72K ./root
4.0K    ./cdrom
16G ./var
4.0K    ./media
5.9G    ./usr
146M    ./boot
12M ./etc
148K    ./tmp
13G ./home
16K ./opt
du: cannot access './run/user/1000/doc': Permission denied
du: cannot access './run/user/1000/gvfs': Permission denied
1.6M    ./run
4.0K    ./srv
4.8G    ./snap
16K ./lost+found
4.0K    ./mnt
0   ./dev
0   ./sys
du: cannot access './proc/9684/task/9684/fd/3': No such file or directory
du: cannot access './proc/9684/task/9684/fdinfo/3': No such file or directory
du: cannot access './proc/9684/fd/4': No such file or directory
du: cannot access './proc/9684/fdinfo/4': No such file or directory
0   ./proc
41G .

Какие мухи я могу удалить, чтобы освободить место на диске?