We use the du command to find out what take the space of the disk in linux systems.
Most Useful
$ du -h --max-depth=1 /
77M /boot
0 /dev
172K /home
0 /proc
65M /run
0 /sys
23M /etc
176K /root
4.0K /tmp
463M /var
976M /usr
0 /media
0 /mnt
0 /opt
11M /srv
1.6G /
Using du With Filters
du -h --max-depth=1 / | sort -n
0 /dev
0 /media
0 /mnt
0 /opt
0 /proc
0 /sys
1.6G /
4.0K /tmp
11M /srv
23M /etc
65M /run
77M /boot
172K /home
176K /root
463M /var
976M /usr