Disk Usage Very Strange

Solution 1:

You could delete the .xsession-errors.old file entering sudo rm ~/.xsession-errors.old in terminal.

This file was the 99% of my drive space :)

Solution 2:

Run df -h in a terminal window. The output should have the proper numbers.

/dev/sda2              16G  5,1G   10G  34% /
udev                  2,0G  4,0K  2,0G   1% /dev
tmpfs                 807M  896K  806M   1% /run
none                  5,0M  8,0K  5,0M   1% /run/lock
none                  2,0G  224K  2,0G   1% /run/shm
/dev/sda6              28G   14G   14G  51% /home

In my example the /home filesystem is located on /dev/sda6 and has 14GB used (3rd column) and 14GB free space (4th).

You can check the total disk usage of a directory by using du -hs. E.g:

$ du -hs /home/username
14G /home/username

You may have hidden directories accumulating large files. The first yellow block in the gparted window shows that the root partition (/dev/sda1) is almost full.