Freeing up disk space in Ubuntu?

Question

linux

I often come across the fact that after some time using Ubuntu (17.04), the disk space is clogged with unknown things and I can’t figure out what is busy.
Right now:

Filesystem      Size  Used Avail Use% Mounted on
udev            5,9G     0  5,9G   0% /dev
tmpfs           1,2G  9,6M  1,2G   1% /run
/dev/sda5        37G   34G  1,4G  97% /
tmpfs           5,9G   76M  5,8G   2% /dev/shm
tmpfs           5,0M  4,0K  5,0M   1% /run/lock
tmpfs           5,9G     0  5,9G   0% /sys/fs/cgroup
tmpfs           1,2G  164K  1,2G   1% /run/user/1000
/dev/sdb1       459G   50G  386G  12% /media/user/backup

As you can see, / the root is 97% full, and this is 34 GB occupied (I have /home mounted to the root, that is, I don’t create a separate partition)
Now I show you how much all the files in the system take:

61G	/
4,7G	/home/
49G	/media/user/backup/

Roughly calculate 61 - 49 (sdb1 external drive) = 12 GB
The Disk Usage Analyzer shows the same information.
Now I have a question, so what is the space occupied by?
Note: I noticed that after I enabled rsnapshot (server backup) on /dev/sdb1 I had such a problem, but the path for backups is /media/user/backup , and this is kind of the path to an external drive.
But when I look separately from windows to the ubuntu root disk, or more precisely, the path / media / user / backup , then there are oh my god there are backups !!! how does it happen? Is it that some kind of cache, or did I make a mistake with the path for folding backups?

Answer 1

unmount /media/user/backup and delete what is on sda5
Apparently you did rsnapshot without mounting sdb1

Answer 2

sudo tune2fs -m0.1 /dev/sda5
will show you the focus :)
free space will increase dramatically.