Pop OS - harddrive is full while only 25 percent are used

Hello, I hope I am correct here.

I have a Thinkpad E15 with an 512 GB SSD in use with Pop!_OS 20.04 LTS x86_64.
The SSD is full and I don’t know why.

df -H shows a usage of the root of 409GB which equals 88% usage.
/dev/mapper/data-root 495G 409G 61G 88% /

Using a graphical tool like Filelight showes me 124 GiB of used space on /
(109GiB in /home/ and some in /var/ and /usr/)

the CL gives me similar results with:
find / -mindepth 1 -maxdepth 1 -type d -exec du -shP {} 1> ~/du-root-plus-one.list ;
104G /home
284M /opt
14M /etc
0 /sys
0 /dev
9,9G /media
1,3G /snap
263M /boot
16K /lost+found
4,0K /root
88K /tmp
4,0K /mnt
3,1G /var
0 /proc
4,0K /srv
4,0K /recovery
11G /usr
2,1M /run

Both commands where done with no network shares mounted.
Due to the mobile nature of a laptop the FS is encrypted.

I also deleted all timeshift backups and finally disabled and deleted timeshift because the system froze due to a full harddrive. I also cleard the trashbin.

What did I miss? I thought if space is not used it should be free - but I am obviously wrong somehow.

Thanks a lot in advance!


I found out that I have a lot of files in /root/.local/share/Trash/files via
sudo baobab
(found at Disk space is missing - Unix & Linux Stack Exchange)

The next step is to find a way to delete them because sudo does not allow me to access atm.

I booted from a USB-stick a linux lite, mounted the partition and went to terminal.
I set a root password → sudo passed root
went to the mount point → cd /media/linux/c5e…
Checked if I am correct → ls -la
went into the folder of concern → cd /root/.local/share/Trash → NO ACCESS
logged in as root → su root
second attempt → cd /root/.local/share/Trash
check if I am correct → ls -la → yes, indeed - they look like multiple backups of the entire file system
deleting the folders (d) recursively (r)–> rm -rd 2022-02-____________
repeated it for all folders that I wanted to delete
leaving root access → exit

Problem solved - how can I change the title of the thread accordingly?