this post was submitted on 20 Jun 2024
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OK, one possibility I can think of. At some point, files may have been created where there is currently a mount point which is hiding folders that are still there, on the root partition.
You can remount just the root partition elsewhere by doing something like
Then use du or similar to see if the numbers more closely resemble the values seen in df. I'm not sure if that graphical tool you used that views the filesystem can see those files hidden this way. So, it's probably worth checking just to rule it out.
Anyway, if you see bigger numbers in /mnt/rootonly, then check the mount points (like /mnt/rootonly/home and /mnt/rootonly/boot/efi). They should be empty, if not those are likely files/folders that are being hidden by the mounts.
When finished you can unmount the bound folder with
umount /mnt/rootonly
Just an idea that might be worth checking.
This! Thank you, this allowed me to find the culprit! It turns out I had an external disk failure some weeks ago, and a cron rsync job was writing in /mnt/thatdrive. When the externaldrive died rsync created a folder /mnt/thatdrive. Now that I replaced the drive, /mnt was disregarded by the disk analyser, but the folder was still there and indeed hidden by the mount... It is just a coincidence that it was half the size of /
SOLVED!
This might help in the future in case you setup a remote mount for backups in the future. Look into using systemd's automount feature. If the mount suddenly fails then it will instead create an unwritable directory in its place. This prevents your rsync from erroneously writing data to your root partition instead.
Thank you for sharing this tip! Very useful indeed
You can also do the following to prevent unwanted writes when something is not mounted at
/mnt/thatdrive
:From
man 1 chattr
:I do this to prevent exactly the situation you’ve encountered. Hope this helps!
I think I would have expected/preferred
mount
to complain that you're trying to mount to a directory that's not empty. I feel like I've run into that error before, is that not a thing?It is with zfs, but I not with regular
mount
I think (at least not by default). It might depend on the filesystem though.Ahh, that might be it. I run TrueNAS too. IMO that should be the default behavior, and you should have to explicitly pass a flag if you want mount to silently mask off part of your filesystem. That seems like almost entirely a tool to shoot yourself in the foot.
Yep, it’s definitely better to have as a default
Aha, glad to hear it.