What is eating my HDD space?

[speedygonzalez]

Have you tried yet to find out what is using up disc space?

(Pressing pause on live tv starts up timeshift, and rebooting will empty the disc space timeshift has used, and recordings use up disc space as well.)

Yes. The list, which may not be exclusive, includes 1) recording programmes, 2) enabling timeshift, and 3) pause even when timeshift is disabled.

I have also tried pointing timeshift to a usb stick instead while it was enabled, which showed me that timeshift files were normal, the issue appears to be that the 3 activities above leave orphan hdd disc space behind, which is invisible to 'ls-a', but is reclaimed by fsck or a restart.

Recording programmes of course use up disc space. The issue is after they are deleted not all the used space is returned, and can only be recovered by fsck or restart. Programme file size looks normal. As an illustration, if free space is 800GB (from menu setup information device), you might find 790GB left after recording a 5GB programme (observed by Filezilla, puttying ls, or the Dream-Explorer plugin), and deleting the programme leaves you with only 795GB free space. You will get the missing 5B back after a restart.

I am speculating, those activities might have used codes that claim hdd disc space (not files, hidden or otherwise, somehow) as workspace, but fail to release the space properly after use.

[birdman]

which is invisible to 'ls-a', but is reclaimed by fsck or a restart.

If it's reclaimed by a restart then something has a (large) file open that has been deleted. The space won't be freed until the file is closed, which will happen on a restart (and in the meantime the process that has it open can still write to it and use more filespace).

You can find open-but-deleted files by running a find command on the box (which I'll work out if you're interested in running it).

[speedygonzalez]

If it's reclaimed by a restart then something has a (large) file open that has been deleted. The space won't be freed until the file is closed, which will happen on a restart (and in the meantime the process that has it open can still write to it and use more filespace).

You can find open-but-deleted files by running a find command on the box (which I'll work out if you're interested in running it).

I agree what you describe sounds like exactly what is happening... I was a unix system administrator decades ago, on a multiuser system that is considerably less powerful than any low-end phone today , so my command of unix/linux is extremely sparse and rusty, to say the least. You are very kind!