Newbie problem with first "compare"

[Wellenreiter27]

Hi,
I've watched the tutorial videos but my first try to compare my internal HDD to an external one failed:
Cannot set directory locks for the following folders:
Cannot write file "/media/db/sync.ffs_lock".
EACCES: Keine Berechtigung [open]

Maybe I need to run this with administrator permissions? But I'm on Linux and I don't see the context menu entry "run as administrator" shown in the tutorial.
I would definitely want to sync "hidden" system files sooner or later (like my browser or mail client profile file), so I would like to know how to run FFS as admin on linux GUI anyway.

Maybe I should unmount the filesystem in question? It's my home folder which is on a separate HDD, so I could run my OS anyway, and FFS has installed it's program data outside home, so it should work.
But I can't imagine that's really necessary because how would people with just one hard drive do backups then?

Please explain what I'm doing wrong.
I want to
a) compare the two HDDs
b) later create different backup profiles, some of which include system folders (see above)

Thanks a lot!

[Plerry]

The problem does not seem to be a lack of admin privileges, but rather a lack of write permissions to the mentioned folder (/media/db/) for the user under which user credentials the FreeFileSync sync is being run.

[Wellenreiter27]

The problem does not seem to be a lack of admin privileges, but rather a lack of write permissions to the mentioned folder (/media/db/) for the user under which user credentials the FreeFileSync sync is being run.

Thank you. The problem disappeared, but I don't know why.
However, now many files are marked as not existing on the second volume that - in my opinion - definitely exist.
I can see files with identical name, date and file size when browsing the volume; the file path is identical too up to the root directory, which is because one is my home HDD and the other an external SSD.

The files should be identical too because the two volumes are clones.
I cloned my home drive in 2019, so if a file was created in 2012 and has last access in 2017, plus has identical name and file size, I think it plausible it is a clone.
In my opinion, FreeFileSync should recognize those files as existing, but it does not.

I don't know what would happen if I pressed "sync" anyway. Would I get a message that the files already exist, or would I end up with loads of duplicates (like documents or cooking recipes)?

[xCSxXenon]

Post a screenshot of your FFS window after running a compare so we can see the paths

[Plerry]

Likely the same issue as here.

[xCSxXenon]

It's always a path issue

[Wellenreiter27]

Likely the same issue as here.

@Plerry
[mention]Plerry[/mention]
@xCSxXenon
[mention]xCSxXenon[/mention]

Sorry for taking so long to reply.
I'm pretty sure that's the issue!
I have not tried yet because
1) I didn't have much time (starting a job)
2) using the clone, I somehow managed to mess up my user profile, so I'd like to find a way to prevent that from happening again before I re-connect the clone and try a new compare (to reproduce the problem/see the path I used/post a screenshot)
If I remember correctly, the volumes I want to compare had root/user/home versus root/media/user/home and I wanted to compare all of their content (whole tree structure).

I thought FreeFileSync could do that. I didn't know/read there was a path problem with subfolders.
Though the thread you linked to names a solution, this will be difficult to do for a whole hard disk drive.
Is there a way to compare/backup a whole HDD with FFS? Does this require setting up loads of single jobs and running them as a script?
However, this wouldn't be helpful if I created a new subfolder but forgot to create a subfolder for it on the backup device, would it, if FFS does not create a tree structure on its own?

Thank you for your help!