sudo chown -v $USER /mnt/ds423 sudo chown -v $USER /mnt/ds423/Backups
that was successful. but trying to list the contents of /mnt/ds423/Backups still results in a permission denied error
Hmm… What happens if you do the following ?
sudo ls -l /mnt/ds423
sudo ls -l /mnt/ds423/Backups
`sysop@PC:~$ sudo ls -l /mnt/ds423
total 0
drwxrwxrwx 1 sysop root 66 Mar 22 08:10 Backups
drwxrwxrwx 1 root root 28 Jan 21 2024 data
drwxrwxrwx 1 root root 54 Apr 25 2024 ‘Media files’
sysop@PC:~$ sudo ls -l /mnt/ds423/Backups
total 0
drwxrwxrwx 1 1027 users 2766 Jul 5 05:34 HomeAssistant
drwxrwxrwx 1 root root 72 Mar 22 08:10 ‘#recycle’
drwxrwxrwx 1 1027 users 20 Jan 21 2024 Ubuntu`
what does total 0 mean?
also, considering the first entry in each line, i get the impression that everyone is allowed to read and write. so why do i get a permission denied error when i try to do the same without sudo?
Hi again, @hmiersch 
Well, at least you now see the subdirectories of the “Backups” directory (which is a NFS mountpoint of a directory that is exported, also via NFS, by your Synology NAS). May I ask what do you see when you type the following command (assuming the output does not contain something that you wish to keep private)?
sudo ls -l /mnt/ds423/Backups/Ubuntu
2 directories appear, harry and sysop, which is exactly what i would expect. listing harry shows me the backup files i would expect to see. the last one is from the 3rd of june, which is the day the problem appeared.
so, is it time to try deja dup again? what should i enter s the location?
Hi again, @hmiersch
Unfortunately, as I’ve written in a previous reply in this topic, I don’t have experience with either “Déjà Dup Backups” or with “Synology NAS”. Reading the accepted answer at https://askubuntu.com/questions/1387485/restore-from-deja-dup-backup-on-samba-share-a-synology-nas for a slightly similar scenario, I would say that MAYBE you can try, in “Déjà Dup”, to do a restore from a Local Folder (instead of selecting a Network Server) and then choose the /mnt/ds423/Backups/Ubuntu/harry as the directory where the backups are stored. IF you then get a permissions error again, by doing that, it’s possible that you may have to launch again “Déjà Dup”, but this time as “root”, to do the restore, by exiting “Déjà Dup” and then launching it with the command sudo deja-dup HOWEVER, I do NOT know if that will work well AND I also do NOT know if using “Déjà Dup” in that way (as the “root” user), for doing restores, could produce any undesirable side effects 
Maybe someone else here in this Community can help you better, with that part?