Re: File permission confusion [Debian 9.1 with MATE]
> What *prevents* a user from destroying his own backup files?
Having multiple backups. Some with long intervals between them and some
on write-once media.
Of course the user must recover from mental incapacity often enough to
produce and verify good backups and to restore spoiled files before doing
the next backups. Insofar "chmod -w" and "chattr +i" can help to keep the
overall user performance sufficient for the purpose.
Have a nice day :)