I need to create a kind of "backup operator" account, which can read all the files on a system for copying to a backup system without the permission to modify any of them, including those belong to
root account seems to be the only one capable of doing that, but then the
root account is not prevented from running anything it wants. The other option I can think of is placing an account in a group that as read rights and make that account a member of every users group. The basic
rwx permissions in Linux don't seem created for that.
Does Linux have something more sophisticated for such a purpose such as something ACLs might offer?
The permissions are for a user who logs in from a remote backup server and backups up all the files to the remote server. If the backup server gets compromised that account should not be able to log into the server being backed up and do some damage. Accounts on the backed up server should also not be able to log into the backup server and do some damage if gets compromised.