I have a time machine backup `/Volumes/MyTimeMachine/Backups.backupdb/MyMachine`. Exactly as Apple creates a `Latest` symlink pointing toward the latest snapshot, I would like to create symlinks toward other snapshots. But I get permission denied when I do, in terminal,
    
    % cd /Volumes/MyTimeMachine/Backups.backupdb/MyMachine
    % ln -s 2018-06-11-xxxx my_link

where `2018-06-11-xxxx` would be one of  the snapshot. I even get permission denied with sudo!! Is there something wrong with my Time Machine disk or is that normal on MacOS High Sierra?