Checks that all permissions are zero ('---------' in ls -l) - nobody but root can read,
        write, exec.

        Returns:
            bool: True if all permissions are zero ('---------')

def all_zero(self):
        """
        Checks that all permissions are zero ('---------' in ls -l) - nobody but root can read,
        write, exec.

        Returns:
            bool: True if all permissions are zero ('---------')
        """
        _PERM_NOTHING = '---'
        return all((
            self.perms_owner == _PERM_NOTHING,
            self.perms_group == _PERM_NOTHING,
            self.perms_other == _PERM_NOTHING,
        ))