I noticed this problem on a system that has the same nfs device mounted in multiple locations. In this case linux_ro_checker complained about one of the *other* mountpoints referencing the same device, rather than the one that was passed in the dir_list argument. The problem code is in this code where the first loop can select paths that are not members of dir_list, since is only accounts for a single path per device: ro_devs = {} for x in ro_filesystems: try: ro_devs[os.stat(x).st_dev] = x except OSError: pass ro_filesystems.clear() for x in set(dir_list): try: dev = os.stat(x).st_dev except OSError: pass else: try: ro_filesystems.add(ro_devs[dev]) except KeyError: pass