if not is_linux():
    raise ValueError('Currently NCCL is only supported on Linux platform.')

  if 'TF_NCCL_VERSION' in environ_cp:
    return

  ask_nccl_version = (
      'Please specify the locally installed NCCL version you want to use. '
      '[Leave empty to use http://github.com/nvidia/nccl]: ')
  tf_nccl_version = get_from_env_or_user_or_default(environ_cp,