ValueError: The file mnist/train does not exist or permission denied!

[lws6885]

Error:
/opt/anaconda3/envs/demo/bin/python3.7 /home/kaikai/warehouse/project/tinyms/demo.py
[WARNING] ME(125322:139821835126592,MainProcess):2021-04-05-15:30:33.756.399 [mindspore/ops/operations/array_ops.py:2302] WARN_DEPRECATED: The usage of Pack is deprecated. Please use Stack.
WARNING: 'ControlDepend' is deprecated from version 1.1 and will be removed in a future version, use 'Depend' instead.
Dataset already exists.*
Traceback (most recent call last):
File "/home/kaikai/warehouse/project/tinyms/demo.py", line 24, in
train_dataset = MindDataset(os.path.join(mnist_path, 'train'), shuffle=True)
File "/opt/anaconda3/envs/demo/lib/python3.7/site-packages/mindspore/dataset/engine/validators.py", line 351, in new_method
check_file(dataset_file)
File "/opt/anaconda3/envs/demo/lib/python3.7/site-packages/mindspore/dataset/core/validator_helpers.py", line 277, in check_file
raise ValueError("The file {} does not exist or permission denied!".format(dataset_file))
ValueError: The file mnist/train does not exist or permission denied!

Error occured in "train_dataset = MindDataset(os.path.join(mnist_path, 'train'), shuffle=True)". My mnist_path is '{my root project}/mnist'.

How do i fix it?