Permission error when reading Django upload files

What you want to solve

-When I try to read the file uploaded by Django and use cron to perform some operation, a permission error occurs if the file cannot be read. -The authority when uploading a file is "600"

What I tried

As a prerequisite, it is an environment that requires administrator privileges when performing chmod.

os.py

import os
os.system('sudo shmod 644 path')

python os.py-> Switch permissions. Run with cron-> without switching permissions.

subprocess.py

import subprocess
subprocess.call('sudo shmod 644 path')

python subprocess.py-> Switch permissions. Run with cron-> without switching permissions.

solution

By writing "FILE_UPLOAD_PERMISSIONS = 0o644" in settings.py, the permission of the uploaded file became "644". It seems that the default is "600" in consideration of security, but it took time. ..

I don't know why it didn't switch in subprocess or os.system when I cron it.