chmod operation not permited
This is an old revision of the document!
The problem lies with the web server, typically run as user ‘nobody’ or ‘apache’, not having sufficient write permissions to the app/etc/use_cache.ser file.
To fix this issue you will need to give ownership of the file to the user that your web server runs as.
chown nobody app/etc/user_cache.ser
Your web server should now have sufficient privileges to manage the cache.