chmod operation not permited
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The Magento system needs write permissions to a specific file in the
app/etc directory to make use of the Admin → System → Cache management. 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.