If you get the Could not determine temp directory, please specify a cache_dir manually error in Magento 2, the shop is not able to access your PHP temporary folder. To solve this problem, simply add sys_temp_dir to your php.ini file and set it to an accessible path.
This could look like this:
Magento 2 error: Could not determine temp directory, please specify a cache_dir manually
You want or need help implementing this solution? Maybe you did not find what you were looking for? Contact me and I will assist you with whatever Magento problem troubles you!