Systemd startup configuration files use the option PrivateTmp to prevent processes from sharing tmp folder.
When this option is set to true, a private tmp folder is created for each process. So if a process attempts to write to the /tmp or /var/tmp folder, the changes will be made only to the process's private tmp folder and not the system wide /tmp and /var/tmp folders. This option may be set to true in the system startup file for Apache web server on Ubuntu and Linux Mint. For example in: /lib/systemd/system/apache2.service