I have set up a custom php.ini for a dev site (the production site will eventually be on the same server) - it sets the session.save path to a directory specific to the site.
You can see the result at https://dev.permaculture.org.nz/info1.php (will be moved or removed once problem is solved).
However, I am still getting permission denied errors for session files attempting to be written to /var/lib/php/session Firstly, I can't understand why the "Master" and "local" values aren't the other way round. Secondly, I've no idea where the "local" value for session.save.path is coming from: I have located three php.ini files on the server: /etc/php.ini /opt/remi/php56/root/etc/php.ini /var/www/dev.permaculture.org.nz/etc/php.ini
The second uses /tmp, and I've also set the first to /tmp The third specifies /var/www/dev.permaculture.org.nz/php/session - which is, as required, owned by the process owner.
The errors are causing a fatal error for phpmyadmin.