sessions and ubuntu

Today I discovered something, that Ubuntu (and Debian) do their own PHP sessions garbage collection but that sessions not prefixed by 'sess_' are ignored. So the CI default session name of 'ci_session' never gets deleted, on my ubuntu 18.04 box they can be found in /var/lib/php/sessions. The script /usr/lib/php/sessionclean which run every half hour does the cleaning and it was in there that I saw the prefix requirement.