The two i find really useful are:

(asdf:system-relative-pathname "dead-air" "_data/config.lisp")

Which will put it relative to the dead-air.asd file in your project.

OR to put it in your home directory:

(format nil "~a/.record_del.db" (uiop:getenv "HOME"))

Either of these should work on any OS type.

CC: @mdhughes@appdot.net