In another issue (sabre-io/Baikal#427) we discussed if there should be an own directory/data/ for persistent files, which differ from each installation, like a user database.

I thought it would be better to add/var/data/ for such files. But then somebody explained me that/var/ is just for temporary installation-based files like log files, cache files, etc.

The Linux Filesystem Hierarchy also use the/var/ directory only for such temporary installation-based files and not for persistent installation-based files.

Currently the fileapp/config/parameters.yml, which differs from each installation, is inapp/config/ and not in something like/var/ or/data/.

I think the Symfony documentation should contain some tips or Best Practices how you should storage persistent installation-based files. Theparameters.yml file is a good example because it differs from each installation but is not temporary like log files or cache files.