Follow up: obviously, I know nothing of gninx, the webserver that volumio uses. This is baked-in behavior for nginx**. It seems that Nginx wraps each virtual host in a meta-configuration that rewrites php.ini and some other configuration files. You need to edit nginx’s configuration files to do it. This is somewhat complicated by the fact that said configuration has already been customized for Volumio.
[size=85]**Officially pronounced ‘engine-x’ but I prefer the phonetic pronunciation, thank you. Engine X sounds like some crappy nu-metal band from the 90’s. ng-inx (one syllable, leading with the ‘ng’ phoneme so unjustly condemned to only ending words) rolls off the tongue musically.[/size]
EDIT: this might be an FPM behavior, actually. In any case, the way I found to make changes stick: it’s hackish, but it works: edit /etc/php5/fpm/conf.d/20-sqlite3.ini and put next PHP load directives in there. It gets loaded last, or near last, so directives in that file supersede php.ini and other files that get overwritten. Once you’ve mad your edits, type:
service php5-fpm restart
to restart PHP with your changes.