I installed Elisa music player from Flathub, but it refuses to see my Music partition, so I can't add any music to it's library unless I copy it to /home/my_user/.
Is there a way to give a Flatpak application permission to access non canonical addresses?
Aside from specifying it when compiling it...
You can do this via the command line. The specific command you need is (it may need to be run with sudo):
flatpak override <package_name_here> --filesystem=<path_here>If you have an odd path & it complains about an "unexpected filesystem suffix", just put the path part in quotes.
If you wish to remove access to a particular address, use "--nofilesystem":
flatpak override <package_name_here> --nofilesystem=<path_here>A more complete list of permissions/commands is found here - http://docs.flatpak.org/en/latest/sandbox-permissions.html
To add to the other answer, another solution that worked for me was installing Flatseal. It makes setting permissions super easy and also has the added benefit of making the existing permissions really clear. Here's what adding a directory to steam looks like in Flatseal:
I added the directory "MediaSSD" there, everything else is default.
Access normal files on the host, not including host os or system internals:
ApplicationID is shown using command:
sudo flatpak list