I just downloaded and installed the latest Volumio on a PI.
I am trying to get it to find/play music from a NAS (technically an Ubuntu server running SMB).
First problem is that when SMB runs on Linux systems (both are Linux) the UID and GID of the server system are used on the client. So, my files are owned by UID 1001, GID 33 on the server, and show up that way on the PI. So on the PI, everything shows up as being owned by volumio:www-data.
I fixed this by added www-data to the group list of mpd (sudo usermod -a -G www-data).
But when I try to update music, I see this in the mpd.log
pi@volumio:/var/log/mpd$ grep -i permission ./mpd.log
Jan 16 23:03 : exclude_list: Failed to open /var/lib/mpd/music/NAS/BigServerMusic/CustomAlbums/.mpdignore: Permission denied
Jan 16 23:03 : exclude_list: Failed to open /var/lib/mpd/music/NAS/BigServerMusic/Various/.mpdignore: Permission denied
Jan 16 23:03 : exclude_list: Failed to open /var/lib/mpd/music/NAS/BigServerMusic/TheRest/.mpdignore: Permission denied
Jan 16 23:03 : exclude_list: Failed to open /var/lib/mpd/music/NAS/BigServerMusic/Billboard/.mpdignore: Permission denied
I created an .mpdignore on the server, and put some test lines in it.
On the PI, I can run a CAT of that under user MPD, and it reads the file fine.
So, I do not know why it thinks Permission is deneid.
In doing some additional research, it turns out that there is a mount option NOUNIX which turns off the use of the server side UID/GID and uses the ones from the mount.
So, I added
RO,NOUNIX,UID=pi,GID=www-data
and that got the mount to work and the library updated.