I wanted to jot this down before I forgot. I spent half a day trying to figure out why Plex wouldn't import my MP3 files into it's library when I could browse to them and open them on the Desktop.
The quickest solution revolves around user groups in Ubuntu.
H/T to stevenrobertlane of Ubuntuforums. It goes like this...
Type this command to edit the plex script.
sudo nano /etc/default/plexmediaserver
Replace the "plex" user account with your own account.
PLEX_MEDIA_SERVER_USER=your user name
control+O to save
sudo service plexmediaserver stop
add user to group:
sudo addgroup plex youruser
sudo addgroup youruser plex
sudo service plexmediaserver start