I just happened to build a Mint box to play with a week ago, and one of the things I immediately did was install Serviio. To have Serviio start up automatically, click the menu, and under Preferences you will find Startup Applications. Open that, then click Add. Enter Serviio for the name, and in the command line enter the path to the serviio.sh file. It will vary depending on where you installed Serviio. On my box it's /opt/serviio-1.9.1/bin/serviio.sh. Then click Save. The next reboot it will start automatically.
Where is your media located? On a local hard drive or on a network share somewhere? Since I built my box with leftover parts, the hard drive is very small, so I'm using media on another computer. However, I cannot get a UNC path to work. It kept adding my home path in front of the UNC, which of course isn't a valid path. So instead, I mounted the remote share locations to the Mint install under the /mnt folder. I haven't had any issue using these file paths, as they appear as a local path, not something on the network.
If the path isn't being saved, I'm wondering if you have a permissions issue with your media location.
Dan
LG NANO85 4K TV, Samsung JU7100 4K TV, Sony BDP-S3500, Sharp 4K Roku TV, Insignia Roku TV, Roku Ultra, Premiere and Stick, Nvidia Shield, Yamaha RX-V583 AVR.
Primary server: Intel i5-6400, 16 gig ram, Windows 10 Pro, 22 TB hard drive space | Test server Windows 10 Pro, AMD Phenom II X4 965, 8 gig ram
HOWTO: Enable debug logging HOWTO: Identify media file contents