@trireme
You are in the Linux section of the forums.
On linux, the metadata is stored in /var/lib/plexmediaserver
On QNAP, the logs can be found in /share/*/.qpkg/PlexMediaServer/Library/Plex Media Server/Logs" As you discovered.
For future reference, You may create the “PlexData” shared folder.
You may read further about it here.
In the future, please be mindful of where you post.
