Plex cannot write to the database.
Verify permissions for the Plex Data Folder.
See Linux Tips: Migration from another OS to Linux.
Specifically (adjusting if needed for running in an LXC):
- Change the ownership of the files to the Plex user on the Linux host.
# chown -R plex:plex "/var/lib/plexmediaserver"
- Make certain Linux file permissions are set correctly
# find /var/lib/plexmediaserver -type d -exec chmod 755 {} \;
# find /var/lib/plexmediaserver -type f -exec chmod 644 {} \;