Plex will not find videos within the folder that I associate with a library

[ChuckPa]

This is normal Linux-Gnome behavior when the automounter is mounting USB or NTFS drives under /media/<username>. Nothing will be visible to user plex.

Your options are:

1. Change the username Plex runs as
2. Change the mount point (make an entry in /etc/fstab)

To change the username Plex runs as, see here -

Linux Tips

Customizing your Plex configuration on systemd based systems This information is intended for those systems where cat /proc/1/comm returns systemd. On systems which use Systemd (Ubuntu 16+, Fedora 26+, Centos 7+, Debian 8+,) you create this customization file which SystemD reads prior to launching PMS. This file is independent of the default configuration and service control mechanisms in /lib/systemd/system/plexmediaserver.service. Your customization override is preserved across updates, un…

To gain control of the USB / NTFS drives and how they mount, see here -

Linux Tips

Using other hard drives (Windows or Linux) with PMS This How-To is written to help with Internal and External drives. It also is written to demonstrate how to cope with NTFS and EXT4 formatted drives. By logical extension, any format supported by Linux can be handled using the technique shown here. In all cases, the goal is to give user plex permission to read your media files which Linux doesn’t allow by default due to its strict security model. We will walk through the steps needed …