xpost from plex.tv forums...
I'm writing this to document the steps i took to resolve an issue i had with PMS where no matter what i did the service wouldn't start. I somehow borked my PMS installation and decided i needed to reinstall it and start fresh. I had installed from the plugins menu so i uninstalled from there. proceeded to purge all pms assets in the command line and rebooted. I reinstalled pms from the gui again and this time the server wouldnt start.
I went through multiple uninstalls and reinstalls, changed the pms database directory multiple times and still no go. so then i reinstalled from a .deb in the command line. no matter what i did the plexmediaservice would show a red dot in the OMV gui services tab and the command line would output "it seems the service isnt running".
welp time to start over completely and totally reinstall OMV. so i reinstalled OMV went through all of the updates, installed the new kernal from the omv-extras repo and then i reinstalled plex. rebooted. I went to the services tab and the plexmediaservice still had a red dot! reinstalled OMV multiple times using default kernel, changing database folders. I searched all over the forums, here and omv.org, tried all manner of purge this, grep that, apt update/upgrade ect. I tried changing ownership of the database folder to root:nogroup, then to plex:users, then to fuck:this. nothing worked. the errors still plagued me.
reading a forum late at night i read an off-comment about manually creating the plex user. I tried to create the plex user but it wasn't showing up in the gui. I read that this was because when you install plex it creates a user "silently". I uninstalled plex, rebooted, created the plex user manually and gave it access to all the shares. When i reinstalled plex lo and behold, works like a charm and somewhat faster than before!
sorry for the rambling, but i wanted to give people the solution that worked for me after days of searching. maybe i can help save people time.
TL;DR
if you're at wits end, try uninstalling plex, create a user with the name "plex" manually and give it access to all your shares and then reinstall plex.