I tried to upgrade PLEX via webif. The upgrade process failed, as you can see below.
Reading package lists...
Building dependency tree...
Reading state information...
The following packages will be upgraded:
plexmediaserver
1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B/101 MB of archives.
After this operation, 2126 kB of additional disk space will be used.
(Reading database ... (Reading database ... 5%(Reading database ... 10%(Reading database ... 15%(Reading database ... 20%(Reading database ... 25%(Reading database ... 30%(Reading database ... 35%(Reading database ... 40%(Reading database ... 45%(Reading database ... 50%(Reading database ... 55%(Reading database ... 60%(Reading database ... 65%(Reading database ... 70%(Reading database ... 75%(Reading database ... 80%(Reading database ... 85%(Reading database ... 90%(Reading database ... 95%(Reading database ... 100%(Reading database ... 55748 files and directories currently installed.)
Preparing to unpack .../plexmediaserver_1.1.3.2700-6f64a8d_amd64.deb ...
Removed symlink /etc/systemd/system/multi-user.target.wants/plexmediaserver.service.
Unpacking plexmediaserver (1.1.3.2700-6f64a8d) over (1.0.3.2461-35f0caa) ...
Processing triggers for mime-support (3.58) ...
Processing triggers for systemd (215-17+deb8u4) ...
Setting up plexmediaserver (1.1.3.2700-6f64a8d) ...
Job for plexmediaserver.service failed. See 'systemctl status plexmediaserver.service' and 'journalctl -xn' for details.
dpkg: error processing package plexmediaserver (--configure):
subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
plexmediaserver
>>> *************** Error ***************
<<< *************************************OMV:~# systemctl status plexmediaserver.service
● plexmediaserver.service - Plex Media Server for Linux
Loaded: loaded (/lib/systemd/system/plexmediaserver.service; enabled)
Drop-In: /etc/systemd/system/plexmediaserver.service.d
└─db_folder.conf
Active: failed (Result: start-limit) since Do 2016-09-08 09:33:17 CEST; 10s ago
Sep 08 09:33:12 OMV systemd[1]: Failed to load environment files: No such file or directory
Sep 08 09:33:12 OMV systemd[1]: plexmediaserver.service failed to run 'start-pre' task: No such file or directory
Sep 08 09:33:12 OMV systemd[1]: Failed to start Plex Media Server for Linux.
Sep 08 09:33:12 OMV systemd[1]: Unit plexmediaserver.service entered failed state.
Sep 08 09:33:17 OMV systemd[1]: plexmediaserver.service start request repeated too quickly, refusing to start.
Sep 08 09:33:17 OMV systemd[1]: Failed to start Plex Media Server for Linux.
Sep 08 09:33:17 OMV systemd[1]: Unit plexmediaserver.service entered failed state.
The solution was to edit the db_folder.conf or to rename the environment file located in /etc/default/
The file was named plexmediaserver.prev instead of plexmediaserver
Now everything is working!