UPDATE: added info on the bottom regarding problem with transcoding and conversion (while using subtitles for example)

About two weeks ago, DSM 7 came out and we were all so eager to upgrade (who could), but there is also an important note here to take away from this update.

Synology was hard at work to bring us many new features, some visible, some not so much as well as some new and exciting apps and services (C2 new lineup), but also, they made some changes when it comes to permissions and how 3rd party apps work with new DSM OS.

With DSM 7 a lot of apps got axed from being supported by the new OS, and those that will continue to work will demand the developers to adapt to the new security rules. One of those rules is that the apps can no longer run as root on the system. This leads up to this article.

PLEX vs DSM 7

While Plex team was aware of this long before the final release was pushed, there is still a process that needs to be respected in order to continue using Plex on DSM 7. In the following tutorial, I will show and demonstrate a short explanation also accessible on the official Plex.tv forums.

ChuckPa (member of the official Plex team) is the one taking credit for all the help and support that he has given all the users struggling to get this off the ground as well as tweaking the Plex install to be compatible with DSM 7.

This tutorial will focus on a bare-metal installation (not Docker), as that's the one that needs attention.

All the needed information are accessible here:

Synology - DSM 7 Release - Plex Installation Issues
This is the FULLEST POSSIBLE DETAIL instruction. Most do not need it. More info here: @fishbert The way this works – ( This is why I loathe DSM 7) Uninstall Plex for DSM 6 Upgrade to DSM 7 Reboot DSM 7 - it fixes itself at next reboot – NO clue why. NOW we can start the installation proc…
IMPORTANT NOTE: Before you rush over and install DSM 7 over your current DSM 6 with Plex already running, DO NOT do that. Read the whole tutorial and then proceed with the update.

PLEX Upgrade process

So before you start with the Plex upgrade on your DSM 6, this tutorial will start with a fresh install of Plex on the active DSM 6 instance, add a new library, just to show that all will be well with the process IF YOU FOLLOW IT to the letter.

STEP01 - running Plex on DSM 6

Use only Plex.tv versions in this tutorial

So if you install Plex on your DSM 6 setup, as always, use the Plex.tv version NOT the Package Center one!

Manual install process wizard

Open Package Center and use the Manual install button in the upper right corner. Follow the wizard to the end and install Plex.

Plex installed on the DSM 6 OS

Once you have Plex installed, access it and add some libraries to it (unless you already have this up and running).

Plex running under DSM 6 with some libraries

STEP02 - Deinstall Plex from DSM 6 (DO NOT SKIP!)

This is the step that most of you will want to start off. So you already have Plex running and you want to upgrade to DSM 7 but also have Plex up and running under it without any problems.

First, we need to uninstall it! So go to Package Center and uninstall your current working version of Plex (under DSM 6).

Uninstall Plex from DSM 6
Once uninstalled, your Plex server will no longer show any content

STEP03 - upgrade DSM 6 to DSM 7

Now that you have uninstalled Plex from your NAS, it is time to upgrade to DSM 7.

Install DSM 7 using the manual process via Control Panel
Leave your DSM 7 to install
Finishing up
Upgrade completed, DSM 7 running

STEP04 - additional reboot (DO NOT SKIP)

Even though the DSM install has rebooted the NAS, the Plex team suggests doing another reboot of the NAS before moving forward. Do it.

STEP05 - Installing Plex on DSM 7 (take 1)

Now we are ready to install Plex so head over to Plex.tv again and download the DSM 7 compatible Plex installation.

Make sure to use the dropdown and select DSM 7!

Before running the install, you can go to File Station to make sure that the Plex folder (where all the metadata and app files are) is still there and has some data in it.

Plex install folder still here after update to DSM 7

Now, open up Package Center and use the manual install to load up the DSM 7 Plex version that you have just downloaded.

Begin loading up the new DSM 7 compatible version of Plex
Select normal installation
You can change or not the location of logs (up to you)
Ready to install Plex, hit "done"
Almost immediately, you will get an error (THIS IS FINE!)

You will get almost immediately an error, and that is fine, no need to panic. The reason is that, as said before, Synology has changed permission rules, and the new version of Plex uses internal account and not local one that will have as a result that the new PlexMediaServer account does not have access to the existing Plex shared folder (the one that holds metadata and application settings).

STEP06 - setting permissions

Now that we are certain that Plex installer has a problem with permissions, we will need to go to Control Panel > Shared folders, and change the permissions for the Plex folder.

Edit the Plex folder and jump over to the Permission tab
Change Permissions view to System internal users

Once you are on the Permissions tab, make sure to change the dropdown menu from Local users to System internal user.

Locate the PlexMediaServer user and customize it

The account in question is PlexMediaServer. Click its Custom column, and add Full Control permissions.

Make sure to add full control permission!

Select Administration, Read, and Write permission for the user and click Done.

Once you have returned to the previous screen YOU MUST SELECT the Apply to this folder, sub-folders and files check box!

DO NOT FORGET THIS CHECKBOX!

After you have selected the checkbox, click Save, and wait. Depending on the size of your folder and the number of files this can take some time. Be patient.

One more final save needed

Finally, click Save one more time, and you are done.

STEP07 - Installing Plex on DSM 7 (take 2)

Repeat the Plex install process once again, and you should have a different result this time around.

Permission look good, time to install

If you get this image, it means you have done it all correctly! Well done. Your Plex instance should be accessible on the old URL as before, and the only thing needed might be that you will need to give PlexMediaServer account permissions to your library folders.

Plex registered as running under DSM 7
Looking good!

STEP08 - adding permission to your library folders

In order for your Plex instance to work as expected, the Plex account needs to have permissions on all the folders that are presenting data to your instance as libraries.

So head over to Control Panel again and in Shared folders view, select the folder(s) needed and give them R/W permissions.

NOTE: Read permissions should be enough (I use it that way), but the Plex team suggested R/W, so I did as well.
Giving R/W permissions to your media folders

Problems with transcoding

In case you start to watch something with subtitles for example and get the following error there is a solution for it.

The problem is the metadata. Use your library menu and open Manage Library > Refresh All Metadata.

I know that permission should have been migrated from the old Plex folder, but in case you get this error, just redownload the new meta and the problem will go away. Obviously running without any subs, there will be no problem.

Conclusion

As you can see the process is straight forward, not much that can go wrong if you stick to the "script". If you have already rushed and updated to DSM 7 without uninstalling Plex beforehand, you will have to consult the Plex forums for more details and potentially some help on the matter.

As said before, uninstalling Plex before DSM 7 update is crucial, and if you do it that way you will be up and running in no time. Good luck!

Feel free to comment and share your experience with the rest of us!