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Step 2: Setting up a restricted Docker user and group then obtaining IDs

Important or Recent Updates
Historic UpdatesDate
First version of the setup01/08/2021
Added a note regarding the /data share
Cleaned up the guide with LanguageTool
General formatting updates
14/03/2022
Swapped out Putty for Terminal (Powershell)01/04/2023
Further improvement to user and now group creation (thanks kalmiya)23/09/2023
Historic Updates

It is good practice to set up a unique user and group with limited share and application access for your containers. We won’t ever be using this user to log into DSM it is purely for Docker.

Creating a Group

First up we will create a specific docker group that our docker user will belong, this allows us to segregate the permissions from the normal ‘users’ group from Docker. This is useful as you may have other users on your NAS that you don’t want to have access to certain folders by default.

Navigate into the DSM control panel and open up ‘User & Group’ then click on Group and Create

In the screen that appears we will name the group ‘dockergroup’ (imaginative right) and you can give it a description if you wish

Click Next, we won’t be adding any users to the group yet (that’s the next section)

On the next screen we will grant the Group Read/Write permissions to the ‘data’ and ‘docker’ shares we created in the previous guide. Click Next.

On the next screen you do not need to amend the groups Quotas so click Next

We will now Deny all access to inbuilt apps as this group and any users within it do not need access.

On the final settings screen we don’t need to set any speed limits

On the final screen click Done.

Creating a User

You can call the user whatever you want, I just kept mine simple and created one called ‘dockerlimited’

It’s also a good idea to generate a very strong random password for the user, while it will be a very limited account you don’t want to give it an easy to guess password. You will never need this password for what we are doing.

Next we are going to add this new user to the ‘dockergroup’ we just created as we don’t want it having any sort of admin access.

On the next screen you should see that the user already has Read/Write access to the two shares and no others.

*Please note if you are not following one of the media setup guides you will not have the /data share so don’t worry if it is missing.

Nothing to change on the User quota settings just click ‘Next’

You will see that our User already has restricted access to apps

Again we don’t need to set any speed limits for this user so click on ‘Next’

The final screen will just confirm your settings make sure the correct shares are in the ‘Writeable’ list, click on ‘Done’ and your user will be created.


Obtaining the new UID (User ID) & GID (Group ID)

Now we need to obtain the IDs for the new dockerlimited user and dockergroup These are used to pass file permissions through to our containers. They can also be known as PUID and PGID.

You will need to SSH into your Diskstation using ‘Terminal’ which is built in to modern versions of Windows, Linux, or Mac.

Go back into the Control Panel again and enable SSH within the Terminal & SNMP section.

Open up ‘Terminal’

Now type ssh then your main admin account username @ your NAS IP Address and hit Enter (Not the docker user)

Bash
ssh drfrankenstein@192.168.0.101

You will then be asked to enter the password for the user you used, you can either type this or right click in the window to paste (you won’t see it paste the info) then press enter.

Once logged in type the below replacing ‘dockerlimited’ with the name of the user you created if you changed it.

Bash
id dockerlimited

You will now see a similar output as the below…

Bash
uid=1027(dockerlimited) gid=100(users)groups=100(users),65537(dockergroup)

Let’s break this down!

uid=1027(dockerlimited) This is our UID write this down!

gid=100(users)groups=100(users) While this is a GID it is not the one we are interested in as it is for the standard users group so ignore this.

65537(dockergroup)This is our actual GID that we want to use for our containers so write this down as your GID.

You have now successfully set up your limited access user and obtained its IDs for use in Docker. Keep note of these somewhere as you will use them a lot with Docker.

You can now disable the SSH service as we won’t be using it.

You can now go back to the guide you were following.


Permission Fixes – only use if you have issues

If you followed one of the guides on this site you can’t see a folder or files inside a container it is likely a permissions issue.

The commands below need to be entered via SSH, so just like in the guide above log into the NAS with your main account user, you will not see an output after each command.

The fix does the following:

  • Make the named user and group, owners of all files and folders in the named paths
  • Change file and folder permissions to 775 (rwxrwxr-x)

Permission fix 1 – For anyone who followed this guide after the 23rd September 2023 and have both the dockerlimited and dockergroup in place (4 digit UID & 5 digit GID)

Bash
sudo chown -R dockerlimited:dockergroup /volume1/docker /volume1/data

Bash
sudo chmod -R a=,a+rX,u+w,g+w /volume1/docker /volume1/data

Permission fix 2 – For anyone who followed this guide before the 23rd September 2023 and just have the dockerlimited and normal user group in place (4 digit UID & 3 digit GID)

Bash
sudo chown -R dockerlimited:users /volume1/docker /volume1/data

Bash
sudo chmod -R a=,a+rX,u+w,g+w /volume1/docker /volume1/data

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60 Comments

  1. Robert Robert

    Hi, I ran the following commands to fix user/group ownership after I disabled the admin account and reorganized my files for Docker earlier today, in order set the permissions of /data/ and /docker/ to be owned by the dockerlimited and dockergroup user/group, although nothing was broken (I should have taken the hint):

    sudo chown -R dockerlimited:dockergroup /volume1/docker /volume1/data
    sudo chmod -R a=,a+rX,u+w,g+w /volume1/docker /volume1/data

    After this I got kicked out of the Synology WebUI and logging in as my normal “robert” administrator user returns a “You are not authorized to use this service.” message that is different from when I log in with “admin”.

    Similarly, SMB/Samba no longer functions, however everything running in a docker container using those directories still functions. I don’t understand how running a chown against just the /docker and /data directories would have messed with anything needed to log in my local admin account (not named “admin”). Any ideas?

    • Dr_Frankenstein Dr_Frankenstein

      Hey, it should not have this impact at all, as it is purely adding the permissions of the dockerlimited and dockergroup to the files and folders under those two shares.

      It’s going to be a little limited on how I can help here. Your ‘Robert’ account is your main administrator user.. You mentioned disabling the ‘admin’ user before doing this was this originally enabled and were you using it to use DSM? Are you sure Robert is part of the administrators group did you manage to somehow remove that?. Something else must being going on with the system as these two shares like any other shares should not impact the day to day running of DSM itself.

  2. Why do you create both a group and a user for docker? If you would only create the dockerlimited user, then chown the docker directory to dockerlimited:users and use the user id of the dockerlimited user as UID for docker images that support it, that would work as well.

    When Linux is testing if a user has permissions on a file, it will consider user-based ownership _before_ group-based ownership. So if a process/container is running as the dockerlimited user and the directory is owned by that user, the group ownership doesn’t matter at all.

    What is the advantage of having the dockergroup?

    • Dr_Frankenstein Dr_Frankenstein

      Hey so it’s funny you mention this as I used to have the guide exactly as you described, then I received another comment suggesting to also add the group, so to be honest I am at odds as to which to actually roll with lol.

  3. Martijn Martijn

    many many thanks for all the info on your website! Really approciate!

    I created user “Kodi” in the steps but at the end I got this error:

    Unable to connect to database:
    SQLSTATE[HY000] [1045] Access denied for user ‘Kodi’@’172.20.0.1’ (using password: YES

    What am I doing wrong?

    Many thanks,
    Martijn

  4. J J

    Thanks for wasting several hours of my life. The “permissions fix” is nonsense and doesn’t fix anything. The permissions should have been corrected in the config. Radarr/sonnar/prowlarr, cannot set root folder for any of them after following all steps. Guess I’ll try another site that claims a good docker setup in the hope that there will be more complete directions that actually have good permission configs.

    • Dr_Frankenstein Dr_Frankenstein

      Hey J

      Not sure what would have gone wrong for you to have issues where even the commands did not work. First time getting this type of feedback sorry you feel that way, always happy to help out via here in comments, email and Discord. My guides are generally considered pretty decent but can’t win them all.

      Thanks Dr F

      • J J

        That was more negative than it should have been, apologies, was frustrated. I am going to review and try again.

        • Dr_Frankenstein Dr_Frankenstein

          All good I understand that some of this is a massive time sink and can be frustrating when it doesn’t work first time… I have abandoned stuff myself due to a bug and come back to fix with a fresh set of eyes, any issues just shout as this should get you a fully running media and download stack. Then you start on the next time sink which is customising all the settings!

  5. CJ Kappa CJ Kappa

    If I never chose to move my media to the data folder in stage 1 (I’ll take the chance of temporarily duplicate data rather than risk messing up my Plex collections and other Plex data in the move), what are the settings I’ll need to do for creating a Docker User Group in this stage?

    Thanks in advance.

    • Dr_Frankenstein Dr_Frankenstein

      Hey, as long as you grant the Docker user and group permissions to the existing folders then you should be good. When you do any mounts make sure you keep them consistent e.g /volume1/mymovies:/mymovies just keeps things easy.

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