That's not something to be run from the prompt... that is part of the docker script (the user was telling you that you shouldn't have to worry about such as it is ALREADY there). If your system doesn't like 1000 change it in that file roughly around line 52 I believe.

Your problem was not ...

You may not need to, the build script creates the dvr user and group and then sets the permissions. So after creating your mount point folders modify the docker run with the new paths, and run it again.
The script contains: # Create default user and group & patch up permissions
RUN addgroup -g ...

The part listed below initially tripped me up on my Unraid setup.

-v /path/to/hdhomerun/tempdata:/dvrdata \
-v /path/to/hdhomerun/recordings:/dvrrec \

You will need to change the "/path/to/hdhomerun/recordings" to a path where you want the recordings to be stored. Same with the Tempdata.

For ...

I don't have a clue what I am doing. But I am trying to get your HDHomeRun engine docker to run under CoreELEC running on one of my inexpensive Android TV boxes.

I installed Docker onto my CoreELEC box. Using Putty, I pasted your command into the putty command window >>
docker run -d --name dvr ...

Major update to Network Monitor, now at version 5.0. Greatly improved logging, you will want this version!

See the previous post here...
http://www.silicondust.com/forum2/viewtopic.php?f=41&t=12216&start=60#p90155

I downloaded and installed your Network Monitor ver. 5. When I run SD.exe, it ...