So - one of the things I love most about the synology is its docker support - I'm now running heaps of different docker containers.
But every time I run into the same problem - I want to run the container as particular user, but I have to specify the gid and uid.
Whcih normally ends up with me...
First, you need to SSH into your NAS.
When you are in your NAS with the user you want the ID for, just type id and hit Enter.
Now you'll get something like this:
uid=1031(your_nas_user) gid=100(users) groups=100(users), 101(administrators)
From that, you can read your UID is 1031, user group...