Persistent multi-user Docker on macOS

Need to make Docker on macOS available to any user who connects in remotely? It can be done!

First, be aware that docker is not designed to be securely shared among multiple users. Please assume that anyone who has access to docker is effectively equivalent to `root'.

This assumes that users will be interacting with docker via the command-line, rather than graphically. It also assumes that the environment is such that allows a single user to be automatically logged into via the GUI, but this is mostly out of laziness rather than an underlying technical restriction.

1. Choose an account that Docker Desktop will run as. I recommend creating a docker user, but it could be any account. This account does not need admin access.

2. Open Settings -> Users & Groups -> Login Options, and ensure that this user is automatically logged into.

3. Created a shared containers directory:

sudo mkdir -p /Users/Shared/Library/Containers
sudo chown docker:staff /Users/Shared/Library/Containers
sudo chmod -R 770 /Users/Shared/Library/Containers/

4. Login graphically with the account that will run Docker and start /Applications/Docker.app, answer any questions it might have.
5. Open Settings -> Users & Groups -> Login Items, and drag the Docker app to it.
6. Quit Docker Desktop via the menu item
7. Open Terminal and move your Docker data to a shared location that can be written to by other users:

mv ~/Library/Containers/com.docker.docker /Users/Shared/Library/Containers
chmod -R 770 /Users/Shared/Library/Containers/com.docker.docker
chmod -R +a "group:staff allow list,add_file,search,add_subdirectory,delete_child,readattr,writeattr,readextattr,writeextattr,readsecurity,file_inherit,directory_inherit" /Users/Shared/Library/Containers/com.docker.docker
chmod -R g+rw /Users/Shared/Library/Containers/com.docker.docker/Data

Then link your local Docker data to this shared source, and make sure that others can traverse into this folder to resolve the socket symlink:

ln -s /Users/Shared/Library/Containers/com.docker.docker ~/Library/Containers/com.docker.docker
chmod g+x ~/Library ~/Library/Containers

6. Restart /Applications/Docker.app to test
7. SSH into the host as another username, and run docker run mariadb to test.
8. Reboot host and reconnect via ssh to test (it may take a moment for Docker to start up)

This is the configuration we use for the #kernelcafe. Please add your improvements to the comments!