The current workflow for starting the `linux-builder` on macOS is to run
`nix run nixpkgs#darwin.linux-builder`, which adds keys to the store and
then starts the builder.
Adding the keys requires user input (due to `sudo`) but the actual
builder should just stay running in the background somewhere.
I'd like to automate this process, but it's currently rather complex:
the first part of the script needs user input for `sudo`, and then
there's no signal when the process has finished starting up. The user
will need to see stdout/stderr during the first part, which makes it
challenging to capture it for the second part to determine when startup
has finished.
To fix this, I've split the `create-builder` script into an `add-keys`
script (interactive) and a `run-builder` script (background). These new
scripts are exposed in the `passthru` attributes for external users. The
`create-builder` script is now a simple call of `add-keys` and then
`run-builder`.
See: https://nixos.org/manual/nixpkgs/unstable/#sec-darwin-builder
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