[Nix-dev] Changing the list of upstream systemd services that is running

[Roger Qiu]

Hello all,

On the boot/systemd.nix, there's a list defining all the upstream 
systemd units to activate:

https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/system/boot/systemd.nix#L27-L165

I would like to override some of the values in this list inside my 
configuration.nix. The only option I can see is 
"systemd.additionalUpstreamSystemUnits" which doesn't remove any units 
from the upstream units.

I found that I can use `builtins.filter function list` to filter out 
specific values.

But how do I actually specify a override for this boot/systemd.nix file. 
I've previously asked with regards to packages, but this is a system 
configuration, not a package.

I want to remove the systemd-machined service.

Thanks,
Roger