Using overlays to change nixos module behaviour

[netixx]

Issue description

Hello,

I have been reading about overlays, and I wonder if it is possible to use them to override behaviour of one or more nixos modules. The only examples I have seen with overlays concerned packages (and not nixos modules).

Say for example, I wanted to implement this PR as an overlay because It is specific to my setup, could it be done with overlays ?

In more details, how could I change nixos/modules/tasks/network-interfaces-systemd.nix code (without having to rebase patches on top of nixpks) ? Could overlays do that ?

Thank you

[Moredread]

I'm not sure that you can do this with overlays, but you can disable a config module and import your own variant.

In your case you could copy nixos/modules/tasks/network-interfaces-systemd.nix to your nixos directory, make your changes and add this to your config:

imports = [ ./network-interfaces-systemd.nix  ];
disabledModules = [ "tasks/network-interfaces-systemd.nix" ];

[netixx]

Ok thank you, I didn't know about this option !

I guess I can also use mkOverride and other related constructs to alter config properties in my config, but doing this, I need to rebuild the code in the let section of the module myself...

By the way, is there an mkSomething construct to undefine a value (say it is set by the module and I want it unset) ?

[rhendric]

By the way, is there an mkSomething construct to undefine a value (say it is set by the module and I want it unset) ?

I wanted this too, so: #63553