Unable to build container with init script

[jtojnar]

Describe the bug

After updating from b2737d4 to d5dae65, my config no longer builds:

error: Cannot merge definitions of `system.build.installBootLoader'. Definition values:
       - In `/nix/store/1q3bx2vjp4afq1wglhxgva9rhs69k8ri-source/nixos/modules/virtualisation/container-config.nix': "/nix/store/176gh50y24c0lx2bnnmsvf9wazb73php-coreutils-9.0/bin/true"
       - In `/nix/store/1q3bx2vjp4afq1wglhxgva9rhs69k8ri-source/nixos/modules/system/boot/loader/init-script/init-script.nix': <derivation /nix/store/65w7c71fli7vh0gnqa11272jrc6bqjxj-init-script-builder.sh.drv>

Those two modules appear to by enabled by the copy of the vpsadminos module I am importing but weirdly, neither of those seem to have changed:

https://github.com/NixOS/nixpkgs/blob/3cbb02087b4c2dfc3be664d7152cec51765e53ef/nixos/modules/virtualisation/container-config.nix
https://github.com/NixOS/nixpkgs/blob/3cbb02087b4c2dfc3be664d7152cec51765e53ef/nixos/modules/system/boot/loader/init-script/init-script.nix

Steps To Reproduce

Run nixos-rebuild build-vm -I nixpkgs=$PWD -I nixos-config=<(echo '{ ... }: { boot.isContainer = true; boot.loader.initScript.enable = true; }')

[jtojnar]

Bisecting points to 4014fb6 cc @roberth

[jtojnar]

Maybe this should be mkDefault?

nixpkgs/nixos/modules/virtualisation/container-config.nix

Line 21 in 3cbb020

system.build.installBootLoader = "${pkgs.coreutils}/bin/true";

[roberth]

This is great! Those were always in conflict, but one of them won, by luck of the imports order. You really don't want to have anything important depend on that, so I'm glad this was caught, although I wish the experience of catching it would be nicer.

Maybe this should be mkDefault?

That line does feel like a default.

[roberth]

Hold on, it seems to be the other way around. That line should be a mkForce instead, to disable boot loader stuff for containers.

[roberth]

It's kind of the wrong way around, imports-ing stuff you don't need and then disabling it, but it's the best we can do without RFC22 / Minimal module list.

I've opened #148456 and #153211 to work towards those goals with minimal impact on regular NixOS.

[jtojnar]

Hold on, it seems to be the other way around. That line should be a mkForce instead, to disable boot loader stuff for containers.

I would assume VPSAdminOS wants the boot loader even for containers if they are explicitly enabling the init scripts. cc @aither64

[aither64]

I don't fully understand all these changes, but yes, I would say that boot.loader.initScript (and system.build.installBootLoader) is needed when NixOS is in a container. I mean a container run e.g. by LXC, which is what we do on vpsAdminOS. We don't know what is inside the container and depend on it having /sbin/init. I think mkDefault on installBootLoader would work.

[roberth]

I thought of the wrong kind of container. #155839 (comment) lgtm.

[jtojnar]

Opened #155962