nixos-rebuild: fix --install-bootloader

[anund]

nixos-rebuild relies on setting an environment variable to change
behaviour during nixos-rebuild boot/switch between calling update or
install via systemd bootctl. Adding sudo -- as a prefix to various exec
calls does not preserve the environment breaking this mechanism.

This is a some what ugly fix that works.

Motivation for this change

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• 21.11 Release Notes (or backporting 21.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

[anund]

Fixes #144007

[anund]

With #144422 merged to staging should this PR also be shifted to target staging? (how long until staging merges back into master?)

[Artturin]

With #144422 merged to staging should this PR also be shifted to target staging?

does this pr depend on that? i dont think so since grub can use this too.

(how long until staging merges back into master?)

not sure

[anund]

No dependencies. I'm curious to know if there's a ~simple way to track when fixed systemd + fixed install process would both be available on unstable. At the moment if you are broken and don't want to work with a custom checkout of nix you need both that change and this one to simplify the fix to nixos-rebuild --install-bootloader....

[Artturin]

you can track the pr at https://nixpk.gs/pr-tracker.html?pr=144422

[anund]

@Artturin is there anything left to do but press merge?

[Artturin]

Has anyone tested this? For example In a vm after removing the bootloader

[anund]

Yes, I relied on this fix while testing changes for #144422. I went from non-functional boot loader and back again several times using this PR to verifying the updated systemd + patchset resulted in a working boot-loader.