Nixpkgs: nixos-install --chroot option

[CMCDragonkai]

Reposting from: https://github.com/NixOS/nixpkgs/commit/186c120bed6b5d4a9b1549159aa567005402000c#commitcomment-26939448

@copumpkin This --chroot option is a bit strange. It enabled me to rebuild my corrupted boot partition by basically setting up my OS while booted in via USB NixOS distro. However before I could I actually run nixos-rebuild, I needed to create /run/user/0. Perhaps this --chroot option should also do this as well. Otherwise it cannot create the temporary files/directories for running nixos-rebuild.

I also had to be careful with NIXOS_CONFIG setting (because the configuration.nix) may not be at the default position. And afterwards NIX_PATH when invoking the nixos-rebuild.

[lheckemann]

Perhaps systemd-nspawn would be a better option for entering the system properly?

[pvgoran]

The nixos-install's man page mentions the --chroot option, but it isn't currently implemented! This is quite confusing. Can we merge the code that re-enables it (https://github.com/NixOS/nixpkgs/commit/186c120bed6b5d4a9b1549159aa567005402000c)?

Luckily, there is now the separate nixos-enter utility that has the same functionality. So I suppose the proper course of actions would be to re-enable nixos-install --chroot but add a deprecation warning that points to nixos-enter.

[CMCDragonkai]

@pvgoran Do you use nixos-enter while booted inside the USB NixOS after running nixos-install? It might be useful to use to run some pre-initilisation before rebooting after installing.

[pvgoran]

@CMCDragonkai I run nixos-enter after nixos-install from a working NixOS in order to prepare a fresh, runnable NixOS tree for transfer to a different machine. (I also manually create /tmp because of #39140.)

[lheckemann]

FWIW I removed the --chroot option from the docs in 152454d9875cc1df645c5aa01ec41451d985199f (#39798)

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[Ekleog]

Closing, as AFAIU the issue no longer exists as the option itself no longer exists.