Support multiple configuration files (selectable from grub)

[TomSmeets]

Description

I was thinking if it is possible to select configurations when booting.
With configurations I mean multiple files that look like configuration.nix but can be selected from the boot menu (grub or efi).

NixOS could really benefit from this feature, and offer something that no other distro has.
And I would use it extensively with my laptop (different places ask for different configurations).

Example

Here are a few example configurations that I had in mind.
These paths could be specified in the standard configuration.nix file.

Path	Description
configurations/default.nix	Default configuration
configurations/work.nix	No games, different host-name and mac-address
configurations/headless.nix	Nixos without starting the x-server
configurations/free.nix	disable all nonfree software
configurations/nvidia.nix	disable bumblebee and directly use the graphics card

Implementation

These configurations will import common configurations (or each-other) to prevent copy-pasting.

I don't have enough knowledge to know if this is actually possible.
But I think so, because we already do something like this with the multiple bootable 'generations'.

[alexeymuranov]

How is a configuration different from a profile?

[Mic92]

Look for profile in the nixos-rebuild manpage:

$ nixos-rebuild switch -p test -I nixos-config=./test.nix

The new configuration will appear in the GRUB 2 submenu “NixOS - Profile 'test'”.

[7c6f434c]

For on-boot choice of configuration, look at config.nesting.children. For advanced sharing of parts of configuration, use the module system and look at nixpkgs/nixos/modules/profiles/

[TomSmeets]

YES, Thanks! 👍
Profiles are exactly what I need.

The manual only talks very briefly about profiles and doesn't explain it's possibility's.

We should add a separate section dedicated to profiles which will improve its visibility.

Thanks for your help,
Closing this issue.

[Taeradan]

@7c6f434c Is the functionality still working ? I tried to use config.nesting.clone with a single option to differentiate it (a window manager), it builds but there is no entry in grub. How am I supposed to access the alternative system ?

[7c6f434c]

I dunno if they still work, as I now use not-exactly-NixOS. Some times ago on switch it additionally created subentries for the default configuration. Maybe yet another config generation update has broken that and a bug needs to be filed… I think I have only ever used .children, though.

[vmandela]

@Taeradan Below link has the information on how to switch between config.nesting.clone configurations at runtime.

https://nixos.org/nix-dev/2017-June/023967.html

You can activate the alternative configuration with
$ sudo /run/current-system/fine-tune/child-1/bin/switch-to-configuration
test

To revert back either reboot, or
$ sudo /run/booted-system/bin/switch-to-configuration test

However the cloned configurations do not show up in the grub menu. config.nesting.children might be the way to go for populating entries in grub but the documentation is sparse.