bootloader script as a replacement for grub/systemd-boot/extlinux NixOS rollback feature

[AleXoundOS]

First of all, thank you for making NixOS on WSL a reality! It works!

Originally, NixOS comes with a handy rollback feature which helps in case the system got broken. At the current (974a7c4) state it's even easier: making some systemd service enter a failed state prevents the login. Though, there is a workaround wsl -u nixos for exact this case with some nasty hacks following it related to namespaces, but I think the problem is clear.

The idea is to develop a not so complex NixOS module or maybe patch the grub/systemd-boot/extlinux module to allow a user select the system configuration to load instead of the most recent.
Without NixOS module, in the most primitive form: listing directories symlinks in /nix/var/nix/profiles and waiting for a user to type the desired one should suffice, residing in syschdemd.sh script.

[willbush]

What is the current way to rollback?

[nzbr]

Currently the only way to do a rollback is through nix-env -p /nix/var/nix/profiles/system --rollback (or --switch-generation)
EDIT: --system does not exist, it's -p /nix/var/nix/profiles/system

[AleXoundOS]

I think no way.

The proposed script is quite easy to write, though. Later I will share a variant of it.

[nzbr]

I like the idea, though having a script that awaits input in the startup process might cause problems. (For example, when the distro gets started by the vscode remote extension). The better way would probably be to add a something for this to /bin, so it can be executed with wsl -d NixOS -e <name>. This can then also be integrated with DistroLauncher, so that we can have something like nixos --rollback from the windows command prompt

[sielicki]

I think ergonomically this is the best solution and I'd like to contribute a PR for it. I've been waiting for input on what we actually want to implement.