Dead man switch for nixos-rebuild switch / boot

aou · May 8, 2025, 12:42am

tldr; switch-fix.nix lets you set an automatic rollback to current generation / profile on nixos-rebuild [switch | boot] unless you cancel with cancel-rollback from a terminal within a set amount of time

github.com

femtodata/nix-utils/blob/d18e28bd23f7b6686565ea96a8786fccde12ec13/modules/switch-fix.nix

{ pkgs, ... }:
let
  switch-fix = pkgs.writeShellScriptBin "switch-fix" ''
    sudo nix-env --profile /nix/var/nix/profiles/system --set /run/current-system
    sudo /run/current-system/bin/switch-to-configuration switch
  '';
  boot-fix = pkgs.writeShellScriptBin "boot-fix" ''
    sudo nix-env --profile /nix/var/nix/profiles/system --set $1
    sudo $1/bin/switch-to-configuration boot
  '';
  rollback-profile-path = "/var/lib/nix-autorollback/profile";
  rollback-delay = "90";
  set-rollback = pkgs.writeShellScriptBin "set-rollback" ''
    sudo mkdir -p $(dirname ${rollback-profile-path})
    sudo ln -sf $(readlink /run/current-system) ${rollback-profile-path}
  '';
  cancel-rollback = pkgs.writeShellScriptBin "cancel-rollback" ''
    sudo systemctl stop nix-autorollback.service
    sudo rm ${rollback-profile-path}
  '';

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TLATER · May 8, 2025, 4:34am

Ooh, nice.

GitHub - serokell/deploy-rs: A simple multi-profile Nix-flake deploy tool. does similar things for anyone interested, I still hope that it eventually gets local deployment as a first class citizen, until then this project seems like a cool alternative

aou · May 8, 2025, 5:02am

Yup, I started with deploy-rs, liked it! The two issues I had were, switch would sometimes not “stick”, in that on reboot, a previous generation would be default, and the auto rollback was sometimes iffy, either because of internet connection issues, or not possible (at least at the time) with boot (instead of switch).

This bit of bits was originally to address that first issue, and eventually the second.