nixos/profiles/nixos-fallback.nix

   1 { config, pkgs, lib, ... }:
   2 {
   3 systemd.services."nixos-fallback" = {
   4   after = [ "sshd.service" ];
   5   #wantedBy = [ "multi-user.target" ];
   6   serviceConfig = {
   7     ExecStart = pkgs.writeShellScript "nixos-fallback-start" ''
   8       set -ux
   9       # Note that even if switch-to-configuration test
  10       # restarts nixos-fallback.service,
  11       # it does not change the system profile.
  12       profile=/nix/var/nix/profiles/system
  13       fallback=$(readlink -e /root/nixos-fallback || readlink -e $profile)
  14       sleep $((10 * 60))
  15       nix-env --profile $profile --set $fallback
  16       $fallback/bin/switch-to-configuration switch
  17       #systemctl reboot
  18     '';
  19   };
  20 };
  21 }