After running nixos-rebuild to switch to a new configuration, you may find that the new configuration doesn’t work very well. In that case, there are several ways to return to a previous configuration. First, the GRUB boot manager allows you to boot into any previous configuration that hasn’t been garbage-collected. These configurations can be found under the GRUB submenu NixOS - All configurations. This is especially useful if the new configuration fails to boot. After the system has booted, you can make the selected configuration the default for subsequent boots: # /run/current-system/bin/switch-to-configuration boot Second, you can switch to the previous configuration in a running system: # nixos-rebuild switch --rollback This is equivalent to running: # /nix/var/nix/profiles/system-N-link/bin/switch-to-configuration switch where N is the number of the NixOS system configuration. To get a list of the available configurations, do: $ ls -l /nix/var/nix/profiles/system-*-link ... lrwxrwxrwx 1 root root 78 Aug 12 13:54 /nix/var/nix/profiles/system-268-link -> /nix/store/202b...-nixos-13.07pre4932_5a676e4-4be1055