nixos-rebuild 8 NixOS nixos-rebuild reconfigure a NixOS machine nixos-rebuild switch boot test build dry-run build-vm build-vm-with-bootloader --upgrade --install-grub --no-build-nix --fast --rollback --show-trace This command updates the system so that it corresponds to the configuration specified in /etc/nixos/configuration.nix. Thus, every time you modify /etc/nixos/configuration.nix or any NixOS module, you must run nixos-rebuild to make the changes take effect. It builds the new system in /nix/store, runs its activation script, and stop and (re)starts any system services if needed. This command has one required argument, which specifies the desired operation. It must be one of the following: switch Build and activate the new configuration, and make it the boot default. That is, the configuration is added to the GRUB boot menu as the default meny entry, so that subsequent reboots will boot the system into the new configuration. Previous configurations activated with nixos-rebuild switch or nixos-rebuild boot remain available in the GRUB menu. boot Build the new configuration and make it the boot default (as with nixos-rebuild switch), but do not activate it. That is, the system continues to run the previous configuration until the next reboot. test Build and activate the new configuration, but do not add it to the GRUB boot menu. Thus, if you reboot the system (or if it crashes), you will automatically revert to the default configuration (i.e. the configuration resulting from the last call to nixos-rebuild switch or nixos-rebuild boot). build Build the new configuration, but neither activate it nor add it to the GRUB boot menu. It leaves a symlink named result in the current directory, which points to the output of the top-level “system” derivation. This is essentially the same as doing $ nix-build /etc/nixos/nixos -A system Note that you do not need to be root to run nixos-rebuild build. dry-run Simply show what store paths would be built or downloaded by any of the operations above. build-vm Build a script that starts a NixOS virtual machine with the desired configuration. It leaves a symlink result in the current directory that points (under result/bin/run-hostname-vm) at the script that starts the VM. Thus, to test a NixOS configuration in a virtual machine, you should do the following: $ nixos-rebuild build-vm $ ./result/bin/run-*-vm The VM is implemented using the qemu-kvm package. For best performance, you should load the kvm-intel or kvm-amd kernel modules. The VM mounts the Nix store of the host through the CIFS filesystem. (qemu-kvm automatically starts a Samba daemon for this purpose.) The host Nix store is read-only, so Nix commands that modify the Nix store will not work in the VM. This includes commands such as nixos-rebuild; to change the VM’s configuration, you must halt the VM and re-run the commands above. The VM has its own ext3 root filesystem, which is automatically created when the VM is first started, and is persistent across reboots of the VM. It is stored in ./hostname.qcow2. build-vm-with-bootloader Like build-vm, but boots using the regular boot loader of your configuration (e.g., GRUB 1 or 2), rather than booting directly into the kernel and initial ramdisk of the system. This allows you to test whether the boot loader works correctly. However, it does not guarantee that your NixOS configuration will boot successfully on the host hardware (i.e., after running nixos-rebuild switch), because the hardware and boot loader configuration in the VM are different. The boot loader is installed on an automatically generated virtual disk containing a /boot partition, which is mounted read-only in the VM. This command accepts the following options: --upgrade Fetch the latest version of NixOS from the NixOS channel. --install-grub Causes the GRUB boot loader to be (re)installed on the device specified by the boot.loader.grub.device configuration option. --no-build-nix Normally, nixos-rebuild first builds the nixUnstable attribute in Nixpkgs, and uses the resulting instance of the Nix package manager to build the new system configuration. This is necessary if the NixOS modules use features not provided by the currently installed version of Nix. This option disables building a new Nix. --fast Equivalent to --no-build-nix --show-trace. This option is useful if you call nixos-rebuild frequently (e.g. if you’re hacking on a NixOS module). --rollback Instead of building a new configuration as specified by /etc/nixos/configuration.nix, roll back to the previous configuration. (The previous configuration is defined as the one before the “current” generation of the profile /nix/var/nix/profiles/system.) In addition, nixos-rebuild accepts various Nix-related flags, including --max-jobs / -j, --show-trace, --keep-failed, --keep-going and --verbose / -v. See the Nix manual for details. NIXOS_CONFIG Path to the main NixOS configuration module. Defaults to /etc/nixos/configuration.nix. /run/current-system A symlink to the currently active system configuration in the Nix store. /nix/var/nix/profiles/system The Nix profile that contains the current and previous system configurations. Used to generate the GRUB boot menu. This command should be renamed to something more descriptive.