# Installing NixOS

1. Boot from the CD.

2. The CD contains a basic NixOS installation. (It also contains Memtest86+, useful if you want to test new hardware). When it’s finished booting, it should have detected most of your hardware.

3. The NixOS manual is available on virtual console 8 (press Alt+F8 to access).

4. You get logged in as `root` (with empty password).

5. If you downloaded the graphical ISO image, you can run `start display-manager` to start KDE. If you want to continue on the terminal, you can use `loadkeys` to switch to your preferred keyboard layout. (We even provide neo2 via `loadkeys de neo`!)

6. The boot process should have brought up networking (check `ip a`). Networking is necessary for the installer, since it will download lots of stuff (such as source tarballs or Nixpkgs channel binaries). It’s best if you have a DHCP server on your network. Otherwise configure networking manually using `ifconfig`.

   To manually configure the network on the graphical installer, first disable network-manager with `systemctl stop network-manager`.

7. The NixOS installer doesn’t do any partitioning or formatting yet, so you need to do that yourself. Use the following commands:

   - For partitioning: `fdisk`.

   - For initialising Ext4 partitions: `mkfs.ext4`. It is recommended that you assign a unique symbolic label to the file system using the option `-L label`, since this makes the file system configuration independent from device changes. For example:

         $ mkfs.ext4 -L nixos /dev/sda1

   - For creating swap partitions: `mkswap`. Again it’s recommended to assign a label to the swap partition: `-L label`.

   - For creating LVM volumes, the LVM commands, e.g.,

         $ pvcreate /dev/sda1 /dev/sdb1
         $ vgcreate MyVolGroup /dev/sda1 /dev/sdb1
         $ lvcreate --size 2G --name bigdisk MyVolGroup
         $ lvcreate --size 1G --name smalldisk MyVolGroup

   - For creating software RAID devices, use `mdadm`.

8. Mount the target file system on which NixOS should be installed on `/mnt`, e.g.

       $ mount /dev/disk/by-label/nixos /mnt

9. If your machine has a limited amount of memory, you may want to activate swap devices now (`swapon device`). The installer (or rather, the build actions that it may spawn) may need quite a bit of RAM, depending on your configuration.

10. You now need to create a file `/mnt/etc/nixos/configuration.nix` that specifies the intended configuration of the system. This is because NixOS has a declarative configuration model: you create or edit a description of the desired configuration of your system, and then NixOS takes care of making it happen. The syntax of the NixOS configuration file is described in , while a list of available configuration options appears in . A minimal example is shown in .

    The command `nixos-generate-config` can generate an initial configuration file for you:

        $ nixos-generate-config --root /mnt

    You should then edit `/mnt/etc/nixos/configuration.nix` to suit your needs:

        $ nano /mnt/etc/nixos/configuration.nix

    If you’re using the graphical ISO image, other editors may be available (such as `vim`). If you have network access, you can also install other editors — for instance, you can install Emacs by running `nix-env -i emacs`.

    You must set the option `boot.loader.grub.device` to specify on which disk the GRUB boot loader is to be installed. Without it, NixOS cannot boot.

    Another critical option is `fileSystems`, specifying the file systems that need to be mounted by NixOS. However, you typically don’t need to set it yourself, because `nixos-generate-config` sets it automatically in `/mnt/etc/nixos/hardware-configuration.nix` from your currently mounted file systems. (The configuration file `hardware-configuration.nix` is included from `configuration.nix` and will be overwritten by future invocations of `nixos-generate-config`; thus, you generally should not modify it.)

    Depending on your hardware configuration or type of file system, you may need to set the option `boot.initrd.kernelModules` to include the kernel modules that are necessary for mounting the root file system, otherwise the installed system will not be able to boot. (If this happens, boot from the CD again, mount the target file system on `/mnt`, fix `/mnt/etc/nixos/configuration.nix` and rerun `nixos-install`.) In most cases, `nixos-generate-config` will figure out the required modules.

    Examples of real-world NixOS configuration files can be found at .

11. Do the installation:

        $ nixos-install

    Cross fingers. If this fails due to a temporary problem (such as a network issue while downloading binaries from the NixOS binary cache), you can just re-run `nixos-install`. Otherwise, fix your `configuration.nix` and then re-run `nixos-install`.

    As the last step, `nixos-install` will ask you to set the password for the `root` user, e.g.

        setting root password...
        Enter new UNIX password: ***
        Retype new UNIX password: ***

12. If everything went well:

        $ reboot

13. You should now be able to boot into the installed NixOS. The GRUB boot menu shows a list of available configurations (initially just one). Every time you change the NixOS configuration (see Changing Configuration ), a new item is added to the menu. This allows you to easily roll back to a previous configuration if something goes wrong.

    You should log in and change the `root` password with `passwd`.

    You’ll probably want to create some user accounts as well, which can be done with `useradd`:

        $ useradd -c 'Eelco Dolstra' -m eelco
        $ passwd eelco

    You may also want to install some software. For instance,

        $ nix-env -qa \*

    shows what packages are available, and

        $ nix-env -i w3m

    install the `w3m` browser.

To summarise, shows a typical sequence of commands for installing NixOS on an empty hard drive (here `/dev/sda`). shows a corresponding configuration Nix expression.

## Commands for Installing NixOS on `/dev/sda`

    $ fdisk /dev/sda # (or whatever device you want to install on)
    $ mkfs.ext4 -L nixos /dev/sda1
    $ mkswap -L swap /dev/sda2
    $ swapon /dev/sda2
    $ mount /dev/disk/by-label/nixos /mnt
    $ nixos-generate-config --root /mnt
    $ nano /mnt/etc/nixos/configuration.nix
    $ nixos-install
    $ reboot

## NixOS Configuration

    { config, pkgs, ... }:

    {
      imports =
        [ # Include the results of the hardware scan.
          ./hardware-configuration.nix
        ];

      boot.loader.grub.device = "/dev/sda";

      # Note: setting fileSystems is generally not
      # necessary, since nixos-generate-config figures them out
      # automatically in hardware-configuration.nix.
      #fileSystems."/".device = "/dev/disk/by-label/nixos";

      # Enable the OpenSSH server.
      services.sshd.enable = true;
    }