# Installing NixOS

## Booting the system

NixOS can be installed on BIOS or UEFI systems. The procedure for a UEFI installation is by and large the same as a BIOS installation. The differences are mentioned in the steps that follow.

The installation media can be burned to a CD, or now more commonly, "burned" to a USB drive (see ).

The installation media contains a basic NixOS installation. When it’s finished booting, it should have detected most of your hardware.

The NixOS manual is available by running `nixos-help`.

You are logged-in automatically as `nixos`. The `nixos` user account has an empty password so you can use `sudo` without a password.

If you downloaded the graphical ISO image, you can run `systemctl start display-manager` to start the desktop environment. 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`!)

If the text is too small to be legible, try `setfont ter-v32n` to increase the font size.

To install over a serial port connect with `115200n8` (e.g. `picocom -b 115200 /dev/ttyUSB0`). When the bootloader lists boot entries, select the serial console boot entry.

### Networking in the installer

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 NetworkManager`.

To manually configure the wifi on the minimal installer, run `wpa_supplicant -B -i interface -c <(wpa_passphrase 'SSID' 'key')`.

If you would like to continue the installation from a different machine you can use activated SSH daemon. You need to copy your ssh key to either `/home/nixos/.ssh/authorized_keys` or `/root/.ssh/authorized_keys` (Tip: For installers with a modifiable filesystem such as the sd-card installer image a key can be manually placed by mounting the image on a different machine). Alternatively you must set a password for either `root` or `nixos` with `passwd` to be able to login.

## Partitioning and formatting

The NixOS installer doesn’t do any partitioning or formatting, so you need to do that yourself.

The NixOS installer ships with multiple partitioning tools. The examples below use `parted`, but also provides `fdisk`, `gdisk`, `cfdisk`, and `cgdisk`.

The recommended partition scheme differs depending if the computer uses Legacy Boot or UEFI.

### UEFI (GPT)

Here's an example partition scheme for UEFI, using `/dev/sda` as the device.

You can safely ignore `parted`'s informational message about needing to update /etc/fstab.

1. Create a GPT partition table.

       # parted /dev/sda -- mklabel gpt

2. Add the root partition. This will fill the disk except for the end part, where the swap will live, and the space left in front (512MiB) which will be used by the boot partition.

       # parted /dev/sda -- mkpart primary 512MiB -8GiB

3. Next, add a swap partition. The size required will vary according to needs, here a 8GiB one is created.

       # parted /dev/sda -- mkpart primary linux-swap -8GiB 100%

   The swap partition size rules are no different than for other Linux distributions.

4. Finally, the boot partition. NixOS by default uses the ESP (EFI system partition) as its /boot partition. It uses the initially reserved 512MiB at the start of the disk.

       # parted /dev/sda -- mkpart ESP fat32 1MiB 512MiB
       # parted /dev/sda -- set 3 esp on

Once complete, you can follow with .

### Legacy Boot (MBR)

Here's an example partition scheme for Legacy Boot, using `/dev/sda` as the device.

You can safely ignore `parted`'s informational message about needing to update /etc/fstab.

1. Create a MBR partition table.

       # parted /dev/sda -- mklabel msdos

2. Add the root partition. This will fill the the disk except for the end part, where the swap will live.

       # parted /dev/sda -- mkpart primary 1MiB -8GiB

3. Finally, add a swap partition. The size required will vary according to needs, here a 8GiB one is created.

       # parted /dev/sda -- mkpart primary linux-swap -8GiB 100%

   The swap partition size rules are no different than for other Linux distributions.

Once complete, you can follow with .

### Formatting

Use the following commands:

- 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 example:

      # mkswap -L swap /dev/sda2

- UEFI systems

    For creating boot partitions: `mkfs.fat`. Again it’s recommended to assign a label to the boot partition: `-n label`. For example:

        # mkfs.fat -F 32 -n boot /dev/sda3

- For creating LVM volumes, the LVM commands, e.g., `pvcreate`, `vgcreate`, and `lvcreate`.

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

## Installing

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

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

2. UEFI systems

     Mount the boot file system on `/mnt/boot`, e.g.

         # mkdir -p /mnt/boot
         # mount /dev/disk/by-label/boot /mnt/boot

3. 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.

       # swapon /dev/sda2

4. 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 -f '<nixpkgs>' -iA emacs`.
   BIOS systems

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

   UEFI systems

     You must set the option to `true`. `nixos-generate-config` should do this automatically for new configurations when booted in UEFI mode.

     You may want to look at the options starting with `boot.loader.efi` and `boot.loader.systemd-boot` as well.

   If there are other operating systems running on the machine before installing NixOS, the option can be set to `true` to automatically add them to the grub menu.

   If you need to configure networking for your machine the configuration options are described in . In particular, while wifi is supported on the installation image, it is not enabled by default in the configuration generated by `nixos-generate-config`.

   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.) Additionally, you may want to look at Hardware configuration for known-hardware at this point or after installation.

   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 installation media 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.

5. Do the installation:

       # nixos-install

   This will install your system based on the configuration you provided. If anything fails due to a configuration problem or any other issue (such as a network outage while downloading binaries from the NixOS binary cache), you can re-run `nixos-install` after fixing your `configuration.nix`.

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

       setting root password...
       New password: ***
       Retype new password: ***

   For unattended installations, it is possible to use `nixos-install --no-root-passwd` in order to disable the password prompt entirely.

6. If everything went well:

       # reboot

7. 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. This will be covered in .

## Installation summary

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.

### Example partition schemes for NixOS on `/dev/sda` (MBR)

    # parted /dev/sda -- mklabel msdos
    # parted /dev/sda -- mkpart primary 1MiB -8GiB
    # parted /dev/sda -- mkpart primary linux-swap -8GiB 100%

### Example partition schemes for NixOS on `/dev/sda` (UEFI)

    # parted /dev/sda -- mklabel gpt
    # parted /dev/sda -- mkpart primary 512MiB -8GiB
    # parted /dev/sda -- mkpart primary linux-swap -8GiB 100%
    # parted /dev/sda -- mkpart ESP fat32 1MiB 512MiB
    # parted /dev/sda -- set 3 esp on

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

With a partitioned disk.

    # mkfs.ext4 -L nixos /dev/sda1
    # mkswap -L swap /dev/sda2
    # swapon /dev/sda2
    # mkfs.fat -F 32 -n boot /dev/sda3        # (for UEFI systems only)
    # mount /dev/disk/by-label/nixos /mnt
    # mkdir -p /mnt/boot                      # (for UEFI systems only)
    # mount /dev/disk/by-label/boot /mnt/boot # (for UEFI systems only)
    # 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
      ];

       = "/dev/sda";   # (for BIOS systems only)
       = true; # (for UEFI systems only)

      # 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;
    }

## Additional installation notes