Installing NixOS

Installation Boot from the CD. 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 and brought up networking (check ifconfig). 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. The NixOS manual is available on virtual console 8 (press Alt+F8 to access). Login as root and the empty password. If you downloaded the graphical ISO image, you can run start display-manager to start KDE. The NixOS installer doesn’t do any partitioning or formatting yet, so you need to 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 . This will make the file system configuration independent from device changes. For creating swap partitions: mkswap. Again it’s recommended to assign a label to the swap partition: . 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. Mount the target file system on which NixOS should be installed on /mnt, e.g. $ mount /dev/disk/by-label/nixos /mnt 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 The vim text editor is also available. You must set the option to specify on which disk the GRUB boot loader is to be installed. Without it, NixOS cannot boot. Another critical option is , 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 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 . 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. Do the installation: $ nixos-install Cross fingers. If everything went well: $ reboot 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 ), a new item appears in the menu. This allows you to easily roll back to another 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. 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 <filename>/dev/sda</filename> $ fdisk /dev/sda (or whatever device you want to install on) $ mkfs.ext4 -L nixos /dev/sda1 (idem) $ mkswap -L swap /dev/sda2 (idem) $ mount LABEL=nixos /mnt $ nixos-generate-config $ nano /mnt/etc/nixos/configuration.nix (in particular, set the fileSystems and swapDevices options) $ nixos-install $ reboot NixOS configuration { imports = [ # Include the results of the hardware scan. ./hardware-configuration.nix ]; boot.loader.grub.device = "/dev/sda"; # Note: setting fileSystems and swapDevices is generally not # necessary, since nixos-generate-config has set them automatically # in hardware-configuration.nix. fileSystems."/".device = "/dev/disk/by-label/nixos"; swapDevices = [ { device = "/dev/disk/by-label/swap"; } ]; services.sshd.enable = true; }

Changing the configuration The file /etc/nixos/configuration.nix contains the current configuration of your machine. Whenever you’ve changed something to that file, you should do $ nixos-rebuild switch to build the new configuration, make it the default configuration for booting, and try to realise the configuration in the running system (e.g., by restarting system services). You can also do $ nixos-rebuild test to build the configuration and switch the running system to it, but without making it the boot default. So if (say) the configuration locks up your machine, you can just reboot to get back to a working configuration. There is also $ nixos-rebuild boot to build the configuration and make it the boot default, but not switch to it now (so it will only take effect after the next reboot). Finally, you can do $ nixos-rebuild build to build the configuration but nothing more. This is useful to see whether everything compiles cleanly. If you have a machine that supports hardware virtualisation, you can also test the new configuration in a sandbox by building and running a virtual machine that contains the desired configuration. Just do $ nixos-rebuild build-vm $ ./result/bin/run-*-vm The VM does not have use any data from your host system, so your existing user accounts and home directories will not be available.