NixOS: Into the deep end

My first experience with a Linux-based operating system was in the early 2000s. I remember a friend and I got hold of a Red Hat installation disk, and thought we’d give it a test run. We managed to boot the image and I remember us ending up in quite an unfamiliar shell environment. We didn’t know how to launch programs, we didn’t even know which programs were accessible. Eventually we did manage to start Pidgin (called GAIM at the time), most likely using some kind of a DOS-inspired command, only working by accident.

I’ve been using several Linux distributions to various degrees over the years since those initial baby steps. Linux-based systems have been my OS of choice for my entire professional career, and for the last couple of years I’ve been using my work laptop as my main home computer as well. I can’t remember exactly which distros I’ve been using over the years, but to name a few, in no particular order: Slackware, Debian, Arch, Ubuntu, and, for the sake of completeness, a very brief stint with BSD (I don’t even remember which). Ubuntu is the only distribution I can say I’ve been running for a significant amount of time.

Although Linux distributions have come a long way with regards to usability, no Linux setup is without its issues or challenges. This post is a consolidation of some of my notes and remarks on how to get NixOS installed, and running.

Why NixOS?

Well, why not? I didn’t really have any particular reason as to why I wanted to try NixOS. I guess it sounded luring for an entire operating system to be based off the Nix build/package management system. Build recipies consumed by Nix (the tool) are written using Nix (the language), which is a pure, lazy programming language. The functional nature of the Nix language makes it ideal for the declarative and deterministic domain of dependency and build management. Using NixOS wouldn’t be possible without me fully embracing the Nix ecosystem.

I was also growing a bit tired of my Ubuntu installations. Both my laptop and desktop workstation had accumulated quite a bit of cruft over the years. Wanting to clean up my laptop would probably resulted in a full reinstall anyways. In the end, I guess I didn’t really need a whole lot of convincing. Once I heard some colleagues were also trying out NixOS, that was enough for me. If somehow it didn’t work out, switching back wouldn’t mean much of a sunk cost.

Having made my decision, I quickly made an encrypted¹ backup of my laptop’s home directory using duplicity, which turned out to be a pleasantly simple and useful little tool. I only used the full backup that duplicity makes initially, but it also supports incremental backups, which I’ll keep in mind for later.

Bookmarks & resources

Access to documentation is vital whenever jumping into new tech. I found that the documentation hosted at nixos.org covered most of the questions and guidance I needed for the initial installation. Here are links to some of the resources I found the most useful:

• NixOS Manual
• Nix Package Manager Guide
• NixOS Packages
• NixOS Options
• Nix Pills
• Nix FAQ

Furthermore, there is also the #nixos IRC channel on freenode, and the NixOS Discourse wiki.

It’s worth noting that Nix is quite the mouthful for newcomers, to put it mildly. In its attempt to be the one and only build and packaging system it has evolved into a large ecosystem of packages, libraries, conventions, and contributors. As a user you might get along nicely with NixOS without having to dive deep into the tech, but as a developer creating your own Nix expressions becomes inevitable fairly quickly².

Downloading NixOS

Of course we can’t start installing anything before having a boot medium with the installer on it. NixOS can be downloaded from here. I don’t exactly remember how I created the installation USB stick that I used, but I would guess I just used dd:

# dd if=nixos.iso of=/dev/usb-device bs=4MB

About the installer

For most Linux users³, actually installing a distribution isn’t something you do all that often. Yet, it’s the installation process we’re first presented with when trying out a new distribution. Making installation as smooth as possible is crucial in order to drive adoption.

The boot menu of the NixOS installer doesn’t let you choose between graphical or terminal based installation. However, you are dropped into a root shell which then notes how to start a graphical user interface. For the novice user, this might be a bit intimidating, seeing just the command line. It is very trivial to spawn the graphical user interface following the notes though. That the distribution chose to default to not starting the GUI does mean quicker boot times.

It is possible to install NixOS using just the command line, meaning you never need to launch the graphical interface. The graphical installer does provide some benefits in that it includes a full browser (Firefox), along with a link to the NixOS manual on the desktop. This helps a lot if you don’t have access to another machine to look up documentation while installing, or if you end up having to do some extra troubleshooting.

Disk partitioning & encryption

The NixOS installer doesn’t come with a managed partitioning wizard, like Ubuntu does. This does imply a bit more fiddling for the user, unfortunately. Even more so for me, as I wanted to run with an encrypted file system as this was for my laptop. The NixOS manual does include some notes regarding disk encryption, but I didn’t find it exhaustive enough, and had to read up on some of the LVM and LUKS commands as well.

If I recall correctly, I had success following mostly just the steps from a couple of “Installing NixOS” blog posts: this one and this one. Following is a (hopefully complete) summary of the required partitioning commands⁴.

Find hard drive

The lsblk command lists block devices on the system. Find the name of the hard drive to install NixOS on.

# lsblk
NAME MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda    8:0    0 24.5G  0 disk /

Partitioning with parted

1. Create a partition table

   # parted /dev/sda -- mklabel gpt
   

2. Add a boot partition

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

3. Add a root partition

   # parted /dev/sda -- mkpart primary 512MiB 100%
   

Setting up LUKS

In order to run with disk encryption the hard drive must be setup with LUKS through cryptsetup.

1. Initialize an empty partition

   # cryptsetup luksFormat /dev/sda2
   

2. Open the partition

   # cryptsetup luksOpen /dev/sda2 enc-pv
   

3. Create lvm groups and volumes

   # pvcreate /dev/mapper/enc-pv
   # vgcreate vg /dev/mapper/enc-pv
   # lvcreate -n swap vg -L 10G
   # lvcreate -n root vg -l 100%FREE
   

4. Format partitions

   # mkfs.vfat -n BOOT /dev/sda1
   # mkfs.ext4 -L root /dev/vg/root
   # mkswap -L swap /dev/vg/swap
   

Mount partitions and enable swap

1. Mount the root partition on /mnt

   mount /dev/vg/root /mnt
   

2. Mount the boot partition on /mnt/boot

   mkdir /mnt/boot
   mount /dev/sda1 /mnt/boot
   

3. Enable swap

   swapon /dev/vg/swap
   

Configuration and installation

Once the file system is correctly setup, it’s time to generate the initial configuration:

# nixos-generate-config --root /mnt

The nixos-generate-config command just generates a default configuration.nix file under /mnt/etc/nixos/configuration.nix. This file is the system-wide configuration file, which declaratively specifies how the base system should be setup.

It’s not uncommon for other distro installers to have some kind of wizard guiding the user through the initial configuration steps. In NixOS though, you’re shot right into your first Nix expression, which is the format in which configuration.nix is written.

The configuration file won’t change after the initial installation, and later system-wide changes have to be made in the same file. It’s worth noting that prior to installing the root filesystem is mounted under /mnt, so on a running system the configuration file is to be found under /etc/nixos.

Depending on the desktop manager⁵ (or lack thereof), it might be necessary to enable networking.networkmanager in order to gain network connectivity:

networking.networkmanager.enable = true;

Users should mostly stick to installing whatever they need into their own user environment. Yet the environment.systemPackages option allows specifying which packages should be exposed by default to all users. Some packages are obviously handy to install globally:

environment.systemPackages = with pkgs; [
  vim
  w3m
  wget
];

There are some NixOS options related to LUKS which are needed to successfully boot the system from the encrypted volume:

# LVM
boot.initrd.luks.devices.root = {
  device = "/dev/disk/by-uuid/<disk-uuid-here>";
  preLVM = true;
  allowDiscards = true;
};

Users can also be defined declaratively (add the networkmanager group to grant access to network settings):

users.users.someuser = {
  isNormalUser = true;
  home = "/home/someuser";
  description = "Some User";
  extraGroups = [ "wheel" "networkmanager" ];
  shell = pkgs.zsh;
};

After saving configuration.nix, it’s time to install everything according to it:

# nixos-install

This causes Nix to start fetching packages, then symlinking everything into place. The install command is idempotent, so running it several times is perfectly fine. That’s also required in order to apply changes made to the configuration. The new system is ready to be booted into once the nixos-install command terminates.

# reboot

Distribution upgrade

Just a few days after I installed NixOS on my laptop a new stable branch was released: 19.03⁶. Switching branches basically means switching the “nixos” channel, then upgrade all the packages to the derivations listed by the new channel:

# nix-channel --add https://nixos.org/channels/nixos-21.05 nixos
# nixos-rebuild --upgrade boot

First impressions

All in all after using NixOS for a couple of months now, I can safely say I’m satisfied with both the distribution and my decision to try it out. There were several things I’ve spent a considerable amount of time scratching my head over, as well as other issues which I frankly haven’t figured out how to best do yet. I do consider this a long term learning experience, and so hopefully I’ll resolve most of these with time and a bit of effort. I plan to write one or more follow-up posts focusing more on NixOS usage, and mainly how I use it for development. So stay tuned!

Footnotes