NixOS Workshop

• https://blog.defaultroutes.de/talks/nixos

• usually NixOS runs on bare metal hardware (or in a VM)
• this workshop runs NixOS inside a systemd container, as it is easy to setup. Goal is to get a first impression of NixOS
• this is how to setup your own NixOS test machine inside a container:
  • you need a modern Linux (amd64 architecture) with systemd and systemd-nspawn (Package systemd-container)
  • approx. 1.6 GB free storage inside /srv
• create a directory for the NixOS linux container images

# mkdir -p /srv/container/nixos

• download and untar the image into the container directory

# curl https://blog.defaultroutes.de/nixos/nixos.tgz | tar -C /srv/container/nixos -xzf -

• launch the NixOS container

# systemd-nspawn -bD /srv/container/nixos

• Login to NixOS with username root and password nixos

• open the file /etc/nixos/configuration.nix with the nano text editor (we will install other editors soon)
• find the part that describes the user accounts (example commented out), and enable the config for a normal user:

# Define a user account. Don't forget to set a password with ‘passwd’.
users.users.jane = {
   isNormalUser = true;
   extraGroups = [ "wheel" ]; # Enable ‘sudo’ for the user.
};

• save the file
• activate the new configuration

# nixos-rebuild switch

• check that the new user exists

# id jane

• set a password for the new user

passwd jane

• exit the shell with exit and try to login with the new user
  • test that the new user can become super user with the sudo command

• the NixOS was originally installed inside an VirtualBox VM
• the NixOS hardware autodetection found VirtualBox and automatically created a filesystem mount for the VirtualBox Guest Additions
• now the NixOS runs inside a Systemd container, and the VirtualBox configuration creates an error message when building a new system configuration (and also during startup):

collision between 
  `/nix/store/n9yllfqp84pwqrpqkk6my9j7hwfrz619-mount.vboxsf/bin/mount.vboxsf' 
  and `/nix/store/bjshbv71j3010pnhnhdxpwdyrj282wkw-VirtualBox-GuestAdditions-6.1.6-5.4.62/bin/mount.vboxsf'

• open the NixOS hardware configuration in /etc/nixos/hardware-configuration.nix and find the line that configures the Virtual-Guest additions. Remove that line (delete or comment)
  • the file hardware-configuration.nix is included from the configuration.nix file and describes hardware configuration that can differ between machines.
• rebuild the NixOS system configuration
• check that the error message has gone

• let's install some global packages that will be visible for all users of the system
• open the file /etc/nixos/configuration.nix and fill in this block almost at the end, but before the last curly brace

environment.systemPackages = with pkgs; [
   tmux
   htop
];

• save the file, exit the editor and rebuild the NixOS system nixos-rebuild switch
• test that the command htop is now available
• use the command which htop to see where the command is located
• use the command realpath on the full path to the htop tool to find its real place in the filesystem
• use the command nix search <pgm-name> to find the name of some Linux tools (non GUI), for example your favorite text editor
  • add the names of the packages to the configuration.nix file
  • rebuild the configuration
  • verify that the software is installed

• open the file /etc/nixos/configuration.nix with yout favorite text editor
• add the package name home-manager to the list of installed packages
• save the file and exit the editor, rebuild the NixOS system
• logout as root and login as the unprivileged user created above

• as the unprivileged user, create the directory ~/.config/nixpkgs
• in that directory, use a text editor to create the file home.nix. This file contains the per-user configuration for home-manager.
• add this content into the file. This will install the packages gnupg, gtop and unzip for this user

{ config, pkgs, ... }:
{
  home.packages = with pkgs; [
      gnupg
      gtop
      unzip
    ];
}

• build the home-directory configuration with home-manager switch
• verify that the command gtop exists
• use the commands which and realpath on gtop to find out where in the filesystem the tools binary is stored
• remove one of the tools from the home.nix file
• rebuild the home-environment with home-manager switch
• verify that the tool is gone from this users environment

• verify that no Python interpreter is currently installed

[jane@nixos:~]$ python
The program ‘python’ is currently not installed. You can install it by typing:
  nix-env -iA nixos.python3Minimal

• enter a new Nix enviroment on the fly with nix-shell containing a current Python3 interpreter

$ nix-shell -p python 

• verify that how this shell has access to the Python interpreter

[nix-shell:~]$ python
Python 2.7.18 (default, Apr 19 2020, 21:45:35) 
[GCC 9.2.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 

• other users, other shells of the same user, even the root user do not see this Python interpreter, because it is not linked into their environment