Nix

Home-manager standalone

home-manager build --flake .#[system name]
home-manager switch --flake .#[system name]

NixOS

Installation on hardware

Build ISO

# Inside the nix/ directory
export NIX_PATH=nixos-config=$PWD/iso.nix:nixpkgs=channel:nixos-25.11
nix-build '<nixpkgs/nixos>' -A config.system.build.isoImage

This will result in a ISO with settings from the iso.nix file. After the build is done you can write the ISO image to a USB stick or similar. The build command will output the Nix store path and it will also be available in ./result/iso/.

Boot and provision

Boot the ISO on the new system, find the host name and provision the device using nixos-anywhere.

First create a configuration for the system in machines/[name]/default.nix. Then add the system to flake.nix. After that is done you can provision the device. We also generate the hardware configuration for the system.

# Example with disk encryption and sops
# --disk-encryption-keys [target host key location] [current host key location]
nix run github:nix-community/nixos-anywhere -- \
  --flake .#[system name]\
  --disk-encryption-keys /tmp/secret.key <(cat /secret/password) \
  --generate-hardware-config nixos-generate-config machines/[system name]/hardware-configuration.nix \
  --copy-host-keys \
  --target-host simon@[ip address]

# Example without disk encryption
nix run github:nix-community/nixos-anywhere -- \
  --flake .#[system name]\
  --generate-hardware-config nixos-generate-config machines/[system name]/hardware-configuration.nix \
  --target-host simon@[ip address]

Reboot the system.

Making changes to a system

Update a remote system.

nix run nixpkgs#nixos-rebuild -- \
  --target-host simon@[hostname] \
  --sudo \
  switch \
  --flake .#[system name]

Update a local system

sudo nixos-rebuild switch --flake .#[systemname]

SOPS

Create age identity for your system:

mkdir -p $HOME/.config/sops/age/
read -s SSH_TO_AGE_PASSPHRASE; export SSH_TO_AGE_PASSPHRASE
nix run nixpkgs#ssh-to-age -- \
  -private-key \
  -i $HOME/.ssh/id_ed25519 \
  -o $HOME/.config/sops/age/keys.txt

Display system age recipient (public key) for you system:

age-keygen -y $HOME/.config/sops/age/keys.txt

Get target host age recipient:

cat /etc/ssh/ssh_host_ed25519_key.pub | nix run nixpkgs#ssh-to-age

Configure sops:

nvim .sops.yaml

Edit secret file:

nix run nixpkgs#sops secrets/example.yaml

Investigate

• https://github.com/notthebee/nix-config/tree/main

Housekeeping

Remove old generations

When you make changes to your system, Nix creates a new system Generation. All of the changes to the system since the previous generation are stored there. Old generations can add up and will not be removed automatically by default. You can see your generations with:

$ nix-env --list-generations

To keep just your current generation and the two older than it:

$ nix-env --delete-generations +3

To remove all but your current generation:

$ nix-env --delete-generations old

Generation trimmer script

For a smart interactive script which can handle all the normally available profile types across NixOS and be more conservative and safe than the built-in Nix generations deletion commands, see NixOS Generations Trimmer.

Garbage collection

As you work with your system (installs, uninstalls, upgrades), files in the Nix store are not automatically removed, even when no longer needed. Nix instead has a garbage collector which must be run periodically (you could set up, e.g., a cron to do this).

$ nix-collect-garbage

This is safe so long as everything you need is listed in an existing generation or garbage collector root (gcroot).

If you are sure you only need your current generation, this will delete all old generations and then do garbage collection:

$ nix-collect-garbage -d

On NixOS, you can enable a service to automatically do daily garbage collection:

/etc/nixos/configuration.nix

nix.gc.automatic = true;

FAQ

HELP cache is down and I can't remove it!

If a substitute is down and you can't remove it from your configuration since it uses the substitute you can run your build with --option build-use-substitutes false

nix run nixpkgs#nixos-rebuild -- \
  --sudo \
  switch \
  --option build-use-substitutes false \
  --flake .#yam