NixOS Configuration

Common Commands

Rebuild & Switch

Apply configuration changes to the running system:

sudo nixos-rebuild switch --flake /etc/nixos

Update Flake Inputs

Update all flake inputs (nixpkgs, vscode-server, nil, etc.) to their latest versions:

cd /etc/nixos && sudo nix flake update

Update a single input:

cd /etc/nixos && sudo nix flake update nixpkgs

Dry Run (test without applying)

Check what would change without switching:

sudo nixos-rebuild dry-activate --flake /etc/nixos

Build Without Switching

Build but don't activate:

sudo nixos-rebuild build --flake /etc/nixos

Roll Back

Roll back to the previous generation:

sudo nixos-rebuild switch --rollback

Or list and switch to a specific generation:

sudo nix-env --list-generations --profile /nix/var/nix/profiles/system
sudo nix-env --switch-generation <number> --profile /nix/var/nix/profiles/system
sudo /nix/var/nix/profiles/system/bin/switch-to-configuration switch

Garbage Collection

Remove old generations and free disk space:

sudo nix-collect-garbage -d

Keep the last N generations:

sudo nix-env --delete-generations +3 --profile /nix/var/nix/profiles/system
sudo nix-collect-garbage

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WireGuard

Generate a WireGuard key pair (run on each k3s node):

sudo mkdir -p /etc/wireguard
wg genkey | sudo tee /etc/wireguard/wg0.key | wg pubkey

Show the public key of an existing private key:

sudo cat /etc/wireguard/wg0.key | wg pubkey

Check WireGuard interface status:

sudo wg show

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k3s

Check cluster node status:

sudo k3s kubectl get nodes

Get kubeconfig (written to /etc/rancher/k3s/k3s.yaml):

sudo cat /etc/rancher/k3s/k3s.yaml

Check k3s service logs:

journalctl -u k3s -f

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Flake Inputs

Input	Source	Purpose
nixpkgs	github:nixos/nixpkgs/nixos-unstable	Main package set
vscode-server	github:nix-community/nixos-vscode-server	VS Code server service
nil	github:oxalica/nil	Nix LSP (nil)

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Files

File	Purpose
flake.nix	Flake definition, inputs and outputs
configuration.nix	Main system configuration
hardware-configuration.nix	Auto-generated hardware config
k3s.nix	k3s 3-server HA embedded-etcd cluster config
wireguard.nix	WireGuard mesh networking for k3s nodes