elodin-nix

name: elodin-nix description: Work with the Nix development environment and NixOS configurations in Elodin. Use when troubleshooting nix develop, modifying flake.nix, adding Nix packages, setting up OrbStack VMs for Linux builds on macOS, or developing Aleph NixOS modules.

Elodin Nix Development

Elodin uses Nix flakes for reproducible builds, CI dependencies, Docker images, and the Aleph NixOS flight computer configuration.

Development Shell

The unified dev shell includes all tools for Rust, Python, C/C++, cloud operations, documentation, and git-lfs:

nix develop                              # Enter interactive shell
nix develop --command "cargo build"      # One-off command

No need to switch shells for different tasks — everything is in one environment.

Nix Installation

Use the Determinate Systems installer (recommended):

curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix | sh -s -- install

Trusted Users

Add your username to trusted users for binary cache access:

Determinate Nix — edit /etc/nix/nix.custom.conf:

trusted-users = root <your_username>

Upstream Nix — edit /etc/nix/nix.conf:

experimental-features = nix-command flakes
trusted-users = root <your_username>

Restart the daemon:

# macOS
sudo launchctl kickstart -k system/systems.determinate.nix-daemon
# Linux
sudo systemctl restart nix-daemon.service

Binary Cache

Elodin maintains a binary cache to avoid rebuilding common dependencies:

elodin-nix-cache.s3.us-west-2.amazonaws.com

This is configured in flake.nix and used automatically by nix develop and nix build.

Flake Structure

Root `flake.nix`

Provides:

Dev shell: nix develop — unified development environment
Packages: elodin-py, elodin-cli, elodin-db, elodinsink
Overlay: elodinOverlay with all Elodin packages
NixOS configs: NixOS 25.11 based

Key inputs: nixpkgs, rust-overlay (for toolchain from rust-toolchain.toml), crane (Rust builds).

`aleph/flake.nix`

NixOS configuration for the Aleph flight computer. Composes modules from aleph/modules/ into a complete system. See the elodin-aleph skill for details.

`aleph/template/flake.nix`

Template for users to create their own Aleph configurations. Imports Elodin's NixOS modules and configures services.

macOS Linux Builds (OrbStack VM)

Build Linux binaries on macOS using an OrbStack NixOS VM for remote builds:

Install OrbStack
Create a NixOS VM named nixos
Configure SSH — add to /var/root/.ssh/config:
```
Host orb
  Hostname 127.0.0.1
  Port 32222
```

ssh://user@orb x86_64-linux,aarch64-linux /Users/user/.orbstack/ssh/id_ed25519 20 20 nixos-test,benchmark,big-parallel,kvm - -

Inside the VM, add to /etc/nixos/configuration.nix:
```
nix.settings.trusted-users = ["root" "@wheel"];
```
Rebuild: sudo nixos-rebuild switch
Test: nix build --impure --expr '(with import <nixpkgs> { system = "x86_64-linux"; }; runCommand "foo" {} "uname > $out")'

OrbStack Disk Exhaustion

Qt builds can overflow /build tmpfs. Fix by using disk-backed build directory:

# In /etc/nixos/configuration.nix on the VM
nix.settings.build-dir = "/var/cache/nix-build";
systemd.tmpfiles.rules = [ "d /var/cache/nix-build 1777 root root -" ];

Then:

sudo install -d -m 1777 /var/cache/nix-build
sudo nixos-rebuild switch

Adding Packages to the Dev Shell

Edit the devShells section in the root flake.nix. The shell is built from a single unified definition that includes:

Rust toolchain (from rust-toolchain.toml)
Python 3.13 + uv + maturin
C/C++ compilers and system libraries
GStreamer (for video streaming)
git-lfs
Cloud operation tools

Nix Formatting

All .nix files are formatted with Alejandra (no configuration):

alejandra

This is enforced by CI.

Troubleshooting

`nix develop` hangs or is slow

First run downloads and builds many dependencies — this is normal
Check binary cache connectivity
Ensure trusted-users is configured

Build failures referencing missing system libraries

These are provided by the Nix shell; make sure you're inside nix develop
For macOS-specific issues, check that Xcode Command Line Tools are installed

Hash mismatch errors

Run nix flake update to refresh the lock file
Or pin specific inputs in flake.lock

Key References

Internal Nix docs: docs/internal/nix.md
Root flake: flake.nix
Aleph flake: aleph/flake.nix
Nix overlay: defined in root flake.nix as elodinOverlay