odysseus + ithaca — Nix configs

• odysseus: barebones NixOS: hardware support, ROCm, ollama, NFS, and neovim.
• ithaca: nix-darwin on the Apple Silicon MacBook Air.

Both machines share the same nix settings, joevim, claude-code/codex, EDITOR=nvim, the authorized SSH keys (key-only sshd), zsh as the login shell, and joe's git + zsh config via home-manager (modules/common.nix, modules/nix.nix, modules/home.nix). ROCm, ollama, ComfyUI and the NFS export exist only on odysseus.

What it targets

Detected on the running Fedora install:

Board	ASRock B550M-ITX/ac (BIOS P3.90), UEFI
CPU	AMD Ryzen 5 4600G, 6C/12T
GPU	Radeon RX 6650 XT — Navi 23, gfx1032
iGPU	Renoir Vega, disabled in firmware (one DRM node present)
RAM	62 GiB
Disk	WD SN730 NVMe, 238 GB (only disk)
Net	enp6s0 Realtek RTL8111 (live, DHCP) · wlp7s0 Intel AC 3168

Layout

flake.nix                     nixpkgs unstable, nix-darwin, home-manager, joevim; comfyui outputs
flake.lock                    pinned, evaluated, ready to install from
hosts/odysseus/
  default.nix                 the system: boot, user, ssh, nfs, nix-cache mount, zram
  hardware-configuration.nix  disks, modules, firmware, microcode
hosts/ithaca/
  default.nix                 hostname, key-only Remote Login, NAS nix-cache automount
modules/
  common.nix                  shared by both hosts: packages, ssh keys, home-manager
  home.nix                    joe's home-manager config: git, zsh + antidote plugins
  nix.nix                     flakes on day 1, caches, gc, optimise
  rocm.nix                    amdgpu + ROCm userspace + the gfx1032 fix
  ai.nix                      ollama on ROCm
shells/comfyui.nix            FHS sandbox for AMD's ROCm torch wheels

The one ROCm detail that matters

The RX 6650 XT is gfx1032. ROCm ships compiled kernels for gfx1030 only in the Navi 2x family — rocmPackages.clr.gpuTargets in nixpkgs lists gfx1010, gfx1030, gfx1100–1201 and no gfx1032, and torch's ROCm target list is that same list minus the RDNA1 entries.

So everything must be told to present the card as gfx1030. That is HSA_OVERRIDE_GFX_VERSION=10.3.0, set globally in modules/rocm.nix and again on the ollama unit. Skip it and rocminfo looks perfectly healthy while torch and rocBLAS fail at kernel launch with "no kernel image is available".

/opt/rocm is assembled by hand in modules/rocm.nix as a symlinkJoin. nixpkgs used to provide rocmPackages.rocmPath for this; it was removed on 2025-09-30 and now throws. Plenty of ComfyUI custom nodes dlopen out of /opt/rocm, so it needs to exist.

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Installing

⚠️ Read this first

This machine is in use and there is only one disk. The steps below erase it. Currently on /dev/nvme0n1: Fedora 44 Server, 124 GB used, 97 GB in /home/joe, a live Docker stack (odysseus, nginx reverse proxy, chromadb, searxng, ntfy — with named volumes odysseus_chromadb-data, odysseus_ntfy-cache, odysseus_searxng-data), and Tailscale state in /var/lib/tailscale.

Back all of that up to another machine before you start. Nothing in this repo migrates it, and none of it was touched while the config was written.

Also worth deciding now: 238 GB is not much once model weights land on it. Ollama models go to /var/lib/ollama/models and ComfyUI checkpoints are tens of GB each — both on the root filesystem. Consider a second drive.

1. Back up, then boot the installer

Use the NixOS 26.05 minimal ISO (that release is what system.stateVersion records). Boot it, then sudo -i.

2. Partition

Erases the disk.

parted /dev/nvme0n1 -- mklabel gpt
parted /dev/nvme0n1 -- mkpart ESP fat32 1MiB 1GiB
parted /dev/nvme0n1 -- set 1 esp on
parted /dev/nvme0n1 -- mkpart root ext4 1GiB 100%

# The labels matter — hardware-configuration.nix mounts by label, not UUID.
mkfs.fat -F 32 -n BOOT /dev/nvme0n1p1
mkfs.ext4 -L nixos /dev/nvme0n1p2

mount /dev/disk/by-label/nixos /mnt
mkdir -p /mnt/boot
mount -o umask=077 /dev/disk/by-label/BOOT /mnt/boot

3. Get this repo onto /mnt

Push it somewhere reachable first, or carry it on a USB stick.

mkdir -p /mnt/etc/nixos
# e.g. from a USB stick mounted at /src:
cp -r /src/nix-config/. /mnt/etc/nixos/

Optional sanity check — generate a config and compare the hardware half:

nixos-generate-config --no-filesystems --root /mnt
diff /mnt/etc/nixos/hardware-configuration.nix \
     /mnt/etc/nixos/hosts/odysseus/hardware-configuration.nix

4. Flakes, on the installer too

The installer ISO ships with flakes off, so enable them for this shell before installing. This is the step people miss.

export NIX_CONFIG="experimental-features = nix-command flakes"

(The installed system needs no such flag — modules/nix.nix turns flakes on permanently, which is the day-1 part of the ask.)

5. Install

nixos-install --flake /mnt/etc/nixos#odysseus
reboot

6. First boot

Log in as joe / changeme and immediately:

passwd

initialPassword is world-readable in the Nix store; it exists only to get you through the first login and first sudo. After passwd it is irrelevant (users.mutableUsers defaults to true). SSH is already key-only using the two ed25519 keys from your Fedora authorized_keys, so password login over the network was never possible.

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Verifying ROCm

rocminfo | grep -i gfx        # expect gfx1032 as the agent…
rocm-smi                      # …and VRAM/temps/clocks for the 6650 XT
systemctl status ollama

rocminfo reports the card's real name, gfx1032 — that is correct and not a sign the override failed. The override acts on what ROCm loads kernels for. The real test is arithmetic on the GPU:

ollama run llama3.2:3b "hi"
rocm-smi                      # watch GPU% move while it generates

Ollama listens on 127.0.0.1:11434 only, and the firewall opens nothing. Reach it over an SSH tunnel, or set host = "0.0.0.0" and openFirewall = true in modules/ai.nix once you've decided who should be able to talk to it.

ComfyUI

Two routes, because the pure one is expensive.

Fast — AMD's prebuilt ROCm wheels in an FHS sandbox. Recommended for getting running today.

nix develop .#comfyui
git clone https://github.com/comfyanonymous/ComfyUI ~/comfyui && cd ~/comfyui
python -m venv .venv && source .venv/bin/activate
pip install --index-url https://download.pytorch.org/whl/rocm6.4 torch torchvision torchaudio
pip install -r requirements.txt
python main.py --listen 127.0.0.1

Check https://pytorch.org/get-started/locally/ for the current rocmX.Y index URL — that is the part of the recipe that moves.

Pure — nixpkgs comfyui built against ROCm.

nix run .#comfyui

Verified to evaluate with torch.rocmSupport = true and torch.cudaSupport = false, so it is genuinely a ROCm build. But it compiles torch, aotriton and composable_kernel from source: expect hours and a very large build directory. This is deliberately a flake output rather than a system package, so it can never hold up a nixos-rebuild switch.

Day-to-day

sudo nixos-rebuild switch --flake /etc/nixos#odysseus
sudo darwin-rebuild switch --flake ~/Projects/nixos#ithaca   # on the Mac
nix flake update                      # all inputs
nix flake update nixpkgs              # just one

Things left out, and why

• No desktop. "Barebones" plus Fedora Server Edition read as headless. Adding one is services.xserver.desktopManager.<x>.enable = true — the amdgpu and ROCm work here is independent of it.
• No Tailscale, no Docker. Both are running on the box today. Neither is hardware or ROCm, so neither is here. services.tailscale.enable = true and virtualisation.docker.enable = true when you want them back — note that reaching the machine after the install relies on LAN SSH, not Tailscale.
• No swap partition. 62 GiB of RAM; zramSwap covers spikes without giving NVMe space to swap.
• Default kernel. Navi 23 has been solid in amdgpu since 5.15. boot.kernelPackages = pkgs.linuxPackages_latest; if you want newer KFD.

Caveats

• joevim is stale. Its HEAD is 2025-03-15 and it pins nixpkgs and nixvim from March 2025. The full system evaluates fine, but 18-month-old derivations may have been garbage-collected out of the binary caches, so neovim could build from source on first install. modules/nix.nix adds the khanelivim and nix-community caches to improve the odds — joevim's own flake dropped the nixConfig block its upstream carries. Running nix flake update inside your joevim fork and pushing is the real fix.
• Unstable, not stable. comfyui does not exist in nixpkgs 26.05 — only in unstable. That drove the channel choice.
• If you git init this directory, remember flakes only see tracked files. A new module you forgot to git add is silently invisible.
• The gfx override is global and correct because there is one GPU. If you ever re-enable the 4600G's iGPU in BIOS, ROCm will enumerate gfx90c as well, 10.3.0 will be wrong for it, and you'll want ROCR_VISIBLE_DEVICES to pin the discrete card.

How this was checked

No Nix on the Fedora host, so everything was evaluated in a nixos/nix container:

• all seven .nix files parse;
• nixosConfigurations.odysseus.config.system.build.toplevel evaluates to a derivation with the real joevim input — so every option name here is valid against nixpkgs e158d9e;
• packages.comfyui and devShells.comfyui both evaluate;
• comfyui.python.pkgs.torch reports rocmSupport = true / cudaSupport = false.

Evaluated, not built, and not booted on hardware.