# Linux host setup — NVIDIA GPU VM (M0/M2)

How to bring up the build environment for the lumen Linux host on an NVIDIA-GPU Ubuntu VM
and run the **M0** capture→encode spike. `lumen-core` already builds and is tested
cross-platform; this is about the platform backends in `crates/lumen-host`.

> Target **Ubuntu 24.04 (noble)**: Sway 1.9, FFmpeg 6.1.1, xdg-desktop-portal 1.18.
> 22.04 (jammy) ships Sway 1.7 / FFmpeg 4.4 — too old for this path; build from source or
> upgrade. Package names/versions below were verified against the live Ubuntu archive.

## 1. Bootstrap

```sh
git clone git@git.unom.io:unom/lumen.git && cd lumen && git checkout m1-lumen-core
bash scripts/bootstrap-ubuntu.sh
```

It **verifies** the (already-installed) NVIDIA + NVENC stack, installs the Rust toolchain
(rustup) and the build/runtime deps (PipeWire, xdg-desktop-portal + the wlroots backend,
Sway, Wayland/DRM/EGL/GBM/VA dev libs, capture tools), **gates** the FFmpeg `-dev`
headers so it can't clobber your custom NVENC FFmpeg, and drops headless-Sway + portal
config templates into `~/.config` (only if absent). It does **not** reboot or edit GRUB.

After it runs, sanity-check the core on Linux:

```sh
cargo test --workspace        # 21 tests; same suite that's green on macOS
```

## 2. NVIDIA prerequisites (one-time, may need a reboot)

Wayland on NVIDIA requires KMS modeset. The bootstrap checks it; if it isn't `Y`:

```sh
echo 'options nvidia-drm modeset=1 fbdev=1' | sudo tee /etc/modprobe.d/nvidia-drm.conf
sudo update-initramfs -u && sudo reboot
cat /sys/module/nvidia_drm/parameters/modeset   # must print Y after reboot
```

- Driver **≥ 535** is the floor for headless wlroots (EGL/dmabuf); 550+ recommended.
- A **headless VM GPU exposes no DRM connectors** — that's expected. We don't use the DRM
  backend; `WLR_BACKENDS=headless` renders to an offscreen GBM/EGL surface and creates a
  virtual `HEADLESS-1` output. Use the render node `/dev/dri/renderD128`.
- **NVENC in a VM:** full PCI **passthrough** = bare-metal NVENC, no license. **vGPU**
  needs a valid license (vWS) or NVENC runs degraded — the bootstrap's smoke-encode tells
  you if it actually works. Consumer GeForce cards also cap concurrent NVENC sessions
  (~8); datacenter/RTX-pro are effectively unlimited — relevant once we serve many clients.

## 3. Bring up the headless compositor + prove capture→NVENC

```sh
# shell 1 — start headless Sway (prints WAYLAND_DISPLAY, default wayland-1)
bash scripts/headless/run-headless-sway.sh

# shell 2 — same user
export XDG_RUNTIME_DIR=/run/user/$(id -u) WAYLAND_DISPLAY=wayland-1
swaymsg -t get_outputs                       # confirm HEADLESS-1
swaymsg output HEADLESS-1 resolution 2560x1440@60Hz   # set your client size
bash scripts/headless/capture-smoke-test.sh  # wf-recorder (wlr-screencopy) -> hevc_nvenc
ffprobe /tmp/lumen-headless-test.mkv         # confirm a real H.265 stream
```

`wf-recorder` uses `wlr-screencopy` directly (no portal/D-Bus) — the fastest way to
de-risk the GPU encode path. **Note:** screencopy encodes straight to a file and *cannot*
feed PipeWire; the real integration uses the ScreenCast portal (see M0).

The wlroots-on-NVIDIA env workarounds (`WLR_RENDERER=gles2`, `WLR_NO_HARDWARE_CURSORS=1`,
`GBM_BACKEND=nvidia-drm`, `sway --unsupported-gpu`, …) live in
`scripts/headless/env.sh` — `source` it before launching anything Wayland.

## 4. M0 proper — wire it into `lumen-core`

Goal (plan §8): headless output → PipeWire ScreenCast → NVENC → a playable file, then feed
the encoded access units into a `lumen_core::Session` (host role). The module seams exist
in `crates/lumen-host/src/{vdisplay,capture,encode,inject,pipeline}.rs`.

Crate choices, verified current:
- **Capture (portal path):** [`ashpd`](https://docs.rs/ashpd) **0.13** with the
  `screencast` + `pipewire` features → `ScreenCast::create_session` → `select_sources`
  (`Monitor`) → `start` → `pipe_wire_node_id()` + `open_pipe_wire_remote()`; pull frames
  with [`pipewire`](https://docs.rs/pipewire) **0.10**. (crates.io's "newest" field shows
  0.9 for ashpd — ignore it, pin `0.13`.) Set `XDG_CURRENT_DESKTOP=sway` so the wlr
  portal backend is chosen.
- **Encode:** [`ffmpeg-next`](https://crates.io/crates/ffmpeg-next) **7.x** (binds the
  system FFmpeg 6.1.1 via pkg-config; needs `clang`/`libclang`). Select the encoder by
  name — `encoder::find_by_name("hevc_nvenc")`, *not* by codec id (that's the SW encoder).
  Low-latency opts: `preset=p1`, `tune=ull`, `rc=cbr`, `bf=0`, `delay=0`, large `g`.
  If your FFmpeg is in a non-standard prefix, `export FFMPEG_DIR=/that/prefix`.
- **Zero-copy is the hard part.** There's no direct dmabuf→CUDA import in FFmpeg.
  **Start with the CPU-copy fallback** (download frame → `hwupload_cuda` → `hevc_nvenc`)
  to get an end-to-end stream, then chase true dmabuf zero-copy. The plan flags this
  (§9) and the `capture` module already has a `cpu_bytes` fallback field.
- **Input (M2):** [`reis`](https://crates.io/crates/reis) (pure-Rust libei — no native
  `libei` needed) with `input-linux`/uinput as the universal fallback.

Then continue toward **M2**: `serverinfo`/RTSP/pairing enough for a stock Moonlight client
to connect, a KWin virtual output created on connect, input via reis/uinput — the
shippable milestone.

## Troubleshooting

| Symptom | Fix |
|---|---|
| Sway aborts on NVIDIA | add `--unsupported-gpu` (the helper scripts do) |
| `not a KMS device` / no connectors | expected on a headless VM GPU — use `WLR_BACKENDS=headless`, not the DRM backend |
| Sway won't start at all | `WLR_RENDERER_ALLOW_SOFTWARE=1 WLR_RENDERER=pixman` to prove the pipeline, then fix EGL |
| ScreenCast portal finds no output | ensure `xdg-desktop-portal-wlr` is running in the same session, `XDG_CURRENT_DESKTOP=sway`, and `~/.config/xdg-desktop-portal-wlr/config` has `output_name=HEADLESS-1` |
| `Cannot load libnvidia-encode.so.1` | NVENC runtime lib missing (driver) or unlicensed vGPU |
| `cargo build` can't find FFmpeg | `export FFMPEG_DIR=$(pkg-config --variable=prefix libavcodec)` or point `PKG_CONFIG_PATH` at the custom build |
| bindgen: libclang not found | `export LIBCLANG_PATH=$(llvm-config --libdir)` |