> **Update (Aug 2, 2026):** the original diagnosis in this report was wrong. The
> SDDM greeter is not the cause. See "Root cause" below — the real trigger is
> Plymouth (`splash`) coexisting with any greeter that shows a password prompt.
> Leaving the original report intact for context.

## Symptom

On a hybrid AMD+NVIDIA laptop, disabling SDDM autologin makes the system hang on
a black screen at boot. Limine loads fine, the Omarchy Plymouth logo appears, and
then nothing — no greeter, no TTY, no recovery. Only a forced power-off works.

With autologin enabled, the machine boots normally. Both `linux-cachyos` and
`linux-cachyos-lts` are affected identically.

## Original hypothesis (incorrect)

I initially assumed the SDDM Wayland greeter's nested Hyprland instance
(`CompositorCommand = start-hyprland -- --config /usr/share/sddm/hyprland.conf`)
was failing to initialize graphics on the hybrid GPU, and that
`/usr/share/sddm/hyprland.conf` was missing GPU environment variables.

Adding `env = LIBVA_DRIVER_NAME,nvidia` and `env = __GLX_VENDOR_LIBRARY_NAME,nvidia`
to that file **did not fix it**. That was the first sign the hypothesis was wrong.

## Root cause

The hang requires **two** conditions at once: the `splash` kernel parameter
(Plymouth) **and** a greeter displaying a password prompt. Remove either one and
the system boots reliably.

| Configuration | Result |
|---|---|
| `splash` + SDDM greeter (no autologin) | **hangs** (3/3) |
| `splash` + SDDM autologin (no greeter shown) | works (days of uptime) |
| `splash` + greetd/tuigreet | works 2×, then **hangs** 3× |
| no `splash` + greetd/tuigreet | works (4/4) |
| no `splash` + SDDM greeter (no autologin) | **works** ✅ |

The last row is decisive: it is the exact configuration that hung three times.
With `splash` removed, the SDDM graphical greeter starts and prompts for a
password normally.

This rules out two things:

- **Not SDDM-specific.** `greetd` + `tuigreet` is a pure-TTY greeter with no
  nested compositor at all, and it hung the same way with `splash` enabled.
- **Not the nested Hyprland instance.** Every SDDM test in the original report
  ran with `splash` enabled; SDDM was never tested without it.

## Why it happens

On this hybrid setup the kernel registers three DRM devices in sequence
immediately before Plymouth starts:

```
[drm] Initialized simpledrm 1.0.0 for simple-framebuffer.0 on minor 0
[drm] [nvidia-drm] [GPU ID 0x00000100] Loading driver
nvidia 0000:01:00.0: [drm] Cannot find any crtc or sizes   <-- no display attached
[drm] Initialized amdgpu 3.64.0 for 0000:c4:00.0 on minor 2
fbcon: amdgpudrmfb (fb0) is primary device
```

The dGPU has no panel wired to it, so it exposes no CRTC. The framebuffer handoff
from Plymouth to the greeter is an intermittent race, which matches the observed
pattern: two clean boots, then three failures within 25 minutes, on both kernels.

In every hung boot the journal stops about one second in, right after
`Started Show Plymouth Boot Screen` — long before any display manager is reached.

## Workaround

Remove `splash` from the kernel command line.

**Important for Limine users:** editing `/boot/limine.conf` directly is not
enough. `limine-update` and `limine-mkinitcpio` regenerate the `cmdline:` lines
from `/etc/default/limine` on every kernel update, silently restoring `splash`.
This caught me once — the fix appeared to work, then reverted. Edit the
`KERNEL_CMDLINE[default]` line in `/etc/default/limine`, then run
`sudo limine-update`.

Also worth checking: `limine-update` warns about "conflicting config" files.
There can be up to four copies of `limine.conf` — `/boot/`, `/boot/EFI/limine/`,
`/boot/EFI/BOOT/` and `/boot/limine/` — and Limine boots whichever it finds
first in its search order. Verify they all match with `sha256sum` after any
change; in my case the fourth copy was stale and still contained `splash`.

## Environment

- Acer Nitro ANV14-61 (BIOS V1.06), Ryzen 7 8845HS
- AMD Radeon 780M (iGPU, drives the built-in panel) + NVIDIA RTX 4050 Max-Q
  (dGPU, no display attached)
- CachyOS + Omarchy, Hyprland 0.56.0, Limine bootloader
- `linux-cachyos` 7.1.5 and `linux-cachyos-lts` 6.18.40 — both affected identically

## Suggested title change

Current title mentions the SDDM greeter, which is misleading. Something like
*"Boot hangs on black screen on hybrid AMD+NVIDIA when Plymouth (`splash`) is
combined with any password-prompting greeter"* would reflect the actual cause.