External GPU (eGPU) + NVIDIA Drivers on Linux: Solving the Display Manager Initialization Problem

TL;DR: If your NVIDIA eGPU works in recovery mode but gives a black screen on normal boot, you're missing one critical Xorg option: AllowExternalGpus . This guide shows how to fix it properly on any X11-based Linux distribution.

Introduction

Installing NVIDIA drivers on a Linux system with an external GPU (eGPU) connected via Thunderbolt can result in a frustrating black screen instead of your login screen. This issue affects LightDM, SDDM, GDM (X11 session), and other display managers across multiple distributions.

This guide documents a complete solution tested on real hardware and explains the root cause that official documentation often omits.

Tested Configuration:

Hardware: GEEKOM GT1 Mega (Intel Core Ultra 9 185H with Intel Arc iGPU) + NVIDIA RTX 5060 Ti in Sonnet eGPU Breakaway Box 750ex

Connection: Thunderbolt 4

OS: Linux Mint 22.3 MATE (applicable to Ubuntu, Fedora, Arch, and any X11-based…