Wenn der nvidia-Treiber beim Hochfahren keine angeschlossenen Monitore findet, bricht er mit einem Fehler ab. Laut http://us.download.nvidia.com/XFree86/Linux-x86_64/430.34/README/xconfigoptions.html kann man ihn anweisen ohne Monitore zu starten:
Option "AllowEmptyInitialConfiguration" "boolean"
Normally, the NVIDIA X driver will fail to start if it cannot find any display devices connected to the NVIDIA GPU. AllowEmptyInitialConfiguration overrides that behavior so that the X server will start anyway, even if no display devices are connected.
Enabling this option makes sense in configurations when starting the X server with no display devices connected to the NVIDIA GPU is expected, but one might be connected later. For example, some monitors do not show up as connected when they are powered off, even if they are physically connected to the GPU.
Another scenario where this is useful is in Optimus-based laptops, where RandR 1.4 display offload (see Chapter 33, Offloading Graphics Display with RandR 1.4) is used to display the screen on the non-NVIDIA internal display panel, but an external display might be connected later.
Default: off. The driver will refuse to start if it can't find at least one connected display device.
Alternativ kann man die Monitore statisch konfigurieren und ihre EDID aus einer Datei statt vom Monitor laden lassen (vgl. z.B. NVIDIA/Tips_and_tricks). Das hat den Vorteil, dass es keine Events gibt, die zu Änderungen der xrandr-Konfiguration führen, wenn man die statisch konfigurierten Monitore im laufenden Betrieb an- und abschaltet.