GRUB2 not showing on HDMI monitor

Question

I have an Acer Aspire E 15 laptop that I use at home most of the time, connected to an HDMI monitor and USB keyboard and mouse. I have Windows, Ubuntu and openSUSE installed on it. I would like to use it with the lid closed, but I always had to open its lid at least for powering it up and selecting the operating system I wanted to use during boot. GRUB2 always showed only on the laptop screen, even if the HDMI monitor was plugged on. There was no way to get GRUB2 displayed on my HDMI monitor.

Answer 1

Here is what worked for me. Make sure your HDMI monitor is connected before turning your laptop on. Try to close the lid right after you press the laptop's power button. Your HDMI monitor will show the BIOS/UEFI splash screen and then GRUB2.

If that works for you, you can also try to place a small refrigerator magnet on the sensor your laptop uses to detect its lid is closed, so you can trick your laptop into thinking it's always closed. Actually I did not try doing that, but it sounds interesting. Later I will try it and post here if it works.

Other possible solutions

Before coming to that solution, I've read many pages. None of the solutions proposed by other people worked for me, but I'm going to list some of them here because maybe someone wants to try them:

• Check for updates to your laptop's BIOS/UEFI firmware (mine was already the latest version)
• Check if your BIOS/UEFI setup has an option for choosing the preferred output device, suggested here and here (mine does not have)
• Switch monitors while on splash screen or GRUB2, also suggested here and here (on my laptop, I can switch monitors by pressing Fn + F5, but I was not able to switch monitors before the operating system loaded)
• Set GRUB_GFXMODE=text in /etc/default/grub (for me, doing that just removed the background image of GRUB2, it still showed up as only text and only on the laptop screen)
• Configure GRUB2 to always use the HDMI monitor, also suggested here and here (please note that, applying that solution, GRUB2 will never display on the laptop screen, even when the HDMI monitor is not connected, I did not try that, although Arch Linux's wiki says it's possible to configure many video outputs within GRUB2's configuration, which was what I actually tried and did not work for me)
• Use GRUB Legacy (version 0.97), alleged to show up on HDMI monitors, maybe it's not available to your Linux distro anymore, if you need an UEFI version of it, follow this tutorial (GRUB Legacy showed to me, but only on my laptop screen)
• Remember how many times you have to hit the down arrow key for each system (that actually would also work for me, but I think it's more a workaround than properly a solution)
• Open your laptop and disconnect its own screen cable (another workaround that you could consider if you don't use your laptop off home)

Answer 2

The only solution that worked for me :

Open the back panel of the laptop and disconnect the screen cable. Then plug in the HDMI cable and switch on the laptop. It'll automatically show the display on the external monitor.