No hdmi output when connecting JetKVM to RPI4 running Home Assistant

Hardware
1

Hi all,

I am running the latest and greatest version of Home Assistant on a Raspberry Pi 4 with 8 GB of RAM. The RPi 4 is housed in an Argon ONE enclosure with an mSATA expansion board, so Home Assistant is running from an SSD rather than an SD card.

This setup has been running fine for several years now.

Yesterday, I had a power outage, and afterwards it seemed that Home Assistant was no longer booting. Obviously, since the thing is headless, this is difficult to diagnose. I tried connecting to it using JetKVM, but it showed nothing.

I started to panic a little, so I took the RPi 4 to the living room and connected it to a normal TV. Luckily, this showed output, so nothing was broken (phew). I guess I just needed to wait a little longer.

Today, I borrowed my son’s display and tried to do the same thing: attach the display, boot the RPi 4, and check the output. This showed output during the first stage of the boot, but nothing during the second stage. Although I could swear that the second stage was also shown on my TV yesterday.

I still need to perform the same test with the JetKVM: attach the display, boot the RPi 4, and check the output in JetKVM.

I also asked Gemini for help, and Gemini indicated that it is normal for no output to be shown because you need to enable some options in config.txt.

Since Gemini is largely based on old text scraped from the Internet, it may be giving me outdated information, so I wanted to ask the question here.

So, TL;DR: I want to attach some kind of display to my RPi 4 so I can see the output from Home Assistant and watch it booting. For example, maybe it is running fsck, which could take a while.

How can I do this?

2

A dummy HDMI plug could be what you want if you don’t want/need a monitor for thePi, they come in different resolutions FUERAN dummy plug,Headless Ghost, Display Emulator HDMI-compatible HDMI-compatible（Fit Headless-1920x1080 New generation@60Hz）: Amazon.co.uk: Electronics & Photo

3

If it boots, all you see is the splash screen with a cli prompt from the HDMI port.
This is the same that you see (if it is running) from one of the SSH apps.
Gemini is just guessing and has no idea.

To me it sounds like the power outage corrupted your database and it took some time for it to recover, which is common when you turn it off in mid write.

SDCards that are going bad also act like this however.

Other tips:

4

Thank you all for you replies. :folded_hands:

I did a test again yesterday.

  • connected the JetKVM
  • no output, so I tried to send keyboard commands; CTRL + ALT + DEL seemed to reboot the PI (which is fine I guess :person_shrugging:)
  • then all of a sudden I got output in the JetKVM
  • both first stage of the boot and second stage seemed to work and I finally got to the banner

So I guess my question was not valid. It seems that when the JetKVM is attached, while booting it shows the whole boot sequence and banner in the end. When attaching the JetKVM on a running instance, it says “no screen”. This is might be something resolution related? Not sure.

I guess indeed the power outage triggered a thorough database check, resulting in a long start of Home Assistant and its services.

As mentioned this is not running from an SD card, but from an m.Sata instead (so a real SSD).

The PI also has an official power supply, so there are no “undervoltage” warnings in the output.

I guess the lesson learnt here is to reserve some time in my busy schedule and connect my Home Assistant instance to an UPS.

Thanks again!

5

No, what you’re doing there is referred to as hotplugging. I believe the Pis had a config option to enable this in config.txt (google says it’s hdmi_force_hotplug=1, but double check).

However, hotplugging any device is generally not recommended due to the voltages carried by HDMI & shorting risks. Safest bet is to plug in while the Pi is off, then switch on the power.