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I got a problem with Ubuntu 20.04. I have disabled every service on the Pi 3b not needed. It used to be a wifi connected device, then I plugged it onto my new router with a cable and it was recognized and worked right on with access to everything it had, home assistant, pi-hole, portioner, etc... Then I tried to re-enable wifi connection to my newly purchased Ubiquiti udr device, using raspi-config country>ssid>password, and it stopped communicating in every way.

It does appear on my router as a connected device, but putty cannot get connected to it, nor does any interface appear when trying to connect using a browser. I've also tried using the network-config file on the sd card to input various lines onto it using DHCP or static addresses and it feels like RPI is not communicating with it in any way.

Is there perhaps a command I could add to the sd card that deletes any configured things on the device so I could add a monitor to it, etc? I only need to get all the logs and configs out of the machine as I'm also going to upgrade the 3b to a 4b.

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  • "so i could add a monitor to it" -> I don't see any reason here why you cannot. Have you tried? "Headless" just means the system can and does meaningfully run without a local HID (human interface device such as a keyboard) or display. It does not mean it cannot run if there is a monitor etc. That shouldn't affect it at all.
    – goldilocks
    Commented Mar 31, 2023 at 19:07
  • yes i had to attempt it, nothing came up on the screen, that was one of the earliest things i remember doing, disable the hdmi output. Dont ask how, likely some guide to make it consume as little power as possible , it was when ubuntu 20.04 was a new thing.
    – Magezilla
    Commented Mar 31, 2023 at 20:02
  • if we Dont ask how then we can't help since we can't know what you did - having said that, searching the internet for raspberry pi 3b disable hdmi ubuntu seems to come up with some results, though, not sure how you could undo that without access - perhaps boot from USB (if you enabled it) and then make changes to the SD card Commented Apr 1, 2023 at 2:04
  • It was likely some quick line that i used on putty to disable hdmi, i just cant remember that one 3 years back. I hear you could run commands through the boot process, cmdline.txt. Can that be used to disable wifi at boot, or command to start up the hdmi output?
    – Magezilla
    Commented Apr 1, 2023 at 10:06

1 Answer 1

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I hear you could run commands through the boot process, cmdline.txt. Can that be used to disable wifi at boot, or command to start up the hdmi output?

Cmdline.txt is the command line for the kernel and systemd/init (whatever doesn't apply to the former is passed on to the latter). You could use this to blacklist some of the modules required for wifi:

module_blacklist=mac80211,brcmfmac

Beware that this file (cmdline.txt) must be all one line of text with the key/value pairs separated by spaces (no space around the = in a pair). Remember: only one line in that file.

nothing came up on the screen, that was one of the earliest things i remember doing, disable the hdmi output. Dont ask how...

Always a good idea when you are doing something unfamiliar to keep notes of what you've done, or at least a link to whatever instructions you followed.1

Anyway, hopefully this is something that was done in config.txt, in the same partition as cmdline.txt. Nothing actually needs to be enabled there, so comment out anything that is not (by adding a # to the start of the line) and leave just one entry uncommented:

hdmi_safe=1

This enables a number of things that are your best chance of getting a display to work.


  1. Pretty sure disabling the HDMI jack saves you diddly squat in terms of power if there is nothing connected to it. You should get a cheap USB inline ammeter and test these kinds of suggestions, many people post things online just to see their own words and the quality of stuff in the Pi user community can be very low.

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