Rpi 4 and two monitors

bhepler

I have to head home, so I can’t investigate any more for some time. But I did find this link on StackOverflow that seems to address the issue. Aren’t we using an X11 based desktop manager?
Anyway, this may help.

sdetweil

@bhepler correct, that is DISPLAY

NathTheDude

thanks @sdetweil , right you are - I was not running npm from within the MagicMirror directory.

When I update ‘Display’ to 1 I still get an error when trying to manually run NPM, however when ‘Display’ is set to 0 and then I run NPM there are no errors with it. The error is:

pi@MagicMirrors:~/MagicMirror $ npm start

> magicmirror@2.10.1 start /home/pi/MagicMirror
> ./run-start.sh

(electron:11918): Gtk-WARNING **: 22:18:00.088: cannot open display: :1
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! magicmirror@2.10.1 start: `./run-start.sh`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the magicmirror@2.10.1 start script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/pi/.npm/_logs/2020-02-04T22_18_00_154Z-debug.log
pi@MagicMirrors:~/MagicMirror $

@bhepler thanks for the link, it is a bit beyond my understanding at the moment. I will have to read up on it a bit more. I tried to run xrandr to see what kind of status it gives on the monitors but it currently comes back with ‘Can’t open display’, I assume it is because another service/application is utilising them?

Anyway, thanks for your help.

sdetweil

@NathTheDude said in Rpi 4 and two monitors:

When I update ‘Display’ to 1 I still get an error

Yes, we just need to find out what the other Display number is.

tvservice is wrong cause it reports display 2 for HDMI 0, and we know it’s really Display 0

NathTheDude

@sdetweil , so using ‘0’ or ‘0.0’ give the same result and start MM on the first monitor.

So far I have tried 1,2,3,4,5,6,7,8,9 and 0.1, 0.2, 0.3, 0.4, 0.5

How far do I go? :)

OldSunGuy

@NathTheDude The 2nd monitor should be display 0, screen 1. Use this:

DISPLAY=:0.1

NathTheDude

Hey @OldSunGuy , thanks. ‘0’ and ‘0.0’ seem to be the first monitor however I get an error when I try anything else. So far I have tried using each of the following: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9

Each time I try to start npm (npm start) apart from when I use 0 or 0.0 I get the following (with the value reflecting the number I changed in ‘run-start.sh’):

(electron:2238): Gtk-WARNING **: 06:14:02.236: cannot open display: :0.1

@sdetweil - not sure if this is relevant but it does not seem to matter what value I set in ‘run-start.sh’, when I reboot the pi it will always start MM on the first screen. Should it not fail if it is using ‘run-start.sh’?

Also with an incorrect value being added to ‘run-start.sh’, when I run ‘mm.sh’ this always works and displays MM on the first screen.

okay, I think I understand it now. When I reboot it is using ‘mm.sh’, within mm.sh is the following:

cd ~/MagicMirror
DISPLAY=:0 npm start

Which I assume means that the ‘run-start.sh’ is not used during boot up?

When I change this value to anything other than 0, this will also fail with the same error seen when trying to run npm previously.

OldSunGuy

@NathTheDude If you start a terminal on one desktop and run:

echo $DISPLAY

Then start a terminal on the other desktop and run:

echo $DISPLAY

do you get the same results?

NathTheDude

@OldSunGuy - I get :0.0

I wonder if both screens are being seen as 0.0, if that is the case I guess I would expect the MM screen to cover both screens and not just the first :-/

NathTheDude

@OldSunGuy , sorry mis read your comment. Not sure how I would start a terminal on one screen and a different terminal on another.