Rpi 4 and two monitors

[sdetweil]

@NathTheDude but is the desktop all the way across as a single desktop, or two separate instances?

[NathTheDude]

@sdetweil , it is seen as two separate monitors. There is not a setting to scretch one screen to the other with the settings. The closest is ‘Strectch to cover screen’ but that does not seem to help.

[bhepler]

@sdetweil - I don’t know if that capability is in the Raspi display drivers. It’s always going to see the two monitors as two separate devices with unique desktops. If you click on the Identify button, it should show you a different number on each monitor.

The only thing I can think of that would treat two monitors as a single continuous desktop is the AMD Eyefinity tech.

[NathTheDude]

Thanks @sdetweil and @bhepler , could you point me in the direction of how I would display a seperate instance of MM each monitor? I know this would mean I would need to update/maintain two different MM’s but maybe that is a better option if I want to add various modules?

[sdetweil]

@bhepler said in Rpi 4 and two monitors:

I don’t know if that capability is in the Raspi display drivers. It’s always going to see the two monitors as two separate devices with unique desktops. If you click on the Identify button, it should show you a different number on each monitor.

well, that is stupid sh… , in this day and age you should be able to config the thing like u want…

I booted ubuntu on my desktop with has two displays and it made one big desktop by default…
can’t understand why raspi should be so dumb

[NathTheDude]

does this help

---

pi@MagicMirrors:~ $ tvservice --list
2 attached device(s), display ID’s are :
Display Number 2, type HDMI 0
Display Number 7, type HDMI 1
pi@MagicMirrors:~ $

[sdetweil]

@NathTheDude MagicMirror startup in the run-start.sh file sets DISPLAY=:0 for the primary display
I would guess that the second display is :1

so, do
export DISPLAY=:1
then npm start

see if it comes up on the second display

[NathTheDude]

@sdetweil na, no joy. I did try this yesterday also but was not sure I was looking in the right place. For the sake of it I tried using numbers 0 to 9, all with the same result. This for example:

npm ERR! code ENOENT
npm ERR! syscall open
npm ERR! path /home/pi/package.json
npm ERR! errno -2
npm ERR! enoent ENOENT: no such file or directory, open '/home/pi/package.json'
npm ERR! enoent This is related to npm not being able to find a file.
npm ERR! enoent 

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/pi/.npm/_logs/2020-02-04T21_33_32_894Z-debug.log

However if I reboot the RPI with run-start having the different value it will still display the MM on the first screen, this made me think that this script was not being used at the startup as I would expect it to fail and not display the MM - perhaps I am wrong.

[bhepler]

I wonder if we’re looking in the wrong place? Perhaps it’s how the MM process is calling Electron that determines where on the desktop the app appears.

[sdetweil]

@NathTheDude said in Rpi 4 and two monitors:

npm ERR! code ENOENT
npm ERR! syscall open
npm ERR! path /home/pi/package.json
npm ERR! errno -2

you are doing npm start in the root, not in the MagicMirror folder…

[sdetweil]

@bhepler that is run-start.sh

~/MagicMirror/package.json

{
  "name": "magicmirror",
  "version": "2.10.1",
  "description": "The open source modular smart mirror platform.",
  "main": "js/electron.js",
  "scripts": {
    "start": "./run-start.sh",     // < ------   when u do npm start this happens

[sdetweil]

@NathTheDude run-start.sh is in the MagicMirror folder

actually the pm2 only on the 1st screen is understandable
as the script used by pm2 is installers/mm.sh

which does

DISPLAY=:0 npm start

and run-start does

# if DISPLAY is not set then set it
if [ -z "$DISPLAY" ]; then #If not set DISPLAY is SSH remote or tty
	export DISPLAY=:0 # Set by default display
fi

so I would just set export DISPLAY=:0
and the execute run-start.sh

[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?