Rpi 4 and two monitors

[NathTheDude]

Hey @sdetweil and @chassain-0 , so my kit for my v2 project has arrived. I have two 21.5 inch (same model) monitors connected up to an RPI4.

I have had a look around the forum but not been able to see what the best method is for this. When we start pm2 or when the RPI reboots it will boot up with the MM on the first screen and the normal desktop seen on the 2nd screen.

I think I would prefer to have two MM’s installed (one for each monitor), I assume this is ok todo or is the best approach to have the one MM on both screens?

Thanks

Nathan

[NathTheDude]

I wondered if I needed to update the ‘mm.sh’ file within the ‘installers’ folder, I tried changing this from ‘0’ to ‘1’ - reboot the RPI but on reboot MM does not get started on either monitor.

---

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

[bhepler]

@NathTheDude - I tried that one-pi-two-instances thing a couple years ago. I wasn’t using an RPI but rather a tiny Ubuntu box. My problem was that I couldn’t find a way to guarantee which instance would appear on which monitor at start. They usually both ended up in the same monitor on top of each other.

You may have more luck than I did. If you do figure it out, please let me know how you did it!

[sdetweil]

@NathTheDude said in Rpi 4 and two monitors:

think I would prefer to have two MM’s installed (one for each monitor), I assume this is ok todo or is the best approach to have the one MM on both screens?

the answer is yes, … depends on what you want to do…

to use two MM on the same full width display you will have to modify custom.css on the one to the right
and make its starting position 1/2 way across the screen

when MM is on the left, is the desktop a full image, or just the right side of the full image?

[NathTheDude]

Hey @sdetweil , I started with stopping MM (pm2 stop all). This then allowed me to use VNC to change the screen settings, as in just rotate the screen’s display.

The screens are showing as two seperate desktops and from VNC the mouse smoothly goes from one display to the other.

When MM is started this completly fills the first screen and a raspbian windows desktop is seen on the 2nd screen.

[sdetweil]

@NathTheDude try the raspian, preferences, appracne settings, desktop stretch across

[NathTheDude]

Thanks @sdetweil , I have just played with those settings again. These seem to only effect the desktop and the desktop background and not the MM site. Always appears on the first screen.

[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.