According to the initial question: w3 needs to clone "LVDS1" to "VGA1" with one single xrandr-command. May man xrandr helps?

I need working this command in Miyo.

sh -c `xrandr --output VGA1 --mode 1600x900 --rate 60.00 --same-as LVDS1 --output LVDS1 --off` &

This command work fine for me in Devuan Netinstall using Pekwm

Are you sure it is sc -c ... and not sh -c .....
But then, why not have the command xrandr ... directly? What does sc do?

I wrote wrong. Correctly is sh -c

IMHO the X server does right automagically in most cases (and miyolinux is a well supported distribution of devuan/ascii ;-)

Now the gory details: According to ralph.ronnquist I don't understand sc -c ..., too. And it is hard to believe in the  need of ~ / .xinitrc. And I've never heard about "the Pekwm window manager" up to now, I believe in slim/xfce :-) Basically slim starts the X server with /var/log/Xorg.0.log, then xfce tooks the windows management, Then you will see errors in tail -f ~/.xsession-errors. To keep a long story short:

xrandr -q -v

is your friend. On MY laptop it looks like:

xrandr program version 1.5.0 devuan/ascii as of this writing
LVDS1 connected ... 1024x768 ... screen of laptop
VGA1 connected ... 1280x1024 ... external monitor

Initially (after 1st install) both screens show the same content.

BTW: I'm using both screens as one "Arbeitsfläche" with
xrandr  --output LVDS1 --primary --auto --rotate normal --pos 0x0 \
        --output VGA1            --auto --rotate normal --left-of LVDS1

According to the initial question: w3 needs to clone "LVDS1" to "VGA1" with one single xrandr-command. May man xrandr helps?

Does xrandr show the other monitor?

Does running that command in the terminal work?

If so, have you tried putting the desktop application that you created in /etc/xdg/autostart ?

What about creating a script; such as...

!#/bin/sh
sc -c `xrandr --output VGA1 --mode 1600x900 --rate 60.00 --same-as LVDS1 --output LVDS1 --off`

...Mark it as executable, and place it in /usr/bin/ (as an example).

Then try adding the script to ~/.config/openbox/autostart

As an example, I'll use "external-monitor" as the name of the script, and it was placed in /usr/bin/.

/usr/bin/external-monitor &

With a convensional install of Devuan netinstall using the Pekwm window manager I manage the resolution of my VGA monitor and turn off the internal monitor of the Notebook with the following command colacado in /home/$USER/.pekwm/start

sh -c `xrandr --output VGA1 --mode 1600x900 --rate 60.00 --same-as LVDS1 --output LVDS1 --off` &

However I can not do the trick using Miyo Modern.

I tried this on:  ~ / .config / openbox / autostart

creating an lxrandr.desktop with this command following the creation standard of this file and putting in:
~ / .config / autostart /

Finally I created a ~ / .xinitrc file, since the default installation did not create one and put the command.

But nothing works. Something new for me to try?