Ok i am now struggling with this problem since a few days. My problem is i am not able to save the current monitor settings, to apply / save after a reboot.
I have 3 monitors and want to mirror 2 of them but not the third. I can do this with the nvidia-settings gui tool or with calling a bash script which uses xrandr. I am not able to do this by moving my monitor on the other in the gnome / debian display settings menu - here i can only put them next to each other but am not able to "only" mirror two of them (i can mirror all but i don't want that). The above mentioned script is able to do this for me (using xrandr) - and now i am looking for the right place to put it in. I am using gdm3 and tried to put it at the start (xor) end of the /etc/gdm3/Xsession file -> did not help. I also created a ~/.xprofile file and put it there -> did not help. The script is executable for each group. And i added a line to create a new file in my home directory to check if it was called. It was in every of the above mentioned cases but did not set my monitor settings to mirror the two.
So what should i do? I googled and googled and googled and read and read but did not find any solution.
I hope someone here can help me.
P.S. using debian 8 jessie, nvidia proprietary driver, gdm3, gnome
and this is my script:
#!/bin/bash xrandr --output DVI-D-0 --mode 1920x1080 --pos 1440x0 --rotate normal --output HDMI-0 --mode 1920x1080 --pos 1440x0 --rotate normal --output DVI-I-1 --off --output DVI-I-0 --mode 1440x900 --pos 0x180 --rotate normal --output DP-1 --off --output DP-0 --off
this script works fine and was generated by arandr. I have saved it in /usr/share/.
TL;DR The script works fine when run manually and it also gets invoked when put in the /etc/gdm3/Xsession or ~/.xprofile. But the monitor setup is not set correct after boot. Only when i run the script manually after everything finished (loading).