lighdm fails to start when prime-select intel

[ramonskie]

i upgraded from 18 to 19.1 (also tried this on a fresh machine with 19 installed)
because mdm is deprecated i needed to move to lightdm as stated in the upgrade notes

i tried nvidia 390,410, 415, 418

the nvidia drivers work great.
but when i switch to intel with `prime-select intel`
and reboot or logout/login
i get a black screen and it seems to hang. sometimes i can to a terminal with ctrl+alt+f1

when googling this of course will lead you down the rabbit hole.
the most of what i could find is that it is an issue in lightdm.

has anyone ever experienced this kind of behavior or has anyone a solution
please advise.

[roblm]

This method has helped some users. Open the Terminal and use this command to open the grub file:
xed admin:///etc/default/grub

Change this line:

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GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

To this:

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GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi=! acpi_osi='windows 2009'"

Use this command to update grub: sudo update-grub

Switch to the Intel GPU and reboot.

If there is a problem getting back to the desktop, then press Ctrl+Alt+F1 to enter the virtual console tty1.
Use this command to open the grub file: sudo nano -t /etc/default/grub

Use the Arrow keys to move the cursor. Remove the changes. Press Ctrl+X
Update grub and reboot. sudo update-grub; reboot

[ramonskie]

unfortunately this didn't help.
i'm not at the point that im just giving up on optimus and linux

EDIT:
i finaly got lightdm to start
after removing xorg conf

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sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf.backup
reboot