Okay, this bug has absolutely nothing to do with grub or netplan. Changing the renderer couldn't possibly affect the behavior of X, and the grub configuration looks, at a glace, to be run-of-the mill; pretty much default if you disregard that there is any number of different installs on the system.
For instance the kernel command-line: BOOT_IMAGE=/boot/vmlinuz-5.0.0-7-generic root=UUID=1d61086d- 275b-4537-bed5-f2d3080670eb ro quiet splash (from various attached output of dmesg) This command-line is pretty much default. The use of kernels 5.0.0-7 or 5.0.0-8 are what I'd expect on disco images; and there are no special kernel parameters being passed. I don't know what partition root= points to; but this is the only possible thing I could see. Grub really doesn't care what you want to start, it will just run the kernel and initrd you tell it to. Unless this is a quite unforeseen and unlikely bad interaction between kernel drivers and the limited gfxmode changes we do in grub... but we'd see this on more than just this system. Could you please attach a video or pictures of what you're seeing on the screen, along with clear details of *any* modifications you do to boot something, how you set up your tests, so that we could potentially reproduce this or see what is happening? I'm cleaning up the title here for clarity; but this seems like either a kernel bug, some missing modules for your particular setup, or bad interactions because of the very complicated multi-boot scenario you're presenting. ** Summary changed: - lightdm login screen briefly appears and then blanks out on Intel(R) Core(TM)2 Duo CPU T5870 (crash in xorg before using "foreign grub") netplan mis-configuration maybe underlying cause. + lightdm login screen briefly appears and then blanks out on Intel(R) Core(TM)2 Duo CPU T5870 ** Changed in: lightdm (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1821609 Title: lightdm login screen briefly appears and then blanks out on Intel(R) Core(TM)2 Duo CPU T5870 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/1821609/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs