How can I change gdm/greeter resolution (Debian-9, Xwayland, VMware)

Question

I have a Retina iMac, and I run Debian-9 under a VMware Fusion 8.5.9 virtual machine. Debian-9 has changed the windowing system to something I can't trace out: ps shows gdm3 running a gdm-wayland-session and Xwayland, and after I log in, there's another gdm-session-worker that runs Xorg (which I am familiar with).

   630 ?        Ssl    0:00 /usr/sbin/gdm3
   656 ?        Sl     0:00  \_ gdm-session-worker [pam/gdm-launch-environment]
   747 tty1     Ssl+   0:00  |   \_ /usr/lib/gdm3/gdm-wayland-session gnome-session --autostart /usr/share/gdm/greeter/a
   823 tty1     Sl+    0:00  |       \_ /usr/lib/gnome-session/gnome-session-binary --autostart /usr/share/gdm/greeter/a
   850 tty1     Sl+    0:01  |           \_ /usr/bin/gnome-shell
   951 tty1     Sl+    0:00  |           |   \_ /usr/bin/Xwayland :1024 -rootless -noreset -listen 4 -listen 5 -displayf
   984 tty1     Sl+    0:00  |           \_ /usr/lib/gnome-settings-daemon/gnome-settings-daemon
  1292 ?        Sl     0:00  \_ gdm-session-worker [pam/gdm-password]
  1306 tty2     Ssl+   0:00      \_ /usr/lib/gdm3/gdm-x-session --run-script default
  1308 tty2     Sl+    0:00          \_ /usr/lib/xorg/Xorg vt2 -displayfd 3 -auth /run/user/501/gdm/Xauthority -backgrou
  1316 tty2     Sl+    0:00          \_ /usr/lib/gnome-session/gnome-session-binary
  1364 ?        Ss     0:00              \_ /usr/bin/ssh-agent x-session-manager
  1396 tty2     Sl+    0:03              \_ /usr/bin/gnome-shell
  1489 tty2     Sl+    0:00              \_ /usr/lib/gnome-settings-daemon/gnome-settings-daemon
  1516 tty2     SNl+   0:00              \_ /usr/lib/tracker/tracker-extract
  1526 tty2     SNl+   0:00              \_ /usr/lib/tracker/tracker-miner-fs
  1530 tty2     SNl+   0:00              \_ /usr/lib/tracker/tracker-miner-apps
  1543 tty2     Sl+    0:00              \_ /usr/bin/gnome-software --gapplication-service
  1546 tty2     Sl+    0:00              \_ /usr/lib/evolution/evolution-alarm-notify
  1550 tty2     SNl+   0:00              \_ /usr/lib/tracker/tracker-miner-user-guides

I got Xorg to use full Retina resolution by adding a config file to /usr/share/X11/xorg.conf.d:

user:/usr/share/X11/xorg.conf.d$ cat 20-imac27.conf 
Section "Monitor"
    Identifier "27-inch iMac Retina Display"
    DisplaySize 597 336
    Modeline "5120x2880"  1276.50  5120 5560 6128 7136  2880 2883 2888 2982 -hsync +vsync
    Modeline "2560x1440"   312.25  2560 2752 3024 3488  1440 1443 1448 1493 -hsync +vsync
EndSection

Section "Screen"
    Identifier "Default Screen"
    Monitor "27-inch iMac Retina Display"
    DefaultDepth 24
    SubSection "Display"
        Modes "5120x2880" "2560x1440"
    EndSubSection
EndSection

But the initial gdm greeter shows up on a low-res screen.

How can I provide a ModeLine to Xwayland so that the greeter screen is also at full Retina resolution?

Answer 1

I don't know if this would work in your setup. But, taken from the Arch documentation that has worked for me, I can refer this:

Some desktop environments store display settings in ~/.config/monitors.xml. xrandr commands are then generated on the base of the file content. GDM has a similar file stored in /var/lib/gdm/.config/monitors.xml.

If you have your monitors setup as you like (orientation, scaling, primary and so on) in ~/.config/monitors.xml and want GDM to honor those settings:

$ sudo cp ~/.config/monitors.xml /var/lib/gdm/.config/

$ sudo chown gdm:gdm /var/lib/gdm/.config/monitors.xml

I hope it helps