Linux – How to force GNOME to use Wayland

arch linuxgnomegnome-shellwaylandxorg

TL;DR

gnome-shell does not want to be a Wayland compositor.

Edit: Sometimes it does want to be, sometimes it doesn't.

Log

Dec 31 06:55:26 speedy-desktop gnome-shell[393]: Can't initialize KMS backend: could not find drm kms device
Dec 31 06:55:29 speedy-desktop /usr/lib/gdm/gdm-x-session[410]: (II) [KMS] Kernel modesetting enabled.

I have 2 video cards. (See LSPCI below)

Extended Problem

I've been told that GNOME uses Wayland by default. But for some reason, I don't know how to get them to work together. Arch wiki just mentions the usage of weston and the GDM & GNOME pages don't say anything about wayland… only the GNOME page, but that's only for manual startup.

⚡ loginctl show-session c6 -p Type 
Type=x11 -- GDM

⚡ loginctl show-session c7 -p Type
Type=x11 -- GNOME

Tries

Putting export XDG_SESSION_TYPE=wayland to /etc/profile => no result
Reinstalling the gnome group (yaourt -S gnome) => messed up my NetworkManager, but I fixed that myself.
Launching weston from an X session => works, but weston-launch from a tty hanged my PC… (I can't find logs, if you can comment their path, I'll post them, journalctl -xe doesn't seem to contain anything wayland-or-weston-related)

The only thing I did find in journalctl -xe -b -1 is this:
```
Dec 31 07:18:08 speedy-desktop kernel: radeon_dp_aux_transfer_native: 158 callbacks suppressed
```
Put MUTTER_ALLOW_HYBRID_GPUS=1 to /etc/environment => no result

Almost working…

I was looking through the journal, and… what did I find?

Dec 31 04:31:57 speedy-desktop /usr/lib/gdm/gdm-wayland-session[382]: /usr/lib/gio/modules/libgvfsdbus.so: file too short
Dec 31 04:31:57 speedy-desktop /usr/lib/gdm/gdm-wayland-session[382]: Failed to load module: /usr/lib/gio/modules/libgvfsdbus.so

The file wasn't simply short, it was EMPTY. How? I have no idea.

After lots of g00gling it turned out that my pacman database was corrupt (somehow), and this one-liner (posted here) fixed it.

LANG= pacman -Qkk 2>&1 | grep "^.*: no mtree file$" | cut -d: -f1 | sudo xargs pacman -S --force --noconfirm

BUT GNOME still uses X11. I have absolutely no idea why. Here's the problem:

Dec 31 06:55:26 speedy-desktop gnome-shell[393]: Can't initialize KMS backend: could not find drm kms device
Dec 31 06:55:29 speedy-desktop /usr/lib/gdm/gdm-x-session[410]: (II) [KMS] Kernel modesetting enabled.

X server knows that there is KMS, but gnome-shell doesn't?! What?

Configs?

DEFAULT. I simply haven't touched them. (Or at least I have reversed my modifications)

LSPCI

⚡ lspci | grep VGA
00:01.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Trinity [Radeon HD 7560D]
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Cape Verde PRO [Radeon HD 7750/8740 / R7 250E]

Any help is appreciated!

PS: Just ran yaourt -Syu a couple seconds ago.

Best Answer

I had a similar problem width GDM ("Just FYI, it now works... Partially. Sometimes it starts wayland, sometimes X") and to solve my problem I had to add a driver card module to my mkinitcpio config file. Was something to do with concurrency load with systemd or something like that. Im not an expert so i really dont know. something like this (i915 for intel or nouveau for nvidia):

in /etc/mkinitcpio.conf

MODULES=(... i915 ...)

and then run:

# mkinitcpio

With Weston (untested)

At first I thought Gnome used Weston for its Wayland layer, but apparently it doesn't work that way. If, however, you are using Weston, you can supposedly configure the resolution of external displays in ~/.config/weston.ini:

[output]
name=VGA1
mode=173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync

The output name should be the name of your display. On Arch, you can run this command to find out what displays are connected:

for p in /sys/class/drm/*/status; do con=${p%/status}; echo -n "${con#*/card?-}: "; cat $p; done

To get the right value for the modeline, you can run cvt 1920 1080, or with whatever resolution you need. More information here: https://wiki.archlinux.org/index.php/Wayland#Configuration

With Gnome

It seems that Gnome doesn't have a way to configure display resolutions (at least yet). So I found a bug report that referenced this kernel boot parameter you can use to override the resolution for displays. Read the linked documentation for full details, but on my system, I needed to configure the display "DP-1" to be 1920x1080 at 60Hz, so I added this line to my boot parameters:

video=DP-1:1920x1080@60

I'm using systemd-boot, so I added that to my options line in /boot/loader/entries/arch.conf. If you're using GRUB or anything else, your steps will be different for adding this boot parameter.

I'm actually not sure what will happen now if I boot with this option set and then plug in a display that needs a different resolution. Will this boot parameter override that, or is this a fallback for when automatic detection fails? I don't know. Because I'm not sure, I added a second boot entry that omits this parameter. So sometimes I may need to reboot to get the correct resolution on an external display. But otherwise, it's working fine.