dotfiles/memo/sddm-blank.md

What

kernel: Linux 6.17.7-5-cachyos nvidia-driver: cachyos-v3/nvidia-open-dkms 580.105.08-3 sddm: cachyos-v3/sddm 0.21.0-8

SDDM shows a blank screen (only with mouse cursor and tty cursor) after booting into graphical target, but starts normally after restarting the SDDM service.

Why

SDDM starts before the NVIDIA driver is fully initialized, causing the greeter to fail to display properly.

evidence

• Logs after booting (many unrelated lines omitted):

...(maybe unrelated lines)...
systemd[1]: Started Simple Desktop Display Manager.
kernel: NVRM: testIfDsmSubFunctionEnabled: GPS ACPI DSM called before _acpiDsmSupportedFuncCacheInit subfunction = 11.
kernel: bridge: filtering via arp/ip/ip6tables is no longer available by default. Update your scripts to load br_netfilter if you need this.
sddm[878]: Initializing...
sddm[878]: Starting...
sddm[878]: Logind interface found
sddm[878]: Adding new display...
sddm[878]: Loaded empty theme configuration
sddm[878]: Xauthority path: "/run/sddm/xauth_yQfUmV"
sddm[878]: Using VT 2
sddm[878]: Display server starting...
sddm[878]: Writing cookie to "/run/sddm/xauth_yQfUmV"
sddm[878]: Running: /usr/bin/X -nolisten tcp -background none -seat seat0 vt2 -auth /run/sddm/xauth_yQfUmV -noreset -displayfd 16
systemd[1]: Starting Authorization Manager...
kernel: nvidia-modeset: WARNING: GPU:0: Unable to read EDID for display device DP-4
kernel: nvidia-modeset: WARNING: GPU:0: Unable to read EDID for display device DP-4
systemd[1]: Started Authorization Manager.
kernel: [drm] Initialized nvidia-drm 0.0.0 for 0000:01:00.0 on minor 0
systemd[1]: Started Power Profiles daemon.
systemd[1]: Reached target Graphical Interface.
kernel: nvidia 0000:01:00.0: [drm] Cannot find any crtc or sizes
systemd[1]: Startup finished in 5.795s (firmware) + 7.387s (loader) + 1.169s (kernel) + 2.477s (initrd) + 3.421s (userspace) = 20.251s.
systemd[1]: Starting Load/Save Screen Backlight Brightness of backlight:nvidia_0...
systemd[1]: Finished Load/Save Screen Backlight Brightness of backlight:nvidia_0.
sddm[878]: Setting default cursor
sddm[878]: Running display setup script  "/usr/share/sddm/scripts/Xsetup"
sddm[878]: Display server started.
sddm[878]: Socket server starting...
sddm[878]: Socket server started.
sddm[878]: Loading theme configuration from "/usr/share/sddm/themes/sugar-candy/theme.conf"
sddm[878]: Greeter starting...
sddm-helper[1006]: [PAM] Starting...
sddm-helper[1006]: [PAM] Authenticating...
sddm-helper[1006]: [PAM] returning.
sddm-helper[1006]: pam_unix(sddm-greeter:session): session opened for user sddm(uid=950) by (uid=0)
systemd[1]: Created slice User Slice of UID 950.
systemd[1]: Starting User Runtime Directory /run/user/950...
systemd-logind[773]: New session 'c1' of user 'sddm' with class 'greeter' and type 'x11'.
systemd[1]: Finished User Runtime Directory /run/user/950.
systemd[1]: Starting User Manager for UID 950...
(systemd)[1015]: pam_warn(systemd-user:setcred): function=[pam_sm_setcred] flags=0x8002 service=[systemd-user] terminal=[] user=[sddm] ruser=[<unknown>] rhost=[<unknown>]
(systemd)[1015]: pam_unix(systemd-user:session): session opened for user sddm(uid=950) by sddm(uid=0)
systemd-logind[773]: New session '1' of user 'sddm' with class 'manager-early' and type 'unspecified'.
systemd[1015]: Queued start job for default target Main User Target.
systemd[1015]: Created slice User Application Slice.
systemd[1015]: Startup finished in 139ms.
systemd[1]: Started User Manager for UID 950.
systemd[1]: Started Session c1 of User sddm.
sddm-helper[1006]: Writing cookie to "/tmp/xauth_FfqCDd"
sddm-helper[1006]: Starting X11 session: "" "/usr/bin/sddm-greeter --socket /tmp/sddm-:0-HQDlHk --theme /usr/share/sddm/themes/sugar-candy"
sddm[878]: Greeter session started successfully
...(maybe unrelated lines)...

Although the greeter session started successfully, it is not able to display anything due to nvidia 0000:01:00.0: [drm] Cannot find any crtc or sizes, resulting in a blank screen.

• Logs after restarting sddm.service:

...(maybe unrelated lines)...
systemd[1]: Started Simple Desktop Display Manager.
sudo[1123]: pam_unix(sudo:session): session closed for user root
sddm[1150]: Initializing...
sddm[1150]: Starting...
sddm[1150]: Logind interface found
sddm[1150]: Adding new display...
sddm[1150]: Loaded empty theme configuration
sddm[1150]: Xauthority path: "/run/sddm/xauth_XyLFOm"
sddm[1150]: Using VT 1
sddm[1150]: Display server starting...
sddm[1150]: Writing cookie to "/run/sddm/xauth_XyLFOm"
sddm[1150]: Running: /usr/bin/X -nolisten tcp -background none -seat seat0 vt1 -auth /run/sddm/xauth_XyLFOm -noreset -displayfd 16
sddm[1150]: Setting default cursor
sddm[1150]: Running display setup script  "/usr/share/sddm/scripts/Xsetup"
sddm[1150]: Display server started.
sddm[1150]: Socket server starting...
sddm[1150]: Socket server started.
sddm[1150]: Loading theme configuration from "/usr/share/sddm/themes/sugar-candy/theme.conf"
sddm[1150]: Greeter starting...
sddm-helper[1217]: [PAM] Starting...
sddm-helper[1217]: [PAM] Authenticating...
sddm-helper[1217]: [PAM] returning.
sddm-helper[1217]: pam_unix(sddm-greeter:session): session opened for user sddm(uid=950) by (uid=0)
systemd-logind[773]: New session 'c2' of user 'sddm' with class 'greeter' and type 'x11'.
systemd[1]: Started Session c2 of User sddm.
sddm-helper[1217]: Writing cookie to "/tmp/xauth_Qghqzs"
sddm-helper[1217]: Starting X11 session: "" "/usr/bin/sddm-greeter --socket /tmp/sddm-:0-YHEwdP --theme /usr/share/sddm/themes/sugar-candy"
sddm[1150]: Greeter session started successfully
...(maybe unrelated lines)...

How

The key is to avoid the timing race between nvidia init and sddm start. There are multiple ways to achieve this, two for example:

Early KMS:

As described in Hyprland WIKI, this ensures that the NVIDIA driver is loaded in the initramfs and is ready before SDDM starts.

1. enable modset in kernel parameters (e.g. in /etc/default/grub):

GRUB_CMDLINE_LINUX_DEFAULT="... nvidia-drm.modeset=1 ..."

and update grub:

sudo grub-mkconfig -o /boot/grub/grub.cfg

2. specify early loaded modules in /etc/mkinitcpio.conf:

MODULES=(... nvidia nvidia_modeset nvidia_uvm nvidia_drm ...)

and regenerate initramfs:

sudo mkinitcpio -P

3. reboot

Delay starting SDDM:

sudo systemctl edit sddm.service

[Service]
ExecStartPre=/bin/sleep 2

should also do the trick, but less elegant.