I'm trying to understand why one PC in particular fails to start SDDM since an update to x11-misc/sddm-0.18.1-r6 and ends up with a blank page on VT7. I suspect some pam module malfunction, but I don't understand why this happens
or how to troubleshoot it. Interestingly, if I restart the display-manager service manually, SDDM starts and no longer exits. :-/

This is what syslog shows upon boot:
================================
Apr 9 09:20:04 localhost sddm-helper[4074]: pam_unix(sddm-greeter:session): session opened for user sddm(uid=104) by (uid=0)
Apr 9 09:20:04 localhost kernel: elogind-daemon[1349]: New session c1 of user sddm.
Apr 9 09:20:05 localhost chronyd[3554]: Selected source 192.169.1.1
Apr 9 09:20:05 localhost sddm-helper[4074]: pam_unix(sddm-greeter:session): session closed for user sddm
Apr 9 09:20:05 localhost kernel: elogind-daemon[1349]: Removed session c1. ==========================================

Checking if the display manager service has died I see rc-service reports it
is running! Then, ps reveals this much:

root 3757 0.1 0.1 137296 17092 ? Ssl 12:21 0:00 /usr/bin/sddm root 3898 5.7 0.5 1009092 85500 tty7 Ssl+ 12:21 0:02 /usr/bin/X - nolisten tcp -auth /var/run/sddm/{77032685-d24f-482b-9634-49fce5f11fa0} - background none -noreset -displayfd 17 -seat seat0 vt7

but all I get on VT7 is a blank screen with a cursor on the top left and no mouse or a graphic DM.


Then I login as root on a console and restart the service: ================================================
Apr 9 09:20:38 localhost login[3935]: pam_unix(login:session): session opened for user root(uid=0) by LOGIN(uid=0)
Apr 9 09:20:38 localhost kernel: elogind-daemon[1349]: New session 2 of user root.
Apr 9 09:20:38 localhost login[4087]: ROOT LOGIN on '/dev/tty1'
Apr 9 09:20:41 localhost start-stop-daemon[4111]: Will stop /usr/bin/sddm
Apr 9 09:20:41 localhost start-stop-daemon[4112]: Will stop /usr/bin/sddm
Apr 9 09:20:41 localhost start-stop-daemon[4112]: Will stop PID 3787
Apr 9 09:20:41 localhost start-stop-daemon[4112]: Sending signal 15 to PID 3787
Apr 9 09:20:41 localhost kernel: [drm] enabling PCIE gen 2 link speeds, disable with radeon.pcie_gen2=0
Apr 9 09:20:41 localhost kernel: [drm] PCIE GART of 1024M enabled (table at 0x0000000000040000).
Apr 9 09:20:41 localhost kernel: radeon 0000:01:00.0: WB enabled
Apr 9 09:20:41 localhost kernel: radeon 0000:01:00.0: fence driver on ring 0 use gpu addr 0x0000000080000c00
Apr 9 09:20:41 localhost kernel: radeon 0000:01:00.0: fence driver on ring 1 use gpu addr 0x0000000080000c04
Apr 9 09:20:41 localhost kernel: radeon 0000:01:00.0: fence driver on ring 2 use gpu addr 0x0000000080000c08
Apr 9 09:20:41 localhost kernel: radeon 0000:01:00.0: fence driver on ring 3 use gpu addr 0x0000000080000c0c
Apr 9 09:20:41 localhost kernel: radeon 0000:01:00.0: fence driver on ring 4 use gpu addr 0x0000000080000c10
Apr 9 09:20:41 localhost kernel: debugfs: File 'radeon_ring_gfx' in directory '1' already present!
Apr 9 09:20:41 localhost kernel: debugfs: File 'radeon_ring_cp1' in directory '1' already present!
Apr 9 09:20:41 localhost kernel: debugfs: File 'radeon_ring_cp2' in directory '1' already present!
Apr 9 09:20:41 localhost kernel: debugfs: File 'radeon_ring_dma1' in
directory '1' already present!
Apr 9 09:20:41 localhost kernel: debugfs: File 'radeon_ring_dma2' in
directory '1' already present!
Apr 9 09:20:42 localhost kernel: [drm] ring test on 0 succeeded in 1 usecs
Apr 9 09:20:42 localhost kernel: [drm] ring test on 1 succeeded in 1 usecs
Apr 9 09:20:42 localhost kernel: [drm] ring test on 2 succeeded in 1 usecs
Apr 9 09:20:42 localhost kernel: [drm] ring test on 3 succeeded in 4 usecs
Apr 9 09:20:42 localhost kernel: [drm] ring test on 4 succeeded in 4 usecs
Apr 9 09:20:42 localhost kernel: [drm] ib test on ring 0 succeeded in 0 usecs Apr 9 09:20:42 localhost kernel: [drm] ib test on ring 1 succeeded in 0 usecs Apr 9 09:20:42 localhost kernel: [drm] ib test on ring 2 succeeded in 0 usecs Apr 9 09:20:42 localhost kernel: [drm] ib test on ring 3 succeeded in 0 usecs Apr 9 09:20:42 localhost kernel: [drm] ib test on ring 4 succeeded in 0 usecs Apr 9 09:20:43 localhost sddm-helper[4209]: pam_unix(sddm-greeter:session): session opened for user sddm(uid=104) by (uid=0)
Apr 9 09:20:43 localhost kernel: elogind-daemon[1349]: Existing logind
session ID 2 used by new audit session, ignoring.
Apr 9 09:20:43 localhost kernel: elogind-daemon[1349]: New session c2 of user sddm.
=====

Thereafter SDDM runs on VT7 as expected without exiting. The ps output shows more:

root 4187 0.0 0.1 137444 15656 ? Ssl 12:22 0:00 /usr/bin/sddm root 4197 3.8 0.5 1009092 83352 tty7 Ssl+ 12:22 0:01 /usr/bin/X - nolisten tcp -auth /var/run/sddm/{9cb9ef8e-f25b-4272-9605-8da9ddbef75c} - background none -noreset -displayfd 17 -seat seat0 vt7
root 4213 0.0 0.0 54060 12948 ? S 12:22 0:00 /usr/libexec/ sddm-helper --socket /tmp/sddm-auth500f20d1-4477-420c-9eec-3a53462ef3e6 --id 2 --start /usr/bin/sddm-greeter --socket /tmp/sddm-:0-ivjakp --user sddm -- greeter
sddm 4214 3.5 0.7 997596 111548 ? Sl 12:22 0:01 /usr/bin/ sddm-greeter --socket /tmp/sddm-:0-ivjakp
sddm 4220 0.0 0.0 4696 2408 ? S 12:22 0:00 dbus-launch --autolaunch dd882e08972cbb412f072c225d00d9b6 --binary-syntax --close-stderr sddm 4221 0.0 0.0 4824 2040 ? Ss 12:22 0:00 /usr/bin/ dbus-daemon --syslog-only --fork --print-pid 5 --print-address 7 --session

Any ideas why this is happening, on this PC only and how to fix it?
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