Kubuntu 24.04 - SDDM fails to start Plasma session

[Kyrylo Bohdanenko]

After upgrade to Kubuntu 24.04 SDDM fails to start Plasma Wayland session:
1. I enter the correct credentials
2. The screen goes black for a few seconds
3. The SDDM greeter appears again, asking for login credentials.

However, I can start plasma session manually by running /usr/bin/startplasma-wayland from a different TTY.

Attaching the output of `journalctl -f` during an attempt to start Plasma from SDDM.
The following lines seem to be connected to the problem:

kwi 20 13:17:29 k-laptop sddm[1197]: Authentication for user "kyrboh" successful
kwi 20 13:17:29 k-laptop sddm-helper[1971]: pam_kwallet5(sddm:setcred): pam_kwallet5: pam_sm_setcred
kwi 20 13:17:29 k-laptop sddm-helper[1971]: pam_unix(sddm:session): session opened for user kyrboh(uid=1000) by kyrboh(uid=0)
kwi 20 13:17:29 k-laptop sddm-greeter[1901]: Message received from daemon: LoginSucceeded
kwi 20 13:17:29 k-laptop systemd-logind[807]: New session 11 of user kyrboh.
kwi 20 13:17:29 k-laptop systemd[1]: Started session-11.scope - Session 11 of User kyrboh.
kwi 20 13:17:29 k-laptop sddm-helper[1971]: pam_kwallet5(sddm:session): pam_kwallet5: pam_sm_open_session
kwi 20 13:17:29 k-laptop sddm-helper[1974]: pam_kwallet5: final socket path: /run/user/1000/kwallet5.socket
kwi 20 13:17:29 k-laptop sddm-helper[1971]: pam_env(sddm:session): Unrecognized Option: SAL_USE_VCLPLUGIN=gtk3
                                             - ignoring line
kwi 20 13:17:29 k-laptop sddm-helper[1971]: [PAM] openSession: Critical error - immediate abort
kwi 20 13:17:29 k-laptop sddm[1197]: Authentication error: SDDM::Auth::ERROR_INTERNAL "Critical error - immediate abort"
kwi 20 13:17:29 k-laptop sddm[1197]: Session started false
kwi 20 13:17:29 k-laptop sddm-helper[1971]: [PAM] Asked to close the session but it wasn't previously open
kwi 20 13:17:29 k-laptop sddm-helper[1971]: [PAM] Ended.
kwi 20 13:17:29 k-laptop sddm[1197]: Auth: sddm-helper exited with 2
kwi 20 13:17:29 k-laptop sddm[1197]: Greeter stopping...
kwi 20 13:17:29 k-laptop sddm-helper[1900]: Signal received: SIGTERM

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: sddm 0.20.0-2ubuntu4
ProcVersionSignature: Ubuntu 6.8.0-28.28-generic 6.8.1
Uname: Linux 6.8.0-28-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.28.1-0ubuntu2
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: KDE
Date: Sat Apr 20 13:18:39 2024
InstallationDate: Installed on 2023-11-04 (168 days ago)
InstallationMedia: Kubuntu 22.04.3 LTS "Jammy Jellyfish" - Release amd64 (20230807.1)
SourcePackage: sddm
UpgradeStatus: Upgraded to noble on 2024-04-20 (0 days ago)

[Kyrylo Bohdanenko (kyrboh)]

It seems this got solved for me by editing the ~/.pam_environment file. Previously I had this:

export SAL_USE_VCLPLUGIN=gtk3

Perhaps something for libreoffice... Commenting out that line allows SDDM to start plasma.