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I have a strange problem. I'm running a Debian testing installation and recently with KDE5 update stream, I got SDDM instead of KDM. However, SDDM does not log me in even when I enter my correct password. When I enter my password:

  • SDDM disappears and looks like login is starting.
  • After some time, SDDM re-appears.

However, if I shutdown SDDM, start X from my user, export display and run startkde, I can use KDE as usual.

The logs doesn't show anything worthy.

Any help is appreciated.

Update 1: Running SDDM from console creates no logs on the console. Other logs (syslog, messages, et al.) show that SDDM tries to start the session, but the session just quits. Strange.

Update 2: I found the relevant log entry: Auth: sddm-helper exited with 2. Which means pam_backend->openSession() somehow gives an error and exits. However, everything is fine with PAM, groups, file permissions and other details. I cannot trace it to the real reason yet, because SDDM logging doesn't help much.

Update 2.1: Looks like it's related with PAM, but PAM stack doesn't give any visible errors.

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    You could check the exact commandline SDDM uses when is runs with ps aux. Then you stop it, and attempt to run is in the foreground on say tty1. Then login as user, and use the root-console to observe any SDDM output. – Alex Stragies Aug 11 '15 at 21:42
  • Looking it now... – bayindirh Aug 11 '15 at 21:52
  • Sorry, but SDDM doesn't give any output to console during its operation. – bayindirh Aug 12 '15 at 23:24
  • This happened to me as well, have you solved it? How did you find out what is happening with PAM? – CMCDragonkai Jan 25 '16 at 11:29
  • Did you try any other display managers? – CMCDragonkai Jan 25 '16 at 11:29
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The problem solved itself after an update. Probably it was a bug with SDDM and there was no problem with the PAM since I've used XDM for the meantime.

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