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I have recently fixed a permission problem of /etc/shadow, changing it from 644 (somehow it has a+r) to 600 (the package default). After that, I cannot unlock the screenlocker in KDE.
kcheckpass[]: pam_unix(kde:auth): authentication failure; logname=USERNAME uid=1000 euid=1000 tty=/dev/pts/2 ruser= rhost= user=USERNAME
kcheckpass[]: Authentication failure for USERNAME (invoked by uid 1000)It seems that it uses PAM kde:auth, which is directed to system-login:auth. However, other components using system-login:auth (for example, sudo) just worked as normal.
I have tried the following:
"chmod 644 /etc/shadow" - Reverting the permission of /etc/shadow to 644 works.
"chmod u+s /usr/lib/kcheckpass" - Granting SUID to kcheckpass also works.
"pacman -Qkk plasma-workspace shadow pam pambase plasma-workspace", thanks for arjoas's direction - No warning displayed.
Tweak /etc/pam.d/system-auth to bypass pam_unix.so and allow all auth attemptes - kscreenlock does allow me to login with any password, so the auth flow shall go through the system-auth:auth.
I've tried with Arch Live USB, and it did work without the need of SUID-ing kcheckpass or changing permission of /etc/shadow, so it seems to be somewhere misconfigured on my side. Do you have suggestion on anywhere else that I can check with?
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