Bug 504583 - Unable to see lock screen UI (perhaps for screensaver-style use case) for user with blank password
Summary: Unable to see lock screen UI (perhaps for screensaver-style use case) for use...
Status: CONFIRMED
Alias: None
Product: plasmashell
Classification: Plasma
Component: Screen locking (other bugs)
Version First Reported In: 6.3.5
Platform: Fedora RPMs Linux
: NOR normal
Target Milestone: 1.0
Assignee: Plasma Bugs List
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2025-05-20 22:42 UTC by nilskemail+kde
Modified: 2025-05-22 17:48 UTC (History)
2 users (show)

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Description nilskemail+kde 2025-05-20 22:42:21 UTC
SUMMARY
Trying to lock the screen using either the action in the app launcher, krunner, or using the keyboard shortcut instantly unlocks the session again.

STEPS TO REPRODUCE
1. Create a user without a password (or clear the password for the current user)
2. Press Meta+L

OBSERVED RESULT
The screen briefly flashes black but instantly returns to the unlocked plasma session

EXPECTED RESULT
The session should get locked and only get unlocked again upon manual confirmation

SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 42
KDE Plasma Version: 6.3.5
KDE Frameworks Version: 6.14.0
Qt Version: 6.9.0
Kernel Version: 6.14.6-300.fc42.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 7840U w/ Radeon  780M Graphics
Memory: 27.2 GiB of RAM
Graphics Processor: AMD Radeon 780M
Comment 1 nilskemail+kde 2025-05-20 23:01:05 UTC
Log excerpt seems to indicate that unix_chkpwd is instantly invoked:

May 21 00:33:45 kscreenlocker_greet[142466]: qt.gui.imageio: libpng warning: iCCP: known incorrect sRGB profile
May 21 00:33:45 audit[142516]: USER_AUTH pid=142516 uid=1000 auid=1000 ses=3 subj=unconfined_u:unconfined_r:chkpwd_t:s0-s0:c0.c1023 msg='op=PAM:unix_chkpwd acct="septatrix" exe="/usr/bin/unix_chkpwd" hostname=? addr=? terminal=? res=success'
May 21 00:33:45 kscreenlocker_greet[142466]: pam_unix(kde:auth): user [septatrix] has blank password; authenticated without it
May 21 00:33:45 kscreenlocker_greet[142466]: qt.gui.imageio: libpng warning: iCCP: known incorrect sRGB profile
May 21 00:33:45 kscreenlocker_greet[142466]: qt.qpa.wayland: Could not create EGL surface (EGL error 0x3000)
May 21 00:33:45 kscreenlocker_greet[142466]: Failed to write to the pipe: Bad file descriptor.
Comment 2 Nate Graham 2025-05-21 13:32:30 UTC
> May 21 00:33:45 kscreenlocker_greet[142466]: pam_unix(kde:auth): user [septatrix] has blank password; authenticated without it
Well that doesn't look quite right!

...That said, what are you expecting to happen for a passwordless user? You'd like to see the lock screen with just an "Unlock" button on it that takes you back to the regular session when clicked?

Another question: how did you manage to set up a passwordless user on Fedora? On my Fedora 42 install, system policies prevent it.
Comment 3 nilskemail+kde 2025-05-21 16:01:39 UTC
(In reply to Nate Graham from comment #2)
> ...That said, what are you expecting to happen for a passwordless user?
> You'd like to see the lock screen with just an "Unlock" button on it that
> takes you back to the regular session when clicked?

Yes, pretty much exactly that. Similar to what one gets for switching users

> Another question: how did you manage to set up a passwordless user on
> Fedora? On my Fedora 42 install, system policies prevent it.

`sudo passwd -d $USER` should do the trick
Comment 4 TraceyC 2025-05-21 20:07:34 UTC
I tested this on Fedora 42 and was able to reproduce, the lock screen never appears.
I am not able to reproduce on Neon Testing where the lock screen appears, and can be unlocked with pressing Enter. 

This may be a configuration problem on Fedora, but I'll let someone more familiar with pam make that call
Comment 5 Nate Graham 2025-05-22 17:48:13 UTC
I can confirm it, thanks.

I suppose in this case you might at least be using the lock screen as a pretty screensaver or something, and would be unable to make that work.