Bug 519400 - Lock screen unresponsive after waking from sleep; requires "Switch User" to SDDM to log in
Summary: Lock screen unresponsive after waking from sleep; requires "Switch User" to S...
Status: RESOLVED DUPLICATE of bug 521900
Alias: None
Product: plasmashell
Classification: Plasma
Component: Screen locking (other bugs)
Version First Reported In: 6.6.4
Platform: Arch Linux Linux
: NOR major
Target Milestone: 1.0
Assignee: Plasma Bugs List
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2026-04-25 12:32 UTC by Prabhat Kumar
Modified: 2026-07-15 20:32 UTC (History)
3 users (show)

See Also:
Latest Commit:
Version Fixed/Implemented In:
Sentry Crash Report:


Attachments
kscreenlocker logs gathered using "journalctl -b 0 | grep -i kscreenlocker" (785 bytes, text/plain)
2026-04-25 12:32 UTC, Prabhat Kumar
Details

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Description Prabhat Kumar 2026-04-25 12:32:05 UTC
Created attachment 191787 [details]
kscreenlocker logs gathered using "journalctl -b 0 | grep -i kscreenlocker"

SUMMARY

After locking the screen and putting the system to sleep, the lock screen becomes unresponsive upon waking up. It will not accept input or unlock the session. Clicking the "Switch User" button drops back to the initial SDDM login screen, which functions correctly and allows successfully logging back into the session.

STEPS TO REPRODUCE
1. Lock the Plasma session.
2. Suspend the system to sleep.
3. Wake the system.
4. Attempt to type the password and unlock the screen

Reproducibility: Sometimes (Intermittent)

OBSERVED RESULT
The lock screen won't unlock.

EXPECTED RESULT
The lock screen should accept the password and successfully unlock the existing session.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 6.19.11-arch1-1 (64-bit)
KDE Plasma Version: 6.6.4
KDE Frameworks Version: 6.25.0
Qt Version: 6.11.0

ADDITIONAL INFORMATION

Note on User Impact: While the "Switch User" workaround technically exists, it is highly unintuitive. For months before discovering it, my only perceived way out of this freeze was a hard hardware shutdown via the power button, resulting in lost sessions. Most regular users encountering this will likely do the same, assuming a total system lockup.
Comment 1 TraceyC 2026-05-06 16:56:07 UTC
Logs for searchability

Apr 25 10:44:50 Rlyeh kscreenlocker_greet[19406]: pam_unix(kde:auth): unexpected response from failed conversation function
Apr 25 10:44:50 Rlyeh kscreenlocker_greet[19406]: pam_unix(kde:auth): conversation failed
Apr 25 10:44:50 Rlyeh kscreenlocker_greet[19406]: pam_unix(kde:auth): auth could not identify password for [cthulhu]
Apr 25 10:45:02 Rlyeh kscreenlocker_greet[19406]: pam_unix(kde:auth): unexpected response from failed conversation function
Apr 25 10:45:02 Rlyeh kscreenlocker_greet[19406]: pam_unix(kde:auth): conversation failed
Apr 25 10:45:02 Rlyeh kscreenlocker_greet[19406]: pam_unix(kde:auth): auth could not identify password for [cthulhu]
Apr 25 17:54:08 Rlyeh kscreenlocker_greet[19406]: [PAM worker kde] Authentication attempt too soon. This shouldn't happen!
Comment 2 TraceyC 2026-05-06 16:57:00 UTC
Thanks for the bug report. The logs indicate this is related to bug 481808, but a worse manifestation

Please can you run the following:

❯ QT_LOGGING_RULES=kscreenlocker_greet.debug=true /opt/kde6/lib/libexec/kscreenlocker_greet --testing
and  reproduce the issue.

Also can you share /etc/pam.d/kde  (they differ per distro)

and output of `faillock --user $USER`

Thanks
Comment 3 Prabhat Kumar 2026-05-07 14:16:11 UTC
Hi, thanks for looking into this! Here is the output you requested. I specifically waited for the bug to trigger again so I could catch the exact output when it happens.

Here is all the output:

`/usr/lib/kscreenlocker_greet --testing` log

kscreenlocker_greet: Greeter is starting up.
kscreenlocker_greet: Greeter is running in testing mode
kscreenlocker_greet: Testing mode enabled: true
kscreenlocker_greet: [PAM worker kde-fingerprint] start: successfully started
kscreenlocker_greet: [PAM worker kde-smartcard] start: successfully started
kscreenlocker_greet: [PAM worker kde] start: successfully started
Locked at 1778156568
kscreenlocker_greet: PamAuthenticators: starting authenticators
kscreenlocker_greet: PamAuthenticators: state changing from PamAuthenticators::Idle to PamAuthenticators::Authenticating
kscreenlocker_greet: [PAM worker kde] Authenticate: Starting authentication
kscreenlocker_greet: [PAM worker kde-fingerprint] Authenticate: Starting authentication
kscreenlocker_greet: [PAM worker kde-smartcard] Authenticate: Starting authentication
kscreenlocker_greet: [PAM worker kde-fingerprint] Authenticate: Authentication done, result code: 28 (Module is unknown)
kscreenlocker_greet: [PAM worker kde-smartcard] Authenticate: Authentication done, result code: 28 (Module is unknown)
kscreenlocker_greet: PamAuthenticators: Availability changed for non-interactive authenticator kde-fingerprint true
kscreenlocker_greet: PamAuthenticators: Availability changed for non-interactive authenticator kde-smartcard true
kscreenlocker_greet: PamAuthenticators: Delay started on login failure for non-interactive authenticator kde-fingerprint duration: 2331494
kscreenlocker_greet: PamAuthenticators: Delay started on login failure for non-interactive authenticator kde-smartcard duration: 2134096
kscreenlocker_greet: PamAuthenticators: Availability changed for non-interactive authenticator kde-smartcard false
kscreenlocker_greet: PamAuthenticators: Availability changed for non-interactive authenticator kde-smartcard false
kscreenlocker_greet: PamAuthenticators: Availability changed for non-interactive authenticator kde-fingerprint false
kscreenlocker_greet: PamAuthenticators: Availability changed for non-interactive authenticator kde-fingerprint false
kscreenlocker_greet: [PAM worker kde] Message: Echo-off prompt: Password: 
kscreenlocker_greet: [PAM worker kde] Starting nested event loop to await response
kscreenlocker_greet: PamAuthenticators: Secret prompt from interactive authenticator kde
kscreenlocker_greet: PamAuthenticators: responding to interactive authenticator
kscreenlocker_greet: [PAM worker kde] Received response, exiting nested event loop
kscreenlocker_greet: PamAuthenticators: Interactive authenticator kde changed business
kscreenlocker_greet: [PAM worker] Fail delay function was called, but authentication result was a success!
kscreenlocker_greet: [PAM worker kde] Authenticate: Authentication done, result code: 0 (Success)
kscreenlocker_greet: PamAuthenticators: Interactive authenticator kde changed business
kscreenlocker_greet: PamAuthenticators: Success from interactive authenticator kde
Unlocked

=========

`faillock --user $USER` output

cthulhu:
When                Type  Source                                           Valid

=========

`/usr/lib/pam.d/kde` content

auth       include                     system-local-login

account    include                     system-local-login

password   include                     system-local-login

session    include                     system-local-login

=========

Let me know if you need me to test anything else!
Comment 4 TraceyC 2026-05-07 16:05:47 UTC
Thanks! That's helpful. The developers will need to take a closer look
Comment 5 Nate Graham 2026-07-15 20:32:35 UTC
Thanks. Looks like the same root cause as Bug 521900.

*** This bug has been marked as a duplicate of bug 521900 ***