[SOLVED] buster/KDE: cannot unlock screen

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[SOLVED] buster/KDE: cannot unlock screen

Postby baldyeti » 2021-02-07 12:12

On a buster system running plasma, the unlock screen dialog does not work. i can see (by making the typed characters visible) that the keyboard layout is correct and the proper password typed, but all i get is "unlocking failed". I have had this problem forever (probably already when the version was still jessie + KDE4).
Last edited by baldyeti on 2021-02-07 14:02, edited 1 time in total.
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Re: buster/KDE: cannot unlock screen

Postby Head_on_a_Stick » 2021-02-07 13:03

Check the logs.
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Re: buster/KDE: cannot unlock screen

Postby baldyeti » 2021-02-07 13:19

from /var/log/auth.log:
Feb 7 14:02:43 shoggoth unix_chkpwd[12355]: check pass; user unknown
Feb 7 14:02:43 shoggoth unix_chkpwd[12355]: password check failed for user (baldyeti)
Feb 7 14:02:43 shoggoth kcheckpass[12344]: pam_unix(kde:auth): authentication failure; logname= uid=1000 euid=1000 tty=:0 ruser= rhost= user=baldyeti

the "user unknown" bit is odd...
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Re: buster/KDE: cannot unlock screen

Postby baldyeti » 2021-02-07 13:22

I forgot to mention I can unlock from a console using "loginctl unlock-session n" , just not from the graphical dialog.
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Re: buster/KDE: cannot unlock screen

Postby baldyeti » 2021-02-07 13:47

Found the following suggestion on reddit:

Code: Select all
chmod 4755 /sbin/unix_chkpwd

This works but i have no idea how these permissions changed on my system and why so very few other users seem affected..
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Re: buster/KDE: cannot unlock screen

Postby baldyeti » 2021-02-07 13:58

looks like a bug was once opened against [libpam-modules-bin], only to be deemed "unreproducible".
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Re: [SOLVED] buster/KDE: cannot unlock screen

Postby Head_on_a_Stick » 2021-02-07 14:16

You should read that report again only properly this time:

https://bugs.debian.org/cgi-bin/bugrepo ... =914541#31

Your system is misconfigured and changing the permission on /sbin/unix_chkpwd just makes that worse. The change will be reverted after an update of the package anyway.

The actual solution is explained in the bug report post to which I have linked above.
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Re: [SOLVED] buster/KDE: cannot unlock screen

Postby baldyeti » 2021-02-07 14:29

Alright I agree changing group membership of /etc/shadow is a better solution (it was set to utmp).

No need to speak in minimalistic riddles, though ("read the logs", "re-read that post properly")
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Re: [SOLVED] buster/KDE: cannot unlock screen

Postby Head_on_a_Stick » 2021-02-07 14:37

baldyeti wrote:No need to speak in minimalistic riddles

You try being verbose after 20,000+ posts...
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