Screen locker broken on KDE and xorg Fatal server error

[Alonso Murillo]

On Linux Mint 18 Cinnamon, works pretty good except for the following errors:

If you install plasma-desktop, login to KDE and lock the screen you get the following message:

The screen locker is broken and unlocking is not possible anymore.
In order to unlock switch to a virtual terminal (e.g. Ctrl+Alt+F2),
log in and execute the command:

loginctl unlock-sessions

Afterwards switch back to the running session (Ctrl+Alt+F9).

This is very annoying.

And if you install SDDM (Simple Desktop Display Manager) and make the default display manager then the screen lock error does away but you start getting Xorg Fatal server error:

_XSERVTransSocketUNIXCreateListener: ...SocketCreateListener() failed
_XSERVTransMakeAllCOTSServerListeners: server already running
(EE)
Fatal server error:
(EE) Cannot establish any listening sockets - Make sure an X server isn'
(EE)
Please consult the The X.Org Foundation support
        at http://wiki.x.org
  for help.
(EE) Okease aksi cgecj tge kif fuke at "/var/log/Xorg.0.log" for additio
(EE)
(EE) Server terminated with error (1). Closing log file.

Regards,
        Alonso Murillo.

[protoman (protomank)]

I have the same problem in Mint 18. Also, if you didn't started a console session before KDE crashes the lock screen, when you switch to console (CTR+ALT+F1) it won't load the login, so you can't even use the suggested command. Solution for me is to CTRL+ALT+BACKSPACE to reset X session. Very annoying.

[Alex Stevenson (clockwork-coder)]

Same problem here too. Mint 18, fresh install.

[gildas (gildas-lepennetier)]

I have the same problem here.
I initially installed Mint 18 Xcfe, then installed the KDE plasma (v5.5.5).

my xscreensaver seem to mess with some things, and this occurs even before I installed KDE, since I have also the problem that the screensaver starts (without really blocking anything, just the image appear) when listening from flash (youtube, soundcloud). I am not just listening, but actually doing something (mouse and keyboard).

It is very annoying, and turning off all some options (lock screen after X minutes) did not help so much.

[Daniel Carvajal (carvajalorama)]

Hello.
I have the same problem. Installed Mint 18 KDE. Fresh Install, running the updates

The screen locker is broken and unlocking is not possible anymore.
In order to unlock switch to a virtual terminal (e.g. Ctrl+Alt+F2),
log in and execute the command:

loginctl unlock-sessions

Afterwards switch back to the running session (Ctrl+Alt+F7).

[jbo5112 (jbo5112)]

I have the same problem on the Linux Mint 18 KDE live installer. It's a live DVD. Why is the screen even locking?!!!

[jbo5112 (jbo5112)]

I also want to add that tab completion is broken for the command loginctl. It completes the argument as "unlock-session", which is a valid argument, but it does so as if there were no "unlock-sessions" command it could use.

[voyager123bg (voyager123bg)]

I confirm Linux Mint 18.2 is also impacted, started off with Mint 18.2 Mate then installed KDE+plasma-desktop on top of it and I get the same irritating behavior when lock screen is performed - black screen with message "The screen locker is broken and unlocking is not possible anymore.
In order to unlock switch to a virtual terminal (e.g. Ctrl+Alt+F2),
log in and execute the command:

loginctl unlock-sessions

Afterwards switch back to the running session (Ctrl+Alt+F9)."

[keildar2005 (keildar2005)]

I have had 18.1 kde mint installed for months no issue. I installed the flatpack ppe ver 3.28 which required a bunch of gnome repository libaries and such and this happened this morning. I also ran the update and upgrade commands.

[Proc (proc)]

Same problem here on KUbuntu since some updates. Additionally after a sleep my whole session crashes with "could not start ksmserver"

[Moses Moore (moses-ubuntu)]

Kubuntu 18.10, every time the screen locks I get this message.

KDE bug report was closed with a not-enough-information status.

$ /usr/lib/x86_64-linux-gnu/libexec/kscreenlocker_greet --testing
QGLXContext: Failed to create dummy context
Locked at 1541199072
Failed to create OpenGL context for format QSurfaceFormat(version 2.0, options QFlags<QSurfaceFormat::FormatOption>(), depthBufferSize 24, redBufferSize -1, greenBufferSize -1, blueBufferSize -1, alphaBufferSize -1, stencilBufferSize 8, samples -1, swapBehavior QSurfaceFormat::SwapBehavior(DoubleBuffer), swapInterval 1, colorSpace QSurfaceFormat::ColorSpace(DefaultColorSpace), profile QSurfaceFormat::OpenGLContextProfile(NoProfile))
KCrash: crashing... crashRecursionCounter = 2
KCrash: Application Name = kscreenlocker_greet path = /usr/lib/x86_64-linux-gnu/libexec pid = 14714
KCrash: Arguments: /usr/lib/x86_64-linux-gnu/libexec/kscreenlocker_greet --testing
Aborted (core dumped)