Plasma 5.11.5 Leave->Switch user doesn't work

[Goverp]

Running a KDE Plasma desktop, the Application Launcher's "Leave" tab contains Session options "Lock", "Logout" and "Switch User". Choosing "Switch user" brings up a Breeze screen that contains the time, date, a big plus sign in a circle labelled "New session", and two buttons Cancel and Switch.

I used to be able to start a new KDE Desktiop under a different userid, and switch between them using this panel. I can't quite recall how it worked.
I think with only one session running, I simply clicked on "New session", or perhaps "Switch user", and got an sddm login screen for the new session.
With two sessions running, I think the got a choice of the "New session", or an icon for the other session, and could click on one or the other, and hit "Switch user" to either start yet another(never tried that) or switch to the other.

I'm now at Plasma 5.11.5, and clicking on New session does nothing. Cancel and Switch user both return me to my current desktop. I can drag the "New session" icon left and right, as if there could be icons for other sessions, but nothing useful happens.

Googling throws up lots of people with slightly different problems that are totally irrelevant as far as I can tell, and an instance of a problem in UserDelegate.qml back in Plasma 5.11.1, but the patch referred to in that is in 5.11.5, as you'd hope! That fix was in
/usr/share/sddm/themes/breeze/components/UserDelegate.qml, which is an identical file to
/usr/share/plasma/look-and-feel/org.kde.breeze.desktop/contents/components/UserDelegate.qml

Digging some more, it looks like it might be something wrong with
/usr/share/plasma/look-and-feel/org.kde.breeze.desktop/contents/userswitcher/UserSwitcher.qml
but I don't know how to debug qml.

Looking at Plasmashell bug 335708, I might be missing a file
/usr/share/plasma/look-and-feel/org.kde.breeze.desktop/contents/components/UserSelect.qml
However, creating one from that bug doesn't appear to fix it.
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Greybeard

[asturm]

It seems to be a regression with consolekit support. The best solution imo is to switch to elogind. We recently stabilised it, and are going to make it the default for Plasma soon.

[Goverp]

Not totally convinced that ConsoleKit's involved; there's nothing in /var/log/ConsoleKit/history after my initial logon.
The trouble with all this damned Plasma stuff is it appears to leave no trace - literally - when it goes wrong.
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Greybeard

[asturm]

My advice is based on multiple similar cases.

[schnitten]

[Moderator note: this post was originally its own thread, but both asturm and fedeliallalinea reported it as a duplicate of this thread. It has been merged here to keep the solutions together. -Hu]

Hi,

I was using the User Switcher widget for years now. After one of the recent emerge @world updates it is broken. The widget itself is still visible, but with my main user I cannot create a new session anymore. When selected, simply nothing happens. 'Lock Screen' and 'Leave' do work normally.

Are there any logs where I might dig into?

thanks
Christian

[Goverp]

Yes, I've read them Don't like all the kernel changes to implement another bleeding (and possibly infectious) hunk hacked out of systemd. That's not to disparage the guys doing the hacking; it is to disparage systemd, of course.
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Greybeard

[Goverp]

I eventually decided to try elogind.

First of all, it works! Thanks asturm, I can now start another session logged in as another user, which is exactly what I wanted.

Second, I can now run KDE Plasma/Wayland sessions instead of Plasma/X. OK, Wayland is a bit fragile and has a few missing bits, but it's nice to ba able to play with it. Using ConsoleKit Wayland just gave a blank screen after login.

Third, the Gentoo wiki entry makes switching to elogind look far more complicated than it needs to. I needed no changes to my kernel; as far as I can see, the "Configure standard kernel features (expert users)" settings are standard (at least they are on my AMD64 box), and elogind appears to work without "Enable different security models->Simplified Mandatory Access Control Kernel Support". OK, the wiki entry says "recommended" rather than "required", but it seems a lot of faff for no benefit.

I hit a minor issue removing ConsoleKit, some bit of antique KDE had left a hanging USE="qt4" that dragged it in, I don't recall what, but emerging without the qt4 requirement let depclean remove ConsoleKit.

Should I edit the wiki entry, or do people know of reasons to leave the intimidating kernel changes?
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Greybeard