That would be really nice as those files are really annoying me

(In reply to Florian Röhrer from comment #1)
> That would be really nice as those files are really annoying me

thank you :)
sometime they fill up the whole root folder...

Created attachment 98110 [details]
screenshot...

I have this problem on Gentoo.  I think the problem might have something to do with the su dolphin picking up the wrong HOME path.

Delete all the .slave-socket files and try prefixing the 'dolphin' command with 'HOME=/root'.

i.e., something like this on the command line:

kdesu HOME=/root dolphin

and see if that is a viable workaround .  I've been running it on and off over the past hour and no new .slave-socket files have been created.

(In reply to nsane457 from comment #4)
> I have this problem on Gentoo.  I think the problem might have something to
> do with the su dolphin picking up the wrong HOME path.
> 
> Delete all the .slave-socket files and try prefixing the 'dolphin' command
> with 'HOME=/root'.
> 
> i.e., something like this on the command line:
> 
> kdesu HOME=/root dolphin
> 
> and see if that is a viable workaround .  I've been running it on and off
> over the past hour and no new .slave-socket files have been created.

Never mind.  They show up after logging-in again.

I'm not sure if this is a systemd bug or a dolphin bug.  The relevant journalctl lines pertinent to the problem are:

May 03 18:47:15 Home-PC su[943]: Successful su for root by hodor
May 03 18:47:15 Home-PC su[943]: + /dev/pts/3 hodor:root
May 03 18:47:15 Home-PC kdesud[939]: org.kde.kdesud: Password set!
May 03 18:47:15 Home-PC su[943]: pam_unix(su:session): session opened for user root by (uid=1000)
May 03 18:47:15 Home-PC kdesud[939]: org.kde.kdesud: priority set to  50
May 03 18:47:15 Home-PC su[943]: pam_systemd(su:session): Cannot create session: Already running in a session
May 03 18:47:15 Home-PC kdesud[939]: org.kde.kdesud: Scheduler set to  0
May 03 18:47:15 Home-PC su[943]: pam_unix(su:session): session closed for user root
May 03 18:47:15 Home-PC kdesud[939]: org.kde.kdesud: Executing command:  " dolphin"
May 03 18:47:15 Home-PC kwin_x11[762]: QXcbConnection: XCB error: 3 (BadWindow), sequence: 6328, resource id: 60817423, major code: 18 (ChangeProperty), minor code: 0
May 03 18:47:15 Home-PC su[949]: Successful su for root by hodor
May 03 18:47:15 Home-PC su[949]: + /dev/pts/3 hodor:root
May 03 18:47:15 Home-PC su[949]: pam_unix(su:session): session opened for user root by (uid=1000)
May 03 18:47:15 Home-PC su[949]: pam_systemd(su:session): Cannot create session: Already running in a session
May 03 18:47:15 Home-PC su[949]: pam_systemd(su:session): Cannot create session: Already running in a session
May 03 18:47:15 Home-PC dolphin[955]: QStandardPaths: wrong ownership on runtime directory /run/user/1000, 1000 instead of 0
May 03 18:47:16 Home-PC dolphin[955]: Cannot creat accessible child interface for object:  PlacesView(0x286c0a0)  index:  21
May 03 18:47:16 Home-PC dolphin[955]: QStandardPaths: wrong ownership on runtime directory /run/user/1000, 1000 instead of 0
May 03 18:47:16 Home-PC dolphin[955]: klauncher not running... launching kdeinit
May 03 18:47:16 Home-PC kdeinit5[966]: QStandardPaths: wrong ownership on runtime directory /run/user/1000, 1000 instead of 0
May 03 18:47:16 Home-PC klauncher[967]: QStandardPaths: wrong ownership on runtime directory /run/user/1000, 1000 instead of 0
May 03 18:47:16 Home-PC klauncher[967]: Connecting to deprecated signal QDBusConnectionInterface::serviceOwnerChanged(QString,QString,QString)
May 03 18:47:16 Home-PC klauncher[967]: QStandardPaths: wrong ownership on runtime directory /run/user/1000, 1000 instead of 0
May 03 18:47:16 Home-PC kdeinit5[972]: QStandardPaths: wrong ownership on runtime directory /run/user/1000, 1000 instead of 0
May 03 18:47:16 Home-PC dolphin[955]: QStandardPaths: wrong ownership on runtime directory /run/user/1000, 1000 instead of 0
May 03 18:47:16 Home-PC kdeinit5[973]: QStandardPaths: wrong ownership on runtime directory /run/user/1000, 1000 instead of 0
May 03 18:47:16 Home-PC dolphin[955]: QStandardPaths: wrong ownership on runtime directory /run/user/1000, 1000 instead of 0
May 03 18:47:16 Home-PC kdeinit5[974]: QStandardPaths: wrong ownership on runtime directory /run/user/1000, 1000 instead of 0

It should be using /run/user/0 for the socket files.  It instead tries to use the user's XDG_RUNTIME_DIR.  It detects the incorrect perms and, I guess, defaults to / instead.

It appears to be similar in nature to this bug:
https://lists.freedesktop.org/archives/systemd-devel/2013-November/014370.html

I can confirm the same issue on my manjaro kde installation and also an other user reported it
in the manjaro forum
https://forum.manjaro.org/index.php?topic=33812.0

This bug seems to have been fixed in recent updates:
    KDE Plasma: 5.6.4
    Qt Version: 5.6.0
    Frameworks Version: 5.22.0
    Operating System: Linux 4.5.4-1-default x86_64
    Distribution: "openSUSE Tumbleweed (20160520) (x86_64)"

maybe....

I'm also using KDE Plasma: 5.6.4, Qt Version: 5.6.0, Frameworks Version: 5.22.0 but have noticed no change.

Yes, it comes back finally. Sorry, my mistake.
Could somebody help to tag my previous comment as spam?

I'm removing them with a nightly cron job but they are annoying.

Also, can confirm on KDE 5.7.4 w/frameworks 5.25.0 on Debian Unstable.

i'm on openSUSE Tumbleweed with KDE/Plasma 5.7.4. kernel 4.7.4-2 and still got the same problem
with all the klauncher<XXX>.slave-socket files piling up in the root directory

This bug affect not only dolphin. I think any kde apps lauched with kdesu have same problem. At least i have same problem with Kate.

(In reply to Anton Kuleshov from comment #15)
> This bug affect not only dolphin. I think any kde apps lauched with kdesu
> have same problem. At least i have same problem with Kate.

Yes, it was a bug in kdesu, and it should be fixed in KDE Frameworks 5.29.0.
https://cgit.kde.org/kdesu.git/commit/?id=e3ff52adec249b7cfa1a375866c268485a1cd344