I'm connecting to Linux box from Windows using Putty with X11 forwarding and xming as xserver at windows side. SSHD is configured, everything looks normal, I'm able to connect and see, for example xterm, xclock at windows' xming, so the forwarding actually works.

But, when I put kdestart instead of xterm in the putty SSH command field I can only see a black screen with KDE cursor over it. No new session login screen, the display is just black. I spent half a day trying to work out the problem experimenting with different setups but nothing seems to help. My last suspicion was that it happens because I have nvidia accelerated xserver at linux side and KDE is somehow not rendered correctly to get it forwarded. I don't see any errors in logs it just works but the screen is black. The only things that points to KDE presence is the mouse cursor over the black screen - it has KDE styling and it's the only thing that works. Could anyone shed a light as to why it happens and how to fix it?

Thanks!

KDM does not start with startkde. What startkde starts is a user session, i.e. after KDM login session. How to use KDM over SSH, I do not know.

Please try:
start xterm and inside of it start KDE as:

startkde&

then verify if Plasma is running;
ps xa|grep plasma

see if other programs work:
dolphin&

dpalacio wrote:KDM does not start with startkde. What startkde starts is a user session, i.e. after KDM login session. How to use KDM over SSH, I do not know.

Please try:
start xterm and inside of it start KDE as:

startkde&

then verify if Plasma is running;
ps xa|grep plasma

see if other programs work:
dolphin&

Thanks for the reply.
I forgot to mention that on the remote linux box KDM is already started with /etc/init.d/xdm start (it's gentoo) and a user is logged in. What I expect is that when forwarding X11 via SSH with /usr/bin/kdestart as SSH command a new display would initiate starting from 10 (it's configured in the sshd.conf), which is actually the case for xterm (/usr/bin/xterm SSH command in putty) and xclock - I can see the correct display in env , and xterm is forwarded fine. But when /usr/bin/startkde is given - alas a black screen with KDE cursor.

Yes, I already tried startkde from xterm - no success, the command is executed giving a feel like the KDE login screen is started somewhere but nothing on the screen except xterm window. I can Ctrl+C startkde and then it exits to xterm. No errors are logged no login screen.

Under xterm no KDE program works, or it might work but I don't see them on the screen. They're started somewhere like startkde. xclock is started fine but everything what is related to KDE starts somewhere in the background which I can't see on the screen. I can only Ctrl+C them and return back to xterm.

I all so tried adding another user to KDE and tried to login with Putty under a different user which is not currently logged in KDE and the result is precisely the same.

I can use vnc to the real display, I can use xrdp - both of them are working but x11 forward somehow doesn't work. I thought that forward might be faster than vnc or XRDP but I can't make it to work.

Addition - just in case if this has anything to do with the problem - at the same time when I try to forward x11 VNC connection to the real display to the same box is established from another computer.

Try "dbus-launch xterm" as SSH command .

dpalacio wrote:Try "dbus-launch xterm" as SSH command .

xterm starts fine, but when I type in startkde - a black screen appears with kde cursor.

the same result is with

dbus-launch startkde

BTW I have dbus started on the box, the KDE, works on 100%, no problems. But I cannot forward a new session to the local xming server. I'm missing something - black screen with KDE cursor. I can start xclock, xterm, anything which is not related to KDE when I start kcalc in the xterm - it's launched somewhere but I don't see it's window. I can only tell that I don't see it neither in the local xming display nor in the xrdp session to the real desktop.

Additional info:
If I type in kcalc in the forwarded xterm terminal, and then login to the box with ssh, giving ps aux | grep kcalc would produce

xxxx 16882 0.0 0.3 385284 23620 ? S Oct01 0:01 kdeinit4: kcalc [kdeinit] -session 000000000000000000000000000000000000_0000000000_000000

where xxxx is the correct user name, so the kcalc is started, 000 - is a replacement of a real sid

Thanks for helping!

I do not have more ideas on what could be happening. I will try to replicate your problem on a Windows machine later.

See this thread:
X11 Forwarding not working in Qt apps

dpalacio wrote:I do not have more ideas on what could be happening. I will try to replicate your problem on a Windows machine later.
See this thread:
X11 Forwarding not working in Qt apps

Thanks. I'm not sure but it looks like a problem of nvida accelerated desktop. I do have special effects turned off but may be the forward is working not at the correct level. It's forwarding a wrong buffer which is in case of nvidia empty - i.e. everything runs but there is no display forward. May be I could even login.