Linux newbie question: problems using XDMCP to remotely start KDE session from a Windows PC

[Jason M. Dolinger]

Hi all,

I am brand new to the Unix/Linux world, just started taking the 
plunge.  First of all, please forgive me if this is not the 
appropriate place to ask such questions...

I just installed Fedora Core 4 and have been playing around with it 
for several weeks now.  I also have a Windows XP machine connected to 
the same router as the linux box.  I'd love to be able to do 
everything from one machine, therefore setting up an X server on the 
windows box to run X programs and have them appear on my windows 
machine.  I downloaded Xwin32 and have been able to do what I just described.

However I'd like to take it to the next level and be able to popup 
the entire KDE desktop on my windows machine.  I believe that the way 
to do this is using XDMCP, and then Xwin32 is only remotely managing 
the KDE session running on the Linux PC.  However, upon trying to use 
the XDMCP option in Xwin32 to connect, my entire Windows desktop 
turns grey, with a slightly linux-y looking mouse pointer, but 
nothing ever happens.  I need to Alt-tab to get back to any of my 
other windows programs.  Has anyone ever seen this before?

A few things:

1.  In the KDE Login settings (I believe that runs gdmsetup), I've 
checked  "Enable XDMCP" on the XDMCP tab (I'm using the SAMS Red Hat 
Fedora 4 book and it led me to believe that this is all I would need to do).
2.  I've edited /etc/X11/xdm/xdm-config to comment out the line 
"DisplayManager.requestPort:   0".  I added a "!" in front of that line.
3.  I've edited /etc/X11/xdm/kdmrc to change the line "Enable=false" 
to "Enable=true" under [Xdmcp].  Both this step and step 2 I found 
from various internet postings and thought I'd give them a try.
4.  On my network, my windows PC gets a dynamic IP address from my 
router and I configured the Linux machine to use a static IP.  I've 
set up Xwin32 to connect to Linux using it's IPaddress, and the 
Xwin32 configuration specifies the IP address of the windows machine 
to route its display back to.  Both machines can only ping each other 
using their IPaddresses, not hostnames (I've nothing set up in the 
host files for either machine).

Between each configuration steps 1, 2 and 3, I restarted the Linux 
machine (the postings mentioned restarting just X, but I didn't know 
how to do that.  They actually mentioned restarting the X server, but 
that didn't make sense to me.  Isn't the Xserver what is running on 
my Windows PC, but I made the changes on the Linux side?  I thought I 
would need to restart whatever is running on the Linux side, is that 
referred to as the X client?).

Well, that's really it.  Have I missed a magic step somewhere along 
the line, or is the problem more complicated, related to my 
hardware/firewall setup perhaps (I tried this while disabling my 
Windows firewall, no luck)?  At this point, I'm not really sure if 
the issue is the Linux configuration, my network or the X server 
configuration on my PC.  Maybe a different X server (CygwinX 
perhaps?) would give me better luck?

Sorry if this is such a basic thing, I really am just barely starting 
to figure this thing out.

Thanks, any help would be appreciated!

Jason

[Nigel Wade]

Jason M. Dolinger wrote:
> Hi all,
>
> I am brand new to the Unix/Linux world, just started taking the plunge.  
> First of all, please forgive me if this is not the appropriate place to 
> ask such questions...
>
> I just installed Fedora Core 4 and have been playing around with it for 
> several weeks now.  I also have a Windows XP machine connected to the 
> same router as the linux box.  I'd love to be able to do everything from 
> one machine, therefore setting up an X server on the windows box to run 
> X programs and have them appear on my windows machine.  I downloaded 
> Xwin32 and have been able to do what I just described.
>
> However I'd like to take it to the next level and be able to popup the 
> entire KDE desktop on my windows machine.  I believe that the way to do 
> this is using XDMCP, and then Xwin32 is only remotely managing the KDE 
> session running on the Linux PC.  However, upon trying to use the XDMCP 
> option in Xwin32 to connect, my entire Windows desktop turns grey, with 
> a slightly linux-y looking mouse pointer, but nothing ever happens.  I 
> need to Alt-tab to get back to any of my other windows programs.  Has 
> anyone ever seen this before?
>
> A few things:
> In the KDE Login settings (I believe that runs gdmsetup), I've
>
> checked  "Enable XDMCP" on the XDMCP tab (I'm using the SAMS Red Hat 
> Fedora 4 book and it led me to believe that this is all I would need to 
> do).

Are you sure? I don't have a Fedora 4 setup to hand at the moment. But the 
default in RHEL 4 is to use gdm, and this is controlled by 
/etc/X11/gdm/gdm.conf. Check which display manager is actually running.

Also, to see if your display manager is accepting connections from the network 
do a 'netstat -l' and see if there is a udp server listening on *:177 or *:xdmcp.
> I've edited /etc/X11/xdm/xdm-config to comment out the line
>
> "DisplayManager.requestPort:   0".  I added a "!" in front of that line.
> 3.  I've edited /etc/X11/xdm/kdmrc to change the line "Enable=false" to 
> "Enable=true" under [Xdmcp].  Both this step and step 2 I found from 
> various internet postings and thought I'd give them a try.
> 4.  On my network, my windows PC gets a dynamic IP address from my 
> router and I configured the Linux machine to use a static IP.  I've set 
> up Xwin32 to connect to Linux using it's IPaddress, and the Xwin32 
> configuration specifies the IP address of the windows machine to route 
> its display back to.  Both machines can only ping each other using their 
> IPaddresses, not hostnames (I've nothing set up in the host files for 
> either machine).

How is the X server started? Does it broadcast, or query the XDMCP server?
It's strange that the X server would need to be configured with its own IP number.
> Between each configuration steps 1, 2 and 3, I restarted the Linux 
> machine (the postings mentioned restarting just X, but I didn't know how 
> to do that.  They actually mentioned restarting the X server, but that 
> didn't make sense to me.  Isn't the Xserver what is running on my 
> Windows PC, but I made the changes on the Linux side?  I thought I would 
> need to restart whatever is running on the Linux side, is that referred 
> to as the X client?).

In these situations the idea of server and client gets somewhat blurred. What 
actually needs restarting is the XDMCP server on the Linux box. This is, in 
fact, the X server on the Linux box, which communicates with the X server on 
your Windows box. During XDMCP the X server on your Windows PC is acting as a 
client to the XDMCP server (X server) on the Linux box. After login the XDMCP 
server is no longer in the loop, and the X clients on the Linux box communicate 
directly with the X server on the PC. Confused? You will be.
> Well, that's really it.  Have I missed a magic step somewhere along the 
> line, or is the problem more complicated, related to my 
> hardware/firewall setup perhaps (I tried this while disabling my Windows 
> firewall, no luck)?  At this point, I'm not really sure if the issue is 
> the Linux configuration, my network or the X server configuration on my 
> PC.  Maybe a different X server (CygwinX perhaps?) would give me better 
> luck?
>
> Sorry if this is such a basic thing, I really am just barely starting to 
> figure this thing out.
>
> Thanks, any help would be appreciated!
>
> Jason

The Windows firewall must permit the X11 port for connections. This is normally 
port 6000 for display number 0, and increments by 1 for each display.

Do you run a firewall on the Linux box? XDMCP requires port 177. You might also 
need to enable the font server (xfs) to listen on the network rather than just 
the UNIX domain socket (/usr/X11R6/lib/X11/fs/config), and also open that up 
through the firewall on port 7100.

[Sundarapandian A]

There is one more easy way of doing this. Just follow the steps below

1) Make sure you have XFree86 with cygwin is installed on your XP, ssh
is available on XP machine <you can use telnet also>, X server is
running on linux/unix host, sshd is running on linux/unix host.
2) Make sure your <cygwin dir>/usr/X11R6/bin is specified in PATH then
start X Windows using the command "XWin.exe -fullscreen -clipboard
-unixkill -nowinkill"
3) Now you will get XWindows sceen without any applications or window
(You can use ALT+TAB to switch between windows and XWindows)
4) Start xterm on your XP machine (terminal will appear on xwindow screen)
5) On the command prompt of xterm say "xhost <linux/unix server name or IP>"
6) Now on xterm type the command "ssh <username@linux/unix
servername>" enter password to complete the login
7) On the xterm now type "export DISPLAY=<windows XP hostname/IP>:0.0
8) Now on xterm execute "startkde &"
9) Boooom!! now you'll see KDE on your XP machine!!!!

NOTE:
     To check if your sshd is running on your linux/unix machine use
command "service sshd status". If not running start it by "service
sshd start".

Regards,
Sundar.

On 11/30/05, Nigel Wade  wrote:
> Jason M. Dolinger wrote:
> > Hi all,
> >
> > I am brand new to the Unix/Linux world, just started taking the plunge.
> > First of all, please forgive me if this is not the appropriate place to
> > ask such questions...
> >
> > I just installed Fedora Core 4 and have been playing around with it for
> > several weeks now.  I also have a Windows XP machine connected to the
> > same router as the linux box.  I'd love to be able to do everything from
> > one machine, therefore setting up an X server on the windows box to run
> > X programs and have them appear on my windows machine.  I downloaded
> > Xwin32 and have been able to do what I just described.
> >
> > However I'd like to take it to the next level and be able to popup the
> > entire KDE desktop on my windows machine.  I believe that the way to do
> > this is using XDMCP, and then Xwin32 is only remotely managing the KDE
> > session running on the Linux PC.  However, upon trying to use the XDMCP
> > option in Xwin32 to connect, my entire Windows desktop turns grey, with
> > a slightly linux-y looking mouse pointer, but nothing ever happens.  I
> > need to Alt-tab to get back to any of my other windows programs.  Has
> > anyone ever seen this before?
> >
> > A few things:
> > In the KDE Login settings (I believe that runs gdmsetup), I've
> >
> > checked  "Enable XDMCP" on the XDMCP tab (I'm using the SAMS Red Hat
> > Fedora 4 book and it led me to believe that this is all I would need to
> > do).
>
> Are you sure? I don't have a Fedora 4 setup to hand at the moment. But the
> default in RHEL 4 is to use gdm, and this is controlled by
> /etc/X11/gdm/gdm.conf. Check which display manager is actually running.
>
> Also, to see if your display manager is accepting connections from the network
> do a 'netstat -l' and see if there is a udp server listening on *:177 or *:xdmcp.
> > I've edited /etc/X11/xdm/xdm-config to comment out the line
> >
> > "DisplayManager.requestPort:   0".  I added a "!" in front of that line.
> > 3.  I've edited /etc/X11/xdm/kdmrc to change the line "Enable=false" to
> > "Enable=true" under [Xdmcp].  Both this step and step 2 I found from
> > various internet postings and thought I'd give them a try.
> > 4.  On my network, my windows PC gets a dynamic IP address from my
> > router and I configured the Linux machine to use a static IP.  I've set
> > up Xwin32 to connect to Linux using it's IPaddress, and the Xwin32
> > configuration specifies the IP address of the windows machine to route
> > its display back to.  Both machines can only ping each other using their
> > IPaddresses, not hostnames (I've nothing set up in the host files for
> > either machine).
>
> How is the X server started? Does it broadcast, or query the XDMCP server?
> It's strange that the X server would need to be configured with its own IP number.
> > Between each configuration steps 1, 2 and 3, I restarted the Linux
> > machine (the postings mentioned restarting just X, but I didn't know how
> > to do that.  They actually mentioned restarting the X server, but that
> > didn't make sense to me.  Isn't the Xserver what is running on my
> > Windows PC, but I made the changes on the Linux side?  I thought I would
> > need to restart whatever is running on the Linux side, is that referred
> > to as the X client?).
>
> In these situations the idea of server and client gets somewhat blurred. What
> actually needs restarting is the XDMCP server on the Linux box. This is, in
> fact, the X server on the Linux box, which communicates with the X server on
> your Windows box. During XDMCP the X server on your Windows PC is acting as a
> client to the XDMCP server (X server) on the Linux box. After login the XDMCP
> server is no longer in the loop, and the X clients on the Linux box communicate
> directly with the X server on the PC. Confused? You will be.
> > Well, that's really it.  Have I missed a magic step somewhere along the
> > line, or is the problem more complicated, related to my
> > hardware/firewall setup perhaps (I tried this while disabling my Windows
> > firewall, no luck)?  At this point, I'm not really sure if the issue is
> > the Linux configuration, my network or the X server configuration on my
> > PC.  Maybe a different X server (CygwinX perhaps?) would give me better
> > luck?
> >
> > Sorry if this is such a basic thing, I really am just barely starting to
> > figure this thing out.
> >
> > Thanks, any help would be appreciated!
> >
> > Jason
>
> The Windows firewall must permit the X11 port for connections. This is normally
> port 6000 for display number 0, and increments by 1 for each display.
>
> Do you run a firewall on the Linux box? XDMCP requires port 177. You might also
> need to enable the font server (xfs) to listen on the network rather than just
> the UNIX domain socket (/usr/X11R6/lib/X11/fs/config), and also open that up
> through the firewall on port 7100.
>
> --
> Nigel Wade, System Administrator, Space Plasma Physics Group,
>              University of Leicester, Leicester, LE1 7RH, UK
> E-mail :    [e-mail]
> Phone :     [phone], Fax : [phone]
>
> --
> fedora-list mailing list
> [e-mail]
> To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list

--
Trinity: Maybe we did something wrong.
Neo: Or didn't do something.
Morpheus: No, what happened happened and couldn't have happened any other way.
Neo: How do you know?
Morpheus: We are still alive.

[Les Mikesell]

On Thu, 2005-12-01 at 05:31, Sundarapandian A wrote:
> There is one more easy way of doing this. Just follow the steps below
> Make sure you have XFree86 with cygwin is installed on your XP, ssh
>
> is available on XP machine <you can use telnet also>, X server is
> running on linux/unix host, sshd is running on linux/unix host.
> 2) Make sure your <cygwin dir>/usr/X11R6/bin is specified in PATH then
> start X Windows using the command "XWin.exe -fullscreen -clipboard
> -unixkill -nowinkill"
> 3) Now you will get XWindows sceen without any applications or window
> (You can use ALT+TAB to switch between windows and XWindows)
> 4) Start xterm on your XP machine (terminal will appear on xwindow screen)
> 5) On the command prompt of xterm say "xhost <linux/unix server name or IP>"
> 6) Now on xterm type the command "ssh <username@linux/unix
> servername>" enter password to complete the login
> 7) On the xterm now type "export DISPLAY=<windows XP hostname/IP>:0.0
> 8) Now on xterm execute "startkde &"
> 9) Boooom!! now you'll see KDE on your XP machine!!!!
>
> NOTE:
>      To check if your sshd is running on your linux/unix machine use
> command "service sshd status". If not running start it by "service
> sshd start".

Two other ways:
Run gdmconfig on the linux side, click the XDMPC tab and enable
XMDPC logins.
On the windows side run
Xwin -query linux_server
You should get a graphic login prompt.
This gives you a complete Linux desktop in what appears as one
MS window.  Note that you have to disable the XP firewall for
this to work.

Or,
> From a cygwin bash prompt on the windows side:

export DISPLAY=:0
Xwin -clipboard -multiwindow &
ssh -y linux_server
  log in, start X program(s) by typing their names
Each program started should open in it's own individual
window on your desktop and appear like separate MS programs.
Note that you can run 'nautilus' and get what looks like
the desktop without menus or task bars, and you can then
start programs which have launchers in the filesystem (and
you can create these easily by dragging them off the gnome
menu during a normal login).  Programs started this way
also get their own window. I'm not sure if there is a KDE
equivalent.

[Nigel Wade]

Sundarapandian A wrote:
> There is one more easy way of doing this. Just follow the steps below
> Make sure you have XFree86 with cygwin is installed on your XP, ssh
>
> is available on XP machine <you can use telnet also>, X server is
> running on linux/unix host, sshd is running on linux/unix host.
> 2) Make sure your <cygwin dir>/usr/X11R6/bin is specified in PATH then
> start X Windows using the command "XWin.exe -fullscreen -clipboard
> -unixkill -nowinkill"
> 3) Now you will get XWindows sceen without any applications or window
> (You can use ALT+TAB to switch between windows and XWindows)
> 4) Start xterm on your XP machine (terminal will appear on xwindow screen)
> 5) On the command prompt of xterm say "xhost <linux/unix server name or IP>"
> 6) Now on xterm type the command "ssh <username@linux/unix
> servername>" enter password to complete the login
> 7) On the xterm now type "export DISPLAY=<windows XP hostname/IP>:0.0
> 8) Now on xterm execute "startkde &"
> 9) Boooom!! now you'll see KDE on your XP machine!!!!

Boooom!! - anyone else who can login to your Linux box can see everything you 
do, and type. Only do this if security isn't an issue for you.

[Sundarapandian A]

You are right Nigel. Telnet is not secure but ssh will not let you down.

Regards,
Sundar.

On 12/2/05, Nigel Wade  wrote:
> Sundarapandian A wrote:
> > There is one more easy way of doing this. Just follow the steps below
> > Make sure you have XFree86 with cygwin is installed on your XP, ssh
> >
> > is available on XP machine <you can use telnet also>, X server is
> > running on linux/unix host, sshd is running on linux/unix host.
> > 2) Make sure your <cygwin dir>/usr/X11R6/bin is specified in PATH then
> > start X Windows using the command "XWin.exe -fullscreen -clipboard
> > -unixkill -nowinkill"
> > 3) Now you will get XWindows sceen without any applications or window
> > (You can use ALT+TAB to switch between windows and XWindows)
> > 4) Start xterm on your XP machine (terminal will appear on xwindow screen)
> > 5) On the command prompt of xterm say "xhost <linux/unix server name or IP>"
> > 6) Now on xterm type the command "ssh <username@linux/unix
> > servername>" enter password to complete the login
> > 7) On the xterm now type "export DISPLAY=<windows XP hostname/IP>:0.0
> > 8) Now on xterm execute "startkde &"
> > 9) Boooom!! now you'll see KDE on your XP machine!!!!
>
> Boooom!! - anyone else who can login to your Linux box can see everything you
> do, and type. Only do this if security isn't an issue for you.
>
> --
> Nigel Wade, System Administrator, Space Plasma Physics Group,
>              University of Leicester, Leicester, LE1 7RH, UK
> E-mail :    [e-mail]
> Phone :     [phone], Fax : [phone]
>
> --
> fedora-list mailing list
> [e-mail]
> To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list

--
Trinity: Maybe we did something wrong.
Neo: Or didn't do something.
Morpheus: No, what happened happened and couldn't have happened any other way.
Neo: How do you know?
Morpheus: We are still alive.

[John Summerfield]

Nigel Wade wrote:
> Sundarapandian A wrote:
> > There is one more easy way of doing this. Just follow the steps below
> > Make sure you have XFree86 with cygwin is installed on your XP, ssh
> >
> > is available on XP machine <you can use telnet also>, X server is
> > running on linux/unix host, sshd is running on linux/unix host.
> > 2) Make sure your <cygwin dir>/usr/X11R6/bin is specified in PATH then
> > start X Windows using the command "XWin.exe -fullscreen -clipboard
> > -unixkill -nowinkill"
> > 3) Now you will get XWindows sceen without any applications or window
> > (You can use ALT+TAB to switch between windows and XWindows)
> > 4) Start xterm on your XP machine (terminal will appear on xwindow 
> > screen)
> > 5) On the command prompt of xterm say "xhost <linux/unix server name 
> > or IP>"
> > 6) Now on xterm type the command "ssh <username@linux/unix
> > servername>" enter password to complete the login
> > 7) On the xterm now type "export DISPLAY=<windows XP hostname/IP>:0.0
> > 8) Now on xterm execute "startkde &"
> > 9) Boooom!! now you'll see KDE on your XP machine!!!!
>
> Boooom!! - anyone else who can login to your Linux box can see 
> everything you do, and type. Only do this if security isn't an issue for 
> you.

How is this Nigel?
Can you suggest a better way, and explain why it's better?

[Nigel Wade]

John Summerfied wrote:
> Nigel Wade wrote:
> > Sundarapandian A wrote:
> > > There is one more easy way of doing this. Just follow the steps below
> > > Make sure you have XFree86 with cygwin is installed on your XP, ssh
> > >
> > > is available on XP machine <you can use telnet also>, X server is
> > > running on linux/unix host, sshd is running on linux/unix host.
> > > 2) Make sure your <cygwin dir>/usr/X11R6/bin is specified in PATH then
> > > start X Windows using the command "XWin.exe -fullscreen -clipboard
> > > -unixkill -nowinkill"
> > > 3) Now you will get XWindows sceen without any applications or window
> > > (You can use ALT+TAB to switch between windows and XWindows)
> > > 4) Start xterm on your XP machine (terminal will appear on xwindow 
> > > screen)
> > > 5) On the command prompt of xterm say "xhost <linux/unix server name 
> > > or IP>"
> > > 6) Now on xterm type the command "ssh <username@linux/unix
> > > servername>" enter password to complete the login
> > > 7) On the xterm now type "export DISPLAY=<windows XP hostname/IP>:0.0
> > > 8) Now on xterm execute "startkde &"
> > > 9) Boooom!! now you'll see KDE on your XP machine!!!!
> >
> > Boooom!! - anyone else who can login to your Linux box can see 
> > everything you do, and type. Only do this if security isn't an issue 
> > for you.
>
> How is this Nigel?
> Can you suggest a better way, and explain why it's better?

The reason is that "xhost host" permits any X client from host "host" to connect 
to your X server, irrespective of who is executing that client. That X client is 
permitted to to anything - post modal windows to block the display, receive 
keyboard events etc.

The way to allow certain clients to connect, whilst refusing others, is to use 
xauth and the standard MIT_MAGIC_COOKIE. Clients which are unable to supply the 
correct cookie for the server will be refused connection. This is only as secure 
as the filesystem security on any system which holds the xauth files for clients 
which are allowed to connect.

ssh X11 forwarding is no more secure in this respect than xauth - it uses xauth 
on the client. It simply provides a secure tunnel over the network between the 
client and the server. Any user who has access to the xauth file containing the 
cookie can use that tunnel.