UNIX for Dummies Questions & Answers

I know this question might have been asked a lot but couldn't find anything that worked. From a windows machine 'A' I can only SSH into Linux server 'B' from where I can SSH into another Linux server 'C'. I need to be able to run GUI interfaces on server C which run on my Windows machine. I have tried the X11 forwarding with a new tunnel but for some reason doesn't seem to work. I know I am doing something wrong. Any ideas?

Code:

  From A: putty.exe -ssh -L [2222]:C:22 B
  From A: putty.exe -ssh -X -p [2222] localhost

Thanks.

Moderator's Comments:

Please use CODE tags when displaying sample code, sample input, and sample output.

Hi Prasan,

Install VNC server on server 'C' and install VNC client on server 'B'.
Then from Server 'B' command prompt trigger command: vncserver, it will launch GUI of Server 'C'.
You can find lot of website for installing and configuring VNC server.

Thanks
LND

What you need is a (running) X-Server on your Windows machine. There are several, commercial ones and free ones. The one i use (if i have to work on a Windows system at all) is "OpenText Exceed", which is a commercial product. You might want to try "Xming", "MobaXTerm" and similar freely available products for a first test, though.

X-Windows works like this:

There are "X-Servers": an X-Server is a program which manages one (or more) graphical displays. At the same time it offers the display to be used over the network. Think of it like a driver for your graphics cards with a network interface. Notice that the "X-Server" usually runs at your local system (the "client").

Then there are "X-Clients": programs, which use the services an X-Server offers to create their interface. One example for such an X-Client would bei "Firefox", another one "Xterm". These programs usually run on the remote system (the "server").

So, basically you do the following: you connect to some remote system, by whatever you wish: putty, other ssh-clients, telnet or something else. Then you start a program at the remote system. If this program is an X-Client it will try to use your (already running) local X-Server to display its GUI.

Some obstacles in the way: first, the X-Client has to know where an X-Server runs and which one to use (there might be several ones on the network). This is done by creating a variable called DISPLAY before starting the X-Client. It points to your system(s display):

Code:

# export DISPLAY=your.local.hostname.com:0.0
# xterm &

Xterm will now start and display its Window on your system. Instead of a hostname you could also use the IP-address. The ":0.0" at the end means "Screen 0 of Display 0", don't care for that if you only have one screen. X-Servers can utilize several displays at once with several screens each. Then you could tell here which one to use, ":0.0" is the first screen and will probably suffice until you create a truly complex scenario.

Another thing is to tell The X-Server that the remote host (and all the X-Clients running there) are indeed entitled to use your X-Server. You can tune this later, for a first test just use the command

Code:

xhost +

To allow every host to use your X-Server. Note that this is a configuration of your server, not the client. You X-Server should have either this command or some graphical equivalent called "access control" or similar.

Lastly, the communication has to work: X-Server and X-Client use a special protocol to communicate (called "X-Protocol"), which uses port 6000(-6063). Make sure these ports are open between server and client (udp and tcp).

I hope this helps.

bakunin

Thanks guys for your inputs and clarifications.

Think we were able to use a more straightforward approach which seems to work fine.

Windows Server - putty.exe -ssh -X LinuxA
LinuxA - ssh -X LinuxB
LinuxB - xclock.

And it displays the xclock in my Windows Server.