X server is the default Graphical User Interface (GUI) toolkit used in almost all flavors of UNIX family of operating systems and most notably Linux and FreeBSD. The famous desktops are KDE and GNOME. X server toolkit has bulit-in support for remote desktops because of its client and server architecture. X server hides the underlying graphics hardware and presents a unified Application Interface (API) for client programs like KDE and GNOME applications. Unlike Microsoft Windows, the client program can reside in another host and X server can reside on another host. i.e A Windows user with a X server software like X-Win32 can login to an UNIX system and open a graphical application like kedit to get the target application appear on the local Windows desktop.

     X Client            X Protocol
      (kedit)  --------------------------- X Server

In the above scenario, X client and X server not necessarily be on same host and can reside on different hosts.

Let us understand how a Windows PC gets a local kedit window that is created by running kedit command at UNIX PC.

     Windows             X Protocol             UNIX
       PC  ----------------------------------    PC
     1.1.1.1                                 2.2.2.2

In this scenario, Windows PC is installed with X server software like X-Win32 and a telnet client or SSH client like PuTTY to access remote UNIX PC. In X-Win32 software, the IP address of UNIX PC (2.2.2.2 in this case) should be given in the access control list. Here X client is kedit program in UNIX PC and X server is X-Win32 server in Windows PC. The following steps explain how it can be done.

1. Install and start X-Wn32 server
2. Open Telnet/SSH connection to UNIX PC to get a remote shell (assuming bash shell in this case)
3. In the remote bash shell, DISPLAY environment variable must be set to specify target X server. In this case the target X server is X-Win32 running in Windows PC so the IP address of Windows PC (1.1.1.1) should be used. The “:0″ in the following command denotes X server display number. Typically it is zero since you have only one X server running in your Windows PC.

   bash# export DISPLAY=1.1.1.1:0

4. Run the command kedit to see kedit window appear in Windows PC. The command can be run as background process by appending “&” to the command so that the remote shell can be closed without disturbing the kedit window.

   bash# kedit &
   bash# exit

Instead of one application, whole desktop like KDE and GNOME can also be viewed. The kedit command can be replaced with startkde for KDE desktop and gnome-session for GNOME desktop.