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What is PuTTY ?

PuTTY is a Windows SSH client that allows you to connect to the CSE servers, giving you a terminal window like you use in the CSE laboratories. PuTTY can be found on the CSE homecomputing CD which can be borrowed from the CSE Help Desk OR can be downloaded from:

What is Xming ?

Xming is a standalone open source X Server for Windows.  Programs that use a graphical user interface like Kate require an X server on your home computer. Xming can be found on the CSE mirror at  You should download the setup program and optionally the fonts package.

Installing PuTTY and XMing

Run the setup programs for PuTTY and Xming. We suggest that you choose the default options for the installation, and choose the options to create icons for PuTTY and Xming on the desktop.

Xming must be running before you run PuTTY.  When it is running, you will see an X icon in the system tray (the bottom right hand side of your Windows screen). If you forget, you can always run it after running PuTTY, even if you are logged on to the CSE login server.

Configuring PuTTY and XMing


STEP 1 - In the box Host Name (or IP Address) enter the server name or IP. If the lecturer for your subject has suggested you use a specific server, enter it instead. For more information about CSE servers and their uses see:

STEP 2 – Make sure SSH is selected.

STEP 3 – Enter Server name in the box below Saved Sessions.

STEP 4 – Click the [-] to expand SSH from the window on the left (if necessary) and click X11.  You should see this screen. Ensure that the checkbox for Enable X11 forwarding is selected.

Under X display location you can have to insert localhosts:0:0

After you have clicked the check box, scroll the left hand window back to the top and click on the Session heading.  You should see the same screen as in Step 1

STEP 5 Click the Save button. The host name you entered should now appear below Default Settings. In the future, you will be able to connect by simply double-clicking this host name.

STEP 6 Click the Open button.

STEP 7 If you see a window like this: click the Yes button.

STEP 8 When you see: login as: enter your CSE username.

STEP 9 When you see: username@servername's password: enter your CSE password.


X11 DISPLAY variables and X forwarding

Assuming we are logged in via "ssh" from WOMBATNET to chinookfe, what are some of the possible problems we can encounter with X11 forwarding ? The first clue, in the following example, is the DISPLAY environment variable.

    $ xterm
    xterm Xt error: Can't open display: :0

Trying to execute a simple "xterm" on chinookfe through "ssh" yields the above error message, which shows that the DISPLAY environment variable is not set correctly. We can confirm this as follows:

    $ echo $DISPLAY

The immediate inclination is to manually set the DISPLAY variable on chinookfe using either "export" or "setenv", depending on your shell. This is not correct, in that the proper operation of "ssh" with X forwarding allows us to avoid setting or trying to set the DISPLAY variable manually, and it even bypasses the need to run the "xhost" command for the chinookfe session on your workstation. A correct DISPLAY setting, assuming a simple X forwarding operation between chinookfe and our hypothetical workstation WOMBATNET, would yield a value such as:

    $ echo $DISPLAY

This varies from what you may have seen in the past, in that often users will place command lines into their login scripts on remote systems that set the DISPLAY variable upon login. Lines like:

      setenv DISPLAY myworkstation:0.0
      export DISPLAY=myworkstation:0.0

should be removed from your dot files (.cshrc, .kshrc, .login, etc.) on NCAR computer systems, as "ssh" will automatically handle forwarding X11 connections for us. This includes setting the DISPLAY environment variable on the remote host, in this case chinookfe.

Assuming we have removed the line(s) setting our DISPLAY variable from our dot files on chinookfe, how do we get "ssh" to do the work for us? Our recommended approach is to use the "-X" option of "ssh" to establish the connection from our hypothetical example workstation WOMBATNET to chinookfe, as follows:

    $ ssh -X

    wombat@chinookfe's password:

After entering our password, we receive the MOTD and are logged into the system.

    Last login: Wed Jul 17 10:34:08 2002 from
    chinookfe: IRIX64 6.5.16, SGI Origin2000 (8 cpus, 8 GB's memory)


We should now have the correct DISPLAY variable set:

    $ echo $DISPLAY

Note that the form of the DISPLAY variable will always be "HOSTNAME:x.y" where "HOSTNAME" is the host we just logged in to, in this case "chinookfe", "x" is a small integer, in this case "10", and "y" is usually "0". What this does, in general terms, is enable X11 forwarding across the established ssh tunnel. The upside is this means we don't have to set DISPLAY through either files or after login, and back on the workstation we don't have to issue a command like "xhost". In addition, all of the X11 traffic is now encrypted. This effect provides better security than the more traditional techniques, and if your facility has a firewall, this may be the only way, because of the tunneling, to get X11 applications to display back to your workstation from the system at NCAR.

You should now be able to execute a simple X11 application like "xterm" and get the window back at your workstation:

    $ xterm &

If this fails to display the "xterm" window, then we need to employ remedial "ssh" diagnostics to try to determine where the X11 authorization problem may exist. With the OpenSSH client software, we can use the same verbose stream debugging we did in our previous example.

Here is also an interesting information

Using X Forwarding on Windows


By Evan Murphy , 4/17/2006. Revised by Mike Vanier , 4/24/2006.

Most CS 11 students do their labs from the comfort and convenience of their own rooms. However, since most people are stuck running Windows, and the CS cluster machines run Linux, there's a problem. If you did your labs on the CS cluster computer, you would get a nice graphical interface to work with. But if you log in remotely to the CS cluster with (say) PuTTY, then all you get is a single terminal. Worse, you can't start up graphical programs, because the graphical interface software on Linux is different from that on Windows.

That being the case, you have these choices:

You can come in to the CS computer lab to do your assignments
You can grin and bear it, and work within one lousy terminal and a non-graphical editor.
You can configure your computer so that it can run Linux programs remotely that have a graphical interface.
This document will cover option 3. If you set this up correctly, you will be able to use all the programs that you would have used in the CS lab on your Windows computer. You'll also be able to run multiple programs on the CS cluster at the same time (e.g. a terminal and a text editor) and all of them will show up on your Windows computer. So working on your labs in your room won't be much different from working on them in the CS lab.

If your computer runs Linux already, you don't need this document -- you just need to know this command:

% ssh -X
where "%" is the terminal prompt. If your computer is a Mac, this document won't help, but I believe there is an X server that works on the Mac (anyone want to look into this?)

The Linux graphical windowing system is called X11, also known as X Windows, or X for short. Note that "X Windows" has nothing whatsoever to do with Microsoft Windows. Nada. Zip. Zero. Forget I even mentioned it.

"X forwarding" is a feature of X where a graphical program runs on one computer, but the user interacts with it on another computer. If you've ever used VNC or Microsoft's Remote Desktop, it's conceptually like that, but it works on a program-by-program or window-by-window basis.

If both computers are running Linux, it's pretty much transparent. However, if you're sitting in front of a Windows computer, it's a little bit trickier -- not much, though! All you need is an X server that runs on Windows, and an SSH client, both of which are freely available.

A Note on Terminology
In X parlance, the "client" is the computer running the program, and the "server" is the computer you're sitting in front of. This might seem backwards: normally the server is the remote computer that's serving you.

Think of it this way: the X server is serving you, the human being, to the programs on the remote computer. The client, a program, makes requests of you through the X server by changing its graphical display, and you respond to it by clicking on it or typing into it.

What You Need
SSH Client
I'm going to explain how to do this with PuTTY, a free and very powerful SSH client for Windows. You can find it here.

You don't need to install PuTTY; just put it in a convenient place and run it. You can leave it on your desktop, or put it in "Program Files" and create a shortcut to the program in your Start Menu. Or you can install it if you like.

X Server and Fonts
You can get the standard X.Org X server ported for Windows; it's called XMing. Actually finding the installer files is a pain, so here are some direct links:

The X server itself
The fonts package
You need both of these!

Now, install both these packages. They have nice Windows installers, so this should be pretty straightforward. Make sure that you put both of them in the same directory (it will do this by default -- be sure to say "yes" even though the directory already exists).

Making It Go
Start XMing
You should have a Start Menu item for XMing. Go ahead and start it. If you're using a firewall, it'll ask you if you want to unblock it. You don't need to.

Look for the "X" icon in your system tray. Hover the mouse over it: it should say something like "Xming server - 0:0". The last bit should be "0:0", but if it's not, pay attention to that and use it below.

I'm assuming you're currently using PuTTY. If not, there's some good documentation on the PuTTY website. It's also very easy to use, so you should be able to start using it without much trouble anyways.

First, open PuTTY. Then, put in your normal settings for connecting to the CS cluster: under host name, put "".

Then, on the left, click on the Connection/SSH/X11 sub-panel. It'll have a few options. Check "Enable X11 Forwarding", and in the "X display location", put "localhost:0:0" in the box (unless you didn't have "0:0" in the section above: then use "localhost:x:y", where "x:y" is whatever you saw on the icon). Leave the radio button on "MIT-Magic-Cookie-1".

Now click back to the main "Session" panel on the left. Put a name (like "CS + XWindows") in the text box in the middle right below "Saved Sessions". Click the "Save" button. From now on, you can double click the connection in the list box when you want to connect to CS; you don't need to do these settings every time.

Press "Open" to start PuTTY. Put in your password or do whatever you do to authenticate. Now run the command "xeyes &". You should get a big pair of googly-eyes that follows the cursor around. It works!

Tips and Tricks
It's important to start the XMing server before you try to start the graphical program you want to run. Otherwise, there won't be anything on your end to draw the windows.

You can put an ampersand ('&') after any command to make it go to the background: i.e. "emacs &" will start emacs and let you continue to use the PuTTY terminal.

Any programs you start in this way will close (and lose your work!) if you close the PuTTY session. So don't do that.

If you need another terminal, instead of running another PuTTY session, try running "xterm &" in your current session. This will create a terminal using the CS cluster's terminal program, and display the window on your computer.

You can run any program that you'd start as if you're sitting in front of one of the terminals in the CS lab. Unfortunately, they're not always installed on login.cs. You can SSH to another computer (try e.g. pacman.cs or pong.cs) if that's the case. Try "mozilla-firefox &", for example. NOTE: In general, you shouldn't be running graphical applications on login.cs anyway, because they often use a lot more computing power than their non-graphical counterparts, and login.cs is not an appropriate computer on which to run computationally-intensive programs. Please keep this in mind.

Very graphics-heavy programs (like, ahem, "mozilla-firefox") may be somewhat slow. Be patient if you're on a slow connection; everything will work eventually. Terminals and editors should be reasonably fast, and that's all you need for most CS 11 tracks.

by Franck Davy (27/09/2004)

Category : Knowledge base - Linux