Displaying X-Windows

ENVIRONMENT
  ssh will normally set the following environment variables:
  DISPLAY
    The DISPLAY variable indicates the location of the X11
    server.   It  is automatically set by ssh to point to a
    value of the form hostname:n where  hostname indicates
    the  host  where  the  shell  runs,  and n is an integer
    >= 1.  ssh uses this special value  to  forward X11
    connections  over  the  secure  channel.  The user should
    normally not set  DISPLAY  explicitly, as that will render
    the  X11  connection  insecure  (and will require the user
    to  manually  copy  any  required authorization cookies).

eXcursion tunneling SSH on a Windows PC

1. Download and install eXcursion. Installation can set up Server and Control Panel shortcuts on your desktop; most computer labs have these shortcuts already setup.
2. Click the Control Panel shortcut to configure eXcursion
   or, click Start, go to Programs, find eXcursion, then Control Panel
   or, if eXcursion is running, find it on the taskbar and right-click it and choose Control Panel.
   
3. Click the Display tab and set Multiple Windows.
4. Click the Access tab.
5. Check the Enable Access Control box.
6. Under Node Name add "localhost" and click the Add--> button. This is required for X-windows to tunnel through SSH.
7. Under Node Name add additional Hosts for which you have accounts from the table below. Enter a Node Name, click the Add--> button, go back and enter the next host, etc.
8. When you have finished adding your hosts, click Apply then the Start/Restart Server button at the bottom of the eXcursion Control Panel.

   Hosts	Which system?
   u.arizona.edu	U-System
   hpc.arizona.edu	Super - HPC
   beowulf.hpc.arizona.edu	Beowulf cluster

9. Start SSH Secure Shell but do not actually connect yet. You need to define SSH Profiles as described in SSH Setup for Windows for those hosts.
10. SSH: under the Profiles pulldown, select Edit.
11. SSH: highlight a host profile you have defined and click the X11 Tunneling tab, and check the Tunnel X11 connections box.
12. SSH: click OK.
13. SSH: under the Profiles pulldown again, select the profile you've just set up, then log in to the system, using your NetID and password.
14. To test your setup, type xclock at the prompt. A new window should pop-up.

eXcursion not tunneling SSH on a Windows PC

If

tunneling seems to be too slow for you (as it might be off-campus because inbound and outbound data are encrypted by the SSH tunnel) and you are not worried about someone intercepting/sniffing your data and you are not using one of the X-windowing applications that works better when tunneled (there's a partial list below),

There is no conflict or harm in having localhost along with the other Hosts defined in eXcursion simultaneously. To switch between tunneling and not tunneling X-windows requires just a minor change.

To bypass the SSH tunnel, no changes are needed to your SSH or eXcursion configurations. You only need to route DISPLAY output directly to your "host"--your PC's display--instead of through the tunnel. Only one override is needed:

1. (Optional) You need to know your DNS hostname. If you don't know your PC's hostname (as might happen you use an ISP from home or use DHCP on campus), you can find it when you'veSSH'ed to the remote host with:
       who | grep your_NetID
   For example, if you entered
       who | grep SilentBob
   you might get a response like
       SilentBob    ttyq50   Feb  6  13:57    (123.45.67.89)
2. (Optional) Within parentheses in the response is the your_hostname or a dynamically assigned IP address which you need to capture
3. At the prompt use the format below to set the DISPLAY variable using your_hostname
       setenv DISPLAY your_hostname:0.0
   Using the earlier example, you would enter
       setenv DISPLAY 123.45.67.89:0.0
4. Try the xclock command

xwin32 on a Windows PC

1. Download and install xwin32.
2. Start X-Win32.
3. Minimize the window.
4. Right-click the icon (X) on the task bar.
5. Select X-Config.
6. When the X-Win Configuration window opens, click the Window tab.
7. For Window Mode choose Multiple.
8. Click the Security tab and click the Add button.
9. In the Add X-Host box type 127.0.0.1 (the name of your internal IP address) and check the Access Control box.
10. Click OK.
11. Start SSH Secure Shell but do not actually connect yet. You need to define a profile as described in SSH Setup for Windows for a host like u.arizona.edu or hpc.arizona.edu.
12. SSH: under the Profiles pulldown, select Edit.
13. SSH: highlight the host profile you have defined and click the X11 Tunneling tab, and check the Tunnel X11 connections box.
14. SSH: click OK.
15. SSH: under the Profiles pulldown again, select the profile you've just set up, then log in to the system, using your NetID and password.
16. To test it, type xclock at the prompt. A new window should pop-up.

Problems?

If you have problems X-windowing:
In your SSH Settings file under Tunneling, Tunnel X11 connections can and should always be set--whether you are tunneling through SSH or not.
Verify that you do not have DISPLAY set in your login or shell script. This interferes with SSH's tunneling X11 windows. Find out by entering the commands
    env | grep DISPLAY
For SSH to work properly you should be seeing a response like
    DISPLAY=localhost:##.0
If the display/application is painfully slow off-campus because you are tunneling, try not tunneling.

Do tunnel - Mathematica and Matlab (software on both the U-System and Super) display better when tunneled.
Do not tunnel - Spartan (on Super) displays only when not tunneled.