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Getting a GUI from the Linux Cluster
    Opening a Display from a VCL (or login) node to the user machine.
    • Case 1) Logging in from a Linux workstation.
    • Case 2) Logging in from a Windows workstation.
    • Case 3) Logging in from an EOS Vista lab machine.

      Long computational jobs on the blade center should be run as batch jobs submitted by LSF. GUI based interactive jobs may be helpful for pre and post processing, for viewing results, etc. Using HPC VCL nodes (32 bit or 64 bit) for GUI based applications is convenient (and also polite to other users). Using an HPC VCL node gives a user access to the HPC file systems and also exclusive use of a node.

      Though GUIs can be instantiated on the login nodes, they are likely to run slowly there due to competition with other users. Moreover, other users on the login nodes may find their activities such as editing and compiling files are slow when other users are performing GUI based processing. When several users simultaneously pop GUIs on the login nodes they can lock up and require rebooting.

      To get an HPC VCL node, use your browser to go to vcl.ncsu.edu. Select the HPC VCL application (32 or 64 bit). After the Connect button gives an IP address, use ssh (or from a Windows box ssh or putty) to login.

    • (Case 1) Logging in from a Linux workstation.
      Connect to the Linux cluster login node using ssh. The X-Window traffic will be tunneled back to your workstation through the ssh connection. Check that the command line entry

      >echo $DISPLAY

      returns

      >localhost:16:0

      "16" is likely to be some other small positive integer, where every new ssh login will give a different integer. These identify the ssh tunnels for the X-Window traffic.

      If a blank line is returned then the X-Window ssh tunnel was not established. Log out out the Linux Cluster login node and reconnect using command like:

      >ssh -X login.hpc.ncsu.edu

      and recheck the value of DISPLAY. Then verify that

      >xclock &

      on the command line produces an xclock window (sometimes this small window appears behind your other open windows so look around a bit).

    • Case 2) Logging in from a Windows workstation.

      While Linux, Unix, and related operating systems (such as Mac OS X) come standard with X-Window server and ssh client, Microsoft Windows operating system does not supply either one. To display an X-Windows GUI on a Windows workstation both an X-Window server and an ssh client that can tunnel X-Window traffic must be obtained and installed on the Windows workstation.

      Once these have been installed, start the X-Window server, then use the ssh client to connect to the Linux cluster login node. Note that some X-Window servers provide a capability to display a remote desktop. This is not the correct method to connect to the Linux cluster. The X-Window server should just be running - it should not be used to establish the connection to the cluster.

      Next configure the ssh client to tunnel X-Window traffic. For Putty this is done from the menu items Go to Connection->SSH->Tunnels and check the box "Enable X11 forwarding".

      Now use the ssh client to connect to a Linux cluster login node. Once connected, verify that the command line command

      >echo $DISPLAY

      returns something like "localhost:16.0". The particular number 16 could be some other small positive integer. If so, verify that

      >xclock &

      command pops up a small xterminal clock on your screen. There are explicit instructions at

      http://www.eos.ncsu.edu/software/xwin32/

      X-Win32 is available to all current NC State faculty, staff, and students. An open source option is X/Cygwin.

      In the case of putty, the DISPLAY variable is forwarded only if X11 forwarding in enabled on the client machine putty program. Go to Connection->SSH->Tunnels and check the box "Enable X11 forwarding". Make sure X-Win32 is already running before again logging into henry2.

    • Case 3) Logging in from an EOS Vista lab workstation

      EOS lab machines required the following Sept. 29, 2009. The link also shows how to get an HPC VCL image.

Last modified: September 29 2009 15:22:01.
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