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Use X forwarding on a personal computer to securely run graphical applications installed on IU's research supercomputers

On this page:

• Overview
• Requirements
• Use SSH with X forwarding
• Use X forwarding for interactive sessions
• Get help

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Overview

The X Window System (also known as X11, or just X) is a software package and network protocol that lets you interact locally, using your personal computer's display, mouse, and keyboard, with the graphical user interface (GUI) of an application running on a remote networked computer.

You can use X forwarding in an SSH session on your personal computer to securely run graphical applications (X clients) installed on the Indiana University research supercomputers.

Requirements

For X forwarding in SSH to work, your personal computer must be running an X server program. The X server program manages the interaction between the remote application (the X client) and your computer's hardware.

Most Linux distributions have the X server installed, but if your personal computer is running Windows or macOS, you will most likely need to install and run an X server application, for example:

• For Windows, download and install Xming. For X forwarding to work, you'll need to start Xming before connecting to the remote system with your SSH client (for example, PuTTY).
• For macOS, download and install XQuartz. For X forwarding to work, you'll need to start XQuartz before making an SSH connection to the remote system. Once XQuartz launches, you can use X forwarding with SSH from the Terminal or from the xterm application in XQuartz.

Additionally, your personal computer's SSH terminal application must have X11 forwarding enabled:

• In Linux, the SSH terminal supports X forwarding by default.
• In macOS, you may need to edit your sshd_config file (typically found at /etc/sshd_config or /etc/ssh/sshd_config) if you have trouble using X forwarding. If sshd_config includes #X11Forwarding no (or just X11Forwarding no), uncomment out the line (remove the leading #), and change it to X11Forwarding yes.
• In PuTTY for Windows, you can enable X forwarding in new or saved SSH sessions by selecting Enable X11 forwarding in the "PuTTY Configuration" window (Connection > SSH > X11).

Also, the remote computer's SSH application must be configured to accept X server connections. The IU research supercomputers all have SSH configured to allow X forwarding (trusted mode only).

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Use SSH with X forwarding

Linux or macOS

To use SSH with X forwarding on your Linux or macOS personal computer to run an X client application installed on an IU research supercomputer:

1. Open your SSH terminal client.
2. On the command line, enter (replacing username with your IU username):
   • For Big Red 3:

     ssh -Y username@bigred3.uits.iu.edu
     

   • For Carbonate:

       ssh -Y username@carbonate.uits.iu.edu

   • For Karst:

       ssh -Y username@karst.uits.iu.edu

   Note:

   The -Y option turns on trusted X forwarding. You should use it only when connecting to secure systems, such as the IU research computers.
3. Log in with your IU passphrase.

To test if X forwarding is working, try running xclock; on the command line, enter:

  xclock

If X forwarding is working, the xclock graphical clock will appear on your personal computer's desktop.

PuTTY for Windows

To use SSH with X forwarding in PuTTY for Windows:

1. Launch your X server application (for example, Xming).
2. Make sure your connection settings for the remote system have Enable X11 forwarding selected; in the "PuTTY Configuration" window, see Connection  > SSH > X11.
3. Open an SSH session to the desired remote system:

   System	Hostname
   Big Red 3	bigred3.uits.iu.edu
   Carbonate	carbonate.uits.iu.edu
   Karst	karst.uits.iu.edu

4. Log in normally with your IU username and passphrase.

To test if X forwarding is working, try running xclock; on the command line, enter:

  xclock

If X forwarding is working, the xclock graphical clock will appear on your personal computer's desktop.

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Use X forwarding for interactive sessions

On Carbonate or Karst

On Carbonate or Karst, if your interactive session requires:

• Less than 20 minutes of processor time: Connect via SSH with X forwarding enabled, and then launch the X client from the command line.
• More than 20 minutes of processor time: Submit a request for an interactive job via the batch system.
  To do so, connect via SSH with X forwarding enabled, and then:
  1. Use the TORQUE qsub command to submit an interactive job request. Add the -I (for interactive) and -X (for X forwarding) flags; for example (on Karst):

       [username@h2 ~]$ qsub -I -X -q interactive -l nodes=1:ppn=1,walltime=1:00:00
       qsub: waiting for job 371037.m2 to start
       qsub: job 371037.m2 ready
       . . . . 
       [username@c5 ~]$ 

  2. If the X client is not already added to your user environment, load the appropriate module; for example:

       [username@c5 ~]$ module load matlab

  3. From the command prompt, launch the X client; for example:

       [username@c5 ~]$ matlab

On Big Red 3

On Big Red 3, submit a request for an interactive job with X11 forwarding in the debug or general partition, and then launch your X application from a compute node:

1. SSH to Big Red 3 with X forwarding enabled.
2. On the command line, use the Slurm srun command with the --x11 flag to request an X11-enabled interactive session in the debug or general partition; for example:

   srun -p general --x11 --pty bash
   

   For more about using the Slurm srun command, see Use Slurm to submit and manage jobs on high-performance computing systems.
3. Once you are placed on a compute node, you can launch graphical X applications (for example, xterm), as well as your own binaries, from the command line. Depending on the application and your ~/.modules file, you may need to load the module for the desired X client before launching the application.

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Get help

Support for IU research supercomputers, software, and services is provided by the Research Technologies  division of UITS. To ask a question or get help, contact UITS Research Technologies .

For more about using Modules to configure your user environment, see Use Modules to manage your software environment on IU's research supercomputers.

ORIGINAL:

https://kb.iu.edu/d/bdnt