Overview

Due to the ease of use and excellent graphics performance of the SCC OnDemand system’s Desktop Session, we recommended its use instead of using VNC as described here.

VNC (Virtual Network Computing) is a graphical desktop sharing system that allows users to remotely work on another computer. It works by transmitting the keyboard and mouse events from your local machine to the remote machine. VNC is available on all of the SCC login nodes; but requires setup before using

Using VNC on the Shared Computing Cluster (SCC) presents two major benefits:

  1. It provides high graphics compression, so you can use GUI-based and
    graphics applications at a speed comparable to if the application was running on your local machine.
  2. VNC session is persistent, so you can suspend your session,
    disconnect your computer and resume your session at a later time.

VNC Server Setup

Table of Contents

  1. VNC Server setup
  2. Configure SSH tunnel
  3. Connect with VNC Client – PC
  4. Connect with VNC Client – Mac
  5. Terminating VNC server
  6. Stop SSH tunneling
  7. Running Interactive Jobs on SCC cluster during VNC session
  8. Frequently Asked Questions

VNC Server setup

Login to the SCC cluster using any login node. The first time you use vncserver, you have to establish your VNC password. This VNC password must be different from your Kerberos password and, if you have one, your local SCC Linux password. To setup VNC password, execute the following command:

scc1$ vncpasswd

To start VNC server, run the following script in your SCC Linux terminal window:

scc1$ vncstart

If vncserver started successfully you will see an output similar to the following:

Launching VNC server ...

=================================================

     *** Your VNC server is now running! ***

         VNC desktop number: 6

         VNC Port number: 5906

=================================================
To connect via VNC client:
1. On your local machine execute the following command:

    ssh ktrn@scc1.bu.edu -L XXXX:localhost:5906

	    where XXXX - some number greater than 1023.

2. Start your local VNC Client application and enter the following address 
in VNC server field:

    localhost:XXXX
=================================================

This output will provide you with a VNC desktop and port information. It will also give you the detailed information about configuring SSH tunneling and setting up the VNC client.

Configure SSH tunnel

Linux and Mac users can execute the ssh command, given in step 1. of the vncstart script output. This should be entered in your local machine’s terminal window, e.g.

> ssh ktrn@scc1.bu.edu -L 7070:localhost:5906

You will be asked to enter your Kerberos/SCC password.

If the number XXXX you chose for SSH tunneling is not available, you might get an error message that includes the text “cannot listen to port:” and “Could not request local forwarding.“. In this situation, try another port number, such as one number higher. It is important that you keep this connection running while using VNC.

Windows users can execute the same command in their MobaXterm local terminal window.

Connect with VNC Client – PC

If you do not have the VNC viewer built into your system, download RealVNC from www.realvnc.com. When you install it, select only the VNC Viewer (you do not need to install VNC server on your local machine). Start the VNC Viewer and when a dialog window appears, enter:

VNC server: localhost:XXXX

where XXXX is the number you selected while configuring SSH tunneling (7070 in the example above). You will be prompted to enter your password. Use your VNC (not Kerberos) password.

Connect with VNC Client – MAC

Recent versions of Mac OSX have a VNC client built into the operating system. To connect on a Mac, click on the desktop then press the key combo ⌘-K, which will open the Screen Sharing application. In the Connect to Server window that opens, enter the following into the Server Address box, using the port number selected earlier in place of the XXXX:

vnc://localhost:XXXX

You will be prompted to enter your password. Use your VNC (not Kerberos) password.

Terminating VNC server

When you quit the VNC viewer, the remote VNC server stays running. You can reconnect to the same session at a later time. Please terminate your VNC server when you no longer need it.
Use the Desktop number you were given in the script output to terminate the server, using vncserver -kill :desktop_number command, e.g.:

% vncserver -kill :6

Stop SSH tunneling

To stop the tunnel, log out of the ssh session you started on your local machine.

Running Interactive Jobs on SCC cluster during VNC session

All usage policies remain the same during your work using a VNC connection. Any job that requires more than 15 minutes of CPU time should be executed on one of the compute nodes. Use the qsh or qrsh command to start an interactive batch job. Please refer to the Running Interactive Jobs page for more information about how to start an interactive batch job.

Frequently Asked Questions

  1. I forgot my VNC password. How can I retrieve it?
    Run the vncpasswd command on the SCC cluster to reset your VNC password.
  2. The script says I am already running a vncserver. How can I check what vncserver I am running?
    Execute the vncserver -list command on the SCC cluster. It will list all vncservers you started along with their desktop numbers.
  3. I tried to use the VNC client built into Mac OS, but it does not work. What should I do?
    Try the RealVNC client.
  4. How can I cut and paste text between my remote desktop and my local machine?
    The VNC connection allows for copying and pasting ASCII text between your local machine and the remote desktop.
  5. There are many log files in the .vnc subdirectory of my home directory. They take up a lot of space. Can I delete them?
    The VNC server creates a log file every time you start it. Eventually these files may take a lot of space. You can delete old log files by running the rm *.log command.
  6. How secure is VNC connection?
    SSH Tunneling required for our VNC connections strongly encrypts all traffic between your local machine and the SCC server. SSH also compresses the encrypted data making the connection even faster which is especially useful while running VNC over slow links. It is also very important that you do not use your Kerberos password as your VNC password.
  7. I do not see my application (such as MATLAB, ENVI, RStudio, etc…) listed in the Applications menu. How do I start it?
    All programs on the SCC should be started from the terminal window within your desktop session (launched by selecting Application->System ->Terminal). If you plan to run the program for more than 15 minutes of CPU time, start an interactive job (qrsh) in your terminal window and then start your program on the compute node you are assigned to.
  8. I have a question not listed here. Who do I contact?
    For questions or to report problems, please send email to help@scc.bu.edu