Visualization and VNC Sessions

Frontera uses Intel's Cascade Lake (CLX) processors for all visualization and rendering operations. We use the Intel OpenSWR library to render raster graphics with OpenGL, and the Intel OSPRay framework for ray traced images inside visualization software. OpenSWR can be loaded by executing module load swr.

Frontera currently has no separate visualization queue. All visualization apps are available on all nodes. VNC and DCV sessions are available on any queue, either through the command line or via the TACC Analysis Portal. We recommend submitting to Frontera's development queue for interactive sessions. If you are interested in an application that is not yet available, please submit a help desk ticket through the Frontera Portal.

Remote Desktop Access

Remote desktop access to Frontera is formed through a DCV or VNC connection to one or more compute nodes. Users must first connect to a Frontera login node (see Accessing the System and submit a special interactive batch job that:

  • allocates a set of Frontera compute nodes
  • starts a dcvserver or vncserver remote desktop process on the first allocated node
  • sets up a tunnel through the login node to the dcvserver or vncserver access port

Once the remote desktop process is running on the compute node and a tunnel through the login node is created, an output message identifies the access port for connecting a remote desktop viewer. A remote desktop viewer application is run on the user's remote system and presents the desktop to the user.

Important

If this is your first time connecting to Frontera using VNC, you must run vncpasswd to create a password for your VNC servers. This should NOT be your login password! This mechanism only deters unauthorized connections; it is not fully secure, as only the first eight characters of the password are saved.

All VNC connections are tunneled through SSH for extra security. Follow the steps below to start an interactive session.

  1. Start a Remote Desktop

    TACC has provided a DCV job script (/share/doc/slurm/job.dcv), a VNC job script (/share/doc/slurm/job.vnc) and a combined job script that prefers DCV and fails over to VNC if a DCV license is not available (/share/doc/slurm/job.dcv2vnc). Each script requests one node in the development queue for two hours, creating a remote desktop session, either DCV or VNC.

    login1$ sbatch /share/doc/slurm/job.vnc
login1$ sbatch /share/doc/slurm/job.dcv
login1$ sbatch /share/doc/slurm/job.dcv2vnc

    You may modify or overwrite script defaults with sbatch command-line options. Note that the command options must be placed between sbatch and the script:

    • -t hours:minutes:seconds modify the job runtime
    • -A projectnumber specify the project/allocation to be charged
    • -N nodes specify number of nodes needed
    • -p partition specify an alternate queue

    See Table 7. Commond sbatch Options for more sbatch options.

    All arguments after the job script name are sent to the vncserver command. For example, to set the desktop resolution to 1440x900, use:

    login1$ sbatch /share/doc/slurm/job.vnc -geometry 1440x900

    The vnc.job script starts a vncserver process and writes to the output file, vncserver.out in the job submission directory, with the connect port for the vncviewer.

    Note that the DCV viewer adjusts desktop resolution to your browser or DCV client, so desktop resolution does not need to be specified.

    Watch for the "To connect" message at the end of the output file, or watch the output stream in a separate window with the commands:

    login1$ touch vncserver.out ; tail -f vncserver.out
login1$ touch dcvserver.out ; tail -f dcvserver.out

    The lightweight window manager, xfce, is the default DCV and VNC desktop and is recommended for remote performance. Gnome is available; to use gnome, open the ~/.vnc/xstartup file (created after your first VNC session) and replace startxfce4 with gnome-session. Note that gnome may lag over slow internet connections.

  2. Create an SSH Tunnel to Frontera

    DCV connections are encrypted via TLS and are secure. For VNC connections, TACC requires users to create an SSH tunnel from the local system to the Frontera login node to assure that the connection is secure. The tunnels created for the VNC job operate only on the localhost interface, so you must use localhost in the port forward argument, not the Frontera hostname. On a Unix or Linux system, execute the following command once the port has been opened on the Frontera login node:

    localhost$ ssh -f -N -L xxxx:localhost:yyyy username@frontera.tacc.utexas.edu

    where:

    • yyyy is the port number given by the vncserver batch job
    • xxxx is a port on the remote system. Generally, the port number specified on the Frontera login node, yyyy, is a good choice to use on your local system as well
    • -f instructs SSH to only forward ports, not to execute a remote command
    • -N puts the ssh command into the background after connecting
    • -L forwards the port

    On Windows systems find the menu in the Windows SSH client where tunnels can be specified, and enter the local and remote ports as required, then ssh to Frontera.

  3. Connecting the vncviewer

    Once the SSH tunnel has been established, use a VNC client to connect to the local port you created, which will then be tunneled to your VNC server on Frontera. Connect to localhost:xxxx, where xxxx is the local port you used for your tunnel. In the examples above, we would connect the VNC client to localhost::xxxx. (Some VNC clients accept localhost:xxxx).

    We recommend the TigerVNC VNC Client, a platform independent client/server application.

    Once the desktop has been established, two initial xterm windows are presented (which may be overlapping). One, which is white-on-black, manages the lifetime of the VNC server process. Killing this window (typically by typing exit or ctrl-D at the prompt) will cause the vncserver to terminate and the original batch job to end. Because of this, we recommend that this window not be used for other purposes; it is just too easy to accidentally kill it and terminate the session.

    The other xterm window is black-on-white, and can be used to start both serial programs running on the node hosting the vncserver process, or parallel jobs running across the set of cores associated with the original batch job. Additional xterm windows can be created using the window-manager left-button menu.

Running Applications on the Remote Desktop

From an interactive desktop, applications can be run from icons or from xterm command prompts. Two special cases arise: running parallel applications, and running applications that use OpenGL.

Running Parallel Applications from the Desktop

Parallel applications are run on the desktop using the same ibrun wrapper described above (see Running). The command:

c101-001$ ibrun ibrunoptions application applicationoptions

will run application on the associated nodes, as modified by the ibrun options.

Running OpenGL/X Applications On The Desktop

Frontera uses the OpenSWR OpenGL library to perform efficient rendering. At present, the compute nodes on Frontera do not support native X instances. All windowing environments should use a DCV desktop launched via the job script in /share/doc/slurm/job.dcv, a VNC desktop launched via the job script in /share/doc/slurm/job.vnc or using the [TACC Analysis Portal][TACCANALYSISPORTAL].

swr: To access the accelerated OpenSWR OpenGL library, it is necessary to use the swr module to point to the swr OpenGL implementation and configure the number of threads to allocate to rendering.

c101-001$ module load swr
c101-001$ swr options application application-args

Parallel VisIt on Frontera

VisIt was compiled under the Intel compiler and the mvapich2 and MPI stacks.

After connecting to a VNC server on Frontera, as described above, load the VisIt module at the beginning of your interactive session before launching the VisIt application:

c101-001$ module load swr visit
c101-001$ swr visit

VisIt first loads a dataset and presents a dialog allowing for selecting either a serial or parallel engine. Select the parallel engine. Note that this dialog will also present options for the number of processes to start and the number of nodes to use; these options are actually ignored in favor of the options specified when the VNC server job was started.

Preparing Data for Parallel Visit

VisIt reads nearly 150 data formats. Except in some limited circumstances (particle or rectilinear meshes in ADIOS, basic netCDF, Pixie, OpenPMD and a few other formats), VisIt piggy-backs its parallel processing off of whatever static parallel decomposition is used by the data producer. This means that VisIt expects the data to be explicitly partitioned into independent subsets (typically distributed over multiple files) at the time of input. Additionally, VisIt supports a metadata file (with a .visit extension) that lists multiple data files of any supported format that hold subsets of a larger logical dataset. VisIt also supports a "brick of values (bov) format which supports a simple specification for the static decomposition to use to load data defined on rectilinear meshes. For more information on importing data into VisIt, see Getting Data Into VisIt.

Parallel ParaView on Frontera

After connecting to a VNC server on Frontera, as described above, do the following:

  1. Set up your environment with the necessary modules. Load the swr, qt5, ospray, and paraview modules in this order:

    c101-001$ module load swr qt5 ospray paraview

  2. Launch ParaView:

    c101-001$ swr -p 1 paraview [paraview client options]

  3. Click the "Connect" button, or select File -> Connect

  4. Select the "auto" configuration, then press "Connect". In the Paraview Output Messages window, you'll see what appears to be an 'lmod' error, but can be ignored. Then you'll see the parallel servers being spawned and the connection established.