Visualize results/graphical access¶

DelftBlue has two visualization nodes, visual01 and visual02, each with an NVIDIA Quadro RTX 4000 GPU for running interactive graphical applications. You reach them through the DelftBlue Desktop app in Open OnDemand: a full Linux desktop that runs on a visualization node and that you use directly in your browser — no VNC client, SSH tunnel or X server on your own machine.

Changed in the 2026 stack

The earlier method — loading a desktop module and running the vnc_desktop script to start a VNC server, then connecting with a local VNC client over an SSH tunnel — has been retired. All graphical sessions now go through the DelftBlue Desktop app described below.

Starting a DelftBlue Desktop session¶

Open the Open OnDemand portal and sign in with your NetID and password.
Choose Interactive Apps → DelftBlue Desktop.
Fill in the form:
- Account — your project account, e.g. research-<faculty>-<department>.
- Runtime [h] — how long the session should last (maximum 4 hours).
- Extra arguments for Slurm — the CPU and memory request for the job, for example:
```
--ntasks=1 --cpus-per-task=8 --mem-per-cpu=2G
```
Click Launch. The session is a normal interactive job: it enters the queue and starts once the resources are free.
When the card shows Running, click Launch DelftBlue Desktop.

You must request cores and memory yourself

The form has no separate fields for cores or memory. If Extra arguments for Slurm is left empty, the job is rejected with sbatch: error: ... Job size specification needs to be provided. Always pass at least --ntasks, --cpus-per-task and --mem-per-cpu. Note that memory is given per core (--mem-per-cpu), not as a total. See the Slurm scheduler page for the full list of options.

The DelftBlue Desktop launch form

A running DelftBlue Desktop session

On this card the Image Quality slider defaults to a low setting — raise it for a sharper desktop. Only lower it again, or raise Compression, if your connection is slow.

Your desktop opens in a new browser tab:

The DelftBlue Desktop session

Using the desktop¶

Open a terminal from the panel at the bottom of the screen. Load the visual software collection, then the application you want — for example MATLAB:

module load 2026 visual
module load matlab
matlab &

module load 2026 visual only makes the visualization software (ParaView, VMD, Qt, VTK, ffmpeg, gmsh, …) available to module load; it does not load any of it for you.

The visual stack is a chain stack

2026 visual resolves its dependencies from the cpu-avx512 stack, which keeps it small and quick to build. If you need extra tools or modules that are not in the visual collection, load cpu-avx512 as well: module load 2026 visual cpu-avx512.

For application-specific instructions, see the how-tos for ParaView, Ansys/Workbench and Abaqus.

Graphics acceleration¶

Applications in the DelftBlue Desktop render with software OpenGL (Mesa). Hardware-accelerated rendering with VirtualGL (vglrun) is not yet available in the DelftBlue Desktop.

For visualization that needs the GPU, use the dedicated ParaView entry under Interactive Apps, which runs ParaView with GPU-accelerated (EGL) rendering. The ParaView how-to also describes a client/server setup where ParaView runs on your own machine against a pvserver on DelftBlue.

Harmless warnings on start-up

Some applications print messages such as X Error: ... BadValue or a warning about "creating an OpenGL feedback context" / indirect GLX when they start. With software rendering these are expected and do not affect normal use.

Ending the session¶

Log out from the desktop (Applications → Log Out), or delete the session from My Interactive Sessions in Open OnDemand. The Slurm job then stops and the resources are released. A session also ends automatically when its runtime expires.