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Ansys Learning Forum › Forums › Discuss Simulation › Photonics › Error when running a topology optimization on a cluster (Linux) › Reply To: Error when running a topology optimization on a cluster (Linux)

January 26, 2024 at 5:29 pm
Lito
Ansys Employee

@samupekkaojanen,

The error below, indicates that the API was not able to open/launch the Lumerical FDTD CAD/GUI, and could not find the CAD/GUI session. 

lumapi.LumApiError: 'Exception [::appOpened]: Session not found'

Are you running CAD jobs (scripts/API) on a headless cluster? You can set the environment variable below on the 2023R2 and newer releases, prior to running the API/script, if you are not using virtual display (Xvfb); 

export QT_QPA_PLATFORM=offscreen

Then set lumapi to "hide" the CAD/GUI session:

lumapi.FDTD(hide=True)

See our KB for details: > Running CAD jobs on headless Linux systems – Ansys Optics

Hope this helps.Â