Running CAD jobs on headless Linux systems

When running a job that requires a CAD instance (eg. Lumerical Script, Python API, or LumOpt), you still need the runtime (RPM) dependencies for the GUI application, but you do not require a Windowing system like Gnome.

Similarly on clusters, you will have to run scripted workflows on a node with the runtime (RPM) dependencies for the GUI application. Then modify the resources to distribute the workload or submit jobs to the nodes.

The guidelines shown in this KB is for running CAD jobs; Lumerical (.lsf) or Python API (.py) scripts on headless Linux systems. 

• Resource configuration elements and controls
• Running simulations using terminal in Linux 

Notes

• When running a simulation using the script, the resource configuration settings in the Lumerical CAD/IDE. 
• Otherwise, if the Resources was not configured in a headless system and there is no 'Product preference.ini', it will try to run the simulation using all the availeble resources/cores on the machine. 
• You can also use the setresource script, to configure your resources when running simulations in your script. 

Running scripts

Starting with Lumerical 2023 R1, you can run Lumerical scripts (.lsf) from Terminal using 'fdtd-solutions-batch'. This will run the script while "hiding" the CAD/GUI. 

Set the environment variable "QT_QPA_PLATFORM" to "offscreen"

#on RHEL/Rocky Linux# 
export QT_QPA_PLATFORM=offscreen
/opt/lumerical/[[verpath]]/bin/fdtd-solutions-batch {script_file.lsf}

When running Python API scripts (.py), set the solver to 'hide=true'  in your Python (.py) script. 

#lumapi settings / contents in {api_script_file.py}# 
import lumapi fdtd = lumapi.FDTD(filename="simulation.fsp",hide=True)

#on RHEL/Rocky Linux# 
export QT_QPA_PLATFORM=offscreen

#run script 
python3 {api_script_file.py} 

Using virtual display (Xvfb)

For Lumerical 2022 R2 and older releases use the process shown below using Xvfb.

1. Install Xvfb and tmux (consult your operating systems documentation for the install process).
   eg. (on RHEL/Rocky Linux)

   $ sudo yum install xorg-x11-server-Xvfb tmux

2. Open a "tmux" session and a virtual display by:

   tmux 
   Xvfb :## &
   export DISPLAY=:##

   e.g.

   tmux
   Xvfb :99 & 
   export DISPLAY=:99

3. Run your Lumerical script with Xvfb:

   xvfb-run --auto-servernum /opt/lumerical/[[verpath]]/bin/fdtd-solutions -nw -run {script_file.lsf}
   xvfb-run --auto-servernum python3 {api_script_file.py}

Notes

• You only need to run the "Xvfb :## &" command once on your "tmux" session. Unless you want to use a different display number.

• You can check the Xvfb display used by:

  ps -ef | grep Xvfb

• You should get the output of the display numbers used for Xvfb.

  username 1639 1 0 12:00 ? 00:00:00 Xvfb :99
  username 1732 1 0 12:03 ? 00:00:00 Xvfb :10
  username 1796 1748 0 12:09 pts/2 00:00:00 grep --color=auto Xvfb

• From the above, we have Xvfb using display :99 and :10. 

• Run the export DISPLAY command every time you enter into a "tmux" session.

  export DISPLAY=:##

See also

Python API overview 

How to run Lumerical API (Python) scripts in Linux 

Lumerical scripting >> Running Simulations >> Resource Configuration - Ansys Optics