When using Julia's GR.jl library on Code Ocean, you may find the following error:

GKS: can't open display on ""
     Is your DISPLAY environment variable set correctly?
     Did you enable X11 and TCP forwarding?

GKS: Open failed in routine OPEN_WS

On a headless system like Code Ocean GR.jl must be configured with the output device.
 To do so, either:

  •  set the environment variable in a shell script: export GKSwstype=100 ; or
  •  set it in your Julia code: ENV["GKSwstype"]="100", before using GR ,

For more information, see this GitHub issue.

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