Some graphics libraries such as Julia's GR.jl and Python's VTK require X11 (Linux's windowing system) support files. You're might encounter the following error when running your code: libXt.so.6: cannot open shared object file: No such file or directory .

Add the following apt-get  dependencies to your capsule (using the package management system):

For VTK, these additional dependencies might be required:

For more information on GR.jl, see this GitHub issue.