Do you have an OpenGL MTR example with saving to files?

Question

3D

Good day.
For my project, I need to render small meshes (100-1000k tri) with simple materials + ID and save the results to files: color, normal, depth, object_id, etc.
Everything will be rendered on headless servers without a GPU. I plan to use OpenGL with Mesa 3D : llvmpipe.
Can you show an example code (and/or a link) for rendering to several FBOs (PBOs?) at once with saving to files?
Thanks a lot.