I installed Processing from the Arch Linux AUR, and it works fine except for adding external libraries. When I use the Add Library GUI, I always get an error saying Could not download [githuburl] to /tmp/download[numbers][library].zip. I have tried running Processing as root, to the same effect. Is there a way to get the GUI to work? If not, how can I manually install libraries?
I’m not sure I would recommend installing processing from Arch Linux AUR at present (looks unstable). But your error looks like for some reason you haven’t got write access to /tmp? Have you tries a manual install to sketchbook folder? Just unzip the library zip file in ~/sketchbook/libraries folder