Trying to do install.packages("rgdal") on my GNU/Linux machine failed at first. It seems that my system had a couple of libraries not installed, so in the terminal:
sudo apt install libgdal-dev
sudo apt install libproj-dev
and then install.packages("rgdal") back in R.
Modified from: https://stackoverflow.com/questions/44382368/rgdal-installation-difficulty-on-ubuntu-16-04-lts
Didier Ruedin 