It’s common that GNU/Linux users have to compile R packages when installing them. For packages with dependencies, cran2deb offers a readily-packaged solution for some of the most common packages on Debian. rgdal doesn’t seem to be one of them, and install.packages(“rgdal”) led to a non-zero exit status. The solution: install the dependencies, of course.
sudo apt-get install libproj-dev libgdal-dev
On my machine this pulled a long list of further dependencies, but subsequently rgdal installed without complaints.