NullUserException error. This should be your first choice. Vincent and Michael do a great job with these "ports" of Debian packages that I support. I actually use these "ported" packages on the Ubuntu devices that I use.
If you want to stay with the standard Ubuntu distribution, everything will work. You have to do something wrong (and you didn’t show what you did), since install.packages() works fine with CRAN mirrors, regardless of whether your R-bit works from Ubuntu or CRAN-for-Ubuntu relay above .
In addition, you can also work from the source - in fact, how many of us are developing our packages on Ubuntu and / or Debian.
Finally, for such questions, the r-sig-debian list is an excellent resource with friendly and timely answers to R on Debian / Ubuntu questions. Sign up before you can post.