Let me start by saying I am completely new to Linux (Ubuntu) and working with R. Currently, I am on R version 2.13 and would like to update to a newer version in order to use some packages that depend on R>= 2.14.
I have the line to my sources.list file as found described here. I then navigate to the terminal and type:
sudo apt-get update
Reading package lists... Done
W: GPG error: http://lib.stat.cmu.edu oneiric/ Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 51716619E084DAB9
Like @Ben Bolker commented (sorry I hijacked your commented, but the correct answer was not yet posted), in the description of the debian package repo there is a section
secure apt which says:
The Debian backports archives on CRAN are signed with the key of "Johannes Ranke (CRAN Debian archive) " with key ID 381BA480. You can fetch this with
gpg --keyserver subkeys.pgp.net --recv-key 381BA480 or alternatively, using another key server,
gpg --keyserver pgp.mit.edu --recv-key 381BA480 If this doesn't work, it might be due to a firewall blocking port 11371. Alternatively, you can search for 0x381BA480 at http://keyserver.noreply.org/ or http://pgp.mit.edu/ and copy the key block into a plain text file, named, for instance, jranke_cran.asc.
If receiving the key with gpg did work, you need to export it to a text file
gpg -a --export 381BA480 > jranke_cran.asc In both cases you need to make the key known to the apt system by running
apt-key add jranke_cran.asc as root.
If you have not already done this, this will probably fix your issue.