Fixing GPG NO_PUBKEY Error

              By default R version 2.14.1 available on my Ubuntu 12.04 LTS system. I decide to generate some interactive graphs in R but I was not able to generate them because 2.14.1 is very old version of R. So, I decided to upgrade my R from 2.14.1 to 3.2.2 version. So, added an entry into sources.list as shown in following picture.

List of R mirrors can be found at https://cran.r-project.org/mirrors.html.

After made an entry into sources.list and update the system by running following command.

sudo apt-get update

This update command some times throws an error like "GPG error NO_PUBKEY". We can fix this error using y-ppa-manager. To install y-ppa-manager run the following list of commands.

sudo add-apt-repository ppa:webupd8team/y-ppa-manager  // adding repository for y-ppa-manager

sudo apt-get update // updating repository

sudo apt-get install y-ppa-manager // Installing y-ppa-manager

After installing y-ppa-manager, start y-ppa-manager by typing the same in the terminal and it will display GUI as shown below.

Click on Advanced Option and then Select "try to import all missing GPG keys" and click on OK as shown in following figure. It will fix the error "GPG error NO_PUBKEY". Run sudo apt-get update again to see error is fixed or not.