If you clicked on “Install Updates” button in update manager (or did “sudo apt-get update” via CLI) and you got this error message then installation stops at that point.
So, how to solve it ?? There are different ways to solve it as the error occurs depending on your action which caused to mess your sources.list (/etc/apt/sources.list). Hence there are 3 possible solutions (which I know). try them in sequence.
(P.S. : take backup of files first before you will play with them, at safe place)
* Method 1: (I have tried this on my laptop & it worked.)
Execute following commands
$ cd /var/lib/apt
$ sudo mv lists lists.old
$ sudo mkdir -p lists/partial
$ sudo apt-get update
* Method 2 : (worked on my friend’s laptop)
Go to “Applications –> Accessories –> Terminal”. and run the command below:
sudo apt-get update
Then take notes of all the numbers (keys) after ‘NO_PUBKEY’. I have underlined my missing keys in the image below.
To install the missing public keys, run the command below for each missing key. Replace XXXXXX with the key shown :
sudo apt-key adv –recv-key –keyserver keyserver.ubuntu.com XXXXXXXXX
then do sudo apt-get update
* Method 3 : (try it & post your results)
1] Go to : “System > Administration > Update Manager”.
2] go to : Settings (at the bottom left corner of the Update Manager) -> Software Sources -> Ubuntu Software
3] Under Downloadable from the Internet, click on (select) Source Code.
Now the problem should be solved.