I’m more or less posting this link for my own benefit. Occasionally I get errors about untrusted packages or “The following packages have been kept back” when I try to update. This blog post explains how to fix that (although in my case, it was a combination of two separate posts that fixed my issue).
If you’re getting the untrusted sources message when using the Ubuntu Update Manager, then open a Terminal, and try this
sudo apt-get update
This should give you an error message about repositories with no public key (NOPUBKEY). You’ll want to use the next command, replacing the ‘XXXXXX’ with the key value after the NOPUBKEY message
sudo apt-key adv –recv-key –keyserver keyserver.ubuntu.com XXXXXXX
So, in my personal case it was something like:
sudo apt-key adv –recv-key –keyserver keyserver.ubuntu.com 4B82DCA0798F627E
After you’ve received the key, you’ll want to try the sudo apt-get update a second time, and then try
sudo apt-get upgrade
If you still get the message about programs being kept back, then use this command:
sudo apt-get install
and it should upgrade the program(s).
Have a great day:)