So I'm trying to apply a boatload of updates and upgrades via Ubuntu's built-in update system... But it tells me the updates/upgrades can't be completed because it requires the installation of "untrusted" packages.
For the most part, my software has been installed via the Ubuntu Software Center... But there are a few odds and ends that I have installed separately...
The thing is, even the "Ubuntu base" updates (which as I understand it, as from Ubuntu themselves) are considered "untrusted" when I try to install them individually!
I've had a play around in the relevant settings, but no matter what I click, Ubuntu simply does not want to apply these updates/upgrades!
What am I doing wrong?
If you've installed packages from ppa it may happen. To unblock the updates, I'd suggest to open the Software Sources and deselect a few of them (temporarily):
After deselecting a ppa, try again to open the Software Updater to request an update. It should quickly give you the untrusted source.
As pointed by karel, you can also update your system using
sudo apt-get update && sudo apt-get upgradeon the command line. It will prompt you if you want to install such packages.