apt-get -update testing to secure
buster InRelease’ changed its ‘Suite’ value from ‘testing’ to
N: This must be accepted explicitly before updates for this repository can be applied. See apt-secure(8) manpage for details.
This error in updating your Pi 4 is due to Buster, the current release of Raspbian, is now in Stable version.
It is a simple fix, phewww.
Instead of the usual
sudo apt-get update
run this instead
sudo apt update -y
if you get asked type “y”
This will update you list of available upgrades
Now you can run
sudo apt-get upgrade
as per normal
You might also want to upgrade the Pi4 using
sudo rpi-update before hand