apt-get update not working: Signing/ Verification errors

Solution 1:

Clear APT cache and regenerate it:

sudo apt-get clean
sudo mv /var/lib/apt/lists /tmp
sudo mkdir -p /var/lib/apt/lists/partial
sudo apt-get clean
sudo apt-get update

Solution 2:

Solved by doing a docker system prune(?!). Is it the image that was in a bad state? Was it a problem caused by not having enough disk space?

Maybe something to consider if you're having the problem inside a docker.

Solution 3:

Maybe there is an invalid link or file in directory /etc/apt/trusted.gpg.d/

Check that the directory contains valid files and links, in example:

# ls -L /etc/apt/trusted.gpg.d/* > /dev/null
ls: cannot access '/etc/apt/trusted.gpg.d/live-net-archive-keyring.gpg': No such file or directory

Therefore, look for the package that must contain the file

# dpkg -S /etc/apt/trusted.gpg.d/live-net-archive-keyring.gpg
live-net-archive-keyring: /etc/apt/trusted.gpg.d/live-net-archive-keyring.gpg

and take some of the following actions:

reinstall it

# aptitude reinstall live-net-archive-keyring

or reinstall all the installed keyrings

# aptitude reinstall $(dpkg -l '*keyring' | awk '$1 == "ii" {print $2}')
The following packages will be REINSTALLED:
debian-archive-keyring gnome-keyring live-net-archive-keyring siduction-archive-keyring 

or remove the invalid link or file

# rm /etc/apt/trusted.gpg.d/live-net-archive-keyring.gpg