Updating from such a repository can't be done securely
2564
apt-get cannot connect to Ubuntu archives
15413
sudo apt update always giving Clearsigned file isn't valid, got 'NOSPLIT' (does the network require authentication?)
54475
How do I pull from a Git repository through an HTTP proxy?
36772
Is it possible to only allow specific packages updates from a PPA
8204
apt-get update only for a specific repository
155179
How to get apt-cacher-ng to download AND cache packages from Apt HTTPS repositories?
5565
How to fix Permission Denied (Public key) error?
90822
How can I install just security updates from the command line?
76241
"no public key available" while upgrading using update-manager
339
How to resolve "Failed to download repository information"?
47010
How can update-manager update without the root password?
112879
W: The repository 'http://download.fpcomplete.com/ubuntu yakkety Release' is not signed
68722
How can I make my local repository available for git-pull?
75879
How do I get add-apt-repository to work through a proxy?
118549
Setting up a repository server
112568
Cannot remove a repository that complains it has no public key
85711
verifiying ubuntu iso with repository gpg-keys