A few times I have gambled with online scripts while working on a server. Recently (today actually) I wanted to upgrade my PHP version from 7.0 to 7.1. After trying out the normal upgrade command, it didn’t work.
A few minutes of Googling and I completely messed up my server… not like the server went down or anything, but I get these weird error messages at the end of sudo apt-get update && sudo apt-get upgrade something like:
W: GPG error: http://ppa.launchpad.net/ondrej/php/ubuntu xenial InRelease: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 4F4EA0AAE5267A6C
W: The repository ‘http://ppa.launchpad.net/ondrej/php/ubuntu xenial InRelease’ is not signed.
N: Data from such a repository can’t be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.`