This happened after I tried to upgrade to Ubuntu 16.04.3 LTS by running ‘do-release-upgrade’

You’re using Debian repos on Ubuntu and you haven’t replaced codename with the codename of your version (which can be found at https://nginx.org/en/linux_packages.html#distributions)

You can remove the nginx lines from sources.list(.d) and follow the instructions on the nginx package install guide to add the repository properly and resolve the error.

@vincent471497

If you would, please try running:

rm -rf /var/lib/apt/lists/*

Once ran, please try running apt-get update once again. Generally, that’ll solve the issue, as long as the repositories in your sources.list file are correct and have not been modified.

…

When running do-release-upgrade, you generally need to modify the source repositories so that the command pulls from the release you want to upgrade to. This isn’t generally a command I would run on a production server though as it can have some unintended side effects and require quite a bit of troubleshooting.

When it comes to major releases, such as upgrading from 14.04 to 16.04, it’s often best to deploy a new server with 16.04 and migrate data over to it. It’s a bit of a manual process, though it’ll ensure everything runs smoothly.