What happens with changed config files when unattended-upgrades runs

What happens when unattended-upgrades installs a new version of a package which has a different config file then on my computer? Normally you get asked if you want to keep yours or overwrite it with the one in the package.

Solution 1:

Packages which would result in configuration file prompts are held back by unattended-upgrades:

It will not install packages that require dependencies that can't be fetched from allowed origins, and it will check for conffile prompts before the install and holds back any package that requires them.

(from its README.md file).

So any upgrade which would require manual intervention won’t happen automatically; it will only happen the next time you run apt upgrade or an equivalent.

This can be configured using the general apt Dpkg::Options setting (in a configuration snippet in a file under /etc/apt/apt.conf.d); for example

Dpkg::Options {"--force-confold"};

will keep the existing version of any conflicting configuration file on upgrade (and unattended-upgrades will process the upgrade if it is configured in this way). Note however that this option would apply to any dpkg invocation by an apt-based tool, which may not be appropriate.