How to full-upgrade without interactive prompt for config file merge (e.g., /etc/ssh/sshd_config)?

Question

I am performing a full upgrade on the Raspberry Pi 4 B+ on the 2020-08-20-raspios-buster-arm64-lite.zip image after I have modified the /etc/ssh/sshd_config file to my liking.

I have tried setting the following:

cat << EOF > /etc/apt/apt.conf.d/local
Dpkg::Options {
  "--force-confdef";
  "--force-confold";
}
EOF

I have also specified --allow-change-held-packages in the command:

apt -y --allow-change-held-packages full-upgrade

Despite these settings, I get prompted with an interactive menu giving me options which include an option to keep the config file I have despite a newer one being available in the new package (this is the option I want).

How can I update my system non-interactively and always keep my config files?

Answer 1

I think you need to add a semicolon. Here are the contents of /etc/apt/apt.conf.d/local on nodes where I need to keep the apt-get scripts that run outside of chef from freaking out over modified files:

quiet "1";
Dpkg::Options {"--force-confold";};