rkidder.com

Prior to upgrading from bullseye, I've found it helpful to install usrmerge.

apt install usrmerge

Upgrade the current stretch installation to the latest packages.

apt update && apt upgrade && apt dist-upgrade && apt clean && echo OK

Perform some cleanup

apt --purge autoremove
apt autoclean

Perform database sanity and consistency check.

dpkg --audit

 Fix any output from this command.Check for any packages which are held back.

apt-mark showhold

Point apt to the buster sources.

sed -e 's/bullseye/bookworm/g' -i /etc/apt/sources.list 

Perform the upgrade, downloading packages in advance.

apt update && apt clean && echo OK

apt upgrade --without-new-pkgs -d -y && echo OK

apt upgrade --without-new-pkgs -y && apt clean && echo OK

Perform the upgrade, downloading packages in advance.

apt full-upgrade -d -y && echo OK

apt full-upgrade -y && apt clean && echo OK

Reboot.

Perform some cleanup

apt --purge autoremove