How to Upgrade Debian 11 to Debian 12

Update apt repo

cp /etc/apt/sources.list /etc/apt/sources.list.bak
sed -i 's|http://security.debian.org/debian-security bullseye-security|http://archive.debian.org/debian-security bullseye-security|' /etc/apt/sources.list

Refresh package lists and upgrade all installed packages:

sudo apt update && sudo apt upgrade -y
sudo apt full-upgrade
sudo apt autoremove

Reboot to ensure all updates are properly applied:

reboot

Change repository references in /etc/apt/sources.list from “bullseye” to “bookworm”.

deb http://deb.debian.org/debian/ bookworm main
deb-src http://deb.debian.org/debian/ bookworm main
deb http://security.debian.org/debian-security bookworm-security main contrib
deb-src http://security.debian.org/debian-security bookworm-security main contrib
deb http://deb.debian.org/debian/ bookworm-updates main contrib
deb-src http://deb.debian.org/debian/ bookworm-updates main contrib

Update the package index and commence the upgrade:

sudo apt update
sudo apt upgrade -y
sudo apt full-upgrade

Remove obsolete packages and reboot for changes to take effect:

sudo apt autoremove
sudo reboot

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