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Upgrade Debian 11 (Bullseye) to Debian 12 (Bookworm)

Upgrading your Debian system is crucial for accessing new features and security enhancements. Here's a comprehensive guide on upgrading from Debian 11 (Bullseye) to Debian 12 (Bookworm), based on reliable sources.

Prerequisites​

  1. Superuser Privileges: You must perform the upgrade with superuser privileges. Log in as root or a user with sudo privileges.
  2. Data Backup: Back up your data before starting the upgrade. If you're using a virtual machine, consider taking a complete system snapshot.

Update All Currently Installed Packages​

Ensure your Debian 11 system is fully updated before the upgrade. Use the following APT commands and then reboot the system.

sudo apt update
sudo apt upgrade
sudo apt full-upgrade
sudo apt --purge autoremove
sudo reboot

Check for Installed Non-Debian Packages​

Inspect your system for non-Debian packages, as they might cause complications during the upgrade. You might need to uninstall non-critical software installed from external repositories.

sudo apt list '?narrow(?installed, ?not(?origin(Debian)))'

Update Software Sources Files​

Reconfigure your APT sources to point to the Debian 12 repositories. Backup current sources first, then update them to target 'Bookworm'.

mkdir ~/apt
cp /etc/apt/sources.list ~/apt
cp -r /etc/apt/sources.list.d/ ~/apt
sudo sed -i 's/bullseye/bookworm/g' /etc/apt/sources.list
sudo sed -i 's/bullseye/bookworm/g' /etc/apt/sources.list.d/*

non-free-firmware​

For Debian 12 onwards, all the packaged non-free firmware binaries that Debian can distribute have been moved to a new component in the Debian archive, called non-free-firmware.

deb http://deb.debian.org/debian/ bookworm main  non-free-firmware

Upgrade to Debian 12 “Bookworm” from Debian 11 “Bullseye”​

Proceed with the full system upgrade using the apt full-upgrade command. Keep an eye on the screen for notifications and prompts during the process, and reboot the system once completed.

sudo apt full-upgrade
sudo reboot

Cleaning up Obsolete Packages​

After upgrading, remove obsolete packages from your Debian 12 system using the following command.

sudo apt --purge autoremove