Upgrade Debian 11 to Debian 12

This guide walks you through upgrading your Debian 11 (Bullseye) system to Debian 12 (Bookworm).

Before you begin:

Pre-Upgrade Preparation

Update Debian 11

Ensure your current system is fully updated:

sudo apt update && sudo apt dist-upgrade -y

Disable third-party repositories

Comment out or remove third-party repository entries in /etc/apt/sources.list and /etc/apt/sources.list.d/.

Update sources list

Replace bullseye with bookworm:

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

Update package lists

sudo apt update

Upgrade packages

sudo apt upgrade -y

Perform distribution upgrade

sudo apt dist-upgrade -y

Follow any on-screen prompts to resolve conflicts.

Reboot

sudo reboot

Verify upgrade

After rebooting, check the new version:

lsb_release -a

Re-enable third-party repositories

Update third-party repositories to their Debian 12 versions if available.

Clean up

Remove obsolete packages:

sudo apt autoremove
sudo apt clean

Verify services

Check that all essential services are running correctly.

If you encounter issues during upgrade, use the KVM Console to access your server and troubleshoot.